Effects of soil fertility management practices on soil aggregation, carbon and nitrogen dynamics

Lelei DK, Karanja NK, Ayuke FO, Kibunja CN, Vanlauwe B. "Effects of soil fertility management practices on soil aggregation, carbon and nitrogen dynamics." East African Agricultural and Forestry Journal. 2013;78(1):113-118.


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

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