19161 



SOILS — FERTILIZERS. 



725 



Summary of 82 comparative tests of acid phosphate and rock phosphate on dif- 

 ferent crops and soils. 



' Value of increase includes value of corn stover and wheat straw. 



It is estimated from the average results that the profit per dollar invested 

 was over seven times as great from acid phosphate as from rock phosphate. 

 The value of the crop increase per pound of phosphorus applied was 28J cts. 

 for acid phosphate and 3.5 cts. for rock phosphate. 



Red soils and phosphatic manuring', J. Aei^ {Bol. Agr. [Sao Faulo], 15. ser., 

 No. 6-7 (191Jf), pp. 535-555, figs. 2; abs. in Internat. Inst. Agr. [Rome], Mo. Bui. 

 Agr. Intel, and Plant Diseases, 6 {1915), No. 8, pp. i042-i0i4)-— This report 

 deals with the problem of manuring red soils, especially those of the State of 

 Sao Paulo, Brazil, derived from the decomposition of diabasic rocks. 



A series of analyses of these soils showed " that out of 48 samples, 4 con- 

 tained only traces of phosphoric acid, 12 up to 0.5 [parts] per thousand, 15 

 from 0.5 up to 1 per thousand, 10 from 1 up to 1.5 per thousand, 6 others up 

 to 3.6, and 1 even 5.2 per thousand. Humus is relatively low, from a minimum 

 of 0.24 per cent up to 2.56 per cent exceptionally, but generally about 1 per cent. 

 The lime content varies from 0.01 to 0.G5 per cent. From these data and from 

 other analyses ... it appears that 60 per cent of the soils examined were in 

 urgent need of phosphatic manuring. . . . 



" Experiments were also made in order to determine the absorptive capacity 

 of red soils for phosphoric acid, solutions of monocalcium phosphate being 

 placed in contact with the soil samples." It was found that the phosphoric 

 acid was almost entirely absorbed after 20 days of contact, but this absorption 

 was accompanied by an insolubility and consequent retrogression of the phos- 

 phate. 



" The most important factors in this fixing of phosphoric acid are lime and 

 humus. When a more calcareous red soil was taken 0.22572 gm. was absorbed 

 at the end of 20 days instead of 0.214608 gm. Humus contributes to regulate 

 the absorption, but ... it serves still more to retard and prevent the retro- 

 gression. Consequently the best way of decreasing the effects of retrogression 

 in red soils is to turn in organic plant manures, and especially dung, as often 

 and as regularly as possible. . . . 



