Bio

DR. FREDRICK O. AYUKE BIO

Dr. Fredrick O. Ayuke, Soil Biologist/Ecologist, graduated with a PhD from the Department of Soil Quality, Wageningen University, the Netherlands in 2010, his studies funded by the World Tropical Research Organization (WOTRO/NWO) of Netherlands.

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Publications


2015

2013

Ayuke, FO, Karanja NK, Awiti A.  2013.  Soil Macrofauna in soils under differing levels of disturbance and land use intensity in Kakamega District, Kenya.. East African Agricultural and Forestry Journal (In Press).
Paul, BK, Vanlauwe B, Ayuke F, Gassnerc A, Hoogmoed M, Hurissoa TT, Koala S, Lelei D, Ndabamenyea T, Six J.  2013.  Medium-term impact of tillage and residue management on soil aggregate stability, soil carbon and crop productivity.. Agriculture, Ecosystems and Environment. 164:14-22. Abstract

Conservation agriculture is widely promoted for soil conservation and crop productivity increase,
although rigorous empirical evidence from sub-Saharan Africa is still limited. This study aimed to quantify
the medium-term impact of tillage (conventional and reduced) and crop residue management (retention
and removal) on soil and crop performance in a maize–soybean rotation. A replicated field trial
was started in sub-humid Western Kenya in 2003, and measurements were taken from 2005 to 2008.
Conventional tillage negatively affected soil aggregate stability when compared to reduced tillage, as
indicated by lower mean weight diameter values upon wet sieving at 0–15 cm (PT < 0.001). This suggests
increased susceptibility to slaking and soil erosion. Tillage and residue management alone did not affect
soil C contents after 11 cropping seasons, but when residue was incorporated by tillage, soil C was higher
at 15–30 cm (PT*R = 0.037). Lack of treatment effects on the C content of different aggregate fractions
indicated that reduced tillage and/or residue retention did not increase physical C protection. The weak
residue effect on aggregate stability and soil C may be attributed to insufficient residue retention. Soybean
grain yields tended to be suppressed under reduced tillage without residue retention, especially
in wet seasons (PT*R = 0.070). Consequently, future research should establish, for different climatic zones
and soil types, the critical minimum residue retention levels for soil conservation and crop productivity.
Keywords: Reduced tillage, Crop residue management, Soil aggregate stability, Crop yields, Soil organic, carbon, Sub-Saharan Africa

2012

Kihara, J, Mukalama J, Ayuke FO, Njoroge S, Waswa B, Okeyo J, Koala S, Bationo A.  2012.  Crop and Soil response to tillage and crop residue application in a tropical Ferralsol in Sub-humid Western Kenya. In: Bationo, A., Waswa, B., Kihara, J., Adolwa, I., Vanlauwe, B., Saidou, K. (Eds), Lessons learned from long-term soil fertility management experiments in Africa, 3:41-57. : Springer Abstract

Conservation agriculture (CA) offers an opportunity to reverse prevailing land degradation and consequent loss of productivity often occasioned by intensive soil tillage in cropping systems in most parts of sub-Saharan Africa (SSA). A long term experiment was established in Nyabeda Western Kenya in 2003 to evaluate the effect of tillage and crop residue application on maize and soybean yields, and on soil properties. The experiment was set up as a split-split-split plot design with four replicates and involved a factorial combination of tillage system (reduced and conventional tillage), cropping system (continuous cereal, soybean-maize rotation and intercropping), crop residue – maize stover – management (plus and minus crop residue) and nitrogen (N) application. Results showed that tillage infl uenced performance
of maize although signifi cant tillage effects were observed in only 5 out of the 15 seasons analyzed. Overall average maize grain yields were 2.9 ton ha −1 in reduced tillage and 3.6 ton ha −1 in conventional tillage systems. Application of crop residue increased seasonal maize grain yield in reduced tillage (340 kg ha −1 ) and in conventional tillage (240 kg ha −1 ), but the only signifi cant crop residue (CR) effect was observed in season 10. Differences in maize yields between the two systems were attributed to phosphorus availability as it was demonstrated that application of crop residue in the reduced tillage resulted in better availability of P than without crop residue application. Under the rotation system, signifi cant tillage effects were observed in 6 of the 15 seasons with greater maize yield in conventional than in reduced tillage system. Soybean yields under reduced tillage were comparable to those from conventional tillage with the good performance of soybean in reduced tillage being related to the effect of its canopy on soil evaporation, and or to changes in microbial diversity and soil structure. For both the conventional and reduced tillage systems, legume
benefi ts on succeeding maize were observed with similar maize yields being observed between maize monocropping and maize rotated with soybean. Reduced tillage improved soil aggregation with greater aggregate mean weight diameters being observed in this system than in conventional tillage. Tests for biological activity showed that the application of crop residue increased termite abundance in both
reduced and conventional tillage systems. The results from this study indicate the importance of long term trials in better understanding the benefi cial effects of conservation agriculture on soil productivity.

Keywords Reduced tillage • Rotation • Soybean • Soil aggregation • Soil organisms

Lelei, DK, Karanja NK, Ayuke FO, Kibunja CN, Vanlauwe B.  2012.  Effects of soil fertility management practices on soil aggregation, carbon and nitrogen dynamics. East African Agricultural and Forestry Journal. Abstract

Poor resource farmers cultivate steep slopes without soil conservation measures and apply insufficient plant nutrients thus degrading the soils. Use of organic and inorganic sources of nutrients is one of the approaches being advocated to farmers as a way of improving soil health and increasing crop production.
A study was conducted from a 31 year-old long-term trial at Kabete, Central Kenya to investigate the effect of inorganic and organic inputs (maize stover and farmyard manure) on soil aggregates, carbon, and nitrogen in a humic nitisol soil under annual maize-bean crop rotation. The treatments for this study were: i) Inorganic fertilizer; ii) Farmyard manure plus or minus inorganic fertilizer; iii) Maize stover plus or minus inorganic fertilizer and iv) control (no inputs applied). The treatments were replicated three times in a randomized complete block design. Soil samples were collected and subjected to wet sieving and fractionation analyses to assess for water stable aggregates. Carbon and total nitrogen were measured for all aggregate fractions and whole soil. Data collected were subjected to analysis of variance.

The results showed significant increase in macroaggregates in 0-15 cm and 15-30 cm depths under manure plus inorganic fertilizer treatment. Also, there was significant increase in mean weight diameter of soil aggregates, soil organic carbon and total nitrogen in macroaggregates and microaggregates, in treatment with farmyard manure plus inorganic fertilizer.
Long-term use of manure plus inorganic fertilizer improved the stability of the macroaggregates and increased mean weight diameter in both 0-15 cm and 15-30 cm depths. Thus integration of farmyard manures and inorganic fertilizers would result in buildup of soil organic matter in the long-term, thus contributing to carbon sequestration in soils.

