26 April 1996

RAC takes a look at lucerne

By Rebecca Austin

LUCERNE establishment is being investigated in trials at The Royal Agricultural College, Cirencester.

A dry summer last year renewed interest in this deep-rooting legume, which fixes about 120kg/ha of nitrogen (96 units/ acre). College lecturer Gerry Lane says this value shows a £50/ha (£20/acre) fertiliser saving over three years.

Direct sowing was compared with under-sowing in spring barley and forage maize in trial plots last year. The variety Vela, which had good resistance to verticulum wilt, was sown in April, June and August.

Direct sowing in April gave the best establishments (137 plants a sq m) and a yield of 7t DM/ha (3t/acre). Direct sowing in June gave lower plant populations and the crop drilled at the end of August showed poor establishment with an average eight plants a sq m. Under-sowing in spring barley produced indifferent results in the dry conditions.

Early weed control was essential to successful establishment, for lucerne is vulnerable to competition at the seedling stage. Weeds were controlled before under-sowing in barley with Deloxil. This was changed to 2,4DB on under-sown and direct-sown lucerne and Bromoxynil was used on maize, at the three-leaf stage, before under-sowing. Carbetamide was used in the autumn to control volunteer cereals and grasses in under-sown plots. Grasses were suppressed by paraquat in the spring.

A Tearaway weeder was used to control spring weeds such as fathen, field pansy and groundsel. Crops were sprayed three times with Decis to control the pea and bean weevil.

"Although lucerne spring plant counts were less when under-sown into forage maize than the direct-sown plots, they showed good vigour and a substantial system advantage of about 5.5t DM/ha of forage maize," says Mr Lane. "This treatment will be further investigated this year to identify field-scale problems. As lucerne established well under a poor crop of maize, we shall use early maturing lucerne hybrids, such as Azis, to minimise competition."

lWork is also underway at The RAC to identify specific strains of Rhizobium meliloti, the bacterium which stimulates rapid nodulation on a lucerne roots. Bacteria are present in the inoculant, which is added to the seed before drilling.

DNA fingerprinting is being used to identify the most productive strains for a range of inoculants suit-able for specific soil conditions. &#42

Lucerne is grown by Oxon producer Mike Trevena as insurance against summer drought.