420 MANAGING ORCHARD SOILS AND FERTILIZING TREES 



branches) is completed about the middle of July, in most sec- 

 tions. This means also that the full leaf area is developed 

 early in the season, and that large amounts of water are thus 

 being transpired. It will also be recalled, from Chapter VIII, 

 'Tollination and Fruit Setting,'' that the ^^sef' of blossoms is 

 influenced considerably by the amount of moisture and nitrates 

 available at blossoming time. 



It is thus evident how essential it is that nothing shall com- 

 pete with the trees so that the maximum amount possible of 

 moisture and nitrates will be available early in the season, 

 when such rapid tree growth and development are taking place. 

 If the cover crop is allowed to grow in the spring, much of the 

 water and nitrates is taken from the trees. Early cultivation 

 not only will prevent moisture loss, but also will help to bring 

 about such favorable conditions of temperature and aeration 

 in the soil that nitrification early in the season will be more 

 rapid and extensive. 



Trees will respond better if plowing is done early than if 

 the plowing is done late, even though later cultivation may be 

 very thorough. 



Determining the Cover Crop to Use. There are, in general, 

 two kinds of cover crops, legumes and non-legumes. The 

 legumes, through the aid of bacteria which are present in the 

 nodules on their roots, are able to fix the nitrogen of the air, 

 but non-legumes do not have this power. It can thus be seen 

 tiiat, with legumes, more nitrogen than that which was already 

 in the soil before the crop was grown is added when the crop 

 is turned under and nitrification has taken place. On land 

 where legumes have never been grown, inoculation may be 

 necessary. If both legumes and non-legumes are used as cover 

 crops, the soil nitrates which might otherwise leach out of the 

 soil or be washed away are absorbed by the plants and thus 

 returned to the soil when the crop is turned under. 



Winter vetch, crimson clover, cow peas, soy beans, alfalfa, 

 and red clover are legumes. Crops such as rye, oats, millet. 



