60 KKl'Uli'l' OF I'HKMKAL LAliOKATOKV 



GrTPSUM AS A FERTILISER FOR SUDAN SOILS 



The benetieial effect of lime ou soil has long been known and its application in one form 

 or another is a common practice, especially in humid regions. In arid regions like those of 

 the Sudan, the removal of the lime originally present as a soil constituent, by the leaching 

 effect of infiltrating rain water, takes place only to a very limited extent, and the soils in 

 such regions are usually so rich in lime that its application as a fertiliser is rarely if ever 

 practised. There is, however, evidence to show that under certain conditions a soil niay 

 be benefited by lime even when the analysis indicates that there is already present a 

 proportion much above that usually laid down as amply sufficient. Thus in certain 

 heavy, difficultly permeable, soils, lime, existing as small nodules of calcium carbonate, 

 may be so enveloped by clay as not to be available, and the application of lime in a soluble 

 form may be distinctly beneficial. 



The chief beneficial effect of lime, in the form of calcium carbonate, is usually stated to 

 be in connection with the growth of nitrifying organisms. Nitrification, the conversion of 

 the nitrogen of the soil into nitrates directly available for plant food, will not take place 

 except in slightly alkaline solutions such as that furnished by the action of water on calcium 

 carbonate. There are many other effects of lime equally important, and these are shared 

 by other compounds of calcium, more especially calcium sulphates. It is especially witli a 

 view to call attention to this latter substance and the possible benefits which may result 

 from its use on Sudan soils that the following notes have been gathered together. It is 

 hoped that they may induce agriculturists in the Sudan to make a trial of gypsum on their 

 lands. If the results obtained are sufficiently favourable, the extensive deposits of gypsum 

 which are known to exist in the Bed Sea Province may possibly be worked ou such a scale 

 as will enable the material to be secured at comparatively low cost. 



Before going into the details of the effects of gypsum in the amelioration of undesirable 

 soil conditions, a glance at the figures in the following table' may not be without interest. 

 They show the results of a very great inmiber of fertiliser experiments on cotton soils carried 

 out between 1887 and 1907 and reported in the official bulletins of the United States 

 Department of Agriculture and of the State Experiment Stations. The actual experiments 

 were performed on one tenth or one twentieth acre plots, but the results are uniformly 

 stated in pounds of cotton per acre. The value assigned to the cotton was only 10 cents 

 {•2 piastres) per pound, but the present value in Egypt is nearly twice that figure. 



Experiments were carried out both with single fertilisers and witli mixtures. The 

 table given includes the trials made with single fertilisers alone, since it is only in this 

 series that gypsum figures. 



It will be seen that the total area treated with gypsum was 11 acres. Since the trials 

 were made on one tenth and one twentieth acre plots, the number of different experiments 

 carried out with this fertiliser was between 110 and 220. The proportion of cases of success 

 to cases of failure was as ten to one, and the average gain per acre over the cost of gypsum 

 was #18 (about P.T. 360.) or, at the present value of cotton, nearly double that figure. This 

 is six times greater than the average gain from the use of any other form of single fertiliser. 



It is fully realised that such a comparison as this is far from scientific; but, as noted 

 by Whitney,'- owing to tlie generally inadequate description of the soils in the rejjorts of 

 experiments, it was not found practicable to group and to analyse the data with relation to 



' Taken from " Fertilizers for Cotton Soils," M. Whitney. U.S. De.pt. of AyrieiiUiirc, Burean «f Soils, 

 Bulletin No. 62. 



- Whitney, Inc. cit. 



