Effects of treatments with water and fertilization on nitrate leaching loss in the piedmont of Taihang mountain

The piedmont of Mt. Taihang, an important agricultural area in North China, is characterized by high crop production and large fertilizer input. Land rotated winter wheat with summer maize accounts for 85 %-95 % of the land used for agricultural purpose in this region. For maximizing grain yield, oversupplied irrigation and fertilization was a common practice here. According to our investigation on the farm field in 2001, the annual fertilizer N application was more than 450kg/hm2 per year (more than N 250kg/hm2 and N 200kg/hm2 for winter wheat and summer maize, respectively) . P2O5 input was 150-390 kg/hm2. Potassium and micronutrients was imbalanced applying. Excessive fertilization brought about crop lodging or slow-maturing and enriched Nitrate in deep soil profile. Moreover, according to the observations from Luancheng station, CAS, groundwater level was continually decreasing during the last decade and many ground-funnels were formed due to time after time irrigations; therefore, agriculture was facing with a serious water deficiency. To co-ordinate the relationship among resources saving, environment safety and sustainable agriculture development , a field experiment on the coupling of water with fertilize was conducted in Luancheng station, CAS. The results showed that the concentration of NH4+-N was less than 5 mg/kg and different treatments had no effect on its distribution and accumulation, whereas distribution and accumulation of NO3--N in the soil profile, the major form of mineral nitrogen, were strongly affected not only by irrigation and fertilization, but also by the soil texture, crop uptake and climatecondition. The accumulation of NO3--N was restricted by water and fertilizer together. After the harvest of two seasonal crops, NO3--N accumulated markedly in the soil profile for treatments with high level water and fertilizer. When water or fertilizer was deficient, the amount of accumulated NO3--N reduced. Dryland crop of winter wheat throughout the period of duration affected not only the NO3--N transformation and formation and N absorption of winter wheat, but also the yield of ersuing maize and the accumulation of NO3--N. There was a coupled relationship between the amount of cumulated nitrate and soil moisture content. Both fertilizer and water are limited factor of winter wheat; especially water deficiency that had directly effect on current and ensuing crops. Therefore, aiming at the shortage of ground water of this region, supposing there is only insufficient water available, irrigation in the sowing and pre-jointing stage should have priority. For each irrigation, at least 60 mm should be applied. The dosage of fertilizer should not be very high; otherwise, it could bring about the accumulation and leaching of NO3--N, The optimal treatment for this region was W2MF.