长期施肥对土壤固定态铵含量及其有效性影响

EFFECT OF LONG-TERM FERTILIZATION ON CONTENT AND AVAILABILITY OF FIXED AMMONIUM IN SOIL

棕壤连续13年定位试验表明，长期施用化肥或低量有机肥对土壤固定态接含量均无显著影响;而施用高量有机肥区固定态接含量比试验前平均增加30.2％。这部分增加的固定态按主要来自土壤有机氮矿化补充。施肥后固定态铵的净增加量超过作物施氮量是土壤激发效应的结果。土壤原有固定态铵含量在113～116mg／kg，对作物无效，而新固定态按时作物有效。生长季耕层土壤固定态铵总释放量（N）对照区为43kg／hm2，化肥区平均为110kg／hm2;有机肥与化肥配合区平均为165kg／hm2。施钾对固定态铵的释放有一定抑制作用。

The results of 13 Years long-term field experiment on Shenyang brown earth showed that application of chemical fertilizers alone or low amount organic manure had little effect on the content of fixed NH4 in soil. However, the continuous application of high amount organic manure increased the content of fixed NH4 in soil significantly. In all high amount organic manure plots the content of flxed NH4 increased by 30. 2% in average after 13 years. The freshly fixed NH4 came mainly from the mineralization of organic nitrogen in soil. The net increase of fixed NH4 after fertilization was more than the application rates of nitrogen fertilizer. It was the resul of priming effect of soil nitrogen. The content of fixed NH4 in soil varied greatly in a growing season due to uptake by crops and mineralization of soil organic nitrogen. During the growth period of soybean the total amount of fixed NH4 released from 0～20cm layer in CK, chemical fertilizer and chemical fertilizer combined with organic manure plots reached up to N 43. 110 and 165kg/hm2, respectively. This showed that the release of fixed NH4 offered a main available nitrogen source for crops.