Characteristics of carbon, nitrogen and phosphorus loss in sloping farmland of purple soil under different fertilization and cultivation methods

  Objectives  Loss of elemental nutrients in sloping land is one of the main causes of water pollution downstream. Exploring the effects of fertilization and cultivation methods on the losses of carbon (C), nitrogen (N) and phosphorus(P) in sloping farmland plays a vital role in field management, promoting the quality of cultivated land and reducing the risk of the aquatic environment pollution.

  Methods  The study site was located in a typical sloping land. The five treatments in this research included down-slope tillage control treatment (CK), down-slope tillage with combining application of chemical fertilizer and pig manure treatment (T1), down-slope tillage with chemical fertilizer application only (T2), down-slope tillage with 1.5 times chemical fertilizer application (T3), and cross-slope tillage with chemical fertilizer application only (T4). The concentrations of C, N, and P in soil and runoff during the growth period of maize (seedling, jointing, heading, maturity) were analyzed. The corresponding quantities of nutrient lost were calculated.

  Results  Compared to CK, T1 and T4 increased the contents of soil C, N, and P (P < 0.05). With down-slope tillage, the soluble organic carbon (DOC) concentration of T1 run-off was 33.66% lower than T2, but the differences of other nutrient concentrations were not significant. The C, N and TDP concentrations in the run-off of T3 were all higher than in T2, and the increase of DOC and NH₄⁺-N reached a significant level (P < 0.05). The NO₃⁻-N concentration in the run-off of T4 was notablely lower than in T2, but the decreases of other nutrients were not remarkable. The highest run-off was in CK and the lowest in T4; T2 and T3 had larger run-off than T1. Compared with other treatments, the run-off of T4 decreased by 44.65%–67.36%, and that of chemical fertilizer + pig manure T1 declined by 15.65% and 22.76% compared with T2 and T3, respectively. Compared with T2, T1 decreased the DOC, TN, and TP lost by 43.10%, 27.51%, and 31.26%, respectively. T4 declined DOC, total N, and total P lost by 59.16%, 58.57%, and 68.42%, respectively. The DOC, total N, and total P quantity lost were the highest in T3, reaching 6.02 kg/hm², 0.86 kg/hm² and 0.20 kg/hm², respectively.

  Conclusions  The combined application of chemical and organic fertilizers decreases the concentration of DOC, total N, and total P in the run-off, and the reduction of DOC is significant, but not the amount of run-off. In contrast, cross-slope tillage is found effective in declining the total run-off but not DOC, total N, and total P concentration. Therefore, combining the application of chemical and organic fertilizers, and cross-tillage are recommended to reduce soil C, N, and P loss through run-off and attenuate the surrounding water pollution in the purple sloping farmland.