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Abstract

The acetylene reduction (AR) assay and a N dilution
technique have been used to estimate N2 fixation by temperate
pasture legumes growing in association with grasses under
field conditions at two sites on the Central Plateau of Tasmania.
An in situ approach which avoided intensive and destructive
sampling was developed for conducting routine. AR assays.
Using this approach seasonal and diurnal patterns of ni trogenase
activity were determined for two clovers, Trifol i um
ambiguum M.bieb. and T. repens L., at one site (Stone Hut )
and for T. repens at a second site (Penstock). The seasonal pattern of nitrogenase activity followed
closely the general growth pattern of the clovers. Nitrogenase
activity was very low from late autumn to early spring as
a result of low temperature (< 5 ° C), but increased rapidly to
be at maximum levels during late spring and early summer.
Activity declined to a low level in mid-summer which coincided
with low soil moisture content. There was a second but much
smaller peak of activity in autumn as soil moisture conditions
improved, and before the onset of winter temperatures. Severe
defoliation of relatively mature plants caused a reduction in
ni trogenase activity and, combined with low soil moisture
conditions, delayed considerably the recovery, of activity. Diurnal variation in nitrogenase activity was demonstrated
for both species under natural field conditions. Overall
these fluctuations were more closely related to soil than air
temperature, and T. repens showed a more variable response
to diurnal variation in environmental conditions than T.
ambiguum.

Item Type:	Thesis - PhD
Authors/Creators:	Lane, PA
Keywords:	Nitrogen, Soils, Clover
Copyright Holders:	The Author
Copyright Information:	Copyright 1984 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.) - University of Tasmania, 1984. Bibliography: leaves 207-236
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