APPLE-ORCHARD CULTURE 



419 



weed control and to some degree by the dust mulch kept on the 

 surface of the soil. 



Organic matter is added by plowing under the cover crops, 

 and nitrogen, in addition to that already in the soil, is incorpo- 

 rated when legume cover crops are used. The organic matter 

 of the cover crops improves the physical condition of the soil 

 and increases its water-holding capacity. The decaying or- 

 ganic matter liberates carbon dioxide, which makes a stronger 

 acid soil solution, so that the other mineral foods already in the 

 soil are more readily dissolved and made available for the 

 tree^s use. Nitrification normally proceeds much earlier and 

 faster in cultivated soils, and as a result more nitrates are 

 available for tree growth than where sod culture or sod mulch 

 is used. 



Plow in the Fall or Early in the Spring. In regions like 

 southern New York and Pennsylvania where there is little 

 danger from winter freezing of roots, and where the cover crops 

 have been sown early enough in the season to produce a large 

 bulk of organic matter, it will probably pay to plow in the fall 

 (except in very sandy soils), especially if the ©rchards are not 

 on steep land. By fall plowing, earlier cultivation can usually 

 be performed in the spring, the organic matter will decay 

 sooner, nitrification will start earlier, and there will be no 

 danger of the cover crops competing with the trees for water 

 and nitrates early in the spring. 



In regions with a climate similar to that of Maryland, Dela- 

 ware, Virginia, and North Carolina, plowing can be done 

 during the fall or in February and March. The important 

 thing is to have the ground plowed before any tree growth 

 starts in the spring. 



The reason for cultivating early in order to increase the 

 amount of water and nitrates available for the tree is readily 

 understood when it is recalled from Chapter IV, ^The Growth 

 of the Tree and the Forming of Fruit Buds," that fruit spur 

 growth in length is completed for the season about two weeks 

 after blossoming and that terminal growth (at the ends of the 



