-6- 



clay soil v;as not raoaaurcibly roducod until at least tho driest 

 part of the root zone approached blic silting percentage. In the 

 case of a moderate drou^jht causing no serious loss of foliage, 

 grovv-th of fruit v;as resumed at an apparently normal rate when the 

 moisture supply was restored, but the ultimate size of the apples 

 v;as reduced in proportion to the length and duration of the drouth. 



^^ ^-^^ .,.^^^ ^^^v-^„^^ ^.. ^ ^^ -.„...^, ^^ appoi. 



Moderate moisture promoted maximum color, while an excess of 

 moisture tended to reduce color. Fruit bud formation was apparent- 

 ly increased by ca.rly season shortage of moisture but after late 

 July there was no apparent effect. The earlier closing of 

 stomates forecast a moisture shortage prior to actual reduction in 

 the growth rate of fruit. 



Soil T e mperat ure and Root Activity 



In a recent bulletin'by Collison of the W. Y. Agricul- 

 tural Sxperlnent Station (Tech, Bui, 237) may be found an ob- 

 servation about an interesting side of orchard behavior. He finds 

 root elongation and therefore nutrient absorption may take place 

 during periods when air temperatures wore below zero. Soil 

 temperatures, however, wore not far from the freezing point. The 

 insulating effect of the soil is shov/n by the follov/ing figures. 

 The lowest soil temperatiire recorded was that in February, 1935, 

 when the A horizon of the soil dropped to 25 degrees F., only 7° 

 below freezing. During the summer the highest recorded soil 

 temperature was 68° P. early in July. The author believes that 

 some root activity goes on while the soil temperature is within 

 2 to 5° of the freezing point or even less. This being true, it 

 is easy to understand hov; the tree can take up nitrogen during 

 the dormant season, as v/cll as moisture to replace that loss made 

 by evaporation. Incidentally, the vegetative cover on the soil is 

 an important factor in water penetration and movement. A humus 

 filled soil may be expected to show less variation in moisture 

 content and probably in soil temperature than a soil deficient 

 in humus. 



Organic Matter in the Soil. TOiy ? 



Because (1) it acts as a reservoir for plant food, 

 liberating some nitrogen as It decays, (2) it acts as a sponge 

 in holding soil moisture, (3) it maintains soil orgrjiisms which 

 have a beneficial effect on the liberation of plant food, (4) it 

 acts as a soil conditioner and tends to loosen heavy soils and 

 bind light soils, (5) it tends to warm the soil by absorbing more 

 of the heat of the sun. In short, it Is responsible for one of 

 the important differences between a real soil and a mere physical 

 mixture of clay, sand and gravel. If organic matter is supplied 

 by moans of a m.ulch, we have such additional benefits as the 

 holding of precipitation, thus preventing surface run-off, 

 smothering of competing vegetation such as grass and weeds, pre- 

 vention of evaporation from the soil, and as a padding for drop 



