The Leaching Properties Of Nitrogen And Phosphorus Under Four Typical Land Use Patterns In Subtropical Region

Nitrogen (N) and phosphorus (P) leaching in soil is regarded as one of the importantaspects of agricultural nonpoint source pollution. Monitoring of nitrogen and phosphorusleaching characteristics for different land use can provide a certain basis for understandingcharacteristics of non-point source pollution and groundwater pollution risk assessment. Inthis study, four types of most common land use (subtropical paddy fields, hilly tea garden,planted forest (pinus elliottii), vegetable garden) were selected as the study object. Placedifferent depth of the suction cup sampling device in situ, by analysis of continuousdynamic observation, and studied the characteristics of dynamic time of nitrogen andphosphorus leaching in soils under different land use types and fertilization. There are sixtreatments, fertilization and no fertilizer in Paddy, conventional fertilizer and rice strawmanure in tea garden, one treatment in woodland and vegetable garden. Each treatmentrepeat3times, and there are4sampling depths:15,30,60and90cm. The main results fromMarch2010to December2011are as follows:(1) N leaching in fertilization soils (paddy, vegetable garden, tea garden) was higherthan that in no fertilizer soils. N leaching in vegetable garden was the highest, and the valueof total nitrogen (TN) concentration in soil solution was up to92mg N/L in the observationperiod. It indicated that N leaching in vegetable garden to groundwater quality had greatthreat. N leaching in tea garden was lower than that in vegetable garden, and TNconcentration under rice straw manure was lower than that under conventional fertilizer.(2) The observation results from N leaching in different soils showed that floodedconditions on paddy in different periods had remarkable effect on the N leaching (P<0.05),the main N leaching in flooded rice growing period (April to November) under the condition was NH4+-N, and the main N leaching in idle field phase was NO3--N. Dry landsystem of the three kinds of land use was almost no leaching of NH4+-N, the main leachingloss was NO3--N. Paddy fields idle phase field leaching pattern were consistent, this wasclosely related with soil aeration change conditions.(3) P leaching in fertilization soils was higher than that in no fertilizer soils. Pleaching in rice growth period under the condition of flooded paddy soil was relatively low.And rice paddies idle field (10to12month) under no flooded conditions may be the mainstages of P leaching. The observation results in vegetable garden showed that, P leachingwas significantly higher than other three kinds of land use because of the seriousaccumulation of soil P. TP concentration in soil solution up to0.35mg P/L, has the high Pleaching risk; Tea gardens and woodlands of P leaching was generally weak.(4) Relevant analysis results under different methods of soil phosphorus leachingcondition and dissolved phosphorus concentrations in the soil solution showed that,compared with the0.01M CaCl2and Olsen (0.5M NaHCO3) extraction methods, theBray-1(0.03M NH4F+0.025M HCl) method performed the best to determine the Pleaching risk of paddy soils in this study area.