Key words: Soil aggregate fractions; carbon; nitrogen

Ayuke, FO, Karanja NK, Okello J, Wachira P, Mutua GK, Lelei, D., Gachene CKK.  2012.  Agrobiodiversity and potential use for enhancing soil health in tropical soils of Africa. In Hester, R.E., Harrison, R.M. (Eds)Soils and Food Security: Issues in Environmental Science and Technology, No 35, 5: 94-133 . , London, United Kingdom: The Royal Society of Chemistry Abstract

Land degradation and soil fertility decline is often cited as a major constraint to crop production in Sub-Saharan Africa (SSA). As mineral and organic fertilisers are often limited in quantity and quality, soil
fertility research has focused on developing integrated management strategies to address soil fertility decline. Soil biotas are an essential component of soil health and constitute a major fraction of global
terrestrial biodiversity. Within the context of Integrated Soil Fertility Management (ISFM), soil biota are responsible for the key ecosystem functions of decomposition and nutrient cycling, soil organic matter
synthesis and mineralisation, soil structural modification and aggregate stabilisation, nitrogen fixation, nutrient acquisition, regulation of atmospheric composition, the production of plant growth substances
and the biological control of soil-borne pests and diseases. Soil biological processes are not as well understood as are soil physical and chemical properties, creating opportunities for breakthroughs in
biotic function to provide better services to agriculture. These services accrue through two basic approaches: indirectly, as a result of promoting beneficial soil biological processes and ecosystem services through land management, or directly, through the introduction of beneficial organisms to the soil. Because of their sensitivity to disturbance and their importance in redistributing and transforming organic inputs, some of the soil biota groups, such as earthworms and termites, represent an important indicator of soil quality. In this chapter we have highlighted the importance of soil biodiversity, especially its potential use for enhancing soil health in tropical soils of SSA.

2011

F.O, A, L B, B V, J. S, Lelei D. K, C.N K, M.M P.  2011.  Soil fertility management: Impacts on soil macrofauna, soil aggregation and soil organic matter allocation. Abstract

Maintenance of soil organic matter through integrated soil fertility management is important for soil quality and agricultural productivity, and for the persistence of soil faunal diversity and biomass. Little is known about the interactive effects of soil fertility management and soil macrofauna diversity on soil aggregation and SOM dynamics in tropical arable cropping systems. A study was conducted in a long-term trial at Kabete, Central Kenya, to investigate the effects of organic inputs (maize stover or manure) and inorganic fertilizers on soil macrofauna abundance, biomass and taxonomic diversity, water stable aggregation, whole soil and aggregate-associated organic C and N, as well as the relations between these variables. Differently managed arable systems were compared to a long-term green fallow system representing a relatively undisturbed reference. Fallowing, and application of farm yard manure (FYM) in combination with fertilizer, significantly enhanced earthworm diversity and biomass as well as aggregate stability and C and N pools in the top 15cm of the soil. Earthworm abundance significantly negatively correlated with the percentage of total macroaggregates and microaggregates within macroaggregates, but all earthworm parameters positively correlated with whole soil and aggregate associated C and N, unlike termite parameters. Factor analysis showed that 35.3% of the total sample variation in aggregation and C and N in total soil and aggregate fractions was explained by earthworm parameters, and 25.5% by termite parameters. Multiple regression analysis confirmed this outcome. The negative correlation between earthworm abundance and total macroaggregates and microaggregates within macroaggregate could be linked to the presence of high numbers of Nematogenia lacuum in the arable treatments without organic amendments, an endogeic species that feeds on excrements of other larger epigeic worms and produces small excrements. Under the conditions studied, differences in earthworm abundance, biomass and diversity were more important drivers of management-induced changes in aggregate stability and soil C and N pools than differences in termite populations.

Mutua, GK, Karanja NK, Ayuke FO, Ndukhu H, Kimenju JW.  2011.  The potential of Bacillus subtilis and Rhizobium leguminosarium in controlling plant parasitic nematodes in farmers’ fields . African Crop Science Conference . :Vol.10,pp207-203., Kampala, Uganda: African Crop Science Society Abstract

Assessment of the potential of dual inoculation of Bacillus subtilis and Rhizobium leguminosarum biovar phaseoli strain USDA 2674 on plant parasitic nematodes in bean was carried out on farmers’ fields. Bean seeds variety Rose Coco, were treated with three B. subtilis isolates namely K158, K194 and K263 singly or in combination with Rhizobium and then planted in nematode infested fields. Plant parasitic nematodes in the genera Meloidogyne, Pratylenchus and Scutellonema were dominant. Nematode diversity assessed by Shannon, Simpson’s, Trophic and Maturity indices declined with increased length of cultivation. Plant
parasitic index was 63% higher in the cultivated farms compared to the natural forest. The dual innoculant enhanced nodulation variably depending on the length of cultivation and increased bean yields compared to the control. Bacillus subtilis isolates K194, K158 and K263 suppressed plant parasitic nematodes by 42, 36 and 28%, respectively. The potential of dual inoculation of Bacillus and Rhizobium in addressing nematode and soil fertility challenges was demonstrated in this study.

Key words: Diversity, Kakemega, Kenya, nodulation, Phaseolus vulgaris

Karanja, NK, Kimenju JM, Esilaba AO, Jefwa, J., Ayuke FO.  2011.  Legume based cropping and soil biodiversity dynamics. In: Bationo, A., Waswa, B., Okeyo, J.M., Maina, F., Kihara, J., Mokwunye, U (Eds), Fighting Poverty in Sub-Saharan Africa: The Multiple Roles of Legumes in Integrated Soil Fertility Management, 4:67-83. : Springer Publishers Abstract

The soil is home to an enormous diversity of organisms, many of which are benefi cial, while a small and equally diverse proportion contains harmful organisms. Legume cropping and husbandry practices impact negatively or positively on diversity. These changes in biodiversity may be quantitative and/or qualitative.
Sustainable management of diversity in soils involves an ecosystem approach which encourages the establishment of equilibria between the organisms in the soil. It is evident that the diversity of benefi cial organisms in the soil can be harnessed to improve and sustain crop productivity with minimal external inputs. Legumes will continue to play a central role in the supply of plant nutrients and in the establishment of a self-regulating ecosystem which is based on a diverse range of organisms.

Ayuke, FO, Brussaard L, Vanlauwe B, Six J, Lelei DK, Kibunja C, Pulleman MM.  2011.  Ayuke, F.O., Brussaard, L., Vanlauwe, B., Six, J., Lelei, D.K., Kibunja, C., Pulleman, M.M. (2011). Soil fertility management: impacts on soil macrofauna, soil aggregation and soil organic matter allocation. Applied Soil Ecology. 48:53-62. Abstract

