(土娄)土中非代换铵(固定态)的有效性

AVAILABILITY OF NONEXCHANGEABLE (FIXED) AMMONIUM OF MANURED LOESSIAL SOIL IN CHINA

通过田间小区试验和^(15)N标记的微区试验,研究了(土娄)土中非代换铵含量、它在小麦生长期的动态变化以及其对小麦的有效性。试验结果表明,(土娄)土具有可观的非代换铵贮量。供试土壤耕层含非代换铵236ppm N,占该层土壤全氮的22.9%。0—75cm土体中平均含252ppm N,占全氮的四分之一多。(土娄)土“新固定”的和“固有的”非代换铵对小麦生长都有重要意义。前者以其高有效性占优势,后者则以其较大的供应量为特点。在小麦生育期内,0—75cm土体中的非代换铵最大净释放率,“新固定”的为38.0—70.5%,“固有的”为10.4—22.2%。以最大净释放量计,“固有的”(12—72ppm N)大于新固定的(7.4—10.9 ppm N)。非代换铵的最大净释放率随土层加深而减小。试验还表明,(土娄)土粘土矿物固定铵作用相当于一个蓄氮库。施用氮肥有增加土壤非代换铵的趋势。

The present work is a part of the cooperative project between Northwestern Agricultural University Shaanxi, China and Justus Liebig University, Gissen, W. Germany. The content and variation of nonexchangeable ammonium in manured loessial soil and its availability for winter wheat were studied through a common plot experiment and a micro plot experiment using ^(15)N-labelled ammonium under field condition during wheat growing period The experimental results showed that manured loessial soil possessed a greater reserve of nonexchangeable ammonium; in the cultivated layer of 0—20 cm of the soil tested, the nonexchangeable ammonium amounted to 236 ppm N, constituting about 23% of the total N, and in the soil layer of 0—75 cm, it was 252 ppm N on average, constituting a quarter of the total N. Both the newly fixed ammonium and the ammonium oringinally fixed by soil played an imortant role in wheat growth; the former was predominated by its higher availability, while the latter was cheristerized by its greater quantity. The maximume net release (MNR) rate of newly fixed ammonium ranged from 38.0 to 70.5% in the soil layer of 0—75 cm, being much higher than that of the ammonium oringinally fixed by soil that ranged from 10.4 to 22.2% in the same soil layer. Howerver, the MNR amount of the ammonium oringinally fixed by soil was 12—72 ppm in the soil layer of 0—75 cm, it is much more than that of the newly fixed ammonium that was only 7.4—10.9 ppm in the same soil layer. It was also proved that the fixation of ammonium by clay minerals in manured loessial soil could act as a pool of N in soil and applying N tended to increase the nonexchangeable ammonium in soil.