n South African Journal of Plant and Soil - Interaction of small-scale supplemental irrigation, sawah preparation intensity and soil amendment type on productivity of lowland sawah-rice system

Volume 34 Number 4
  • ISSN : 0257-1862
  • E-ISSN: 2167-034X
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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 springsupplemented 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.

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