Maintenance of soil organic matter through integrated soil fertility management is important for soil
quality and agricultural productivity, and for the persistence of soil faunal diversity and biomass. Little
is known about the interactive effects of soil fertility management and soil macrofauna diversity on
soil aggregation and SOM dynamics in tropical arable cropping systems. A study was conducted in a
long-term trial at Kabete, Central Kenya, to investigate the effects of organic inputs (maize stover or
manure) and inorganic fertilizers on soil macrofauna abundance, biomass and taxonomic diversity, water
stable aggregation, whole soil and aggregate-associated organic C and N, as well as the relations between
these variables. Differently managed arable systems were compared to a long-term green fallow system
representing a relatively undisturbed reference.
Fallowing, and application of farm yard manure (FYM) in combination with fertilizer, significantly
enhanced earthworm diversity and biomass as well as aggregate stability and C and N pools in the top
15cm of the soil. Earthworm abundance significantly negatively correlated with the percentage of total
macroaggregates and microaggregates within macroaggregates, but all earthworm parameters positively
correlated with whole soil and aggregate associated C and N, unlike termite parameters. Factor analysis
showed that 35.3% of the total sample variation in aggregation and C and N in total soil and aggregate
fractions was explained by earthworm parameters, and 25.5% by termite parameters. Multiple regression
analysis confirmed this outcome.
The negative correlation between earthworm abundance and total macroaggregates and microaggregates
within macroaggregate could be linked to the presence of high numbers of Nematogenia lacuum
in the arable treatments without organic amendments, an endogeic species that feeds on excrements of
other larger epigeic worms and produces small excrements. Under the conditions studied, differences
in earthworm abundance, biomass and diversity were more important drivers of management-induced
changes in aggregate stability and soil C and N pools than differences in termite populations.
Keywords: Earthworm, Termite, Taxonomic richness, Soil organic matter, Carbon, Nitrogen, Soil aggregate fraction

Ayuke, FO, Pulleman MM, Vanlauwe B, de Goede RGM, Six J, Csuzdi C, Brussaard L.  2011.  Agricultural management affects earthworm and termite diversity across humid to semi-arid tropical zones. Agriculture, Ecosystems and Environment. 148:148-154. Abstract

Earthworm and termite diversity were studied in 12 long-term agricultural field trials across the subhumid
to semi-arid tropical zones of Eastern and Western Africa. In each trial, treatments with high and low soil organic C were chosen to represent contrasts in long-term soil management effects, including tillage intensity, organic matter and nutrient management and crop rotations. For each trial, a fallow representing a relatively undisturbed reference was also sampled. Earthworm taxonomic richness decreased in the direction fallow > high-C soil > low-C soil and earthworm abundance was higher in fallow than under continuous crop production. Termite abundance was not significantly different between fallow and high and low-C treatments and termite taxonomic richness was higher in fallow soil than in the two cropping systems. We concluded that fewer species of earthworms and termites were favored under agricultural management that led to lower soil C. Results indicated that the soil disturbance induced by continuous crop production was more detrimental to earthworms than to termites, when compared to the fallow.
Keywords: Soil biodiversity, Earthworms, Termites, Agriculture, Crop management, Soil carbon, Climate

Karanja, NK, Kimenju JM, Esilaba AO, Jefwa J, Ayuke F.  2011.  Legume Based Cropping and Soil Biodiversity Dynamics. Springer Science+Business Media B.V.. :67-83. Abstract

The soil is home to an enormous diversity of organisms, many of which
are beneficial, while a small and equally diverse proportion contains harmful organisms.
Legume cropping and husbandry practices impact negatively or positively on
diversity. These changes in biodiversity may be quantitative and/or qualitative.
Sustainable management of diversity in soils involves an ecosystem approach which
encourages the establishment of equilibria between the organisms in the soil. It is
evident that the diversity of beneficial organisms in the soil can be harnessed to
improve and sustain crop productivity with minimal external inputs. Legumes will
continue to play a central role in the supply of plant nutrients and in the establishment
of a self-regulating ecosystem which is based on a diverse range of
organisms.

2010

Ayuke, FO.  2010.  Biodiversity of soil macrofauna functional groups and their effects on soil structure in West and East African cropping systems, as related to organic resource management, crop rotation and tillage. , Wageningen, The Netherlands: Wageningen University Abstract

Soil macrofauna, especially earthworms and termites are important components of the soil ecosystem and, as ecosystem engineers, they influence formation and maintenance of the soil structure and regulate soil processes. Despite advances made in understanding the links between soil macrofauna and agricultural productivity, this component of biodiversity is still very much a “black box”. In this thesis, I proposed to link soil biodiversity to soil functioning through the diversity of the soil structures produced by ‘ecosystem engineers’ like earthworms and termites, i.e. organisms, which physically modify and create habitats for other soil organisms and plant roots. This study aimed at providing an understanding of the link between soil macrofauna and crop management practices on soil aggregation and soil organic matter (SOM) dynamics as this is key to the improvement and the management of infertile or degrading soils.
The methodological approach used in this study involved assessment of:
1. How agricultural management affects earthworm and termite diversity across sub-humid to semi-arid tropical zones.
2. The influence of soil macrofauna on soil aggregation and SOM dynamics in agro-ecosystems of sub-Saharan Africa as influenced by management practices.
3. How management practices (e.g. tillage and use of organic inputs) influence macrofauna-induced biogenic structures in East and West African soils.
4. Disclosing farmers’ knowledge and perception on the roles of termites in Western Kenya.

In chapter 2, I examined how agricultural management affects earthworm and termite diversity across sub-humid to semi-arid tropical zones. This study, conducted in 12 long-term agricultural field trials of Eastern and Western Africa, provides new insights on diversity of earthworms and termites in SSA, since it is the first time that a study like this is done on this scale. In each trial, treatments with high and low soil organic C were chosen to represent contrasts in long-term soil management effects, including tillage intensity, organic matter and nutrient management and crop rotations. High soil C was considered to reflect relatively favorable conditions, and low soil C less favourable conditions for soil macrofauna. For each trial, a fallow representing a relatively undisturbed reference was also sampled.
I have shown that earthworm and termite diversity and abundance were low in fallow, high-C and low-C agricultural treatments in 12 long-term trial fields across the sub-humid to semi-arid tropical zones in Eastern and Western Africa. This is in contrast to most typical native or undisturbed forest ecosystems of the tropical zones. Environmental variables contributed 42% and 25% of variation observed in earthworm and termite taxonomic abundance, respectively. Earthworm and termite taxa were less abundant in the relatively cooler, wetter and more clayey sites characteristic of Eastern Africa, compared to the warmer, drier and more sandy sites in West Africa. Continuous crop production has significant negative effects on earthworm-, but little effect on termite diversity, as compared to long-term fallow, and agricultural management resulting in high soil C increases earthworm and termite diversity as compared to low-C soil. I conclude that fewer species of earthworms and termites are favored under agricultural management that leads to lower soil C. Results indicate that soil disturbance that goes with continuous crop production is more detrimental to earthworms than to termites as compared to fallow.

In chapter 3, a broad regional study was conducted to examine how management intensity affects soil macrofauna, and how macrofauna in turn influence soil aggregation in agro-ecosystems of sub-Saharan Africa.
My study has shown that macrofauna, especially earthworms, and to a smaller extent termites, are important drivers of stable soil aggregation, in conjunction with climate, soil organic C content and soil texture in sub-Saharan agroecosystems. However, the beneficial impact of earthworms and termites on soil aggregation is reduced with increasing management intensity and associated soil disturbance due to cultivation. I suggest that this knowledge is important in designing agricultural management systems aimed at increasing long-term soil fertility in sub-Saharan Africa.

