Nutrients enhance genotype and water responses in rainfed lowland rice in southern Lao PDR

Food security in Lao PDR, a small nation in southeast Asia categorized as low-income food-deficit, is strongly dependent on the success of the rainfed lowland rice crop in the southern provinces. Soils there are sandy in texture, low in water-holding capacity, and low in pH and available nutrients. Farmers are reluctant to apply recommended fertilizer doses, as rainfall and crop responses are unreliable. This paper examines fertilizer response, and considers opportunities to improve the risk profile. The effects of 12 fertilizer-water-genotype treatment combinations were examined across 60 locations, and combined analysis of variance and pattern analysis was used to examine crop response and its relationship to soil fertility, genotype, and climatic variability. The results showed there was little relationship between soil test and grain yield in unfertilized plots, suggesting nutrient release and capture were more important than soil nutrient concentration, so integrative measures of soil nutrient release should be more promising. Despite low yield in the absence of applied nutrients (0.89–2.66, mean 2.18 t ha-1), NPK alone increased yields by 1.0 t ha-1 on average (1.48–3.86, mean 3.12 t ha-1), while water and genotype together with NPK increased yields by up to a further 1.0 t ha-1 (1.95–4.76, mean 3.42 t ha-1). Fertilizer responses were greater and more reliable when soil nutrient buffering capacity was greater, which, together with seasonal expectations, could be used to better inform decisions on fertilizer application in relation to risk. A longer-term and moderate input strategy was proposed in order to gradually improve fine-fraction SOC, soil nutrient buffering, and soil microbial biomass, in order to improve soil nutrient and water retention and release characteristics. This strategy should be evaluated in future research.

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