Modelling the surface of a paddock affected by urine and faeces deposition during grazing by dairy cows

摘要

In grazed grassland, urine and faeces, returned by grazing animals and added to the nitrogen (N) from fertilizer, augments the N fluxes and also the risk of N losses (leaching, ammonia volatilization). Urine and faeces deposition by the grazing animalresult in large applications of N to a small area within the paddock. Many agronomic models do not take into account this aspect of grazing systems. As the area affected by urine and faeces at each deposition is reported to be 2 m2, the Moorepark GrassGrowth model (MGGm) describes the N fluxes in a grid basis at a 2 m level. The MGGm assumes that within any given grazing event the localisation of the urine and faeces deposition will be random with overlapping being a possibility. The objective of thispaper is to compare the consequences of a uniform deposition over the paddock versus localize at 2 m2 individual animal depositions, in four different grazing simulations. At 2 m~2 level, the urine and dung deposition induces a huge variation in term ofmineral N available (maximal difference of335 kgofN), grass growth (maximal difference of 5,052 kg of DM) and N leached (maximal difference of 134 kgofN leached). At the paddock level, the uniform simulation has a slightly higher net grass growth and Nuptake compared to the 2 m2 simulation. Finally, within a simulation, the average N leached evaluated between November and April of year 2 are identical between the uniform and a 2 m2 localized applications.