An Artificial Capillary Barrier to Improve Root-Zone Conditions for Horticultural Crops.

Capillary barriers (CBs) occur at the interface of two soil layers having distinct differences in textural and hydraulic characteristics. The primary objective of this study was to introduce an artificial CB, created by a layer of gravel below the root zone substrate, in order to optimize conditions for the cultivation of horticultural crops. A secondary objective was to test the hypothesis that the increased soil matric head created by CB would improve plant production, especially when irrigated with brackish water.

Potential root zone formats were analyzed with and without the gravel CBs for variables including: depth of CB; barrier separating the root zone from the surrounding soil; and root zone soil texture. Field and lysimeter studies were conducted with bell pepper (Capsicum annuum) plants, comparing root-zones with and without an underlying CB and irrigated at various rates with either desalinated (DW, EC = 0.2 dSm^-1)) or brackish (SW, EC = 3.8 dS m^-1) water.

Field and simulated results revealed that artificial CBs increased root zone water content and changed water flow dynamics. Plants grown above a CB, when irrigated with SW, yielded 24% higher biomass than control plants for all irrigation applications, but when DW was irrigated, only a 6% advantage for the CB root-zone was observed. Biomass yield for the root-zone containing a CB was only slightly affected by water salinity, while yields significantly decreased when irrigated with SW in the control. The extent of water uptake, plant growth and yield responses to the presence of a CB were found to be climate dependent. When VPD was low, smaller responses were measured, while more pronounced response was found when VPD increased.