Nitrate leaching on loess soils in north-west China: Appropriate fertilizer rates for winter wheat

Nitrate leaching is an important factor affecting N fertilizer consumption in the agroecosystem of the Loess Plateau of China. Therefore, the movement and residual amounts of nitrate within the soil profile under different fertilizer application rates were studied to determine the most appropriate rates of fertilizer application. Soil samples were collected from a longterm experimental site to determine the concentration of nitrate in mid-September 1999 and 2007. The results showed that NO(3)(-)-N had moved more than 100 cm down the soil profile from 1999 to 2007, and two peaks of NO(3)(-)-N were present at different depths after 23 years of high rates of N application. NO(3)(-)-N had leached to depths exceeding 300 cm in plots where > 90 kg ha(-1) N had been applied alone. At the fertilization rate of 180 kg N ha(-1), up to 1500 kg ha(-1) residual NO(3)(-)-N was detected, equivalent to 34.8% of the total input of N fertilizer during the experiment. The total amount of residual nitrate increased with increases in the N application rate, but decreased with increases in P(2)O(5) application when the N application was up to 90 kg ha(-1) or more. The results indicate that fertilization using a 1: 1 mixture of N: P(2)O(5) at 90 kg ha(-1) p.a. could prevent NO(3)(-)-N from leaching in soil used to grow continuous winter wheat (Triticum aestivum L.) crops in the rain-fed agricultural areas of China, while providing optimum yields.