
%0 Journal Article
%A Silsbury, JH 
%A Zuill, D 
%A Brown, PH 
%T Effects of temperature on germination, emergence and early seedling growth of swards of Mt Barker subterranean clover plants grown with and without nitrate
%J Australian Journal of Agricultural Research
%D 1984/08/01
%V 35
%N 4
%P 539-549
%K 
%R https://doi.org/10.1071/AR9840539
%U https://www.publish.csiro.au/paper/AR9840539 
%X Effects of constant temperatures of 10, 15, 20, 25 and 30¦C on the germination, emergence and early vegetative growth of Trifolium subterraneum L. cv. Mt Barker grown as swards were examined in temperature-controlled glasshouses and in a growth cabinet. Seedlings were established at a density of about 2000 plants m-2 and grown for up to 70 days. Plants were either inoculated and grown without mineral nitrogen (-N), or supplied with 7.5 mM NO-3 (+ N). Percentage germination and emergence were hardly affected by temperatures of 10-20¦C, but at 25¦C were reduced to 50%, and at 30¦C to about 10%. The rates of germination and emergence were slowest at 10¦C, but showed little change with temperature over the range 15-30¦C. Time to closed canopy (leaf area index 3) and time to a dry weight of 133 g m-2 were shorter where plants were supplied with NO; than where mineral nitrogen was withheld and a symbiotic system established. Rates of N2-fixation, as measured by acetylene reduction assay, were not markedly affected by temperature over the range 10-25¦C. Relative efficiency ranged from about 0.55 at 10, 15, and 20¦C to about 0.66 at 25¦C. At 30¦C nodulation still occurred, but nitrogenase activity was very slight. It is concluded that, where swards of subterranean clover are grown in the absence of any mineral N, a period of N-starvation limits growth during the time taken for symbiotic N2-fixation to become established. Such retardation of growth is small at about 20¦C, but becomes more marked at lower and higher temperatures. The establishment of subterranean clover swards in soils of low N status are likely to be retarded following an early (March) or a late (July) start in the growing season. In such cases a 'starter' application of mineral nitrogen may promote the early growth of the legume. 
