6 MASS. EXPERIMENT STATION BULLETIN 328 



the Mcintosh plots was increased. The moisture-conserving effect of the mulch 

 was more apparent in dry periods in midsummer and may be more significant 

 than the averages indicate. There was less fluctuation from week to week 

 under the mulch. 



The most astonishing result of these studies was the great accumulation of 

 soil nitrates under the mulch. This has been reported by Beaumont (2 ). The 

 general nature of his results is indicated in Table 1 which gives some averages 

 for the Mcintosh and Wealthy plots. Probably a seasonal average of 30 parts 

 of nitrates per million parts of soil indicates a sufficient supply of nitrogen for 

 the needs of the tree. 



Table 1. — Soil Nitrates under Cultivation and Mulch. 

 (Parts per Million) 



1925 1926 



Mulch Cultivation Mulch Cultivation 



Maxium 89 27 452 83 



Minimum 12 1 29 Trace 



Average 38 10 128 20 



Not only were soil nitrates under the mulch very high during the growing 

 season but they continued high during the fall and winter. In 1926 samples 

 were taken at intervals up to January 15, 1927, when the average from the 

 two mulched plots was 10 p.p.m. During November and December the six 

 determinations of soil nitrates showed between 10 and 160 p.p.m. 



During the years 1928-31 less extensive determinations of soil nitrates were 

 made ( 1) . In these years, while lower than in 1925-26, they were still much 

 higher on the mulched than on the cultivated plots and continued high during 

 August and September. 



Determinations of soil nitrates under a similar mulch in another orchard on 

 a similar soil, beginning with the first application of poor hay, showed no 

 nitrates during the first season, very low nitrates during the second and third, 

 and abundant nitrates during the fourth season. While no measure was taken 

 in the Mcintosh and Wealthy blocks during the early years of mulching, the 

 appearance of the trees indicated a similar condition. No difference in foliage 

 color was noted during the first two years of mulching, but the foliage was dis- 

 tinctly darker green in the third year and this difference continued until nitrate 

 was applied to the cultivated plots in the ninth year of the experiment, since 

 when there has been no noticeable difference in leaf color on the different plots. 



The mulching material contained about 1 percent of nitrogen. In view of 

 the large amounts applied, the nitrogen in the mulch is enough to account for 

 the high nitrates found in the soil. 



Growth of the Trees 



The high soil nitrates continuing through the late summer and fall might 

 be expected to bring about a growth of the trees indicative of a high-nitrogen 

 - low-carbohydrate ratio, excessive growth, and a condition favorable to 

 winterkilling. This is not the case. While there was considerable bark injury 



