Intelligent drip fertigation increases water and nutrient use efficiency of watermelon in greenhouse without compromising the yield

Intelligent drip fertigation (IF) is an efficient way to tailor water and nutrient requirement for crops to reduce their adverse impacts on environment. A three-year (2019–2021) field trials of watermelon was conducted to evaluate the effects of IF on yields and irrigation water and nutrient use efficiency of watermelon in a plastic greenhouse. The soil moisture was monitored with sensors (FDR) in the field in real time and interconnected with the computing devices embedded in the internet of things (IOT) to automatically control the irrigation and fertilization. The lower-upper limit of irrigation and the wetting soil depth were controlled accordingly to the crop stage. The fertilization rates were allocated based on the nutrient uptake characteristics of watermelon at different growth stages. The results showed the dry matter accumulation and N, P2O5, K2O uptakes of watermelon were fitted well with the "S" logistic growth function. The average proportions of dry matter accumulation, and N, P2O5, and K2O uptakes during the fruit expanding stage to the whole growth stage were 79.0%, 67.9%, 72.4%, and 71.8%, respectively. IF significantly reduced the application rates of irrigation water, N, P2O5, and K2O by 33%, 46%, 72% and 57%, respectively, without compromising watermelon yield and fruit quality. The irrigation water use efficiency, partial factor productivity, and agronomic efficiency in three years were increased significantly. The mechanism of IF treatment could be explained by tailoring the water and nutrient needs of crop by increasing root characteristics of watermelon to the water and nutrient uptake and translocation capacity of the root system. Intelligent drip fertigation is an efficient way to realize water and fertilizer space-time coupling and improve water and nutrient use efficiency.