The Influence of Waste Bark on Plant Growth 



By STUART DUNN 



Plant Physiologist 

 New Hampshire Agricultural Experiment Station 



Introduction 



MANY pulp and paper manufacturers, including the Brown Company, 

 Berlin, New Hampshire, have to dispose of several tons of fresh bark 

 produced at the mill every day. Present practice is to truck it away and 

 dump it. This necessitates the use of trucks, grading equipment and labor. 

 Experiments, therefore, were started in an effort to discover, if possible, a 

 profitable outlet for waste bark, including possible benefits to agriculture 

 through soil improvement. 



A search of the literature reveals that very little work has been done on 

 the effects of bark from pulpwood on soil and plants. Very little has been 

 published on the subject. Rettie and Simmons (6) report that water-soaked 

 bark, as it comes from the barking drums, contains upwards of 80 percent 

 moisture. In this condition the fuel value is almost nil. Other reviews (5) 

 indicate that bark may have possible industrial uses as well as soil building 

 potentialities. 



Studies with sawdust (1, 3, 4, 7) applied either directly to soil or as 

 compost show that when well decomposed it may in either case benefit 

 plant growth. 



The experimental work with bark may be divided into two parts: (1) 

 that dealing with greenhouse pot and bench cultures, and (2) field plot 

 trials, and will be considered in that order. 



Part I Greenhouse Cultures 



Effects on Plant Growth of Various Ratios 

 of Bark to Soil and of Peat to Soil 



An attempt was made to determine what proportion of bark or peat mixed 

 with soil is necessary for optimum plant growth, compared to soil alone 

 as control. Peat was used in this and many subsequent tests because it is 

 a standard merchantable organic material used as a soil improver, and bark 

 would have to compete with it in the market. The bark materials used were 

 of four types: new softwood bark, new hardwood bark, old softwood bark, 

 and old hardwood bark. The term 'new' means that the bark was fresh 

 from the mill; the term 'old' means that it had been standing in piles for 

 several years and was partly weathered and decomposed. Some of this latter 

 material was in a fine powdery condition. The concentrations used for each 

 of these and for peat were 10, 30, and 50 percent by volume as shown in 

 Table 1. Each was thoroughly mixed with soil in these proportions. Enough 

 of each mixture was prepared to fill 10 pails of 14-quart capacity. These 

 pails were previously coated on the inside with a waterproof varnish. 



