I6O THE FIRST BOOK OF FARMING 



tices which properly control and regulate soil water 

 to a large degree control and regulate soil fertility. 



SELECTION OF CROPS WITH REFERENCE TO SOIL 

 WATER 



While climatic conditions determine the general 

 distribution of plants, the amount of water which 

 a soil holds and can give up to plants during the 

 growing season determines very largely the crops 

 to which it is locally best adapted. 



With crops that can be grown on a wide range 

 of soils the water which the soil can furnish largely 

 determines the time of maturing, the yield, and often 

 the quality of the crop. With such a crop a small 

 supply of water tends to hasten maturity at the ex- 

 pense of yield. 



The sweet potato, when wanted for early market 

 and high prices, is grown on the light sandy soils 

 called early truck soils. These soils hold from five 

 to seven per cent, of water. That is, the texture is 

 such that during the early part of the growing sea- 

 son one hundred pounds of this soil is found to hold 

 an average of from five to seven pounds of water 

 under field conditions. This soil, holding little 

 water, warms up early and thus hastens growth. 

 Then as the warmer summer weather advances, the 

 water supply diminishes, growth is checked, and 

 the crop matures rapidly. On account of the small 

 amount of water and the early checking of growth, 



