The spatial coverage of dairy cattle urine patches in an intensively grazed pasture system

Accurate field data on the paddock area affected by cow urine depositions are critical to the estimation and modelling of nitrogen (N) losses and N management in grazed pasture systems. A new technique using survey-grade global positioning system (GPS) technology was developed to precisely measure the paddock spatial area coverage, diversity and distribution of dairy cattle urine patches in grazed paddocks over time. A 4-year study was conducted on the Lincoln University Dairy Farm (LUDF), Canterbury, New Zealand, from 2003 to 2007. Twelve field plots, each 100m(2) in area, were established on typical grazing areas of the farm. All urine and dung deposits within the plots were visually identified, the pasture response area (radius) measured and position marked with survey-grade GPS. The plots were grazed as part of the normal grazing rotation of the farm and urine and dung deposits measured at 12-week intervals. The data were collated using spatial (GIS) software and an assessment of annual urine patch coverage and spatial distribution was made. Grazing intensities ranged from 17645 to 30295 cow grazing h/ha/yr. Mean annual areas of urine patches ranged from 0.34 to 0.40 m(2) (4-year mean 0.37 +/- 0.009m(2)), with small but significant variation between years and seasons. Mean annual urine patch numbers were 6240 +/- 124 patches/ha/yr. The mean proportional area coverage for a single sampling event or season was 0.058 and the mean proportional annual urine patch coverage was 0.232 +/- 0.0071. There was a strong linear relationship between annual cow grazing h/ha and urine patch numbers/ha (R-2=0.69) and also annual urine patch area coverage (R-2=0.77). Within the stocking densities observed in this study, an annual increase of 10 000 cow grazing h/ha increased urine patch numbers by 1800 urine patches/ha/yr and annual urine patch area coverage by 0.07. This study presents new quantitative data on urine patch size, numbers and the spatial coverage of patches on a temporal basis.