LUCERNE ESTABLISHMENT

Press, Volume CIV, Issue 30763, 29 May 1965, Page 9

LUCERNE ESTABLISHMENT

ATOST of the problems enx countered in the past with the establishment of lucerne had now been solved, Mr J. G. H. White, a lecturer in plant science at Lincoln College, told the farmers’ conference last week. “If farmers are prepared to observe a few simple precautions in seed inoculation, obtain a soil pH test and lime adequately, and sow the seed at the correct time, many of the failures which have occurred in the past are unlikely to occur again. “The stage is now set for a rapid increase in lucerne acreage on light land in Canterbury and elsewhere.” Lucerne, he said, required a different species of rhizobia bacteria from that needed by clovers for nodulation, and this species was absent in most soils in New Zealand. It was therefore essential to supply these bacteria as an inoculum on the seed at sowing. Even when sowing lucerne after lucerne it was a good insurance to inoculate the seed. Lucerne rhizobia were easily killed by drying, said Mr White, and freshly inoculated seed should not be dried in the sun or under hot conditions. If sowing of inoculated seed was delayed for several days death of rhizobia might also be high. The seed should be sown within 24 to 48 hours of inoculation if possible. Nodulation failture due to desiccation of the inoculum could also occur if seed was sown into dry soil, especially when temperatures were high. Seed should always be drilled into moist soil, unless it had been pelleted.

Contact with soluble fertilisers such as superphosphate could cause complete death of the inoculum on the seed,

and inoculated seed was best sown with lime, equal parts of lime and super, reverted super or serpentine super. Lucerne rhizobia were particularly sensitive to acid soil conditions. Nodulation failure could occur when the soil pH was less than 6.0, and the optimum pH was nearer 6.5 to 7.0. Until more acidtolerant strains of lucerne rhizobia were isolated it was essential to raise the soil pH near the seed to 6.5 if good nodulation was to be obtained. At Lincoln College it had so far been found that finely ground lime was the most successful pelleting material for lucerne. Pelleted seed could be sown with super without damaging the inoculum, it could be stored for up to a month after inoculation and would still give good nodulation, the bacteria were protected by the pellet against desiccation and could therefore survive longer, and it could be used in aeid soils where conventional liming was uneconomic.

On the other side of the story pelleting took much more time than, simple inoculation and was more expensive, and if the pellets were poorly made most of the advantages of the procedure might be lost If liming had been adequate pelleting should not be necessary on most light land on the Canterbury plains, said Mr White, so long as normal precautions were observed with simple inoculation. In Canterbury most soils on light land were slightly to moderately acid and application of lime was essential before lucerne was established. The two major effects of lime in lucerne establishment were raising the soil pH near the seed to improve survival and multiplication of the rhizobia

and thus obtain good modulation, and raising the pH of the whole soil mass to obtain good root development and plant growth. Mr White warned that if lime was broadcast on acid soils immediately before sowing the pH was raised in only the top inch or two of the soil and acid conditions might still occur just below this. Lucerne might nodulate well under these conditions but the plants would not thrive due to poor root development. The best way to combat these effects was to plough lime down with the previous crop, followed by further lime cultivated in before sowing. Farmers, said Mr White, should obtain a reliable soil pH test before sowing lucerne as this would give them some guide as to lime requirement. On silt loams he suggested that if the soil pH was less than 5.7 then a ton of lime should be ploughed in with the previous crop and another ton cultivated in before sowing. If the pH was between 5.7 and 6.0 then a total of only one ton of lime might be sufficient. It was most important to raise the pH to 6.5 by adequate liming before sowing rather than use a minimum at this time and apply heavier dressings after establishment. Mr White said that the most reliable time to sow lucerne on light stoney soils in Canterbury was in late September or early October when the soil was still moist and temperatures were high enough to cause rapid germination.

Drilling of the seed should be done slowly on a fine, firm rolled seedbed with the coulters all in one line, and the seed should be placed no deeper than half to threequarters of an inch.