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

VARELLA A.C.; MOOT D.J.; POLLOCK K.M.; PERI P.L.; LUCAS R.J.

AGROFORESTRY SYSTEMS

SPRINGER

Lugar: Berlin; Año: 2011 vol. 81 p. 157 - 173

0167-4366

Plastic shade cloth is the most common artificial shade material applied in agroforestry research. It results in a continuous and uniform light regime. However, shade cloth may not accurately mimic the intermittent light regime of an agroforestry system. As an alternative, a slatted structure was constructed to produce a fluctuating light regime. The aim was to replicate the duration of direct sunlight and shade under an agroforestry environment. This study compares the light regimes from the two artificial shade materials and their accuracy to reproduce an agroforestry light environment. The experimental design was a split-plot randomised block with the main plots as covering status (with or without radiata pine trees) and sub-plots as artificial shade structures (none, shade cloth or wooden slats) in three replicates. Both artificial shade structures successfully simulated the quantity of light transmission (41% and 44% transmissivity) observed under the agroforestry site (49% transmissivity). However, the temporal pattern and spectral composition under the slats were closer to that observed under the trees than the shade cloth. The R/FR ratio was equivalent between the slatted (0.74) and tree (0.64) regimes during the shade period compared with 1.28 under shade cloth and 1.26 under the slats during sun period and 1.31 in full sunlight.  The two artificial shading materials produced similar total DM yield to that measured under the trees, but lower than that observed in full sunlight (30.3 t.ha-1). The DM yield was 56, 57 and 68% of the full sun yield under cloth, slats and trees treatments, respectively. Leaf photosynthesis rates decreased rapidly when exposed to shade after a period of full sun under either the slats or trees. The slatted structure was a more accurate method than shade cloth to artificially simulate the intermittent light environment observed under an agroforestry system.