[Effects of different straw returning amount on the potential gross nitrogen transformation rates of fertilized...

Straw returning is one of the important measures for improving soil fertility. It is unclear, however, whether the regulation function of soil on nitrogen (N) cycle after fertilization is sustainable and the relationship between the regulation function and the amount of straw returned to the field. In this study, a 3-year straw returning field trial was set up in a field had been carried out straw returning of all the havested straw for nine years. The amount of straw returned was 100%, 67%, 33% and 0 of the average annual straw yield (7500 kg·hm^-2) to identify the effects of different straw returned amount on N transformation in the fertilized soil (0-10 cm). Results showed that the amount of straw returning affected the production and consumption of NH₄⁺-N and NO₃^--N by affecting the potential gross N transformation rate. When the amount of straw returning was less than 67%, the production rate of NH₄⁺-N significantly reduced and the consumption rate significantly increased, and thus led to the decrease in soil NH₄⁺-N retention capacity. The NO₃^--N production rate increased and the retention capacity decreased, and the NO₃^--N accumulation and leaching loss risk increased. Therefore, returning more than 67% of harvested straw was necessary to maintain the function of soil N conservation.