EFFECT OF ANNUAL APPLICATIONS OF SULPHATE OF AMMONIA AND SULPHATE OF POTASH ON YIELD OF A PHOSPHATED PASTURE.

New Zealand Journal of Agriculture, Volume 53, Issue 4, 20 October 1936, Page 219

EFFECT OF ANNUAL APPLICATIONS OF SULPHATE OF AMMONIA AND SULPHATE OF POTASH ON YIELD OF A PHOSPHATED PASTURE.

H. O. Askew and D. J. Stanton,

Cawthron Institute, Nelson.

In a paper presented last year to the Grassland Association Conference attention was directed to an apparent effect of sulphate of potash, in overcoming the depression in yield that follows the repeated use of sulphate of ammonia and superphosphate on the pastures at the Marsden Research Farm, Stoke, Nelson. It is the purpose of this article to show how this effect has operated during the past four years. Seasonal Production. It will be necessary first to. examine the distribution of the yield of dry matter over the season. In Table I data are presented showing the distribution of yield of dry matter for different treatments during the 1935-36 season.

It is clear from these data that where nitrogen has been used .markedly increased yields were obtained in the first, or earlyspring, period, but that later in the season where nitrogen and phosphate only, were used the yields fall below those for phosphate ■only, so that over the whole season the total yield in the former case may fall below that of the latter. On the other hand, when potash was added to the fertilizer treatment the depression in yield in the second period was not so great as for nitrogen in conjunction with phosphate, and in the third period the yield from the complete treatment was actually the highest of all the treatments. For the whole season the complete treatment of nitrogen, phosphate, and potash gave the highest yield. The increase in yield for the season of the complete treatment over that of nitrogen .and phosphate has' amounted to 340 lb. of dry matter per acre. This increase, together with that of 224 lb. for the third period, was statistically significant. Now compare the yields for the phosphate and the complete treatments. Except for the initial period when the nitrogen was ■exerting its full effect, the complete treatment did not show a very marked advantage in yield over the phosphate treatment, the total increase of the second and third periods for the complete treatment being only 70 lb. of dry matter above the yield of the phosphate treatment. It must be pointed out, however, that the use of potash has very largely overcome the depression in yield' shown in the second period under nitrogen treatment, and in the third period the ■complete ' treatment shows a statistically significant increase over both the phosphate and the phosphate-plus-nitrogen treatment. It appears therefore that on this Nelson pasture in the presence of potash the depressing, effect of annual applications of sulphate of ammonia on yield was not so marked, and that potash acted in the direction of making the distribution of production on the completely fertilized area approach more closely to that on which phosphate only has been used. This is important in Nelson, because any reduction in pasture-production during the summer period has a serious effect in limiting the carrying-capacity of a farm.

Examination of the yield data for the same three fertilizer treatments shown in Table I over the past four seasons yields some interesting results. The requisite data are given in Table IE It is clear from these data that the complete fertilizer has given the best result in terms of pounds of dry matter per acre in all four seasons. If allowance is made for the exceptionally dry season of 1933-34, the increases in yield shown in favour of the complete treatment were appreciable, and almost in proportion to the total yield of the corresponding season. Moreover, except in 1933-34, these increases were statistically significant. But when a comparison is' made of the yields from treatments A and B, it is seen that, except in the first season, decreases in yield, not statistically significant, however, have followed the annual use of sulphate of ammonia in conjunction with 3 cwt. superphosphate. The use of sulphate of ammonia usually on this pasture does not appear to be advisable, even though annual phosphate applications are also provided.

To obtain the direct effect of the potash application, the differences in yield of treatments B and C must be taken. These are given below in Table 111 :

Summary of Results. These data indicate that potash when used in conjunction with a manurial programme involving the annual use of superphosphate and sulphate of ammonia was having an increasing beneficial effect on the pasture, as the increments have increased to a much greater extent than would be expected from the annual totals. As these increases have been obtained in seasons of varying moisture conditions, it would appear that potash has maintained the pasture in a better state of productivity than would have been the case if nitrogen and phosphate only were used for top-dressing purposes. Not only has the use of potash enabled the depressing effect of sulphate of ammonia to be overcome, but, as indicated in Table 11, the complete treatment has given materially improved yields over the use of superphosphate alone. This does not mean, however, that the use of a complete fertilizer will be profitable. Indeed, the data indicate that, compared with the cost of 3 cwt. of superphosphate per acre, the complete treatment cannot be payable. But the data show the value of potash applications in promoting an optimum yield of pasture in those cases where sulphate of ammonia is used frequently in addition to a top-dressing of superphosphate. Summary. The use of a complete fertilizer gave the highest yield of pasture in mowing-trials at the Marsden Research Farm, Stoke, Nelson.

The use of sulphate of potash at the rate of | cwt. per acre overcame the depression in yield following the annual use of sulphate of ammonia on a phosphated pasture. Where nitrogen is used annually in conjunction with phosphate, application of potash appears to be necessary if optimum yields are to be obtained.

Note.—Treatment A : 3 cwt. superphosphate per acre ; Treatment B : As A plus cwt. sulphate of ammonia ; Treatment C : As B plus | cwt. sulphate of potash.

Period. Yield in Pounds of Dry Matter per Acre. 3 cwt. Superphosphate. 3 cwt. Superphosphate, i| cwt. Sulphate of Ammonia. 3 cwt. Superphosphate, i| cwt. Sulphate of Ammonia, J cwt. Sulphate of Potash. 24/7/35 to 30/9/35 •• 686 872 907 1/10/35 to 23/12/35 . . . 2,628 2,467 ' 2,548 24/ I2 /35 to 20/5/36 . . 2,527 2,453 2,677 Total . . 5.841 5,792 6,132

Table I.

Season. Treatment A. Treatment B. Difference B-A. Treatment C. Difference C-A. 1932-33 • • 3,869 4,006 137 4,077 208 1933-34 • • 3,192 3>ii9 73* 3,265 73 1934-35 • • 4,830 •4,828 2* 5,052 222 1935-36 • • 5,841 5,792 49* 6,132 291. * Decrease in yield.

Table II. —Yield in Pounds of Dry Matter per Acre.

Season. Pounds of Dry Matter per Acre: Increase following Use of £ cwt. Sulphate of Potash per Acre. 1932-33 71 1933-34 • 146 1934-35 224 1935-36 34°

Table III.