Effects of different nitrogen forms on microbial quantity and  enzymes activities in soybean field

In this paper, pot experiments were conducted to study the effects of different N forms, including biological nitrogen fixation(N0), NO-3-N(N1), NH+4-N(N2), amino acid-N(N3), protein-N(N4) and amide-N(N5) on microbial quantity and enzyme activities in soil at the growth stages of soybean. All N fertilizers were applied as base fertilizers with the same amount. The results show that bacteria are the predominant ones among microorganisms. The maximum population of bacteria, actinomyces and fungi are observed at the flowering stage, and the change of microorganism is a single-peaked curve at the whole growth stages. As the growing phases of soybean, the total amounts of microorganisms and biodiversity indices were different among treatments supplied with different forms of nitrogen. Moreover, the amounts of the microorganisms change with different forms of nitrogen treatments at the flowering stage with an order: N5>N3>N2>N1>N4>N0. In addition, the change of the biodiversity indices shows a slowly decreased trend. Therefore, the two important factors should be combined to evaluate quality of the soil. The activities of urease and invertase were single-peaked curves with the growing phases as well, however, the maximum urease activity appears at the podding stage while that of the invertase activity at the flowering stage.