4 THE HANDBOOK FOR PRACTICAL FARMERS 



down the soil may lose its loose friable structure and take on 

 a poor physical condition. Plowing a field when it is too wet 

 breaks down the crumb structure and puddles the soil, causing 

 it to form hard clods and making it difficult if not impossible to 

 prepare a good seed-bed. Old poorly farmed land that has been 

 depleted of its organic matter is very difficult to keep in good 

 tilth and may become very compact at the surface as the result 

 of heavy beating rains. 



The following treatments are most effective in bringing old 

 worn lands back into good condition and keeping them in good 

 tilth after they have been restored : (1) Plowing in the fall and 

 winter and thus exposing the soil to alternate freezing and thaw- 

 ing in the northern states; (2) working organic matter such as 

 stable or green manures into the soil; (3) providing good drain- 

 age; (4) applying liberal amounts of lime; (5) plowing down 

 clover or grass sod frequently; and (6) working the soil only 

 under proper moisture conditions. 



The ease with which a soil can be tilled is very frequently a 

 matter of as much imjDortance as the question of fertility and 

 is dependent on the texture and condition. Soils of fine texture 

 are much more difficult to keep in condition than sands and 

 sandy loams. The latter can be plowed earlier in the spring and 

 w^orked with much more water in them than can the clays and 

 clay loams. Similarly, soils that are rich in organic matter, 

 such as sod land, can be plowed earlier and worked under a 

 wider range of conditions than soils that are deficient in organic 

 matter. 



Pore space and soil moisture. — The space occupied by the 

 soil is taken up, partly by the soil particles themselves, partly 

 by air, and partly by water. About one-third of the total space 

 occupied by sand and about one-half of that occupied by clay is 

 taken up by the soil particles themselves, the remainder being 

 occupied by air if the soil be dry. For the best growth of crops 

 about half of the space not occupied by the soil particles should 

 be taken up by water. For the proper growth of staple farm 

 crops, a fertile soil must have a certain proportion of these con- 

 stituents at all times. If there is too much soil there may be a 

 deficiency of water or air or both, while if there is not sufficient 

 soil the pore space may be so great as to permit the leaching 

 out of plant food materials and the soil will be unable to retain 

 sufficient moisture to meet the demands of the growing crop. 

 B-eavy clay soils have a larger total volume of pore space than 

 sands, but the individual spaces are so small that they are more 



