Variability of dry matter loss rates of 18% moisture soybeans at 35°C

Soybeans are biologically active after harvest, continuing to respire during storage and postharvest processing. The soybeans' respiration is affected by moisture content and temperature, and directly relate to deterioration, or dry matter loss (DML), rates. Several corn storage experiments have been conducted using respiration rates as a measure of DML rates. These data were used to develop ASABE Standard D535 which presents a maximum allowable storage time (MAST) table to provide safe storage time guidelines for shelled corn at 16.4-34% moisture and 1.7-48.9°C. This type of table would be valuable in understanding and minimizing losses during handling and storage of soybeans, especially in low-latitude countries where infrastructure for harvest, transportation, storage, and handling of soybeans are often rudimentary. But before such a table can be developed, several tests need to be conducted to understand better the variance in respiration or DML rates measurements. From literature, grain respiration rates have ranged from 0-2040 mg CO₂ kg^-1 d^-1 (0-0.14 % DML d^-1) for test moisture contents ranging from 9-23% and storage temperatures 15-30°C. It is unclear how much of this reported variability is due to measurement method vs. underlying natural variability. Historically, data were often collected on 2-3 replications. Therefore, in this paper, we explored the variance of replicated DML rates of soybeans at 18% moisture and 35°C and use this information to better design future experiments to develop a MAST table for soybeans appropriate to low-latitude countries. Results showed that DML rates ranged from 0.235-0.339 % d^-1. Variance of DML rates was ± 0.013 % d^-1. Statistical power analysis revealed that, for a future experiment testing DML rates of soybeans at three moisture contents and one storage temperature, a minimum of four replications are necessary for robust experimental design.