Changing Drip Fertigation Strategy to Decrease Greenhouse Agroecosystem Soil Nitrate Residue and Improve Tomato Production in Northwest of China

Greenhouse vegetable production has often been accomplished by over-application of chemical fertilizers, which has caused a series of consequences, especially soil degradation, nutrient imbalance and a high risk of nutrient loss to the environment. To seek an optimal fertilization strategy in greenhouse is an urgent task for soil health and sustainable productivity. A drip-fertigation experiment was conducted on greenhouse tomato over four consecutive growing seasons (Autumn 2015–Spring 2017) to explore the responses of soil nutrients, enzyme activity and microbial population to various fertilization strategies. Five fertilization treatments were set up: (1) chicken manure basal application and chemical fertilizer topdressing (CC); (2) only soluble organic fertilizer (SO); (3) only soluble chemical fertilizer (SC); (4) soluble organic fertilizer and chemical fertilizer (SOSC); and (5) a control with no fertilization (CK). Results showed that soil nitrate-nitrogen leaching to the 40 − 60 cm soil layer occurred in SC. Although soil nitrate-nitrogen content in SOSC increased over time during each growing season, less soil nitrate-nitrogen residue (155.99 kg ha⁻¹ in 0 − 60 cm soil layer) was observed compared with that in the other treatments. Interestingly, organic fertilizers or ingredients, including CC, SO and SOSC, improved soil organic matter pool and soil microbial population. Based on path analysis, soil urease activity had the greatest direct impact on fruit yield (1.16), however, soil bacteria (−0.35) and organic matter (−0.18) had a certain negative direct effect on fruit yield. According to the results of the principal component analysis, it was concluded that combined application of soluble organic and chemical fertilizers in drip fertigation has the potential of alleviating soil nitrate-nitrogen losses, enhancing soil biochemical environment and contributing to the sustainable production of drip-fertigated greenhouse tomato.