• ISSN 1008-505X
  • CN 11-3996/S

潮土磷库组成及累积磷的消耗转化特征

Composition of phosphorus pool and the consumption and transformation characteristics of accumulated phosphorus in fluvo-aquic soil

  • 摘要:
    目的 长期施用磷肥致使潮土中累积了大量的磷,为精确管控和合理利用累积磷素,我们研究了小麦–玉米连续种植下,停止使用磷肥后磷库的组成和消耗转化特征。
    方法 本研究依托位于河南新乡的“国家潮土肥力与肥料效益长期定位试验基地”进行,连续26年施用不同量磷肥,处理间土壤磷积累量差异很大。利用单个处理或两个处理耕层土壤混合的方法,制备Olsen-P含量分别为6.7、14.3、27.6、55.4、72.3 mg/kg的土壤 (分别记为L1、L2、L3、L4、L5),用于进行微区耗竭试验,种植制度为冬小麦–夏玉米轮作。在耗竭试验的5年间,测定了土壤全磷、Olsen-P和各磷库组分含量。
    结果 潮土磷库中无机磷占比超过90%,L5处理土壤中的有效磷库组分Resin-P、NaHCO3-Pt、NaOH-Pt含量分别为L1的5.0、3.5、2.8倍。L1处理(缺磷土壤)的有效磷组分在全磷中的比例仅为10.4%,而难利用磷组分(C.HCl-Pt, Residual-P)的比例高达24.0%;L5处理(高磷土壤)有效磷组分比例高达20.6%,难利用组分比例低至14.3%。缓效磷组分(D.HCl-Pi)在全磷中的比例基本维持在66%。有效磷水平高于农学阈值(L2处理)之后,Resin-P组分才开始增加,增加量占有效磷库增加量的17.3%~22.6%。磷库耗竭过程中,有效磷库是作物吸收的第一磷库,且以Resin-P、NaHCO3-Pi、NaOH-Pi的先后顺序被利用。Resin-P、NaHCO3-Pi、NaOH-Pi每消耗1 mg/kg,Olsen-P分别减少1.3、0.7和1.0 mg/kg。有效磷库组分与缓效磷库、难利用磷库组分可以互相转化。5年耗竭过程中,L1处理有18.0 mg/kg 难利用磷转化为D.HCl-Pi,L2、L3处理分别有22.3和7.2 mg/kg D.HCl-Pi转化为有效态磷,提升了土壤累积磷素的生物有效性;而L4、L5处理分别有29.9和43.1 mg/kg有效态磷组分转化为D.HCl-Pi,降低了土壤累积磷的生物有效性。
    结论 随着土壤Olsen-P水平的提高,有效磷库组分Resin-P、NaHCO3-Pt、NaOH-Pt占比增加,难利用磷库占比减少,而缓效磷库占比高且稳定。有效态Resin-P在Olsen-P超过农学阈值后才开始累积。作物吸收可促进缺磷土壤难利用磷库组分转化为缓效磷库组分,中磷土壤缓效磷库组分转化为有效磷库组分,最终土壤累积磷素均被活化利用;而高磷土壤中30%以上的有效磷库组分被转化为缓效磷库组分,作物奢侈吸磷量显著增加,造成一定的磷肥养分浪费。中磷土壤是维持磷资源高效利用和作物高产的最佳磷库组成状态。

     

    Abstract:
    Objectives Long-term application of phosphate fertilizer resulted in the accumulation of a large amount of phosphorus (P) in fluvo-aquic soil. We studied the composition and consumption characteristics of phosphorus pool after cessation of phosphorous application, to provide a theoretical base for the P nutrient management.
    Methods The research was based on the “National Long-term Monitoring Station of Fluvo-aquic Soil Fertility and Fertilizer Effects”, where P was applied in different rates for 26 years and the soil P accumulation amounts in different treatments varied greatly. The top layer soils from a single treatment or a mixture of two treatments were used to prepare the test soils with different Olsen-P contents for a P exhausting micro-plot trial, under wheat-maize rotation. The soils with Olsen-P content 6.7 mg/kg was defined as P deficient (L1), 14.3 and 27.6 mg/kg as moderate (L2, and L3), and 55.4 and 72.3 mg/kg as sufficient (L4, and L5), respectively. During the five years of exhausting, the total P (TP), Olsen-P content, and P fractions were analyzed.
    Results Inorganic P accounted for more than 90% of total P in fluvo-aquic soil. The Resin-P, NaHCO3-Pt and NaOH-Pt in L5 soil were 5.0, 3.5 and 2.8 times of those in L1 soil, respectively. The proportion of labile and difficult-utilization P fractions were 10.4% and 24.0% of TP in L1 soil, and the proportion were 20.6% and 14.3% in L5 soil. The proportion of moderately labile P fraction was basically maintained at 66% of TP in all the test soils. Resin-P content would not increase until the Olsen-P level was higher than the agronomic threshold (L2 soil), and the increase contributed 17.3%–22.6% of the total increase of labile P pool. During the depletion process, crops absorbed the labile P fractions first and in order of Resin-P, NaHCO3-Pi and NaOH-Pi. For each 1 mg/kg of Resin-P, NaHCO3-Pi, and NaOH-Pi consumption, the soil Olsen-P content was reduced by 1.3, 0.7, and 1.0 mg/kg, respectively. The P pools with different availability converted with each other. After five years of depletion, 18.0 mg/kg of difficult-utilization P fractions converted into moderately labile P (D.HCl-Pi) in L1 soil, and 22.3 and 7.2 mg/kg of moderately labile P converted into labile P in L2 and L3 soils, showing a trend of activation of accumulated P. While in L4 and L5 soils, 29.9 and 43.1 mg/kg labile P converted into moderately labile P, showing a trend of immobilization of accumulated P.
    Conclusions With the increase of Olsen-P level in fluvo-aquic soil, the proportion of labile P pool (Resin-P, NaHCO3-Pt, and NaOH-Pt) is increased, the proportion of difficult-utilization P pool is decreased, and the proportion of moderately labile P pool keeps stable. When the Olsen-P exceeds the agronomic threshold, the Resin-P content will begin to increase. Crop absorption drive the conversion of P pools, depending on the soil Olsen-P levels. In P deficient soil, the conversion is mainly from difficult-utilization P to moderately labile P, and in moderate P level soils, the conversion is from moderately labile P to labile P, the accumulated P in phosphorous deficient and moderate soils are in procession of activation, and will be used by crops at last. In high P soil, however, more than 30% of labile P fractions will be converted to moderately labile ones, and luxury P absorption of crops is common, resulting in the waste of phosphorus fertilizer nutrients. Moderate P level in soil is the most favorable for efficient utilization of phosphorus resources and high yield of crops.

     

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