Wednesday, November 15, 2006 - 12:45 PM

A Water Use Based System for Deriving Nitrogen Recommendations in the Canadian Prairies.

Rigas Karamanos, Western Co-Op Fertilizers Ltd, Box 2500, 11111 SE Barlow Trail, Calgary, AB T2P 2N1, Canada and Harold Dickey, Retired, 127 Santa Fe Drive, Baldwin, SK 66006.

The maximum genetic potential yield of any given crop under any given set of climatic conditions and with no nutritional restrictions is determined by solar energy.  The main modifier to this potential in the Canadian prairies is water use.  A series of experiments on summer fallow land and under weed-free conditions were utilized to derive water use efficiency of crops by agro-ecological zone.  A system was thus developed and was originally put in place in 1991.  Target yields are derived based on water use by a crop during the growing season and water use efficiency.  Water use in the system is defined as the sum of soil moisture in a given year as of May 1 and precipitation in May, June and July; the system is equipped with default soil moisture and precipitation data (30 year averages organized as 25, 50 and 75% probabilities), but actual data can be entered at any given time to allow for refinement of target yield predictions.  Water use efficiency for each crop is defined as the seed yield per unit of water and is a function of precipitation.  An evaporation factor for each agro-ecological zone is also included in deriving target yields.  Once a target yield is established, a nitrogen (N) recommendation is derived based on a N balance between major inputs , i.e., uptake by a crop , fixation (where applicable),  fertilizer, plant residues and mineralization and major outputs, i.e., crop removal, leaching loss, denitrification loss and immobilization.  Mathematical functions directly relating an input or output to water use have been developed for mineralization, leaching, denitrification and immobilization.  The original system was “truthed” using a series of independent experiments that included both soil moisture and precipitation data.  The system is updated constantly as relevant research is being generated.