Abstract
Declining soil fertility is the main cause of low and uncertain yields of sorghum and cassava traditional crops in arid and semi-arid areas of Kenya. Against this backdrop, this study investigated the effect of organic based technologies; application of organic fertilizers and integration of legumes in cassava and sorghum based cropping systems on soil chemical properties (Organic C, N, P and K). Field experiments were conducted in Katangi and Ikombe divisions of Yatta sub-County, Kenya during the short rain seasons (SRS) of 2010 and 2011 and long rain seasons (LRS) of 2011 and 2012. A randomised complete block design with a split plot arrangement was used. The main plots were three cropping systems: (i) intercropping (dolichos/cassava, dolichos/sorghum, pigeon pea/sorghum and pigeon pea/cassava); (ii) rotation (dolichos-cassava, dolichos-sorghum, pigeon pea-cassava and pigeon pea-sorghum); (iii) monocrop (cassava and sorghum). The split plots were organic fertilizers; Farm Yard manure (FYM), compost and control -no organic fertilizer added. Sorghum/dolichos+FYM had highest soil OC in LRS of 2011 at both sites and SRS of 2011 and 2010 at Katangi and Ikombe respectively. Cassava/dolichos+FYM had the highest soil OC in the SRS of 2011 and LRS of 2012 and 2011 at both sites. Sorghum/dolichos+FYM had highest soil N in LRS and SRS of 2011 in Katangi. Cassava-dolichos rotation accumulated highest soil N in SRS of 2010 and LRS of 2011 at both sites. Sorghum/dolichos intercrop accumulated higher soil P during the LRS of 2012 at both sites; and SRS of 2010 and LRS of 2011 in Katangi and Ikombe respectively. Cassava/dolichos intercrop produced higher soil P during the SRS of 2010 at both sites; and LRS of 2011 and SRS of 2011 in Katangi and Ikombe respectively. Higher soil K was observed under sorghum/dolichos intercrop in SRS of 2010 at both sites and LRS of 2011, SRS of 2011 and LRS of 2012 in Ikombe. Cassava/dolichos intercrop also had higher soil K during SRS of 2010, LRS of 2011 at both sites; LRS of 2012 at Katangi and SRS of 2011 at Ikombe. Application of FYM to sorghum/dolichos and cassava/pigeon pea intercrops is therefore a viable and sustainable trajectory to enhanced organic C and NPK levels in smallholder farming systems.
Highlights
The production potential of sorghum (Sorghum bicolor L.) and and cassava (Manihot esculenta Crantz) staple crops in semi-arid Yatta sub-county of Kenya is limited primarily by soil constraints, notably nitrogen and phosphorus deficiencies (Janssens, 2001; Shittu & Fasina, 2004; Pholsen & Sornsungnoen, 2004), the two critical nutrients for crop growth (Marschner, 1996)
This study investigated the effect of organic based technologies; application of organic fertilizers and integration of legumes in cassava and sorghum based cropping systems on soil chemical properties (Organic C, N, P and K)
Higher soil K was observed under sorghum/dolichos intercrop in short rain seasons (SRS) of 2010 at both sites and long rain seasons (LRS) of 2011, SRS of 2011 and LRS of 2012 in Ikombe
Summary
The production potential of sorghum (Sorghum bicolor L.) and and cassava (Manihot esculenta Crantz) staple crops in semi-arid Yatta sub-county of Kenya is limited primarily by soil constraints, notably nitrogen and phosphorus deficiencies (Janssens, 2001; Shittu & Fasina, 2004; Pholsen & Sornsungnoen, 2004), the two critical nutrients for crop growth (Marschner, 1996). Nutrients lost from soil during crop production are not adequately replenished due to prohibitive cost of inorganic fertilizers (Kherallah et al, 2002; Smestad et al, 2002; Mwanga, 2004). Inappropriate management of these lands, further poses a risk for irreversible degradation (Smaling et al, 1997; Stoorvogel & Smaling, 1998; Morris et al, 2007). This scenario calls for innovative approaches to restore soil fertility and manage the land sustainably. Organic based technologies such as Integration of legumes either as intercrops or in rotation with other crops with the use of organic fertilizers can restore soil fertility and stabilize crop yields in marginal environments thereby providing a sustainable alternative to the use of inorganic fertilizers
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