Summary 



This is a report on experiments to determine the possible value of waste 

 bark as a soil improver. The bark was used in greenhouse cultures with 

 plants and in field plot tests. 



In the greenhouse, the effect of bark on plant growth was tested both in 

 mixtures with soil and in the pure state. Both pot and bed cultures were 

 employed. Usually it was compared with soil alone as control cultures, and 

 often with peat under similar conditions. The greenhouse experiments com- 

 prise nine sets of cultures, and one of tests of water holding capacity, 



1. A set of pot cultures designed to show the effects on plant growth of 

 varying proportions of bark to soil, and peat to soil, showed that low con- 

 centrations of these organic substances gave better yields than higher ones. 

 Older bark gave higher yields than fresh ones and peat for the first crop 

 (cabbage) and significantly higher yields than soil controls. However, ad- 

 vantages for these additives tended to disappear with successive crops 

 (radish and corn), probably due to decay of the organic matter. 



2. Flower yields of two ornamentals were tested in greenhouse bench 

 cultures with (a) old bark-soil mixture, (b) peat-soil, and (c) soil only. 

 With snapdragons the yield was best in bark and next best in peat. Carna- 

 tions yielded best in the peat mixture. However, none of the differences 

 were very great, probably due to high compost content of the original soil. 



3. Old bark, undiluted with soil but with added fertilizer, was compared 

 with other wood wastes and soil as growing media for cabbage and barley. 

 Yields for both in bark was significantly greater than in soil. 



4. Even old bark will not increase yields of plants in bark-soil mixtures 

 above that of soil controls, unless fertilizer is added. This was demonstrated 

 by growing wax beans in a one-to-two ratio of bark to soil, with no fertilizer. 

 The yield from soil-grown plants was significantly greater. 



5. The statements in 3 and 4 above were further substantiated by results 

 with tomatoes grown in pure old bark in comparison with pure peat and 

 soil. Each was liberally fertilized. The crop in peat was a total failure. Total 

 yields of fruit, as well as size of fruit, was greater in the bark than in soil 

 by a very wide margin. 



6. Pot cultures of cabbage were grown in mixtures of old bark and 

 sewage sludge (no added fertilizer), in comparison to soil. The old hardwood 

 bark-sewage mixtures produced significantly better growth than did soil. 

 Yields in those of old softwood bark were close to yields of the controls. 



7. The root growth of three kinds of seedlings in the four kinds of 

 bark was compared with root growth in other kinds of media, such as sand. 

 Growth was best in old bark, but that in vermiculite was about as good 

 for two kinds of seedlings. 



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8. Tests of old bark, alone and mixed with sand, as rooting media for 

 grape cuttings showed that these media have good possibilities for such use. 

 Bark was also satisfactory for rooting geranium. 



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