364 



SOIL PHYSICS AND MANAGEMENT 



and retain more of the rainfall. Owing to its granulating effect 

 organic matter reduces the tendency to run together and keeps the 

 soil open, so there is less run-off and less erosion. 



Legumes must have a large place in the agriculture of these 

 lands. It is advisable to feed most crops to stock on the farm. All 

 the manure produced should be carefully preserved and returned to 

 the soil. All stalks, straw, stubble or other residues not fed should 

 be plowed under. Plow.ing under the entire crop of cowpeas, or at 

 least the straw, is a practice to be recommended. 



5. Deep Contour Plowing. A loose soil has more pore space 

 than a compact one, consequently it will absorb more water. A 



' 



Fia. 176. Cultivated terraces in China. (Bailey Willis.) 



silt loam in loose open condition will absorb 10 to 15 per cent more 

 water than when compact. The pores in a compact soil are so small 

 that it absorbs rain very slowly and much of the water is lost as 

 run-off. The surface soil may be kept loose by plowing to a depth 

 of eight to ten inches. Eight inches of loose silt loam fairly well 

 supplied with organic matter is capable of absorbing two inches of 

 water. While a greater depth of plowing would increase the storage 

 capacity, experiments show such to be unprofitable. The Georgia 

 Station 6 reports results which indicate that plowing more than 

 eight inches deep lessens the yield of cotton. It is believed, how- 

 ever, that loessial soils may be plowed to a greater depth with profit. 

 Plowing on sloping land is best done across the slope with a 