In chapter 4, a long-term trial at Kabete, Kenya was selected to examine in detail the interactive effects of organic and inorganic fertilizerson soil macrofauna diversity and soil aggregation and SOM dynamics in arable cropping systems. Differently managed arable systems were compared to a long-term green fallow system representing a relatively undisturbed reference.
Application of manure in combination with fertilizer significantly improved aggregate stability and C and N stabilization in arable soil. Furthermore, manure-fertilizer application enhanced earthworm diversity and biomass. Significant correlations between the amount and C and N contents of aggregate fractions and whole soil C and N were observed with earthworm parameters (Shannon diversity index, abundance and biomass), but not with termite parameters. Factor and regression analyses showed that earthworms had a profound effect on aggregation, C and N stabilization in whole soil and in aggregate fractions, whereas contributions of termites were limited. Therefore, my results indicate that long-term application of manure in combination with fertilizer result in higher earthworm Shannon diversity and biomass, which leads to improved soil aggregation and enhanced C and N stabilization within this more stable soil structure. These practices therefore result in the dual benefits of improving soil physical and chemical properties. In contrast, no significant improvements in soil aggregation and C and N stabilization were found when organic inputs were applied in the form of maize stover as compared to the no-input control, irrespective of fertilizer addition. Under the conditions studied, earthworms were more important drivers of aggregate stability and C and N stabilization in aggregate fractions, but termites less so.

In chapter 5, a micromorphological approach was used to describe and quantify macrofauna-induced biogenic structures in undisturbed soil samples (i.e. thin sections) from long-term field experiments in East and West Africa. Management systems differing in tillage intensity and with or without organic amendments (manure/crop residue) were compared.
My study has shown the soil management practices tillage type and addition of organic inputs influence soil fauna activities with a significant impact on soil structure and hence soil physical properties. Among the management practices assessed across two agroecological zones, fallowing, conservation tillage plus residue application (in East Africa) and hand-hoeing plus manure (in West Africa) enhanced biogenic soil structure formation, resulting in a well developed soil structure and a continuous pore system through many faunal channels. By contrast, intensive tillage and absence of organic inputs resulted in soil with less biogenic soil structural features and was, therefore, prone to slaking.

Chapter 6 describes farmers’ knowledge on the occurrence and behavior of termites, their perception of the importance of termites in their cropping systems and the management of termite activities in their farm fields in Nyabeda, Western Kenya. Being the main actors in environmental conservation or degradation, farmers’ knowledge and perception can enrich scientific understanding of the ecology and sustainable management of termites under different agroecological conditions.
My research has shown that farmers in Nyabeda were aware of the existence of termites, their activities and nesting habits and had local names for termites that they frequently encountered. Geographic location explained 23% of the variance in farmers’ perception and management of termites, whereas socio-economic variables explained only 5%. Ninety percent of the farmers perceived termites as pests and maize was rated as the most susceptible crop to termite attack, especially during the flowering/tasseling stage and in wet periods. More than 88% of the farmers used control measures against termites, further indicating a lack of awareness or appreciation of the beneficial effects often ascribed to termites with respect to soil properties in crop production. There is an urgent need for more research to assess the trade-offs between positive and negative impacts of termites on crop yields, as well as to get an understanding of the effects of different termite control strategies used by farmers on agroecosystem functions.

Karanja, NK, Mutua GK, Ayuke FO, Njenga M, Prain G, Kimenju J.  2010.  Dynamics of soil nematodes and earthworms in urban vegetable irrigated with wastewater in the Nairobi River Basin, Kenya. Journal of Tropical & Subtropical Agroecosystems. 12:521-530. Abstract

The effects of heavy metals lead (Pb), Cadmium (Cd) and Cromium (Cr) on nematode communities and earthworm density and biomass were studied in the wastewater irrigated farms of the Nairobi river basin. The levels of Cr and Pb in the wastewater were below the threshold values considered to be toxic while those of Cd exceeded the permissible limit. Heavy metal accumulation in soils in the Kibera and Maili Saba farms were Cd (14.3 mg kg-1), Cr (9.7 mg kg-1) and Pb (1.7 mg kg-1) and 98.7 mg Cd kg-1, 4.0 mg Cr kg-1 and 74.3 mg Pb kg-1, respectively. High heavy metal concentrations as well as soil organic matter were negatively correlated with plant feeding nematodes in the genera Criconema, Meloidogyne, Paratylenchus, Pratylenchus and Scutellonema. Bacterial feeding nematodes genera Rhabditis, Plectus, Cephalobus and Acrobeles were predominant in the gardens treated with wastewater. An average density of 198 m-2 earthworms and a biomass of 68 g m-2 and 102 earthworms m-2 with 33g m-2 biomass were recorded in Kibera and Maili Saba, respectively. The earthworms isolated from both sites were all epigeic with the metal content in Maili Saba suppressing their populations. This study has demonstrated that the use of untreated urban wastewater for irrigation has adverse effects on nematode and earthworm abundance and diversity and their potential as bioindicators of heavy metal presence.
Key words: Heavy metal accumulation; soil fauna; diversity

2009

Karanja, NK, Ayuke FO, Muya EM, Musombi BK, Nyamasyo GHN.  2009.  Soil macrofauna community structure across land use systems of Taita, Kenya.. Journal of Tropical & Subtropical Agroecosystems. 11(2):385-396. Abstract

This paper presents data on diversity and abundance of soil macrofauna in various land use systems in Taita (natural forest, plantation forest, fallow, coffee, napier, and maize, Horticulture. Each was sampled for
macrofauna using three sampling methods (monolith, transect and pitfall trapping). Seventy eight (78)
genera/species were recorded across the different land use systems of Taita. Rényi diversity profile indicated
no significant differences in species richness across land use systems as reflected by the very close
diversity profiles at α = 0. However, the two diversity indices (Shannon index: α = 1 and Simpson’s index: α
= 2) indicated that plantation forest was the most diverse of the land use systems, while fallow and maize were least diverse. Rényi evenness profile indicated that the plantation forest was most even in terms of species distribution which was least in maize. However because some of the profiles for some land
use systems cross each other, they could not be ranked. The major macrofauna groups recorded in the Taita
benchmark site included: Hymenoptera, Isoptera, Coleoptera, Oligochaeta and Orthoptera and Arenae.
Generally Hymenoptera were the most abundant of the macrofauna groups constituting about 36% of the total followed by Isoptera (22%), Oligochaeta (16%), Coleoptera (10%). The other macrofauna (Arenae,
Diplopoda, Diptera, Orthoptera, Blattidae, Isopoda, Chilopoda- Geopholomorpha, Hemiptera, Opiliones,Chiopoda-Scolopendromorpha, Lepidoptera, Dermaptera, Phasmidae, Blattelidae and Mantodea
each constituted <10% of the total macrofauna recorded. Hymenoptera was ranked 1st as it had the
highest total abundance (59,440 individuals m-2), while Mantodea was ranked 18th and had the lowest total
abundance (6 individuals m-2). Generally macrofauna density was higher in arable systems than forests,
although the differences were not always significant. Except for Chilopoda-Geopholomorpha, Chilopoda-
Scolopendromorpha and Isopoda, all the other macroafauna groups were not significantly different
across land use systems. The three groups (Chilopoda-Geopholomorpha, Chilopoda- Scolopendromorpha and Isopoda) were significantly highest in the forests than in all the other land use systems. These variation
appear to be associated with management practices that consequently results in the destruction of nesting
habitats, modification of soil microclimate within these habitats and removal of substrate, low diversity
and availability of food sources for the associated macrofauna groups. The significant correlations between some soil macrofauna groups with selected soil chemical properties too show that, soil chemical characteristics may indirectly play a role in influencing the density, distribution and structure of macrofauna
communities. This indicates the potential of using these fauna groups as bio-indicators of soil productivity.

