Growth of Subterranean Clover in a Range Soil as Affected by Microclimate and Phosphorus Availability. III. Comparative Growth of Subterranean and Rose Clovers at Cold Soil Temperatures1
- Charles A. Raguse and
- Kenneth L. Taggard2
The biological yield potential of winter annual range legumes is influenced by the timing of rainfall adequate to ensure germination. If rains are late, the establishment phase of growth must occur at cold soil and air temperatures. On low-P soils, this combination of abiotic factor constraints can limit symbiotic N fixation.
We conducted three controlled-environment experiments to compare the seedling growth of rose clover (Trifolium hirtum All., ‘Hykon’) and subterranean clover (T subterrateum L., ‘Mt. Barker’, hereafter referred to as subclover) on a P-deficient soil (Sobrante-Las Posas association), simulating winter conditions of cold soils and low light. Comparative growth responses, especially intraplant dry matter partitioning and nodulation, were observed for several soil P availability levels.
A sunlit phytotron provided a common shoot environment of seasonal (fall/winter) ambient light intensity and photoperiod, with a programmed smooth diurnal temperature cycle of 20 C maxunum and 5 C minimum. Three independently-controlled water baths maintained soil temperature experiments at a constant 5 C, a constant 10 C, and a diurnal 5 C to 10 C alternation. Phosphorus levels were 0, 45, 90, and 180 kg/ha equivalents. Growth intervals (5 ± 0.5 trifoliolate-leaf stage), varied between 58 and 114 days.
Leaf area of subclover was greater than that of rose clover, and responded more to increasing P levels. Leaf areas tended to increase with higher soil temperatures. Nodule weight was positively correlated with leaf area; nodule weight:leaf area regressions suggested that nodule development was adequate at 5 C and that nodule development was primarily related to time rather than to morphological development of the shoot. Nodule weights were similar for the two species, and low at 0 P.
The results suggest that while the practical soil threshold temperature for overall growth is near 5 C, some intraplant growth processes may proceed, but only at adequate, availability levels of mineral nutrients. These relationships may be particularly important where range annual legumes are being introduced as part of a more general range improvement program.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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