Open interest measures the degree or level of participation in the market. Usually it reflects new participants coming into the market and old ones dropping out. If the seller on the other end of your transaction was closing out a previous long position in wheat, open interest would not change. You would, in effect, replace him in the market. But if the seller was establishing a new short position, volume would increase by one because there would be a new long and a new short.
Open interest is more subject to seasonal fluctuations than is trading volume.
The low point usually occurs just before new crop harvest. It usually peaks when grain storage stocks are at their apex because as the commodity is stored, the number of hedged transactions increases. Both volume totals and open interest rates are published in the market sections of most daily newspapers. Both volume and open interest are measured in bushels for grain and in contracts for meats. Looking at the combination of volume, open interest and price action can give the producer clues to how prices may behave in the future.