Diversity, abundance and function of soil invertebrate fauna in relation to quality of organic residues

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

Thesis Type:

M.Phil thesis


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.

UoN Websites Search