HOW TO BUY FERTILIZERS 153 



In mixing these they should be combined in the same propor- 

 tions, but home mixing, as already explained, is, above all, desirable. 



Owing to their cheapness, lime and gypsum are not ordinarily 

 classed with the commercial fertilizers, but they (especially gyp- 

 sum) may exert similar effects to the potash and sulphur fertilizers, 

 and in some ways to the other fertilizers in accordance with the 

 conceptions explained in more detail in the opening paragraphs of 

 this chapter.* 



Time to Apply Commercial Fertilizers. As more and more ex- 

 perimental evidence accumulates regarding the responses of plants 

 to the treatment of soils, on which they are grown, it is becoming 

 increasingly clear that the time of application of certain of the plant 

 food elements, or of other chemicals, is an important consideration. 

 Unfortunately, however, the evidence which we have does not per- 

 mit, as yet, of the formulation and definition of an accurate plan 

 for the time of fertilization of soils. We are obliged, therefore, to 

 fall back for the present upon the best observations which we possess 

 relative to that question. Summarizing such observations under 

 California conditions, it seems proper to say that the months of 

 February and March are the best periods of the year to make fer- 

 tilizer applications. The choice of those months usually secures the 

 requisite supply of moisture in the soil for the solution of the fertil- 

 izers directly or indirectly. Besides the low temperature of the soil 

 at those periods does not permit of the energetic bacterial and fun- 

 gous action which will insure the solution of enough of the soil's 

 own supply of the necessary elements to supply the rapidly feeding 

 roots, hence, the value of the supplementary materials furnished by 

 the fertilizers at that time. 



Generally, the whole fertilizer application may be made at once, 

 though there is no objection to dividing it into two or three appli- 

 cations made three or four weeks apart. There are no results of 

 experimental work to give a more trustworthy guide than this for 

 the present. 



THE PURCHASE AND COST OF COMMERCIAL 

 FERTILIZERS 



Commercial fertilizers are sold exclusively on the basis of their 

 content of three of the essential elements to plant growth, viz., nitro- 

 gen, phosphorus, and potassium. The adoption of this arbitrary 

 standard has something to commend it, but it is, nevertheless, purely 

 arbitrary, as has been made clear above. The production by large 

 syndicates of commercial fertilizers for the market, and especially 

 the mixed fertilizers, is largely responsible for the standards set and 

 the prices adopted. Such prices are usually very high and frequently 

 render the use of fertilizers on some crops unprofitable, even where 

 the fertilizer elements may be needed. It is incumbent upon the pur- 



*Detailed information relative to the use of lime and gypsum on California soils will 

 be found in Circular III of the California Agricultural Experiment Station, which will be 

 sent free to anyone on request. 



