Collaborative soft rot tests: Tests conducted at Princes Risborough and Delft on soil samples from collaborating laboratories

IRG/WP 210

J G Savory

The laboratories which took part in the original collaborative soft rot test (Savory and Bravery, Holz u Org 5 (1) 58-90, 1970) sent samples of the soil used in the original test to Princes Risborough. Portions of this material were sent to Dr Hof for soil analyses at TNO and the remainder was employed at Princes Risborough for the conduct of comparative tests of soil virulence when used as a combined inoculum and nutrient source against beech and pine blocks as in the standard soil burial method. The Princes Risborough tests were conducted on untreated beech and pine sapwood by the methods laid down in Document IRG/WP/208 with the following exceptions: - No leaching was carried out; all test blocks were sterilised and 100 gm of soil were used per test block (2 blocks per 450 ml test bottle). As noted below, the initial soil moisture contents in the test bottles were rather high and incubation at 30°C was maintained for 6 weeks only in initial tests. The soils were moist when received. Their water holding capacities (WHC) were determined by the method given in IRG/WP/208 and are recorded in Table 1 column 2. Inadvertently moisture contents of the test bottles were raised slightly above the established WHCs as indicated in Table 1 column 3. Final moisture contents of the soils (column 4) approximated more closely to the soil WHCs. None the less the final moisture contents of the test blocks (columns 5 and 7) were high and weight losses were not as high in the beech as had been anticipated. In a second test, in which the CTB sand sample was tested along with FPRL soil as control, soil moisture contents were adjusted precisely to the established WHCs. The results for weight losses in the FPRL soil in this instance come up to expectation. Despite the relatively low weight losses in the first test, there were statistically significant differences between some of the soils. In an attempt to ascertain the cause of the low weight losses a further series of tests were carried out using FPRL soil samples. Sets of six replicate blocks were exposed by burial in soil as indicated in IRG/WP/208. Soil moisture contents were adjusted to give a range from relatively dry to very moist and after burial of the test blocks the test bottles were incubated at 30°C for 14 days only. On completion of incubation moisture contents of the test blocks were determined. The results are presented in Figure I. It becomes apparent that with beech there is a tendency towards waterlogging of the test blocks as soil moisture contents approach the WHC, so it would appear that waterlogging has probably invalidated the test results obtained with beech. In contrast waterlogging with pine does not begin until soil moisture contents are in excess of the WHC. Sufficient soil was available to permit a further test with pine blocks using the full 16 week incubation period required by the Document IRG/WP/208. Results from this test are not yet available.


Keywords: COLLABORATION; MOISTURE CONTENT; SOFT ROT; SOIL ANALYSES; SOIL VIRULENCE TESTS; TESTING; WHC

Conference: 72-10-26/28 Berlin (West), Germany (FRG)


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