Early-season nutrient competition between weeds and soybean

Abstract

Soybean [Glycine max (L.) Merr.] yield losses may be attributable to early-season nutrient competition with weeds; however, research investigating macro- and micronutrient accumulation of weeds in soybean is scarce. Field experiments were conducted across eight site-years in Illinois, USA to determine which soybean nutrients are most susceptible to weed competition. Weeds were controlled by applying glyphosate at 10-, 20-, 30-, or 45-cm weed heights during which accumulation of 11 nutrients were measured in soybean and broadleaf and grass weeds. For both weed groups, K and Fe were the macro- and micronutrient, respectively, with the greatest rate of accumulation. Variations in nutrient uptake between broadleaf and grass weeds were largely explained by differences in weed density, except for Ca and B, which were greater in broadleaf weeds regardless of density. Canonical discriminant analysis (CDA) identified soybean accumulation of N, P, K, Fe, and Cu as the nutrients most affected by weed competition, with P, K, and Fe uptake being particularly susceptible during droughty conditions. The weed height causing a 10% reduction in uptake was 11, 12, 12, 7, and 10 cm for N, P, K, Fe, and Cu, respectively. Soybean grain yield, seed weight, pods plant−1, and seed oil content were identified through CDA as the yield parameters most affected by weed competition. Results indicate weeds should be removed before reaching 18 cm (V2 to V3 soybean) to avoid a 5% loss in grain yield. Early-season weed control preserves yield potential and may improve efficiency of nutrient management programs in soybean.