YIELD AND NUTRIENT MAPPING FOR SITE-SPECIFIC FERTILIZER MANAGEMENT

Soil sampling using a 67 m x 67 m grid was carried out at four locatio ns in conjunction with a precision (site-specific) farming study. The four locations were on undulating to rolling topography, distributed a cross the Brown, Dark Brown and Black soil zones of the plains region of western Canada. A Differential Global Positioning System (DGPS) was used for positioning to map yield, terrain, fertility, and salinity. These attribute maps were used to develop maps for variable rate ferti lization. At each grid-line intersection (node), a composite sample co nsisting of 15 cores was taken within a 5 m radius. Sample depths were 0-15, 15-30, 30-60, and 60-90 cm. The nutrient levels within the area s sampled (15-25 ha) generally had a wide range, high standard deviati on, and strong positive skewness. The large variations found in nutrie nt levels and crop yields support the need for variable rate fertiliza tion. For conventional, constant rate fertilizer application, the stro ng positive skewness of nutrient levels obtained with grid sampling in dicates that systematic errors occur with the current method of compos ite sampling of large fields. When grid sampling results have frequenc y distributions that are positively skewed, fertilizer recommendations based on composite sampling will under fertilize the majority of the field.