Buried seed counts to help with new cultivars

Press, 31 May 1985, Page 12

Buried seed counts to help with new cultivars

An independent facility for buried clover seed testing is essential for the development of a seed multiplication industry for varieties other than Huia, according to a D.S.I.R. scientist, Dr Peter Clifford, of Lincoln.

He was giving a paper to the Herbage Seed Conference of the Grassland Association, held recently at Lincoln College. The paper was called “Possible solutions to contamination of white clover seed crops by buried seed.” “Even at a substantial fee, buried seed counts would prove far cheaper than roguing costs for the production of uncertified seed coupled with a further five years out of clover crop,” he said. Dr Clifford’s paper followed one by the D.S.I.R. Grasslands Division’s director, Mr John Lancashire, which demonstrated the extent of the hard seed problem which presented itself whenever a change in clover cultivar was attempted. Up to 90 per cent of clover seed, depending on the season, was classified as hard and a good specialist grower averaged about 1000 kg a hectare in seed yield. However, the average seed loss was about 30 per cent at harvesting and the over-all mean loss has been determined by Dr Clifford and Mr John McCartin, manager of the Lincoln Collge cropping farm, as 200 kg a ha, containing 130 kg of hard seed. Crop retrieval losses were slightly less when a counterrotating beater-type pick-up (“Murphy”) was used to deliver the cut crop to the header for threshing and separation, Dr Clifford said. However hard seed returned to the soil (not picked up) varied from 40 to 210 kg a ha, a very high rate compared with the normal clover sowing rate of 3kg a ha. “The lowest seed losses, 5 per cent, were recorded for a dessicated crop cut the morning of harvest with a double-reciprocating knife mower, retrieved for threshing with a Murphy pick-up the same afternoon Over-all losses were highest with twin-spindled rotary mowers. “Separation losses, though of economic importance, should not add to the hard seed content of the soil. “Scarification of seed in the threshing and separation cycle should ensure that any losses in the header offal are of immediately viable seed.” But a poorly set

header could deliver up to 400 kg a ha out the back instead of into the bin. Dr Clifford outlined research by the Grasslands Division and the New Zealand Agricultural Engineering Institute into upgrading the efficiency of beater-type pick-ups and direct heading of dessicated crops.

He then said that no satisfactory method had yet been developed either to encourage a high level of germination or mortality within the buried seed load. Several experiments into different row spacings with variations of inter-row sprayings and cultivations have been tried at Lincoln. From this work Dr Clifford has been able to speculate on the possibilities of a successful change in cultivar away from Huia. He predicted the eventual seed contaminations in average yields of about 1350 to 1600 kg a ha, over two harvests, from different row spacings (30, 45 and 60cm); seeding rates (3, 2 and I.skg a ha) and inter-row contaminant control (50, 67 and 75 per cent of total surface area). He predicted 7.5, 5.6 and 5 per cent physical contamination of the crop respectively. “Without roguing, none of these crops meet any of the inspection requirements for physical purity as laid down by the M.A.F. “The less contaminated crop, 60cm spacings, could be rogued to a level satisfactory for second generation certified Tahora seed. “At best the costs of culivar change will be high. “And should the initial crop not meet certification standards it will be out of clover seed production for up to another five years. “For many farmers who include peas in their rotation, this is an unacceptable situation because of disease problems.

"Ultimately only buried seed counts will give the grower some idea of the potential for success in changing from the growing of one cultivar to another.” The Grasslands Division is also assessing the possibility of minimising the activation of buried seed through direct drilling as an alternative to annual cultivations. But at present the regulations state that paddocks proposed for new cultivars must have annual cultivations in the five years before sowing. Other techniques for killing or inactivating hard seed are possibilities for the future, according to Dr Clifford, including carbon banding, irradiation, microwaves and selective spraying.

In the meantime a decision to change cultivars from Huia, particularly to overseas varieties which may look like Huia, is a very serious one, he said. Growers would have to be sure that the new cultivar was going to set seed and produce an economic yield in New Zealand conditions. They would be introducing the seed for a long time thereafter and would probably want the crop down for a few years. They would need to be sure that “genetic shift” was not going to occur to any detrimental extent. Under a new climate a clover could shift back towards one of its parent lines and its growth characteristics would alter. Growers would also need to be assured of a long-term market for the new seed.