Hoof, formalized hoof, formalized casein, leather wastes and dried blood were compared with ammonium sulphate for vegetables in several field experiments which were continued for a number of years. Residual effects were measured in one experiment at Rothamsted.

For crops which had a high requirement for nitrogen, hoof and formalized casein tended to give somewhat lower yields than equivalent ammonium sulphate. Organic nitrogen fertilizers tended to be slightly superior to ammonium sulphate for less responsive crops, and also in experiments where the high rate of ammonium gave lower yields than the medium rate.

Crushed hoof and a formalized casein product gave similar yields of most crops. There were no marked gains from treating hoof with formalin; a coarse (5·7 mm.) sample of formalized casein did not give materially different yields from the ordinary fine (2 mm.) product.

One leather product made by simple roasting was inferior to ammonium sulphate and to hoof. Other leather wastes processed by alkalis did not behave very differently from crushed hoof or from ammonium sulphate. Dried blood was tested in a few experiments, there were no significant differences between yields given by blood and by ammonium sulphate.

In experiments on a light soil, spring cabbages planted in autumn were very sensitive to the time of applying nitrogen fertilizer; there were much larger gains in yield from ammonium sulphate applied half at planting and half in spring, than from either ammonium sulphate or organic nitrogen fertilizers applied wholly at planting.