Leaching losses of nitrate nitrogen and dissolved organic nitrogen from a yearly two crops system, wheat-maize, under monsoon situations

A large amount of nitrogen (N) fertilizers applied to the winter wheat-summer maize double cropping systems in the North China Plain (NCP) contributes largely to N leaching to the groundwater. A series of field experiments were carried out during October 2004 and September 2007 in a lysimeter field to reveal the temporal changes of N leaching losses below 2-m depth from this land system as well as the effects of N fertilizer application rates on N leaching. Four N rates (0, 180, 260, and 360 kg N ha(-1) as urea) were applied in the study area. Seasonal leachate volumes were 87 and 72 mm in the first and second maize season, respectively, and 13 and 4 mm during the winter wheat and maize season in the third rotational year, respectively. The average seasonal flow-weighted NO(3)-N concentrations in leachate for the four N fertilizer application rates ranged from 8.1 to 103.7 mg N l(-1), and seasonal flow-weighted dissolved organic nitrogen (DON) concentrations in leachate varied from 0.8 to 6.0 mg N l(-1). Total amounts of NO(3)-N leaching lost throughout the 3 years were in the range of 14.6 to 177.8 kg ha(-1) for the four N application rates, corresponding to N leaching losses in the range of 4.0-7.6% of the fertilizers applied. DON losses throughout the 3 years were 1.4, 2.1, 3.6, and 6.3 kg N ha(-1) for the four corresponding fertilization rates. The application rate of 180 kg N ha(-1) was recommended based on the balance between reducing N leaching and maintaining crop yields. The results indicated that there is a potential risk of N leaching during the winter wheat season, and over-fertilization of chemical N can result in substantial N leaching losses by high-intensity rainfalls in summer

Irrigation scheduling for cotton cultivation

Crops need water for evaporation (E) and transpiration (T), known as evapotranspiration (ET). However, too much water is not good for various crops. Crop water need depends on growth stage, climate, and crop type. Approximately 40% cotton is produced under irrigated conditions. Water for irrigation is becoming limited in many cotton-growing regions and competition for water is increasing speedily in areas normally having plentiful water resources. So, many cotton producers and the associations representing cotton producers are interested in the scheduling of irrigation strategies that increase water use efficiency (WUE). Responses of cotton under water stress depend on stage of growth, duration, time, and extent of stress. Cotton is a drought-tolerant crop; however, it performs better under optimum water conditions. The water requirement of cotton is 27-51 acre inches depending upon growing duration and prevailing climatic conditions. However, it is essential to apply uniform and accurate amount of water at proper time for maximum cotton yield. Normally, cotton uses less water from sowing to emergence. However, pre-sowing irrigation is mandatory to ensure good cotton seed germination. After germination, crop water demand increases from 0.2 to 0.44 in. per day. Lack of water can reduce plant growth, the number of fruiting sites because of shedding of young bolls, and boll size, consequently resulting in loss of yield potential. There are various irrigation scheduling tools, the main purpose of which is to supply water according to the need of the plant. Water balance method, estimating crop water use, and sensor-based scheduling are a few important tools to maintain irrigation scheduling in cotton