The importance of roots and rhizomes as storage organs of nutrients in the persistence of Caucasian clover

Abstract

Caucasian clover is the only one of nine sown legumes species still persisting in the absence of maintenance fertiliser in a fertility gradient field trial established by FRI at Mt. Possession Station, mid Canterbury in 1979. The aim of this study was to quantify the underground biomass of Caucasian clover and determine the role it plays in the storage of P, S, N and starch in relation to persistence.

Caucasian clover plants were collected in February 1993 from 6.25, 50, 200 and 800 kgha ⁻¹ applied P treatments and analysed for below-ground biomass and P, S and N content. Additional root material was collected in April and total starch in taproots, old and new rhizomes was measured.

Total root biomass in the 800, 200, 50 and 6.25 kgha ⁻¹ P treatments were over 20, 15, 2.5 and 0.8 t ha ⁻¹ respectively. Percent P, Sand N was less than 0.29, 0.12 and 2.25 respectively but P level was significantly higher in the 800 kg P treatments. Total nutrient storage in underground biomass was substantial with 58, 22 and 455 kgha ⁻¹ of P, Sand N respectively stored in the 800 kg P treatment.

Total starch was about 20% of dry matter with little difference between taproot, new and old rhizome.

Caucasian clover growth in the 6.25 kg P plots that contained coniferous trees was more vigorous than clover in plots without trees and was found to have higher root and top biomass. Soil samples were collected at three increasing distances from the tree and at two depths, and analysed for total, inorganic and organic P. Although total P levels were similar, inorganic P at 20 cm depth was highest at 0.35 m from the tree and decreased at 0.70 and 1 m distance. The higher level of plant available P in the soil under the tree was not reflected in increased root P% in Caucasian clover. However a total of 2.5 kg P per hectare was stored in the clover root biomass compared to only 1.5 kg in the minus tree treatment. It is suggested that this higher level of inorganic P was an important factor in the improved clover growth under trees.

The extensive underground biomass and the storage of nutrients within it was concluded as playing a large role in the persistence of Caucasian clover.