Comparison of dry matter loss rates from static and dynamic grain respiration measurement systems for soybeans at 18% moisture content and 30°C

Time to reach 0.5% dry matter loss (DML) is the estimated maximum allowable storage time (MAST) for shelled corn and has been suggested for use with other grains. Respiration studies have reported various estimates of this threshold depending on the type of grain respiration measurement system (GRMS) and storage conditions tested. The objectives of this study were (1) to design and evaluate two GRMS in which oxygen needed for respiration was limited in a static system (S-GRMS) or continuously supplied in a dynamic system (D-GRMS) during storage and (2) to compare the effects of GRMS on DML rates (vDML) for 18% moisture content soybeans stored at 30°C for 20 d. In this study, S-GRMS and D-GRMS units were designed to conduct respiration tests. Respired CO2 (mg CO2) was measured over time and used to calculate the specific mass of respired CO2 (mg CO2 kg-1 d.b. beans) and subsequent DML (%) using stoichiometric ratios from the respiration chemical reaction. DML rates, vDML (% d-1), were estimated by least squares linear regression of DML and time data. Four replications of respiration tests were conducted in each GRMS. Average estimates of vDML were 0.0157% d-1 and 0.0189% d-1 for S-GRMS and D-GRMS, respectively. Mean vDML from D-GRMS tests was 1.2 times greater than mean vDML from S-GRMS but not statistically different (p = 0.09). However, the coefficient of variation was 8 times greater for DGRMS than for S-GRMS. More studies with a wider range of storage conditions should be conducted for development of a safety factor between both systems prior to using data from respiration of soybeans in the literature to estimate MAST.