MINERAL COMPOSITION OF CROPS 53 



grown in Washington. Each of these three cuttings was studied at 

 the one-fourth, one-half, and three-fourths bloom. His data show 

 that the protein content of the hay decreased and the fiber content 

 increased as the plant matured. Plants cut at one-half bloom stage 

 contained more calcium than similar samples harvested at the one- 

 fourth and three-fourths stages. 



Radu (JflJi) in 1936 reported a maximum concentration of calcium 

 in the alfalfa plant during its growth, but Bettini (69) f studying the 

 composition of alfalfa in Italy, found a progressive increase in calcium 

 throughout the life of the plant until the advanced-bloom stage, after 

 which it remained constant until the seeds were mature. 



Determination of the variation in composition of spinach was made 

 by Fondard and Margaillan (187) in France in 1928. They reported 

 that the phosphorus content increased for about the first 30 days of 

 growth, after which it rapidly decreased until it was less in 48 days 

 than it had been at the end of 10 days. The potash increased during 

 the first 17 days but remained quite constant thereafter. According 

 to Tuorila (568), the potash content of potatoes grown in Finland 

 decreased with maturity. 



A comprehensive study of the composition of the different parts of 

 the soybean plant at different stages of growth was reported by Borst 

 and Thatcher (84). Their data show that a reduction of calcium, 

 magnesium, potassium, and phosphorus occurred in the stems as the 

 plant approached maturity. A reduction in the potassium and 

 phosphorus contents was also found in the leaves, but the other ele- 

 ments remained fairly constant. 



A number of investigations in changes in the composition of grasses 

 itave been conducted by workers in Great Britain (171, 172, 601). 

 In general, except for timothy, they reported that the phosphorus 

 content is reduced with the age of the plant. 



Van Itallie (292), working with three Dutch soils, reported in 1934 

 that the differences in composition of one variety or species of grass 

 at different stages of growth are greater than differences between 

 different species at the same stage of growth. 



Murphy (423) in 1936 found that both the calcium and phosphorus 

 content of the cotton plant decreased with age, and that the rate of 

 decrease in calcium was accelerated after the bolls started to form. 



Considerable attention was given in the compilation of the mineral 

 composition of crops to classifying the crop as to its age or stage of 

 maturity (see appendix). Thus, with alfalfa the average contents 

 of calcium and of phosphorus at the bud stage were 2.45 and 0.36 

 percent, respectively, while the corresponding values at one-half 

 bloom were 2.01 and 0.27 percent. The alfalfa data are not suffi- 

 ciently numerous to illustrate the change in composition throughout 

 the life of the plant, but other examples include the compilation of 

 data on Kentucky bluegrass and on rape plant. In the latter case 

 single analyses of the plant grown in Iowa show a maximum in the 

 calcium content during the life of the plant and a steadily diminishing 

 phosphorus content. 



Variations in the nutritive value of plants at different stages of 

 growth and the stage of maturity at which most plants have the 

 highest nutritive value are well-known. In general, the nutritive 

 elements attain maximum values during the life of the plant although 

 some differences in observations of how the mineral composition of 



