Soil acidity and nutrient deficiency cause poor legume nodulation in the permanent pasture and mixed farming zones of south-eastern Australia

Document Type

Article

Publication Date

10-26-2019

Journal Title

Crop and Pasture Science

ISSN

1836-0947 eISSN: 1836-5795

Keywords

CEC, field survey, inoculant, N2 fixation, rhizobia, soil constraints

Disciplines

Agronomy and Crop Sciences | Plant Breeding and Genetics

Abstract

Pasture legumes must be adequately and effectively nodulated in order to reach nitrogen-fixation targets. Of 225 pasture paddocks sampled across the Central Tablelands, Central West, Monaro and Riverina regions of New South Wales, 93% had inadequate legume nodulation. Legume content was significantly higher in the mixed faming zone (>50%, Central West and Riverina) than the permanent pasture zone (26%, Central Tablelands; 28% Monaro). Available phosphorus (P) was below critical levels in 40% of paddocks sampled and sulfur (S) in 73% of paddocks; >35% of all paddocks had soil pHCa <5.0. Deficiency of P was more prevalent in the Central Tablelands (63% of paddocks), whereas S deficiency occurred more frequently in the Central West (95% of paddocks). Legume nodule scores were associated with host legume species, soil pH, available P and/or S, and cation exchange capacity, which collectively accounted for 73% of variation. For Trifolium spp., at soil pHCa >5.55, nodulation was predicted to be near adequate (score 3.95, where adequate = 4). At pHCa <5.55, higher available S resulted in a higher nodulation score (2.42) than in paddocks where S was deficient (score 0–1.97). These results suggest that improving the capacity of legumes to supply nitrogen should focus on addressing soil acidity and plant nutrition, specifically P and S.

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Digital Object Identifier (DOI)

https://doi.org/10.1071/CP19039