464 Journal of Agriculture , Victoria. [lo Aug., 1912. 



It is not, of course, expected that all these rotations will succeed. In- 

 deed, some of them must obviously be of little value in the district. The 

 systematic recording of the results of the tests over a period of years, how- 

 ever, should throw considerable light on the subject of crop rotations for 

 wheat in dry districts. The best rotation, of course, will be the one which 

 continues to yield the best financial returns over a period of years, under 

 i.he economic and climatic conditions of the district. 



The restoration of organic matter to the soil can be brought about by 

 grccii manuring, as well as by the feeding down of forage crops. Green 

 manuring, i.e., the ploughing in of green crops such as peas, rye, and 

 vetches, &c., is a much more effective method of restoring organic matter 

 to depleted soils than the feeding down of forage crops. As, however, the 

 feeding value of a green crop is usuallv greater than its manurial value, 

 the general practice is to convert the crop into milk, mutton, or beef, in- 

 stead of ploughing it under. 



Crof rotation mint be supplemented hv Soil Fertilization. — Before 

 leaving the subject of crop rotation there is one important point to bear 

 in mind. No system of crop rotation — however well conceived and carried 

 out — can make up for any shortcomings in either cultivation or manur- 

 ing. There are manv who think that crop rotation is a substitute for 

 manuring, i.e., rotation of crops in itself will maintain the fertility of 

 the soil. Crop rotation alone, witJiout adecjuate manuring, will not in- 

 crease, nor even maintain, the soil's fertilitv. No system of crop rota- 

 tion can add one .single pound of any of those inorganic elements so 

 essential for plant growth. Moreover, unless legumes are grown, or un- 

 less they appear naturally in the pastures, even the nitrogen content will 

 not be maintained. A rational system of crop rotation does increase the 

 organic content of the s;;il. simply because the plant can obtain its organic 

 matter from the carbon dioxide of the atmosphere. We have already seen 

 (P. 201) that 95 ])er cent, of the dry weight of the plant is obtained 

 from the air. and. therefore, when a crop is ploughed in as a green 

 manure, or fed down on the land with stock, the soil is enriched by the 

 organic matter which the plant has secured from the atmosphere. But 

 no scheme of crop rotation, in itself, can add one iota to the inorganic 

 portion of the .soil. Rotation of crops must, therefore, be supplemented 

 bv the application of inorganic manures, if the fertility of the soil is to 

 be maintained or increased. Nothing could be clearer on this funda- 

 mental point than the results obtained during the last seventy years at the 

 Rothamsted Experimental Station. The results obtained in the Agdell 

 field represent the world's best information on this point. In the Agdell 

 field the famous Norfolk four-course rotation — turnips, barley, clover, 

 wheat — has been practised for over se\-enty years. In any one year there 

 were three plots for each crop, ^"iz. : — 



(i) Unmanured. 



(2) Manured regularlv with phosphates. 



(3) Manured regularly with phosphates and nitrogen. 



The following table shows very clearlv that (i) on Section I., where rota- 

 tion was carried on without soil fermentation, the yields in turnips, barley, 

 and wheat have regularlv and continuallv declined. After the first year the 

 turnip yield on this plot never exceeded 3 tons per acre, i.e., they were 

 always grown at a loss. The barlev average dropped from 46.5 to 13.7 

 bushels, whilst the wheat dropped from 29.7 bushels to 18.9. 



