Soil Carbon Emission In Rainfed Maize Field As Affected By Soil Amendment And Its Underline Mechanisms

Maize?Zea mays L.?has become one of the major cultivated crops in dry farming areas of central Gansu,China because of the adoption of complete film surface mulching and double ridge-furrow.However,the high output of maize under this technology results soil nutrients exhaustion and fertility decrease.It is an important way to increase crop yield continuously through soil nutrients supplement and improved material circulation level in the farmland ecosystem.However,soil amendments also affect soil carbon emission.The objective of this study was to determine soil carbon emission and carbon budget in rainfed maize field as affected by soil amendment.We discuss the main mechanism about the effects on soil carbon emission based on soil temperature,soil water content and soil physical and chemical properties under different soil amendment treatments.The study relied on a soil amendment field experiment established by Rainfed Agricultural Comprehensive Experiment Station of Gansu Agricultural University that was set up in 2012 at Dingxi,Longzhong region.The experimental treatments consisted of a no nitrogen fertilizer control?NA?and four fertilizer treatments with the same nitrogen level:chemical nitrogen fertilizer?CF?,combined chemical nitrogen fertilizer with organic fertilizer?SC?,organic fertilizer?SM?and maize straw?MS?.The main results are as follows:1.All four soil amendment treatments increased soil respiration rate and carbon emission.Soil respiration rate first increased and then decreased and the greatest soil respiration was occurred at 25^th in July.Treatments CF,SC,SM and MS increased soil respiration and carbon emission by 21.72,28.09,10.33,48.31% and 31.86,41.92,10.91,56.65%compared to NA,respectively.2.Soil amendment treatments increased maize yield,water use efficiency,carbon emission efficiency and enhanced carbon sink effect,among which CF and SC increased the most significantly.Treatments CF and SC increased yield,biomass, water use efficiency,carbon emission efficiency by 151.41 and 121.23%,131.53 and 117.10%,66.04 and 51.04%,92.93 and 54.55%compared to NA respectively.All treatments showed sink effect for atmospheric CO₂ and the sink under CF and SC was significantly higher than other treatments.3.Soil respiration rate was significantly positively correlated with soil temperature,but not with soil water content.The pattern of soil temperature was basically consistent with respiration rate.Average soil temperature of 0-25cm showed treatment rank of CF>SM>NA>MS>SC.Soil temperature explained 54.6%-76.9%of the variation range of soil respiration rate.4.Total carbon emissions were positively correlated with soil organic carbon,total nitrogen and porosity,and negatively correlated with soil pH,bulk density and density.Organic fertilizer treatments increased soil organic carbon significantly.SC,SM,SM increased soil organic carbon by 18.40,16.22 and 22.46%,CF,SC,SM and MS increased soil total nitrogen by 0.11g·kg^-1,0.11g·kg^-1,0.10g·kg^-1 and 0.14g·kg^-1compared to NA,respectively.All the four soil amendment treatments decreased soil bulk density and density of 0-10cm but increased soil porosity.To sum up,in this study,soil amendment treatments increased soil carbon emissions in rainfed maize field by increasing soil temperature,organic carbon,total nitrogen,reducing soil bulk density and other indices.Meanwhile,increased maize yield significantly than increased soil carbon emission efficiency and enhanced soil carbon sink effect.The single application of chemical fertilizer and combined chemical nitrogen fertilizer with organic fertilizer had the best effect on increasing maize yield and carbon emission efficiency.However,the combined chemical nitrogen fertilizer with organic fertilizer was better than that of chemical fertilizer in improving soil organic carbon and soil structure.Therefore,in order to improve maize production and carbon efficiency continuously,combined chemical nitrogen fertilizer with organic fertilizer was a suitable soil amendment in rainfed maize field with complete film surface mulching and double ridge-furrow.