Interaction between Organic Resource Quality, Aggregate Turnover, Carbon and Nitrogen Cycling in the Central Highlands of Kenya

Kavoo, Agnes Mumo (2008) Interaction between Organic Resource Quality, Aggregate Turnover, Carbon and Nitrogen Cycling in the Central Highlands of Kenya. Masters thesis, Kenyatta University.

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Abstract

Combined use of organic (OR) and mineral sources (MR) of nutrients is accepted as one of the most appropriate ways to address the problems of declining soil fertility and poor crop yields facing small-scale farming in sub-Saharan Africa. A field study was conducted at Embu in Central Kenya to investigate the effect of OR and MR management on aggregate turnover, C sequestration and N stabilization. The study comprised of ORs of differing quality; Tithonia diversifolia (high quality), Calliandra calothyrsus (medium quality), Zea mays stover (medium quality), Grevillea robusta sawdust (low quality) and farmyard manure applied at a rate of 4 ton C ha-1 with or without 120 kg N ha' mineral fertilizer. Soil organic matter (SOM) fractions from soils sampled from the top soil (0-15cm depth) at the establishment of the field trial in 2002 and before the long rains in 2005 were analyzed for C, Nand C-13 signatures, All the data collected was analyzed with the PROC MIXED procedure of SAS and the means separated at (p> 0.05). The quality of ORs did not significantly affect the proportions of aggregates size classes. A significant positive interaction between OR and mineral fertilizer was observed on the sawdust treatment resulting in a higher proportion of large macroaggregates. There was a general increase in C and N for the soils amended with calliandra, stover and manure (for both combined and the sole applications) compared to the total C and N contents of the soils at the beginning of the trials. Higher concentrations of C and N were also observed in the microaggregate intra particulate organic matter (iPOM) compared to the macroaggregate iPOM indicating accumulation of SOM in the smaller aggregate classes. High and medium quality ORs (class I and II) had the highest C and N input into the SOM pool compared to low quality (class IV) ORs. This was indicated by the high C and N contents of small macro aggregate distinct SOM fractions as well as the more negative C-13 signatures observed within the macro aggregate and microaggregate free light fractions and iPOM fractions amended with high and medium quality ORs compared to the low quality ORs C, N and C-13 signatures. The knowledge generated in this study is therefore essential in devising soil management options that contribute to short-term plant production, C sequestration to mitigate increasing CO2, N retention to mitigate N losses and long-term soil fertility.

Item Type:	Thesis (Masters)
Subjects:	Q Science > QH Natural history > QH301 Biology T Technology > TP Chemical technology
Divisions:	Africana
Depositing User:	Tim Khabala
Date Deposited:	27 Sep 2017 14:42
Last Modified:	27 Sep 2017 14:42
URI:	http://thesisbank.jhia.ac.ke/id/eprint/2411

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