THE SIMULATION OF ANIMAL RETURNS IN GRASSLAND EXPERIMENTATION

An experiment was carried out on a grass/white-clover sward at North Wyke to evaluate the use of mixtures of inorganic and organic nutrient sources to simulate the nutrient effect of animal excreta, both with and without overall PK fertilizer. Grazing with sheep and the return of excreta from caged sheep both increased herbage yields, as did artificial return treatments. Artificial return treatments giving 75% of the nutrient level returned by excreta gave yields comparable with grazing. The effect of the simulated return treatments was not influenced by PK application. Grazing gave a very different botanical composition to that from the treatments in wbich natural or simulated excreta were returned to cut swards. Mixtures simulating excreta may replace the nutrient effect of the grazing animal, but not its physical effect, in some forms of grassland experimentation. They are not recommended for fertilizer trials.     

THE EFFECT OF FERTILIZER NITROGEN AND WHITE CLOVER ON HERBAGE PRODUCTION

The effect of a range of N rates on herbage production from grass/white-clover and grass swards was investigated in two long-term grazed experiments. The mixed sward yielded more than the grass swards over the range of fertilizer rates tested which were 0–120 lb N/ac (134.5 kg/ha), but the response of the mixed sward to fertilizer N was less than that of tbe grass sward. Tbis was due to the direct and indirect effect of clover, which was considerable with no fertilizer N but decreased witb increasing rates of application. However, clover was not completely suppressed by N at eitber site and contributed to berhage yields at all N rates. Rate and time of N application and the amount of clover in tbe sward affected tbe seasonal distribution of DM yields. The mid-season decline was less marked at bigb- tban at intermediate-levels of N supply.