Dynamic Optimization of Greenhouse Tomato Irrigation Schedule Based on Water, Fertilizer and Air Coupled Production Function

Abstract

A vegetable water production function has been one of the most significant parameters to improve the use efficiency and economic benefit of agricultural water in the greenhouse. Meanwhile, aerated irrigation unlocks the high yield potential for greenhouse crop production. Thus, water, fertilizer and air coupled production function is proposed for the optimization of the irrigation scheme during the greenhouse tomato growth period. Two seasons of greenhouse tomato experiments were conducted under aerated subsurface drip irrigation (ASDI). There were three nitrogen application rates (N1, 120 kg ha−1; N2, 180 kg ha−1; N3, 240 kg ha−1) and three aeration rates with dissolved oxygen (DO) in irrigation water (A2, 15 mg L−1; A3, 40 mg L−1 and A1, 5 mg L−1 in the non-aeration treatment) in the first crop season, while three irrigation rates of soil moisture content (W1, 50–60% field capacity; W2, 60–70% field capacity; W3, 70–80% field capacity) and two aeration rates with DO in irrigation water (25 mg L−1 and 5 mg L−1) in the second crop season. The potential yield function of tomato was constructed, and the water sensitivity index was resolved. The production function of greenhouse tomato under water, fertilizer, and air coupled irrigation was established based on the Jensen function. The water allocation scheme under multiple irrigation quotas was optimized by the dynamic programming (DP) method. The results showed that with the elapse of crop growth stages, the cumulative curve of the water sensitivity index showed an S-shaped curve, which first rose slowly and then fast, and eventually tended to be stable. The optimized irrigation increased the yield by 4.25% averagely compared with the irrigation method of fixed moisture content interval, while the crop yield in the optimized ASDI increased by 26.13% compared with non-aeration treatment. In summary, the optimal combination was the aeration rate DO of 24.55mg L−1 in irrigation water and nitrogen application rate of 281.43 kg ha−1, and the irrigation quota of 420 mm. The net yield increased by 11,012 USD ha−1 in a single crop season when compared with the non-aeration treatment. The results would provide a reference method for the optimization of technical parameters of water—fertilizer—air coupled irrigation.