by Simon Moloney (consulting agronomist)

Regional Introduction – Climate and Soils

The West Coast of the South Island is a unique NZ province with weather patterns dominated by cooler westerly flows from the Tasman Sea and warmer northerly flows moving down from the tropics, often delivering torrential rainfall as these flows move over the Southern Alps. Coastal annual rainfall ranges between 2,000 – 3,000 mm, increasing to 6,000 – 11,000 mm in areas close to and within the Alps. Temperatures are generally mild for coastal locations with minimal seasonal fluctuation (<10^oC difference summer to winter) while sunshine hours are lower than many NZ regions, averaging 1950 hours.

Westland soils broadly fall into three groups: Podzols (Pakihi soils, very poorly drained and highly leached), Gley lowland soils (imperfect drainage, medium fertility) and Recent soils (alluvial, free draining with medium fertility). The last two groups are comparatively easier to farm and form the basis of much of the region’s dairying. However, with expansion in recent years there has been increasing development of the marginal Pakihi soils, with their cemented gravels (iron and aluminium) ‘humped & hollowed’ and coastal sands ‘flipped’, resulting in significant increases in livestock carrying capacity and animal production.

Pasture Renewal Systems

Profitability: Costs will vary depending on the method of pasture renewal selected (oversowing – low, to full cultivation – high). The profitability will depend on the degree of establishment and subsequent pasture management. There are a lot of variables, many within the farmer’s control and some key variables, like weather, out of their control. Typically, internal rates of return (IRR) on renewal range from 15 to 50%+.

Benefits: New pastures will increase annual DM yield, provide additional seasonal yield (early-spring growth), increase pasture quality (higher digestible organic matter – DOM, higher ME) leading to higher voluntary feed intake (VFI), greater pasture utilisation, increased MS production and reduced GHG emissions.

Pasture Renewal Techniques

Oversowing: Lowest cost normally with the highest variability in success, but not so much on the West Coast with its relatively mild climate and even rainfall distribution. Most pasture species respond well to oversowing including: chicory, plantain, clovers and ryegrasses, especially hybrid and Italian ryegrasses.

Undersowing: The use of a direct drill without a non-selective herbicide. Paddocks need to be hard grazed prior to drilling with covers managed carefully following establishment. Like oversowing, this is a viable option for the West Coast dairy farmer with plenty of flexibility around timing ie. from mid-spring right through to mid-autumn. Both techniques have minimal impact on cow carrying capacity (CCC) allowing larger proportions of the farm to be sown annually (10-25%). Owning your own drill can definitely improve timing and flexibility. Ensure that seed placement depth does not exceed 20 mm (aim for 15 mm) with small seed species (clovers, forage herbs) all sensitive to sowing depth. This system suits the high seedling vigour associated with modern perennial and hybrid ryegrass cultivars. Both techniques will encounter a degree of competition from old resident pasture species ultimately impacting on seedling establishment percentage.

Spray direct-drill: A more costly establishment technique where managing pests (e.g. slugs, porina, grass grub) and broadleaf weed challenges (post-establishment herbicide) are essential to ensuring high levels of success. As there is a greater impact on CCC with these paddocks out of the rotation longer, the proportion of the farm renovated annually will be lower (5-10% p.a.).

Spray cultivation: The most costly technique with the potential for the greatest establishment success rate if executed well. Typically, less pest control is needed, but greater broadleaf weed challenge that has to be managed early (MCPB as soon as white clover seedlings have their third trifoliate leaf). Can impact heavily on CCC with only a 5-10% p.a. renewal rate being feasible. Although this can be offset to some extent by sowing a summer forage crop (eg. brassica, chicory) before regrassing in the autumn. However, the biggest likely limitation to this technique on the West Coast will be soil type, with many soils containing significant amounts of rock and gravels. This might only the leave the Gley soils (eg. Harihari soils) and the better quality areas of the Recent soils (eg. Hokitika, Tasman soils), as being suitable for cultivation.

