Effects of combined application of organic and inorganic nitrogen fertilizer on the soil nitrogn leaching and the growth of leaf-used lettuce

In net room, pot experiments were conducted to study the effects of different proportions of organic and inorganic nitrogen(0∶4, 1∶3, 1∶1, 3∶1 and 4∶0) on growth of leaf-used lettuce and soil nitrogen leaching under the same nitrogen application rate. The results showed that, the highest leakage amount of total nitrogen, nitrate nitrogen and ammonium nitrogen were observed as 926.6, 648.3 and 194.7 mg respectively and the lowest soil leachate pH value was found in treatement of 0∶4. The leaf-used lettuce yield and soil leachate pH value were improved and nitrogen leaching was decreased significantly combined with organic manure application; The highest yeild of leaf-used lettuce was obtained in in treatment of 1∶1. It was also found that soil nitrogen leakage amount decreased dramatically with the increase of the ratio of organic manure applied. The main leaching form in soil leachate was dominated by nitrate nitrogen due to the higher leakage amount of nitrate nitrogen than the ammonium nitrogen; The leakage ammount of soil total nitrogen and nitrate nitrogen reached the peak after the leaf-used lettuce was transplanted for five days and eighteen days while the top application of inorganic nitrogen fertilizer could increase the nitrogen leaching. The leakage amount of ammonium nitrogen in different treatments showed a decreasing trend during the whole growing period of the leaf-used lettuce. Based on the point of leaf-used lettuce yield and environment protection consideration, the proportion of organic nitrogen and nitrogen was 1∶1 should be suggested in the leaf-used lettuce fertilization.