Urine patches indicate yield potential of cocksfoot

PERI P.L; LUCAS R.J.; MOOT D.J.

New Zealand

Congreso; New Zealand Grassland Association Congress; 2002

New Zealand Grassland Association

The main yield changes in cocksfoot DM production due to nitrogen (N) from synthetic urine (300 kg N/ha), water stress and regrowth duration in exclosure areas and the dynamics of urine patches (production and crude protein) during all seasons from sheep urine returns in the main grazed area (28 day rotation with 21¡¾1 days regrowth) were measured from September 1999 to May 2001 at Lincoln University Experiment (Canterbury). To explain the responses of cocksfoot to urine patches in different environmental conditions a leaf photosynthesis model was used. The application of N (1500 kg N/ha/yr) and five harvests (four 60-days and one 110-days regrowth periods) increased the annual yield by ~14 t DM/ha/yr and irrigation increased annual yield by ~4.4 t DM/ha/yr. The potential growth was recorded for the Canterbury sub-humid temperate environment in irrigated and N fertilised pastures (total annual yield of 28.6 t DM/ha/yr and maximum growth rate of 158 kg DM/ha/d). In the grazed plots, the mean area covered by visually obvious urine patches varied from 25 to 32% with a mean diameter of 0.22 m. The rate of N applied per hectare for an individual urine patch varied from 173 to 448 kg N/ha depending on the season. The mean DM production of individual new urine patches was 60% higher than non-urine controls which represented an increase in DM production over the total area of 35%. On average the CP% of the total cocksfoot pasture increased by 15% with sheep urine returns. The relative difference in DM production between urine and non-urine patches and the duration of the effect of urine patches (when could not be distinguished from controls) on pasture production varied over seasons with temperature, soil water content and urine strength. The maximum difference in DM production between urine patches and controls was 380 kg DM/ha during summer and winter grazing periods, and 1970 kg DM/ha during spring. The maximum difference in CP% between urine patches and controls was 4.3 units during summer, 7.8 units during winter and 8.3 units during spring. The duration of the effect of urine on DM production and CP% was 56, 112 and 84 days in summer, winter and spring, respectively. Net leaf photosynthesis varied over seasons with a range between 23.5 to 4.5 ¥ìmol CO2 m-2 s-1. The leaf photosynthesis analysis indicated that pasture production and duration of urine patches during summer was limited mainly by soil water stress (mean soil volumetric water content in the top 500 mm < 20%) and limited N (< 3 %N). During winter low temperatures (mean daily air temperatures < 9 ¨¬C) limited DM production but determined the longer duration of the effect of urine patches compared with controls.