758 Journal of the Department of Agriculture. 



Care in the use of nitrogenous fertilizer is necessary, because 

 sometimes their free use would defeat the object in view by making 

 it hard or impossible to secure a seed crop. For these reasons mixed 

 fertilizers do not contain high percentages of nitrogen. 



Nitrogen may be bought in three forms: — 



(a) As nitrate. This is always soluble and highly available. 



(6) As an ammonium salt. This is also highly soluble and avail- 

 able and frequently undergoes conversion into nitrate. 



(c) As organic nitrogen. This is of many kinds and varies 

 greatly in value according to the ease with which it undergoes decay 

 and oxidation. Some kinds like those occurring in blood and urine 

 are of high value ; other forms such as those found in leather and 

 horn are of low value because they are so slow to become available. 

 If a highly active concentrated nitrogenous fertilizer is ever used, it 

 ought only to be applied sparingly, with full knowledge of its effects 

 and limitations. 



IV. A fourtli necessary in building up fertility is potash. This 

 is a requirement of all crops, but especially of potatoes and tobacco. 

 Leguminous and root crops also benefit notably by its use, and in the 

 absence of kraal manure it is needed by all crops on sandy soils. 



Potash salts to be useful should be soluble in water. Potash 

 occurs plentifully in some felspars, but it is highly insoluble and of 

 very low fertilizing power. The nitrate is too costly for use as a 

 fertilizer. The carbonate is not suitable owing to its caustic 

 properties, which make it an acive plant poison. The chloride is 

 objectionable owing to the formation of calcium chloride in the soil 

 by double decomposition. The only really useful and available salt 

 of potash, then, is the sulphate. This is very soluble in water, and 

 cannot be used freely because of that property. A reserve of potash 

 cannot be built up, and the farmer must use it as and when it is 

 required by crop and soil and lack of kraal manure. 



It is this danger of too great concentration in a droughty time 

 which limits the amount of potash which may be used with advantage 

 in a mixed fertilizer. When concentrated salts of potash are used 

 alone, they ought to be applied sparingly with full knowledge that 

 the most profitable limit is soon reached and that an overdose will 

 result always in a reduced crop. This has been proved over and over 

 again in many countries, more especially with the potato crop. 



V. Phosphoric oxide is a most important factor in building up 

 fertility. Supplies are obtainable in many forms, and all are useful 

 when ajjplied to soil. It may be accumulated in the soil with advan- 

 tage, because it is not subject to loss by fermentation or volatilization 

 or drainage. Its compounds in the soil are only slig-htly soluble in 

 water, and are, therefore, not dangerous to crops however plentiful 

 they may be. They are not caustic nor usually acid. The typical 

 form in fertilizers is that occurring in bone-dust. When this material 

 is properly prepared and of sufficient fineness, and applied to a soil 

 not wanting in humus or moisture, it is highly available, being readily 

 dissolved by the soil water as lequired. For permanent crops, as 

 lucerne, and fruit trees coarse bone-meal may be used with profit. 

 For crops with a short season of growth, and particulaj-ly on soils 

 deficient in organic matter recourse must be had sometimes to 

 dissolved phosphates. Bone and mineral superphosphates are forms 



