秸秆还田的植硅体影响紫色土锌有效性的机制

Soil zinc (Zn) deficiency limits crop yield, quality and finally human health. Phytolith is amorphous silica particle deposited in plant cell and it represents 5% to 10% dry weight of rice straw. We propose that straw-returned phytolith may increase silicic acid (H4SiO4) in soil solution, and the latter may compete adsorption site on surface of iron oxides and soil organic matter with Zn in soil. This process would change Zn transformation and distribution in soil, affect Zn adsorption-desorption characteristics and Zn extractability of soil, finally have an influence on soil Zn availability and thereafter Zn accumulation in crops. .The aim of this study, therefore, is to uncover their relationship on the basis of a long-term field experiment with rice-wheat rotation on a representative purple soil within Sichuan Basin where soils with potential Zn deficiency are widespread. Firstly, the influence of phytolith on Zn availability in purple soil and Zn accumulation in straw and grain of rice and wheat will be quantified through Zn and phytolith analysis of past collected soil and plant samples during last 24 years. Secondly, rice and wheat plant will be grown in three-room rhizobox with varied rates of phytolith, thereafter dynamic of Zn and Si in rhizosphere and soil solution will be explored. Thirdly, soil samples treated with and without rice straw return will be modified to remove iron oxide and/or soil organic matter and their Zn supplying capacity will be studied to indicate the pathway how phytolith affects soil Zn availability. And finally, distributions of phytolith among different microaggregates and their effects on Zn fraction and availability in microaggregates will be further pursued to show the site where phytolith may affect Zn availability in soil particles. .This study will improve our understanding in new aspect of soil Zn availability as affected by rice straw return, and therefore aid to management of Zn fertilizer in rice and wheat production.

土壤缺锌影响作物产量、品质及人体健康。植物细胞中无定形氧化硅颗粒称为植硅体，占水稻秸秆干重的5%~10%。水稻秸秆还田的植硅体增加土壤溶液中原硅酸含量，可能会与土壤中的锌竞争铁氧化物和有机质表面的吸附位点，促使土壤锌形态及存在位点改变，影响土壤锌的吸附-解吸和可提取性，从而改变土壤锌有效性并影响作物锌吸收。.为此，本研究拟基于国家紫色土监测基地稻-麦轮作的长期定位试验展开研究：（1）通过该田间试验定量秸秆还田的植硅体对紫色土锌有效性及稻麦植株和籽粒中锌积累的影响程度；（2）通过外源施入植硅体，明确根际/非根际土及土壤溶液中锌形态和有效性对植硅体的响应过程；（3）研究土壤中铁氧化物和有机质对土壤供锌能力的影响，探明植硅体影响土壤锌有效性的途径；（4）研究植硅体在不同粒径团聚体中的分布及其对锌形态转化和有效性的影响，明确交互作用位点。.这将增加人们对秸秆还田的科学认识，利于稻麦生产的锌肥管理。

土壤缺锌影响作物产量、品质及人体健康。水稻秸秆还田的植硅体可能会与土壤中的锌竞争铁氧化物和有机质表面的吸附位点，促使土壤锌形态及存在位点改变，影响土壤锌的吸附-解吸和可提取性，从而改变土壤锌有效性并影响作物锌吸收。.按照任务书要求，本研究基于国家紫色土肥力与肥料效益监测基地稻-麦轮作的长期定位试验开展了以下研究：（1）通过该田间试验定量秸秆还田的植硅体对紫色土锌有效性及稻麦植株和籽粒中锌积累、平衡的影响程度；（2）通过外源施入植硅体，明确秸秆腐解过程中硅、锌的释放特征及根际/非根际土土壤溶液中锌形态和有效性对植物硅、锌吸收的响应过程；（3）研究土壤中铁氧化物和有机质对土壤供锌能力的影响，探明植硅体影响土壤锌有效性的途径；（4）研究植硅体在不同粒径团聚体中的分布及其对锌形态转化和有效性的影响，明确交互作用位点。.结果表明，模拟条件下秸秆中的植硅体（以硅计，下同）平缓释放，120d累积释放64.6%，能显著增加土壤有效锌含量，并随秸秆还田量的增加而增加，对土壤有效硅则影响不大。土壤去掉有机质、游离氧化铁和无定形氧化铁锰后有效锌、有效硅的含量增加0.7~1.1倍。土壤小团聚体（<1 mm）中有效锌较高，而大团聚体中植硅体较高，表明土壤团聚体本身并不是锌-硅的主要交互位点。土壤长期田间试验中，稻草还田量7.5 t/ha/yr条件下，每年可补充锌376.4 g/ha，补充硅642.0 kg/ha；稻草还田显著提高了土壤有效锌含量，稻草还田配施化肥（NPKS）较仅施化肥处理（NPK）土壤有效锌增加0.33 mg/kg；与化肥（NPK）处理相比，稻草还田配施化肥（NPKS）显著提高了稻麦植株中硅的含量和吸收量，小麦地上部硅吸收量提高47.4%，水稻地上部硅吸收量提高27.6%。但是，稻麦吸收过多的硅对锌的吸收有降低的趋势，NPKS处理较NPK处理地上部锌吸收量水稻降低12.3%，小麦降低4.6%，但稻草还田对水稻、小麦籽粒锌含量无明显影响。.这些结果与研究假设基本一致，增加了我们对秸秆还田硅、锌循环的科学认识，利于稻麦生产的锌肥调控。