No. 6. DEPARTMENT OP AGRICULTURE. 403 



that there is plenty of I'ockI in the sod land but for some reas^on it is 

 not available to the apple treees. The trees are starving in a land of 

 plenty. 



Second. The sod-mulch does not conserve moisture as well as 

 tillage. The chief study in the Auchter oichard for the summer 

 of 1907 was that of the water content of the soil in the tAvo plots. 

 One hundred twenty-eight samples of soil were taken at ditferent 

 times during the summer and under conditions safe-guarded in every 

 way possible to determine accurately the amount of moisture in the 

 soil. The analyses showed, approximately, that the water content 

 in the tilled soil during the past summer, was twice as great as in 

 the sod plot, thereby substantiating what has long been called that 

 tillage is a better means of conserving moisture than mulching. 



Trees must have water. If an apple tree bears ten barrels of 

 fruit, there are about eight and one-half barrels of water in the tree's 

 output. In a full grosvn ai)ple tree it is estimated that the total leaf 

 area is about l,OUO,(i()0 square inches. Mr. F. C. Stewart of the 

 Geneva Station has counted the stomata or pores on a square inch 

 of the apple leaf and finds that a fair average is about 150,000 per 

 square inch. Or for the leaf area of the whole tree, 150,000,000,000 

 pores. Now to supply the demands of its ten barrels of apple chil- 

 dren while these 150,000,000,000 pores are constantly giving mois- 

 ture is enough to drive a tree to drink and the apple tree becomes 

 hard drinker. When in the heat and drought of summer, the 

 apple tree in compelled to share its scant supply of water with the 

 thirsty horde ;f hangers-on found in an orchard sod the trees 

 must sutler. 'oiiU further, a diminished water supply entails a cut- 

 ting otf or \'uy food supply. Plant food enters the tree as a solu- 

 tion and an ap])le tree suffering from lack of water as a necessary 

 conseciuen-.-e suffers from a lack of food. A thirsty plant is a hungry 

 plant. 



Third. The sod-mulch soil is less well aerated. In the experi- 

 ments we are carrying on I have not attempted to secure evidence 

 on this point. It is obvious that sod interferes with the air supply 

 in the ground beneath it and it is not hard to believe that such 

 interference would hinder the proper development and prevent the 

 proper work of roots. The mutHer of mulch which forms a part 

 of this system of orchard management would of course intensify the 

 deleterious effects of the sod in the above respect. 



Fourth. The soil temperature is lower in the sod-mulch plots 

 than in the tilled plots. It is possible that the harmful action of 

 grass on trees may be accounted for in part by the influence of the 

 sod on the temperature of the soil. During the summer of 1907 

 the soil temperatures were taken in the tilled and mulched plots 

 twice a day for 41 days at the depth of six and twelve inches and 

 liuder as nearly comparable conditions as circumstances would per- 

 mit. At both depths the difference was in favor of the tilled plot. 

 At six inches the ditlerence was slight, being only one-third of a 

 degree but for the greater depth, twelve inches, the average in 

 favor of the tilled plot was If degrees. It is not an assumption 

 to say that the higher temperature is most favorable to the growth 

 of the apple tree, for plant physiologists, soil physicists and bacter- 



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