磷肥减施对玉米根系生长及根际土壤磷组分的影响

摘要

[Objectives]Winter wheat-summer maize rotation is the most common agricultural production system in the North China Plain. Excessive phosphorus (P) fertilization in wheat is concerned in this area, which might result in low fertilizer use efficiency and potentially pressure on the environment. The objective of this paper was to investigate the possibility and potential of reducing application rate of P fertilizer in winter wheat-summer maize crop rotation systems.[Methods]A field experiment was conducted on fluvo aquic soil in Hengshui City, Hebei Province. Four rates of P2O5 application rate of 0, 112.5, 150.0 and 187.5 kg/hm2 were set in winter wheat. After harvest of wheat, summer maize was planted without tillage. The grain yields, biomass and P content in above ground parts of maize were investigated; Root analysis system WinRHIZO was used to determine the root length and diameter; and the contents of different fraction of soil P were analyzed at harvest.[Results]Compared to current farm’s P2O5 input rate of 187.5 kg/hm2, the maize grain yield, total root length, average root diameter and soil Olsen-P contents were not significantly affected in treatment of P2O5112.5 and 150.0 kg/hm2 for three years’ period. Under no P fertilizer application treatment, the maize yield and soil available P contents in the third year started to decline, the organic P contents in the rhizosphere soils were lower than in the non-rhizosphere soils in 2009 and 2010 year; the amounts of moderately labile organic P in soils were higher at maize seedling and mature stage than at other growth stages in 2008. When less P fertilizer was applied, moderately labile organic P contents in rhizosphere soils were remarkably lower than in non-rhizosphere at maize seedling stage. The concentrations of Ca2-P, one of inorganic P forms in soils, declined during maize growth season. The contents of Ca10-P, Ca8-P, O-P (Occluded phosphorus), Al-P and Fe-P in the rhizosphere and non-rhizosphere soils presented no significant change among various P fertilizer rates. The concentrations of microbial biomass P in the rhizosphere soils were higher than in the non-rhizosphere soils at maize seedling stage in 2008. Compared with farmers conventional P application (187.5 kg/hm2 P2O5), reducing P application rates did not significantly affect on the contents of microbial biomass P in rhzosphere soils at maize seedling stage.[Conclusions]Under the intensive rotation system of winter wheat and summer maize in North China Plain with high soil fertility, the yield and root development of maize, and the contents of Olsen-P, organic P and microbial biomass P in the rhizosphere soils do not show significant variation when the P fertilizer input was reduced by 20% or 40% in wheat season, but those happened when no P fertilizer were applied. It is suggested that it would be available to reduce the P input by 20%–40% in winter wheat-summer maize crop rotation systems under the tested conditions.%【目的】我国农业过量和不合理施用磷肥现象普遍存在，导致磷资源的浪费，对环境也造成潜在威胁。研究减少磷肥用量对玉米产量、根系形态及根际中磷转化特征的影响，为集约化农业生产体系中磷肥合理施用提供技术基础。【方法】在河北省衡水小麦玉米轮作体系下连续三年进行了田间试验，在冬小麦季设置4个P2O5用量处理：0、112.5、150.0、187.5 kg/hm2，收获后在原处理小区免耕播种夏玉米。利用 WinRHIZO根系分析系统分析获取根长、直径等数据，测定玉米籽粒产量、生物量和地上部磷含量及根际土壤中磷形态等指标。【结果】与农民习惯磷肥用量(P2O5187.5 kg/hm2)相比，3年磷肥用量减施20%～40%处理(P2O5150和112.5 kg/hm2)，玉米籽粒产量、根系长度与直径和土壤有效磷含量尚未发生明显变化。但3年不施磷处理，根际土壤有效形态磷含量和玉米籽粒产量开始出现下降趋势。2009年和2010年玉米收获期，不施磷肥处理根际土壤有机磷含量低于非根际土壤。2008年玉米苗期和收获期土壤有机磷分组中，中等活性有机磷含量最高；磷肥减施20%～40%处理苗期根际中中等活性有机磷含量显著低于非根际土壤。土壤无机磷形态分组研究发现：从玉米苗期到收获期，各磷肥处理根际和非根际土壤中 Ca2-P下降明显；而不同磷肥处理间土壤中 Ca10-P、Ca8-P、O-P (闭蓄态磷)、Al-P和 Fe-P含量差异不显著。减施磷肥处理2008年玉米苗期根际土壤微生物量 P含量较非根际土壤高；与习惯施肥量相比，磷肥减施未明显降低根际土壤微生物量磷。【结论】在华北小麦玉米轮作种植体系下，在土壤肥力水平较高地区，连续3年将小麦季磷肥的习惯用量减少20%～40%，对夏玉米产量、根系形态以及根际土壤无机磷、有机磷、微生物量磷含量影响尚不明显，因此，该地区磷肥施用量可从习惯用量的P2O5180 kg/hm2减至112.5 kg/hm2。