Dynamics Of Soil Mineralized Nitrogen During Non-growing Season In Agricultural Region Harvesting Once A Year Of Northern China

With the experimental ecological methods, the dynamics of soil mineralized nitrogen during non-growing season in the agricultural region harvesting once a year of northern China is studied. The field experiment is a medium and long term one, which locates at Shenyang ecological experimental station, Chinese Academy of Sciences. Three different fertilization treatments are set in dry land and paddy field respectively. The following results are obtained:The dry land fertilized N 150 kg hm-2, P 16.4 kg hm-2 and K 62.3 kg hm-2 or fertilized same quantity of NPK combined with pig manure by a nutrient re-utilization of 80% agro-products, with a maize-maize-soybean rotation, irrigated by nature, may accumulates high quantity of mineralized nitrogen in 1m soil before freezing. In the three-year experiment, N accumulation of NPK+M treatment averages at 128.75 kg hm-2; NPK treatment averages at 94.94 kg hm-2; control does only at 29.22 kg hm-2. The difference is significant. Similarly to the phenomenon in late autumn, NPK+M, NPK and control treatment accumulate mineralized nitrogen average at 36.17 kg hm-2, 36.06 kg hm-2 and 22.01 kg hm-2 respectively in 0-20cm top soil next spring, and the difference is significant( =0.15). The higher quantity of mineralized nitrogen accumulated in top soil will benefit crop growth during seedling period.The farming land without fertilization also can cause nitrogen loss average at 12.24 kg hm-2 during the whole non-growing season. Even normal fertilization can increase nitrogen loss significantly, N losses of NPK treatment and NPK+M treatment average at 57.75 kg hm-2and 76.75 kg hm-2 respectively. On the basis of fertilizing NPK, the combination of pig manure by the nutrient re-utilization of 80% agro-products can neither significantly increase the mineralized nitrogen accumulation nor reduce nitrogen loss during the whole non-growing season.Fertilization has no obvious impact on nitrogen accumulation and loss to paddy land during non-growing season. All the treatments lose nitrogen at about 20 kg hm-2. The first irrigation in spring may cause nitrate leaching out of 1m soil,yet it is not serious. Irrigation prompts nitrification, and-NH4+-N turns to NO2--N and NO3--N swiftly, thus the concentration of NH4+-N in soil decreases. The reason may be the concentration of oxygen dissolved in irrigating water is high, which eliminates the restriction to nitrification. With the consumption of oxygen, the positive impact on nitrification would not persist too long.Dynamics of NH4+-N is uniform during non-growing for external factors can have little impact on it, in contrast, the dynamics of NO3--N shows great variance for it is sensitive to external factors, especially climate factors. Fertilization can increase the proportion of in total mineralized nitrogen sampled in non-growing season, and with the decreasing of depth, the proportion is reducing for the concentration of oxygen in soil decreasing also.