Short-rotation ryegrasses have the potential to provide extra production to spring-calving dairy farm systems.
They have a greater cool season growth potential, and have superior dry matter (DM) production over winter and early spring when compared with perennial ryegrass.
Some studies have also indicated that herbage may be of a higher feed value during the winter and early spring period.
Short-rotation ryegrasses could help address low pasture growth rates in early spring and their higher DM production could translate into increased pasture DM intake and increased milk production.
The greater cool season activity of short-rotation ryegrasses also allows these species to take up more plant-available nitrogen (N) in the soil over late-autumn, winter, and early-spring, when the risk of N leaching is greatest.
However, there has been little research done to test short-rotation ryegrass performance on farms, where environmental and managerial conditions can prevent pasture species growing to their full potential.
Also, short-rotation ryegrasses do have some drawbacks, including typically having a short lifespan (1-3 years) and persistency issues in dry summer conditions, especially if over grazed in summer.
From the limited number of paddock/whole-farm system evaluations using short-rotation ryegrasses on seasonal dairy farms, the results have varied considerably.
Based on this, the greatest benefit from short-rotation ryegrasses would probably be as part of a pasture renewal programme, augmenting perennial ryegrass-based pastures to meet feed supply requirements of seasonal spring-calving dairy farm systems.
Pasture renewal
We evaluated early-spring pasture supply and milk production of a seasonal calving dairy farmlet, where 20-30 per cent of the milking platform was planted in short-rotation ryegrass as part of an annual pasture renewal programme.
The trial was conducted at the Telford Farm Training Institute in Balclutha, New Zealand, as part of the Pastoral 21 Next Generation Dairy Systems research funded by MBIE, DairyNZ, Fonterra, DCANZ and Beef + Lamb NZ.
A 39ha demonstration farmlet was established carrying 110 cows over the milking season, peaking at 2.8 cows/ha during November.
Planned start of calving was August 24, with an aim to have all cows calving at BCS 5 or greater.
Cows were dried off in April/May at a minimum BCS of 3.5. The herd was rotationally grazed, with pasture and supplement allocated on a daily basis.
Both whole-crop cereal silage and short-rotation ryegrass (cultivars Shogun NEA endophyte and Tabu nil endophyte) were planted on this farmlet as complementary forages to the existing perennial ryegrass-based pastures.
The crop (barley) was sown in mid-to-late November, harvested in mid-February, and fed to cows in autumn as a supplement to fill any feed supply deficit.
The short-rotation ryegrass was used as a two-to-three year pasture option following the crop and sown shortly after the crop was harvested.
More grass grown
Short-rotation ryegrasses provided more feed in spring, as was predicted (Table 1).
This increase of 10kg DM/ha/day translated into more grazing days/ha, as reflected in the grazing record and the lack of supplement fed, but not significantly different milk production per cow (19.1kg compared with 19.2kg milk/day for perennial ryegrass pastures).
This may have been due to the pasture allocation/grazing management processes, with frequent switching of grazing between the two pasture types.
Additional analysis, however, indicated an upward trend in milk production when more continuous grazing days of short-rotation ryegrass were able to be achieved in any two week period.
This effect added another 0.103kg milk/day for every extra full grazing day. This indicates that a greater proportion of the farm should be sown in short-rotation grasses in order for their traits to be more fully expressed and to allow the cows to adjust to the different feed type.
A balance between perennial and short-rotation ryegrass will be best.
Managing short-rotation ryegrasses
The pasture growth of the short-rotation ryegrasses was significantly greater in spring.
However, more N fertiliser was used on the short-rotation ryegrass (about 60kg N/ha) than on the perennial pastures (about 30kg N/ha).
The extra N was used in late spring to encourage the development of new tillers in the post-heading phase in an attempt to improve summer production and persistence.
This would have boosted summer production of the short-rotation ryegrass. Using the industry standard N response of 10kg DM/kg N, the extra N applied would equate to 3kg DM/ha/d grown by the short-rotation ryegrass in summer.
This may explain why there was no difference between the perennial and the short-rotation ryegrass in summer, when lower production from short-rotation ryegrass would be expected.
Short-rotation ryegrasses has been shown to provide more feed in spring.
Winter growth of the short-rotation ryegrass appeared to be affected by the establishment technique. The planned approach of sowing after harvesting the crop led to relatively late sowing and emergence dates (late March and early April).
This meant pasture was still too immature for grazing before autumn rains saturated the soil, resulting in the pastures entering winter as recently germinated seedlings.
In the final year of the study, a change to under-sowing the crop with the pasture mix in spring created a pasture that provided two grazings in autumn, increasing total DM production of the short-rotation ryegrass.
This tactic is also likely to improve pasture production in the first winter.
Due to the higher potential growth rate of short-rotation ryegrasses in spring, shorter grazing intervals were needed to prevent the rapid development of seedhead as pasture cover increased above approximately 2600kg DM/ha in spring.
We found that, if left to accumulate above 3000kg DM/ha, the feed quality declined and the targeted post-grazing residuals of 1500kg DM/ha were harder to achieve.
Key findings:
• Short rotation ryegrasses have greater cool season growth potential than perennial ryegrass. • However, they have shorter lifespans and are less persistent. • Using short-rotation ryegrasses as part of a pasture renewal strategy can boost spring pasture production, decreasing reliance on supplements. • Researchers used shorter grazing intervals to maintain pasture quality.
