Sustainability of soil-crop systems under different long-term fertilizations in Chestnut Cinnamon soil areas

The sustainability of soil-crop systems was evaluated based on a long-term fertilization experiment to provide theoretical support for farmland fertilization and management. The long-term fertilizer experiment consisting of 8 treatments and a CK was carried out in the Chestnut Cinnamon soil of loess hilly-gully region for 26 years. The treatments included:non-fertilization (CK), 120.0 kg(N)·hm^-2 urea (N), 120.0 kg(N)·hm^-2 urea + 75 kg(P₂O₅)·hm^-2 calcium superphosphate (NP), 22 500 kg·hm^-2 organic fertilizer (M₁), M₁ + N (M₁N), M₁ + NP (M₁NP), 45 000 kg·hm^-2 organic fertilizer + 120.0 kg(N)·hm^-2 urea (M₂N) and M₂ + NP (M₂NP). A total of 19 indicators of the soil-crop system were measured, and soil nutrient index, soil microbial index, crop index and sustainability index were calculated by the triangle area method. The effects of long-term fertilization on the sustainability of soil-crop systems in the Chestnut Cinnamon soil region were discussed. The results indicated that:1) the sustainability indexes of N and M₁ treatments increased respectively by 27.1% and 141.7% compared with CK, but were 53.1% and 10.8% lower than the critical value (1.30). Although the sustainability index of NP treatment was 62.3% higher than N treatment, it was 23.8% lower than the critical value (1.30). This indicated that soil-crop systems under long-term application of single nitrogen, or low organic fertilizer or nitrogen and phosphorus were all unsustainable. 2) Nutrient index, microbial index and crop index of inorganic fertilizer (N, NP) treatments increased respectively by 7.1% and 46.4%, -6.0% and 25.4%, 40.0% and 60.0% compared with CK. Nutrient index, microbial index and crop index of single application of organic fertilizer (M₁) were respectively 98.2%, 41.8% and 31.7% higher than those of CK, showing inorganic fertilizer application improved crop index, organic fertilizer application improved nutrient index and microbial index. 3) Soil nutrient index (1.06), soil microbial index (1.04), crop index (1.00) and sustainability index (1.38) of M₁N all exceeded or equaled the critical value, which was good for the sustainability of soil-crop systems. 4) Soil nutrient indexes of M₁NP, M₂N and M₂NP increased respectively by 21.7%, 37.7% and 72.6% compared with M₁N, and the corresponding soil microbial index increased by 15.4%, 7.7% and 18.3% over M₁N. There were small differences in crop indexes of the above treatments, compared with M₁N. Sustainability indexes of the above treatments increased respectively by 28.3%, 32.6% and 68.1% compared with M₁N. The results indicated that increasing application of phosphorus or organic fertilizer over M₁N further enhanced sustainability index because of enhanced soil nutrient index and microbial index, but also increased potential environmental risk. A combination of moderate amounts of organic and inorganic N application (M₁N) was a comparatively better fertilization model, which ensured sustainable production of soil-crop systems in Chestnut Cinnamon soil region.