Rainwater harvesting, leucaena biomass transfer and integrated nutrient management in improving sorghum (sorghum bicolor [l moench]) productivity in semi-arid regions of Zimbabwe

Abstract

Yield decline in rain-fed agriculture is mainly caused by moisture stress and poor soil fertility in semi-arid areas. Current mineral fertiliser application rates cannot replenish soil fertility and improve yields. The aim of the study was to assess the role of rainwater harvesting; Leucaena leucocephala biomass combination with cattle manure and mineral fertiliser in improving sorghum productivity in semi-arid areas of Zimbabwe. Three experiments were arranged in split-split-plot designs with three rainwater harvesting techniques, nutrient management and two sorghum varieties (Macia and SV1) used as the sub-sub plot factor. The first experiment had rainwater harvesting as the main factor at three levels (tied contour, infiltration pit and standard contour) and Leucaena biomass was the sub-plot factor at five levels (0, 5, 10, 20 and 30 t ha-1 ). The second experiment had rainwater harvesting techniques as main factor and Leucaena/cattle manure combinations as sub plot factor with five levels (0, 5, 10, 20 and 30 t ha-1 ). The third experiment had rainwater harvesting as main factor, Leucaena + NPK fertiliser (7% N: 14%P2O5: 7%K2O) as sub-plot factor at five levels (0, 2.5/25, 5/50, 10/100 and 15/150). Soil moisture content was higher (p<0.05) across all the seasons in the depth ranges of 0–20cm and 21–40cm for tied contours. Moisture content of 7.18 % was highest from 0-20 cm and 9.34 % from 20-40 cm under tied contour. Lowest moisture content from 0-20 cm was 6.69 % and 8.04% from 20-40 cm under standard contour treatments. Tied contour had significantly (p<0.05) higher sorghum grain and stover yields followed by infiltration pit and the least was under standard contour. Highest grain yield (1.15 t ha1 ) obtained from SV1 under tied contour treatments amended with 30 t ha-1 biomass. Interaction of rainwater harvesting techniques and Leucaena biomass had significant (p<0.05) effect on stover yields with highest (4.47 t ha-1 ) yield observed from tied contour + 30 t ha-1 Leucaena biomass in 2018/19 from Macia variety. Rainwater-use efficiency was significantly (p<0.05) affected by rainwater harvesting techniques with the highest efficiency of 3.28 kg ha-1 mm-1 from Macia and 3.24 kg ha-1 mm-1 for SV1 all under tied contours. The relationships between Rainwater use efficiency were positively correlated to Leucaena biomass (r 2= 0.76-0.99) for both sorghum varieties over three seasons. Results showed significant (p<0.05) increase in sorghum grain and stover yield with increased applications of Leucaena/cattle manure. Macia variety had statistically greater (p<0.05) grain yield than SV1 variety. Tied contour show considerably higher yield for both varieties in all seasons. Harvest Indices show significant differences (p<0.05) as influenced by rainwater harvesting technique, with tied contour and infiltration pit having comparably higher value than standard contour. Leucaena/cattle manure significantly influenced (p<0.05) sorghum net return in all seasons except at 5 t ha-1 where no significant effect was observed. Macia variety had higher (US$263.16) net return compared with SV1. Grain and stover yields show significant (p<0.05) difference among treatments under Leucaena/NPK fertiliser combination. Highest grain yield from Macia (1.146 t ha-1 ) and 1.1 t ha-1 from SV1 were from tied contour with 15 t ha-1 biomass + 150 kg ha-1 NPK fertiliser. Agronomic efficiency was significantly (p<0.05) affected by rainwater harvesting, Leucaena/NPK fertiliser and their interaction. Highest (0.075kg kg-1 ) agronomic efficiency was observed from treatments with tied contour + 2.5 t ha-1 Leucaena biomass + 25 kg ha-1 NPK fertiliser. It can be concluded that tied contours and infiltration pits have better yield benefits than standard contours when amended with organic and inorganic nutrient sources. Basing on results of this study, agriculture policy makers are encouraged to implement technologies which improve yields, net benefits and show agronomic efficiency. This will enable smallholder farmers in semiarid areas to improve food security and improve resilience to climate change. Keywords: Rainwater harvesting; Leucaena Leucocephala; sorghum; soil moisture content; Leucaena/cattle manure; rainwater use efficiency; net returns