Section 8
Chapter 7,653

Phosphorus efficiency in pasture species iv. yield efficiency parameters and partitioning of phosphorus in two white clover accessions under varying levels of phosphorus supply in solution culture

Blair, G.J.; Wilson, E.J.

Australian Journal of Agricultural Research 41(6): 1071-1082


ISSN/ISBN: 0004-9409
Accession: 007652060

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An experiment was conducted under controlled environment conditions in nutrient solution over four P levels (1, 4, 8, 16 .mu.mol P m-3) to evaluate the yield performance and P uptake of two accessions of white clover (Trifolium repens). The two accessions used were Naturalized, which was grown from a seed collection made from a low P soil on the Northern Tablelands of N.S.W., and cv. Ladino. Nutrient solutions were renewed when the P concentrations fell by a maximum of 10% and were pumped so that there was a flow rate of 4.4 L min-1 over the plant roots. The shoot and root fresh weight of yield of Ladino was higher than Naturalized at all P levels. At 16 .mu.mol P m-3 the shoot yield of Ladino was fourfold that of Naturalized; however, the relative yield response of Ladino between 1 and 16 .mu.mol P m-3 was only 20% of the response of that in Naturalized. Phosphorus uptake was highest in Ladino at all P levels. The minimum shoot labile P concentrations recorded in this study were 1.1 and 2.5 .mu.mol P g F.wt-1 for Ladino and Naturalized respectively, indicating that Naturalized is capable of maintaining relatively high soluble tissue P levels under low P supply. The generally higher labile, lipid and residue P levels in new leaf, old leaf, stem and root in the Naturalized white clover accession indicate a lower efficacy of nutrient utilization in this collection compared to Ladino. In contrast to Ladino, Naturalized white clover may be able to control its P accumulation at high levels of supply, as toxic levels do no accumlate in old leaf. Ladino was the more efficient accession when P efficiency was defined as shoot yield per unit of P in solution. When P efficiency was defined as shoot or plant yield per unit of P absorbed or as the inverse of P concentration (utilization quotient), Ladino was the more efficient accession at 1 and 4 .mu.mol P m-3, with only small differences between the accessions at 8 and 16 .mu.mol P m-3. The results suggest that Naturalized may be adapted to low P supply through its low inherent growth rate which lowers its demand for exogenous P.

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