65 



This fxperiinent has a direct practical licarin<T on the question of goil ventilation. 

 Soil air is essential to the life uf nitrifying and other bacteria which develop fertility. 

 Other things equal, the more readily soil will allow air to circulate through it, the 

 more favorable conditions will Ije for t!u' formation of plant food. 



• l-'iii. 1-3.— Apparatus U< deterniiiiu the ratt- uf tluw ni air thnjugh siiil<. 



ExperhiH'ut No. 7. 



EFFECT OF MULCHES OX EVAI'OKATIOX OF WATEli KKOM SOILS. 



The cylinders (tig. 16) are IS inches deej) by 4 inches in diameter, and are tilled 

 with tirst bottom S(jil from the Ohio State University faruL The compacting 



Fig. 16. — Soil tubes for showing the effect of mulches on evaporation of water from soils. 



machine was used in lilling the cylinders to insure coujparatively uniform compact- 

 ness of soil in all cylinders. 



No. 1. Not mulched. 



No. 2. Not mulched. 



No. o. Surface cultivated 2 inches deep. (Soil mulch). 



No. 4. Surface cultivated 2 inches deep. (Soil mulch). 



No. 5. Mulched with 2 inches of coarse gravel. 



No. 6. Mulched with 2 inches of tine sand. 



No. 7. Mulched with 2 inches of sawdust. 



No. 8. Mulched witli 2 inches of cut straw. 



26777— No. 127—03 5 



