Root morphology and phosphorus requirements of 12 tropical pasture species grown in a controlled environment

Jonathan W. McLachlan; Richard J. Flavel; Chris N. Guppy

doi:10.1071/CP25049

RESEARCH ARTICLE (Open Access)

Next Contents Vol 76(9)

Root morphology and phosphorus requirements of 12 tropical pasture species grown in a controlled environment

Jonathan W. McLachlan

^A ^* , Richard J. Flavel ^A and Chris N. Guppy ^A

+ Author Affiliations

- Author Affiliations

^A School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia.

^* Correspondence to: jmclach7@une.edu.au

Handling Editor: Brendan Cullen

Crop & Pasture Science 76, CP25049 https://doi.org/10.1071/CP25049

Submitted: 20 February 2025 Accepted: 21 August 2025 Published: 16 September 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

Tropical pasture species are often established in phosphorus (P)-deficient soils that can limit plant productivity and persistence. Little is known about the root traits and critical P requirements of many tropical grasses and legumes. Characterisation of these traits would allow P-efficient species to be used when soil fertility is poor and agricultural inputs are limited, or for important root traits to be considered if selecting for P efficiency.

Aims

To assess the shoot yield, root morphology, P acquisition and critical P requirements of a range of commonly grown tropical pasture species.

Methods

Five tropical grasses and seven tropical legumes were grown in pots containing a light-textured, low-P soil to investigate shoot growth and root traits in response to applied P (0–120 mg P kg⁻¹ soil).

Key results

The shoot yield of each species increased in response to applied P, yet there were differences in maximum shoot yield (1.7–9.8 g DM pot⁻¹) and critical external P requirements (12.8–38.0 mg P kg⁻¹ soil) among the species. The acquisition of P was associated to varying degrees with the development of root length when plants were grown in soil that enabled near-maximum growth (e.g. R² = 0.71–0.77 for the grasses and R² = 0.14–0.43 for the legumes in the 15–30 mg P kg⁻¹ soil treatments).

Conclusions

Longer roots were associated with higher shoot yields and better P-acquisition efficiency, and the grasses generally had comparable or lower critical P requirements than the legumes.

Implications

Phosphorus-efficient species should be used when soils are known to be P deficient, or where P fertilisation is not an option, and grasses and legumes could be paired on the basis of their P requirements.

Keywords: biomass allocation, C₄ grasses, critical phosphorus requirements, pasture production, phosphorus-acquisition efficiency, phosphorus fertiliser, root traits, tropical legumes.

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