PLANT NUTRIENTS AND THEIR ABSORPTION 



111 



effects. These may just about neutralize each other and leave the plants 

 practically uninfluenced by the treatment, or the one influence may 

 greatly outweigh the other. Caution should be exercised, however, in 

 making applications of lime to the orchard. 



Influenced by Methods of Soil Management. — Moreover different 

 methods of soil management, particularly as they effect aeration and soil 

 temperature have a marked effect on nitrate production. 



Gourley and Shunk*' found that "the ratio of nitrates between sod, tillage 

 and tillage with cover crops is as 1 : 5.4 : 10.6 in the surface soil and in the sub- 

 soil as 1 : 3.3 : 3.7. At no time during the experiment have we obtained a 

 sample under sod that showed more than 14.78 parts nitrates per million and the 

 average for the 4 years is 3.18 p. p.m. with an average of 17.40 p. p.m. and for 

 tillage plus a leguminous cover crop it has shown as high as 132 p.p.m. and the 

 average is 33.91 p.p.m. for the 4 years." 



The nitrate determinations showing the result of 4 years' experiments 

 on orchard soils are summarized in Table 12, Whether the small 

 amount of nitrate under sod is the result of reduced nitrate produc- 

 tion or merely the residue from a greater nitrate consumption by the 

 plants constituting the sod, the effect on the orchard trees is the same. 

 Under sod there is but little available nitrate. In Indiana also, it was 

 found that in a young orchard most nitrates are formed under the clean 

 culture-cover crop system of soil management, and the straw mulch 

 ranked next.-"*^ The heavier the mulch, the later in the spring does 

 bacterial activity begin because of the lower temperature and the later 

 in the fall does it persist as a result of the higher temperature of 

 the soil. 



It is probably because of their influence upon nitrate formation that 

 various tillage methods have so generafly proved superior to sod manage- 

 ment methods in promoting both vegetative growth and fruit production. 

 This is true particularly in areas that are more humid or have deeper 

 soils. On the other hand, in sections having a long dry period during 



