VIII. APPLICATION OF MANUBES 163 



Repeated comparisons made at Woburn, 1 however, indicate that 

 no advantage is gained by growing and ploughing in a leguminous crop 

 as against a non-leguminous one. The green crops tried were tares 

 and mustard, and the subsequent yields of wheat were in favour of the 

 mustard. 



It was proved, however, that the growth of tares gave a greater 

 gain of nitrogen to the soil than that of mustard, and the results ob- 

 tained are difficult to explain, as general experience, as well as theory, 

 agree in indicating a decided advantage of leguminosce over other crops 

 for green manuring. 



Various crops may be used for green manuring. In England, 

 mustard, rape, tares, barley and rye are often employed, while in 

 Germany, lupines have been successfully used and have converted large 

 tracts of comparatively worthless sand into fertile land. 



It must be remembered, however, that green manuring under the 

 most favourable conditions can only improve the physical condition of 

 the soil and enrich it in organic matter and nitrogen, but cannot effect 

 any increase in its inorganic constituents. The stores of phosphates, 

 potash and lime in the soil are not augmented, though these constitu- 

 ents are probably rendered more available. Its utility in preventing 

 losses by drainage, however, is undoubted. 



In warm climates, many leguminous crops are well suited for the 

 purpose. Cow-peas, Vigna catjang, velvet beans, Mucuna utilis, and 

 the soy bean, Glycine hispida, have all proved successful in this 

 capacity. 



Sometimes the catch crops are eaten off in the early winter by 

 stock, penned on the ground, before the land is ploughed. In this 

 case, the benefit to the soil, especially as regards increasing its store 

 of bulky organic matter, is considerably less than when the whole 

 crop is ploughed in, though the same saving of loss of nitrates in the 

 drainage is effected. 



The nitrogen in the portion of the crop eaten by the animals is 

 partially returned to the land in their excrement, and is in a form 

 (chiefly urea) which quickly becomes available again. 



In cases of soils extremely poor in organic matter, the plan of 

 growing a crop with the aid of manures and then ploughing it in, is 

 sometimes resorted to and results in rapidly enriching and improving 

 the soil. 



CONCENTRATED MANURES. In the case of artificial manures, 

 which are costly, i.e., of high price per ton, very different dressings aie 

 required. It will be convenient, perhaps, to deal with the commoner 

 special manures separately, but a few remarks applicable to them in 

 general may first be made. Since uniformity of distribution of a 

 manure in the soil is almost invariably desirable, all artificial manures 

 should be finely ground and, whenever possible, dry. As the quantity 

 to be applied per acre is often only about 1 cwt. it is advisable to 

 mix the manure with some diluent before application. Dry, sandy 



1 Jour. Roy. Agric. Soc., 1906, 299 ; 1905, 198 ; 1903, 335. 



