| Abstrakt: |
Over 13 years, 12 cwt/ac of ground rock phosphate (29% P2O5) were applied to an old grass sward, either completely in the first year or in equal amounts in each of the first 4 years; alternatively, 18 cwt superphosphate/ac were applied either in 3 equal amounts at 4-yearly intervals, or in equal amounts annually over the first 12 years. In the first year, the larger dressing of superphosphate gave the best response, measured as fresh herbage cut in mid-July each year, but during the next 7 years all methods of application gave similar yields. Dressings of rock phosphate gave progressively poorer response after 7 years and plots so treated were not significantly better than the control in the final year. At the end of the experiment, plots receiving annual applications of superphosphate yielded most herbage and those which had received superphosphate at 4-yearly intervals still showed a significant response. Phosphate in rock phosphate applied as a single dressing was two-thirds as effective over an 8-year period as that in superphosphate applied annually. The small difference over 12 years in phosphate uptake from 3 dressings of super-phosphate compared with its equivalent in annual applications suggested that little phosphate fixation was taking place. The fact that a single dressing of rock phosphate was able to maintain yields and phosphate uptake close to that obtained from annual applications over 7 years supports this and suggests that the failure to utilize one third of the phosphate in rock phosphate was mostly due to initial insolubility. [ABSTRACT FROM AUTHOR] |
