The Effects Of The Human Performances On The Nitrate In The Agricultural Soil

In desert area, the nitrate in the vadose zone is always crucial to the ecosystem, and has directly effect on the safety of groundwater. In these areas, the soil organic matter is low and the soil fertility is poor. Therefore, excessive chemical fertilizers have been used in order to ensure the production. The conduction returns to impact the nitrate in the vadose zone. At the same time, a great amount of nitrate always infiltrate downward with the water from the upward for the flood irrigation method, which brings a great threat to the safety of the groundwater. So this essay is intend to pay attention to the nitrate distribution in the profiles with the chloride, with using the dual isotopic compositions of the nitrate to tracing the sources and the transportation in the aeration zone, which then reflects the influences of the human performances on the nitrate in the agricultural soil. The main results are as following:Firstly, the chloride in the two agricultural soil profiles changes in accordance, both increasing with the depth. The maximum in the topsoil is probably due to the severe evapotranspiration, which the information of the H-H2O�'�18O-H2O has revealed. The different coverage densities cause different extents of the evapotranspiration, which makes the chloride between corn field and wheat field have slightly difference. The distribution of nitrate in the two profiles shows differently. In the wheat field, the possibilities of the leakage of the nitrate from the upward, the nitrification of the urea and ammonium in the topsoil, the preferential up-taking of the ammonium makes the nitrate to be the maximum in the topsoil. And in the corn field, the nitrate reduces gradually above the root zone, which is possible to nitrate up-taken by the plant root. However, the chloride in the desert soil profile is consistent with the water content, decreasing with the depth and then tending to be stable on account of the uniform soil texture. And the nitrate change with the chloride, which is owing to the infiltration of the nitrate and chloride with water from the upward in the possible deep infiltration events.In order to reflect the distribution of nitrate well, ammonium, nitrite nitrogen, the total nitrogen (TN) and the total phosphorus (TP) have been taken into consideration. The second result is as follow. In two agricultural field, the distribution of TN、TP and nitrate is consistent, trending to decrease. And the content of TN、TP and nitrate in the desert profile is low,and stays relatively stable. The nitrification and plant’s up-taking of ammonium makes the ammonium is lower in the agricultural profiles than that in the desert profiles. The utilization of urea and ammonium in the agricultural fields makes the TN、TP are obviously higher than those in the desert profile. In the corn field, the nitrate and nitrite nitrogen in the topsoil get the maximum, and the variation of the environment makes nitrate changes with the ammonium and nitrite nitrogen below the root zone.Thirdly, the concentration of NO3and the NO3-/Cl-molar ratios can reflect the differentiation of the enrichment of nitrate. The values of the nitrate and chloride are higher in the agricultural field profiles than those in the desert profile, whose are slightly higher than those of water samples, which is probably due to using the chemical fertilizers in the agricultural fields. And the relatively higher concentration of the nitrate and NO3/Cl-molar ratios demonstrate that the anthropogenic inputs possibly have great impact on the distribution of the nitration.And the last, the dual isotopic compositions of nitrate reveal that δ15N-NO3-of the water samples varies from0.59%o to9.69‰,and the average is4.79%o,which is higher than those in the soil profiles. The sources of nitrate in the corn field profile are rainfall and ammonium; and in the desert profile the nitrate mainly comes from the atmospheric sedimentation with few from desert sedimentation. The δ18O-NO3-of the corn field and water samples is very close, both are within the scope of the δ180-NO3-of the nitrification. In the corn field, the distributions of15N-NO3-and18O-NO3-with the depth are different. The δ15N-NO3-value gradually reduces with some increase in the topsoil, And then δ15N-NO3-gradually decrease and finally tend to be stable, which is possibly due to the volatilization of the urea and ammonium in the topsoil, and due to the de-nitrification that makes the815N-NO3-increase under the flooded condition. However, the δ15N-NO3-value is consistent with the δ18O-NO3-in the desert profile with the high δ18O-NO3-and low δ15N-NO3-, which is due to the interactions between nitrification and de-nitrification. And the δ18O-NO3-value decrease to19.99%o in the2.0m, which is probably on account of the mixing between the nitrate from the upward that takes20%and the nitrate produced by nitrification which is80%with the corresponding δ18O-NO3-being75%o and+3‰.