Using Natural Air Grain Drying in the Spring

By John Ippolito PAg, Crops Extension Specialist, Kindersley

Grain bins with mounted fan dryers
Photo Credit: Author

There is tough grain currently sitting in bins from last fall and now the question is, “How do I effectively dry that grain this spring using natural air systems?”

Natural air drying systems can be effective tools for spring grain drying. An understanding of when conditions are right for drying is important to be effective and minimize drying costs.

Natural air drying works when the air has the “capacity to dry.” This concept refers to the air being at a temperature and relative humidity that allows it to take on moisture as it moves through the grain. The warmer the temperature and lower the relative humidity of the outside air, the more water it can take up as it moves through the grain mass. The chart below demonstrates this relationship:

Water holding capacity and capacity to take up water for 1 m3 of air

Temperature (oC) Water holding capacity (g) Relative Humidity (%) Actual water in air (g) Capacity to take up water (g)
30 30 50 15 15
20 20 65 13 7
10 8 75 6 2

Source: PAMI

Temperature and relative humidity also plays a role defining the equilibrium moisture content of the grain. Equilibrium moisture content is the point where the moisture content of the air and grain are the same and no exchange of moisture will occur regardless of air flow rates. The equilibrium moisture content chart below for wheat has a circle around 12.4 which is the moisture content you could achieve using outside air of 5o C and 50 per cent relative humidity. Also, note further to the right that if the relative humidity of the air was 70 per cent, the grain moisture content that can be achieved is 15.5 per cent. Operating fans under these conditions would not dry grain to the desired moisture content.

Equilibrium moisture content chart
Source: PAMI

Daily air temperatures can fluctuate significantly in the spring. Ideally, producers should not plan on starting to dry wheat with natural air systems until average daily air temperatures are 10o C. Fans can be started when air temperatures are 5o C to warm the grain as the warming process will take about 15 hours provided the air flow is 1 cfm/bu. When air temperatures are below 5o C, you may turn the fans off as no drying is occurring.

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