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.
