MINERAL COMPOSITION OF CROPS 55 



straw and chaff in dry years as in good years. Both the calcium and 

 potassium contents were much higher in the dry years, that in the 

 straw and chaff often being double the amount found in these parts 

 in normal years. 



The data of Daniel and Harper (135), reported in 1935 from their 

 study of the relation between effective rainfall in Oklahoma and total 

 calcium and phosphorus in alfalfa and prairie hay, support these find- 

 ings. They state that 



Although the mathematical correlation between the actual amount of rain and 

 the phosphorus in the alfalfa hay is not high, the figures show that the phosphorus 

 content of alfalfa fluctuates with the rainfall, and that the calcium content of 

 the hay is inversely proportional to the quantity of effective rainfall which occurs. 

 The moisture requirement of a crop is affected by the temperature and humidity 

 of the atmosphere; consequently, the total rainfall could influence plant growth 

 quite differently, depending upon whether high rainfall occurs during the spring 

 or summer months. A greater variation in the calcium and phosphorus content 

 of alfalfa occurred between the rainfall and the different cuttings of hay harvested 

 in 1932 than in the hay harvested in 1933. During the season of 1932, the period 

 of high rainfall was in May and June, while in 1933 the period of high rainfall 

 was in March, April, and May. 



Salgues (501), working with two soils in France, reported in 1938 

 that the phosphorus content of plants grown in calcareous soils was 

 increased with high rainfall, but that this was not true of plants 

 growing in siliceous soils. With lower precipitations, the phosphorus- 

 calcium ratio was lowered for all species grown in calcareous soils, 

 but the ratio was actually higher for the same species grown in 

 siliceous soils. 



The effect of rainfall on leaching of minerals from plants was in- 

 vestigated by LeClerc and Breazeale (337) in 1909. They found that 

 mineral nutrients, exuded upon the surface of the leaves of plants, 

 are washed off by rain and dew. They concluded, therefore, that the 

 analysis of plants gathered at maturity may give erroneous or mis- 

 leading results, especially for comparative purposes. Guilbert, 

 Mead, and Jackson (233), found that leached plants contained con- 

 siderably less phosphorus than did normal plants, although the calcium 

 contents of the leached and normal plants did not materially differ. 



While plants are dependent upon the soil for their mineral nutrients, 

 climatic conditions so affect respiration, assimilation, photosynthesis, 

 metabolism, and other physiological processes that the composition 

 of both the mineral and the organic matter of crops may be greatly 

 modified even though the crops are grown upon identical soils. In- 

 direct influences of climate are also reflected in the composition of 

 the plant, for the significant differences in the characteristics of our 

 great soil groups are largely differences due to climate. Thus, in the 

 Southeast we have well-leached acid soils low in the basic constituents, 

 while in the Northwest the soils are more nearly neutral and high in 

 bases. Differences within any soil group have, furthermore, been 

 effected by the particular vegetation growing in the soil, which in 

 turn was influenced by climatic factors. Thus, a soil developed under 

 grass will be quite different from one developed under forest. 



Investigations that show clearly the effect of climate on the mineral 

 metabolism and composition of the plant are not available, however 

 because differences in soils, species of plants, time of rainfall in 

 relation to the growing season, and other factors have not always been 



