[Effects of Fertilization on the Nitrogen Residual Amounts and Leaching from Citrus Orchard Soil in the Three Gorges Reservoir Area].

This experiment has the citrus orchard soil in the basin of the Zigui County Ecological Station in the Three Gorges Reservoir Area as its research object. Leaching tests of an undisturbed soil column at 0-20, 0-40, and 0-60 cm depth were performed in a citrus orchard. The effects of nitrogen leaching and residual amounts in the soil were studied. Four kinds of fertilization treatments were set up in the experiment:no fertilization treatment (CK), low nitrogen fertilization treatment (T1:250kg·hm), medium nitrogen fertilization treatment (T2:500kg·hm), and high nitrogen fertilization treatment (T3:750kg·hm). The results showed that:① The main form of nitrogen leaching in citrus orchard soil was nitrate nitrogen (NO-N), accounting for 36.93%-60.07% of total nitrogen (TN) leaching. The ratio of TN to ammonium nitrogen (NH-N) was 4.40% to 5.79%. The ratio of NO-N residues in soil to TN residues was 11.31‰-45.66‰, and the ratio of NH-N residues to TN residues was 1.051‰-2.07‰. ② Nitrogen leaching and residual amounts in citrus orchards at the same depth showed significant positive correlation with the amount of fertilizer applied. The leaching losses and residual amounts of TN in soil at different fertilization rates were 11.35-30.11 kg·hmand 0.30-1.86 g·kg, respectively. Among them, the ratio of leaching losses of NO-N and NH-N to TN leaching amounts peaked under T2 treatment, and the peaks of NO-N and NH-N residues in TN residual amounts appeared in T1 and T2 treatment, respectively. ③ Given the same fertilization amounts, the leaching amounts and residual amounts of different forms of nitrogen in the soil were greatly affected by soil depth. After fertilization, the peaks of NO-N leaching and residual amounts appeared at 20 cm and 40 cm, respectively, and the peaks of NH-N leaching and residual amounts mainly appeared at 20 cm depth. Inferred from the results of the experiment, the neutral nitrogen treatment in the 0-40 cm soil column is more conducive to the conversion of fertilizer nitrogen to inorganic nitrogen for plant absorption, and reduces the risk of nitrogen leaching after fertilization.