WATER PENETEATIOlSr IN GUMBO SOILS. 3 



these depths may be somewhat higher than in the first foot. The 

 difference is not great, and as a whole the mechanical composition 

 of the first 3 feet may be considered uniform. 



WATER CAPACITY OF THE GUMBO SOIL. 



The water-carrying capacity of this soil is high, and the minimum 

 point to which crops can utilize the water is correspondingly high. 

 The soil, when filled, will carry about 30 per cent of water, of which 

 about 15 per cent is available for the use of crops. The character of 

 the soil is such, however, that the crops do not root deeply, owing 

 either to the lack of water in the lower depths or to the impervious 

 nature of the soil. In spite, therefore, of the large quantity of 

 water that can be obtained by the crop from the soil near the surface, 

 the shallowness of feeding materially reduces the quantity of water 

 actually available. 



PRODUCTIVITY OF THE GUMBO SOIL. 



The producing capacity of the soil is high. There is no evidence of 

 a deficiency of any mineral element essential to crop production. 

 When sufficient water is supplied, abundant crops are obtained. The 

 high productive capacity of this soil is evidenced by the yields ob- 

 tained on plats not irrigated in 1915, when the rainfall was unusually 

 favorable both in amount and in distribution. The average acre 

 yields obtained were 72.2 bushels of barley, 36.2 bushels of winter 

 wheat, 57.6 bushels of spring wheat, 12.5.6 bushels of oats, and 44.5 

 bushels of corn. 



CHANGES IN THE VOLUME OF THE SOIL DUE TO WETTING AND 



DRYING. 



The large amount of clay present makes this soil subject to extreme 

 changes in volume with changes in its water content. Wlien the soil 

 is wet it swells and compacts; when dried it shrinks and cracks. 

 That the change in volume is great enough to cause a material 

 change in physical structure is shown by the results of the follow- 

 ing experiment, which was made for the purpose of obtaining a 

 measure of this cliange. 



The volume of oven-dried compact samples of soil was determined. 

 These samples were then immersed in water and allowed to expand 

 i'i-('(']y and the volume redetermined. The A'olume of the soil from 

 the first foot increased 2.2 times. The volume of that from both the 

 second and third feet increased 2.5 times. 



Thes<! changes in volume, due to variations in moisture content, 

 resiilt in the following structural differences: 



When dry this soil is iisuiilly covered with n nntunil mulch idxnit 2 inches 

 de<'i» cauKe(J hy the crurriltlin^,' of the surface soil. lierieuth this inulcli is a 

 layer of soil iioticvf oiuiied witii <-racl{s. The nuiuher of these cruclis and the 



