How Important are Crop Spatial Pattern and Density for Weed Suppression by Spring Wheat?

Abstract

Previous research has shown that both the density and spatial pattern of wheat have an influence on crop growth and weed suppression, but it is not clear what degree of uniformity is necessary to achieve major improvements in weed suppression. Field experiments were performed over 3 yr to investigate the effects of crop density and different spatial distributions on weed suppression. The spatial pattern of spring wheat sown in five patterns and three densities in small weed-infested plots were analyzed with the use of digitized photographs of field plots to describe the locations of individual wheat plants asxandycoordinates. We used a simple quantitative measure, Morisita's index, to measure the degree of spatial uniformity. Increased crop density resulted in reduced weed biomass and increased crop biomass every year, but crop pattern had significant effects on weed and crop biomass in the first year only. Weather conditions during the second and third years were very dry, resulting in very low weed biomass production. We hypothesize that water deficiency increased the importance of belowground relative to aboveground competition by reducing biomass production, making competition more size symmetric, and reducing the effect of crop spatial pattern on weed growth. The results indicate that increased crop density in cereals can play an important role in increasing the crop's competitive advantage over weeds, and that spatial uniformity maximizes the effect of density when low resource levels or abiotic stress do not limit total biomass production.

EFFECTS OF PLANTING DATE AND SPATIAL ARRANGEMENT ON COMMON BEAN (Phaseolus vulgaris) YIELD UNDER WEED-FREE AND WEEDY CONDITIONS

“…Crop spatial pattern is another agronomic factor that can affect grain yield and crop competitiveness against weeds (Olsen et al, 2012). It has been suggested that uniform planting pattern increases the spatial uniformity in leaf area index (LAI), reduces mutual shading, and hastens canopy closure, all of which result in increased radiation interception (RI) by the canopy (Olsen & Weiner, 2007) and increased crop growth and yield (Mashingaidze et al, 2009).…”

“…Some researchers (Weiner et al, 2001;Olsen & Weiner, 2005;Olsen et al, 2012;Dusabumuremyi et al, 2014) noted that increased crop uniformity had a negative effect on weed biomass. However, some other researchers (Teasdale, 1995;Westgate et al, 1997) reported that crop growth and yield does not always increase in narrow-row planting.…”

Weed Management Options in Conservation Agriculture

“…A narrow row spacing of 15 cm was reported to perform better in suppressing P. minor compared with the 23 cm spacing (Mahajan et al, 2004). Though the effectiveness of reduced row spacing on weed control depends on several other factors, including water limitations, nutrient placement, ratio between crop to weed height, and timing of emergence of crops and weeds, several recent studies have shown increased uniformity can help in reducing weed biomass as well as increasing yields in a variety of crops (Weiner et al, 2001;Olsen et al, 2012;Marin and Weiner, 2014).…”

Effects of spatial pattern and cultivar on weed control and grain yield in rice at reduced rates of herbicide

“…The use of these machines is increasing because manual transplanting is a labour intensive operation in the cultivation of rice. At the same time, previous studies have shown that crop spatial pattern can affect crop growth, grain yield and herbicide efficacy (OLSEN et al, 2012, OLSEN et al, 2005, WEINER et al, 2001. A recent study, Olsen et al (2012) observed that increased crop uniformity had a negative effect on weed biomass, and concluded that crop pattern effects on weeds occur only through size-asymmetric competition.…”

“…At the same time, previous studies have shown that crop spatial pattern can affect crop growth, grain yield and herbicide efficacy (OLSEN et al, 2012, OLSEN et al, 2005, WEINER et al, 2001. A recent study, Olsen et al (2012) observed that increased crop uniformity had a negative effect on weed biomass, and concluded that crop pattern effects on weeds occur only through size-asymmetric competition. Olsen et al (2005) have shown that a highly uniform pattern of wheat plants suppresses weeds 30% better than plants distributed in row pattern.…”