Economics of row spacing and integrated weed management in soybean (Glycine max L.)

Abstract

The high cost of cultivation and weed management are major limiting factors to increasing soybean productivity and net returns. Field experiments were conducted in 2016 and 2017 at the Teaching and Research Farm of the Federal University of Agriculture, Abeokuta to evaluate the economic performance of different row spacings and integrated weed management system in soybean. Three row spacings (50, 75 and 100 cm) as the main plots and six weed control methods and a weedy check as sub-plot treatments were accommodated in a split-plot arrangement of a randomized complete block design with three replications. There was a significant reduction in weed biomass with a reduction in row spacing from 100 cm to 75 cm and 50 cm. Furthermore, the cost of production, grain yield and gross profit increased with a reduction in row spacing from 100 to 75 and 50. When soybean was sown at 50-cm row spacing, the application of Probaben 400EC (metolachlor 20% w/v + prometryn 20% w/v) or Butachlor 60EC (butachlor) at 2.0 kg a.i/ha each followed by supplementary hoe-weeding at 6 weeks after sowing (WAS) resulted in the highest yield of 2301-2484 kg/ha and total revenue of 2129-1972 $/ha. Conversely, three hoe-weedings resulted in the highest yield of 2155-2081 kg/ha and total revenue of 1848-1783 $/ha for crops grown at 75- and 100-cm row spacings. Despite the higher yield and revenue obtained with three hoe-weedings for crops grown at 75- and 100-cm row spacings, the gross profit and benefit-cost ratios obtained were lower than those obtained with herbicide treatments applied alone or followed by supplementary hoe-weeding. In terms of profitability, soybean planted at 50-cm row spacing and treated with Probaben 400EC at 2.0 kg a.i/ha followed by supplementary hoe-weeding gave the highest gross profit of 1479 $/ha. Two or three hoe-weedings in soybean planted at narrow-row (50 cm) spacing did not guarantee the highest yield, but rather increased the cost of weed control. This study suggests that narrow-row spacing (50 cm) and pre-emergence herbicides will help to reduce the number of hoe-weedings and consequently the high cost of production required for optimum yield and increase profitability in soybean production.