PASTURE MANAGEMENT

Otago Daily Times, Issue 22114, 18 November 1933, Page 3

PASTURE MANAGEMENT

- INFLUENCE OF AMMONIUM SULPHATE INTERESTING TRIALS AND RESULTS Within recent years much attention has been given to the intensive manuring of pastures. In some cases a great response has been shown by the. use of ammonium sulphate, and investigations have been made to determine the effect of this fertiliser upon both production and quality of the pasture. It is now known that ammonium sulphate depresses the lime content of a mixed pasture, and several workers have shown that this depression in the lime content is connected with a suppression of clover growth. To determine the effect ammonium sulphate exerts on the .chemical composition of individual species in, mixed patsures, and whether the chahges induced are of a transient or more permanent nature, investigations were carried out by H. 0. Askew for the Cawthron Institute, and the results were published in the New Zealand Journal of Science and Technology. Opportunity was taken of examining the chemical composition of samples of perennial ryegrass and white clover collected at intervals from a mixed pasture which was being used for' production trials under repeated mowing conditions. Two scries of plots were available for sampling, one treated with a base mixture of superphosphate and sulphate of potash, and the other similarly treated plus top-dressing with ammonium sulphate. The samples were in all cases collected by hand-picking from plots (10 replications) kept in shortgrowth stage of 2in to Sin in height. After sampling the areas were cut with a lawn mower. On the nitrogen treated plots sulphate of ammonia was applied at the rate of lewt to the acre on September 4, November 12, and January 21. All samples w'ere collected in oiled-silk bags and protected as far as possible from evaporation and moisture from the herbage, and the percentage of dry matter determined. The percentages of dry matter dn the perennial ryegrass showed distinct variations throughout the season, whether nitrogen was applied or not. There was no significant difference between the nitrogen-treated plots and the control plots except for the first samples collected after the first application of ammonium sulphate, when the treated areas showed about 2 per cent, lower content of dry matter than the controls. A somewhat similar variation occurred with the white clover. Over most of the season its dry matter content was distinctly less than that of the ryegrass, especially during the drier periods of the. year. The distinguishing fact about the white clover was its ability to remain comparatively succulent during dry weather. Its chemical composition was also less affected by dry weather than that of perennial ryegrass. CHEMICAL COMPOSITION.

The highest percentages of the various chemical constituents with the exception of lime were found in the early spring

period. After the middle of October there were rapid decreases in the percentages of soluble ash, phosphoric acid, potash, and nitrogen. From then onwards steady decreases were shown until the February period, when another sudden decrease in the percentages of these constituents was shown: this corresponded to the dry weather experienced at that time of the year.’ Drying winds in November caused decreased, percentages of nitrogen, phosphoric acid, and soluble asb for the herbage grown in the second half of that month. After rains in February and in April the percentages of these mineral constituents increased very appreciably. . The percentage of lime in the spring fell to the low figure of 0.35 per cent., thereafter increasing to a maximum value of 0.80 per cent, for the February neriod. Throughout the year the percentage of this constituent was low. In the spring the percentage of nitrogen in the control plots reached the high value of 4.50 per cent., but in the driest period of the year this percentage fell to only 2.37 per cent., or about half the spring value. Indeed, after October, the percentage of nitrogen was low throughout the season. It appears that the soluble ash is depressed in drought, with a corresponding increase in the percentage of insoluble ash or silica. The sulphur figures show that most of the sulphur in perennial ryegrass is in the inorganic form. The application of ammonium sulphate has resulted in changes in the chemical composition of the ryegrass. It would appear that the ammonium sulphate dressings had little effect on the lime content during most of the season. Later in the season the nitrogen-treated plots showed distinctly lower percentages than the control samples, but 'at no time were the reductions very great. Other investigators have found depressions in the lime content after nitrogenous manuring of 5 to 10 per cent, of the value of the controls. There is a tendency for the phosphoric acid content of the grass to fall with the use of ammonium sulphate, except in the early spring period. Ammonium sulphate has helped to maintain better the potash content of the grass. In the first sample after top-dress-ing in the spring the potash content on the nitrogen plots was 3.97 per cent., compared with 3.57 per cent, on tl\e control. After the November application the nitrogen plot showed 3.21 per cent., w'hile the control had fallen as low ns 2,55 per cent. In fact, right through the season the nitrogen plots show the higher percentages of potash. The very early growth on the control plots, sampled before the first application of ammonium sulphate, contained the greatest percentage of nitrogen, 4,50 per cent. _ The first sample taken after the application of ammonium sulphate shows 4.26 per cent, of nitrogen ns compared with the control figure'of 3.57 per cent. The soluble ash content during good growing periods has been distinctly increased by the_ nitrogenous fertiliser; in summer periods both treated and untreated samples tend towards the same percentages. In the autumn the soluble ash content of the ■rtreated samples was again jbigher than for the controls. white Clover. White clover, as compared with ryegrass, is distinguished by its high lime and nitrogen content and by its low, insoluble ash. The effect of sulphate of ammonia on the chemical composition of white clover was much less marked than for perennial ryegrass. In the case of the lime contents there was a tendency for the nitrogen-treated plots t 6 fall slightly below the controls, but in the first spring period immediately following the application of ammonium sulphate the higher value was obtained on the nitrogen-treated plots. The figures for phosphoric acid were very similar, but in the early spring as found for lime the higher values were obtained on the nitrogen-treated plots. The potash percentages showed very jittle effect of the nitrogenous manure in the case of white clover. In the early spring period slightly higher values were found on the nitrogen plots. The nitrogen figures showed a slight increase for the ammonium sulphate plots after each application of the fertiliser, but the effect was of short duration. The soluble ash content of the samples from the treated plots tended to exceed that of the controls only in the samples immediately following the application of the nitrogenous fertiliser. Over most of the season slightly lower values to the extent of about 0.2 per cent. *are found. Small increases in both total and inorganic sulphur have resulted from the use of ammonium sulphate. In the cases of the insoluble ash, soda, chlorine, and iron contents no definite statement can be made as to the effect of ammonium sulphate. In conclusion it is noted that ammonium .sulphate increases the potash, soluble ash, and total and inorganic sulphur contents of ryegrass, particularly in the periods immediately following the application of the fertiliser. Lime, phosphoric acid, and silica tend to be lower on the nitrogen plots than on the controls. With white clover the lime, phosphoric acid, nitrogen, and soluble ash contents are increased after each application of ammonium sulphate; later they all tend to fall to lower values than those for the control plots. Potash tends to be lower on the nitrogen-treated clover than on the controls. The depression in the lime content of perennial ryegrass and of white clover due to _ manuring with ammonium sulphate is insufficient to account for the large decreases in the lime content of mixed pastures following the use of nitrogenous fertilisers. The nitrogen to phosphoric acid ratio tends to fall during the summer periods in the case of perennial ryegrass, but tends to increase' in the case of white clover. This ratio for. white clover is almost double that of ryegrass.