Successful Cooling Of Grass Seed

Press, Volume CVI, Issue 31304, 25 February 1967, Page 9

Successful Cooling Of Grass Seed

A most spectacular example of the cooling properties of ambient air occurred on the farm of Mr J. W. Crombie, of Waitohi, South Canterbury, last month when he used ordinary air to cool a mass of about 1750 bushels of out-of-condition grass seed that had been harvested in bulk from a field of 30 acres.

Readers of this page will recall that last season a small fan was used to cool and to bold safely a small line of bulk grass seed for three days until it could be conveniently dried on the continuous flow drier on this property. Having amply demonstrated that damp grass seed could be safely held cool by such means, Mr Crombie this season excavated a trench across a 16ft wide by 20ft long holding bay in his granary and concreted into it a 2ft wide by 18 inches deep transverse air duct and fitted a heavy metal grill that would support a loaded farm truck.

Initially five lateral wooden ducts in the shape of an inverted U were built from 6in by lin timbers about 13ft long and raised above the floor on short 4in by 2in offcuts. They were placed at right angles over the main duct and spaced 30in to 36in apart to suit the dual wheels of the truck so that it could be reversed up between the laterals and the seed unloaded on to them after they had been covered with strips of hessian to prevent seed entry under the laterals. In this

way on the first occasion some 650 bushels of bulk grass seed was spread to a depth of 2ft Bin on the cooling floor. It was harvested on a day of temperatures in the shade of 67 dropping to 64 degrees Fahrenheit and the seed arrived on the floor at a temperature of 95 degrees dropping down to 88 degrees for the last load. The fan used was the engine functioned unit described on these pages last November and is rated at about 8500 cubic feet per minute at 5 inches water gauge. It was started at 7 p.m. when the outside temperature was 64 degrees, and the air entering the duct was measured at 69 degrees at a pressure of 4f inches water guage.

The effect was most spectacular. Within minutes the whole of the 80ft by 90ft granary was filled with hot humid air reminiscent of that encountered at Singapore when one steps out of an air conditioned 707. The temperature was over 90 and the humidity just under 100 per cent. But shortly this phase passed and within half an hour the temperature of the seed had dropped to 72 degrees. In of an hour the seed temperature was down to 70 and the fan was stopped for the evening because no cooler airs were available before midnight Over the next two days the fan was run for 13 hours using a hot north-west air or an ambient air plus 15 degrees temperature rise from waste engine heat and this dried the line from an average of 22} per cent moisture content to an average of 16} per cent. The line was then unloaded on the third day and run quickly over the drier to condition it for safe storage at 14 per cent or lower.

The following week a 30 acre field was harvested at about 16} per cent moisture content and because the drier was being used on

another line, this seed was bulked on to the cooling floor to a depth of 6ft on the lateral ducts which had been extended in length so that the whole 16ft by 20ft floor could be utilised with the aid of shutters across the open end.

This seed came in at temperatures of the order of 95 degrees and again the fan was started in the cool of the evening. Within an hour this mass of some 1750 bushels had cooled to about 70 degrees and the fan was shut off. Subsequent blowings kept the seed safe and cool for a period of a week. The pressure in the main duct was in the region of 51 inches water gauge for this deeper mass and air flow through the mass would be in the order of 7000 c.fjn. It has now been amply shown that cooling hot lines of grass seed is an easy, quick and most efficient undertaking that is within the reach of any grower who has a fan capable of generating a pressure of about one inch water gauge for each foot of depth of seed on the floor.

The object in cooling a line is to prevent germination damage that is associated with heating—the damage being greater for lines of higher moister content A temperature of 100 degrees F can be regarded as the danger point at which cooling action is urgently required. Hyde of the Seeding Testing Station reported in 1952 that all the germination capacity of a line of seed of 15} per cent moisture content was destroyed when it was held at 100 degrees for 15 weeks. On a good harvesting day, grass seed of 100 or more degrees temperature has been

recorded on a header and even though the lines of H.l were of safe moisture levels, they were noted to heat when stored in bulk structures. Accordingly, all growers who bulk hot lines of seed, irrespective of their moistures, should check the temperatures with a thermometer (retail cost under 10s each) and, where conditions of heating are noted, take action to cool the line. Growers, who noted that some lines heated in bulk this season, would be well advised to check their germination certificates later in the year for heat damage —it will show up in lowered interim germination figures as compared with the final result. Then after due consideration of the lower price received for the damaged line, a decision can be made as to whether a fan should be purchased to prevent recurrence in future years.

Thf, article hat been written bu Mr C. J. CROSBIE. oi the Department oj Agriculture, Christchurch.