Do light and alfalfa responses to cloth and slatted shade represent those measured under an agroforestry system?

Abstract

Shade cloth is commonly used in agroforestry research. It produces a continuous, uniform reduced light environment. Shade cloth and a slatted structure were compared in relation to the inability to represent the light regime and plant responses of an agroforestry system. The split-split-plot randomised block experiment had main plots as covering status (with or without radiata pine trees), subplots as artificial shade (none, shade cloth or wooden slats) and sub-subplots as growth rotation, over sown alfalfa, in three replicates. The quantity of light transmittance was 49% under trees, 41% under cloth and 44% under slats. Temporal changes and spectral composition under trees were more accurately reproduced under the slats than shade cloth. The red to far red ratio was 0.64 under tree shade and 0.74 during the shaded period under slats. This compared with 1.31 in open pasture, 1.28 under shade cloth in open and 1.26 under slats during sunny periods. To compensate for low light quantity and quality, alfalfa had elongated stems and internodes. In open pasture and under cloth in the open, it produced short stems. The mean dry matter yield under trees was 68% of the 30.3 t ha -1 in open pasture, 56% under cloth and 57% under slats. The slats induced similar morphological responses in alfalfa to those in the agroforestry system. The magnitude of changes had little effect on growth and yield responses. The artificial slatted structure approximated the intermittent light environment and consequent plant responses observed in an agroforestry system.

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

“…Earlier articles evaluated the ability of artificial shade materials to mimic the fluctuating agroforestry light environment over the day or through the cropping season. Varella et al (2010) demonstrated that wooden slatted structures reproduced well the daily periodic light fluctuation and the spectral composition observed under trees. In comparison, conventional plastic shade-cloth only produced a predetermined level of light reduction.…”

“…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.…”

“…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).…”

Forage yield, rate of CO 2 assimilation, and quality of temperate annual forage species grown under artificial shading conditions

“…Each structure was square with sides measuring 2.5m and was composed of transversely mounted boards covering a graduated wooden stand, such that the slats were always 0.3m above the top of the canopy. During the experimental period the slats were raised relative to increases in plant height, following the methodology described by VARELLA et al (2010).…”

“…In each plot, two readings were taken at 12:00 hours on clear days, to assess how much photosynthetically active radiation (PAR) each slatted structure was blocking at the time of maximum PAR incidence (VARELLA et al, 2010;PERI et al, 2002). PAR readings were made both above and below each shaded structure.…”