19191 H0RTI0T7LTUBB. 739 



hut the clean culture cover crop plat, which has made an equally good tree 

 growth, has lost in organic matter. 

 Variations In soil temperature under different systems ol managemenl showed 



no direct relation to tree growth. The Influence ol the bacterial population of 

 the soil upon tree growth has been difficult to determine, but there is an indi- 

 cation that the field efficiency (ratio between tin- nitrates present In the Held 

 and the nitrifying power of the soil) does hear a relation to tree -rowtlt. 



The results of pruning experiments are still inconclusive as regards tree 

 growth when measured by circumference increase. Seme new experiments 

 bave been planned with the idea of removing several trees From time to time 

 to determine the actual plant tissue laid down in new wood under different 

 systems of pruning. In the work at Laurel lightly pruned trees bave pro- 

 duced more fruit, and fruit of a higher color, than heavily pruned trees, al- 

 though the average size of the fruit was slightly smaller. The pruning work 

 at Bedford continues to show that heavy cutting hack of the annual growth 

 results in smaller gains in trunk girth than are made by trees nol SO cut hack. 



The cover-crop experiments conducted at the station have shown, as a whole, 

 that the most important consideration in choosing a cover crop is to select one 

 which can be depended upon to produce a large annual yield of cover material 

 in tin- locality in which it is expected to he grown. The trees have reacted 

 very favorably where the ranker growing cover crops were used, and in all 

 cases the trees of the bare check plats made the least growth. The various 

 cover crops under investigation had marked effects on the bacterial content 

 of the soil and on the nitrates present in the soil during the growing periods 

 of the trees. In the fall and winter the number of bacteria in soil carrying a 

 .•over crop is greater than where no cover crop is present. Nitrification is 

 greatest on the plats where cover crops are grown, and starts much quicker on 

 those plats where green rye is turned under than on the others. The effects 

 of the cover crop in general are to increase the bacterial activities of the soil 

 rather than to increase the soil organic matter. 



In order to throw more light on some of the problems of soil aeration and 

 the relation of decomposition of organic materials to plant nutrition suggested 

 by the orchard soil management investigations, controlled greenhouse experi- 

 ments in Wagner pots were conducted with peppers, lettuce, and string beans. 

 The results of the carbon dioxid treatment with the different plants are noted. 

 They indicate, in brief, that the effects of carbon dioxid appeared to be to 

 increase the available plant food in the soil, thereby increasing soil acidity; 

 to prevent normal root development of the plants; and to allow 1 gm. of dry 

 matter to be produced on much less moisture than is normally the case. As 

 applied to orchard soil management it appears that the addition of organic 

 matter, instead of increasing soil moisture, allows larger crops to be grown 

 on less moisture than otherwise would be the case, this being due to the carbon 

 dioxid present and the measured bacterial activities of the soil. 



Incubation tests have shown that those plats having the more compact con- 

 ditions of soil contain the largest percentage of carbon dioxid surviving or- 

 ganisms. Extensive tests were made to determine the best media for the 

 cultivation of soil micro-organisms. The results of these tests indicate that 

 bacteria multiply excessively in neutral or alkaline soils containing decompos- 

 able organic matter that is of a carbohydrate nature. 



Work was undertaken with a number of greenhouse crops to determine the 

 effect of variation in the quality and abundance of plant food in the soil on the 

 composition of the plant and its fruit. The experiment is essentially a com- 

 parison of manure, with and without chemical fertilizers, and fertilizers in 



