r.YPSUM AS A FKRTTLISER FOR SUDAN SOILS 63 



In othor woi'ds, if, in ordinary soil, one part of iiiiigncsinm sulphate was foinid to be 

 suillcient to prevent plant f,'ro\vtli, in the presence of calcium sulphate the proportion of 

 magnesium sulphate could be increased to 480 parts before the same poisonous efi'ect was 

 manifest. 



The experiments mentioned were carried out with wheat seedlings. The results 

 obtained in 1902 have been confirmed by later investigations. Kearney and Harter in 

 a bulletin' which appeared in 1907 have detailed the results obtained with four varieties of 

 dura, two of oats and two species of cotton (the Jannovitch Egyptian and an American 

 variety). The results establish the fact that different genera and species differ greatly in 

 their power of resistance to the salts of so-called alkali soils, and that in the presence 

 of salts of calcium, especially calcium sulphate, these differences are much less pronounced. 

 They, however, still exist to such a degree as to leave no escape from the conclusion that 

 some species and varieties of these plants are better adapted than others to grow in 

 soils containing a relatively large amount of these salts. 



The extent to which gypsum neutralises the poisonous effect of salts, thus increasing the 

 resistance of the plant to the same, varies with the nature of the salt. In the case of sodium 

 chloride the resistance of the plant was increased as follows :— 



Lupine (white) ... ... ... ... 5 to 10 times 



Wheat 5 to 10 ,, 



Dura ... ... ... ... about 10 ,, 



Oats „ 9 „ 



Cotton ((V. harhadense) ... ... ... ,, 32 ,, 



Beet ,, 8 ,, 



These experiments were carried out with solutions saturated with gypsum. It was 

 found, further, that when the latter was present even in very small amount, its effect was 

 still marked. Thus, when present to the extent of only one sixteenth part of that 

 required for saturation, the neutralising effect was more than one half that observed for the 

 concentrated solution. It may l)e stated here that very little calcium sulphate is required 

 to form a saturated solution in pure water — approximately two parts in one thousand parts 

 of water. 



The experiments detailed above were all on a small scale, in the laboratory. A very 

 interesting series of field experiments on a larger scale was made at the Experiment 

 Station of the Hawaiian Sugar Planters' Association.- These were directed to the 

 determination of the effect of salt in the irrigation water of sugar plantations and the extent 

 to which neutralisation miglit be effected by the addition of calcium carbonate (in the form 

 of ground coral) and of gypsum. Very large amounts of salt were used in those experiments 

 (200 grains per gallon of irrigation water, amounting in all to over 30 tons of salt per acre) 

 so that the effect on the yield of cane was very marked. 



It was found that when gypsum or ground coral were employed, the effect of the salt 

 was to a certain extent neutralised, the yield of sugar being increased by about 46 per cent. 

 The quality of the juice was also slightly improved, the sugar being associated with less 

 impurity. 



(c) The importance of maintaining a good "tilth" — that loose friable condition of the 

 soil in which the clay exists, not in the puddled state, but agglomerated into small 

 aggregates, thus permitting the free access of moisture and air — is so well known as to 



' Bulletin No. 113. Bureau of Plant Industry, U.S. Dept. of Agriculture 



- Report of the work of the Experiment Station of the Hawaiian Sugar Planters' .\ssociation, Division 

 of -Agriculture and Clicmistry, Bulletin No. 11. 



