38 



SOIL CONDITIONS AND PLANT GROWTH 



ceeded normally, and the resulting grain was nearly full weight per 

 individual ; as the phosphate supply increased the percentage of grain 

 increased, but soon reached a maximum beyond which it would not go. 



Table XIV. — Effect of Varying Phosphate Supply on the Growth of Barley 

 IN Sand Cultures. Hellriegel (131). 



It is in the total growth of straw and of grain that the effect of 

 phosphate is manifested as shown in Table XV. : — 



Table XV. — Results of Withholding Phosphates, Potassium Compounds, and 

 Nitrogen Compounds from Barley. Hoos Field Experiments, Rothamsted. 



These results are plotted in Fig. 5. The effect of phosphate starva- 

 tion shows itself in depressing the yield of straw and of grain, the straw 

 being the first to suffer. Potash starvation takes longer to set in, 

 not because potassium is less necessary but because the soil contains 



