A comparison under grazing of pasture production, pasture N content and soil mineral N levels between granular urea and ONEsystem® on two contrasting dairy farms in New Zealand

Abstract

Field trials under grazing on two contrasting dairy farms in mid-Canterbury (Site C) on a stony silt loam under irrigation, and in rain-fed central Waikato (Site W) on a volcanic ash-derived soil, compared standard granular urea (4-5 mm diameter granules) with ONEsystem®. This uses prilled urea (0.8-2.8 mm diameter prills), passed through a fine water spray (50 litres/ha) that contains the urease inhibitor nbpt (2 gm nbpt/kg N) during application. A nil N control and three rates of each fertiliser were applied to 12 × 25 m plots on four occasions after rotational grazing during spring/early summer 2014. ONEsystem® resulted in extra dry matter (EDM) to N applied compared with granular urea at Site C. At Site W, the initial advantage to ONEsystem® in Period 1 (early spring) was not maintained. To produce EDM of 1250 (±750) kg/ha required 120 and 126 kg N/ha as granular urea at Sites C and W, respectively (giving EDM factors of 10.4 and 9.9 (± 2) kgDM/ kgN applied respectively). This compares with 50 and 74 kg N/ha required with ONEsystem® for higher EDM factors of 24 and 17 (± 5) kg DM/ kg N. Pasture N concentrations were higher at Site C following ONEsystem® application, and total N uptake was increased 3-fold compared to granular urea. At Site W, increases in EDM with ONEsystem® only occurred in the first period. The results of this study have implications for both the economic and environmental efficiency of fertiliser urea use on grazed pastures. Keywords: ONEsystem®, prilled urea, nbpt, granular urea, N efficiency, pasture, N uptake