长期施肥对黑土磷和锌形态转化的影响

【目的】东北黑土地为我国重要粮食生产基地高肥力的黑土仍需施用磷肥以保障粮食高产。探讨长期施肥对土壤磷和锌形态转化机制,为确保黑土区粮食和环境安全提供理论依据。【方法】本研究以设在典型黑土区13年的长期施肥定位试验为研究对象,设不施肥(CK)、施氮磷钾肥(NPK)、施氮磷钾加不同量有机肥(NPK+OM_1、NPK+OM_2、NPK+OM_3)共5个处理分析土壤不同形态磷和锌含量。【结果】长期施化肥对土壤有机磷含量影响不显著但土壤无机磷含量显著增加;长期不施肥黑土有效磷含量为32.6 mg/kg,长期施化肥加有机肥可显著增加土壤有效磷含量;连续13年施用磷肥,土壤中的磷每年平均累积16 kg/hm~2,其主要以铝磷(A1-P)和铁磷(Fe-P)的形态在土壤中储存,其中约20%仍为有效磷;而磷肥加有机肥的3个处理,连续施用13年后有机磷含量增加了47.2~67.9 mg/kg无机磷含量增加253.4~410.6 mg/kg,土壤全磷平均分别以每年49.4(NPK+OM_1)、64.2(NPK+OM_2)、70.4(NPK+OM_3)kg/hm~2的量累积在土壤中,其中15%~21%仍为有效磷主要以有效性较高的二钙磷(Ca_2-P)、八钙磷(Ca_8-P)、Al-P、Fe-P存在于土壤中,只有10%~21%的磷以有机磷的形态累积在土壤中,并且这个比例随有机肥施用量的增加而降低。黑土长期不施肥土壤有效锌(DTPA-Zn)含量可达1.96mg/kg,长期施化肥、化肥加有机肥均可显著增加土壤DTPA-Zn含量;长期施化肥使黑土酸化,改变了土壤锌形态增加了土壤交换态锌和无定型铁氧化物结合态锌的含量,化肥加有机肥显著增加了除矿物态锌以外的其他各形态锌的含量其中55%~88%以无定型铁氧化物结合态锌储存在土壤中。通径分析结果显示,Ca_2-P对DTPA--Zn影响最大,Ca_8-P、Al-P、Fe-P通过Ca2-P间接影响DTPA-Zn含量。【结论】长期施入黑土的磷主要以有效性较高的无机态磷储存在土壤中,锌主要以无定型铁氧化物结合态储存在土壤中。黑土中磷与锌未表现出拮抗作用且有效性高的Ca_2-P对DTPA-Zn含量的影响最大且二者呈正相关关系。

Effect of long-term fertilization on phosphorus and zinc fractions in a Mollisol

【Objectives】 Phosphorous fertilizer is often applied in a Mollisol with high fertility for obtaining higher crop yields in Mollisol regions in Northeast China which are important grain production bases in China. It could provide guarantee for security of food and environment by researching the effect of long term fertilization on soil phosphorous (P) and zinc (Zn) fractions.【Methods】 Different P and Zn fractions were tested based on a 13-year long term field experiment in a typical Mollisol region. There were 5 treatments, no fertilizer (CK), chemical fertilizer (NPK) and chemical fertilizer plus different amounts of organic manure (NPK+OM1, NPK+OM2 and NPK+OM3). 【Results】 The content of organic P (T-Po) was not significantly affected under the NPK treatment, while the content of inorganic P (T-Pi) was increased significantly, and the content of Olsen-P is 32.6 mg/kg in CK treatment and was increased significantly in the treatments with combination application of chemical fertilizer and organic manure. P was accumulated in soil at a rate of 16 kg/hm2/year during 13 years of the P fertilizer application, the cumulated P mainly included fractions of Al-P and Fe-P, about 20% of which was Olsen-P. After 13 years of the combination application of P fertilizer and organic manure the contents of T-Po and T-Pi were increased by 47.2-67.9 mg/kg and 253.4-410.6 mg/kg, respectively, and the P accumulated rates in the NPK+OM1, NPK+OM2 and NPK+OM3 treatments were 49.4, 64.2 and 70.4 kg/hm2/year, respectively, 15%-21% of which was Olsen-P including mainly Ca2-P, Ca8-P, Al-P and Fe-P fractions. About 10%-21% P was stored in soil as T-Po fraction, and the proportion was decreased with the increase of the amount of organic manure application. The DTPA-Zn contents were increased significantly in NPK, NPK+OM1, NPK+OM2 and NPK+OM3 treatments, and the contents was as high as 1.96 mg/kg in the CK treatment. The contents of Exch.-Zn and AFeO-Zn in the NPK treatment were increased due to soil acidification resulting from the long term chemical fertilizer application. The combination application of chemical fertilizer and organic manure increased significantly the contents of different Zn fractions with exception of the Res-Zn content, and 55%-88% of Zn stored in soil was AFeO-Zn fraction. The path analysis result showed that the Ca2-P content impacted directly DTPA-Zn content, and the Ca8-P, Al-P and Fe-P contents impacted indirectly the DTPA-Zn content by the Ca2-P content. 【Conclusions】 P was stored in soil as high available T-Pi after the application of P fertilizer, and Zn was stored in soil as mainly AFeO-Zn fraction. The antagonism between P and Zn was not observed in the Mollisol, and the Ca2-P content had the largest impact on the DTPA-Zn content, and a positive relation was found.