Dr. Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist, offers herd health advice as part of the weekly series known as the "Cow Calf Corner" published electronically by Dr. Peel and Dr. Glenn Selk. Today, Dr. Selk addresses the time of day when harvest occurs and how it can impact the concentration of harmful nitrates in forages.
"Forage sorghums are used by cattle producers for summer grazing or harvested for hay. Forage sorghums can be very productive and high quality, but can also accumulate toxic levels of nitrate when stressed. Based on the assumption that the plant continues soil nitrate uptake during nighttime hours, followed by accelerated conversion of the nitrate to protein during daylight hours, previous extension recommendations have been to wait until afternoon to cut forage sorghum for hay if anticipated nitrate levels are marginally high.
"To evaluate the significance of the change in nitrate concentration in forage sorghums during the day, Oklahoma State University Extension Educators collected samples at two hour intervals from 8 AM to 6 PM. Five cooperator’s fields ('farm') were divided into quadrants. Three random samples, consisting of ten stems each, were taken from each quadrant at the specified interval. The samples were analyzed at the Oklahoma State University Soil, Water, and Forage Analytical Laboratory to determine the level of nitrates, in parts per million (ppm).
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