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Evaluating the accuracy of using reinforcing bar and an infrared thermometer versus long-stemmed thermometers in monitoring mortality compost pile temperature
Two mortality compost piles were constructed using a mixture of goat mortality and butcher waste with ground hay as the carbon source to compare core temperature recorded by long-stemmed thermometers (LST) vs. an infra-red thermometer (IR) to read temperature of a reinforcing bar (RB) thrust into the pile. One LST was inserted into the core of each pile along with a 3 m length of 0.95 cm thick RB so that tips of both the RB and LST were in close proximity. For 30 d following pile construction, LST temperature was recorded daily between 1500 and 1600 h. Each RB was then withdrawn from the pile and the tip’s temperature determined using an IR. Data were analyzed using repeated measures in a mixed model containing treatment (T = LST and RB), date as a covariate (D), and the interaction to test for heterogeneity of slope. Compost pile was a random effect. Date (P < 0.001) and T×D (P < 0.001) showed differences, whereas T was not significant (P = 0.48; 57.8 and 54.5°C for LST and RB, respectively, SE=3.04). Date was used as a covariate as temperature in working mortality compost piles will spike soon after pile formation and slowly decline. As an example, LST recorded a temperature of 64.6°C on d 3 of data collection but only 50.4°C on d 30. The T×D test recorded a slope estimate of -0.320 for LST and -0.018 for RB (probability of slope > 0 of P < 0.001 and P = 0.75 for LST and RB, respectively). These results suggest that RB can be used to monitor mortality compost pile temperature but is not accurate enough to model the normal decline in temperature over time. Temperature of RB may have differed from LST due to location upon reinsertion into the pile (cooler or hotter spot than LST tip) and alignment of IR on RB to record accurate RB temperature and not temperature of surrounding material. Using an IR with RB may be an acceptable method for monitoring mortality compost pile temperature and would be a cheaper alternative for producers composting multiple mortalities than to purchase LST for each pile. However, RB is not appropriate for use when precise temperature measurement is needed.
Keywords: goats, mortality compost, temperature