Persistence of perennial ryegrass, tall fescue and cocksfoot following annual sowings: influence of grass species, ryegrass cultivar and pasture age on yield, composition and density

Persistence is an important component of perennial pasture-grass productivity. Defining traits that affect persistence is essential for improving pasture longevity through plant breeding and for identifying persistence traits that should be included in cultivar ranking indices. Compared with conventional longitudinal studies, where a single sowing is monitored over time, repeated annual sowings allow the effects on persistence of sowing year and the ensuing interactions between environment and age of pasture to be identified. An experiment was commenced in 2015 under sheep grazing in Canterbury and in 2016 under cattle grazing in Waikato, where eight cultivars of perennial ryegrass representing different ploidy, flowering date, and cultivar age (release date), and one cultivar each of tall fescue and cocksfoot were sown in four randomised complete blocks in autumn each year. This paper reports interim data on spring and autumn pasture yield, composition, and density of 3-year-old, 2-year-old and 1-year-old pastures exposed to the same environmental conditions within the same, single year. There were significant effects on yield, botanical composition, basal cover and tiller density due to cultivar, pasture age, and their interaction. When the confounding effect of year-to-year variation was removed by comparing each age cohort in the same year, the underlying differences among grass species and cultivars, and ages of pasture, is starting to reveal the nature of this influence on pasture persistence.

Annual yield and botanical composition of four dryland grass species with or without nitrogen over six years

Nitrogen (N) and water availability affect pasture production and persistence. Yield and botanical composition of four monocultures of brome (BR), cocksfoot (CF), perennial ryegrass (RG) and tall fescue (TF) were evaluated with (+N) or without (-N) N at Ashley Dene farm, Canterbury, over six growth seasons from establishment in 2014/15 (Year 1) to 2019/20 (Year 6). Total annual yields ranged from 2.04 (RG-N; Year 1) to 12.7 t DM/ha/yr (CF+N; Year 3). Yields differed among species in Years 1, 3, 4 and 6 when TF pastures had the lowest production. There was no difference in DM production from BR, CF and RG pastures. Additionally, +N pastures produced ~55% more yield than –N pastures in Years 3 and 5 when spring/summer rainfall was adequate to maintain growth. Sown grasses accounted for >89% of total DM yield in Years 1 and 2 but the proportion of total annual DM production from sown species declined from Year 3. By Year 6, sown species accounted for 48±3.3 (TF) to 64±3.3% (BR, CF and RG) of total annual DM production. Generally, TF failed to perform in this dryland environment. In contrast, the production and persistence of the other three species were not different when subjected to water deficits alone.

Climatic factors influencing New Zealand pasture resilience under scenarios of future climate change

New Zealand’s intensively managed pastoral agricultural systems are vulnerable to climate change because of their dependence on grazing livestock and pasture as the primary feed supply. Drawing from recent modelling results, annual pasture yields in New Zealand are projected to be robust to a changing climate due to more favourable growing conditions in winter and early spring and increased plant efficiencies from the CO2 fertilization effect. However, growth is also expected to become more variable and unpredictable, particularly in water-limited regions. A combination of short-term, incremental changes (already part of current practice) and longer-term strategic interventions will be necessary to maintain consistent feed supply under future climate change.

Attributes of resilient pasture for achieving environmental outcomes at farm scale

Pasture resilience commonly refers to a pasture’s ability to withstand or rebound from pressures to maintain production and quality of sown species. We suggest that a broader definition of pasture resilience is needed that also includes environmental responses, thus ensuring that productivity and environmental outcomes are considered together. Key attributes of resilient pastures to minimise soil erosion and nutrient, greenhouse gas and soil carbon losses are summarised based on current understanding of environmental losses from pastoral systems. These attributes include maintaining consistent pasture cover, high energy and/or low nitrogen species and species diversity that provides complementary root morphology and/or growth seasonality; all are likely to have positive benefits for production and productivity. There is a potential tension, however, between productivity and methane emissions, as methane production increases with increased feed intake. Increasing pasture quality is therefore also an important consideration for pasture resilience as it can maintain animal productivity at lower levels of feed intake. From a farm systems perspective, the choice of pasture species should reflect the desired attributes for both productivity and environmental outcomes, and ensure that the sown species persist in the sward. Finally, we note that none of the environmental attributes/benefits are likely to deliver major farm-scale improvements on their own; progress will likely be incremental improvements upon implementing a range of attributes.

