Effects of long-term application of organic fertilizer on soil available phosphorus content and leaching risk in greenhouse tomato cultivation

This study explored the soil available phosphorus content and leaching risk of long-term application of organic fertilizers under greenhouse tomato cultivation to provide an important reference for rational fertilization in greenhouse tomato cultivation. Based on a field experiment of located fertilization in greenhouse tomato cultivation over eight years, five treatments were selected: no fertilization (CK), application of chemical fertilizers (NPK), and combined application of low, medium, and high amounts of organic fertilizer and chemical fertilizers (M1NPK, M2NPK, M3NPK). The contents and profile distribution of soil total phosphorus (Total-P), available phosphorus (Olsen-P), and soluble phosphorus (CaCl₂-P) in each fertilization treatment were studied. The changes in the soil phosphorus environmental and agricultural thresholds with profile distribution, and appropriate phosphorus application amount in greenhouse tomato cultivation were analyzed. The results showed that the contents of Total-P, Olsen-P, and CaCl₂-P in all treatments decreased gradually with increasing soil depth in the 0–50 cm soil layer, and their contents in the 0–10 cm soil layer were significantly higher than those in the 30–50 cm soil layer (P<0.05). Total-P, Olsen-P, and CaCl₂-P contents increased in all fertilizer treatments compared with CK, and they increased with the amount of organic fertilizer applied, and the effect of medium (M2) and high (M3) organic fertilizer application on Total-P, Olsen-P, and CaCl₂-P contents in the 0–20 cm soil layer was significant (P<0.05). In the 0–10 cm, 10–20 cm, 20–30 cm, 30–40 cm, and 40–50 cm soil layers, the environmental thresholds of soil phosphorus increased first and then decreased with increasing soil depth, which were 139.6 mg·kg⁻¹, 152.4 mg·kg⁻¹, 133.5 mg·kg⁻¹, 86.1 mg·kg⁻¹ and 42.3 mg·kg⁻¹, respectively. In the 0–10 cm, 10–20 cm, 20–30 cm, and 30–40 cm soil layers, the agriculture thresholds of soil phosphorus decreased gradually with increasing soil depth, which were 185.1 mg·kg⁻¹, 120.5 mg·kg⁻¹, 92.8 mg·kg⁻¹, and 56.0 mg·kg⁻¹, respectively. Taking the soil Olsen-P content corresponding to the soil phosphorus agriculture threshold as the risk assessment criterion of phosphorus leaching, through the relationship between soil Olsen-P content and phosphorus application rate (P₂O₅), it was inferred that the suitable amount of phosphorus (P₂O₅) for greenhouse tomato cultivation was 344.9−530.3 kg·hm⁻², and the amount of P₂O₅ supplied by organic fertilizer was 119.9−305.3 kg·hm⁻². Under the condition of located fertilization in greenhouse tomato cultivation for 8 years, on the basis of chemical nitrogen, phosphorus, and potassium fertilizers (N 375 kg∙hm⁻², P₂O₅ 225 kg∙hm⁻², and K₂O 450 kg∙hm⁻²), the application of a low amount of organic fertilizer (15 000 kg·hm⁻²) could not only improve the available soil phosphorus content at 0–20 cm and significantly increase the tomato yield but also effectively control the risk of soil phosphorus leaching.