Effect of temperature on dicyandiamide (DCD) longevity in pastoral soils under field conditions

Data were analysed from five trials begun in autumn at a field site and a relationship between time for concentration of the nitrification inhibitor dicyandiamide (DCD) in soil to halve (t½, days) and the mean soil temperature (T, °C) was developed: t½ = 54–1.8 T. For example, when T was 8 and 16 °C, t½ was 39 ± 6 and 25 ± 3 days (±95% confidence limit), respectively. Previously, under laboratory conditions at equivalent temperatures, the corresponding values of t½ were 86 ± 31 and 44 ± 24 days. Thus, the proportional responses of t½ to increasing T from 8 to 16 °C were similar, but under field conditions t½ was about half that under laboratory conditions.