78 Fruitgrowing under Irrigation 



by means of a cover crop will of course depend upon 

 the nature of the crop. A ton of wheaten hay to the 

 acre is considered an average crop on our Australian 

 wheat fields, and it is unlikely that the amount of 

 dry matter added to the land by an average cover 

 crop of peas will exceed this weight, more especially 

 as the whole of the land is not taken up by the crop, 

 as strips near the trees and vines are usually 

 implanted. Where only alternate rows are sown, 

 and these moreover in strips along the middle of 

 the rows, the weight of humus added to the soil will 

 probably not exceed half a ton in weight to the acre. 



The amount of nitrogen that is added to the soil 

 by the ploughing in of green crops varies of course 

 with the kind of plants grown and the weight of the 

 crop. Experiments made at various experimental 

 stations in Australia, United States, and elsewhere 

 seem to indicate that about half per cent, of the 

 total green weight, or roughly three per cent, of the 

 total dry weight of a leguminous crop consists of 

 nitrogen. A leguminous crop which would increase 

 the dry vegetable matter in the soil to the extent of 

 a ton would therefore add to the soil about 66 Ibs. 

 of nitrogen, which would be equal to a nitrate value 

 of 3 cwt. of sulphate of ammonia or 5 cwt. of blood 

 manure. 



Another way of adding to the humus contents of 

 the soil is by bringing farmyard manure, dry veget- 

 able matter, such as straw or grasses, or vegetable 

 mould on to the land. Where this class of matter is 

 available in sufficient quantities, this method of 

 manuring has many advantages over the growing 

 of cover crops in among trees, as in the first place 

 it does not interfere with the cultivation of the 

 orchard, does away with the need of an extra irri- 

 gation in a dry autumn, and allows for the heaviest 

 dressings to be applied on the ' land that is most 



