Nutrient management options for enhancing maize production under conservation agriculture in Embu County, Kenya
Murimi, Njue D.
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Smallholder farmers in Runyenjes are experiencing decline in agricultural productivity. The yield decline has been caused by degraded soils as a result soil erosion and inappropriate soil management, nutrients mining due to continuous cropping as well as leaching of minerals. To address these crop production challenges, there is need for balanced nutrient management options with appropriate tillage system. This study was therefore carried out under on-farm trials to: i) assess maize yield response to nutrient management options under conservation agriculture (CA) and conventional tillage (CT) methods, ii) assess the effects of NPK management options in contrasting tillage systems on soil macro-nutrient changes, iii) evaluate the economic feasibility of NPK management options in different tillage systems and iv) to assess effects of NPK, Ca, Zn and Mg nutrients on maize grain yields and the added benefits of Zn, Ca and Mg on maize grain and stover quality. The study was carried out in Runyenjes, Embu County. Two trials were established; i) Macro-nutrient omission trial which was laid out in a split plot design and arranged in a randomized complete block design and replicated 27 times, with tillage as the main factor while the sub-plots were the NPK inputs. ii) The micronutrient trial which was laid out in a randomized complete block design (RCBD) and replicated thrice. The treatments for micro-nutrients trials were NPKMgCa, NPKMg, NPKZn, NPKCa, NPK and the control. The key variables measured were soil macronutrients (nitrogen, phosphorus, and potassium), micronutrients (magnesium, zinc and calcium), grain and stover yields, maize and stover prices and labour costs. Soil samples were analysed using standard procedures. Data was subjected to analysis of variance (ANOVA) GLM procedure of SAS 9.3. Differences between treatments means were examined using fischer’s LSD at 5% level of significance. Paired t-test was carried out to determine whether changes in soil chemical properties mean values were significant using fisher’s LSD at (p<0.05). Post-analysis of variance was done using Proc GLM class orthogonal contrast to partition and compare the treatment means. The results showed that in SR2015 season, maize grain yields were significantly (p≤.0073) higher under CT than CA. Application of NPK inputs led to significant (p≤.0001) higher maize grain yields over control. Total soil N decreased by 15, 20, 15 and 10% in NPK, NP, NK and PK treatments, respectively. Soil P concentration increased by 18, 19, 36, and 13% under NPK, NP, NK and PK respectively. Extractable soil K increased by 5, 7, 11 and 12% under NPK, NK, NP and PK treatments, respectively. Total variable cost (TVC) was 4 and 2% higher under CT than CA while under NPK inputs, it was significantly (p≤.0001) different and in the order NPK>NP>NK>PK>Control. Net benefit (NB) in both seasons was 2% higher under CA than CT. Benefit cost ratio (BCR) was increased by 8 and 13% under CA over CT in LR2015 and SR2015 seasons, respectively. Further, BCR was decreased by 37 and 36% with NP omission, 35 and 30% with NK omission and 22 and 24% with NPK omission in LR2015 and SR2015 seasons, respectively. Grain magnesium concentration was increased by 13, 6, 6 and 3% under NPKMg, NPKMgZnCa, NPKCa and NPKZn over NPK treatment, respectively. Maize Zn grain concentration was increased by 34, 27 and 25% under NPKZn, NPKMg and NPKMgZnCa over NPK treatment, respectively. Grain calcium concentration was increased by 19, 16 and 5% under NPKMg, NPKCa and NPKZn over NPK, respectively. Maize zinc stover concentration increased by 6 and 28% under NPKZn and NPKMgZnCa over NPK treatment. The NPKMgZnCa and NPKCa increased Ca stover concentration by 12% while NPKMg increased Ca stover concentration by 13% over NPK treatments. The findings of this study highlight the importance of NPK inputs with supplementation of other nutrients in enhancing crop yields, quality of maize grain and stover yields, soil nutrition and profitability. Use of the NPK, Ca, Mg and Zn should therefore be recommended to smallholder farmers in Runjenjes, Embu for sustained crop production.