Grade. 

 Date. . 



EXERCISE 24 (63) 



Optimum and Critical ]\Ioisture 



Purpose. — To determine optimum and critical moisture content and amount 



of available moisture in different soils. 

 Optimum moisture content is that amount of water in the soil with which a 



plant is able to make its best growth. 

 Critical moisture content is the minimum amount of water with which a plant 



is aljle to survive. 



PLAN 



1. Take five one-gallon glass battery jars (or tin cans) having a small hole 



close to the bottom. Into the hole fit a drain tube made of glass tubing 

 with a glass-wool filter at the inner end, so that it will take licjuid from 

 the lowest place in the jar. 



2. Weigh each jar and record weight. 



3. Fill each jar to within one inch of the top with soil compacted to a moder- 



ate degree. Use the sand, sandy loam, loam, clay and muck. 



4. Pour the soil out and mix with water until the soil is in the best possible 



field condition. Keep careful record of the amount of water added to 

 each soil. 



5. Fill the jars with the moist soil and weigh. 



6. Plant five kernels of corn three-fourths of an inch deep in each jar. 



7. Cover the tops of the jars with oilcloth or waxed paper to prevent evapora- 



tion until the com is up. 



8. Water them at intervals when necessary, adding enough water so that a 



drop or two will be forced out at the drain. Always add the same amount 

 of water to each pot. 



9. When the corn is a foot high, cease watering antl record the number of 



days before the plants commence to wilt. 

 10. Then empty the pots and determine the amount of capillary moisture 

 in each soil. 



