Effect of deferred grazing during late spring and summer on pasture productivity in Waikato and Bay of Plenty hill country

Abstract

Deferred grazing is a commonly used tool to manage feed surpluses. The effect of deferred grazing on pasture nutritive value and productivity was quantified in a split-paddock trial on three hill country farms in Waikato and Bay of Plenty from October 2018 until May 2020. Livestock were excluded from the deferred pasture between mid-October 2018 and March 2019. Thereafter, both treatments were rotationally grazed in common with cattle or sheep depending on the farm. Total annual dry matter production was 15% greater in the deferred than grazed treatment for the 12 months after deferring (8.9 vs 7.7 t DM/ha, P<0.05). Metabolisable energy (ME) values at the end of the deferred period were lower in the deferred than grazed treatment (P<0.01) but similar in both treatments thereafter. The content of legumes other than white clover (Trifolium repens) was higher in deferred than grazed pastures in spring 2019 on one of the farms (treatment × farm interaction P<0.05). Ground cover of perennial ryegrass was greater and the area of bare ground smaller, in the deferred than grazed treatment on three of five occasions from after the beginning of the deferred period until up to 8 months after deferring (P<0.05). There was no difference between treatments in decomposition and stabilisation of organic matter (P>0.05). The topsoil water content was higher in the deferred than grazed treatment for 12 months after deferring. In comparison to regular grazing between October and March, deferred pastures provided drought feed in autumn 2019. Pasture productivity was increased after the deferred period without negative impacts on ME.

Management options to recover perennial ryegrass populations and productivity in run-out pastures

“…Pastures closed for 6-8 weeks hold their nutritive value well (Bishop-Hurley 1997), as supported by the ME in the current study for the LSR treatment. Extending beyond 6-8 weeks and out to approximately 4 months, the ME of deferred standing pasture declined significantly, as expected, and the estimated ME of approximately 7 or 8 MJ/kg DM was similar with that reported by Tozer et al (2020) for hill country sheep and beef farms. During a dry summer as experienced in the current study, there was little difference in ME between the deferred pasture and the control for the late-season heading group.…”

“…Less desirable species can maintain overall yield well, as indicated by the late spring and summer yields for the control treatment in Table 1 vs. Table 2. The deferred pastures produced approximately 11% more total DM (+ 926 kg DM/ha) than the control in the year following deferral, and the response was in the range of 6-20% reported in other studies investigating pasture deferral (McCallum et al 1991;Harris et al 1999;Tozer et al 2020). Rejuvenation of pastures through recruitment of new plants via pasture deferral was more successful than via the mode of increased tillering of existing plants in the LSR treatment.…”

“…The second option is to defer grazing for a much longer period from late spring to mid summer (L'Huillier & Aislabie 1988). This practice has been used to shift surplus pasture from late spring into summer when feed deficits occur, and DM has greater value (Harris et al 1999;Devantier et al 2017;Tozer et al 2020). However, if managed in synchrony with the phenology of the ryegrass plant, it also enables recruitment of new ryegrass seedlings from seed shed by plants that have completed their reproductive cycle (L'Huillier & Aislabie 1988).…”

Using new insights in grazing management to buffer the impacts of climatic variability on pasture resilience

“…Areas where we can improve must include opportunities to move feed between seasons, acknowledging that we need to consider summer as an on-going feed deficit period, similar to winter, in future climate change scenarios due to emerging increases in meteorological drought (Stats NZ 2020). Traditional methods of forage cropping have a role in this approach (Stevens 2009), alongside techniques such as deferred grazing (Tozer et al 2020).…”

“…The second would be to provide a bulk of feed available in the latter stages of a dry period, for maintaining livestock. Studies have identified the advantage of shifting this bulk of feed (Devantier et al 2017) from late spring to summer and autumn (Tozer et al 2020).…”