Evaluation of fertilizer efficiency corresponding to nutrient variations in cow slurry applied to timothy grassland

In order to elucidate the differences in chemical constituent of cow slurry on dry matter production of timothy (Phleum pratense L.) grassland in a field experiment, 18 different types of slurries collected from dairy farms in Konsen district, Hokkaido, were applied to grassland surfaces. The range of dry matter, total nitrogen (N), and ammonium N content in the cow slurry was 53 to 116, 2.9 to 6.1, and 0.9 to 3.3 g kg(-1), respectively, in fresh weights. The application rate of the cow slurry was 50 Mg ha(-1). 1. In the first year, grass yield on cow slurry-treated plots was higher than that on non-slurry treated plots. Although the application rate of the cow slurry was the same, great differences were found in the grass yield among the slurry applications. However, in the following year, small amounts of increases in the grass yield on cow slurry-treated plots compared with that on non-slurry-treated plots were found. 2. The form of N in the applied cow slurry which showed close relations between the uptake of N by the timothy differed between the 1st and 2nd cutting : ammonium N in the applied cow slurry for the 1st cutting and organic N in the applied cow slurry for the 2nd cutting. 3. Great differences were found in the recovery rate of N from the timothy grasslands when cow slurry was applied. It was considered that the fertilizer efficiency of cow slurry applied to timothy grasslands fluctuated depending on the difference between the chemical constituents of cow slurry. 4. It was possible to evaluate the fluctuations in N efficiency of the cow slurry by the ratio of NH4-N/ DM of the cow slurry. 5. From these results, N efficiency of the cow slurry applied to timothy grassland can be evaluated by multiplying the total N content of the cow slurry with the N fertilizer efficiency rate. Other factors, such as quality of the cow slurry, application rate of the cow slurry, time of application of the cow slurry, weather conditions when the cow slurry was applied, and soil conditions of grassland should also be considered.