162 



POMOLOGY 



portance to the orchardist. A system of cultivation which 

 will maintain a sufficient supply of nitrates and produce a 

 good growth of the trees together with high yield is to be 

 sought. The effect of the standard cultural methods in this 

 regard seems to be marked. (Fig. 28.) 



In several investigations in both young and mature or- 

 chards, it has been found that the amount of nitrates under 

 sod is likely to be very low, in fact so low as to be the lim- 

 iting factor in production. However, Lyon and Bizzell 

 have shown that nitrification is not depressed when leg- 

 uminous crops are grown, in contrast to the conditions un- 

 der rye and the grasses. When the soil on which grass has 

 been growing is stirred by cultivation, the nitrates are 

 greatly increased, especially when a leguminous crop is 

 plowed into the soil annually. In cases in which the moisture 

 is conserved also, the results of cultivation on the orchard 

 are likely to be very beneficial; in fact, this practice is usu- 

 alty one of the first steps in orchard renovation. 



The following data indicate the results of the investiga- 

 tions along this line: 



Table XLI 



NITRATES IN LAUREL SOIL [PARTS (NO3) PER MILLION PARTS SOIl] 



average of 8 determinations made during growing seasons op 

 1914, '15, '16. (adapted from woodbury et al.) 



Here, as in the experiments that follow, it was found 

 that nitrates were reduced under grass land and also under 

 rye as a cover-crop. The highest nitrates were present 

 1 Seven determinations only. 



