Increased root zone oxygen by a capillary barrier is beneficial to bell pepper irrigated with brackish water in an arid region

Limitations to growth and biomass production are expected under high (>30 °C) soil temperatures due to low soil oxygen levels and insufficient oxygen transport to roots. These limitations will be exacerbated when irrigation with brackish water dictates large amounts of water application for leaching salts. We hypothesized that the introduction of an artificial capillary barrier (CB), in the form of a gravel layer at the lower root-zone boundary, can increase yields of irrigated horticultural crops due to better soil aeration and improved oxygen supply to roots. The specific objectives of the study were (1) to isolate scenarios where insufficient oxygen concentrations may limit pepper plant growth, (2) to measure oxygen concentrations in media under varied scenarios of CB placement below the active root zone and (3) to understand the environmental factors leading to sub-optimum oxygen concentrations in horticultural soils in a desert environment where supra-optimal soil temperatures are prevalent. At high root-zone temperatures oxygen flux to the roots was lower than the potential uptake rate and therefore soil oxygen concentrations were sub-optimal. These conditions led to reduced plant biomass and fruit yield. Fruit yield was found to decrease by 1% for every soil oxygen concentration decrease of 700 ppm. In a fine textured Reg soil, allowing roots to penetrate into the capillary barrier gravel layer increased oxygen concentration in the root zone by 5% and improved biomass and fruit yield by 16% and 18%, respectively.