Effect of Tillage Methods and Nutrient Application Levels on Soil Properties and Soghum and Greengram Yields in Siakago, Embu County, Kenya

Abstract

Declining soil fertility is a significant constraint to sorghum and green gram yields for smallholder farmers in semi-arid regions of Kenya. This research was carried out in Siakago, Embu County, Kenya, with the aim of assessing the efficacy of different tillage methods and inorganic and organic fertilizers for sorghum and green gram production. The research was performed for four consecutive seasons from October 2018 to February 2021 at the Agricultural Technology Development Centre, Siakago in Mbeere North sub-County. In the study, there were a total of 24 different treatments using a randomized full block design with three replicates. The treatments comprised of two different types of tilling, namely conventional and tied ridges, three cropping systems (sole-green grams, sole-sorghum, and green grams + sorghum intercrops) and four soil fertility input regimes (no inputs), (60 kg DAP ha-1 ), (5.0 t ha-1 manure) and a combination of manure and inorganic fertilizer as (2.5 t ha-1 + 30 kg DAP ha-1 ). Soil properties, including organic carbon, nitrogen, phosphorus, potassium, calcium, magnesium, manganese, iron, zinc, and copper, were analyzed before and after the experiment. Crop parameters, such as days to 50% flowering, plant height, leaf chlorophyll content, biomass, and grain yields, were also measured. The treatment effects were analyzed using ANOVA, and a significance level of p ≤0.05 was used to differentiate the treatment means using post hoc Turkey’s HSD test. Differences in treatment means were analyzed using Fisher's test for the test with the least significant difference, which was performed at a significance level of p ≤ 0.05. The results showed that tied ridge tillage practice significantly increased exchangeable phosphorus and magnesium contents. The green gram cropping system registered higher but insignificant nutrient status compared to sole sorghum or sorghum-green gram cropping systems. Organic-based fertility inputs positively affected soil organic carbon, although these increases were not statistically significant. Soil inputs significantly influenced soil carbon concentrations, with the lowest values observed in the control treatment. The study found that sorghum supplied with full-rate inorganic fertilizer had greener leaves and produced 75% higher grain than in the control. The pure farmyard manure treatment produced 45% more grain compared to the control. Tied ridges did not significantly increase yields p ≤ 0.05. Similar trends were observed in green grams. This research emphasizes the significance of applying soil conservation techniques, such as tied-ridging, in conjunction with organic input applications, to improve the availability of multiple nutrients for better crop performance and human nutrition in dryland farming systems.