COVER CROPS 93 



Classification of cover crops. Horticultural writers commonly 

 separate cover crops into two classes — leguminous and nonlegumi- 

 nous. The first are the nitrogen gatherers — plants which, through 

 the agency of the bacteria in their roots, add to the store of nitrogen 

 in the soil. Some of these are beans, peas, vetch, cowpeas, soy 

 beans, etc. Cover crops of the second class add no nitrogen to the 

 soil ; they simply return to it when they decompose what they took 

 from it in growth. Plants of this class are rape, buckwheat, millet, 

 cane, oats, and the like. This classification has come into use 

 largely because the literature of horticulture is for the most part 

 from the East. The classification is no doubt the best one for 

 regions where the fertilizer problem is all-important. But in the 

 West the question of orchard fertilizers is generally insignificant 

 in comparison with the moisture problem ; Westerners, therefore, 

 must consider cover crops just as they do other culture problems — 

 from the standpoint of soil moisture and winter injury. 



All cover crops dry the soil more or less during the late summer 

 and early fall. Some crops are killed by the early frosts and no 

 longer keep the ground dry, but act something as a litter mulch does 

 in checking evaporation from the soil. Other crops are uninjured 

 by early frosts and continue growth until severe freezing weather 

 kills them, thus keeping the soil dry late into fall. Still others live 

 through the winter, and early in the spring begin again to dry 

 the soil. 



Some cover crops mat down, thus forming a fair mulch for winter 

 protection, but do not hold the snow ; others stand erect, and, 

 although furnishing little direct winter protection, by catching the 

 drifting snow give excellent indirect protection to tree roots. 



Erect snow-holding versus prostrate mulch-forming cover crops. 

 Certain plants are sometimes recommended for cover crops, because 

 on the approach of winter they mat down and protect the soil like 

 a mulch. There is no doubt that mulches of any coarse material 

 are an excellent means of preventing deep freezing of the ground 

 and the consequent injury to tree roots, but no crop known to the 

 writer will, when sown in midsummer, form a mulch of sufficient 

 depth to prevent freezing, however thoroughly it mats down. 

 Observations that have been made indicate that cover crops are 

 less effective as soil mulches than as snow holders. Nothing known 



