Cool Air Prevents Seed Damage

Press, Volume CV, Issue 30965, 22 January 1966, Page 9

Cool Air Prevents Seed Damage

A technique that promises to be a useful adjunct to grass seed drying was used, for what is believed to be the first time in New Zealand, on the property of Mr J. W. Crombie at Pleasant Point, South Canterbury, last week. It involves the blowing of cool night air through seed awaiting drying so that the temperature is kept at reasonably low levels and seed is not harmed by heating.

Discussing this trial Mr C. J. Crosbie, a farm machinery instructor of the Department of Agriculture in Christchurch, said this week that under recent unfavourable harvesting conditions quite a large amount of grass seed being harvested was heating in the bag or in the box. This was a serious matter, for depending on the degree of heating and the length of time that heating continued, there could be a serious reduction in germination capacity of the seed. It was important, therefore, that thermometer readings be taken to establish the exact level of heating. A temperature of 100 degrees Fahrenheit might be regarded as the danger point and where temperature of seed rose above this point it should be immediately put on a flat floor and turned over with a shovel periodically until it returned to close to air temperature. Two years ago it had been shown that a temperature of 120 degress established over a period of two or three days led to a reduction in germination to at least half of the original level. Last year a sack of Manawa ryegrass (or short rotation) had been deliberately insulated in a stack of hay bales and allowed to

heat up. Over a period of three days it rose to a temperature of 130 degrees Fahrenheit and germination dropped from 90 per cent to 43 per cent. In a further three days the germination was down to 27 per cent and in three months it was back to 8 per cent. Thermometers, readily available for about 7s 6d each, would give the answer—just plunging the hand into a sack gave a false impression depending on the air temperature at the time (on a hot day the seed did not feel as hot as it really was).

In the present season at least two lines of short rotation had been threshed at 34 and 32 per cent moisture respectively (the safe level was 14 per cent). Other lines had been threshed at 21 per cent moisture and many more at the borderline levels of 17 and 18 per cent Past experience indicated that those crops harvested at borderline levels would heat up to 80 degrees and come down again over a period of three days, but all lines harvested at above 17 per cent had to be dried to remove the factor that caused the heating. There were six continuous flow contract driers in Can-terbury-three in Christchurch and one at Hinds and two at Waimate—but the practical difficulty for farmers was in keeping the line of seed cool until it could be dried.

As already indicated it could be put on to a floor and turned as required; or it could be put in half sacks on top of a fence line. A third possibility was to cool it with a fan using night air and seed growers would be interested in a trial with this method last week on Mr Crombie’s farm.

On this farm in the current season both Ariki and Manawa had been deliberately harvested out of condition and dried in a continuous drier as a method of reducing field losses. Because of the poor drying conditions in the field and in an attempt to get on with the harvest a field of short rotation had been headed at 30 per cent moisture. This seed had to be passed over the drier three or four times to reduce it to 14 per cent To avoid confusion and enable other lines to be dealt with half of the original line (now down to 21 per cent moisture content) had been placed on a cooling floor and left there until it could be dealt with. A 6in diameter straightbladed centrifugal fan driven by a one-horsepower electric motor had been obtained and placed just outside the doorway of the granary. Two lengths of 6in ducting had taken the air to the centre of the cooling floor, which was made by laying two pipe drafting yard gates on a series of 6in wooden blocks to a make a raised floor some 6ft square. Because the mesh between the gate rails was too large some 6in by lin timbers were laid across the gates at 12in centres and the top and sides of the floor covered with two strips of hessian, as used as a protective covering around bales of now cupltq Forty-eight sacks of seed were put on the cooling floor covering it to a depth of 2ft and extending about 2ft out all round it. Thermocouple ropes were inserted horizontally and vertically through the mass and connected to a potentiometer for

accurate temperature determination.

The original temperature of the seed was of the order of 75 degrees Fahrenheit and it could be anticipated that it would rise to about 100 degrees over night. The fan was switched on at 9 p.m. to blow in air at 51 degrees. One hour later the bottom foot of seed on the cooling floor was down to about 55 degrees and in two hours the cold zone had moved to the top of the mass. At this stage another 10 sacks of seed at 80 degrees were added to the heap and the fan allowed to nm until midnight when the whole mass was below 60 degrees and the fan was then shut off. On the following day; the centre of the mass had wanned a little and the fan was run again on the second

night for three hours, using the air at 50 degrees Fahrenheit On the second day the seed was examihed at midday and found to be in the 55 to 60 degree ; range and no mould growth was discernible. Until it eould be dealt with the practice with this line of seed would be to cool it with night air by blowing two or three hours each evening and it was anticipated that no harm would esult to the seed in the holding period because microbiological activity would be low and the mass would not heat up to a dangerous level. This, said Mr Crosbie, was a technique used by Mr John Rowsell, of Stoke Charity, near Winchester, England, who was now visiting New Zealand, when Mr Crosbie visited him in 1961. That season Mr Rowsell had held some thousands of bushels of damp seed on a cooling floor until the barley harvest was completed and staff could be released to dry grass seed. In

this case Mr Rowsell kept the fan running day and night, using air in the 60 to 65 degrees temperature range. But in New Zealand there seemed to be no reason for using day air for this often rose to the 70 to 80 degree mark and this would seem to defeat the object of the exercise. Mr Crosbie said that the trial on Mr Crombie’s farm was the first occasion on which this technique had been used in New Zealand and it promised to be a useful adjunct to grass seed drying. The equipment could be readily assembled by farmers and practically any old fan could be used—that off a big mill would be suitable. The fan in the trial used on Mr Crombie’s place developed just over 1000 cubic feet of air per minute against a pressure of a half inch on the water gauge and was found to be suitable for the mass of more than 300 bushels of seed.