Research On Nitrogen Recycle And Its Effect On Environment In Dry-Land Of Loess Plateau

Crop yield, N recycle and its environment effect in the year 2004 to 2007, based on 20years long-term fertilization experiment with fixed site on continuous wheat was carried out in Hei Lu soil in North China, were analyzed. It indicated the amount of N sources, goes and its effect on environment, in older to provide the scientific proof for N fertilizer suitable used and fertility the soil in dry land farmland ecosystem. The results show that yields varies with the precipitation, The effect of applying N chemical fertilizer on yields is increased significantly, but while applying P chemical fertilizer is on the contrary. In the drought years, the yields were increased. The ability of drought-fight and calamity-diminished increased significantly while applying NP,NPM and M, the yields could be maintained above 4000 kg hm-2 . The combination of N and P is an effective ways to increased wheat yields, the wheat yields increased 15.7%～220.8%, the relation between the yields and the amount of P fertilizer applying is y =-0.1242 x2 + 44.039x + 1793.3.Not only wheat yields, but also N content in wheat and NUE was increased, while the fertilizer use reasonable. The NUE is low, applying N fertilizer, but while applying M and NPM treatment can reach 36.0% and 26.6%, The NUE of NP treatment is 57.8%, is higher than the conventional point (35%～40%).Rational use of chemical fertilizer not only increased wheat yield, but also N content in wheat to some extent, but the combination of N and P had a more pronounced effect. The combination of N, P and Manure can increase seed nutrient content and improvement grain quality, the soil organic matter,total N,total P,available N,available P and available potassium increased by 69.0%, 57.5%, 54.8%, 73.1%, 830.5% and 119.1%,respectively. It indicated that applying manure can increase soil fertility.Ammonia volatilization is one of the important ways of N losses in dry-land. Loess. In the 5th -10th days, ammonia volatilization reach the maximum, about 0.471 to 0.523 mg/h*m2,in 15 days it reach stable, while fertilizer was applied. Compared with CK, The M treatment varies was not so significantly. The chemical fertilizer accelerate the ammonia volatilization of Manure treatment, the volatilization rate is higher than N and NP treatment. The percentage that ammonia volatilization take the N fertilizer of NPM treatment is 7.02%, compared with N treatment it decreased 34.3%, but while compared with NP treatment it increased 45.5%.The Nitrous oxide (N2O) emission from fertilizer can reach 283.9 ug/m2*hour,after N fertilizer was applied, in the 5th days it reach the maximum, about 372.3ug/m2*hour,it become stable in 13th days(about 15.0ug/m2*hour). The trends of NP and NPM treatment is the same as N treatment, but its emission speeds is lower than single N treatment. Evaluate the N2O emission of M, N, NP and NPM treatment is0.02%, 0.68%,0.52% and 0.30%in the whole year,respectively. The main ways of N input in dry land farmland ecosystem, The nitrite content in soil increased under 200 cm, it shows the tendency that goes more, has the potential danger to lead the environment problem.The amount in a year is 12.3 kg/hm2 and 0.2 kg/hm2 , N input with seeds is about 4.7 kg/hm2 , with the strews and roots stubble is 1.2 kg/hm2 to 5.9 kg/hm2.The crops can't grow well and N lost reach 104.5 kg/hm2, limited by the minimum factor P, while applying N 120 kg/hm2, in the loess plateau, The N lost decreased to 37.8% of NP treatment. The main N lost of N and NP treatment is NO3-N leach, take 52.5% and 31.0% respectively,Crop yields could be maintained at a high level (4000 kg/hm2) and its variation is low, but also can decreased the NO3-N leach, by application of N, P and Manure together. The NUE of manure is lower; maybe about 50% nitrogen was residue .blew the 20cm layer.