Tillage and Residual Effect of Some Organic Amendments on Aggregate Associated Soil Carbon of an Ultisol, Growth and Yield of Maize and Cowpea Intercrop

We investigated the tillage and residual effects of some organic amendments on aggregate -associated soil carbon (C WSA) and yield of maize and cowpea intercrop in an Ultisol, Southeastern Nigeria. A land area of 0.1125 ha was planted to sole cowpea, sole maize and maize-cowpea intercrop using minimum tillage (NT) and conventional tillage (CT) with poultry droppings (PD), pig waste (PW), and Cassava peels (CP) as amendments at the rates of 20, 90, 100 t/ha respectively and a control. The experimental design was a split -split plot in a Randomized Complete Block Design (RCBD) with three replications. The same crops, treatments, and replications were maintained for two experimental years (2011 and 2012), after that the residual effect of the amendments on aggregate-associated soil carbon (C WSA) and yield of the test crops was investigated in 2013. Consecutive application of organic amendments for the two years necessitated great improvement on aggregate-associated soil carbon (C WSA) for aggregate sizes > 0.25mm. However, when the amendments were withdrawn, there was a reduction in C WSA values though still significant except for aggregate sizes 1-0.5mm. Pig waste was observed to perform better than all the other amendments followed by Poultry Droppings in aggregating the soil. Tillage had a significant effect on C WSA for aggregate sizes >0.05mm, CT performed better than NT. Organic amendments significantly influenced cowpea and Maize both as sole and intercrop, however, it was observed that the intercrop had a tremendous improvement at the residual compared to the previous years.