长期免耕和秸秆覆盖下黄土高原旱作土壤不同粒级复合体中酸解有机氮含量及分配比例变化
Acid hydrolysis organic N content and the distribution in different sizes of soil complexes in Loess Plateau dryland under long-term no-tillage and straw mulching
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摘要: 【目的】探明不同保护性耕作措施对黄土高原旱作土壤不同粒级复合体中有机氮含量与分配的影响,可对评价耕作措施的效果提供科学依据。【方法】基于黄土高原旱区14年的长期定位试验,采用Bremner法, 对传统耕作(T)、免耕(NT)、秸秆覆盖(TS)及免耕+秸秆覆盖(NTS)四种耕作措施条件下不同土壤粒级复合体中的有机氮含量和分配进行了研究。【结果】保护性耕作方式均增加了2~10 μm粒级土壤复合体的比例,增幅为20.0%~31.7%;降低了0~2 μm粒级土壤复合体在土壤中所占的比例,降幅为27.6%~31.0%。在所有耕作措施下,耕层土壤中不同粒级复合体所占的比例为10~50 μm＞2~10 μm＞0~2 μm＞50~100 μm＞100 μm。保护性耕作方式均明显提高了耕层0~2 μm粒级土壤复合体中氨基糖氮的含量,增幅在46.9%~107.1%,降低了单位质量0~2 μm粒级土壤复合体中的NH+4-N含量,降幅在14.8%~27.0%;明显提高了耕层单位质量2~10 μm粒级土壤复合体中酸解总氮、氨基酸氮和氨基糖氮的含量,增幅分别为8.2%~14.3%、16.2%~31.5%和154.9%~184.3%;降低了单位质量2~10 μm粒级土壤复合体中NH+ 4-N的含量,降幅为28.7%~46.6%。传统耕作(T)条件下,与各粒级土壤复合体相结合的有机氮量顺序为10~50 μm＞0~2 μm＞2~10 μm＞50~100 μm＞100 μm以上,而保护性耕作条件下,与各粒级土壤复合体相结合的有机氮量顺序为10~50 μm＞2~10 μm＞0~2 μm＞50~100 μm＞100 μm以上;与传统耕作相比,保护性耕作措施显著地增加了耕层土壤中酸解总氮、氨基酸氮、氨基糖氮的含量,增幅分别为6.6%~20.4%、89.0%~113.0%和11.9%~31.6%,降低了NH+4-N的含量。【结论】与传统耕作(T)处理相比,保护性耕作(NT、TS、NTS)措施明显提高了土壤2~10 μm粒级复合体的比例,降低了0~2 μm粒级复合体的比例;增加了耕层土壤中酸解氮总氮、氨基糖态氮和氨基酸态氮的含量,降低了NH+ 4-N的含量。土壤中以氨基酸态氮占优势地位,其它形态的有机氮无明显分布规律。Abstract: 【Objectives】 Conservation tillage measurements have different effect on the organic N content and its distribution in different sizes of soil complexes. This study will provide scientific base for the evaluation of different conservation tillage methods in the dryland in Loess Plateau.【Methods】 Soil samples were collected from a 14-years’long-term experiment in dryland in Loess Plateau, in which, four tillage treatments were set up including conventional tillage (T), no-tillage (NT), straw mulching (TS) and no-tillage + straw mulching (NTS). The Bremner method was used to determine the organic N contents and their proportion in different sizes of soil complexes.【Results】Under all the three conservation tillage treatments, the percentage of soil complexes in 2-10 μm was increased by 20.0%-31.7%, while that of 0-2 μm was decreased by 27.6%-31.0%. The percentage of different soil size complexes was all in order of 10-50 μm＞2-10 μm＞0-2 μm＞50-100 μm＞100 μm. The amino sugar nitrogen content in 0-2 μm of soil complexes was significantly increased by 46.9%-107.1%, while the NH+ 4-N content decreased by14.8%-27.0%; the contents of acid hydrolysis nitrogen, amino acid N and amino sugar N in 2-10 μm of soil complexes were increased by 8.2%-14.3%, 16.2%-31.5%, 154.9%-184.3%, respectively, while the NH+4-N content was decreased by 28.7%-46.6%. The contents of soil complexes combined organic nitrogen was in order of 10-50 μm＞0-2 μm＞2-10 μm＞50-100 μm＞100 μm under all the conventional treatments, while it followed 10-50 μm＞2-10 μm＞0-2 μm＞50-100 μm＞100 μm under conservation tillage. Compared to conventional tillage measures, the contents of acid hydrolysis nitrogen, amino acid N and amino sugar nitrogen were significantly promoted and increased by 6.6%-20.4%, 11.9%-31.6% and 89.0%-113.0%, respectively, while the NH+ 4-N content decreased under conservation tillage treatments. 【Conclusions】In the long term, all the no-tillage and straw-mulching are effective in increasing the percentage of soil complexes in 2-10 μm while decreasing that in 0-2 μm, and increasing the contents of organic nitrogen while decrease NH+4-N content in dryland in Loess Plateau. So both no-tillage and straw mulching in long run will improve soil texture and the capability of regulating nutrient supply to crops.
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