Lowland rice improvement in northern and northeast Thailand 1. Effects of fertiliser application and irrigation

Yield of rainfed lowland rice is commonly low because of frequent drought and low fertiliser input. Seven experiments were conducted in Thailand in the period 1993-1995 where effects of various fertiliser regimes: nil, farmyard manure, chemical fertiliser with different rates of N were examined under irrigated and rainfed conditions. The objective of these experiments was to quantify irrigation, fertiliser and their combined effects on crop growth and grain yield of lowland rice. While there was not always standing water in the rainfed paddy, no severe water stress developed in any experiment. The yield, however, was lower by up to 65% under rain fed conditions compared to that obtained under irrigated conditions, and the reduction in yield was greater when no fertiliser was applied. Fertiliser application improved yield under both rainfed and lowland conditions in all experiments, and was particularly effective under rainfed conditions. The mean yield increase due to the farmyard manure application was 850 kg ha, while that of chemical fertiliser was 1000 kg ha. Farmyard manure was as effective as chemical fertiliser, provided the manure contained high nutrient content. Increased N rate at an adequate level of P and K supply increased grain yield by about 10 kg kg (applied N) in treatments with adequate water. The positive effect of fertiliser and irrigation was mostly through greater total dry matter production and panicle number with little effect on harvest index. It is concluded that without severe water stress, grain yield of rainfed lowland rice can be increased with increased nutrient availability. This can be achieved by maintaining standing water for longer or by applying an appropriate fertiliser