Physiological and Economic Aspects of Lettuce Production under Deficit Water and Nitrogen Conditions

This paper presents research on lettuce production's physiological and economic aspects under deficit water and nitrogen conditions. Lettuce (Lactuca sativa L. var. longifolia) is an essential crop for the economy of California. Two experiments were conducted during fall 2017 and spring 2018 to evaluate the effect of different water applications (0, 25, 50, and 100% of required water to replenish weekly crop evapotranspiration). Nitrogen fertilizer levels (0, 25, 50, and 100 percent of nitrogen required for optimum plant growth based on soil chemical analysis) on lettuce optimize the best water and nitrogen level to achieve the highest input efficiency economically justifiable yield. Soil moisture followed a decreasing trend as the irrigation level decreased, while there was no identical trend in soil moisture content in response to nitrogen treatments. The highest leaf water potential was measured for 100% nitrogen application (N100), whereas the lowest one was recorded in the plants with zero nitrogen (N0). The higher irrigation levels caused lower leaf water potential in lettuce, while the zero irrigation level (IR0) demonstrated the highest leaf water potential. Across all treatments, leaf chlorophyll content was more significantly affected by irrigation levels compared to nitrogen treatments. The higher irrigation and nitrogen levels up to 100% produced the highest lettuce yield. However, the highest water and nitrogen use efficiency was recorded at IR50N25 treatment in both growing seasons. The same treatment produced an economically justifiable yield.