The buzz around the Crop

Date posted: 22 April 2016

With the City Crop’s lucerne reaching its peak flowering phase, our horticultural team is ready to lend a hand… or a hive of bees.

Research has found that honey bees play an important role in pollinating (conveying pollen to or depositing on a plant to allow fertilisation) lucerne crops, which in turn helps plants set seed. In fact, with the help of bees a lucerne crop can achieve seed yields of 100 kilograms per hectare or more – that’s good news for farmers, cows and humans who like eating alfalfa sprouts (the sprouting of a lucerne seedling)!

The reproductive life of flowers is far from boring when self-pollination and cross-pollination are possible.

Lucerne flowers can be self-pollinated, when the male pollen falls on and then fertilises the female stigma (a pointy tip that receives pollen) of the same flower, or they can be cross-pollinated, where the pollen from one flower is transferred to another flower’s stigma (by either the wind or another insect).

Cross-pollination of lucerne is preferred as it helps improve the quantity and quality of seed. In comparison, self-pollinated flowers tends to produce smaller seeds which produce less vigorous seedlings.

To increase the occurrence of cross-pollination, farmers work with beekeepers to place bee hives throughout the crop. A general trend is to place three-to-five hives in up to 12 hectares – a rate that ensures between six and 10 worker bees are servicing, or pollinating, each square metre of lucerne.

Bees and flowers have an important symbiotic relationship. That means, they both benefit by helping each other out. The flowers provide bees with food (nectar is their basic carbohydrate or energy source and pollen is their basic protein source) while bees provide flowers with cross-pollination. Everyone’s kicked a goal!

Cross-pollination occurs when the bees land on the main lucerne petal and trigger the release of the female organ (the sexual column) from the two winged petals (the keel) of the flower. The pressure of the bees landing causes the column to flick up and bop the bee on the head.

This process, known as tripping, allows the male pollen, which is often stuck on the honey bee, to be transferred to the female sexual column. And voila! Fertilisation occurs and a baby seed is produced.

It is easy to pick if a crop is being adequately pollinated by its appearance. Unpollinated flowers are bright blue in colour and stay open for about a week. Pollinated flowers wither or wilt in about two hours, and turn dull blue-grey. By monitoring the flowers, bee hive rates can be adjusted to maximise cross pollination.

Farmers appreciate the role of bees. They know that more pollination means more seeds, so managing bee numbers and bee health is paramount. Ensuring water is readily available and monitoring overall bee nutrition is a must. After all, these little fellas are integral to Australia’s agricultural industry!

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