Proportional replacement of organic N in chemical fertilizer for tomato production in a greenhouse system

Objectives The partial replacement of chemical fertilizers with organic fertilizer is one of the technical pathways to increase crop yield and quality, fertilizer efficiency, and soil fertility. This paper investigates the effects of different proportions of organic and chemical fertilizers on tomato yield, quality, nitrogen absorption and soil physicochemical characteristics in a newly-built greenhouse. The study aims at providing a theoretical basis and technical support for the efficiency of greenhouse-based vegetable production under the proportional use of chemical and organic fertilizers.

Method The experiments were carried out in 2017 and 2018 in two newly-built greenhouses in the southwestern part of Shandong Province using Atlanta tomato variety. Based on the N-P₂O₅-K₂O application rate (1108-955-1108) recommended for local tomato, the treatments imposed in this study were 100% chemical fertilizer (FP), 10%, 20%, 30%, and 40% organic N replacement in the chemical fertilizer (FM10, FM20, FM30, FM40), and no N input (i.e., control; CK). The contents of N, P and K in the tomato fruits and plants, tomato NO₃^–-N, Vc, total sugar, acidity, soil nutrient content, bulk density and porosity in 0–30 cm soil layer were analyzed. The economic benefit of the production system was also estimated.

Results Tomato yield increases with the proportional increase in organic N replacement in the chemical fertilizer. Compared with the FP treatment, the yield and net income from tomato production in FM30 treatment were significantly higher, increasing by 4.03% and 6.09%, respectively. The NO₃^–-N content in the tomato fruit produced from FM30 and FM40 all decreased by 21.2% compared with the FP treatment. The contents of Vc, sugar-acid ratio, and total sugar were higher in FM10 than other treatments. The contents of Vc, sugar-acid ratio and total sugar decrease as the proportion of organic N replacement increases. The highest N utilization rate was recorded in FM30 (value), surpassing that recorded in the FP treatment by 17.7%. Compared with the FP treatment, the soil NO₃^–-N, soil bulk density, available P and K contents in FM30 and FM40 significantly decreased in the 0–30 cm soil layer, while the organic carbon contents significantly increased.

Conclusion The proportional replacement of chemical fertilizer with organic N improves the yield, quality and efficiency of tomato production. Appropriate inclusion of organic N in chemical fertilizer has the potential to improve soil fertility and slowdown soil salinization. Finally, this study recommends 20%–30% inclusion of organic N in total chemical N input for tomato production in the newly-built greenhouse.