A review of pasture yields and growth rates in Northland

Pastoral grazing is the major land use in Northland, New Zealand. This study analysed the distribution and variability of pasture dry matter (DM) yields across four distinct physiographic regions, using published and original unpublished datasets collected from 1958–2021. Dargaville had the highest mean annual pasture yield of 11900 kg DM/ha, Kaitaia 9970 kg DM/ha and Kaikohe and Whangarei at ∼8400 kgDM/ha. Pasture water use (DM yield/mm rainfall) ranged from 10.8 kg DM/mm/ha (Kaikohe) to 16.4 kg DM/mm/ha (Dargaville). Kaitaia showed the largest annual yield variability (>2300 kg DM/ha). The relationship between pasture growth and temperature was quantified to estimate temperature adjusted growth rates for these regions. Whangarei spring growth was low at 3.19 kg DM/°Cd before it declined after 2560°Cd, or ∼7630 kg DM/ha, to 1.85 kg DM/°Cd, due to summer dry conditions. These results suggest pasture production was low compared with other regions of New Zealand. The low production and persistence may be compounded by the lack of readily available supplementary feed during summer dry or winter wet conditions. This increases the risk of overgrazing which reduces plant reserves and total light interception which results in physical damage to pasture plants and lower than potential yields.