324 MANAGEMENT OF CLAYS AND DEPLETED SILT LOAMS 



were originally covered with forest growth. The growing of grasses 

 and pasturing have been mentioned as means of increasing the 

 organic matter. The plowing under of clover and green manuring 

 crops, and the use of manm*e are especially recommended as means 

 of increasing the nitrogen supply. 



Phosphates for Clays. — Heavy soils usually contain large 

 amounts of potassium. When well drained and sufficiently supplied 

 with organic matter potash fertilizers are seldom required on 

 these soils. 



The phosphorus needs of clays are quite general, so that the 

 use of phosphate fertilizers is usually highly profitable. For imme- 

 diate results, acid phosphate may be used at the rate of 200 to 300 

 pounds per acre for grain and 400 to 500 pounds per acre for corn. 

 Rock phosphate, when mixed with manure or plowed under with 

 clover or green rye, has given excellent results (Fig. 148, p 198. 

 See Rock Phosphate, index). Basic slag is especially good to 

 use on clays, but in most sections of the United States it is 

 not obtainable. 



Many clays are red in color, due largely to the presence of 

 iron compounds. Frequently this iron makes the phosphorus 

 unavailable. On some of these soils acid phosphate is rendered 

 entirely ineffective within a year or two after it is applied. The 

 application of agricultural lime is an effective remedy. 



Erosion. — ^Because of their location or topography, many 

 clay soils are particularly subject to washing, or erosion. The 

 cultivation of these lands greatly increases thek tendency to wash. 

 In most cases it is best to keep such lands in grass. When some 

 of the more gentle slopes are brought under cultivation, plowing 

 should be done at right angles to the slopes. Often it is advisable 

 to terrace a slope or leave open dead furrows in such a way as to 

 enable the surface water to run off by following more gentle inclines. 



Deep fall plowing and subsoiling also aid in preventing erosion 

 (see index). A further discussion of erosion may be found in 

 Chapter XVI. 



Other Points on Clay Management. — Clearing clay lands of 

 underbrush, small stumps and dead timber is not, as a rule, a 

 very expensive process. Removing stumps by combining the use 

 of dynamite and the stimip puller seems to be the most economical 

 method. It is much easier to blast out stumps when the ground is 

 moist or wet and when they are given a few years to rot after the 

 timber is cut. 



