17 



conjunction with phosphoric acid. When even the poor white sand 

 which I saw in the Hundred of Ramsay, Yorke's Peninsula, gave a 

 fair crop of wheat with only 80 Ib. of superphosphate per acre, as 

 applied by Mr. C. Smith, what may we not expect? Plants cannot 

 shift quarters to collect food that may be at even only a little dis- 

 tance away, like animals ; so you must bring their food to them, and 

 plenty of it, not merely an apology of a complete feeding. 



After saying so much on the use of phosphates, I wish to at least 

 call attention to some paragraphs from Dr. Benjamin H. Paul, F.C.S. 

 in his "Dictionary of Chemistry," that, in regard to cereals, nitrogen 

 is generally the minimum constituent of a soil, and that, therefore, 

 the removal of this element is the main cause of the exhaustion pro- 

 duced by the exportation of these crops, and that the value of a 

 manure can, other circumstances being equal, be determined by the 

 amount of nitrogen it contains. A wheat crop, consisting of 25 

 Imshels and 3,000 Ib. of straw, contains 46 Ib. of nitrogen, equivalent 

 to 55.7 Ib. of ammonia. The falling-off in fertility of wheat 

 rields appears, therefore, to be mainly due to the abstraction of 

 nitrogen. When dressed with an ammoniacal guano these soils 

 should, and, I believe, do, yield again increased crops. The ammonia 

 restores the equilibrium, rendering previous unavailable mineral 

 constituents in the soil active. But Lawes and Gilbert also say that 

 of n ineral constituents phosphoric acid (in the form of superphos- 

 phate of lime) is by far the most effective manure; but, when this 

 manure (or any other phosphatic manure) is used alone, the imme* 

 diately available nitrogen in the soil is rapidly exhausted. Really 

 large crops can be obtained only when the soil contains, in addition 

 to ash constituents or mineral salts, a due proportion of nitrogenous 

 food. We must not in any case forget Baron von Liebig's "law of 

 minimum," which means that if one of the nutritive substances, be 

 it potash nitrogen, phosphoric acid, lime (to some 1 extent also 

 the less important salts as magnesium and others), 

 are not present in sufficient quantities, the result, 

 so far as a crop is concerned, will be almost the same as if all 

 were deficient. To revive the productive power we must restore 

 the equilibrium, and add as a special manure the substance which 

 was not present in the soil. But, while we may supply the soil with 

 all needed plant food, we are impotent even by adding fertilisers 

 to counteract to any very marked degree unfavorable weather con- 

 ditions here mostly drought. This was in another place most 

 clearly shown at the central and sub-stations of the Ohio Experiment 

 Station (TT.S.) cturinq- 1895 and 1896, when the wheat crop on the 

 thin land suffered severely from winter killing, followed by spring 

 drought, the average, notwithstanding fertilisers, being very low. 

 while unfertilised blocks fell in 1895 to 3 bushels) per acre, and for 

 1896 to 1 bushel. On the heavy clay the wheat was completely des- 

 troyed, with but little wheat even on that fertilised. The harvests 

 of 1897, however, showed a handsome profit on the fertilisers in 

 every case, except where nitrogen and potash were used singly, or 

 with these two onlv. in combination. 



