CONTENTS. 



PART I. 



A synopsis of conditions 7 



Purpose of the study 7 



Important winds of the United States 9 



The utility of windbreaks 12 



How windbreaks act I 3 



System of measuring influences 14 



PART II. 



Measurements of physical factors Physiological effects upon plants and 



animals Crop yields 1 G 



Method of measuring factors 16 



Sunlight 16 



Soil moisture 17 



Mechanical force of wind 18 



Evaporation 18 



Heat 19 



Humidity 20 



Results of measurements 21 



I. Light Effects of shading 21 



Amount of shading 21 



Crown density and branching 22 



Orientation 23 



Crop effects 27 



Remedies 28 



II. Soil moisture Sapping ' 33 



Extent of sapping 33 



Conditions that influence root extent 35 



Effects of sapping 36 



Orchards. 36 



Grainfields 37 



Remedies 38 



III. Soil fertility 38 



Analyses for nitrogen 39 



IV. Mechanical power of winds 40 



Damage to crops 41 



Movement of soils 41 



Drifting of snow 43 



V. Evaporation 43 



Importance of evaporation 44 



Windbreak efficiency determined by evaporation 45 



Results of checking evaporation 51 



Relation to crops 52 



Relation to irrigation 54 



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