Key words: Macrofauna; community structure; diversity; abundance; land use systems.

Ayuke, FO, Karanja NK, Muya EM, Musombi BK, Mungatu J, Nyamasyo GHN.  2009.  Macrofauna diversity and abundance across different land use systems in Embu, Kenya. Tropical and Subtropical Agroecosystems. 11 (2):371-384. Abstract

This paper presents data on diversity and abundance of soil macrofauna of various land use systems in Embu, Kenya (natural forest, plantation forest, fallow, coffee, tea, napier, and maize). Each was sampled for
macrofauna using three sampling methods (monolith, transect and pitfall traps). Thirty four (34) genera/species of soil macrofauna were recorded, the highest number (27) being observed in napier. Majority of these genera/species being Coleoptera. Rényi diversity profile indicated that in terms of
species richness (α at 0), maize was the richest of all the land use systems, but plantation forest the least. It
was however not possible to clearly order or rank the land use system in terms of diversity because of the
bias of each of the two diversity indices as indicated by the numerous crossings observed for the diversity
profiles/curves. Shannon index of diversity (α = 1) indicated that coffee was the most diverse of the land
use systems followed by plantation forest > natural forest > napier > maize > tea, while fallow/pasture was
the least diverse (Figure 1). On the other hand, Simpson’s diversity (α = 2) indicated that plantation
forest was the most diverse followed by fallowed by coffee > natural forest > napier > maize >tea >
fallow/pasture. Rényi evenness profile indicated that the plantation forest was most even in terms of species
distribution followed by natural forest and coffee > napier > tea > maize but least even in the
fallow/pasture. Hymenoptera were most abundant of the macrofauna groups constituting about 45% of the
total followed by Isoptera (39%), Coleoptera (6%), Oligochaeta (5%), Orthoptera (3%) and Arenae (2%). The other groups that comprised of Hemiptera, Diptera, Phasmidae and Blattelidae each constituted
<1% of the total marofauna recorded. Highest macrofauna density (1566) was recorded in the napier
followed by fallow (1356) > coffee (1170) > natural forest (1110) > tea (755), but lowest in plantation
forest (309), although analysis of variance indicated no significant variation among the land use systems. This study however, demonstrates that quantitative changes in diversity and density of soil fauna communities occur when various land use systems are subjected to varying levels of intensification. These changes appear to be associated with management practices such as use of agrochemicals, consequent destruction of nesting habitats, modification of soil microclimate within habitats, removal of substrate, low diversity and availability of food sources for the associated macrofauna groups. The significant correlations
between some soil macrofauna groups with selected soil chemical properties shows that, soil chemical
characteristics may indirectly play a role in influencing the density, distribution and structure of macrofauna
communities.

Key words: Macrofauna; diversity; abundance; land use systems.

2008

Wall, DH, Bradford MA, John MGST, Trofymows JA, Behan-Pelletier V, Bignell DE, Dangerfield JM, Parton WM, Rusek, J. FOI, Voight, W., Wolters V, Gardel HZ, Ayuke FO, Bashford R, Beljakova OI, Bohlen PJ, Brauman A, Flemming S, Henschel JR, Johnson DL, Jones TF, Kovarova, M., Kranabetter JM, Kutny L, Kuo-Chuan L, Maryati M, Masse D, Pokarzhevskii A, Rahman H, Sabara MG, Joerg-Alfred S, Swift MJ, Varela A, Vasconcelos HL, White D, Zou X.  2008.  Global decomposition experiment shows soil animal impacts on decomposition are climate- dependent.. Global Change Biology. 14:2661-2677. Abstract

Climate and litter quality are primary drivers of terrestrial decomposition and, based on evidence from multisite experiments at regional and global scales, are universally factored into global decomposition models. In contrast, soil animals are considered key regulators of decomposition at local scales but their role at larger scales is unresolved. Soil animals are consequently excluded from global models of organic
mineralization processes. Incomplete assessment of the roles of soil animals stems from the difficulties of manipulating invertebrate animals experimentally across large geographic gradients. This is compounded by deficient or inconsistent taxonomy. We report a global decomposition experiment to assess the importance of soil animals in C mineralization, in which a common grass litter substrate was exposed to natural decomposition in either control or reduced animal treatments across 30 sites distributed from 431S to 681N on six continents. Animals in the mesofaunal size range were recovered from the litter by Tullgren extraction and identified to common specifications, mostly at the ordinal level. The design of the trials enabled faunal contribution to be evaluated against abiotic parameters between sites. Soil animals increase decomposition rates in temperate and wet tropical climates, but have neutral effects where temperature or moisture constrain biological activity. Our findings highlight that faunal influences on
decomposition are dependent on prevailing climatic conditions. We conclude that (1) inclusion of soil animals will improve the predictive capabilities of region- or biomescale decomposition models, (2) soil animal influences on decomposition are important at the regional scale when attempting to predict global change scenarios, and (3) the statistical relationship between decomposition rates and climate, at the global scale, is robust against changes in soil faunal abundance and diversity.

Keywords: climate decomposition index, decomposition, litter, mesofauna, soil biodiversity, soil
carbon, soil fauna

2007

Ayuke, FO, Karanja NK, Wickama J, Awiti A, Hella J.  2007.  Soil fauna community structure across land management systems of Kenya and Tanzania. Proceedings of National Conference on Agricultural Research Outputs, 26-27 March. :396-406., Kigali, Rwanda Abstract

Changes in soil fauna communities were studied across land use systems in parts of Lake Victoria basin in Kenya and Tanzania. The study sites included primary forest, secondary forest, plantation forest, fallow and arable lands under different cropping systems and intensity, with cultivation in some systems ranging from one to more than 40 years. In Kenya, a total of 47 species were recorded across the land use systems while in Tanzania, a total of 36 species were recorded of which 25 species were unique to the forest soils. Isopterans were the most abundant of the total macrofauna groups observed across the two benchmark sites, constituting between 38 and 46%. Forest disturbance, cultivation and higher levels of intensification had a substantial effect on macrofauna diversity. This study has demonstrated that macofauna species and their density declined, particularly when natural forest was disturbed, cleared or cultivated, and when agro-chemicals were applied in the cropping systems.

