BULLETIN 1059, U. S. DEPARTMENT OF AGRICULTURE. 



Measurement of environmental con- Page, 

 ditions affecting vegetation — Con. 

 Solar radiation — light — Contd. 

 Apparatus and methods for 

 radiant energy measure- 

 ments — Continued. 

 Spectroscopic measure- 

 ments 56 



Spectro-photographs 57 



Spectro-bolometer 58 



Evaporimeters 58 



Instruments 59 



Precipitation 60 



Exposure of gauges 60 



Snow depths '61 



Snow-scale readings 61 



Tabulation , 63 



Instruments 63 



Soil moisture and soil qualities- 66 

 Osmosis as a factor in water 



absorption 66 



Problems and some definitions- 71 

 Total moisture determinations 73 

 Soil wells for representa- 

 tive points 73 



Technique of periodic sam- 

 pling 76 



Determination of non-avail- 

 able moisture 79 



Direct determination of 



wilting coefficient 80 



Indirect methods for wilt- 

 ing coefficient 84 



Capillary moisture 85 



Moisture equivalent 93 



Hygroscopic coefficient __ 97 

 Calculation of the available 



moisture 100 



Availability of the moisture. 101 



Coefficient of availability__ 101 

 Osmotic pressure in plant 



tissues J.03 



Method of determining 



freezing points 107 



Osmotic pressure in soils- 109 



Vapor transfer in soils- 109 



Vapor transfer method- 112 



Computing the coefficient- 12* 



Other soil properties to be 



studied 121 



Acidity and alkilinity 121 



Hydrogen-ion concentra- 

 tion 122 



Mechanical analysis of soils 12ft 



Determination of humus 126 



Loss on ignition 127 



Ammonia-soluble humus. 127 



Measurement of environmental con- Page, 

 ditions affecting vegetation — Con. 

 Soil moisture and soil qualities — 

 Continued. 

 Other soil properties to be 

 studied — Continued. 



Capillary conductivity 128 



Chemical analyses for nu- 

 trients 129 



Summary of soils discussion- 136 



Special equipment 142 



Atmospheric humidity 143 



Instruments 146 



Wind movement 146 



Instruments 150 



Evaporation 151 



Objects and nature of evapo- 

 ration measurements 151 



Instrumental methods 154 



Free-water surface 154 



Measurement 154 



Nonfree-water surface 155 



Piche evaporimeter 155 



Porous cup atmometer 156 



Slave's nonabsorbent por- 

 ous-cup atmometer 157 



Standardization 159 



Computation of field re- 

 sults 159 



Exposure 160 



Forest Service evaporim- 

 eters 161 



Observations 162 



Tabulation 163 



Direct transpirationmethod- 164 



Cobalt-chloride method 164 



Method of excised twigs- 165 



Method of potted plants- 166 



Instruments 168 



Phenology 168 



External field observations 170 



Internal or physiological observa- 

 tions 171 



Field observations, photographs, and 



maps 172 



Appendices 175 



A. Vapor pressure tables for ba- 



rometric pressure 21.42 



inches 175 



B. Osmotic pressures and freez- 



ing-point depressions 198 



C. Titration methods for alka- 



linity and acidity 199 



Alkalinity test 199 



Acidity test 200 



List of references 202 



INTRODUCTION. 



OBJECT. 



Forestry, like engineering or medicine, is largely an applied 

 science. Its development is based on fundamental knowledge of the 

 Knowledge of the tree itself is purely botanical 



natural sciences. 



