Effects of selected soil water conservation strategies on maize yield in farmer managed trials in Embu and Tharaka-Nithi Counties, Kenya
Kiboi, Milka Ngonyo
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Smallholder farmers in Embu and Tharaka-Nithi counties have experienced a decline in crop yields in the recent decades due to continuous cropping without addition of adequate fertilizers and manures, and nutrient loss through crop harvest, soil erosion and leaching. The problem is intensified by low and erratic rainfall, low inherent water storage (by the soils) and poor water harvesting techniques that cause high rate of runoff leading to low soil profile water recharge and loss of soil nutrients essential for crop growth. On-farm trials were set up to determine effects of selected soil water conservation (SWC) strategies on maize yields, soil organic matter (SOM) and yield stability, and to assess farmers' likelihood to take up the strategies in two subcounties. The study was carried out in Mbeere South and Meru South sub-counties for four consecutive cropping seasons: short rains 2011 (SR 11), long rains 2012 (LR 12), short rains 2012 (SRI2), and long rains 2013 (LR13). The experimental design was an unbalanced randomized complete block design (RCBD) with three SWC treatments replicated four times and control practiced by all farmers. Treatments were mulching (MC), tied ridging (TR), minimum tillage (MT) and conventional tillage (CT). Key variables measured were maize grain yield, rainfall amount, SOM and farmers' likelihood to take up SWC strategies. Experimental data were subjected to analysis of variance (ANOVA) using general linear model (GLM) in SAS 9.2 and mean separation done using least significant difference (LSD) at p=0.05. Descriptive statistics were used to summarize demographic characteristics of respondents and transcripts searched to find themes of analysis. Results showed disparities in rainfall amounts; Mbeere South received cumulative rainfall of 654mm during SRll and LR12 seasons while Meru South, received 1519 mm. During SR12 and LR13, Mbeere South cumulatively received 609 mm while Meru South received 970 mm. In comparison with CT, results showed that in Mbeere South grain yields increased by 50 and 28% under TR and MC, respectively, during LR12 (p=0.002). During SRI2, yields increased by 100 and 33% under TR and MC (p<0.001), respectively. Maize grain yields increased by 27 and 18% under TR and MC treatments during LR13 (p=0.02). In Meru South, grain yields increased by 52, 24 and 7% under MC, MT and TR, respectively, in comparison with CT during the SRll (p=0.01). During LR12 season, grain yields increased by 42% under MC and TR and by 29% under MT. During SR12 grain yields increased by 59, 41, and 29% under TR, MC, and MT, respectively Soil organic matter in Mbeere South increased by 50%, 10% and 9% under MT, TR and MC, respectively. In Meru South SOM under MC, TR, and MT increased by 43, 18 and 12%, respectively. In the control treatment SOM decreased by 9% and 4% in Mbeere South and Meru South, respectively. When compared with CT, maize grain yields were more stable under TR and MC with residual variances of 107.4 Mg ha-I and, 183.3 Mg ha" respectively in Mbeere South. Mulching, MT and TR indicated yield stability with residual variances of 17.2 Mg ha-I, 39.6 Mg ha', and, 155.2 Mg ha" respectively in Meru South. There was statistical significance at p<.OOOI in treatment by site interaction. Farmers depicted a high positive likelihood to take up TR in Mbeere South followed by Me. Tied ridging and MC had similar likelihood of being taken up by the farmers in Meru South. The findings highlight the importance of SWC strategies for high yields, stabilizing maize yield, and SOM improvement. These results will be useful to researchers and other stakeholders in recommending effective SWC strategies for improved and sustainable production.