水改设施蔬菜地土壤质量演变与泡沫砂改良机理研究

The effect of high-intensity artificial procession has been concerned by soil Scientist at home and abroad. Greenhouse vegetable cultivation is one of the land use with strong anthropogenic effect. The research of its soil evolution is important to reveal the processes and mechanisms of human action. Paddy fields in the areas on the lower-middle reaches of Yangtze River have rapidly changed to greenhouse vegetables because of the city development and an increasing market demand. Greenhouse planting with high temperature, high humidity, high fertilizer and no precipitation lead to soil structure degradation, which resulting in a serious impact on the growth and yield of vegetables. A vegetable base of Nanjing is selected as the study area. Based on the CT technique for getting three-dimensional imaging of soil pore, one paddy filed and four plastic greenhouses which converted from paddy field and has 3, 6, 10, 15 years of vegetable history respectively as the time series are selected for soil sampling. Secondly, soils in the worst degradation plastic greenhouse are brought back to the glass greenhouse laboratory and mixed with an inorganic porous media which named foamy sand at some volume ratios into pots, take soil samples from the pots after the mixtures are saturated 5 times by simulating plastic greenhouse irrigation. According to results of the analysis of soil sample to investigate the change process of soil quality with the time, especially the three-dimensional structure of the soil pore; the improvement effect of foamy sand on soil pore structure, soil water retention and soil aeration. The study result may provide a theoretical basis for the mechanism of soil degradation, and new theory and technology for the improvement of compacted degradation soil.

高强度人为作用过程最近受到国内外土壤学界关注，设施蔬菜种植人为作用强烈，其土壤演变研究对揭示人为作用过程与机理具有重要意义。为满足城镇化对蔬菜的需求，长江中下游等地区把质地粘重的水稻田改种设施蔬菜，高温、高湿、高肥等栽培环境使土壤板结退化，严重影响了蔬菜产量和品质。本项目以南京市设施蔬菜基地为研究区，以CT扫描成像为新的技术支撑点，以水稻田为对照，选择水稻田转设施蔬菜地后种植3、6、10和15年的大棚为研究时间序列；并从中选取严重板结退化土壤，与自主研发无机多孔泡沫砂按不同体积比混合，在温室进行盆栽试验，模拟蔬菜大棚灌溉过程；采集不同蔬菜种植年限大棚土壤和掺入泡沫砂盆栽试验土壤，研究水稻田改设施蔬菜种植后土壤质量，尤其是三维孔隙结构的演变及其对土壤通气性的影响机理；泡沫砂掺入量对板结退化土壤三维孔隙结构的改良机理。研究结果可为设施栽培土壤退化机理和板结退化土壤改良提供新的理论和技术。

在我国长江中下游地区，城镇化的快速发展使长期种植水稻的农田改为设施蔬菜地以满足人们日益增长的蔬菜需求。水田改种蔬菜地后土壤环境和管理措施发生重大变化，必然影响土壤质量。前人研究重要集中在土壤化学或微生物方面，物理结构方面结构关注较少。本研究在南京郊区采集水田改种设施蔬菜地后2、6和8年时间序列的土壤样品，基于CT扫描和图像分析对土壤大孔隙特征进行了分析，研究水稻田改设施蔬菜种植后土壤孔隙结构的演变；并从中选取严重板结退化土壤，用自主研发无机多孔泡沫砂进行盆栽改良实验，研究泡沫砂掺入量对板结退化土壤三维孔隙结构的改良机理。研究结果表明，水改设施蔬菜地后土壤退化，一方面，土壤耕层变浅，耕层之下形成了新的犁底层，新犁底层随着设施种植年限增加逐渐向老犁底层退化；另一方面，耕层孔隙结构变化显著，表现为大孔隙度减小，孔隙的连通性降低，孔网结构弱化，但是耕层退化过程与设施种植年限无显著相关性，与2和6年大棚相比，8年大棚的孔隙联通性更高，容重也最低，这是应为8年大棚有相对高的有机肥投入量。研究结果显示，有机质含量与大孔隙度、连通性和孔网节点数呈显著相关（P <0.01），这意味着增施有机肥可以改善土壤结构。但在设施种植高位高湿的环境下，有机质的分解速度很快，时效短，长期投入增加成本，在常规设施蔬菜种植中不适用。无机多孔改良材料泡沫砂对板结土壤的改良效果显著。盆栽实验结果显示，泡沫砂改良后小青菜的发芽率增加了2倍多，单株生物量最高增加了50%。土壤大孔隙随泡沫砂掺入量呈线性增加，每增加1%体积的泡沫砂，CT孔隙度增加约0.7%。而土壤大孔隙的增加，提高了土壤养分的利用率，从而增加了生物量。因此，对于粘重板结土壤，泡沫砂是一种非常高效的改良材料。