石灰性土壤水稻膜下滴灌苗期黄化失绿机理研究

Rice cultivated under drip irrigation with film mulch (RCDIFM) showed significant water-saving potential and yielding closely similar yield to paddy rice. However, Fe-deficiency chlorosis is a common symptom in RCDIFM, which severely constrain RCDIFM to be developed in a wide scope. Hence, to study the mechanism of rice chlorosis in calcareous soil and correspondingly measurement to ameliorate chlorosis is urgent. This research study soil factors that affect soil Fe availability, rice genotypes variation in Fe-deficiency tolerance to explore rice chlorosis mechanism under RCDIFM, and to interpolate the soil process that result in weak soil Fe availability in the shift that soil shift from flooding to upland by drip irrigation. Based on high frequency irrigation and locally irrigation characterized by drip irrigation, multiple measures, e.g., micro-domain soil acidify, nitrafication inhibitor plus NH4-N fertilizer application, Fe salt or chelated Fe salt application to check rice chlorosis retrieve effects and to propose measurements for rice chlorosis amelioration. This research is proposed to focus on scientific issues: (1) how soil pH, soil redox and soil humidity restrains soil Fe availability in calcareous soil when shift from flooding to drip irrigation, (2) if NH4-N fertilizer plus nitrate inhibitor application can create an ammonia enhanced environment for rice seedlings and hence lead to rhizosphere acidify by ammonia physiological metabolize process, and finally indirectly improve rice Fe nutrition, (3) Take advantage of locally and high frequency irrigation characteristic of drip irrigation, if chemical acid materials input in soil can create a long-standing locally acidify soil environment to improve soil Fe availability and improve rice Fe nutrition.

水稻膜下滴灌具有显著的节水效应和产量潜力，是缺水地区水稻栽培的新方向。但是在石灰性土壤上，缺铁黄化是水稻膜下滴灌栽培的重大障碍，研究石灰性土壤上水稻膜下滴灌缺铁失绿的机理以及纠正对策，是该技术在更大范围应用的重要保障。本研究以滴灌为背景，从土壤条件变化导致土壤铁有效性变化入手，阐明石灰性土壤铁有效性降低的主要土壤过程和水稻苗期黄化的主要原因；以滴灌高频灌溉和局部灌溉为手段，通过增铵营养实现土壤局部生理酸化、多次局部向土壤释放酸性物质实现土壤局部酸化，提高土壤铁有效性并改善水稻铁营养。主要科学问题：（1）滴灌条件后，石灰性土壤pH、氧化还原电位变化、土壤含水量导致土壤铁有效性降低的机理；（2）滴灌条件下，通过施用铵态氮肥和硝化抑制剂实现苗期增铵营养，是否可实现水稻根际酸化并间接改善水稻铁营养。（3）滴灌局部灌溉和高频灌溉条件下，少量多次向土壤相同部位投放酸化剂是否能提高石灰性土壤铁有效性。

水稻膜下滴灌具有显著的节水效应和产量潜力，是缺水地区水稻栽培的新方向。但是在石灰性土壤上，缺铁黄化是水稻膜下滴灌栽培的重大障碍，研究石灰性土壤上水稻膜下滴灌缺铁失绿的机理以及纠正对策，是该技术在更大范围应用的重要保障。本研究以滴灌为背景，从土壤条件变化导致土壤铁有效性变化入手，阐明石灰性土壤铁有效性降低的主要土壤过程和水稻苗期黄化的主要原因；以滴灌高频灌溉和局部灌溉为手段，通过增铵营养实现土壤局部生理酸化、多次局部向土壤释放酸性物质实现土壤局部酸化，提高土壤铁有效性并改善水稻铁营养。主要科学问题：（1）滴灌条件后，石灰性土壤pH、氧化还原电位变化、土壤含水量导致土壤铁有效性降低的机理；（2）滴灌条件下，通过施用铵态氮肥和硝化抑制剂实现苗期增铵营养，是否可实现水稻根际酸化并间接改善水稻铁营养。（3）滴灌局部灌溉和高频灌溉条件下，少量多次向土壤相同部位投放酸化剂是否能提高石灰性土壤铁有效性。.四年研究表明，石灰性土壤滴灌水稻缺铁黄化的主要机理是(I)滴灌条件下85%-100%田间持水量下，对水稻是一种温和的水分胁迫环境。这种胁迫诱导水稻气孔关闭，降低蒸腾强度。这是一种节水适应性特征。然而，水稻铁吸收依赖蒸腾拉力，蒸腾作用下降导致Fe吸收降低；（II）旱地且不淹水的土壤其土壤氮素主要组成为硝态氮，水稻吸收硝态氮导致根际酸化作用消失，不利于Fe有效化以及水稻Fe吸收；（III）硝态氮营养导致水稻植株通气组织大量形成，降低水稻水分输送能力，这是一种抗旱适应性机制，同时也降低Fe向地上部运输的强度。课题还发现石灰性土壤中广泛关注的HCO3-不是导致滴灌水稻缺铁的主要因素。