Published online by Cambridge University Press: 27 March 2009
The comparative effects of very heavy dressings of ammonium sulphate and urea on the growth of established plants of white clover (S100) have been studied in pot culture. Five applications each of 263 kg N/ha were applied over 9 months in 3 different ways (i) direct contact of the fertilizers with the leaves, (ii) only with the stolons or surface roots or (iii) applied 12·5 cm below the soil surface.
The ammonium sulphate broadcast over the leaves reduced the growth of the clover whilst urea under the same conditions caused temporary damage with very little reduction in dry weight compared with the control. When the ammonium sulphate was applied to the soil surface or 12·5 cm below, there was appreciable reduction in dry weight but less than when the fertilizer was in contact with the leaves. Under the same conditions, urea did not reduce growth.
The pH of the soil fell to about 4·6 with ammonium sulphate (control 6·1) but only slightly with urea.
Root development was not affected by urea but greatly reduced with ammonium sulphate. With both fertilizers the root nodules were very pale in colour and few in number compared with the control.
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