施用粪肥对农田土壤磷素累积和饱和度增加速率的影响

针对施用粪肥导致的我国集约化种养区域农田土壤磷素高量累积和高环境风险问题,利用长期定位试验定量分析了施用粪肥对农田土壤磷素累积和磷饱和度(DPS,degree of P saturation)增加速率(每年1 kg P·hm~(-2)磷素盈余所导致的土壤磷素含量或DPS变化量)的影响。结果表明:连续22年过量磷素投入明显提高了土壤磷素含量和DPS,0~20 cm土层土壤磷素累积、DPS增加与磷素盈余均存在明显的线性相关性。与单施化肥相比,施用粪肥对土壤全磷的累积速率影响不大,但是明显提高了土壤Olsen-P累积和DPS增加速率。施用粪肥下,每年1 kg P·hm~(-2)的磷盈余所导致的0~20 cm土层土壤Olsen-P、CaCl_2-P累积和DPS增加量分别为0.071 mg P·kg~(-1)(r=0.608,P=0.029)、0.003 mg P·kg~(-1)(r=0.528,P=0.066)和0.036%(r=0.863,P=0.002),分别为不施粪肥的3.3、6.0倍和1.2倍。土壤DPS变化与磷含量变化之间也存在明显的线性关系,0~20 cm土层土壤每年全磷、Olsen-P和CaCl_2-P含量增加1mg P·kg~(-1)所导致的土壤DPS增加值分别为0.13%、0.42%和7.78%。20~40 cm土层土壤磷素累积、DPS增加与磷素盈余之间的线性相关性均较差,但与0~20 cm土层相比,施用粪肥和不施粪肥之间累积速率的差异性有增大的趋势,说明施用粪肥促进了磷素向下层土壤的移动。施用粪肥加速了土壤有效磷累积和DPS增加,进而提高了土壤中磷素损失风险,合理施用粪肥是控制集约化种养区域农田磷面源污染的关键。

Effects of manure applications on rates of phosphorus accumulation and phosphorus saturation degree increase in arable soils

In intensive farming regions of China, high rates of manure applications to arable field over years have caused high phosphorus(P)accumulation in soil and the associated environmental risks. Here a long-term field experiment was conducted to quantify the effects of manure applications on rates of soil P accumulation and the degree of P saturation(DPS) increase, i.e., the increment in soil P content or DPS per 1 kg P surplus, in an effort to develop guidelines for rational P management and non-point source pollution reduction. Results showed that 22 years of continuous excessive P inputs increased soil P content and DPS. In 0~20 cm soil depth, soil P and DPS increased linearly with increasing P surplus. Compared with single chemical fertilizer application, manure incorporation had no significant effects on the ratios of soil total P increments to P surplus increments, but significantly increased the ratios of soil available P and DPS to P surplus increments. The increases in soil Olsen-P, CaCl₂-P, and DPS per 1 kg P surplus were 0.071 mg P·kg^-1(r=0.608, P=0.029), 0.003 mg P·kg^-1(r=0.528, P=0.066), and 0.036%(r=0.863, P=0.002) in the 0~20 cm soil depth under manure incorporations each year, which were 3.3-, 6.0- and 1.2-fold greater than those under single chemical fertilizer application, respectively. The changes of soil DPS also increased linearly with the changes of soil P. In the 0~20 cm soil depth, the increments in DPS per 1 mg P·kg^-1 increase in total P, Olsen-P, and CaCl₂-P were 0.13%, 0.42%, and 7.78%, each year, respectively. In 20~40 cm soil depth, there was no significant linear correlation between the increases of soil P, DPS and P surplus. However, the difference of increase rates between manure incorporation and single chemical fertilizer application tended to be greater in 20~40 cm soil depth than in 0~20 cm depth, suggesting that manure applications favored the movement of P to subsoil. Manure applications accelerated the increases of soil available P and DPS, which in turn promoted the losses of P. In conclusion, rational manure management is the key to mitigating non-point source pollution in intensive farming areas.