Water stress and watertable depth influence yield, water use efficiency, and nitrogen recovery in bell pepper: lysimeter studies

Lysimeters of size 1.5 by 1.5 by 1.5 m, containing a loamy soil, were used to study the effects of both water stress during the reproductive stage and underground water supply on bell pepper (Capsicum annuum L.). Continuous water stress treatments were obtained providing irrigation equal to 40%, 50%, 60%, 80%, and 120% of maximum evapotranspiration (ET), evenly applied from flowering to end of the season. Another set of treatments involved a transient drought stress imposed by withholding 80 mm of irrigation, based on ET, beginning at 2 growth stages (early fruit set, or mid fruit growth). A well-watered control (irrigated restoring the entire ET) was included for comparison. The underground water supply treatments involved 3 permanent watertable depths (0.40, 0.70,and 1.10 m below soil surface) and one variable depth increasing from 0.40 to 1.30 m. Continuous water stress significantly reduced total fresh weight of fruit, which was linearly related to the water consumption. The highest marketable yield was found at irrigation of 120% ET; the lowest at 40% ET. Marketable yield did not differ among 60%, 80%, and 100% ET. Withholding water during early fruit set restricted fruit yield significantly, whereas plants undergoing drought later in fruit growth yielded as well as the well-watered control. Total fruit yield with a shallow watertable (0.40 m depth) was comparable to above-ground irrigation restoring 100% ET, but marketable yield was significantly reduced. Highest marketable yield was obtained with watertable at 0.7 m depth, but was reduced by lowering watertable depth. The lower yield observed in water shortage conditions was generally due to a reduced fruit number. In most cases, water use efficiency decreased with increasing water consumption, but was not affected by transient drought stress. Crop nitrogen content was the highest when irrigation provided 100% and 120% ET restoration. It was significantly reduced only by both 40% ET and watertable irrigated treatments. Generally, a shallow watertable allowed less nitrogen rescue than a deeper one. The critical period for water was identified between the beginning of fruit set and first maturing fruits when soil water potential should be maintained above -0.02 MPa.