Assessing Light Competition for Cereal Production in Temperate Agroforestry Systems using Experimentation and Crop Modelling

Abstract

In every agroforestry system, the tree canopy reduces the incident radiation for the crop. However, cereal varieties were selected, and most crop growth models were designed for unshaded conditions, so both may be unsuited to agroforestry conditions and performance. In southern France, durum wheat productivity was monitored over 2 years in an agroforestry system including walnut trees and under artificial shade conditions. Yield components were measured in both full and reduced light conditions. The cereal yield was always decreased by shade; by almost 50% for the heaviest shade conditions (31% of light reduction). The main effect of the shade was the reduction in the number of grains per spike (35% at the most) and in the weight of grains (16% at the most). The mean grain weight was moderately affected, while the protein content was increased in shaded conditions (by up to 38% for artificial shade). Consequently, the protein yield per hectare was less reduced by the shade than the dry matter grain yield. A crop model (STICS) was also used to simulate the crop productivity in full light and shaded conditions, but the crop LAI and the yield components were not correctly simulated in the shade. The simulations emphasized the sensitivity of the wheat grain filling to shade during the critical period, 30 days before flowering, for yield elaboration. Further experimental and modelling studies should take into account the heterogeneity of shade intensity due to the shape of the tree crown, the width of the crop alley and the orientation of the tree rows and the modification of carbon allocation inside the plant. 2004). In Mediterranean areas, water stress is one of the main production constraints for cereals, particularly durum wheat. This is a consequence of the variability of the frequency and amount of rainfall during the growing season (Garcia del Moral et al. 2005, Katerji et al. 2008). Light availability is greatly modified in agroforestry systems compared to cropping systems based on annual crops such as soybean (Rivest et al. 2009), corn (Reynolds et al.

Impact of spatio-temporal shade dynamics on wheat growth and yield, perspectives for temperate agroforestry

“…Several authors have shown that reducing incident light on a wheat crop leads to growth and yield repercussions and our study is no exception (Chirko et al, 1996;Dufour et al, 2013;Li et al, 2010;Mu et al, 2010). According to these studies, the magnitude of wheat response varies with the level and period of shade application.…”

“…Finally, grain yield, as well as grain protein concentration, has to be taken into consideration when evaluating the wheat production: quantity and quality (protein content). Just like Dufour et al (2013), we measured an increase of protein grain content with increasing shade intensity, but the increase did not compensate the final yield decrease. The protein content of the grain resulted from the remobilization of N accumulated by the plant and is negatively related to final grain yield due to a dilution effect.…”

“…Furthermore, the crop components, such as final grain yield, are related in a non-linear way to the reduction in cumulative global radiation from sowing date to harvest. Dufour et al (2013) and Li et al (2008) reported that an average reduction of transmitted cumulated global radiation by 17% or 34% led to an average yield depression of 20% and 51% respectively. Here, we demonstrated that a reduction of 61% and 43% of the global radiation cumulated during the shade period induced a final yield reduction of 45% and 25% respectively under CS and PS treatment, in 2015.…”

“…These studies show a systematic reduction of final crop yield but the intensity of this decrease varies between species, as does the shade level and possible below-ground interactions. In order to differentiate the effect of light from the other possible abiotic and biotic interactions occurring between trees and crops in agroforestry system, several authors designed and used an artificial shade system (Dufour et al, 2013;Peri et al, 2002;Varella et al, 2010). Earlier articles evaluated the ability of artificial shade materials to mimic the fluctuating agroforestry light environment over the day or through the cropping season.…”

“…In comparison, conventional plastic shade-cloth only produced a predetermined level of light reduction. Dufour et al (2013) presented the potential of adding overlapping shade cloths during the cropping season in order to mimic the increasing leaf area of trees. These artificial structures were used to analyze crop and forage development, yield and physiological responses to shade (Dufour et al, 2013;Peri et al, 2002;Varella et al, 2010).…”