The response of permanent grassland to nitrogen and the efficiency of its recovery

Extract

Experiments over six years on the use of different kinds and amounts of nitrogenous fertilizers on small plots of permanent pasture are described and summarized.

Up to a level of 4·5 cwt. sulphate of ammonia per acre applied in February there was a proportionate response in dry matter production in April. Omitting the single year when scorching occurred, the average increase per cwt. of sulphate of ammonia applied was 2·3 cwt. dry matter with an additional 0·85 cwt. in the second (May) cut. The average recovery of the nitrogen applied in February was 35·9% in April, and 8·6% in May.

With nitrogen applied in June the response in dry matter production in July and September–October was similar, but the recovery varied widely with the varying effect of nitrogen on clover production. With heavy depression of clover, percentage recovery was low or negative.

On plots not receiving nitrogen the dry matter production for the whole year was at the rate of 1·92 cwt. per inch of rain reckoned on the harvest year (Oct.–Sept.). The largest variation from this was only 0·1 cwt.

For the whole year the response to nitrogen was greatest in the years of lowest rainfall.

The nitrogen applied in February considerably increased the protein in the “grasses” at the first cut, and to a small extent in the second cut. For the third and fourth cut it is suggested that the protein differences are correlated with differences in amounts of clover.

For the first cut of the year “clovers” also show a much higher protein content on the nitrogen plots.