The Tillage of Peach Orchards 103 



extreme cases due to larger quantities of moisture being 

 transpired through the leaves than is replaced by absorp- 

 tion through the roots. 



The continuous clean tillage of apple orchards is a mooted 

 point with many growers. The exponent of each of the 

 different methods of maintenance, which include clean 

 tillage, tillage and cover-crops, sod mulch, and the like, 

 becomes skillful in adducing evidence, which to him is con- 

 vincing, in support of his favorite system. The fact is not 

 as well recognized as it ought to be that each system where 

 effectively maintained in an orchard is an expression of the 

 operation of fundamental principles. If clean tillage is 

 the best system under certain conditions and the sod-mulch 

 system proves best under other conditions, the important 

 thing is to determine what the relation of the different con- 

 ditions is to the results obtained. 



A correlation of cause and effect, in other words the es- 

 tablishment of the principles that govern or determine the 

 results, is not always easy, nor is it always possible with the 

 present knowledge of what actually constitutes fertility in 

 soils. The fact is more or less frequently observed, however, 

 that clean tillage or tillage and cover-crops give entirely 

 satisfactory results in some orchards where under a sod- 

 mulch system the trees show evident signs of distress ; and 

 that in other cases the sod-mulch method of maintenance 

 may give unmistakable evidence of superiority as compared 

 with clean tillage or tillage with cover-crops. 



The present conception of what constitutes fertility can- 

 not be expressed in simple terms of available plant-food. It 

 was a great advance when the soil physicist comprehended 

 the importance of the physical condition of the soil in ad- 

 dition to the presence of certain chemical constituents. The 