Pasture Species and Cultivar Selection

First, account for farm’s soil type, climate, topography and when feed is required by considering stocking rate, calving date and expected days in milk (DIM). Generally speaking, the three main component species of modern dairy pastures are all applicable to West Coast farming. These include: grasses (perennial and hybrid ryegrass types), legumes (white clover, red clover), and forage herbs (chicory, plantain).

Ryegrasses

As a base pasture species, ryegrass is difficult to go past in the West Coast environment with its vigorous establishment, efficient solar radiation capture and flexibility in management styles. Weaknesses can include: reduced persistence and dominance from establishment of important companion species (clover, forage herbs) that contribute much needed additional dietary energy (ME) and minerals.

Selection criteria for perennial and hybrid ryegrasses

Ploidy type (chromosome number): For some years most ryegrass cultivars have been released in the diploid format, with their higher tiller density (numbers) offering increased persistency potential. Increasingly there are a number of perennial, hybrid, Italian and annual ryegrass cultivars being released as tetraploids (ie. double the chromosomes). Advantages of these relative to diploids include: greater DOM and ME, higher VFI, reduced GHGs and increased animal performance (8-10%+). Weaknesses can include: reduced persistency (ie. selective grazing pressure), lower tiller density, and, depending on grazing management, increased dominance of the important companion species (white clover and forage herbs).

Endophyte type: It is now generally accepted that in order to gain both performance (yield) and persistence in our changing climate, a ryegrass cultivar benefits from having a bred stain of novel endophyte, almost irrespective of the NZ region it is used in. The more forgiving regions of Southland and the West Coast may still get good performance from the earlier novel endophytes (AR1 and NEA), while for many other regions the more modern types (AR37, NEA 2, NEA4, NEA12) are better suited as they offer wider pest species tolerance and therefore increased persistency and yield.

Heading date (seedhead emergence): Most diploid perennial ryegrass cultivars have mid-heading dates (+0-8 days) with associated early spring growth, early seedhead emergence and persistent aftermath heading. Increasingly, more ‘late’ heading date (+12-20 days) cultivars have been released to the market with the aim of holding pasture quality later into the spring and reducing the post-peak lactation decline. There also a group of ‘very-late’ cultivars with heading dates of +21-25 days. Care needs to be taken not to have a farm dominance (ie. > 40%) of late-heading cultivars to avoid early-spring feed deficits. In pasture mixtures sow tetraploid cultivars at a 20-35% higher rate than diploids, as their seed weight is 2x heavier.

For the final selection from the myriad of ryegrass cultivars currently on the market, check how these three characteristics integrate and match the farm’s production objectives. NZ plant breeders have invested heavily to bring the farmer superior plant genetics to their older regressive pastures. Replacement rates of a minimum of 10% p.a. are needed to maximise the gains from these innovative and highly productive plants.

Companion pasture species

Clovers: An essential component of any NZ pasture. Advantages relative to ryegrass include: high forage quality (high levels of protein and soluble carbohydrate with MS responses 2.5x greater). Increased VFI. Greater mineral concentrations (macro and micronutrients). Ability to fix atmospheric N for utilisation by grass species (rates linked to DM yield – 25 kg N/t of DM). Increasing the proportion of white clover in our modern dairy pastures will reduce dependence on urea N keeping farmers well inside the current annual cap for synthetic N. Aim for a clover contribution of 25-40% of total pasture DM.

Forage herbs:

Chicory – is an energy dense, short-lived (1-4 years) perennial species that is highly palatable to all forms of livestock. Characterised by: strong growth from mid spring through to the late autumn. Chicory leaf has high levels of ME (12.5+) with low levels of structural fibre (high VFI). For persistence, chicory does require relatively free draining soils and rotational grazing. Can be used as an annual forage crop, typically sown in the spring for boosting cow energy intake throughout the lactation.

Plantain – A valuable companion species that has good energy and mineral contribution, that is more durable than chicory. Importantly, plantain also reduces the levels of soil nitrate N and therefore leaching.