Climate change impacts on pest ecology and risks to pasture resilience

It is well understood that damage by insect pests can have serious consequences for pasture resilience. However, the impacts of climate change on pastoral systems, the responses of insect pests, and implications for pest impact mitigation are unclear. This paper reviews pest responses to climate change, including direct impacts such as temperature and carbon dioxide levels, geographic range expansion, sleeper pests, and outbreaks resulting from disturbance such as drought and farm system changes. The paper concludes with a plea for transdisciplinary research into pasture resilience under climate change that has insect pests as an integral component – not as an afterthought.

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

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.

Direct and indirect effects of resilient pastures at farm scale

I farm a 550-ha property at coastal Whangarei Heads, Northland, in partnership with my wife Helen. While some land has been in family ownership since the 1850s, our farm has grown over the years through land and farm acquisitions. The farm consists of a dairy platform of 220 ha and 330 ha of dairy beef and dairy support. The farm is kikuyu dominant and summer dry with rainfall varying between 650 and 1100 mm per annum. Summer cropping, in-shed meal feeding, sowing Italian ryegrass and kikuyu mulching are all practices used with the aim of running a sustainable system. Perennial ryegrass pastures have limited persistence and are no longer a focus as more resilient pasture species and varieties are sown.

Plant diversity with species drilled in the same or alternate rows enhanced pasture yield and quality over 4 years

This paper reports on the effects of plant species diversity and sowing method on pasture yield and quality. Nineteen seed mixtures of perennial ryegrass (PR), plantain (Pl), white clover (WC) and red clover (RC) were sown on 26 March 2015 at Lincoln University. Four mixtures of PR, Pl and WC were repeated with species separated in alternate drill rows. Plots were grazed by sheep and irrigated. After 4 years, a mixture with 25% of each species based on seed count – equivalent to 7.5 kg PR, 5.6 kg Pl, 1.9 kg WC and 4.4 kg RC (19.4 kg total seed)/ha – produced an optimal balance of increased total yield (17.44 t DM/ha/yr), weed suppression (0% of total yield), metabolisable energy (11.4 MJ/kg DM) and crude protein (19% of DM). Sowing method had no effect. Plant diversity enhanced pasture production through positive interactions and identity effects among the legumes (WC and RC) and non-legumes (PR and Pl). The strength of interactions between species depended on the identity and relative abundances of the species involved. The diversity effects occurred alongside shifts in species relative abundances over time. This study demonstrated an experimental basis for the evaluation of multi-species pasture mixtures.

Soil and nutrient management: the practitioner’s perspective

The fundamentals of nutrient cycling over the past three decades are basically the same but the breadth of subject matter and scale of implementation of soil and nutrient management have changed. Soil is considered for its biological and physical attributes in addition to chemical properties. Farms/orchards are managed at significantly finer scales at paddock or sub-paddock level. The resilience of nutrient management now must consider the contexts of climate change influences, social licence, water quality outcomes and those decisions made and implemented by a more highly trained and scarce people resource.

What’s next for the New Zealand dairy feed-base? Learnings from climate analogues

• The reviewed literature suggests that the likely main impact of climate change on New Zealand dairy systems will be a reduction in total annual rainfall and increased inter- and intra-season rainfall and associated soil moisture variability.• Future climate analogues for New Zealand’s current dairying regions are provided from both within New Zealand and Australia.• Future climate scenarios for New Zealand dairy systems can be found within New Zealand with the exception of Northland whose most similar climate analogue is in Australia.• A conceptual framework to increase the boundaries of the ‘zone of system control’ (ZSC) by the farmer is provided here for the first time. The ZSC is defined as the optimal range for a critical input (rainfall or soil moisture in this case) where productive and profitable farming can occur.• Risk of failure increases as the frequency inputs fall above (excess) or below (deficit) the ZSC. Options to reduce the risk of system failure (outside of this zone) are provided with emphasis on soil moisture.• This framework could be used to focus future research and development investment to make the New Zealand and Australian dairy industries more resilient to climate change.