Tied-Ridging and Integrated Soil Fertility Management Technologies’ Effects on Soybean-Maize Yields and Selected Soil Physical Properties in Tharaka-Nithi County, Kenya

Abstract

Deficits in soil moisture and low soil fertility are major constraints to smallholder farming systems in Sub-Saharan Africa. Farmers in Tharaka-Nithi County, Kenya, have over the decades suffered huge declines in crop yields as a result of continuous cultivation with inadequate replenishments of the lost soil nutrients and lack of appropriate soil water conservation technologies. Experiments were set up at Kigogo primary school, Mukuuni location in Tharaka-Nithi County to determine the effects of tied ridging and integrated soil fertility management technologies on: - i) Soil water content at different soil depths, ii) Soil bulk density and aggregate stability, iii) Soybean and maize yields, iv) Economic feasibility during the long and short rains of 2016. A randomized complete block design with eight treatments replicated four times on 6 m × 4.5 m plots was employed. The treatments were: - control, no inputs with tied ridging, T. diversifolia + inorganic fertilizer with or without tied ridging, manure + inorganic fertilizer with or without tied ridging and sole inorganic fertilizer with or without tied ridging. H516 maize variety and gazelle soybean variety were used as the test crops. Soil moisture was monitored using Diviner 2000® fortnightly at 0-100 cm depth. Soil samples were collected at 0-5 cm depth using core rings for bulk density and at 0-20 cm depth for aggregate stability analysis. Maize grain and stover, soybean grain and biomass yields were determined at harvesting and labour data collected throughout the experiment. Data was subjected to Analysis of variance using Statistical analysis software version 9.2 and means separated using Least Significant Difference (LSD) at p≤0.05. The results showed that at the 20 depth, treatments had a significant effect (p=0.05) on soil moisture under soybean during the LR 2016 season. During the SR 2016 season, treatments also significantly affected (p<.0001) soil moisture content under soybean and (p=0.0005) in treatments under maize within the 30 cm depths. Manure and/or T. diversifolia plus fertilizer with or without tied ridging had the highest soil moisture content during the two cropping seasons. The highest (-7.69%) decrease in soil bulk density was observed in T. diversifolia plus fertilizer with tied ridging and the same treatment had the highest (+4.76%) increase in aggregate stability in soybean over the control. In SR 2016, soybean grain yields were significantly (p<0.0001) affected by the treatments. Manure plus inorganic fertilizer under tied ridging numerically recorded the highest (3.15 t ha-1) soybean grain yields in LR 2016 while T. diversifolia plus fertilizer without tied ridging gave the highest (1.08 t ha-1) in SR 2016. During the LR 2016, maize grain yields were significantly highest (4.87 t ha-1) in the treatment with T. diversifolia plus fertilizer under tied ridging while manure + inorganic fertilizer without tied ridging gave the highest (1.27 t ha-1) in SR 2016. The highest net benefits under soybean were recorded in the tied ridging with no inputs treatment in LR 2016 and in the control during SR 2016. The highest net benefits were recorded under T. diversifolia plus inorganic fertilizer with tied ridging during the LR 2016 and SR 2016 under maize. Short-term implementation of a combination of either T. diversifolia or manure with inorganic fertilizer is recommended for enhancing maize and soybean production while improving soil physical conditions in Kigogo Tharaka-Nithi County.