Lucerne is an important component of the farming system in the Murray region as it extends the growing season with quality green feed.
However, a challenge producers face when growing dryland lucerne is persistence. The importance of resting lucerne after grazing or cutting is well documented. Without adequate recovery, both persistence of the stand and potential dry matter production are reduced. Current guidelines for recovery after grazing or cutting are usually discussed in terms of the percentage of flowering or the length of new shoots from the crown. These guidelines can be difficult to explain or easily misinterpreted.
Lucerne growth (accumulation of dry matter) and development (maturity of the regrowth crop within a cycle) are strongly linked. Regrowth after grazing or cutting occurs from new basal buds located at the crown of the plant and is driven by remobilisation of carbohydrates reserves from the crown and tap root. Once these shoots are mature, the plant will replenish the depleted carbohydrates to the root and crown. Removing these shoots through set stocking or a longer grazing period will delay regrowth and require more plant reserves. The stand will lose vigour and plants will begin to die, resulting in a thinning stand.
A recent project, completed at the Agriculture Victoria Rutherglen Research Institute, trialled a number of grazing management options to determine the grazing regime that will increase lucerne quality and persistence. Four grazing management options were trialled on SARDI 7 lucerne variety. They were:
- S- short recovery of three weeks after grazing or cutting.
- LR – long recovery of six weeks after grazing or cutting.
- NS - New shoots from crown have grown to 2cm post-grazing.
- NSF - As for NS, except no cutting (grazing) in late summer to autumn when plants are allowed to reach full flowering (common in New Zealand).
The experiment measured persistence in the form of basal frequency, herbage mass and taproot mass. Defoliation was achieved by mowing the plots to a height of 5cm.
The following graph is the cumulative herbage mass (DM kg/ha) of each of the treatments for the 18-month period of the experiment (January 2015 to June 2016).
The calendar-based LR system fared well, as it produced the most herbage, had a robust taproot system and could be easily implemented. Ideally, graze the paddock between 7 – 14 days (depending on paddock size and stock numbers) and try not graze the plant lower than 5cm. This highlights another challenge for producers with large lucerne paddocks, as high stock numbers are required to gain optimum value from the lucerne. Producers need to decide if they are grazing the lucerne for persistence or to meet nutritional requirement to achieve growth rates of stock.