半干旱区覆盖农田作物-土壤体系有机碳定量研究及秸秆还田阈值分析

There are two parts of organic carbon in soil-plant-atmosphere continuous system, one is aboveground organic carbon (i.e. plant biomass), the other is underground organic carbon (i.e. soil organic carbon), the both significantly affected by agricultural cultivation. The mulching technology, whole field soil-plastic mulching and no-tillage farming system with furrow-ridge fully covered by plastic film, increased crop organic carbon accumulation (biomass) and decreased soil organic carbon content significantly in northwest semi-arid rain-fed areas. But the researches to quantify organic carbon content changes on crop-soil system under coverage conditions, as well as the effect of the straw (the increased part while plastic mulched) return to field on organic carbon inter-annual balance of crop-soil system on the plastic mulched field, were not reported. The located field experiment, which carried out from 2012 and rotated as wheat-maize-potato, treated by different quantities of straw and nitrogen application, will be used to understand the above problems. The effects of organic carbon accumulation of crop-soil system, and its response to nitrogen application under coverage conditions, will be investigated by measuring crop biomass and soil organic carbon content; the contribution of straw return to field on soil organic carbon content and components under mulching conditions, will be analysis by measuring particulate organic carbon, easily oxidized organic carbon, dissolved organic carbon, microbial biomass organic carbon; the total organic carbon and its components storage would be calculated, to confirm that whether or not the straw return to field could achieve the inter-annual balance of crop-soil system organic carbon while nitrogen reasonably applied on plastic mulched field. This work may provide theoretic and technological support for exploring the methods to increase agricultural productivity, and improve soil quality of rain-fed cropland.

农田土壤-作物-大气连续体中，有机碳包括地上（作物生物量）、地下（土壤有机碳）两部分，均受耕作栽培技术的显著影响。地膜覆盖使作物地上有机碳显著增加、地下有机碳下降。但从作物-土壤体系角度对覆盖农田有机碳变化的定性分析和量化研究较少；且在技术上对覆盖农田秸秆还田量和施氮量阈值无确定分析。本研究利用已有大田定位试验（2012年布设），在全膜覆盖条件下采用小麦-玉米-马铃薯轮作，设不同秸秆还田量和施氮量处理，测定秸秆和土壤有机碳含量，明确覆盖对作物-土壤体系有机碳累积的影响及其氮素响应；测定土壤颗粒有机碳、易氧化有机碳、可溶性有机碳、微生物量有机碳等，分析秸秆还田对地膜覆盖农田土壤有机碳含量及组分的贡献；计算有机碳及其组分的储量，明确覆盖种植后增加的作物有机碳还田，在合理氮素的配合下能否实现土壤有机碳平衡或富集。这一工作可为探索旱作覆盖农田耕地质量调优、作物生产力持续提高的技术途径提供理论支撑。

地膜覆盖可增加作物生物量和提高产量，但长期地膜覆盖导致土壤有机质含量下降，对农田生产力的可持续性具有难以逆转的潜在威胁。覆盖种植增加的作物有机碳（秸秆）还田能否实现作物-土壤体系有机碳含量平衡，是需要关注的科学和技术问题。本研究在全膜覆盖条件下采用小麦-玉米-马铃薯轮作，设3个秸秆还田量和3个施氮量水平，测定作物生物量、叶片SPAD值、冠层温度、作物有机碳、土壤有机碳，土壤颗粒有机碳、易氧化有机碳等有机碳组分含量，以期明确覆盖种植的秸秆还田量和施氮阈值。研究结果表明，1）小麦、马铃薯秸秆还田量3000 kg/hm2，施纯N、P2O5、K2O 分别为150、90和75 kg/hm2，玉米秸秆还田量12000 kg/hm2，施纯N、P2O5、K2O分别225、120和90 kg/hm2时，能显著提高小麦、马铃薯和玉米的地上生物量和叶片SPAD值，降低冠层温度，显著提高作物产量和水分利用效率；2）以上秸秆还田量和施肥量条件下，0-30 cm土壤有机碳含量，土壤颗粒有机碳和土壤易氧化有机碳等碳组分含量均高于其他处理，分别增加了0.5-10.8%、-1.1-17.0%和5.1-69.5%；3）明确了在半干旱区覆盖条件下基于作物-土壤体系有机碳长期平衡的秸秆还田量小麦、马铃薯阈值为3000 kg/hm2、玉米阈值为12000 kg/hm2；满足秸秆降解和作物正常生长的施氮量小麦、马铃薯阈值为150 kg/hm2，玉米阈值为225 kg/hm2。项目实施超额完成了合同指标，发表科技论文13篇，其中1篇SCI和8篇中文已见刊，1篇中文和2篇SCI已接收，1篇中文审稿中；授权实用新型专利2项；颁布甘肃省地方标准1项。