48 PRINCIPLES OF FARM PRACTICE 



It is through tillage that the greatest effort is expended 

 in helping plants to secure their needs for growth and de- 

 velopment. Much skill and intelligence are needed in order 

 that the expenditure of time and energy may be most ef- 

 fective. 



Rotation of crops. By crop rotation is meant a system 

 of planting in which there is a change of crops on the same 

 soil from year to year. There are a number of advantages to 

 be secured by a proper rotation of crops. Some have already 

 been noticed, such as legumes in rotation for fixing the atmos- 

 pheric nitrogen into compounds available for other crops. 

 Others are to be considered in discussing cropping systems. 

 But crop rotation has also some direct effects on the soil 

 that deserve attention in soil management. Roots of plants 

 affect soil structure, especially in clay soils, by making it 

 more open and porous. Some plants, such as barley, millet, 

 and wheat, are shallow-rooted; some, such as clover, alfalfa, 

 and sugar beets, are deep-rooted; others, such as corn and 

 oats, are neither very shallow nor very deep. A rotation of 

 crops having different root depths would do more to improve 

 soil structure than a rotation of crops having similar root 

 systems. 



The greatest effect of crop rotation on soil improvement is 

 gained by alternating tilled crops, such as corn or cotton, 

 with un tilled crops, such as clovers and grasses. In this kind 

 of rotation tillage will bring about a thorough mingling in 

 the soil of the roots and crop residue of the previous, untilled 

 crop. 



Barnyard and green manure. The value of organic matter 

 in increasing the water-holding capacity of the soil and 

 keeping up the nitrogen supply has already been emphasized. 

 Organic matter derived from either barnyard or green manure 



