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Studies on the Early Growth Rates of Selected Nitrogen-Fixing Trees
|Title:||Studies on the Early Growth Rates of Selected Nitrogen-Fixing Trees|
|Authors:||Macdicken, Kenneth Glenn|
|Abstract:||A series of five species comparison trials were planted in Hawaii and the Philippines during 1981-82. These trials were of the augmented block design and included a total of 23 species of nitrogen-fixing trees (NFT). Height, diameter and wood volume growth were measured at 3, 6 or 12 month intervals. Additional data were collected to allow estimation of the minimum sample and plot sizes required to obtain various levels of precision.|
Leucaena leucocephala and Leucaena diversifolia were the most productive species over all sites in height growth and wood volume. L. leucocephala was more productive than L. diversifolia on the best sites in the trial, while L. diversifolia significantly outgrew L. leucocephala on the less productive sites at Waipio and Niulii. It appears that L. diversifolia is more tolerant to the cooler temperatures at Niulii than L. leucocephala.
Yields of all species were lower at the Waipio site than those at the Waimanalo and Molokai sites, yet wood volume yields of the leucaena species still exceeded 24m3/ha/yr. This suggests that the acidic Ap horizons at Waipio did not severely limit the growth of these species which are thought to be intolerant of acid soils. The fact that Acacia auriculiformis, which is reportedly an acid tolerant species did poorly on the Waipio site further suggests that this soil acidity is not the only important limiting factor at work.
Sesbania grandiflora exhibited rapid early growth overall and equaled at least one of the leucaena species in wood volume yields at every site at one year. Calliandra calothyrsus did not grow as rapidly as expected overall, but was least affected by the cooler temperatures at the Niulii site. Acacia auriculiformis was generally the slowest growing core species at each site and was most severely stunted at Niulii.
Volume prediction equations were derived from 100 sample trees at 3 locations for the replicated species. Three variable equations using easily measurable parameters explained between 89 and 95% of the variation for wood volume.
Of the augmented species, Eucalyptus saligna, Casuarina eguisitifolia. Albizia falcataria and Acacia mearnsii merit inclusion as replicated species in all future trials.
Assuming height, basal area and wood volume are all characteristics which must be measured over time in future NFT trials, a minimum sample size of 20 samples per plot is required to attain an estimate with a margin of error of less than 20 % for all of the measured characteristics. Ten samples per plot appears adequate for site adaptability trials utilizing height as a measure of species adaptation.
Border effects were found between border and data rows in the 28 m2 plots used in these experiments. The minimum plot size required to supply 20 samples per plot appears to be 72 m2 assuming border effects to be severe before two years of age on some sites. The use of 8 x 9 row plots would insure the availability of 20 samples free of border effects.
|Appears in Collections:||
M.S. - Agronomy and Soil Science|
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