409 



Scientific Agriculture. 



for soils poor in nitrogen, .and are of high value in enriching the soil with this 

 ingredient. There are, however, many other crops which are suitable for the 

 purpose, and frequently used, such as mustard, buckwheat, vetches or tares, &c. 

 These are all rapid growers, and can be grown as catch-crops— that is to say, after 

 the main crop has been harvested and before the succeeding one is sown. For 

 instance, the practice of growing a crop of tares or vetches after the wheat crop 

 has been harvested is very common in Europe, and can be followed successfully 

 here in districts where the autumn rainfall is sufficient. Such a catch-crop occupies 

 the ground only at a time when it would be otherwise unoccupied, and, during 

 its growth, is collecting plant-food from air and soil, Avhich is utilised for manuring 

 the succeeding crop. 



The practice of green-manuring is of special value in orchard work, where 

 the green crop can be grown and ploughed under between the rows. 



It must be borne in mind, in all cases, that green-manuring depends for its 

 success upon conditions favourable to the decomposition of the buried green 

 crop, namely, sufficient warmth and moisture. A crop ploughed under in the 

 late autumn or winter will nitrify only slightly, and the same thing applies 

 to ploughing under a crop in a dry season. If the land is quite dry the crop 

 will remain buried without decomposition for a considerable period, and its 

 benefit is lost. 



With regard to the actual amount of material supplied to the land by 

 ploughing under a green crop, some experiments were carried out at the suggestion 

 of Mr. Allen, the Fruit Expert of the Department of Agriculture, New South 

 Wales. 



The produce of one square yard of crops of vetches, at Wagga, Bathurst, and 

 Hawkesbury College, was harvested carefully, tops and roots, and forwarded for 

 analysis. In the case of the Wagga sample, the roots were obtained by washing 

 away the soil, and Mr. McKeown calculates that he succeeded in obtaining 95 per 

 cent, of the total weight of roots in the soil. The produce of tops from one 

 square yard was 41b. 14£ oz., or 10 tons 12 cwt. per acre; and of roots, 1 lb. 

 9 oz. per square yard, or 3 tons 7 cwt. per acre. Analysis showed that the tops 

 contained 87 per cent, water (13 per cent, dry matter), and "506 per cent, nitrogen ; 

 the roots contained 83 per cent, water (17 per cent, dry matter), and '213 per 

 cent, nitrogen. 



When, therefore, this crop is ploughed under, it will add to each acre 

 of the soil, in the shape of dry matter, 1 ton 7 cwt. tops, and 11£ cwts roots 

 including 120 lb. nitrogen from the tops and 16 lb. nitrogen from the roots ; a 

 total of 136 lb. nitrogen per acre. Assuming that conditions are favourable for 

 nitrification, this will be equivalent to a dressing of nearly 7 cwt. sulphate of 

 ammonia per acre, or over 11 cwt dried blood, an enormous dressing. 



The soil in which the crop was grown was a light loam with about 

 25 per cent. clay. The clay is of a tenacious character, and has a tendency 

 to cake hard on drying. The soil is low in humus containing only about 

 4 per cent of this ingredient. It is fairly rich in potash and satisfactorily 

 supplied with lime, but rather low in nitrogen and phosphates- It is, conse- 

 quently, just the type of soil in which green-manuring should be effective, as 

 the effect of ploughing under the crop will be to break it up and render it 

 more friable, and to supply the deficiencies in humus and nitrogen. Its efficacy 

 is, of course, dependent upon conditions as to rainfall being favourable to its 

 decomposition in the soil. The climate of Wagga is not very favourable to the 

 growth of these crops. 



