Harvest interval affects lucerne (Medicago sativa L.) taproot total yield, starch, nitrogen and water‐soluble carbohydrates

Abstract

Lucerne (Medicago sativa L.) has a large taproot to store and release starch, carbohydrates and nutrients during the plant's growth. Recommended management of the lucerne crop aims to keep the taproot stable subject to the demands for feed provision and stand longevity. Field experiments were conducted in Victoria, Australia, to examine the effects of recovery period on taproot mass and nutritive status. Both experiments used established SARDI Seven lucerne crops and were either cut every 21 days (short recovery SR) or every 42 days (long recovery LR). At each defoliation, taproots were extracted for determination of DM yield and starch, water‐soluble carbohydrate (WSC) and nitrogen (N) concentration and DM yield. At both sites, WSC and N DM yields along with total taproot DM yield did not change greatly as the experiment progressed. Starch was responsive to herbage accumulation with both concentration and DM yield, increasing when herbage accumulation rates were high and decreasing when herbage accumulation rates were low. At both sites, LR taproots had starch levels equal to or higher than those of SR taproots. We conclude that short intervals between defoliations disrupt the energy cycling between shoots and roots. This is likely to reduce lucerne productivity, particularly during periods of rapid growth.

Potassium and Phosphorus Fertilizer Impacts on Alfalfa Taproot Carbon and Nitrogen Reserve Accumulation and Use During Fall Acclimation and Initial Growth in Spring

“…Nearly a century of research has supported the premise that taproot carbohydrate and protein reserves provide C and N for growth and respiration of alfalfa during periods when photosynthesis and N 2 -fixation are reduced by defoliation in summer or other environmental stresses (Graber et al, 1927;Jung and Smith, 1961a;Avice et al, 1996;Volenec et al, 1996;Berg et al, 2018;Mitchell et al, 2020). Numerous studies have also shown that plant nutrition, and in particular P and K fertility, plays a key role in alfalfa growth and stress tolerance (Brown, 1928;Roberts and Olson, 1944;Jung and Smith, 1959;Cooper et al, 1967;Wolf et al, 1976;Kitchen et al, 1990;Volenec et al, 2021).…”

Lucerne (Medicago sativa L.) Persistence Remains Unchanged under Variable Cutting Regimes

“…For instance, the cumulative herbage production, over 18 months, of 42 day cutting intervals (LR) was greater than that of 21 day cutting intervals (SR) by 30% at Hamilton and 40% at Rutherglen. Mitchell et al [18] provided evidence that this reduction in productivity with shorter cutting intervals was associated with a disruption in the energy cycling between shoots and roots.…”

“…The inference from this is that there are strong physiological processes in the lucerne plant that make it resilient to more frequent defoliation in terms of survival. This resilience in terms of plant survival is much greater than its general resilience in terms of growth and occurs despite the major disruption of energy cycling between roots and shoots [18] and shoot dynamics [8]. This resilience relates to the plant's intrinsic tolerance to defoliation and includes factors such as increased photosynthetic rate after grazing, high relative growth rates, increased branching or tillering after apical dominance has been disrupted, pre-existing high levels of carbon storage in roots for allocation to above-ground growth and the ability to move carbon stores from the roots to the shoots after defoliation and the availability of residual meristems [31,32].…”

“…The plot size was 10 m × 5.5 m. Above ground and below ground measurements were taken for the first 18 months of these two experiments, and the above ground measurements, including basal cover, have been previously reported [13]. During this time, the defoliation interval had major effects on both the amount and nutrient concentrations and the yield of both above ground [13] and below ground [18] material, but only minor, if any, effect on basal cover. At each of the two sites, the defoliation treatments were continued for a further 18 months, but only basal cover measurements were continued.…”

Biological Nitrogen Fixation, Carbon assimilation and plant performance of Lotus tenuis, contribute to define a strategic role in the lowlands in the Salado River Basin (Argentina)

“…As was reported in Medicago sativa, total or partial removal of the photosynthetic area results in the mobilization of C and N reserves from roots to shoots generating an inversion of source and sink organs (Teixeira et al 2007). The management system imposed and specially the defoliation periods will affect the patter of reserves accumulation and subsequent regrowth (Vignolio et al 2018;Mitchell et al 2020). After shoot removal, regrowth of the new shoots in L. tenuis plants must be supported by non-structural carbohydrates along with N compounds (such as proteins and amino acids) stored in the taproots (Striker et al 2011), specially during early regrowth (Avice et al 1996).…”