Effects of rhizosphere fertilization on nitrate content of rape

A diffusion experiment was conducted to determine the changes of nitrate and ammonium concentration at different distance around the placement of fertilization in soil, and a pot trial was carried out to validate the effects of different means of fertilizer application on the nitrate content and yield of rape on a calcareous soil. Two kinds of fertilizers, the Acidic ball-like Rhizosphere Fertilizer (pH1.0-2.0) and normal concentrated fertilizer, were used. The results indicated that the sphere of influence on the concentration of nitrate and ammonium in soil were mainly within 4 cm apart from fertilization point; however, the difference of influence sphere of these two fertilizers was significant within 2 cm. The diffusion of ammonium and nitrification of the acidic fertilizer were slower than that of concentrate fertilizer. Therein, within 1 cm from fertilization point, the increment of the soil ammonium of the concentrated fertilizer measured up to the maximum after a week of application, but for the acidic fertilizer, the maximum was reached after two weeks, meanwhile, the difference of increment of these two fertilizers was significant. Within 2 cm from fertilization point, for both fertilizers, the maximum of ammonium was reached one week later than that at 1 cm, and the increment of ammonium of the concentrated fertilizer was lower than that of the acidic fertilizer. But the increment of nitrate of concentrated fertilizer was lower than that of acidic fertilizer. The results of pot experiment indicated that the application of acidic rhizosphere fertilizer increased ammonium concentration remarkably, but decreased nitrate concentration. Comparing with the concentrated fertilization, the application of acidic rhizoshpere increased ammonium concentration by 13% and decreased nitrate concentration by 71%-89%, respectively. As the result, the application of acidic rhizoshpere fertilizer decreased the amount of nitrate accumulated in the rape by 28% and increased the output of rape by 39%.