Pasture resilience reflects differences in root and shoot responses to defoliation, and water and nitrogen deficits

Authors

  • Derrick Moot Lincoln University
  • Alistair Black Lincoln University
  • Eric Lyons University of Guelph
  • Lucy Egan Lincoln University
  • Rainer Hofmann Lincoln University

DOI:

https://doi.org/10.33584/rps.17.2021.3472

Keywords:

alfalfa, Lolium perenne L., Medicago sativa L., plant development, plant growth

Abstract

The yield of a pasture is directly proportional to the amount of light plants intercept and allocate to different organs. When plants are carbon (C) limited, due to defoliation, they allocate more C preferentially to shoots to restore leaf area. In contrast, water and nitrogen (N) limitations lead to a greater allocation of C to roots. Changes in the root:shoot ratio therefore reflect changes in C and N partitioning and indicate their relative priority. A major factor that influences plant responses to stress is their ability to store and remobilise reserves to restore leaf area. Species with tap roots, like lucerne, have a large potential C and N storage capacity that is utilised seasonally for storage and remobilisation. This has been used to develop seasonally based grazing management rules. Similarly, recommendations to graze perennial ryegrass at the 2- or 3-leaf stage are based on the balance between maximizing growth rates and the need to replenish water-soluble carbohydrate reserves. However, perennial ryegrass has lower levels of perennial reserves than other grass species. This reduces its resilience to concurrent water deficits or N deficiency. Under these conditions maintaining the recommended 3-leaf grazing intervals and/or leaving higher post-grazing pasture masses are recommended to assist canopy recovery. Other grass species, such as cocksfoot and tall fescue, provide more resilience, particularly in response to water deficits.

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Published

2021-10-19

Issue

Section

Resilient Pastures Symposium 2021