CULTURAL METHODS IN ORCHARDS 



165 



Table XLIII 



nitrates, parts to the million op dry soil 



surface soil 



These results are not in accord with the findings of some 

 writers ^ who state that neither moisture nor nitrates are 

 influenced by cultivation. The chief reason given for loss 

 of moisture and nitrates is the weeds that utilize them, 

 and if the weeds are removed, it is contended, the nitrates 

 will be found as abundantly with no tillage as with it. 

 An explanation of these observations in regard to mois- 

 ture is suggested by Lyon - as follows: "It seems possible 

 that the latter result may occur only in those regions in 

 which conditions are such that a natural mulch is formed 

 by a rapid diying of the surface soil in which process mois- 

 ture is removed so rapidly that the capillary colmim is 

 broken and further loss of moisture is stopped. This would 

 confine it to semi-arid and arid regions of high summer 

 temperatures." 



139. The toxic theory. — It is accepted at the present 

 time that toxic substances are found in certain soils, i. e., 

 compounds poisonous to certain plants. Lack of soil aera- 

 tion, proper "sanitary" conditions, or poor drainage seems 

 to explain their existence. Some writers hold that the whole 

 problem of soil fertihty is largely one of toxicity, and that 

 the application of the various fertilizers merely results in 

 neutralizing the toxic effect. This theory has been used 



iCall, L. E., and M. C. Sewell. Jour. Amer. Soc. Agron. Vol. 10, 

 No. 1, Jan., 1918. 



2 Lyon, T. L. Soils and Fertilizers. Rural Text-Book Series. 



