Sparse-shading red net improves water relations in Valencia orange trees

Top-netting technology improves crop microclimate, and its utilization in fruit tree plantations may mitigate deleterious weather effects. The technology is associated with improved tree water relations, and may result in significant water savings. Photoselective nets may provide additional, crop- and target-dependent, beneficial effects. A previous paper reported results of a five-year trial in Valencia orange, in which three nets were used, pearl, transparent and low shading red, in combination with three irrigation regimes, 100% (I100), standard commercial fertigation, and two reduced rates, 80% (I80) and 60% (I60). Among the different netting types, the combination of red nets and I80 resulted in the highest yield on a multi-annual basis. The current study provides data regarding water relations during stage II, i.e., cell expansion, of fruit development. The red net had higher radiation transmittance and canopy resistance than the pearl net. The higher resistance is an expression of the lower transpiration of the red net, monitored by sap flow, as compared to the other treatments, especially under deficient irrigation. The beneficial effect of the red net was also evidenced from multi-annual stem water potential. These data supplement the enhanced yield effect of the red net, suggesting they are associated with its spectral properties