Identifying Soybean Traits of Interest for Weed Competition

Abstract

Organic soybean [Glycine Max (L.) Merr.] producers rely on a variety of tactics for weed management. The use of soybean cultivars with enhanced ability to compete with weeds may increase weed control. Our objective was to identify genetic traits that may enhance soybean's competitive ability to suppress weeds. Experimental design was a split-split plot with sets of contrasting soybean genotypes assigned to the main plots, individual genotypes assigned to subplots, and weedy and weed-free sub-subplots stripped across blocks for side by side comparison of treatments in weedy and weed-free conditions. Differences in weed biomass were detected among genotypes in both years at 7 wk after emergence. Narrow-leaflet small-seeded natto types were generally poor competitors with weeds. Cultivars released as forage types did not have a consistent advantage over the control. Larger-seeded tofu genotypes were also variable in weed suppressive ability. However, N04-8906, the genotype with the greatest 100-seed weight in this study (24 g), stood out as being among the best for weed suppression, soybean biomass accumulation, ground cover at 3 wk, and early season plant height. Optimum models from multiple regression showed seed size to be the most significant trait measured in overall genotype competitive ability in both years. However, seed size effects on ground cover largely dissipated by 5 wk after emergence.

Relative competitiveness of soybean cultivars with barnyardgrass

“…This can be explained mainly by the high demand for nitrogen of barnyardgrass (Kissmann 2007), so that, in the weed monoculture, intraspecific competition for nitrogen is greater, but without discarding the competition for other environmental resources. In contrast, the highest growth rate of the weed, both in plant height and leaf area production, makes it capture the light more efficiently and, consequently, at more advanced growth stages, it may shade the crop and reduce its growth (Place et al 2011). From this study, it is not possible to conclude that barnyardgrass is more competitive than soybean crop because the main negative effect of the competitor on the cultivars was to decrease plant height, especially for BMX Apolo RR, while all other morphophysiological parameters remained virtually unchanged.…”

Soybeans Competitiveness with Morning Glory

“…For RYT higher than 1, a convex line is obtained, indicating that competition is prevented, because the supply of resources exceeds demand or because the species have different demands from the environment. The highest relative yield total (RYT) compared to what is expected reflects the behavior that demonstrates that a species is more aggressive than the other and contributes to total yield more than what is expected (Radosevich, 1987). According to Rizzardi et al (2004), the reduction in soybean biomass is more intense when in the presence of morning glory (Ipomoea ramosissima) than milkweed (Euphorbia heterophylla) and this is aggravated in situations in which the weed is established prior to culturing.…”

“…The first experiment was in an additive series, using soybeans and morning glory monocultures to obtain the population of plants m -2 , from which dry matter of shoots (SDMM) per area unit (g m -2 ) becomes independent of the population, according to the "constant final production law" (Radosevich et al, 2007). Populations tested were 1, 2, 4, 8, 16 and 32 plants pot -1 , equivalent to 37, 74, Soybeans competitiveness with morning glory 148, 296, 592 and 1,184 plants m -2 soybeans, respectively, as well as for morning glory species.…”

“…Furthermore, the presence of weeds can affect the quality of seeds, particularly the protein and oil content, increasingly important parameters to determine soybeans economic value (Millar et al, 2011). Although weeds cause damage to crops, soybeans have a higher competitive ability, and this is attributed to some growth characteristics inherent in the improvement of cultivars, including emergence speed, plant height, canopy architecture, dry matter accumulation and plants spatial arrangement (Shaw et al, 1997;Place et al, 2011).…”

“…A suitable alternative for studies of this magnitude is the use of experiments in series of replacement, for they allow the determination of which species or biotype is more competitive and, consequently, if the competition is inter-or intraspecific (Cousens, 1991). In these experiments, the ratio of each of the genotypes varies, while the total population remains constant (Radosevich et al, 2007).…”