Effect of fertilizer reduction on nitrogen utilization efficiency and fate during overwinter long-season tomato production in greenhouse

Objectives Excessive application of fertilizers in vegetable production is quite often happened in China. We studied the effects of reduced chemical fertilizers on the yield and nitrogen fertilizer efficiency of tomato grown in greenhouse. We also studied the fate of applied nitrogen after harvest, so as to provide scientific references for rational chemical fertilizer application in this region.

Methods A fertilizer subtraction and a ¹⁵N labeled microplot experiment were conducted simultaneously in a greenhouse from 2017 to 2018 in Dingxing County, Hebei Province. The tomato cultivar used is ‘Provence’, which is often grown overwinter and for about 8 months. There were four treatments in the fertilizer subtraction experiment, including: the farmers’ average N–P₂O₅–K₂O input of 858–594–1284 kg/hm²(CF); the reduced 40% fertilizer treatment (RF), with the N–P₂O₅–K₂O input of 608–297–720 kg/hm² ; the left two treatments were the above two deleted nitrogen (CFNN, RFNN). In the ¹⁵N labeled experiment, the nitrogen in RF and CF were replaced by ¹⁵N labeled urea (¹⁵NRF and ¹⁵NCF). The tomato yield and fallen leaves were collected with the ripe of fruits, and the whole plant and soil samples (0–20, 20–40 and 40–60 cm layer) were collected after the final harvest. The N contents were measured and fertilizer utilization efficiencies were calculated.

Results In the fertilizer subtraction experiment, the yield, total N uptake of RF treatment were significantly increased by 10.4% and 14.8%, and the chemical N recovery rate was increased by 15.4 percentage points, compared with those of CF. In the ¹⁵N labeled experiment, the tomato yield, the total N uptake and ¹⁵N uptake in ¹⁵NRF treatment were increased by 12.1%, 25.3% and 13.8%, compared with those of ¹⁵NCF. The difference in chemical N recovery rate was significant between ¹⁵NRF (36.4%) and ¹⁵NCF (20.3%). From the ¹⁵N labeled experiment, the total soil N content and ¹⁵N atom% content decreased with the soil depths increased. The fertilizer N fate was in order of loss > tomato uptake > soil residue, with detailed ratio of loss, tomato uptake and soil residue of 40.4%, 36.4% and 23.2% in the ¹⁵NRF treatment, and 59.6%, 20.6% and 19.6% in the ¹⁵NCF treatment. The fertilizer N loss rate of ¹⁵NRF was 19.2 percentage points lower than that of the ¹⁵NCF. The fertilizer N residue in the 0−20 cm soil layer of ¹⁵NRF and ¹⁵NCF accounted for 88.9% and 87.9% of the total, respectively.

Conclusions On the base of applying 30 t/hm² of organic fertilizer, reducing 40% chemical NPK nutrient input and adjusting the N−P₂O₅−K₂O ratio could achieve significantly higher tomato yield, decrease the nitrogen loss, keep similar nitrogen residue in the soil, and increase chemical N use efficiency more than 15 percentage points.