152 Irrigation and Drainage 



grow slowly, until time enough shall have elapsed for 

 the processes of fermentation to be set up in the green 

 crop which shall reconvert it into available plant- 

 food. But if the spring should chance to be a dry 

 one, so that the crop of green manure has itself left 

 the soil deficient in moisture, or if the capacity of the 

 soil for moisture is naturally small, then there will be 

 present in the soil neither moisture enough to make 

 the green crop turned under ferment rapidly, nor to 

 enable the planted crop to make the best growth, even 

 where there is an abundance of plant -food in the 

 soil. 



The sowing of a catch crop in the fall in humid 

 climates is not open to the same objection, for then 

 this crop has a tendency to gather up available ni- 

 trates which develop during the warm part of the fall, 

 after the crop has been taken off the ground, and to 

 carry them through the winter in an insoluble form, 

 so that they are not lost by drainage. But to bring 

 them into requisition, especially if the season or soil 

 is at all dry, it is important that this should be turned 

 under early, and a sufficient interval of time allowed 

 to intervene for fermentation to take place before the 

 seed of the new crop is put upon the ground. 



In sub -humid climates, on soils that are not sub- 

 ject to washing, it is very doubtful if there is any 

 advantage to be gained from catch crops, as such, 

 even when sown in the fall ; for in those cases there is 

 neither winter nor spring leaching of the soil, and as 

 there is naturally a deficiency of soil moisture, the indi- 

 cations are that very early fall plowing, to develop a 



