THE AMERICAN GRAPES. 249 



have impressed the belief that the spring plowing 

 between the rows of bearing vines should not be deeper 

 than four inches. Many grape-growers in the prairie 

 States use the plow before pruning and laying down the 

 vines in the fall, turning the furrows toward the rows as 

 a help in protecting the roots over winter. This also 

 favors the work of laying down the canes and banking the 

 crowns (233). 



With the fall plowing the culture in the spring is 

 deferred until the vines are tied up and the weeds start in 

 the rows. The hoe is then used and the after culture is 

 wholly with the cultivator and harrow. 



238. Need of Humus in Cultivated Soils. In speaking 

 of soil selection (228) the need of fertilizing soils after 

 several crops have been gathered was indicated. In this 

 connection the absolute need of humus in the soil con- 

 tinually cultivated must be considered more in detail. 

 Even on good corn soils continued culture soon uses up or 

 "burns out" the fresh vegetable humus that has much to 

 do with the physical texture of the soil. An experiment 

 conducted by the writer illustrated this fact forcibly. For 

 a period of five years crops were grown on half an acre of 

 quite rich prairie soil that could be taken away, including 

 the roots,. such as beans, currant cuttings, and apple and 

 plum seedlings. The sixth year the plot including the 

 adjacent field with the same soil was sown to barley. The 

 crop made fine growth on the untreated ground, but did 

 not get high enough on the experimental plot to be reached 

 by the cutting sections of the reaper. In this case the 

 beans gave nitrogen to the soil, but nothing was left to give 

 the heeded humus. In the orchard the use of cover-crops 

 (126) give nitrogen and a plentiful supply of humus to the 

 soil. In the vineyard the cover-crop cannot be used and 

 we must rely on barnyard manure with possible use of 



