Abstract

Soybean is an important economic crop for the food and livestock industries. However, the cultivated area and yield of soybean have been continuously declining, making it necessary to find ways to increase productivity and expand cultivation areas. This study aimed to evaluate the yield of soybean varieties under different planting distances and fertilizer rates, as well as analyze the economic returns of each method. The experiment was conducted on six soybean varieties: Chiang Mai 6, Chiang Mai 60, Kwok Chiang Mai 7, Kasetsart 80, Suiyuan, and SB007. Three planting distances were tested: row spacing of 50 cm, plant spacing of 20 cm (SP1); row spacing of 40 cm, plant spacing of 20 cm (SP2); and row spacing of 30 cm, plant spacing of 20 cm (SP3). Additionally, two fertilizer rates were applied: N:P:K 3:6:9 kg/rai (F1) and N:P:K 3:9:12 kg/rai (F2). The results showed that all three factors significantly affected yield. Among the varieties, Kasetsart 80 had the highest average yield of 439 kg/rai. For planting distance, SP3 produced the highest average yield of 408.5 kg/rai, followed by SP2 and SP1. Regarding fertilizer rates, F1 resulted in a higher yield than F2 by 10 kg/rai. The highest yield was obtained from Kasetsart 80 at planting distance SP2 with fertilizer F2 (489 kg/rai), followed by Kasetsart 80 at planting distance SP3 with F2 (472 kg/rai). Therefore, selecting a high-yielding variety along with planting distances of SP2 or SP3 and applying an appropriate fertilizer rate can help maximize soybean yield and net profit.