Effects of organic and inorganic nitrogen fertilizer on maize (Zea mays L.) nitrogen uptake and nitrate leaching measured in field lysimeters
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Maize (Zea mays L.) production in the smallholder farming areas of Zimbabwe is based on both organic and inorganic nutrient sources. A study was conducted to determine the effect of cattle manure, N fertiliser, and their combinations on nitrate concentration in leachate leaving the root zone and to establish N fertilisation levels which minimise N leaching. Maize was grown for two seasons (1996/97 and 1997/98) in field lysimeters repacked with a coarse-grained sandy soil. Average leachate volumes over the two seasons were similar between different treatments, and ranged from 388 to 418 mm yr1. Nitrogen fertiliser, especially the high rate (120 kg N ha1), and manure plus N fertiliser combinations resulted in high nitrate leachate concentrations (up to 37 mg N L-1) and nitrate losses (up to 56 kg N ha-1 yr1) which represent both environmental and economic concerns. Nitrate leaching from manure only treatments was relatively low (average less than 23 kg N ha-1 yr1), and plant availability in these treatments tended to be higher in the second season. It was concluded that N leaching at high inorganic N fertiliser rates posed a serious economic and environmental risk when all the fertiliser was applied at planting. It was also concluded that the risk of N leaching from aerobically composted cattle manure was low in the short term.