46 FUNDAMENTALS OF FRUIT PRODUCTION 



miles per hour as in a calm atmosphere; 3.8, at 10 miles per hour; 4,9, at 15 

 miles per hour; 5.7 at 20 miles per hour; 6.1, at 25 miles per hour and 6.3 

 at 30 miles per hour.^"^ The influence of windbreaks upon wind velocity 

 varies with their height and density and much depends also on the topog- 

 raphy, Card^^ measured the evaporation in Nebraska at varying 

 distances from the protected side of a windbreak of forest trees some 30 

 feet high, during the period July 15 to Sept. 15, and for those portions of 

 the period when the wind was from the south, southeast and southwest, 

 these being the most drying winds. Expressing the evaporation at a 

 point 300 feet south of the windbreak as 100, evaporation 200 feet north 

 was 83 and 50 feet north, 55. During a 12-hour period on Aug. 3, when 

 the weather was hot and dry with a high wind, evaporation 50 feet north 

 of the windbreak was 29 and 200 feet north it was 67, compared with 100 

 at a point 300 feet south. It is thus evident that wind barriers of one 

 kind or another reduce evaporation very materially. However, the 

 moisture required for the growth of the windbreak materially reduces 

 their total moisture-conserving effect, though deep plowing or subsoiling 

 close to the windbreak reduces its injurious influence in this direction. 



Summary. — There are six fairly distinct methods of soil management 

 commonly used in the deciduous fruit plantation: (1) clean cultivation, 

 (2) clean culture with cover crop, (3) artificial mulch, (4) sod mulch, 

 (5) sod, (6) intercropping. The sod and sod-mulch systems are most 

 effective in reducing run-off and in preventing erosion; in certain situa- 

 tions their use is to be recommended for these reasons if for no other. 

 The various systems of soil management employing tillage generally 

 conserve a larger percentage of the water that enters the soil and conse- 

 quently they are more effective in preventing injury from drought. The 

 sod-mulch method has its place where abundant summer rainfall, deep 

 rooting or availability of irrigation water largely removes the trees from 

 competition with the surface cultures for water. The moisture-conserv- 

 ing effects of tillage increase somewhat with its frequency and depth, but 

 when cost is considered there is a decreasing margin of profit with the 

 deeper and more frequent cultivation. Cultivated intercrops may be 

 used safely in the orchard, but the small grains are apt to make too serious 

 a draft on moisture at a period when the trees should be abundantly 

 supplied. Cover crops consume considerable moisture but unless planted 

 too early they are not likely to injure the trees seriously by their growth 

 in the fall. In fact they may actually conserve moisture for the trees 

 by cutting down surface evaporation and holding snow. In some sections 

 winter-surviving cover crops should not be used because of their draft the 

 on moisture supply in the spring when the trees require it. This is partic- 

 ularly true in sections with only moderate rainfall and long dry summers. 

 Evaporation increases rapidly with wind velocity and moisture losses 

 from this cause can be lessened materially in many cases by choice of 

 sites and use of windbreaks. 



