Nutrient Balances and the Sustainability of Sugarcane Fields in a Mini -Watershed Agroecosystem of Northeast Thailand(<Special Issue>Sustainable Agro-resources Management in the Mountainous Region of Mainland Southeast Asia)

Abstract

Large areas of undulating terrain in Northeast Thailand are dominated by farming systems based on rainfed upland crops and lowland rice. Evidence of a substantial decline in land productivity from current land uses and management points out the need for a more detailed assessment on land-use sustainability of the region. The present study evaluated nutrient balances of different types of sugarcane fields as an indicator of land-use sustainability. The crop is currently the most widely grown field crop in the region, and its production practices involve high fertilizer inputs and considerable soil disturbances. Kham Muang village in Khon Kaen province was selected as a study site. Four types of sugarcane subsystems were recognized based on their differences in nutrient input and output parameters. These included combinations of two rates (high and low) of fertilizers and two practices of field burning prior to harvesting (burned and not burned). Sources of nutrient inputs and outputs were identified for the individual subsystems. Amounts of major nutrients (N, P and K) were determined for the individual sources, based primarily on actual field measurements in farmers' fields in Kham Muang and adjacent villages and in a mini-watershed in Kham Muang village. Nutrient balances were then calculated for the full three-year cycle of the individual subsystems and at three yield levels (high, moderate and low). The results showed that N balances were mostly positive but P and K balances were negative for all subsystems. Positive balances of N were high at the high fertilizer rate and low yield level, declined at the low fertilizer rate and higher yield levels, and became negative when the field was burned. Negative P and K balances increased as yield level increased and when the low rate of fertilizer was applied. Field burning caused significant losses for all three nutrients, making negative balances even higher for P and K in burned field; the amounts were quite substantial in all subsystems. Excess N is likely to be lost through water flow, but continuation of current practices can cause P and K depletion in the long run. Measures to adjust the balances of these two nutrients are needed to improve land-use sustainability of sugarcane production in the region.