Tolerance and selectivity of cereal species and cultivars to postemergence weed harrowing

Summary

Post-emergence weed harrowing and other cultivation methods to control weeds in early crop growth stages may result in crop damage due to low selectivity between crop and weeds. Crop tolerance to cultivation plays an important role but it has not been clearly defined and analysed. We introduce a procedure for analysing crop tolerance based on digital image analysis. Crop tolerance is defined as the ability of the crop to avoid yield loss from cultivation in the absence of weeds, and it has two components: resistance and recovery. Resistance is the ability of the crop to resist soil covering and recovery is the ability of recover from it. Soil covering is the percentage of the crop that has been buried due to cultivation. We analysed data from six field experiments, four experiments with species of small-grains, barley, oat, wheat and triticale, and two experiments with barley cultivars with different abilities to suppress weeds. The order of species’ tolerance to weed harrowing was triticale > wheat > barley > oat and the differences were mainly caused by different abilities to recover from soil covering. At 25% soil covering, grain yield loss in triticale was 0.5% (95%-CI: -2.3%-3.3%), in wheat 2.5% (95%-CI: -0.1%-5.0%), in barley 3.7% (95%-CI: 1.3%-6.1%), and in oat 6.5% (95%-CI: 4.3%-8.6%). Tolerance, resistance and recovery, however, were influenced by year, especially for oat and barley. There was no evidence of differences between barley cultivars in terms of tolerance indicating that differences among species are more important than differences among cultivars. Selectivity analysis made it possible to calculate the crop yield loss due to crop damage associated with a certain percentage of weed control. In triticale, 80% weed control was associated with 22% crop soil cover on average, which reduced grain yield 0.4% on average in the absence of weeds. Corresponding values for wheat, barley and oat were 23%, 21% and 20% crop soil cover and 2.3%, 3.6% and 5.1% grain yield loss.