TOP-DRESSING METHODS

New Zealand Herald, Volume LXIX, Issue 21253, 5 August 1932, Page 5

TOP-DRESSING METHODS

APPLYING SUPERPHOSPHATE FREQUENT LIGHT DRESSINGS EXPERIMENTS AT MARTON ■ ■ Definite evidence of the valuo of frequent light applications of superphosphate, in preference to heavy annual dressings, has been obtained as a result of the experiments at Marton concerning the effect of different frequencies of application on yield and tho chemical composition of pasture herbage. The principal object of tho investigation was to determine the influence on total production, and on production at various times of the year, of applyihg superphosphate in heavy dressings at long intervals, compared with lighter, but more frequent dressings. Varying treatments, arranged so that each plot, with one exception, would receive Bcwt. of superphosphate over a period of two years, were applied. No. 1 plot received no phosphate, No. 2 Bcwt. of superphosphate (44-46 per cent tricalcic) once in the two years, No. 3 4cwt. once a .year, No. 4 2cwt. twice a year, No. 5, 1 l-3cwt. throe times a year, No. 6 4cwt. at the commencement of the experiment, followed by 1 l-3cwt. three times a year, tho actual application received in the last case being 10 2-3cwt. over the two years. All plots received lime at the commencement and a dressing of potash each year to ensure that lack of these would not act as limiting factors. A good ryegrass-white clover pasture was utilised in the trials. First Year's Results According to Mr. A. W. Hutson, crop experimentalist,, and Mr. B. W. Doak, analytical chemist, of the Plant Research Station, who discuss tho results in the Journal of Agriculture, the heavy applications made at the commencement on plots 2, 3 and 6 gave the best results in the first year. Over the two-year period, however, the application made twice and three times a year (plots 4 and 5) gave much better results than the Bcwt. applied at the beginning (plot 2) and slightly better results than plot 3, which received one application of 4cwt. per annum. Plot '6, which received more super than any of tho others, actually gave the highost production. Treatments receiving two or throe applications a year gave a better production during the low-production period covered by the lata summer, autumn and winter. In •addition to this, the applications made two or three times a year gave a greater proportion of their production during the lowproduction period than did the control plot or plots 2 and 3. Tho result of this was that the difference, as a percentage of the total production, between the highest an<J lowest production periods, was reduced. In the second season the highestyielding treatment produced 95061b. _of dry matter per acre, which is about equal to a 34-ton per acre crop of swedes. Sixteen months from the commencement of the trial, plots 4 and 5, which had then received 6cwt. and 5 l-3cwt. of super respectively, had produced elightly more total herbage than plot 2, which had -received Bcwt. in one dressing. .'£?■ Analysis ol Herbage During the whole of the second year the herbage from plots 1, 2, 3 and 6 was submitted to chemical The application three times a year in plot 6 kept the phosphate, limo and protein content of the herbage at a more uniform level throughout the year than did less frequent applications. The beneficial effect in keeping the phosphato content up to a higher level during dry weather, when herbage is normally low in phosphate, is undoubtedly an important feature of summer dressings. All phosphate treatments increased the phosphate, limo and protein content of tho herbage over that of the control plot for tho year as a whole. The experiment is being continued and it is considered that future results should be more informative than those for tho first two years. The heavy applications made at tho commencement had an initial advantage over those applied in smaller dressings more frequently. At the end of the two years, however, the more frequent applications had a decidedly favourable balanco of phosphate, as was indicated by their higher production at this time. They should show a greater superiority, at least over the dressing made once in two years, than was the case in the first twoyear period.