小麦-水稻秸秆还田对土壤有机质组成及不同形态氮含量的影响

通过4年田间定位试验,研究小麦-水稻轮作方式下秸秆还田对土壤有机质组成及不同形态氮含量的影响.试验设置不施秸秆不施肥对照(CK)、秸秆还田不施肥(S)、秸秆还田+基肥增施N肥45 kg·hm^-2(SF1,C/N=12:1)、秸秆还田+基肥正常N肥施用量(SF2,C/N=18:1)、秸秆还田+基肥减施N肥45 kg·hm^-2(SF3,C/N=24:1)共5个处理.结果表明:与对照处理(CK)相比,秸秆还田不施肥处理(S)使土壤有机质、全氮和有机氮的含量分别增加7.8%、10.6%和10.9%,而使土壤中无机氮的含量减少17.1%;秸秆还田配施不同化肥处理中,当碳氮比为18:1时,土壤全氮、有机氮和无机氮含量最高,分别比对照处理增加27.2%,27.2%和25.7%.元素分析结果显示,秸秆还田S、SF1、SF2、SF3处理土壤全量有机质(SOM)中的碳、氮元素含量均有所增加,同时SOM中的C/N、H/C和O/C比值都下降.红外光谱结果表明,秸秆还田S、SF1、SF2、SF3处理,在1650~1640 cm^-1和3400 cm^-1处的峰强度增加,表明土壤有机质中含氮基团、酚羟基、羟基或羧基含量增加;2920 cm^-1处的吸收峰增强,表明SOM中脂肪族结构增加,芳香性增强.与对照处理(CK)相比,秸秆还田不施肥(S)处理的当年水稻产量下降8.8%;配施化肥后,SF1、SF2、SF3处理水稻实际产量分别比对照(CK)处理增加12.6%、22.7%、19.1%,且当碳氮比为18:1时,增产效果最为明显;单独秸秆还田提高了土壤有机质含量,降低了其碳氮和氢碳比例,使SOM中脂肪族化合物增加,酰胺结构和芳香性增强,同时提高了土壤全氮和有机氮的含量,减少了土壤无机氮含量.

Effects of Wheat and Rice Straw Returning on Soil Organic Matter Composition and Content of Different Nitrogen Forms in Soil

Effects of continuous wheat and rice straw returning on the content of different soil nitrogen forms and the composition of soil organic matter(SOM) were investigated in a 4-year field experiment. Five treatments included no straw returning and no fertilizer application(CK), straw returning without fertilizer application(S), straw returning with fertilization 1(SF1, C/N:12:1), straw returning with fertilization 2(SF2, C/N:18:1), and straw returning with fertilization 3(SF3, C/N:24:1). Compared with CK, content of SOM, soil total nitrogen and soil organic nitrogen increased by 7.8%, 10.6% and 10.9%, respectively, whereas soil inorganic nitrogen content decreased by 17.1% in treatment S. The content of soil total nitrogen, organic nitrogen and inorganic nitrogen in the SF2 treatment was 27.2%,27.2% and 25.7% higher than those in CK, respectively. Straw returning increased C% and N% of SOM and soil organic matter content, but decreased the ratios of C/N, H/C and O/C in SOM. FTIR analysis revealed that the signal intensities of 1650~1640 cm^-1 and 3400 cm^-1 of straw returning treatments were strengthened, demonstrating that the amounts of nitrogen compounds, alcohols, phenols and carboxylic acids in SOM increased. The strengthened signal intensity at 2920 cm^-1 indicated an increase in the content of aliphatic compounds in SOM. Compared with CK, rice yields decreased by 8.8% in straw returning treatment with no fertilizer applied(S), but increased by 12.6%,22.7%,and 19.1% in SF1, SF2, and SF3 treatments,respectively. These findings indicate that wheat and rice straw returning increased the amounts of soil organic matter, soil total nitrogen and soil organic nitrogen, but decreased soil inorganic nitrogen and the ratios of C/N and C/H of SOM. Furthermore, straw returning elevated the content of soil organic nitrogen, such as amides and aromatic nitrogen in SOM, which are ready for crop utilization, while it lowered the amount of soil inorganic nitrogen including NH₄⁺ and NO₃^-.