Timing of weed management and yield penalty due to delayed weed management in soybean

Olumide S Daramola

doi:10.1590/s0100-83582020380100072

Abstract

Background: Weed interference is a major limiting factor for economically viable soybean production. Appropriate timing of weed management would enable farmers to make more efficient use of resources for weed management. Objective: The objective of this study was to determine the critical period for weed competition and appropriate timing of weed management for optimum yield of soybean. Methods: The treatments consisted of periods of weed infestation and weed removal for the first 14, 28, 42 and 56 days after sowing (DAS), and till harvest in a randomized complete block design with three replications in 2016 and 2017. Results: Soybean yields in both years ranged from 914-945 kg ha-1 with no weed control to 1,984-2,127 kg ha-1 in the weed-free plots; a yield loss of 53-56. Weed infestation for the first 14 DAS had no detrimental effect on growth and yield of soybean provided the weeds were subsequently removed. Increasing period of weed interference from 14 to 42 DAS resulted in a steady decline in growth and yield of soybean. Yield losses equivalent of 32-37 kg ha-1 resulted for each day that weed control was delayed between 14 and 42 DAS. Subsequent weed control after 42 DAS did not improve growth and yield significantly, nor obviate yield depression of the crop compared to crop weed-infested till harvest. Conclusions: Results indicated that the critical period of weed competition in soybean was between 14 and 42 DAS. Hence soybean should be maintained weed-free during this period to avoid high yield loss.

Highlights

Soybean (Glycine max (L.) Merrill) is the most important legume crop globally, with a harvested area of 118 million ha and total production of 308 million Mg (FAOSTAT, 2017), accounting for 56% of total global oil seed production (Wilson, 2008)
Plots kept weed-free until 14 days after sowing (DAS) (WF14) and those weedinfested until 42 DAS (WI42), 56 DAS (WI56) and harvest (WIhar) had similar weed density and dry weight in both years (Table 3)
Weed interference between 14 and 42 DAS (WI14 - weed interference increased to 28 DAS (WI28) - WI42) reduced number of leaves by 32 - 46%, leaf area index by 26 - 35%, dry weight by 13 - 15%, crop growth rate by 7 - 22% compared to crops kept weed-free till harvest in both years (Table 4)

Summary

INTRODUCTION

Soybean (Glycine max (L.) Merrill) is the most important legume crop globally, with a harvested area of 118 million ha and total production of 308 million Mg (FAOSTAT, 2017), accounting for 56% of total global oil seed production (Wilson, 2008). Soybean present a feasible alternative to addressing malnutrition in SSA because of its high protein, oil content and essential amino acids (Joubert and Jooste, 2013). It has ability in fixing nitrogen (44-103 kg ha-1) for its own use and the benefit of intercropped cereals and subsequent crop in rotation (Ronner et al, 2016). This is a major benefit in Africa farming systems, where soils have become exhausted by the need to produce more food for increasing populations, and where fertilizers are hardly available and are expensive for farmers. This study was carried out to evaluate growth and yield response of soybean to different periods of weed interference and timing of weed control

MATERIALS AND METHODS

AND DISCUSSION

Findings

CONCLUSIONS