Effect of urine, potassium and dicyandiamide application on pasture production from a free-draining Canterbury dairy pasture soil

A cut-and-carry trial was conducted on a low quick-test potassium (QTK ≤ 4) Lismore soil during 2012-13 in Springston, Canterbury to test the responsiveness of a dairy pasture to urine, dicyandiamide (DCD) and potassium (K) applications. Over the full year the applications of urine-only, urine + K, urine + DCD, and urine + DCD + K increased pasture production significantly over the non-urine control treatment by 23%, 29%, 36% and 42%, respectively. Applications of K, DCD and DCD + K increased production over the urine-only treatments by 5%, 10% and 15%, respectively, for both spring and full-year totals. There were no significant increases to K or DCD applications for non-urine treatments. The pasture responses to K and DCD applications were attributed to maintaining better balanced plant nutrition, rather than to soil K deficiency per se, as urine application maintained QTK levels to recommended values (QTK c. 6) for the duration of the trial. However, K deficiency may still have occurred at times of high demand where K uptake was restricted by the shallow soil depth. Although these differences were considered to have their roots, at least partly, in K nutrition, it may also reflect differences that are particular to cut-and-carry trial management and measurement. Continual harvesting of dry matter (DM) reduces K availability quickly in some soils even after large initial K applications in urine (> 800 kg K/ha). The findings of this cut-and-carry trial show that regular K application can influence pasture DM responses to the urine-nitrogen retained in soil, and to the use of a nitrification inhibitor, and not just when soil K levels are low