556 Report of the Department of Horticulture of the 



in all parts of this orchard is necessary for the apple. Fruit trees 

 thrive in many soils in all parts of America where scarcely a tithe 

 of the humus in either the tilled or sodded part of this orchard 

 exists. The highest yields during the past five years in this orchard 

 were in the plat having least humus. It can not be said that the excess 

 of humus, as humus, in the tilled land of this experiment has made 

 any great difference in either yield of fruit or growth of tree. But 

 one of the postulates of agriculture is that humus increases the 

 water-holding capacity of soils and it is not an assumption to say 

 that in this way the greater amount of humus in the tilled land 

 has been helpful. 



The " burning out " of humus is one of the bugaboos that those 

 who keep their orchards in sod see in tillage. Analyses made in 

 1908 1 and again in 1913 as shown in Table II, give satisfactory proof 

 to those who till, that the reduction of humus in a soil through 

 tillage is an imaginary evil. This statement holds, provided, of 

 course, that a cover-crop is used with the tillage. It is not too 

 much to assume, in the light of this and other experiments, that 

 the difference in the amount of humus in a tilled orchard and a sod- 

 mulched orchard will be about the difference in the quantity of cover- 

 crop turned under in the former and the amount of grass left as 

 a mulch in the latter. 



Sod injures apples by lowering the temperature of the soil. — Evapor- 

 ation is a cooling process. It is to be expected, then, that the 

 greater evaporation through the grass and the compact earth in the 

 sodded land gives a cooler soil. The mulch obtained by cultivation, 

 too, is a protection against evaporation with its cooling effects. 

 Facts follow theory in this case and the expected happens. A series 

 of observations made at depths of 6 and 12 inches in the soil in the 

 summer of 1908 2 shows that the tilled soil in June and July is 1.1 

 degrees warmer at seven in the morning and 2.3 warmer at six in 

 the even ng than the sodded soil. Observations were not made 

 at night but it is doubtful if the soil temperature of the early morning, 

 at least, would be reversed though we might expect it to be less 

 than that of the evening after a day of sunshine. The reversals 

 of night would probably be more than offset by the higher tem- 



1 N. Y. Sta. Bui. 314: 124. 1909. 



2 For a table showing the temperatures see Bulletin 314: 126. 1909. 



