Purpose

The residual phosphorus (P) in Hedley’s sequential fractionation procedure is considered to be a relatively stable soil P pool and unavailable for plant uptake. In the present study, we investigated the effect of wetting-drying events on the dynamics of the residual soil P fraction in a flooded rice and aerobic wheat rotation.

Methods

Soils were taken from a long-term field trial after flooded (rice), and aerobic (wheat) crops were harvested. Hedley’s sequential fractionation method was used to assess the distribution of various P fractions. These changes in these P fractions were then related to Fe cycling in the soil.

Results

The residual P (H₂SO₄-H₂O₂ digested) was the dominant P fraction (37–51% of total P) in the aerobic soil under wheat, while it was decreased by 18–27% in flooded soil under rice cultivation. In contrast, the sparingly soluble Ca-bound P (HCl-Pi) increased from 25–31% under wheat cultivation to 41–50% under flooded rice (paddy) cultivation where reducing conditions are expected to prevail under submerged paddy soil conditions. The crop rotation not only altered the sparingly available P fraction but also influenced soil labile P, especially the organic P form. Compared with the rice soil, a 4-fold increase in the labile P fraction (NaHCO₃-Po) was observed in wheat soil. The moderately labile P fraction (NaOH-extractable) showed a similar trend to that of labile P pool, but the increased NaOH-Po in wheat soil was relatively small. The relatively rapid change in the residual P fraction was attributed to oxidation-reduction cycles of Fe oxides between flooded (rice) and aerobic (wheat) soil conditions.

Conclusions

Wetting and drying cycles associated with a rice-wheat crop rotation promoted the transformation of the sparingly soluble soil P fraction between crops, which was attributed to changes in soil redox conditions, particularly Fe cycling. This indicated that the rice-wheat crop rotation can draw upon the sparingly soluble P fraction for crop production, thus relying less on fertilizer-applied P.

中文翻译：

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稻麦轮作过程中的干湿循环快速（不动）使顽固的土壤磷动员

目的

Hedley的顺序分馏程序中的残留磷（P）被认为是相对稳定的土壤P库，无法用于植物吸收。在本研究中，我们调查了干湿事件对水淹稻田和需氧小麦轮作过程中残留土壤P组分动态的影响。

方法

在淹没（大米）后，从长期的田间试验中获取土壤，并收获了好氧（小麦）作物。Hedley的顺序分馏方法用于评估各种P馏分的分布。这些P分数的变化与土壤中的Fe循环有关。

结果

小麦下好氧土壤中的残留磷（H ₂ SO ₄ -H ₂ O ₂被消化）是主要的磷含量（占总磷的37–51％），而水稻下水淹土壤中的残留磷减少了18–27％。培养。相反，难溶的钙结合磷（HCl-Pi）从小麦栽培中的25-31％增加到洪水稻（水稻）栽培中的41-50％，在淹水的水稻土条件下，还原条件将普遍存在。轮作不仅改变了少量的有效磷含量，而且还影响了土壤不稳定的磷，特别是有机磷的形态。与水稻土相比，不稳定的P分数（NaHCO ₃-Po）在小麦土壤中观察到。中等不稳定的P组分（可提取的NaOH）与不稳定的P库表现出相似的趋势，但小麦土壤中NaOH-Po的增加相对较小。残留P分数的相对快速变化归因于水土（水稻）和好氧（小麦）条件下Fe氧化物的氧化还原循环。

结论

稻麦轮作相关的湿润和干燥循环促进了作物之间难溶性土壤P组分的转化，这归因于土壤氧化还原条件的变化，特别是铁循环。这表明稻麦轮作可以利用微溶的P组分进行作物生产，因此较少依赖施肥的P.