Results are recorded of experiments over four years to study the effects of various rates of N fertilizer applied early (soon after each cut) and late (1 or 2 weeks before cutting) to grass-clover swards cut repeatedly for conservation.

N fertilizer proved essential for high yields of dry matter and protein per acre. It reduced the amount of clover, but it is clear that clovers are not as productive as grasses adequately manured, and that any N excreted by clovers into the soil is far from enough to enable associated grasses to make full growth.

The amount of N fertilizer applied proved more important than the time of its application. Early N gave higher yields of dry matter but rather lower percentages of crude protein in the herbage than late N dressings.

To increase yields substantially and at the same time to maintain the protein content of the herbage on a par with a grass-clover ley it seems necessary to apply a minimum of 4 cwt. ‘Nitro -Chalk’/acre as an early dressing before each cut. An additional 2 or 3 cwt. ‘Nitro-Chalk’/acre may be applied from one to two weeks before cutting if even higher crude protein values are required.