The impact of long-term fertilization on nitrogen leaching from double rice field of Hunan, China
To investigate the impact of long-term (1981-2007) fertilization on nitrogen leaching in soil solution of double rice field, a two years’ study was conducted in Hunan, China. Porous suction pipes was employed to extract soil solutions from different aquifers (in depth of 20-30 cm, 50-60 cm and 80-90 cm) of rice field to analyze the concentration of ammonium-N (NH4+–N) and nitrate-N (NO3––N) and the total loss of nitrogen. Results showed that nitrate-N was the primary form of N leaching in studied area. Significant seasonal variance as well vertical distribution of N leaching was found. NH4+–N in soil leachate mainly occurs in submerged situation before mid-season drainage, while NO3 ––N could primarily be found in situation of saturation especially in late growing stage. Concentration of NH4+–N decreased with the increasing sampling depth in range of 0-100 cm; whereas for the NO3––N, the vertical distribution was complicated: it increased in 0-60 cm and then decreased in 60-90 cm. Long-term incorporation with rice straw (NPKS) causes greater total N losses than applied chemical fertilizer only (NPK), and N leaching of CK (No fertilizer) was significantly less than these two treatments. For the studied area, comparatively higher N leaching losses occurred due to long-term fertilization, but with low potential hazards for nitrate contamination due to no extreme high NO3––N was found in all samples.
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