Key words: Community structure, diversity, land use system, soil fauna

Ayuke, FO, Karanja NK, Bunyasi SW.  2007.  Evaluating effect of mixtures of organic resources on nutrient release patterns and uptake by maize. In: Bationo, A., Waswa B., Kihara, J., Kimetu, J. (Eds). Advances in Integrated Soil Fertility Research in sub-Saharan Africa: Challenges and Opportunities, 79: 833-844 . : Springer Publishers Abstract

To supplement high costs of inorganic fertilizers, smallholder farmers in the tropics are likely to increase the use of appropriate plant residues as an alternative source of plant nutrients especially nitrogen (N) and phosphorus (P). To maximize benefit accrued from these materials, synchronizing nutrient release patterns of the materials with crop’s nutrient requirements need to be understood. Consequently, this study was undertaken to: (1) evaluate the effect of plant residues on mineralization and N-release patterns, (2) evaluate the N release patterns of mixtures of low and high quality organic materials and synchrony with maize uptake. Incubation studies were established for 12 weeks using six selected plant residues: which included Leucaena leucocephala, Croton macrostachyus, Calliandra calothyrsus, Tithonia diversifolia, Sorghum bicolor and rice (Oryza sativa) husks. Soil samples were taken at 2 weeks interval for ammonium nitrogen (NH+4 -N) and nitrate nitrogen (NO−3 -N) determination. The organic residues differed in their chemical composition and this was found to influence mineralization rates and nitrogen release patterns. Two distinctive NO−3 -N + NH+4 N release patterns were observed over the incubation period. L. leucocephala, C. macrostachyus, C. calothyrsus, T. diversifolia had a net N release throughout while S. bicolor and rice husks (O. sativa) had a significant N immobilization. Nitrogen-release was best correlated with C:N ratio (r2= –0.84 to –0.90) for most of the sampling periods. Polyphenol:N ratio also had a significantly high
correlation with cumulative N mineralized (r2 = –0.65 to –0.95). Two organic resource with contrasting C:N and PP:N ratios i.e. C. macrostachyus and O. sativa were selected for use and in depth effect of mixing high quality C. macrostachyus (Cm) and low quality O. sativa (Os) at different ratios on mineralization N release patterns. Agronomic effectiveness of the best mixture, which was based on N release, was measured using maize as the test crop in a glasshouse experiment. The dynamics of N-mineralization of the various mixture of C. macrostachyus (Cm) and O. sativa (Os) were in general not significantly different from those predicted from the O. sativa and C. macrostachyus treatments alone with the exception of the ¾ Cm + ¼ Os which gave significant N immobilization at 6–8 weeks and the ¼ Cm+¾Os which enhanced N mineralization at 2
and 12 weeks respectively. Addition of plant residues significantly increased maize biomass in the glasshouse with potted mixtures of plant residues giving the highest maize dry matter yield and N uptake.

Key words: Agronomic effectiveness, chemical composition, mineralization, nutrient release, nutrient uptake,
organic resources

2006

Karanja, NK, Ayuke FO, Swift MJ.  2006.  Organic Resource Quality and Soil Fauna: Their role on the microbial Biomass, Decomposition and nutrient release patterns in Kenya Soils . Tropical & Subtropical Agroecosystems. 6:73-83. Abstract

Five organic resources commonly used for soil fertility maintenance in large parts of Kenya were selected for litter decay and nutrient mineralization studies that were conducted in three farms (Machakos, Kabete and Njabini) located at an elevational transect ranging from 1500 to 2800 m above sea level. These organic residues included: bean trash, maize stover, tree prunnings (Grevillea robusta), Senna spectabilis foliage, cow and poultry manures. Organic residues were either mulched or incorporated in the soil. Satellite experiments were also carried out in each of the three sites with one additional site at Maseno based in western Kenya. These experiments aimed at assessing the role of soil biota in the decomposition
and nutrient release. Soil fauna were excluded from control plots using 1-mm mesh litterbags. The organic residues were different in chemical composition i.e. nitrogen (N), phosphorus (P), potassium (K), carbon (C), lignin (L) and polyphenol (PP) contents, which in turn influenced their rate of decomposition and nutrient release patterns. Bean trash decomposed and released N and P faster than either the maize stover or Grevillea prunings. The slowest rate of decomposition observed for Grevillea prunings could be attributed to the high lignin content (24%). The N release was influenced by (L+PP):N ratio. Bean trash having a ratio of 10 released N faster than either maize stover or Grevillea prunings whose respective ratios of 20 and 13. P release was influenced by both C:P and N:P ratios. Maize stover with C:P and N:P ratios that were higher than the critical levels of 123 and 10 respectively, mineralized and released P more slowly than either bean trash or Grevillea prunings. Incorporated materials decomposed and released nutrients faster than surface applied materials. For surface applied organic materials, the delay in litter decay ranged from 4.1 to 4.4 days for every 100 m increase in altitude, while for incorporated materials the delay in litter decay ranged from 1 to 3 days per 100 m increase in elevation. This implies that farmers at higher elevations would benefit more by incorporating residues before planting, while at low elevations post emergence surface application would lead to improved nutrient availability. Njabini and Kabete recorded significantly higher microbial biomass (C, N and P) than Machakos. This could be linked to the higher organic C, higher total N, higher moisture content but lower temperatures reported for Njabini and Kabete than Machakos. Soil fauna enhanced decomposition of organic residues, although their role in influencing nutrient availability to crops from the organic residues may depend on the nature of the material. Fauna had no significant influence on nutrient release patterns of Senna possibly due to secondary compounds present in Senna, which were lower than the critical levels of 15 for lignin and 4 for polyphenol respectively.

Key words: Resource quality, placement, soil fauna, decomposition, nutrient release, microbial biomass

2003

Ayuke, FO, Rao MR, Swift MJ, Opondo-Mbai ML.  2003.  Impact of soil fertility management strategies on diversity and populations of soil macrofauna in agroecosystem. East African Agricultural & Forestry Journal. 69(2):131-137. Abstract

The role of soil invertebrate fauna in decomposition of organic residues and thus nutrient release, soil structure and soil-water relations is well appreciated. The scope, however, of their manipulation to derive the potential benefits is little understood. A study was undertaken to assess how soil fertility management strategies within an Agroforestry system affect soil biodiversity (macrofauna diversity and populations). The study was conducted on-farm during the 1997 short rains (Oct 1997Feb 1998) on farm in western Kenya with the following treatments: (1) control without any input, (2) fertilizer at 120 kg N, 150 kg P and 100 kg K ha1, (3) Tithonia diversifolia biomass at 5 t ha1 dry weight and (4) Senna spectabilis at 5 t ha1 dry weight. Riparian natural forest and a 6-year grassland fallow were assessed and used as reference standards. Macrofauna diversity and populations were monitored in soil monoliths (25 x 25 x 30 cm) at the beginning of the season, 6 weeks after sowing maize and at maize harvest. Faunal diversity was assessed using the Shannon-Wiener index of diversity (H′). Data were subjected to analyses of variance (ANOVA) in a split-plot design and treatment differences evaluated using least significance difference (LSD) at P=0.05. Macrofauna diversity and populations of most of the macrofauna groups were significantly higher under natural forest (H′ = 2.31) than in all the other treatments (each H′ = < 1). Although the 2 organic residues did not affect faunal diversity, addition of senna significantly increased earthworm population by 400% and tithonia by 240% over the no input control. Even though termite population increased by 145% in senna and 118% in tithonia over the control, the increase was not significant because of high variability between replications of the same treatment. Fertilizer use did not change either diversity or population of termites and earthworms. The study indicates that: (1) short-term addition of organic residues do not significantly increase faunal diversity, (2) Soil invertebrates fauna populations can be manipulated by external additions of organic residues such as senna and (3) Changes in land use systems, especially those that reduce the amount, range and diversity of food resources for macrofauna bring about instability in below ground biodiversity. There is therefore need to clearly define the conditions in which such impairment is critically important to agricultural production and sustainability and to determine what management interventions may be made to alleviate or ameliorate problems resulting from loss of diversity.

