Choosing the right ryegrass

What do I need to consider when selecting a ryegrass for my farm? 

Selecting the correct ryegrass for your enterprise is key to the success of your business.  

Knowing the rainfall, temperature, and soil type of your environment, allows you to make a better-informed decision as to which ryegrasses are best for your farm. By understanding heading dates and how to differently manage tetraploids and diploids, you can create an effective pasture plan to spread your risk across your farm. Selecting suitable varieties allows you to produce the most feed, at the highest quality possible for your enterprise. Therefore, growing your livestock and increasing your profit. It also provides you with peace of mind, knowing you have a wide variety of grasses across your farm, allowing you to adapt to different climatic events.

Heading date

A heading date of a ryegrass is when there are 50% of the plant’s tillers with seed heads fully emerged from the flag leaf. At this point, a variety will express its highest dry matter (DM) yield, as 60% of the annual DM yield of a ryegrass happens around the heading date of a variety. For example, a +1 heading date is around the 1st of November.  A variety with a +22 heading date will flower around the 22nd of November.  

On average, most Italian ryegrasses head around mid to late November eg. Achieve Italian ryegrass has a heading date of +12. The annual ryegrasses, such as Astound, head around the end of October. Annual ryegrasses have the greatest winter production and are suited to areas with a shorter growing season. Italian ryegrasses are ideal for late-season production if there is moisture to support growth. Perennial ryegrasses have a wide range of heading dates and provide a quality perennial pasture option in areas with higher rainfall (750mm+ or irrigation). 

Ask yourself: What is the average rainfall for my location? What are the chances of having good soil moisture throughout the growing season?  No plant can grow without moisture.  Therefore, if you sow a late heading variety and it runs out of moisture, it could lose up to 60% of its genetic annual DM yield.   

Spread the risk and plant different heading dates across your farm. If the season goes longer, you can take advantage of this with late heading varieties.  If the season cuts short, you can have an earlier heading variety that will reach its heading date and potential yield before the moisture runs out.   

Image 1. Comparison of different heading dates and their growth. From left to right – Very early diploid perennial ryegrass (PRG), Early diploid PRG, Mid diploid PRG, Late diploid PRG, Very Late tetraploid PRG. Sown 5/5/20, Yambuk, Victoria. Photo taken 5/11/20.

It is also important to consider the temperature when choosing the heading date. Ryegrass grows best at 18℃, with increases above this temperature seeing a decrease in growth (Image 2).

Many environments in southeastern Australia experience temperatures above 30℃ from 1st of November onwards. The lack of rain and moisture that would occur in most of these environments from 1st of November onwards means poor growing conditions for a late heading variety

Even with irrigation, the growth of a late heading ryegrass is limited due to high temperatures and rust pressure.  

Image 2. Temperature effect on ryegrass vs white clover

Diploid vs tetraploid

Within ryegrasses, there are diploids and tetraploids. This refers to the number of chromosomes sets per cell, diploids having two and tetraploids having four. These plants have different traits and require different management strategies.  

Diploids are finer leaved and have a high tiller density. They are suited to set stocking and recover well from heavy grazing. Due to the fineness of the stems at the beginning of the reproductive phase, they are the best option for hay production.  

Tetraploids have an increased cell size and due to this they have a higher water-soluble carbohydrate content (WSC). This makes them ideal for silage production. They have great palatability and higher grazing preference. However, tetraploids require more precise grazing management. They should not be grazed too heavily as they take longer to recover. This is because they require more time to regrow their larger leaves. They should also not be left to grow too tall as they are more prone to lodging due to the heavier stem.  

Tetraploids have a larger seed and require a higher sowing rate to achieve the same plant density as diploids. Sow diploids at 20-25kg/ha and tetraploids at 25-40kg/ha.  

Image 3. Tetraploid Italian ryegrass (top) vs Diploid Italian ryegrass (bottom).

Lastly, consider the soil type of the paddock. A well-drained paddock during winter is best suited to an annual ryegrass as this species will give the maximum DM production when feed is most limiting. Place later heading varieties in wet paddocks.