Economic analysis of agricultural nutrient management practices in the South Tobacco Creek Watershed in Manitoba, Canada

Abstract

Beneficial management practices (BMPs), including nutrient management plans and reduced tillage, have been assessed at a subwatershed and watershed level to examine their impacts on nutrient export, economic opportunity cost, and producer incomes. In assessing nutrient effects on crop production, a crop-specific yield function was estimated. The linear and quadratic nitrogen (N) fertilizer terms were found to have correct signs, with a positive linear relationship, and were significant for major crops grown in the South Tobacco Creek (STC) Watershed. Crop response to phosphorus (P) occurred only for wheat (Triticum aestivum L.). Nutrient application rates within the STC Watershed were generally within provincial recommended rates; however, data shows an increasing trend in the application of N in wheat, canola (Brassica napus L.), barley (Hordeum vulgare L.), and oat (Avena sativa L.) production over course of the study. Nutrient export parameters at the field scale (4 to 5 ha [10 to 12 ac]), subwatershed scale (210 ha [519 ac]), and watershed scale (7,700 ha [19,000 ac]) were compared to production inputs. At the field scale, in a paired watershed study, N exported was not significantly related to the N applied. The relationships between P exported and P applied and conservation tillage management practices were statistically significant. At a larger subwatershed, the export of P from the subwatershed was significantly influenced by the volume of flow of water runoff and previous year P application. The export of N was only influenced by volume of flow but not by N application. For the STC Watershed, applied N did not affect N export. Assessment of P export found that the conversion to conservation tillage practices increased the P export. The opportunity value of the lost nutrients for the 210 ha (519 ac) subwatershed averaged about C$5.50 ha⁻¹ y⁻¹ (C$2.23 ac⁻¹ yr⁻¹), while on the paired subwatershed, the average loss was C$4.50 ha⁻¹ y⁻¹ (C$1.82 ac⁻¹ yr⁻¹) on a conventionally managed field and C$2.75 ha⁻¹ y⁻¹ (C$1.11 ac⁻¹ yr⁻¹) on a field under reduced tillage. For the entire STC Watershed, the export of nutrients represented a loss of opportunity of C$6.80 ha⁻¹ y⁻¹ (C$2.75 ac⁻¹ yr⁻¹) or about 7% of annual fertilizer cost. Assessment of STC manure-applied data on an annual basis shows that the hauling and application of hog manure from 1998 to 2006 was generally more expensive than the nutrient value of the manure; however, in recent years, due to the increase in the value of commercial nutrients, the nutrient value of hog manure exceeds the cost.