Effect Of Long-term Rotation And Fertilization On Transformation And Supply Of Soil Nitrogen

The soil nitrogen is the important component of soil fertility and the main source of crop's nitrogen nutrition. Most soil nitrogen cannot meet the crop growth needs, it depends on fertilization to complement and adjust. But the unreasonable use of fertilizer not only cause the vast waste and the decline of economic benefit but also bring a series of environmental problems. The basic approach of improving the nitrogen use efficiency, decreasing environmental pollution and raising crop's yield is the understanding of the supplying nitrogen capacity and reasonable fertilization. According to the current actual situation, different fertilization treatments were used in a long-term fertilizer location experiment of Shenyang Agricultural University. After 29 years of long-term rotation and fertilization, the effect of different fertilization treatments on the distribution of N content, the mineralization of organic N and soil N supplying capacity were studied; The developing law and the supplying mechanism of soil N were discussed under long-term rotation and fertilization. They provide a theoretical basis for the utilization of N nutrient resource in brown soil. The main results as follows:1. After 29 years of long-term fertilization, the concentration of organic matter, total N, alkali hydrolyze N, inorganic N ( NO₃^--N, exchangeable NH₄⁺-N, fixed ammonium ) and SMBN in topsoil ( 0～20 cm) differed significantly at P<0.01. The general trend of soil N indexes was high level of organic manure treatment >low level of organic manure treatment > fertilizer treatment > control, expecially applying the higher level organic manure and inorganic fertilizer has the best effect. With the soil layers deeper, the concentration of soil organic matter, total N, alkali hydrolyze N, inorganic N reduced gradually, but the distribution of soil fixed ammonium was contrary trend.2. Long-term fertilization could increase the contents of soil organic N forms, especially the content of amino acid N. The general trend of organic N forms was amino acid N >non-hydrolysable N > ammonia N > hydrolysable unidentified N > amino sugar N. The distributions of acid hydrolysable organic N forms decreased with layers' depth. The basic rule was organic-inorganic fertilizer treatment > single organic manure fertilizer treatment > single inorganic fertilizer treatment and the control. Non-hydrolysable N in each soil layers appeared out-of-order.3. In two rotation cycles, the concentration of each soil nitrogen indexes always showed the corn year >the soybean year.4. First-order kinetic equation (One pool model) could preferably described the mineralized process of brown soil ( 0～60 cm soil layer) organic N, and the parameters which were fitted by one pool model expressed the mineralization characteristics of soil organic N.5. Long-term fertilization could significantly increase the N mineralization potential of topsoil. The trend of soil N mineralization potential was high level of organic manure treatment >low level of organic manure treatment >fertilizer treatment >control >soil before the trial, expecially applying the higher level organic manure and inorganic fertilizer had the best effect and the biggest capacity on N supplying. With the soil layers deeper, the concentration of soil N mineralization potential had a sudden decrease and the different soil layers differed significantly.6. Soil N mineralization potential was correlated with soil organic N forms intimately. Amino acid N had the biggest direct contribution to N mineralization potential, and other components made indirect contribution through amino acid N. In addition, soil total N was also an important effect factor for soil N mineralization potential.7. Every soil N indexes were significantly correlated with crop yield and sorption contents of crop at P<0.01. It indicated that soil N forms had certain effects on assessing the N supplying level, especially N mineralization potential, mineralized N, alkali hydrolyze N.8. The sequence of soil N supplying amount was high level of organic manure treatment >low level of organic manure treatment > fertilizer treatment >control,expecially applying the higher level organic manure and inorganic fertilizer had the best effect. With the soil layers deeper, the amount of soil N supplying dropped fast. The topsoil had the stronger N supplying capacity, and that of the subsoil should not be ignored.In short, long-term fertilization of organic and inorganic, expecially applying the higher level organic manure and inorganic fertilizer, is considered the best way for maintaining the soil fertility. It can significantly improve the concentration of soil N forms, which affects soil N mineralization potential, in order to improve the capacity of soil N supplying. Therefore, we should attach importance to applying organic manure in agricultural production and pay attention to the combination of organic manure and inorganic fertilizer.It is the first time to study roundly N supplying characteristics of brown soil under long-term location experiment. The results enrich the theoretical study of soil N, and have great significance for forming fertilization programs, protecting environment and products safety.