Variation in lowland rice yield and its determinants in a rainfed area in Savannakhet Province, Laos

Abstract

Irrigated areas in the Lao People’s Democratic Republic (Laos) constitute only 12% of the total agricultural land. Most of the lowland rice is cultivated under rainfed conditions. The rice yield in rainfed fields is lower and more unstable than that in irrigated fields. Most of the lowland rice fields in Savannakhet Province, which is the main rice-producing region, cover not only lowlands but also gradual hilly terrain, with sandy soils. The water and nutrient conditions of the lowland rice fields likely differ with location and geological conditions, and rice production may be insufficient in some areas. The objectives of this study are (1) to assess rice yield and water and soil conditions in the rainfed rice fields of Savannakhet Province and (2) to identify the determinants of variation in rice yield. We selected a village with rainfed rice fields as the research site. Sixty plots were set in the rice fields, from the lowland to middle and upper positions of the terrain. The rice grain yield varied from 0.6 to 3.6 t ha−1, averaging 1.9 t ha−1, and the yield in the lower positioned fields was significantly higher than that in the upper positioned fields. Surface water in the observed fields was mostly maintained above ground level throughout the planting period, and the average surface water depth in the lower position fields was deeper than that in the upper and middle position fields. The total carbon (TC), total nitrogen, available phosphorus, and exchangeable potassium were extremely poor, while the exchangeable calcium (ExCa) and exchangeable magnesium were relatively rich, and the ExCa in the lower positioned fields was higher than that in the upper and middle positioned fields. ExCa was the main determinant of difference in rice grain yield, followed by TC.