Timely Hints for Farmers. 73 



in No. i of "Timely Hints," where alfalfa for summer and "sour" 

 clover for winter are recommended. 



But it must not be supposed that humus once added to the 

 soil is permanent. Eternal vigilance is the price of humus, for it 

 has enemies. The hot, dry desert air burns it up, and water con- 

 taining the much dreaded black alkali dissolves it and carries it 

 away. 



The effect of heat upon humus may be seen by contrasting 

 the soils of Arizona with those of Montana. The soils of Mon- 

 tana are alkaline, and the climate is arid and largely cold; the soils 

 of southern Arizona are likewise alkaline, and the climate arid 

 but hot. The average humus in 39 Montana soils is 3.32 per cent: 

 in 20 Arizona soils it is .65 per cent. This great difference is 

 chiefly due to the difference in temperature of these two states. 



To prevent the loss of humus through the sun's action it is 

 necessary to grow cover crops which shall protect the ground from 

 the sun's direct rays, especially in hot, dry weather. Thus far 

 the results at the Experimental Farm favor cow peas for summer and 

 "sour" clover for winter. The broad leaves of the cow peas seem 

 specially effective in shading the ground, while the plant is also 

 valuable as a green-manuring and forage crop. 



It is a matter of almost common observation that grain, roots, 

 and even trees do better upon old alfalfa ground than upon virgin 

 soil, a fact largely due to the enrichment of the soil in humus and 

 nitrogen and its improvement in tilth in the ways stated above. 

 In 1898, during the work of the Experiment Station with sugar 

 beets it was noticed that the beets coming from old alfalfa 

 ground were richer in sugar and of greater purity than those from 

 virgin desert soil. On the Experimental Farm a careful observer 

 can see the effect of one year's green-manuring in a small peach 

 orchard. 



It may be stated, in conclusion, that green-manuring is a 

 leading means for the improvement of most Arizona soils in tilth, 

 and in their humus and nitrogen content. 



R. H. Forbes, 



Department of Chemistry. 