2001

Ayuke, FO, Opondo-Mbai ML, Rao MR, Swift MJ.  2001.  Effect of organic and inorganic sources of nutrients on soil mineral nitrogen (ammonium and nitrate N) and maize yields in western Kenya, 7-10 May. proceedings of the 8th Tropical Soil Biology and Fertility and Programme African Network meeting. , Arusha, Tanzania Abstract

The effects of organic and inorganic fertilizers on soil mineral N and maize yields were evaluated in a Kandiudalfic Eutrodox soil of western Kenya. Leaf biomass of tithonia (Tithonia diversifolia [Hemseley] A. Grey) and senna (Senna spectabilis D.C. & H.S. Irwin) at 5 t ha-1 dry weight were incorporated into the soil and compared with the response obtained from control without any input and fertilizer at 120 kg N, 150 kg P and 100 kg K ha-1 from urea and triple super phosphate (TSP). Soil mineral (inorganic), N, was measured at the beginning of the trial and subsequently at 1, 2, 4, 8 and 12 weeks after applying the treatments. Maize grain and stover yields were estimated at harvest. Total inorganic nitrogen in the soil at the beginning of the season was at a similar level in all treatments. It increased rapidly after applying the materials and at the onset of rains for all treatments probably because of rapid nitrogen mineralisation in all treatments. After four weeks, inorganic nitrogen decreased progressively until end of the experiment in all the treatments. The highest contribution of mineral N to the soil by the organic residues was noted at four weeks stage and this was significantly higher with tithonia than senna. This could be due to rapid N mineralization by these residues. Senna treatment that had the lowest mineral N during the first weeks of the trial, showed that N mineralization was slow with the mineral N reaching highest level at four-week stage. However, it is interesting to note that while soil N under tithonia was statistically higher than in senna at four weeks, it was higher under senna at later stage observations. Thus tithonia decomposed completely in about four weeks, while senna was still mineralizing at 8 weeks. Fertilizer use increased maize grain yield by 63% over the control. Although tithonia biomass increased maize grain yield by 38% over the control and did not differ significantly from fertilizer treatment, senna increased maize yield by only 6% over the no input control. Higher yield with tithonia than senna was partly because of higher nutrient concentration and hence greater amounts of nutrients added for the same quantity of material applied. The study indicates that high quality residues such as tithonia can be used as sources of nutrients to improve crop yields.

Keywords: Biomass transfer, Tithonia diversifolia, Senna spectabilis, mineral nitrogen, maize yield.

Ayuke, FO, Opondo-Mbai ML, Rao MR, Swift MJ.  2001.  An assessment of Soil Fertility Management strategies in Agroecosystems (biomass transfer technology) on Belowground Biodiversity-Soil macrofauna biomass, 7-10 May. proceedings of the 8th Tropical Soil Biology and Fertility and Programme African Network meeting. , Arusha, Tanzania Abstract

During 1997 short rains (Oct 1997-Feb 1998), a study was undertaken to assess how biomass transfer within
agroecosystem influence soil biodiversity (soil macrofauna biomass). This was part of a larger experiment conducted to test the hypothesis that diversity, abundance and function of soil invertebrate fauna are related to the quality of organic residues used. Leaf biomass of tithonia (Tithonia diversifolia [Hemseley) A. Grey) biomass and senna (Senna spectabilis D.C. & H.S. Irwin) biomass at 5 t ha -1 dry weight were incorporated into the soil and these were compared with the control without any input and fertilizer at 120 kg N, 150 kg P and 100 kg K ha-1 from urea and triple super phosphate (TSP). Macrofauna biomass (fresh weight), was monitored in soil monoliths (25cm x 25cm x 30cm) at the beginning of the season, six weeks after sowing maize and at maize harvest. Addition of organic residues increased faunal biomass substantially over the fertilized and unfertilized controls. Whereas senna increased total biomass by 45% and tithonia by 49%, the two organic residues did not differ significantly between them. Addition of either senna or tithonia significantly increased earthworm biomass by 390% over no input control. Even though termite biomass increased by 160% in senna and 120% in tithonia over no input control, F test was not significant because of high variability between replications of the same treatment. Fertilizer use did not change biomass of termites and earthworms. This study shows that: (1) addition of organic residues significantly increase faunal biomass indicating a likelihood that soil invertebrate functions can be manipulated by external inputs of organic residues (2) under arable land use system characterized by low amount, range and diversity of food resources, quality of organic residues do not play a significant role in influencing foraging behaviour of soil invertebrates. It therefore remains to be demonstrated whether mixing litter of organic residues of different quality may change this foraging behaviour and consequently the invertebrate functions in agroecosystem.

Key words: Biomass transfer, macrofauna, biomass, earthworms, termites

Ayuke, FO, Opondo-Mbai ML, Rao MR, Swift MJ.  2001.  Soil fertility management strategies in agroecosystem and implication on Soil Macrofauna diversity and populations, 4-8 December. Soil Science Society of East Africa (SSSEA) Proceedings of the 18th Conference and End of the Millennium Celebrations . , Mombasa, Kenya Abstract

Soil fauna functions in decomposition of organic residues and thus nutrient release, soil structure and soil-water relations are well appreciated. However the scope for their manipulation to derive the potential benefits is little understood. A study was undertaken to assess how soil fertility management strategies within an Agroforestry system affect soil biodiversity (macrofauna diversity and populations). The study was conducted on farm during the 1997 short rains (Oct 1997Feb 1998) on farm in western Kenya with the following treatments: (1) control without any input, (2) fertilizer at 120 kg N, 150 kg P and 100 kg K ha1, (3) Tithonia diversifolia biomass at 5 t ha1 dry weight and (4) Senna spectabilis at 5 t ha1 dry weight. Riparian natural forest and a six-year grassland fallow were assessed and used as reference standards. Macrofauna diversity and populations were monitored in soil monoliths (25 x 25 x 30 cm) at the beginning of the season, 6 weeks after sowing maize and at maize harvest. Faunal diversity was assessed using the Shannon-Wiener index of diversity (H′). Data were subjected to analyses of variance (ANOVA) in a split-plot design and treatment differences evaluated using least significance difference (LSD) at P=0.05. Macrofauna diversity and populations of most of the macrofauna groups were significantly higher under natural forest (H′ = 2.31) than in all the other treatments (each H′ = < 1). Although the 2 organic residues did not affect faunal diversity, addition of senna significantly increased earthworm population by 400% and tithonia by 240% over the no input control. Even though termite population increased by 145% in senna and 118% in tithonia over the control, the increase was not significant because of high variability between replications of the same treatment. Fertilizer use did not change either diversity or population of termites and earthworms. The study indicates that: (1) short-term addition of organic residues do not significantly increase faunal diversity, (2) Soil invertebrates fauna populations can be manipulated by external additions of organic residues such as senna and (3) Changes in land use systems, especially those that reduce the amount, range and diversity of food resources for macrofauna bring about instability in below ground biodiversity. There is therefore need to clearly define the conditions in which such impairment is critically important to agricultural production and sustainability and to determine what management interventions may be made to alleviate or ameliorate problems resulting from loss of diversity.

