/AnMtgsAbsts2009.52925 Overcoming Excessive Use of Nitrogen Fertilizer in North-West China: Technical and Behavioural Approaches in a China-UK Project.

Monday, November 2, 2009
Convention Center, Exhibit Hall BC, Second Floor

David Powlson1, Yanan Tong2, Yuelai Lu3, Shulan Zhang2, Gao Pengchang2 and David Norse4, (1)Soil Science Department, Rothamsted Res., Harpenden, Herts., United Kingdom
(2)College of Resources and Environment, Northwest A&F Univ., Yangling, China
(3)Overseas Development Group, Univ. of East Anglia, Norwich, United Kingdom
(4)Department of Geography, Univ. College London, London, United Kingdom
Poster Presentation
  • Soil Organic Matter in the Rothamsted Plots.ppt (8.8 MB)
  • 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.