Role of Irrigation and Nitrogen Fertilizer Stress on Lettuce Growth and Development in Precision Agricultural System

Lettuce as an important vegetable crop warrants special research and attention because California dominates the U.S. lettuce production. Thus, because of environmental and economic concerns, it is necessary to determine the most efficient levels of irrigation, and nutrients such as nitrogen to achieve the optimum yield in lettuce. Two field experiments were conducted to test the effect of irrigation and nitrogen fertilizer on agronomic and physiologic characteristics of lettuce (Lactuca sativa L.) through the precision agricultural system. Treatments were arranged in a split - strip plots based on a completely randomized block design with three replications. The irrigation and nitrogen treatments were considered at four levels (0, 25, 50, and 100% of the required water and N fertilizer to achieve the maximum yield). Results showed that 50% of required irrigation and 25% required nitrogen (IR50N25) treatment led to a significantly higher water (4.4 kg/m3) and N (45 kg DM/kg N) use efficiencies for the Fall experiment in 2017, respectively. The same results for water of 3.9 kg/m3 and N of 73.1 kg DM/kg N were achieved in the Spring experiment 2018, respectively. The optimum lettuce biomass yield was obtained in IR50N25 treatment for both experiments. Leaf chlorophyll content did not follow any significant trend under different irrigation and nitrogen treatments in the Fall experiment. However, in the Spring experiment significantly higher (p≤0.0.5) chlorophyll content was measured in IR100N50 treatment compared to control. Negative leaf water potential was significantly (p≤0.0.5) higher at IR0N100 compared to other corresponding treatments in both experiments. Correlation between UAV-NDVI leaf chlorophyll content measurements and SPAD readings for chlorophyll was two times higher in the Spring compared to the Fall experiment.