基于全膜双垄沟播免耕多茬种植的土壤氮素形态转化特征及氮去向研究

This research aims to address the practical issue in production that under the no tillage dry-land multi crop planting pattern for Plastic-Covered Ridge and Furrow Planting, phenomena of off fat appeared during the late stage of maize growth and development. Main tests of field localization were set, designating the following treatments: no tillage dry-land multi crop planting pattern for Plastic-Covered Ridge and Furrow Planting，Plastic-Covered Ridge and Furrow Planting (annual ploughing, CK1) and bare land trench sowing planting (annual ploughing, CK2). Main tests were in combination with such set tests as 15N tracer, nitrogen in situ mineralization and ammonia volatilization. By monitoring the features of nitrogen transformation and nitrogen direction in the ecological system of corn-soil during the growth period of corn and the fallow period, in combination with the measurements of physiological communities of soil nitrogen, nutrition dynamics, water and heat factors and physical and chemical properties of soil during the critical growth period of corn and the fallow period, this research demonstrated the differences of nitrogen transformation and nitrogen direction in the ecological system of corn-soil under different cultivation patterns, and clarified the causes for the phenomena of off fat occurring during the late stage of maize growth and development under these patterns, thus providing theoretical basis for the optimization of technologies concerning nitrogen fertilizer application, and for the improvement of nitrogen use efficiency in dry-land fields of corn.

针对旱地全膜双垄沟播免耕多茬种植模式在玉米生长发育后期出现脱肥现象这一生产实际问题，以全膜双垄沟播免耕多茬种植、全膜双垄沟播（每年翻耕，CK1）种植和露地沟播种植（每年翻耕，CK2）为处理设置大田定位主试验，并与在其中设置的15N示踪、氮原位矿化及氨挥发试验相结合，通过对玉米—土壤生态系统中玉米生长季和休闲期氮素形态转化特征及氮去向的监测，结合玉米关键生育期和休闲期土壤氮素生理群落、养分动态、水热因子、土壤理化性状的测定，查明不同栽培模式下玉米—土壤生态系统中氮素形态转化特征及氮去向的差异性，明确该栽培模式玉米在生长发育后期脱肥现象产生的原因，为该栽培模式氮肥施用技术的优化和旱地玉米农田氮素利用效率的提高提供理论依据。

通过对旱地留膜留茬免耕多茬种植（T1）、全膜双垄沟播（T2）种植玉米—土壤生态系统氮素形态转化特征及去向、生理生化指标的分析发现：T1土壤温度5~25cm土层低于T2，T1较T2播前0-2m多贮水27.0mm，耗水量增加31.8mm。产量和水分利用效率T1显著低于T2，分别降低了8.0%和13.0%。T1显著提高了收获期0-10cm土壤有机质、全量磷钾及速效磷钾含量，随土层深度增加，有机质及全量和速效磷钾含量呈递减趋势。T1碱解氮含量在0-20cm土层降低，20-40cm土层富集。显著增加0-30cm土壤容重7.1%-12.4%。2种耕作方式0-40cm土层微生物数量为细菌＞放线菌＞真菌，不同土层各生育期微生物数量为T1显著高于T2，同一生育期随土层增加微生物数量呈减少趋势，以0-10cm最高。细菌和真菌在苗期至收获期增幅5.6%-64.5%和10.5%-91.7%。放线菌在苗期、拔节期、收获期分别增加79.8%、15.1%、17.6%，抽雄期、灌浆期分别减少17.2%、33.2%。耕作方式对各土层各生育期酶活性为T1＞T2，同一生育期随土层深度增加，酶活性逐渐降低，0-10cm最高，T1效果优于T2。蔗糖酶、脲酶、磷酸酶、过氧化氢酶玉米全生育期较T2增幅为4.7%-126.1%、9.8%-47.0%、5.4%-33.7%、2.3%-43.2%。硝态氮和铵态氮含量从表层到底层依次降低，主要发生在0-20 cm土层。耕作方式间玉米全生育期0-20 cm土层T1处理硝态氮和铵态氮含量显著低于T2，0-10 cm和10-20cm降幅分别为24.7%-59.9%、4.4%-46.8%和20.5%-58.0%、8.7%-31.7%。玉米进入拔节期后，20-100 cm土层T1硝态氮和铵态氮含量出现明显的累积效应。耕作方式间0-20 cm土层，T1碱解氮含量在玉米进入抽雄期后显著低于T2，0-10 cm和10-20cm降幅分别为0.3%-26.0%和17.7%-23.8%。15N示踪显示：T1氮残留显著低于T2，且残留率与土层深度成反比，收获期各器官氮残留率显著高于T2。T1提高了农田土壤有机质及磷钾养分、酶活性及微生物数量，减少氮素残留。因此，综合土壤氮素分配及残留，认为T1玉米生育后期出现早衰的原因为玉米整个生育期0-20cm土层NO-3-N和NH+4-N供应量不足引起的。