Regulation of nitrogen forms on growth of eggplant under partial root-zone irrigation

Water and nitrogen (N) supply in eggplant (Solanum melongena L.) cropping system is an essential factor for controlling the production level, especially in water-limited areas. Shortage of available water and escalating irrigation costs along with high prices of fertilizers dictate adoption of practices that improve water- and N-use efficiency. This study investigated the effects of different irrigation amounts and modes as well as N forms on yield, photosynthesis and irrigated water-use efficiency (IWUE) of a local eggplant cultivar (Jing Yuan No. 1) under partial root-zone irrigation. Two irrigation treatments were sufficient irrigation (enough water to keep the soil moisture in the top 0–40 cm at 90% of field water capacity) and deficit irrigation (60% of the water irrigated in sufficient irrigation treatment was applied). Three irrigation modes were conventional irrigation, alternate partial root-zone irrigation (APRI) and fixed partial root-zone irrigation (FPRI). The N treatments were nitrate-N and ammonium-N forms. Under sufficient irrigation, N forms had little effect on yield, leaf N concentration, IWUE, chlorophyll content, leaf water potential and the distribution of root mass, whereas the total length of root was higher in the irrigated furrow than in the non-irrigated furrow. Under deficit irrigation, eggplant had significantly higher biomass when supplied with nitrate-N than with ammonium-N. In addition, IWUE increased under deficit irrigation, particularly with nitrate-N than ammonium-N. With deficit irrigation, APRI increased eggplant growth, and improved fertilizer and water use efficiency more than FPRI at a given form of N fertilizer. Hence, under deficit irrigation, nitrogen forms had a significant effect on the growth of eggplant under partial root-zone irrigation; APRI as a water-saving irrigation technology could play a vital role in saving water and getting high yields in agricultural production.