Key words: Biodiversity, macrofauna, population, Tithonia diversifolia, Senna spectabilis

2000

Ayuke, FO.  2000.  Diversity, abundance and function of soil invertebrate fauna in relation to quality of organic residues. , Eldoret, Kenya: Moi University Abstract

Although the role of soil invertebrate fauna in decomposition of organic residues and thus nutrient release, soil structure and soil-water relations is well recognized, the scope for their manipulation to derive the potential benefits is little understood. A study was undertaken to test the hypothesis that the diversity, abundance and function of soil fauna are related to quality of organic residues used.
The study was conducted during the 1997 short rains (Oct 1997Feb 1998) on farm in western Kenya with the following treatments: (1) control without any input, (2) fertilizer at 120 kg N, 150 kg P and 100 kg K ha1, (3) tithonia (Tithonia diversifolia (Hemsely) A. Grey) biomass and (4) senna (Senna spectabilis D.C & H.S. Irwin) biomass. The organic residues were applied in fresh condition at 5 t ha1 dry weight. The treatments were replicated four times in a randomized block design. Macro- and meso-fauna diversity and abundance were monitored in soil monoliths (25 x 25 x 30 cm) and soil cores (10 cm diameter and 30 cm depth), respectively, at the beginning of the season, six weeks after sowing maize and at maize harvest.
A satellite experiment was conducted simultaneously to quantify the role of soil fauna in the decomposition of organic residues, using senna foliage (5 t ha1) as the test material and maize as a test crop. Two treatments, with and without soil fauna, were evaluated replicated six times. Fauna were eliminated by treating the soil with furadan at 40 kg ha1at the start of the study, 2, 4, 6 and 10 weeks after crop sowing. The standard litterbag technique was used to monitor litter decomposition at 1, 2, 4, 8 and 12 weeks and N, P and K concentration in the undecomposed material at each of these sampling periods was determined. First order exponential equations were fitted between undecomposed material or nutrients contained therein (y) and time (t), and decomposition constants (k) worked out.
Diversity and populations of soil fauna were found to be low in the arable land use system under study. Macrofauna constituted 90% of the total fauna recovered, while mesofauna constituted only 10%. Termites were the most abundant of the fauna (55%) followed by earthworms (31%). Although the two organic residues did not affect faunal diversity, addition of senna increased total population by 200% and tithonia by 140% over the no input control. Fertilizer use did not change either diversity or total population.
Soil fauna enhanced decomposition of organic residues. While only 45% of the material decomposed by two weeks in the absence of fauna, 60% material decomposed in the presence of fauna in the same period. After 8 weeks, hardly any material was recovered in the presence of fauna compared with 9 to 12% material recovered in the absence of fauna. Nutrient release was not influenced by fauna probably because of the nature of material used. As the secondary compounds were lower than the critical level (<4% polyphenol and <15% lignin), nutrient release progressed rapidly with the microbial action and fauna did not play a significant role.
Fertilizer use increased maize grain yield by 63% over the control. Although tithonia biomass increased maize grain yield by 38% over the control and did not differ significantly from fertilizer treatment, senna increased maize yield by only 6% over the no input control. Higher yield with tithonia than senna was partly because of higher nutrient concentration and hence greater amounts of nutrients added for the same quantity of material applied. Despite less faunal activity compared with that under senna, tithonia decomposed and released nutrients faster than senna probably because of increased microbial activity. The study indicates that (1) the relative effect of soil fauna on decomposition to that of soil microbes is small, (2) several parameters have to be considered in determining the quality of organic residues, (3) organic residues can be used to manipulate soil fauna and (4) high quality residues can be used as sources of nutrients to improve crop yields.

1999

Ayuke, FO, Opondo-Mbai ML, Rao MR, Swift MJ.  1999.  Diversity, abundance and function fauna in relation in relation to quality of organic residues., 6-17 September. Soil Science Society of East Africa (SSSEA) and African Research Network (AfNet) workshops. , Kampala, Uganda Abstract

Although the role of soil invertebrate fauna in decomposition of organic residues and thus nutrient release, soil structure and soil-water relations is well recognized, the scope for their manipulation to derive the potential benefits is little understood. A study was undertaken to test the hypothesis that the diversity, abundance and function of soil fauna are related to quality of organic residues used. The study was conducted during the 1997 short rains (Oct 1997Feb 1998) on farm in western Kenya with the following treatments: (1) control without any input, (2) fertilizer at 120 kg N, 150 kg P and 100 kg K ha1, (3) tithonia (Tithonia diversifolia (Hemsely) A. Grey) biomass and (4) senna (Senna spectabilis D.C & H.S. Irwin) biomass. The organic residues were applied in fresh condition at 5 t ha1 dry weight. The treatments were replicated four times in a randomized block design. Macro- and meso-fauna diversity and abundance were monitored in soil monoliths (25 x 25 x 30 cm) and soil cores (10 cm diameter and 30 cm depth), respectively, at the beginning of the season, six weeks after sowing maize and at maize harvest. A satellite experiment was conducted simultaneously to quantify the role of soil fauna in the decomposition of organic residues, using senna foliage (5 t ha1) as the test material and maize as a test crop. Two treatments, with and without soil fauna, were evaluated replicated six times. Fauna were eliminated by treating the soil with furadan at 40 kg ha1at the start of the study, 2, 4, 6 and 10 weeks after crop sowing. The standard litterbag technique was used to monitor litter decomposition at 1, 2, 4, 8 and 12 weeks and N, P and K concentration in the undecomposed material at each of these sampling periods was determined. First order exponential equations were fitted between undecomposed material or nutrients contained therein (y) and time (t), and decomposition constants (k) worked out. Diversity and populations of soil fauna were found to be low in the arable land use system under study. Macrofauna constituted 90% of the total fauna recovered, while mesofauna constituted only 10%. Termites were the most abundant of the fauna (55%) followed by earthworms (31%). Although the two organic residues did not affect faunal diversity, addition of senna increased total population by 200% and tithonia by 140% over the no input control. Fertilizer use did not change either diversity or total population. Soil fauna enhanced decomposition of organic residues. While only 45% of the material decomposed by two weeks in the absence of fauna, 60% material decomposed in the presence of fauna in the same period. After 8 weeks, hardly any material was recovered in the presence of fauna compared with 9 to 12% material recovered in the absence of fauna. Nutrient release was not influenced by fauna probably because of the nature of material used. As the secondary compounds were lower than the critical level (<4% polyphenol and <15% lignin), nutrient release progressed rapidly with the microbial action and fauna did not play a significant role. Despite less faunal activity compared with that under senna, tithonia decomposed and released nutrients faster than senna probably because of increased microbial activity. The study indicates that (1) the relative effect of soil fauna on decomposition to that of soil microbes is small, (2) several parameters have to be considered in determining the quality of organic residues, (3) organic residues can be used to manipulate soil fauna population hence activity.

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