砂质潮土长期施磷的农学效应及有效性演变

Agronomic effect and variation of P availability under long-term phosphorus application in sandy fluvo-aquic soil

【目的】研究冬小麦–夏玉米轮作体系下砂质潮土长期施磷的作物产量效应、磷肥利用效率、土壤有效磷农学阈值及有效磷对土壤磷素盈亏的响应关系,为农田磷素养分管理提供依据。【方法】磷肥长期定位试验自2008年起在河北廊坊进行,种植制度为冬小麦–夏玉米轮作,供试土壤为砂质潮土,设置6个施磷(P2O5)水平(0、45、90、135、180、225 kg/hm^(2)),依次表示为P0、P45、P90、P135、P180、P225。在2020年(试验的第12年)测定作物产量、作物吸磷量、土壤有效磷含量,分析了周年产量和土壤有效磷演变特征、作物有效磷农学阈值、土壤有效磷与累积磷盈亏的关系。【结果】施磷显著提高了冬小麦–夏玉米周年产量和作物吸磷量,产量与吸磷量随施磷水平提高先升高后降低。达到最高周年产量(14627 kg/hm^(2))的施磷量为152 kg/hm^(2)。以该最高产量的90%为实际生产目标,适宜施磷量为90 kg/hm^(2)。磷肥利用率随轮作周期延长而提高,12年平均磷素表观利用率和累积利用率变幅分别为36.98%~98.10%和26.26%~71.85%。周年施磷量超过90 kg/hm^(2)时,施磷对作物吸磷量影响不显著,且磷肥表观利用率、累积利用率显著降低。P0~P225处理表观磷盈余12年平均值分别为–11.30、–7.38、0.94、20.05、37.21、57.68 kg/hm^(2);至2020年累积磷盈亏分别为–144.92、–88.57、11.33、240.56、446.48、692.15 kg/hm^(2)。砂质潮土有效磷含量随累积磷盈余量的变化呈现两段线性关系,拐点出现在土壤累积磷盈余量P 218.81 kg/hm^(2)。低于此值时,土壤每盈余P 100 kg/hm^(2),有效磷含量上升0.48 mg/kg;当土壤累积磷盈余高于此值时,土壤每盈余P 100 kg/hm^(2),有效磷含量上升3.37 mg/kg。冬小麦、夏玉米有效磷农学阈值分别为10.20、5.93 mg/kg,施磷量为90 kg/hm^(2)时,冬小麦、夏玉米季土壤有效磷含量最接近农学阈值。【结论】在作物秸秆还田条件下,砂质潮土冬小麦–夏玉米轮作体系周年施磷量为90 kg/hm^(2),可以兼顾冬小麦–夏玉米轮作周年对磷素的需求,维持土壤磷素的表观平衡,在保证产量的前提下实现磷素平衡和磷肥高效施用。砂质潮土磷的储存阈值为218.81 kg/hm^(2),当土壤磷累积量低于该阈值时,施磷提高土壤有效磷含量的效果较低;而当磷累积量高于该阈值时,施磷可显著提升土壤磷的有效性。

【Objectives】We studied the appropriate P fertilizer application rate,the critical Olsen-P value for crop yield and the response of Olsen-P to soil P balance under long-term P application in sandy fluvo-aquic soil.We aimed to provide a basis for P nutrient management in agricultural fields.【Methods】A long-term experiment was conducted since 2008 in Langfang,Hebei Province.The planting system is winter wheatsummer maize rotation on sandy fluvo-aquic soil,with phosphorus fertilizer(P_(2)O_(5)) levels of 0,45,90,135,180,and 225 kg/(hm^(2)·a),and expressed as P0,P45,P90,P135,P180,P225.Crop yield and P uptake were analyzed every year,and soil Olsen-P was measured after harvesting winter wheat and summer maize.【Results】P application increased yield and P uptake in winter wheat and summer maize,but they did not always increase with the increased P application level.For the highest annual yield(14627 kg/m^(2)),the application rate of 152 kg/hm^(2) was required.The appropriate application rate was 90 kg/hm^(2) if the actual production target was 90% of the highest yield.Over time,the efficiency of P fertilizer use in sandy fluvo-aquic soil increased.For the 12-year average,P fertilizer’s apparent and cumulative use efficiency was 36.98%–98.10% and 26.26%–71.85%,respectively.P application did not affect crop P absorption when the annual application rate exceeded 90 kg/hm^(2),resulting in lower apparent and cumulative P fertilizer use efficiencies.The apparent P balance for treatments P0 to P225 was –11.30,–7.38,0.94,20.05,37.21,and 57.68 kg/hm^(2),respectively,over the 12-year period.–144.92,–88.57,11.33,240.56,446.48,and 692.15 kg/hm^(2) were the cumulative P balances from 2010 to2020,respectively.The linear relationship between Olsen-P and P accumulation was shown in two sections,with a turning point of 218.81 kg/hm^(2) for P accumulation.Every 100 mg/hm^(2) of P cumulative increment resulted in 0.48 mg/kg increase in Olsen-P,which increased to 3.37 mg/kg after the point.The Olsen-P agronomic thresholds for winter wheat and summer maize were 10.20 mg/kg and 5.93 mg/kg,respectively.When the P_(2)O_(5) application rate was 90 kg/hm^(2),the soil available P content in both seasons was close to the agronomic threshold.【Conclusions】The appropriate annual P_(2)O_(5) application rate in sandy fluvo-aquic soil under a winter wheat-summer maize rotation system with the return of crop stalks to the field is 90 kg/hm^(2).This results in the soil available content required for the agronomic threshold to attain a high crop yield.The storage P threshold of sandy fluvo-aquic soil was 218.81 kg/hm^(2).When the cumulative P amount is less than the threshold,the available soil P will be increased less by P application.On the other hand,when the cumulative P amount exceeds the threshold,the soil available P will greatly increase.