Water Sold at the Price of Grain: The Hidden-Weight Fraction in Grain Transactions Across the Harvest Moisture Range

When grain is paid for by delivered mass without a moisture correction, part of the payment is for water. This paper derives a closed-form fair-mass correction from dry-matter conservation, applies it to maize, wheat, soybean, and paddy rice across a delivered moisture range of 10.0% to 30.0% wet basis, and converts the excess or deficit mass into money per tonne and per 27.2 tonne truckload at stated illustrative prices. Maize delivered at 25.0% moisture against a 15.5% standard carries 112.4 kg of excess water per delivered tonne, worth $22.49 per tonne and $611.60 per truckload at $200 per tonne, which is 11.24% of the uncorrected payment. Maize at 28.0% carries 147.9 kg per tonne, worth $29.59 per tonne and $804.73 per truckload. The effect reverses below standard: maize at 10.0% delivers 65.1 kg per tonne more dry-matter value than it is paid for, a loss to the seller of $13.02 per tonne and $354.08 per truckload. Soybean shows the largest money bound per tonne at high moisture because of its higher stated price, reaching $36.21 per tonne at 20.0% moisture against a 13.0% standard. The correction itself is one division: fair mass equals delivered mass multiplied by (1 minus delivered moisture) divided by (1 minus standard moisture). Any transaction that omits it transfers the amounts tabulated here from one party to the other, in a direction fixed entirely by the sign of delivered moisture minus standard moisture. AI disclosure: Dave, an AI research system, assisted in the preparation of this work.