176 PLANT PRODUCTS 



encourage surface roots. The influence of the different 

 manures upon the composition of pasture is very marked 

 indeed. In the experiments at Tree Field, Cockle Park, 

 the addition of phosphatic manures not merely increased the 

 amount of grazing, but also increased the feeding value of 

 the grass that was cut from this pasture. The phosphoric 

 acid was more than doubled in amount, the potash increased 

 about 80 per cent., and the nitrogen increased about the 

 same figure, although no nitrogen or potash was applied. 

 The addition of lime produced comparatively little effect, 

 either in the quality or quantity of the herbage, since this 

 was not the material which was most urgently needed. This 

 large increase in the percentage composition of nitrogen and 

 potash as well as phosphoric acid has been brought about by 

 the application of a phosphatic manure. As explained 

 before, in the case of the hay crop more general manurial 

 treatment is desirable, and the results are, therefore, not 

 so striking, but the use of a manure like sulphate of ammonia 

 does not increase the albuminoids in the hay to any appreci- 

 able extent. In the case of the swede turnip crop, manures 

 containing little phosphates produce, on the whole, swedes 

 which contain less sugar than those manures which are 

 deficient in potash and nitrogen. 



Food and Growth. — When very wet periods intervene 

 there is a liability to considerable loss of nitrogen in the 

 form of nitrates, and under these circumstances only a 

 portion of the nitrogen supplied will go into the crop. 

 Plants having, therefore, a short period of growth are much 

 more likely to miss a large fraction of the fertilizing materials 

 than those very slow growing crops that only reach maturity 

 after many months of growth. In tropical climates, where the 

 growth of the plant and the chemical changes in the soil are 

 both very rapid, the manure has a greater fertilizing efficiency 

 than in cold climates. Where soils are excessively cold, or 

 excessively hot, full utilization of the fertilizers is impossible. 

 Water and manure must be considered together. To some 

 extent, a large supply of moisture, either from the sky or 

 by means of irrigation, will make up for a deficiency in the 



