Effects Of Combined Application Of Potassium With Urea And Organic Manure On Quality Of Soil Environment And Vegetables

In the past few years, the role of organic fertilizer in agronomic practices has long been replaced by chemical fertilizer. It has also brought about some unfavourable results. Besides the impairment of soil environmental and vegetable quality in protected field, this practice also caused a decline in soil productivity through excessive soil erosion, nutrient runoff, imbalanced nutrient, and deteriorated soil chemical properties. Much work has been done and a wide range of techniques have been developed and put into practice to improve soil environmental and vegetable quality, especially the effect of application single fertilizer in vegetable field. However, little information is available on the effects of combined application of potassium with urea and organic manure on soil environmental and vegetable quality. It is very important to understand the combined application of potassium with urea and organic manure management on nitrogen transformation and accumulation, and improve vegetable and environmental quality. Therefore, the objective of this study is to gain some information, by using incubation experiment, pot experiment and soil column leaching experiment, on soil environmental and vegetable quality in spinach and Amaranthus hypochondriacus as affected by combined application of types of nitrogen fertilizers under different K supply levels. The results are summarized as follows:1. The results from the soil incubation experiment showed that lower NO3--N content and higher NH4+-N content in soil was observed in the treatment of combined application urea with DCD, but addition organic manure to urea did not show notable effect on NO3-N and NH4+-N content in soil. The contents of available and slowly available potassium in vegetable soil significantly increased with the higher of potassium, and application organic manure combined with urea higher than that of single urea treatment. The soil urease and invertase activity was significantly higher in combined application of organic manure with urea than that of single urea or urea with DCD treatments, but insignificant difference was found among different potassium levels. The treatment did not have notable effect on pH within earlier seven days of incubation period, but pH of the vegetable soil in later incubation stage varied: U+DCD >U+DM U+PM>U, and pH of the soil was enhanced by the increase of potassium application. The soil electrical conductivity was higher in organic manure with urea than that of single urea within seven days, but higher soil electrical conductivity was observed in single urea treatment in later stage.2. In soil column leaching experiment, the NO3- concentration of leachate increased with the increase of leaching times within earlier thirty-five days, and decreased with the increase leaching times after thirty-five days, but the NH4+ concentration of leachate decreased with the increase of leaching times. Combined application of urea with organic manure or DCD distinctly decreased total amount of NO3-N, NH4+-N and inorganic nitrogen leached, and electrical conductivity of leachate, while enhanced NO3-N and NH4+-N contents, and pH of leachate in vegetable soil after leaching. Potassium supply not only increased pH, EC of leachate, and NO3-N and NH4+-N accumulation in soil after leaching, but also decreased the total amount of NO3-N and inorganic nitrogen leached. It is evident that combined application of urea with organic manure or DCD could effectively decrease nutrient leaching and the risk of nitrate pollution to underground water.3. It was found in the pot experiment that NO3-N content in soil was gradually decreased with the increase of potassium concentration, but NH/-N content was not obviously affected. Combined application of urea with DCD reduced NO3-N content in soil and maintained higher content of NH4+-N due to the inhibition of nitrification by DCD, but addition of organic manure did not have notable effect on NO3-N and NH4+-N content in vegetable soil in comparison with the treatment of urea. Urea combined with org...