Mar. 2, 1920.] Ayricultural Gazette of N.S.W. 179^ 



the soil, though it would increase the organic matter anil to some extent the 

 easily available nitrogen. At Rothanisted it was found that in land under- 

 legumes for twenty years the gain of nitrogen per acre was 6 cwt. This is. 

 equal to an average gain of 33 lb. nitrogen ppi year, equivalent to an annual 

 dressing of about 2 ewt. nitrate of soda or sulphate of ammonia per acre 

 (which would be at a cost of about 40s.), 



Another question of interest is how much nitrogen is added to the soil 

 from a leguminous crop which is grown for seed ? An average crop of cow- 

 peas will contain 120 lb. nitrogen per acre in the whole plant including the 

 roots, and of this amount about 60 lb. will be contained in tke seed. As- 

 two-thirds of the total nitiogen is obtained from the air, 80 lb. will therefore 

 be added to the soil from this source and there Avill be a balance of 20 lb., 

 nitrogen per acre to the credit of the soil if the straw is returned to it and 

 only the seed is removed. 



Tlie nitrogen added to the soil per acre by different methods of dealing; 



with an avei'age annual leguminous crop like cowpeas or field peas, uiay be 



therefore roughly expressed as follows : — 



Ploughing in whole crop as green manure ... ... ... ... 801b. 



Feeding off (or soiling and returning animal manure to the soil) ... 60 lb. 



Growing crop for seed (returning straw to soil) ... ... ... 20 1b. 



Removing crop (ploughing in only roots and stubble) ... ... Nil. 



Tt was once thought that legumes obtained practically all the nitrogen for 

 their growth from the atmosphere, but it will be seen that until the nodules 

 form on the roots no nitrogen can be taken from this source. Easily avail- 

 able or soluble fertilisers containing nitrogen may be therefore of value in 

 giving these legumes a good start until the nodules form. There isadanger,^ 

 however, in providing these plants with too much nitrogen in this form, as 

 they will take the available nitrogen from the soil in preference to fixing 

 this element from the air. The object of growing the legumes would thus 

 be lost, as all efforts should be directed towards making thiy transfer from the 

 air to the soil as large as possible for the benefit of following crops like 

 maize, which consume such large quantities of nitrogen. Inoculation of seed 

 or soil with soil containing the organisms (from an old field) is now largely 

 used with success in America to take the place of these nitrogenous fertilisers^ 

 for legumes, to give them the quick start required and to save drawing on the- 

 soil's supply of nitrogen. It has been found that where inoculation in this way 

 has been properly done, the increase of nitrogen in the plant, and con.sequently 

 in the soil, is much greater than would take place without inoculation. 



Another reason why it is better to rely on legumes rather than on soluble 

 fertilisers for adding the bulk of the nitrogen necessary for maize growing is- 

 that in the case of the latter, which are either in the form of soluble nitrates- 

 or which are soon oxidised to that form, up to one-third or more of the 

 nitrogen may be lost through leaching. This loss takes place most in a sandy 

 or sandy loam soil. The nitrogen from legumes ploughed into the soil as green 

 manure is in an organic form and is converted slowly into soluble nitrates, 

 (nitrification) with rising soil temperatures, so that no great loss of this- 

 element can occur in this method of application. 



