砾石覆盖对小麦玉米轮作农田碳排放强度的影响

为研究砾石覆盖对农田土壤水热条件及温室气体排放的影响,探讨小麦-玉米轮作农田碳排放强度对砾石覆盖的响应,开展了基于静态暗箱-气象色谱法的小麦-玉米轮作田间试验,测定了土壤CO2、CH4和N2O3种温室气体的排放,结合产量、全球增温潜势和碳排放强度等指标评估砾石覆盖的农田生态效应及固碳减排作用.试验在作物关键需水期设置0和50mm2个灌溉水平,土壤表面设置无覆盖和100%覆盖2个砾石覆盖度水平,形成无覆盖对照(W0M0)、灌溉对照(W1M0)、砾石覆盖(W0M1)和灌溉砾石覆盖(W1M1)4个处理.结果表明:1)砾石覆盖能有效改善土壤水热状况,显著增加作物产量.与对照处理W0M0相比,W1M0,W0M1和W1M13个处理的作物年际总产量分别增加了18.1%、32.6%和51.8%;2)各处理对3种温室气体排放的影响具体表现为,相比W0M0处理,W1M0,W0M1和W1M13个处理的CO2年际排放总量分别降低了7.8%、12.1%和18.0%,CH4年际吸收总量分别增加了32.5%、80.2%和124.3%,而各处理N2O年际排放总量差异不显著;3)砾石覆盖显著降低了农田温室气体碳排放强度,W1M0,W0M1和W1M13个处理的碳排放强度相比W0M0处理分别降低了14.9%、20.7%和33.6%.比较产量和碳排放强度,经济产量越高,固碳潜力越大,碳排放强度越小.双因素方差分析表明砾石覆盖结合农田灌溉使得作物产量达到最高,碳排放强度最小.综合考虑,砾石覆盖结合农田灌溉能有效改善土壤水热状况,有利于增加作物产量和降低农田温室气体碳排放强度,该研究为干旱半干旱地区实现稳定增产和固碳减排提供一种可行途径.

Effects of gravel mulching on greenhouse gas emissions intensity in wheat-maize rotation system

Abstract: With growing concern on climate change, agriculture has received attention over last few decades as it is a significant contributor to global warming and total greenhouse gas (GHG) emission. GHG emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) can be affected by various field managements. Gravel mulching technology, as a distinct field management technique, has been long used to decrease water evaporation and improve crop production in the semi-arid Loess Plateau of northwest China, but systematic field studies concerning the impacts of surface gravel mulching on dryland agricultural soils water and heat conditions and GHG emissions are scarce. Therefore, we conducted a field study of wheat-maize rotation cycle in Yangling District of Shaanxi Province in the year of 2014-2015. The annual GHG emissions (CO2, CH4 and N2O) were monitored using a static opaque chamber and chromatography method. This study focuses on the interactive role of gravel mulching and irrigation practices on both crop yield and GHG emissions. We also calculated the global warming potential (GWP) and greenhouse gas emissions intensity (GHGI) to evaluate the farmland ecological effect and GHG reduction effect. In this experiment, 4 field treatments were arranged with 2 gravel mulching levels (M0: No mulching, M1: covering 100% of soil surface) and 2 supplemental irrigation levels at key growing periods (W0: without irrigation, W1: 50 mm). The results showed that: 1) Compared with the control treatment of W0M0, the annual wheat-maize yields were significantly increased by 18.1%, 32.6% and 51.8% under the other 3 treatments of W1M0, W0M1 and W1M1, respectively; the annual CO2 emissions were decreased by 7.8%, 12.1% and 18.0% under W1M0, W0M1 and W1M1, respectively. And there was not significant difference for annual N2O emissions for different treatments. The total annual absorption amounts of methane were increased by 32.5%, 80.2% and 124.3% under W1M0, W0M1 and W1M1 compared with the W0M0, respectively. 2) Gravel mulching gives positive contribution to the soil temperature and soil moisture. The correlation analysis of annual GHG emissions with soil temperature (5 cm) or soil water content (10 cm) under different experimental treatments over the wheat-maize growing period indicated that, the dependence of soil CO2 emissions on soil water and soil temperature was pronounced for the 4 treatments with significant correlations (P<0.05), while the dependence of soil CH4 or N2O emissions on soil water and temperature was partly with significant correlations (P<0.05). 3) Annual GWP values were more complicated in all treatments ranging from 522.8±204.6 to 629.5±328.5 kg/hm2 (CO2 equivalent) Compared with W0M0, irrigation practice could decrease the value of GWP, while gravel mulching practice could increase the value of GWP, and the interaction of gravel mulching coupled with irrigation could balance the GWP. 4) For the W1M0, W0M1 and W1M1 treatments, GHGI was significantly decreased compared with W0M0 by the values of 14.9%, 20.7% and 33.6%, respectively. The above results suggested the application of gravel mulching coupled with irrigation may obtain a balance between the increase of crop yield and the decrease of GHG emissions. Overall, gravel mulching practices could effectively increase soil moisture and temperature, and greatly lower the GHGI with the significant increase of crop yield. The basic case study provides a feasible way to realize stable crop productivity increase and GHG emissions reduction in arid and semi-arid region.