A study on the productivity under the continuous maize cultivation in Sainyabuli Province, Laos I. Yield trend under continuous maize cultivation

Continuous maize cropping has increased in Laos. Because maize is continuously cultivated without fertilizer or any soil conservation practices, there is a concern that maize yield is decreasing. In this study, we conducted a field survey and interviews with farmers to quantify maize production sustainability under continuous cultivation in relation to topographical characteristics in farmers’ fields within Sainyabuli Province, Laos. Yield was investigated over a two-year period at three sample sites in each of the 40 farmers’ fields, including sloped and flat fields. In addition, to analyze the difference in yield trend due to topo-sequential position, the sample sites were categorized into four topo-sequential positions per slope angle and relative elevation: “upper,” “middle,” and “lower” positions for sloped fields and “flat” for flat fields. The period of continuous maize cultivation in each field varied from 1 to 30 years. The average yield of the three sample sites in each field varied from 1.1 to 6.0 t ha⁻¹ and tended to be lower as the period of continuous cultivation was longer. ANCOVA and regression analysis for each topo-sequential position indicated that the decreasing yield trend in each field were mainly derived from the upper position of sloped fields. Cost of 1.7 t ha⁻¹, in terms of maize yield, were required for purchasing seed, herbicide, and outsourcing plowing in maize cultivation. The linear regression line of the yield based on the period of continuous cultivation suggested that maize production decreased at −0.06 t ha⁻¹ year⁻¹; but it could be economically viable for 43 years. However, yield in six of the 36 fields was evaluated as below profitable levels, indicating that urgent improvements in field and crop management are required to produce maize sustainably.