Interaction of small-scale supplemental irrigation, sawah preparation intensity and soil amendment type on productivity of lowland sawah-rice system

Abstract

Sole dependence on rainfall, poor water management and low soil fertility largely explain the fluctuations in agricultural productivity in West Africa. Lowlands for sawah-based rice farming often offer opportunities for small-scale supplemental irrigation but these are rarely explored and their interaction with other critical factors on sawah-rice productivity remains unclear. Interaction of supplemental irrigation (using pond and spring water), sawah preparation intensity (giving complete, quasi-complete, incomplete and non-sawah control) and soil amendment type (rice husks [RH], rice husk ash [RHA], poultry droppings [PD] and N-P-K fertiliser [NPK]) on lowland sawah-rice was assessed in south-eastern Nigeria for two years. Soil pH was highest in spring-supplemented complete sawah on RHA and lowest in control plots in both years. There were no interactions for soil organic carbon; however, its concentrations were highest and lowest in spring-supplemented and non-supplemented sawah, respectively. The concentrations also decreased with decreasing sawah preparation intensity and were lower without than with amendment (RH ≥ PD ≥ NPK ≥ RHA). Total nitrogen was highest in spring-supplemented complete sawah in the second year and lowest in control plots in both years. Cation exchange capacity was lowest in non-supplemented (solely rainfed) sawah, decreased with decreasing preparation intensity but was improved by amendments, particularly PD and RHA. Interaction showed highest and lowest grain yields in spring-supplemented complete sawah and spring-/non-supplemented non-sawah in both years. Of the three factors investigated, amendment type had the largest effect on yield, with PD ≥ RH ≥ others. Therefore, spring-based supplemental irrigation of complete sawah on PD/RH could improve lowland sawah-rice productivity. Soil cation exchange capacity explained approximately 81% of the variation in rice yield.