54 MASS. EXPERIMENT STATION BULLETIN 209. 



acre. This amount of bone supplies only about one-tenth as much nitrogen 

 as plot 1 has received, and j^et it is doubtless enough to account in part, 

 at least, for the greater growth than that observed on the unfertilized 

 plot. The uniformity of the several potash plots in the Graves orchard 

 indicates that this may have been a nitrogen response rather than one to 

 potash. All indications are that the Graves orchard soil is deficient in 

 nitrogen, and a small supply of this element might be expected to produce 

 marked results. 



The relatively strong growth of the trees on the ashes plots and on the 

 slag-sulfate plot in the Graves orchard indicates that added nitrogen 

 cannot wholly account for the greater growth of the fertilized trees. 

 Probably the presence of lime has favored greater availabihty of the 

 nitrogen-carrjdng humus, even though this may have been present in 

 only small amount in this soil, and so operated to increase the nitrogen 

 available for the trees. The striking response to cultivation of the trees 

 on the unfertilized plot in the station orchard may be fairl}^ taken to 

 indicate that lime is not always necessary to render the humus nitrogen 

 available. 



Manure has had a more persistent residual effect in both orchards than 

 the other materials used. Evidently the effect of greater nitrogen supply 

 because of cultivation, on plots not receiving manure, lasted about five 

 years, after which the nitrogen supply was insufficient to maintain the 

 increased growth of the trees. 



The fact of inferior growth and production of the muriate plot in the 

 station orchard as compared with the low-grade sulfate plot is interesting, 

 and seems to have been peculiar to sod mulch management. Its inferiority 

 apparently disappeared when the soil was cultivated. There is no evidence 

 of such a difference on the lighter, better-drained soil of the Graves orchard. 

 It is probable that this superiority of the low-grade sulfate was a real one. 

 It has been suggested that the difference was due to the poorer drainage 

 of the muriate plot. But the adjoining unfertilized plot is still more in- 

 ferior in this respect, and yet this plot gave very good results when strip 

 cultivation was adopted. It has been shown that muriate of potash may 

 exert a depressing effect on nitrification, and this may possibly explain 

 the results obtained. The attempt to explain whether this difference was 

 due to the difference in the form of potash or to the presence of magnesium 

 in the low-grade sulfate was unsuccessful, as no significant differences were 

 obtained in the Graves orchard even with the trees in sod. The Graves 

 orchard received a lighter application of potash and for a shorter period 

 of years. Possibly this may have been a factor in bringing about different 

 responses. 



Summary. 



1. In the two orchard experiments here reported, growth and fruit 

 production were closely correlated. Increased growth was followed by 

 increased production. 



2. In one of the orchards, trees in cultivation gave better growth and 

 higher production than when in sod. 



