CULTURAL METHODS IN ORCHARDS 



163 



where the system of tillage and cover-crops was practiced, 

 and the straw mulch ranked second to the tillage plots. 

 While not indicated in the data in the above table, very- 

 little nitrate was found in late fall and winter, but nitrifica- 

 tion continued later in the fall in the warmer soil under the 

 straw mulch than elsewhere. The gains made by the trees 

 in this experiment were roughly proportional to the nitrate- 

 content of the soil. 



The New Hampshire Station reports the same results, al- 

 though the averages are lower in all cases. The averages in- 

 clude samples taken each week throughout the growing sea- 

 son for the four years and this may account at least in part 

 for the difference. The following table and Fig. 28 epitomize 

 this work: 



Table XLII 



summary of nitrate determinations, water soluble parts to the 



million of dry soil 



Average to a plot 



Surface soil 



