Reducing Chemical Fertilizer Application in Greenhouse Vegetable Cultivation under Different Residual Levels of Nutrient

Excessive chemical fertilizer application in greenhouse vegetable cultivation results in environmental risks and residual nutrients in the soil. Conventional plot experiments conducted in one field cannot recommend fertilizer reduction to farmers when the residual nutrient levels were various among different fields. In this study, nine plot experiments were simultaneously conducted in nine greenhouse fields where the soils could reflect different residual levels of nutrient, with two application rates (100 and 0%) for each nitrogen, phosphorus, and potassium fertilizer. The results showed that fertilizer reduction did not decrease vegetable yield when soil nitrate, Olsen–phosphorus, and exchangeable potassium were ≥173.3, 45.8, and 93.1 mg kg −1 , respectively. However, no N treatment decreased vegetable yields in fields 1–3 because the inadequately residual nitrate (≤103.9 mg kg −1 ) in these fields led to low nitrate absorbed from sources other than chemical fertilizer, high recovery efficiencies of N, and high productivity of N absorbed from chemical fertilizer. Residual nitrate that soil EC could reflect was the limiting factor of yield under fertilizer reduction. This study indicated that reducing fertilizer in greenhouse vegetable cultivation should be based on the residual level of nutrients in the soil, which is meaningful in agricultural sustainability and environmental safety.