Evaluating on-farm methods for measuring dry matter content of potatoes
Measuring dry matter content is critical for pricing cull potatoes and for effectively managing potato feeding rates on livestock operations. In this study, dry matter determinations from three on-farm methods (microwave, dehydrator, and Koster Moisture tester) were compared with a laboratory oven. Twenty lots of potatoes were obtained for the study (1 blue, 3 red, 3 yellow, and 14 burbank varieties). Ten potatoes from each lot were cleaned then sliced horizontally into 7mm thick slices. Duplicate 100g sub-samples were run with each drying method. Lab (L) samples were dried for 24 h at 55 C. Equipment for the on-farm methods included two 1000-watt microwaves (M), four 500-watt Nesco FD60 food dehydrators (D) set at 68 C, and two Koster Moisture Testers (K). Samples were weighed at specified time intervals during the drying process with the on-farm methods and a run was deemed complete when two identical weights were obtained. Drying time and dry matter (DM) data were analyzed as a completely randomized block design. Drying time differed significantly between on-farm methods (p<0.001) and averaged 8.6, 248.5, and 428.6 minutes for M, K, and D, respectively. Mean DM was significantly higher (p<0.05) for M (23.4%) and D (23.5%) than K (22.6%) or L (22.7%). A Bland-Altman assessment for agreement was used to compare difference in DM between each on-farm method and L. A range of agreement was defined as mean bias + or – 2 SD. The 95% limits of agreement between the lab oven and M, K, and D were: -0.7% to 1.5%; -1.6% to 1.4%; -1.0% to 1.6%, respectively. Overall, the three on-farm methods provided closely corresponding DM to L. The trend lines between Bland-Altman differences and oven DM were not statistically significant (p>0.75) for D and K but was significant (p<0.05) for M with a negative slope across the range of DM in the study. Drying potatoes with all three on-farm methods did not create objectionable odors and can therefore be conducted indoors if desired. This study indicates that the three on-farm methods are effective tools for measuring DM content of potatoes.
Keywords: potatoes, dry matter, on-farm testing