Lucerne management in El Niño summers
Date: 15 December 2015
Lucerne silage quality varies from year to year because of many factors, including weather conditions, harvest maturity, age of stand, drymatter content and fermentation quality. Cooler and drier than average summer conditions, as is predicted for the upcoming El Niño summer, should result in higher quality lucerne silage. For best results, cut stands in the morning and aim for a 6 – 8 cm cutting height.
The weather has a tremendous influence on the nutritional value of lucerne. In fact, growing environment and harvest maturity affect lucerne more than genetic differences. The four biggest environmental factors impacting lucerne quality are temperature, water availability, solar radiation and soil fertility.
Warmer temperatures accelerate neutral detergent fibre (NDF) development and lignification, which decreases quality and digestibility. Thus, forages grown in cooler areas tend to be higher in quality.
Drought conditions can limit yields but they tend to result in superior nutritional quality. Protein level and digestibility are higher because of a higher leaf-to-stem ratio. Hot and dry weather generally results in better-than-normal lucerne quality but quality is best when conditions are cool and dry. The predicted El Niño summer should therefore result in higher lucerne quality but yields may be reduced.
Solar radiation promotes both yield and quality. Sunny weather increases carbohydrate production, improving digestibility (quality) and photosynthesis (yield). Cloudy weather does just the opposite, decreasing both yield and quality. In autumn, as day length decreases digestibility may increase thanks to cooler temperatures.
Time of harvesting
Determining the time of day to harvest is a challenge. Some growers cut later in the day because crops are able to accumulate more sugars (energy). This improves palatability and helps with silage fermentation. However, research is unclear about whether differences exist after wilting and/or fermentation.
When harvesting for silage, morning cutting generally works best as the crop is usually ready for harvest late that day, or the next day providing conditions are warm. When mowed in the afternoon, lucerne generally takes another day to dry and this may expose the crop to weather risks.
Lowering the cutter bar increases yield. Research shows cutting for a 2.5 - 5 cm stubble height results in higher yields with little or no damage to the plant. Any lower, and equipment can damage the crown buds and curb regrowth.
However, cutting at this low level can allow disc mowers to pull soil into the harvested crop, a practice that decreases digestibility and increases the potential to pick up soil-borne bacteria and spores that hamper fermentation.
For most producers, a 6 – 8 cm cutting height is a good compromise. The exception is the final harvest of the season in regions that face cold winters. In these situations, it’s best to leave 10 – 15 cm of stubble to ensure good insulation for the crowns.