222 IRRIGATION PRACTICE 



undoubtedly of very wide application. In the above 

 table, the percentage of protein in plant parts is also given. 

 In general, the percentage of protein is diminished in 

 every part of the plant when the irrigation is increased. 

 The little existing knowledge indicates that the proteid 

 parts of protein, used in the production of blood and 

 muscle, are affected by varying irrigations, even more 

 strongly than is the protein, and in the same direction. 

 Some little work has also been done upon protein digesti- 

 bility as affected by irrigation; and it seems safe to assert 

 that when crops are grown with increasing quantities of 

 water there is a decreasing percentage of digestible, 

 nitrogenous substances in the plant. It is clear, there- 

 fore, that plants and plant parts are more valuable as 

 animal foods, pound for pound, when grown with little 

 water. 



The quantity of nitrogen taken up by a crop is not, 

 however, largely affected by irrigation. Whether the crop 

 has received much or little irrigation water during the 

 period of growth, the total quantity of protein that it 

 contains per acre is approximately the same. For most 

 crops the tendency is for the total yield of protein to 

 increase with much irrigation, though the percentage 

 decreases. 



The compounds of nitrogen from which protein is 

 made, are taken, as is the ash previously discussed, by 

 the roots from the soil. It would be expected, therefore, 

 that the protein should vary as does the ash content. 

 Instead, the variation is the opposite. Nitrogen is pres- 

 ent in the soil in relatively small amounts, and, in its 

 soluble and available forms, in even smaller amounts. 

 Nitrification and similar processes which convert the 

 organic nitrogen into forms available to plants go on at 



