New York Agricultural Experiment Station. 937 



(7) Sod may " poison " apple trees. This conclusion has been 

 reached by very careful investigators in England, who assign to 

 this factor, principally, the evil effects which they have found 

 to follow attempts to grow apple trees in sod land. The sudden 

 changes from good to ill results when trees in the Auchter 

 orchard were changed from tillage to sod, and from ill to good 

 when changed from sod to tillage, lend some support to this 

 theory that the grass roots excrete some substance harmful to 

 apple trees; but the other factors previously mentioned, particularly 

 the lowering of the water content of the soil, seem quite sufficient 

 to account for the evil influence of sod without laying much stress 

 upon its excretion of an actual " poison." 



It is hardly necessary to repeat again, or to 



Deductions emphasize the main conclusion from this ten- 



from these year test, that tillage and cover crops rather 



tests. than sod-mulch should be generally adopted by 



commercial orchardists in New York State. 



But some other statements may be made regarding the applica- 

 tion of this experiment in other directions. 



In orchards on deep soils the sod-mulch method is less of a detri- 

 ment than on shallow soils. In the deep soil the tree roots have some 

 chance to escape the drought-producing influence of the grass roots. 

 Under some conditions, as where moisture is over abundant and 

 apple trees make too luxuriant growth, sod may occasionally be 

 used with benefit to check growth and promote fruitfulness. There 

 is, however, nothing in the experiment to indicate that on ordinary 

 soils the grass roots and tree roots ever establish amicable relations; 

 for the difference between the tilled and sodded plats was greater 

 at the end of ten years than during the first half of the test. That 

 is, apples do not become adapted to grass. The injurious effects 

 of the grass on apple trees occur, no matter what the variety or 

 age of the tree or other cultural treatment; and are even more liable 

 to be shown by dwarfs than by standard trees because of the shallow 

 root systems of the trees on dwarf stocks. Pasturing orchards in 

 sod may reduce the injury from the grass just to the extent that the 

 pasturing reduces the growth of the grass; but it can never wholly 

 overcome the evil. The owners of sod orchards may not realize 

 how their trees are weakened and their crops lessened by the growth 

 of the grass, since they have no tilled trees under the same conditions 

 to compare with them; but a trained observer can usually detect, 

 even from a distance, signs of poor health and diminished vitality 

 in the light color of the foliage. 



The sod-mulch system is bad enough; but grass grown in the 

 orchard, not for a mulch, is all but fatal — it makes the trees sterile 

 and paralyzes their growth. It is the chief cause of unprofitable 

 orchards in New York State. 



