2021 was the 2nd full grazing season on our trial blocks at Upper Nisbet, Jedburgh. Following on from our initial measurements and observations in 2020, we have looked at how the 30 individual varieties of perennial ryegrass and 15 bespoke mixtures have performed under rotational grazing with a group of bulling heifers. The 8.4 ha field with 8 paddocks has been stocked at 2600kg LW/ha in the early and mid-season and then dropping to 2400kg in September, October & November.
The grazing season at Upper Nisbet has been challenging due to low rainfall in the 6 key months of April-September. Total rainfall was 192mm or 32mm/month on average, whereas March and October were 193mm in total. After getting on with 45kg nitrogen & sulphur in late March, we then had 20 nights of white frost in April that showed us which were the resilient varieties and mixtures. Some of the tetraploid varieties with their higher water content turned blue and went backwards but then compensated during the dry summer months with their deeper roots hanging in and outperforming the shallower rooting diploids. The mixtures with a range of varieties and species including excellent clover content grew 3.2 tonnes of dry matter per ha more than the average single stand varieties over the season. They also consistently analysed well and, in contrast to the monoculture varieties, never looked stressed or lacking in nutrients.
KEY MESSAGES FROM THE SEASON
- Clover mixtures once again are preferentially grazed over straight ryegrass, leading to better DM intakes and cattle being more content and lying for longer periods. The sight of 52 cattle heading straight for the 12 meter end rig and preferentially grazing the clover mixtures over the PRG varieties and cleaning them up seems ample proof.
- The diverse combination of PRG varieties alongside timothy, cocksfoot, fescues and smooth stalked meadow grass has increased growth. It is particularly evident early season in colder conditions or under periods of stress, such as drought. These mixtures also analysed very well provided they were grazed at the optimum stage. As soon as moisture and warmth return, the PRG will kick in and move again.
- The 30 single stand varieties have been tested for quality parameters in early, mid & late season. The most palatable varieties, with lowest residual grazing heights, consistently test above average in their paddocks whereas some diploid varieties, with poor clean outs, needed mowed to reset them. Under rotational paddock grazing, this becomes more evident as the season progresses and our quality index on testing is certainly reflecting this. Palatability is a vital factor and it needs animal intervention to identify those varieties and mixtures with this key trait.
- The resilience and soil health under the mixtures is apparent, as we walk the paddocks weekly with a plate meter during the season. The combination of rooting depth and microbes from the clovers and herbs keep the plots green and vigorous. It also makes minerals and trace elements more available in our quality samples. Each individual forage sample is tested for calcium, magnesium, phosphorous, sodium, potassium, sulphur, chloride, iron, zinc, manganese, copper and aluminium as well as the nutritional data.
- Keeping the grass length at the optimum stage for grazing (no more than 12cm) and allowing rest periods of 21-28 days, allows recovery and the plants to build reserves. As soon as you lose the tight rotation by failing to keep on top of the growth, your quality will also fall away and it becomes difficult to regain unless you increase stocking rates or remove paddocks for silage.
- The peak week of growth in early June saw average rates at over 90kg DM/ha/day, whereas August saw the lowest at 35kg. This calls for some degree of flexibility and adaptability to be built into systems. To maintain high ME you need to be introducing stock when the grass is at or just below the 3 leaf stage, as once the 4th leaf starts to appear, the 1st leaf will die off. Aim to leave residuals at around 1500kg DM/ha (4-5cm).