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Implications of spatio-temporal variations in crop growth and nutrient supply for sustainable farm management

M. T. F. Wong

CSIRO Land and Water
Private Bag No. 5, Wembley WA 6913 Australia
Phone number +61 -8 9333 6299, Fax number +61 -8 9387 8991
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Fluctuations in soil nutrient concentration, especially nitrate occur as a result of seasonal variations in temperature, rainfall and plant growth. Seasonal nitrate concentration commonly fluctuates between 1 to 100 mg N / kg soil in the 0-10 cm layer. This fluctuation is driven by biogeochemical processes controlling the release of nitrate from soil and fertilisers, crop uptake and leaching and gaseous losses. The implications of these seasonal trends are well understood and have led to the development of management strategies aimed at synchronising the supply of nutrient from soil and fertilisers with the crop demand. The ensuing recommendations include the timing of fertiliser application, planting time and the farming system design required to ensure this synchronisation.

At paddock scale, both nutrient supply and crop demand vary spatially due to (1) edaphic factors especially the quantity and quality of soil organic matter and clay content which influence nutrient release (2) soil texture and drainage which influence leaching and gaseous losses and plant available water and (3) nutrient removal by crop. The implications of large spatial variability offer opportunities for the next quantum leap in farm productivity and sustainability improvement by identifying areas that can be managed more efficiently to produce better crops and areas that would chronically perform poorly and leak water and nutrients. Such areas would be candidates for reassignment to perennial plantations that would use more water and alleviate salinity problems. Management tools are being developed to capitalise on those opportunities and to redress our biased focus on temporal variability.

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