Transfer of fertility from sprinkler‐irrigated pasture under two cattle grazing systems

Two summer grazing systems were compared for 10 years on sprinkler‐irrigated pasture: grazing for 2–3 h at a time, where cattle go in “empty” and come out “full” (depletion grazing), and rotational grazing with no transfer of fertility. The effects of these treatments on the responsiveness of pasture yield to fertiliser K and N were tested. Under rotational grazing an application of 60 kg K/ha/year sustained a mean pasture yield of 18 380 kg DM/ha/year and the response to an additional 120 kg K/ha/year was only 6.4%. Under depletion grazing the corresponding yield was 15 280 kg DM/ha/year and the response to additional K was 15.2%. The estimated loss of K by transfer exceeded the fertiliser K application by 40–60 kg K/ha/year at both application rates of K. It is suggested that this was obtained from non‐exchangeable sources. The response to fertiliser N appeared to be highest at medium levels of K fertility.