Inter-lighting and defoliation in a soilless culture system require more dynamic water management for improving the yield-promotion effect

Abstract

Defoliation and inter-lighting affect yield and evapotranspiration. Practically, these agronomic manipulations are mainly performed on a seasonal basis. Evapotranspiration causes significant changes in the drainage volume and its electrical conductivity (EC) on a finer scale than on a seasonal basis, and these water management variables subsequently affect yield. However, the dynamic interactions between agronomic manipulations and water management variables are not well understood, despite these systematic relationships. In this study, seven tomato gutter lines consisting of three different treatment timeline schemes were designed: (1) continuous application of regular defoliation level during the experimental period, (2) intermediate transition from regular to additional defoliation level, and (3) time-varying (in the order of 12-*5-*2 h per day) inter-lighing. The time series responses of evapotranspiration, drainage, drainage EC, and tomato yield were analyzed by normalization and principal component analysis (PCA). Normalized water management variables and yield showed sensitive responses to the application of time-variable inter-lighting and two different defoliations. Increasing yield trends in the regular defoliation lines were reversed after the initiation of additional defoliation gutter lines. The yield promotion effect of inter-lighting was observed after the final time adjustment (2 h per day). Overall, these yield changes accompanied trend reversal in water management variables. PCA results summarized a perturbation effect on the yield-evapotranspiration correlations with increases in drainage volume-drainage EC covariance from the application of inter-lighting. The results indicate that defoliation and inter-lighting should be accompanied by a more flexible water management scheme. This study suggests an agronomic background for the technical optimization of defoliation and inter-lighting.