Abstract:

In order to study the effect of the method of returning maize straw (to the field) on soil dissolved organic matter (DOM) components under low temperature and drought stress conditions, a 4-year fixed-site straw returning experiment was conducted at Zhangjiakou Yuxian Experimental Station. Three methods of returning straw to the field were set up, including tillage (ploughing), rotary tillage, and large ridge rotation. With no straw retention onto the field as a control, the DOM composition characteristics of different soil layers (0-20, 20-40, 40-60, 60-80, and 80-100 cm), at various maize crop growth stages (pre-sowing, seedling, jointing, grouting, and harvesting), were measured using three-dimensional fluorescence spectrum and ultraviolet spectrum, in order to optimize the method of returning spring corn straw to the field in cold and arid areas of China. The results showed that the soil DOM content from 202-364 mg?kg^-1. DOM humic acid components (23.6%-54.3%) accounted for the highest proportion, followed by fulvic acid like components (23.6%-31.6%). Straw retention reduced the proportion of DOM humic acid components in the soil (0-20 cm), and increased the proportion of DOM protein components, microbial and enzyme activities in the soil. As the soil depth increases, the DOM content increased, the proportion of humic acid like components, humification degree, and biological activities decreased, and hydrophobic molecules increased. Large ridge rotation increased the percentage of DOM humic acid components, humification degree, and microbial and enzyme activities in the 0-40 cm soil layer, whereas tillage increased the percentage of DOM protein components and hydrophobic components in the 20-40 cm soil layer. On the other hand, rotary tillage increased the percentage of DOM fulvic acid components, humification degree and aromaticity in the 0-20 cm soil layer. With the growth of corn, the soil DOM content decreased, and the humic acid components exhibited a decreasing and then increasing trend. Additionally, the proportion of DOM small molecules increased, whilst the biological source strengthened, and the degree of humification weakened. Meanwhile, large ridge rotation increased the proportion of soil DOM rich acids and protein components during the grain filling stage. On the other hand, ploughing reduced the proportion of DOM humic acid components during the jointing stage, and rotary tillage increased the proportion of DOM protein components during the seedling stage. Overall, returning straw to the field affects the DOM components by increasing microbial and enzyme activities and crop yield. Large ridge rotation affects the soil DOM components by prolonging the straw decomposition time in the rhizosphere, improving the DOM nutrient supply capacity and spring corn yield. Ploughing and rotary tillage affect DOM content and components through mechanical action, that accelerates DOM decomposition. In conclusion, our study reveals that the suitable method for returning spring corn straw to the field in cold and arid areas of China is through the use of large ridge rotation.

Key words: straw return method, soil DOM, three-dimensional fluorescence spectroscopy, ultraviolet spectroscopy

摘要：

通过连续4年定点秸秆还田试验，设置大垄轮播、翻耕、旋耕3种还田方式，以秸秆不还田为对照，利用三维荧光光谱和紫外光谱测定不同土层（0－20、20－40、40－60、60－80、80－100 cm）及玉米各生育时期（播种前期、苗期、拔节期、灌浆期、收获期）0－20 cm土层DOM组分特征，以期优化寒旱区春玉米秸秆还田方式。结果表明，土壤DOC质量分数在202－364 mg?kg^-1之间，DOM类胡敏酸组分（23.6%－54.3%）占比最高，类富里酸组分（23.6%－31.6%）占比次之，秸秆还田降低土壤（0－20 cm）DOM类胡敏酸组分占比，增加土壤DOM类蛋白组分占比、陆源特征及芳香性。随着土壤深度的增加DOM质量分数增加，类胡敏酸组分占比、腐殖化程度和生物源特征降低，疏水性分子增加。大垄轮播提高0－40 cm土层DOM类胡敏酸组分占比、腐殖化程度及芳香性，翻耕提高20－40 cm土层DOM类蛋白组分、疏水性组分占比，旋耕提高0－20 cm土层DOM类富里酸组分占比、腐殖化程度及芳香性。随着玉米的生长土壤DOM质量分数降低，类胡敏酸组分呈先降后升趋势，DOM小分子组分占比增加，生物源增强，腐殖化程度减弱。大垄轮播增加灌浆期土壤DOM类富里酸、类蛋白组分占比，翻耕降低拔节期DOM类胡敏酸组分占比，旋耕增加苗期DOM类蛋白组分占比。秸秆还田通过提高微生物及酶活性和作物产量影响DOM组分，大垄轮播通过延长根际秸秆腐解时间影响土壤DOM组分，提高DOM供肥能力及春玉米产量；翻耕和旋耕通过机械作用影响DOM含量和组分，增强DOM腐解。因此，寒旱区春玉米秸秆还田适宜采用大垄轮播秸秆还田方式。

关键词: 秸秆还田方式, 土壤DOM, 三维荧光光谱, 紫外光谱