轮作提高土壤磷生物有效性改善后茬作物磷素营养

Rotation increases soil phosphorous bioavailability and improves phosphorous nutrition of the latter crop in rotation

【目的】豆科作物与禾本科作物轮作能够提高轮作体系的磷效率,本研究调查了前茬作物收获后的土壤磷状况,并尝试采用基于生物有效性的磷素分级方法(BBP)评价其对后茬玉米磷营养状况的影响。【方法】设置室内模拟盆栽试验,前茬作物处理包括蚕豆(Vicia faba)、小麦(Triticum aestivum)、黑麦草(Lolium perenne)和毛叶苕子(Vicia villosa Roth),以不种植作物为对照。作物收获后,后茬均轮作玉米。每个轮作前茬作物处理均分为基施P2O560 mg/kg和不施磷肥两个处理。在前茬作物收获后,测定土壤Olsen-P含量,并将土壤磷分为CaCl2-P、Citrate-P、Enzyme-P、HCl-P,评价土壤的有效磷状况。玉米收获后,测定产量和植株地上部磷含量及吸收累积量。【结果】轮作显著提高了后茬玉米地上部生物量,前茬不施磷肥处理对后茬玉米的增产效果高于施用磷肥处理。不施磷肥条件下,与对照相比,蚕豆后茬玉米的地上部生物量增加最多(185.7%),且增幅显著高于小麦和毛叶苕子的后茬;施磷条件下,蚕豆、黑麦草后茬玉米的地上部生物量之间没有显著差异,但均显著高于小麦和毛叶苕子后茬。不施磷条件下,轮作显著提高了后茬玉米地上部含磷量,以黑麦草茬口的增幅最高,达到66.7%,且显著高于蚕豆和毛叶苕子;施磷条件下,4个茬口玉米地上部磷含量与无前茬作物对照没有显著差异,但黑麦草茬口仍显著高于蚕豆、小麦和毛叶苕子茬口的。前茬不施磷肥条件下,Enzyme-P在蚕豆、小麦、黑麦草和毛叶苕子茬土壤显著高于对照土壤;施磷肥条件下,只有蚕豆和黑麦草茬土壤显著高于对照土壤,这与轮作处理的促生效应相吻合。不施磷蚕豆、小麦、黑麦草和毛叶苕子土壤Citrate-P含量比其对照显著低20.99%、13.30%、5.05%和10.66%,而施磷土壤降幅更大,分别比对照低32.56%、22.86%、20.32%和27.62%。不论是否施磷肥,蚕豆与毛叶苕子均显著降低了土壤的HCl-P含量,而小麦茬对土壤的HCl-P含量无显著影响。【结论】不论是否施用磷肥,轮作显著降低了土壤中Olsen-P的含量,但是却显著促进了后茬玉米的生长。依据BBP分级方法,轮作不同程度地降低了土壤中Citrate-P和HCl-P含量,而增加了Enzyme-P的含量,进而提高了土壤中磷的生物有效性,增加了玉米吸磷量。在4种前茬作物中,黑麦草挖掘土壤供磷能力的潜力最大。

【Objectives】We assessed the bioavailability of soil P to crops in a rotational system using a biological P fractionation method(BBP).The aim was to provide a reference for choosing a suitable crop rotation with the highest nutrient use efficiency and crop output potential.【Methods】A pot experiment was used for the research,no planting crops as control,and the preceding crops planted in the rotation were faba bean(Vicia faba),wheat(Triticum aestivum),ryegrass(Lolium perenne),and hairy vetch(Vicia villosa Roth).For all the treatments,the latter crop planted in the roration was maize(Zea mays).All the treatments were either not fertilized or received 60 mg/kg P2O5 while planting the preceding crops.Soil samples were taken for Olsen-P and biological P fractionation(CaCl2-P,Citrate-P,Enzyme-P and HCl-P)to evaluate available soil P when the crops were harvested.Yield and P content and accumulation in aboveground biomass were measured after harvesting maize.【Results】Crop rotation(P<0.05)increased maize aboveground biomass.The biomass increase under no P application was higher than that under P application,with the highest increase(185.7%)recorded for the faba bean plant.With P application,there was no significant difference in the aboveground biomass of maize rotated with fababean or ryegrass,but it was significantly higher than that rotated with wheat and hairy vetch.Without P application,rotation(P<0.05)increased the aboveground P content of maize.Among the preceding crops,ryegrass had the highest P content(66.7%).There was no significant increase in the aboveground P content of maize with the P application compared with the control.However,ryegrass recorded(P<0.05)higher P content than the other rotation crops.Without P fertilization,planting faba bean,wheat,ryegrass,and hairy vetch increased soil enzyme-P by 20%,19%,29%and 15%compared with no planting crops control.In contrast,P application only enhanced soil enzyme-P in faba bean and ryegrass,consistent with their growth-promoting effect.Without P application,planting faba bean,wheat,ryegrass,and hairy vetch decreased citrate-P by 20.99%,13.30%,5.05%,and 10.66%,respectively.With P application,the Citrate-P reduction was 32.56%,22.86%,20.33%and 27.62%,respectively.Irrespective of applying P or not,planting faba bean and hairy vetch(P<0.05)decreased soil HCl-P content,but not wheat.【Conclusions】Whether P fertilizer was applied or not,crop rotation reduces soil Olsen-P but promotes subsequent maize growth planted in the rotation.According to the biological P fractionation method,rotation reduced Citrate-P,HCl-P and increased Enzyme-P in soil to some extent,thereby improving the bioavailability of P and the subsequent uptake of P by maize.Ryegrass has the greatest potential to excavate soil P supply capacity among the four preceding crops in the rotation.