MINERAL COMPOSITION OIF CROPS 51 



tural workers concerning the effect of fertilizers on the quality of the 

 crops. A brief tabulation of some of the replies follows. 



1 . Effect of fertilizers on carbohydrates : 



(a) Phosphorus increases the starch content of barley and alfalfa. 



(b) Potassium produces greater hardness of rice kernels. 



(c) Calcium and magnesium, by making potassium more available, increase 

 carbohydrate content. 



(d) Manganese increases the sugar content of beets. 



2. Effect of fertilizers on proteins: 



(a) Nitrogen generally increases the protein content of seeds and tubers. 



(b) Phosphorus increases phosphorus and nitrogen of cereals. 



(c) Phosphorus usually decreases gluten of wheat. 



(d) Potassium tends to reduce protein content. 



(e) Sulfur increases protein content of barley and wheat. 



3. Effect of fertilizers on fats: 



(a) Phosphorus has no influence on fat of flax. 



(b) Potassium favors production of fat in flax, mustard, and pecans. 



4. Effect of fertilizers on fiber: 



(a) Too much nitrogen affects fiber unfavorably. 



(b) Potassium increases length and strength of cotton fiber. 



5. Effect of fertilizers on enzymes and vitamins: 



(a) Phosphorus hinders enzymatic activity in plant tissues. 



(b) Lack of manganese in spinach is correlated with decreased vitamin A. 



Ashton (17) observed that the strength of oat straw was associated 

 with a relatively high content of certain ash constituents, particularly 

 silica, and a low fiber content. Studies on the relationship between 

 the calcium content of the plant and the organic acids in the plant 

 have been made by Iljin (290) in 1938; and Pfutzer and Pfaff (464) 

 have recently reported on the effect of minerals on the vitamin con- 

 tent of plants. 



Garner, McMurtrey, Bowling, and Moss (202) reported in 1930 

 that 



From the standpoint of quality the chloride content of the cured [tobacco] leaf 

 may affect its properties either favorably or adversely depending on the quantity 

 of chlorine present, the use to be made of the tobacco, and the stage in handling 

 and manufacturing operations which it has reached. 



SUMMARY OF EFFECT OF FERTILIZERS ON PLANT COMPOSITION 



Out of the confusion of contradictory results of fertilizer experi- 

 ments one can draw a very few definite conclusions. First among 

 these is the important fact that no fundamental study has ever been 

 made of the effect of soil amendments on plant composition taking 

 into consideration that most important of factors, the characteristics 

 of the soil used in the experiment. It is true that physical charac- 

 teristics of the soil such as structure have been observed, and that the 

 availabilities of a few of the principal plant nutrients have been 

 arbitrarily measured; but fundamental studies of what changes take 

 place in the soil when the fertilizers are applied and the effect these 

 changes will have on the plat are lacking. 



One or two recent empirical investigations have quite definitely 

 shown that Liebig's "law of the minimum" never represented the 

 mechanism of absorption of nutrients by plants, and that the actual 

 facts seem to indicate that when one of the principal nutrients is 

 deficient in the soil solution the others are taken up by the plant in 

 amounts greater than normal, while even less of the deficient nutrient 

 is absorbed than would be expected normally. The necessity for a 

 balanced source of nutrients for the plant is thus indicated, and the 



