COVER CROPS 71 



a detriment at times. Considerable judgment should 

 be exercised with regard to this point. 



2. Cover crops which grow late in the autumn, 

 especially those like hairy vetch, which live over win- 

 ter, s?ve considerable amounts of fertility from leach- 

 ing away. Soluble plant food in porous soils is quite 

 apt to drain away during late fall and early spring 

 when the tree roots are not actively foraging for it. 

 Such plant food is caught by the cover crop, and 

 when plowed under and rotted, becomes available for 

 the trees. Cover crops, like buckwheat, which die early 

 in the year, evidently are less useful in this way. 



3. A good cover crop prevents washing of the land 

 in winter and early spring. On loose sloping lands 

 serious damage often occurs from erosion ; and this is 

 one of the strongest facts in favor of growing grass 

 in orchards. However, the benefits of tillage can be 

 combined with this advantage of grass management, 

 to a great extent at least, by sowing a suitable cover 

 crop. For this purpose the vetches are good, the 

 hairy or winter vetch especially so. 



4. The cover crop adds humus to the soil. The 

 greatest drawback to a system of constant tillage in 

 an orchard is that it exhausts the supply of humus in 

 the soil. On light, warm soils this exhaustion comes 

 early; it is apt to be very complete and very detri- 

 mental to the trees. On heavier soils the humus sup- 

 ply will last longer, but its final depletion is likely 

 to be even more disastrous. The supply of humus 

 may be kept up by the application of barnyard 

 manure; but the cover crop offers a cheaper and a 

 better way of doing the same thing. 



5. Leguminous cover crops (that is, those belonging 

 to the pea family of plants) add nitrogen to the soil. 



