Summer pasture yield variation in a central Waikato location from 1979 to 2010: implications for pasture persistence.
DOI:
https://doi.org/10.33584/rps.15.2011.3214Abstract
Three datasets spanning 31 years (1979-2010) of net herbage accumulation (HA) for Waikato dairy pastures were studied to determine between-year variability in summer HA. In addition, a dairy farm at the same location was modelled with the DairyNZ Whole Farm Model, using climate data for 15 years to predict HA, and milksolids production. Measured extremes for HA over 5 months (1st December to 30th April inclusive) were from 4.7 to 9.1 t DM/ha, with a mean of 7.0 t DM/ ha ±1.2 t DM/ha SD. Rainfall during these months had a positive impact on HA, with an extra 849 kg DM/ ha (r2=0.43, p<0.001) grown in December to April for every additional 100 mm of rainfall. December- April rainfall during 1979-1993 was 17% more than December to April 2004-2010. For the modelled farm stocked at 3.1 cows/ ha, December to April HA was predicted to average 6.6 ±1.3 t DM/ha, ranging from 4.7 to 8.7 t DM/ha. In 2 years out of 3, HA was predicted to be below feed demand from December to April. Clearly, managing pastures to recommended post-grazing residuals and pre-grazing leaf stage in summer can be problematic when the variability in HA is large and there is limited capacity to reduce stocking rate and hence feed demand. Repeatedly exceeding pre-grazing herbage mass targets in good summer HA years and post-grazing residual targets in poor summer HA years are both scenarios consistent with the loss of perennial ryegrass plants from dairy pastures and this study examines the historical frequency and size of such events. Keywords: annual variation, grazing management, Lolium perenne, summer herbage accumulation, stocking rate
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