Experimental Study On Nitrate Transfer Under Intermittent Infiltration And Groundwater Environmental Effect

Based on reviewing previous research on surge flow irrigation, nitrogenous fertilizer (NO3-) transfer transformation and its pollution to the groundwater environment, combined with the National Nature Science Found Project "The study on the characteristics of the field N transfer and effective usage with the surge flow irrigation under the fertilization" and the practice of irrigation and fertilization in Guanzhong, Shaanxi province, adopts technical way of experiment and theory analysis, this paper leads the way of research on the nitrate transfer transformation and its distribution in the groundwater (vertically, especially), with a 70cm groundwater table under intermittent infiltration . The main conclusions are as follows:1. With a fixed groundwater table and a neglected field surface evaporation, capillary water ascending period has 2 stages. In the first stage, the ascending rate is greater, while in the second, it's decreased apparently. The initial soil moisture is high, so is the ascending rate. The relationship between the time needed and the accumulative amount of attracted water can be simulated by exponential and stepped functions.2. The solute KON3 accelerates this ascending; For the forming of the water-sealing layer, the intermittent infiltration achieves a decreased infiltration rate, a decreased NO3- advancing rate , a higher NO3- content on the surface soil and less NO3-leaching compared with the continuous.3. Under a shallower groundwater table, the soil moisture is higher. In the deeperlayer an anaerobe layer is formed, and dinitrification weaken the accumulation of NO3-both in the soil and in the groundwater.4. The main effects of surge flow irrigation technological elements on the infiltrated water and NO3- transfer and distribution with a 70cm groundwater table are as follows: (l)To some extent, infiltration rate decreases with a decreased cycle rate; In this experiment, the optimal cycle rate is 1/5, which leads to a shallower distribution of the moisture and NO3- in soil and weakens the trend of NO3" leaching. The concentration of NO3- in the groundwater increases with an increased cycle rate. (2) To some extent, the average infiltration rate decreases with an increasing cycle number; (3) The function of decrease infiltration will reduce as the irrigating water quota increases. It showed that the concentration of NO3- in the deeper soil and the groundwater and the lost of dinitrification increase with an increased quota; The relationship of the concentration of NO3- in the groundwater (3 hours redistributed) and the irrigating water quota can be simulated by exponential functions.5. With a same irrigating quota, the max. concentration of NO3- in the soil , the percentage of NO3- distributed in 0~30cm and the concentration of NO3- in the groundwater will increase as the concentration of the infiltrated solution increases. Under the surface and deep-lying fertilization, the NO3- in the soil centralized at the depth it's applied. Concentration peak of chemigation's NO3- is smaller and the NO3- is well-distributed in the soil. The NO3- is well-distributed in the groundwater under surface applying and chemigation, while with deep-lying fertilization, the concentration of NO3- is high and the gradient of the concentration of NO3- is great.6. The NO3- is mainly distributed in upper layer (0~5cm) in the groundwater, and the concentration decreases vertically downward. During the redistribution, the gradient of concentration decreases, the NO3- is getting well-distributed.