不同施磷量下稻田土壤磷素平衡及其潜在环境风险评估

【目的】对南方赤红壤区不同施磷量下稻田土壤的磷素平衡及其潜在环境风险进行评估,为该地区合理施磷、 减轻农业面源污染提供依据。【方法】采用大田定位监测试验,3个不同年份(2011~2013年)早、 晚稻分别设置4个施磷水平(施磷范围为P2O5 0、 63~81、 126~162、 252~324 kg/hm2,分别用P0、 P1、P2、P3表示),连续3年测定早、 晚稻的稻谷和稻秆产量,分析其磷养分含量,以施磷水平与水稻地上部磷素累积量间的差值表示土壤磷素表观盈余量。同时,采集施基肥和穗肥后1、 2、 3、 5、 7和9 d的田面水,测定总磷含量,利用Split-line模型对2011~2012年每造水稻收获后小区耕层土壤Olsen-P含量和所有监测时间点的田面水总磷平均浓度进行分段回归,并对二者之间的相关关系进行分段回归拟合。【结果】 施磷量P2O5 63~81 kg/hm2的处理稻谷产量显著提高,但磷肥施用量增至2倍时,稻谷产量无明显增加,继续增至4倍时,前3造水稻稻谷的产量增加也不明显。施磷可不同程度地提高水稻地上部的磷素累积量、 土壤表观磷素盈余量和Olsen-P含量,且三者均随施磷量的增加而增加。在施肥后1~3 d内无磷处理田面水总磷浓度较高,是磷素流失的高危险期; 施磷量P2O5 63~81 kg/hm2的处理显著提高了施肥后2 d内田面水的总磷浓度,而P2O5 252~324 kg/hm2的处理在监测期间田面水总磷浓度均显著高于无磷处理。 Split-line模型模拟土壤Olsen-P与田面水总磷的关系,得出在本试验区土壤环境条件下,可能导致田面水中磷激增的土壤Olsen-P临界含量为19.0 mg/kg,对应的施磷量为P2O5 63 kg/hm2,与土壤磷素持平的施磷量一致。【结论】综合考虑水稻产量效应、 土壤磷素表观平衡和磷素环境风险,在本研究区域目前的土壤环境条件下,P2O5 63 kg/hm2为水稻产量较高、 环境风险较小的推荐施磷量。

Phosphorus balance in paddy soils and its environmental effect under different phosphorus application rates

Objectives] The objective is to provide the basis for reducing agricultural non-poimt source pollution by evaluating phosphorus (P) balance in paddy soils in red soil zone of south China and its environmental effect under different P application rates. Methods] A continuous 3 -year (2011 -2013) field experiment design was used, and 4 different P application rates were selected, P2 O5 0, 63 -81, 126 -162 and 252 -324 kg / hm2 . In this study, yields and P concentrations of grain and straw of both early cropping rice and late cropping rice were detected, and P surplus was calculated by the difference of P levels and aboveground P accumulation. Moreover, total P in field water above soil surface at 1, 2, 3, 5,7 and 9 days after the basal and earing fertilizing was also detected, then the relation between total P in field water above soil surface and soil Olsen-P concentration from 2011 to 2012 year was analyzed by the split-line model. Results]The P2 O5 63 -81 kg / hm2 phosphorus treatment significantly improves the rice yield as compared with the non P fertilization control, and not significant as compared with the treatment of double and 4 times P rates of the fertilizer. The fertilizer-P application increases the aboveground P accumulation, soil P surplus and soil Olsen-P concentration which are increased with the increment of the P fertilizer amounts. The total phosphorus (TP) in the field water is high during the first 1 -3 days in the control, which is the dangerous duration for P running off. Compared with the control, the TP content in the surface water of the P2 O5 63 -81 kg / hm2 treatment is significantly higher within 2 days after the fertilization, and always high during the monitoring period in the P2 O5 252 -324 kg / hm2 treatment. The simulation with the split line model on the relationship between soil Olsen-P and field water TP above soil surface shows that the change point of soil Olsen-P which relates to the field water TP concentration above soil surface is 19. 0 mg / kg, corresponding to a P application rate of about P2 O5 63 kg / hm2 , and equals to the recommended fertilizer rate based on the line relationship model between fertilizer-P application rate and P surplus. Conclusions] As far as the rice yield, soil P surplus and its environmental effect are considered, P2 O5 63 kg / hm2 is suitable for the double rice cropping system in red soils of South China.