CROP REQUIREMENTS 155 



The figures given in Table 23 are based upon averages of large 

 numbers of analyses of normal products, of which some have been 

 made by the author and his associates, and many others by various 

 chemists in America and Europe. These averages are trustworthy 

 for large crops of good quality. Abnormal or special crops may 

 vary considerably from these averages. Thus, we have high-protein 

 corn and low-protein corn, one strain requiring 50 per cent more 

 nitrogen, and somewhat more phosphorus, than the other (Illinois 

 Bulletins 87 and 128); and it has been shown, for example, that 

 alfalfa and cowpeas are not only much more productive, but also 

 much richer in nitrogen, when grown on normal soils with the 

 proper root-tubercle bacteria than without bacteria. On the 

 whole, however, it is as nearly correct to say that a fifty-bushel 

 crop of wheat requires 96 pounds of nitrogen and 16 pounds of 

 phosphorus as it is to say that a measured bushel of wheat weighs 

 60 pounds. 



It may be said that other similar crops resemble somewhat 

 closely those given in Table 23 as to plant-food requirements. 

 Thus rye and barley are not markedly different in requirements 

 from wheat and oats, considering equal yields in pounds of grain 

 and straw. Other root crops may be compared with sugar beets, 

 other grasses with timothy, hay from other annual legumes with 

 cowpea hay, and other biennial and perennial legumes may be 

 compared in a general way with red clover and alfalfa. 



How many years would be required to sell as much phosphorus 

 from the farm in cotton lint yielding 2 bales (of 500 pounds each) 

 per acre as in 4 tons of clover hay, which may be produced in the 

 two cuttings in one season? Compare the nitrogen and potassium 

 contained in 100 bushels of corn and in 20 tons of sugar beets. 

 Compare wheat and clover in plant-food requirements. 



Assuming that two thirds of the nitrogen used by the clover 

 plant is deposited in the tops and only one third in the roots, and 

 that a given soil will furnish as much nitrogen to a growing clover 

 crop as to a growing wheat crop, what is the effect upon the total 

 nitrogen content of the soil of growing clover if all of the tops are 

 removed ? Compute the cost of commercial nitrogen for a 5o-bushel 

 crop of corn, assuming that 40 per cent of the nitrogen applied will 

 be lost in drainage waters. 



