Characteristics Of Nitrogen And Phosphorus Losses From Different Farmlands In Tai Lake Riverine Area

Nitrogen and phosphorus losses from farmland is one of the major sources of Tai lake eutrophication, In order to control nitrogen and phosphorus losses effectively, how nitrogen and phosphorus lose from farmland should be studied firstly. Processes and characteristics of nitrogen and phosphorus losses vary with not only precipitation but also site-specific characteristics, namely different factors of site-specific location, including crop types, cultivation systems, groundwater table, terrain, irrigation and drainage conditions, soil N, P concentrations and fertilization etc. And the differences of all these site-specific characteristics can result in significantly different nitrogen and phosphorus losses way and characteristics.To study the characteristics of nitrogen and phosphorus losses from farmlands in Tai Lake riverine area, 39 representative farmlands, including differential crop types, fertilization, soil, irrigation and drainage conditions etc., were selected as monitoring site-specific locations in Jiaxing area. These farmlands represent 8 main types: vegetables with no covering, vegetables with covering, vegetables-paddy rotation, fruit trees (or nursery), cereal, paddy-cereal rotation, only paddy and aquatic vegetable.By continuous site-specific sampling and monitoring, we have monitored farmlands, ditches, watercourses near farmlands at 39 site-specific locations 2-45 times in the flood season (May-September 2004, 2005 May-September) and the non-flood season ( October 2004 -2005 in April).The main conclusions are as follows:It has 39 times precipitation during June 2004-September 2005 in research region and the average monthly rainfall is 90 mm. Precipitation frequencies and amount have little differences in the flood season and the non-flood season. In the flood season there were averagely twice precipitations per month, and each precipitation averagely lasted for three days, with an average precipitation of 40mm. While there were averagely twice precipitation a month in the non-flood season, and each precipitation averagely lasted for five days, with an average precipitation of 36mm. In addition, the largest one-time precipitation was 125mm, the longest last days is 15 days, and the largest precipitation intensity is 71mm/24h in the monitoring period. There is less precipitation in the monitoring period comparing with the former years. The ditches adjacent farmlands flowing probability is 46%-100% after precipitation with 15mm/24h.The characteristics of nitrogen loss from farmland are: The whole year is the riskful days for nitrogen loss in three types of farmlands: vegetable with no covering, fruit trees (or nursery), cereal. While the riskful days is in the flood season in vegetable with covering, and is in the non-flood season in paddy-cereal rotation. Nitrogen loss from only paddy and aquatic vegetable farmlands is low riskful in the full year, and from paddy-cereal rotation farmland is low riskful in the flood season.When ditch water flows to watercourse near farmland, some results are gained as the followings. In the whole year the average concentration of TDN in farmland water, ditch water, watercourse watergradually decrease in 6 types farmlands, namely vegetables with no covering, vegetables with covering, fruit trees(or nursery), cereal, paddy-cereal rotation, vegetables-paddy rotation.. And in the flood season the same result can be found in the paddy field. However, the average concentration of TDN in farmland water, ditch water, watercourse water gradually increase in the aquatic vegetable field in the whole year, and the same result is got in the only paddy field in the non-flood season.Full-year nitrogen losses is in high intensity from the 4 types farmlands which are vegetables with no covering, fruit trees (or nursery), cereal, while in low intensity from farmlands with paddy and aquatic vegetable. In the flood season nitrogen losses is in high intensity from farmland of vegetable with covering besides the above 4 types, but in low intensity from farmlands of paddy-cereal rotation. In the non-flood season, nitrogen losses are in high intensity from the above 4 types farmland, and moderate intensity from farmlands of vegetables with covering and paddy-cereal.NCV-N and NH/-N are the main forms in terms of nitrogen losses from farmlands, accounted for 67% of TN. The rate of NO3"-N to TDN is 21% higher than that of NH/-N to TDN.Farmland surface soil (0-30cm) nitrogen concentration directly affects the intensity and frequency of nitrogen loss. At the same time, it affects surface mud (0-5cm) nitrogen concentration of adjacent ditches of farmlands. When other influencing factors are coincident, the loss intensity of farmland N, P losses is higher with the higher TN concentration in surface soil (0-30cm), and higher TDN concentration occurred more times. When available nitrogen concentration of surface soil (0-30cm) from farmland is higher, that of surface mud (0-5cm) in ditches of adjacent farmland is higher.Characteristics of phosphorus loss from farmland are: The riskful days of phosphorus loss is in the whole year from vegetable field with no covering, and in the flood season from vegetable field with covering. The whole year is low riskful of phosphorus loss for the only paddy field.When water flows from ditch to watercourse near the farmland, TP loss intensity is high from vegetable field with no covering throughout the year and from vegetable field with covering in the flood season. TP loss intensity is low from Paddy field all the year.Surface soil (0-5cm) Olsen-P concentrations of farmland impacts not only Olsen-P concentrations of surface mud (0-5cm) in ditches but also water TP concentrations of ditches adjacent farmlands. The former and the latter two are positive correlation.