Effect of Different Levels of Nitrogen and Potassium Fertilization on Pasture on Mineral Contents in Grass and Grazing Sheep Serum

Abstract

This experiment was carried out to find the effect of different levels of nitrogen and potassium fertilization on pasture on mineral contents in grass and grazing sheep serum. Orchardgrass sward was divided into four blocks, following to the amount of nitrogen and potassium fertilizers: N 100kg and K_2O 100kg (per ha) in block I, N 100kg and K_2O 600kg in block II, N 400kg and K_2O 100kg in block III and N 400kg and K_2O 600kg in block IV, respectively. Each block was sub-divided into four paddocks for rotational grazing. Each paddock was grazed five times for about 7 days in each time by 3 wethers. The dressing amount of each time was one-fifth for yearly amount. The mineral contents in herbage were as follows: on the average throughout the grazing period, 2.68, 2.61, 3.67 and 3.42% for nitrogen, 0.45, 0.44, 0.37 and 0.35% for phospho rus, 3.36, 4.22, 3.82 and 4.53% for potassium, 0.25, 0.23, 0.27 and 0.22% for calcium and 0.19, 0.181 0.22 and 0.19% for magnesium in block I, II, III and IV, respectively. Seasonal change was observed in mineral contents of herbage. In early spring, nitrogen content in herbage was higher, but calcium and magnesium contents were lower than these in the other period. Calcium and magnesium contents in herbage increased with season advanced. Phosphorus content in herbage of block I and II was higher in summer than that in spring, while this content in block III and IV was reversely lower in summer. Seasonal change of potassium content in herbage was not observed clearly. The concentration of urea-nitrogen and minerals in blood serum were as follows: on the average throughout the grazing period, 26.4, 25.4, 31.0 and 29.0mg/dl for urea-nitrogen, 5.40, 5.89, 6.43 and 5.60mg/dl for inorganic phosphorus, 21.9, 21.9, 20.9 and 20.9 mg/ dl for potassium, 10.6, 10.2, 10.3 and 10.3mg/dl for calcium and 2.39, 2.23, 2.29 and 2.29 mg/dl for magnesium in block I, II, III and IV, respectively. The concentration of urea-nitrogen in serum was higher in block III or IV than that in I or II, but the effect of different levels of nitrogen and potassium fertilizers was not observed clearly in those of other elements. The concentration in some of these elements in serum was changed rapidly after pasturing: namely, urea-nitrogen concentration increased on one day after pasturing in all blocks, and calcium, inorganic phosphorus and potassium concentrations depressed on 2 or 3 days after pasturing. But, depression of magnesium concentration in serum after pasturing was not found clearly in this experiment.