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Monday, November 2, 2009
Convention Center, Exhibit Hall BC, Second Floor
Abstract:
In the highly developed regions of China it is well documented that amounts of synthetic nitrogen (N) fertilizer used by farmers often exceed requirements for maximum crop yield. This causes a range of environmental problems and decreases farmer’s incomes. It is perhaps surprising that N over-use is also prevalent in less developed regions, such as the north-west. For numerous reasons farmers regularly exceed recommendations from government agencies; surveys in Shaanxi Province show that 80% of farmers exceed recommendations for maize and >25% for wheat. In on-farm trials with maize in 2008, a 50% reduction in N fertilizer compared to farmers’ rates (from 250 to 125 kgN/ha) caused, on average, a small increase in yield. Horticultural crops under plastic are given particularly high rates of N fertilizer; experiments with cucumbers were conducted where farmers applied 850 kgN/ha. In one greenhouse 340 kgN/ha gave the same yield; in another it was attained with no N fertilizer. In situations of long-term N over-use, residual nitrate from previous fertilizer and mineralization from manure accumulates in soil. This, plus nitrate in irrigation water, may provide the entire N requirement of one or more subsequent crops but more N will gradually be required as the residues from over-use are exhausted. Thus formulating advice in these situations is complex and dynamic.
In a UK-China collaborative project, three approaches are being developed for providing farmers and advisers with information on which to base more rational decisions on N fertilzer rates:
(1) Constructing nitrogen budgets by estimating N inputs from all sources especially soil, manure, irrigation water and atmospheric deposition. Currently N from past manure applications and from irrigation are generally ignored.
(2) A simple method for measuring nitrate in soil under field conditions.
(3) Economic assessment to show farmers that they are waste money by over-applying N.
In a UK-China collaborative project, three approaches are being developed for providing farmers and advisers with information on which to base more rational decisions on N fertilzer rates:
(1) Constructing nitrogen budgets by estimating N inputs from all sources especially soil, manure, irrigation water and atmospheric deposition. Currently N from past manure applications and from irrigation are generally ignored.
(2) A simple method for measuring nitrate in soil under field conditions.
(3) Economic assessment to show farmers that they are waste money by over-applying N.