THE MOST IMPORTANT PURPOSES 109 



prevent wash or make humus. A plan which has been tried 

 with considerable satisfaction, *on lands where it was difficult to 

 get a good growth of cover crop, is to reserve a part or even all 

 of the fertilizer that is intended for that block and apply it just 

 previous to sowing the cover crop. A little nitrogen in particular 

 applied at this time is likely to be a great help in giving the crop 

 a start. 



The cover crop takes up and holds plant food at a time when 

 the trees are not active. The importance of this may have been 

 over-emphasized, but it is certainly worth considering, and it is 

 one argument in favor of those crops which are not killed by 

 frost. With buckwheat, for example, one gets little of this 

 effect because it is killed before the trees have stopped growing. 

 With any plant which lives over winter we get this benefit, but 

 the amount of it varies with the amount of root growth of the 

 cover plant. If the soil is occupied fully by the roots there is 

 little chance of loss. 



Add Nitrogen. A leguminous cover crop such as clover, or 

 beans, or vetch will add nitrogen to the soil (Fig. 44). This is 

 generally understood by all who are familiar with farm matters 

 but is frequently overlooked in orchard practice as well as else- 

 where. These plants are able, through the bacteria which live 

 in the little nodules on their roots, to take up and " fix " the 

 free nitrogen of the air. They thus offer to the orchard man an 

 abundant supply of nitrogen for his orchard in return for the 

 effort and expense of sowing the seed. In fact the writer recalls 

 one orchard in which crimson clover was used as a cover crop 

 for a series of years, where the soil actually became too rich 

 in nitrogen for the best condition of the trees. They made 

 too much growth and the fruit was under-colored. The owner 

 suspected what the trouble was, had the soil analyzed by his 

 experiment station, which told him that his soil was too rich in 

 nitrogen and advised him to change cover crops. He did so, 

 using buckwheat for a few years, and the trouble was entirely 

 corrected. This is not a common difficulty, but is mentioned to 

 show the possibilities of the leguminous crop. As nitrogen 



