I4I6 



METHODS OF SOIL CULTIVATION 



METHODS 



O SOIL 



CULTIVATION 



straw and both were analysed. It was found that the phosphoric acid 

 content of the grain varied very Httle while that of the straw reflected to 

 a much greater extent the phosphoric acid content of the culture medium. 

 The sand cultures gave the following figures : 



Xormal strength 

 Double " 

 Treble 



Phosphoric acid content 

 in straw in grain 



'\6503 pti cent ').28^4 per cent 

 1.458 " " 0.2982 " " 



1.834 " " 0.2865 " " 



In the grain the phosphorus was present almost whoU}' in the form 

 of organic compounds while in the straw only phosphates were found. The 

 phosphate content of the plant, therefore, varied considerabl}' according 

 to the available amount of phosphoric acid in the culture medium, but the 

 organic phosphorus remained almost constant varying only within the 

 limits of 0.41 and 0.60 per cent. The organic phosphorus was not affected 

 by the total weight of the plant and only to a slight extent by the amount 

 of phosphoric acid absorbed by the plant. Where the nutrient solution 

 was used in a concentrated form, considerable amounts of phosphoric acid 

 were taken up by the plant, but onh' a very small portion of this was con- 

 verted into organic compounds of phosphorus, the main part being deposit- 

 ed as phosphate in the straw. 



From these results, it should be possible to draw the practical conclu- 

 sion that a high percentage of phosphate in oat straw indicates the presence 

 of a considerable amount of phosphoric acid in the soil. But it is pointed 

 out that other causes such as general conditions of growth may also affect 

 the percentage of phosphates in plants, indeed the writer's own experiments 

 of 1913 and 1914 gave results directlj^ contradictory to those obtained in the 

 above trials and are supported by the evidence of other authorities (Hall, 

 SeeLHORST, Atterberg). On the whole, therefore, it cannot be consider- 

 ed that the determination of the phosphate content in oat straw affords 

 a reliable guide to the condition of the soil, but in special cases it may yield 

 useful information. 



1062 - The Influence of Relative Area in Intertilled and Other Classes of Crops on Crop 



Yield.- — Brodie D. a. in United States Department cf Agriculture, Office of the Secretary, 

 Circular No. 57, pp. 1-8. Washington, March 31, 1916. 



Experience has taught that there is a Umit to the extent to which 

 land may be occupied by the same class of crops without detriment to crop 

 yield, and this experience has led to the adoption of rotations. Just 

 what proportion of the crop should be planted to intertilled crop {i. e. corn, 

 potatoes, tobacco, etc., planted in rows and cultivated between the rows), 

 what to grain crops, and what to perennial grass, to prevent serious 

 injury to the soil, are questions that the farmer has alwa^'s had to answer 

 for himself, largely from his own experience or from the established custom 

 of his locality. 



During the past two years studies as to the relation of the type of 



