Black soil region in Northeast is an important commodity grain production base in China. Improving fertilizer N use efficiency this area is one of the important scientific and technological issues related to national food security and environmental quality.

To enhance fertilizer N use efficiency and reduce N losses, appropriate fertilization practices should be developed to regulate the transformation and release processes of fertilizer N for enhancing N retention in the soil and its availability for subsequent crops.

Dr. LU Caiyan, a researcher of Institute of Applied Ecology, Chinese Academy of Sciences, evaluated the effects of N inputs rate and maize straw amendment on the transformation and fate of fertilizer N by ¹⁵N-labeled outdoor pot experiment.

The transformation of fertilizer N into soil organic N pool is a biological process mediated by soil microorganisms. Thus, energy (carbon source) and N nutrient availability for soil microbial growth may be critical for fertilizer N retention in the soil and subsequent N utilization by crops. Amending the soil by adding crop residues is a common agricultural practice that can significantly contribute to enhance soil fertility and C sequestration. At the same time, crop residues with available energy and nutrients strongly influence soil microorganism activity as well as the transformation of fertilizer N to soil organic N and its availability for crop growth.

Soil fixed NH₄⁺ pool is of significance in soil N fertility and crop N nutrition. The fixed NH₄⁺-N is in equilibrium with soil exchangeable and soluble NH₄⁺-N, while applying ammonium fertilizers can break the equilibrium, affecting soil N supply and the fates of applied N.

They found that the temporary microbial immobilization and clay mineral fixation of applied fertilizer N are two important mechanisms of N storage and N synchrony supply for subsequent crops in Black soil region of Northeast China. The majority of applied fertilizer N was rapidly transformed into soil organic N pool, and followed by clay mineral fixed ammonium.

Maize straw amendment with a high C/N ratio is an important regulator of transformation and fate of applied fertilizer N, and it increased fertilizer N retention and utilization and decreased N loss in soil-crop systems by accelerating the conversion of fertilizer N to organic N or clay mineral fixed ammonium.

The study entitled "Effects of N fertilization and maize straw on the transformation and fate of labeled (¹⁵NH₄)₂SO₄ among three continuous crop cultivations" has been accepted in Agricultural Water Management.

This research is financially supported by the National Key Research and Development Program of China and the National Natural Science Foundation of China.