Abstract – Agronomic potential of brewers’ spent grains
The agronomic potential of brewers’ spent grains (BSG) was evaluated on two texturally contrasting tropical soils, using a split-plot design with three replications. The main plot treatments were the two soils S1 (Ultisol) and S2 (Entisol), whereas the subplot treatments were different rates of BSG and complete fertiliser (F): 0%, 2·5%, 2·5% + F, 5·0%, 7·5%, 10·0% and F. Complete fertiliser consisted of 60 ppm N, 15 ppm P, 60 ppm K and 20 ppm Mg. The test crop was maize Zea mays L. On both soils the highest plant height and dry matter yields were obtained at the 2·5% BSG rate. This rate out-performed the F treatment by 293% on S1 and 46% on S2. Generally there was higher maize response to BSG on the less fertile S1 than S2.Progressively increasing rates of BSG increased the residual organic matter contents, aggregate stability, moisture retention and available water capacity of both soils but did not alter the soils’ pH levels. On the two soils a BSG rate of 10% was the best for optimizing these physical conditions. Increase in organic matter contents of these soils following BSG additions accounted for more than 70% of the variability in the stability of the aggregates to water, between 58 and 66% of the variability in the moisture retained at different tensions by S1, and 51–82% of the variability in the moisture retained at different tensions and total and readily available water capacity in S2. The improvements in the productivity of these two fragile soils induced by the BSG amendment were due to high contents of N, P, K, Ca, Mg and carbon as well as the low C : N ratio of this waste product.