WALNUT PRODUCTION AND QUALITY AS INFLUENCED BY ORCHARD AND WITHIN TREE CANOPY ENVIRONMENT

Differences in walnut quality through the tree canopy may be related to water relations and/or light gradients. The data we have at present suggests that photosynthate reduction early in the season (due to leaf loss related to shading) results in shriveled nuts while later reduction results in either yellow or black pellicles, depending on the timing. Some of the yellow nuts occurred in positions where the spur was in a well lit position early in the season but became shaded as the season progressed due to higher limbs coming down on top of them. All of the nuts with yellow and black pellicles had a mushy, wet hull surrounding the nut. The photosynthate reduction can be caused by low light conditions and/or loss of leaves. In addition, it appears that orchards running near the fully watered baseline (in the -4 to -5.5 bar midday stem water potential range) have a decrease in nut quality compared to orchards in the -6 to -7 bar range although the mechanism is not yet known.