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variability of pasture dry matter (DM) yields across four distinct physiographic regions, using published and original unpublished datasets collected from 1958–2021.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.

新西兰北地大区（Northland）的核心土地利用类型为牧场放牧业。本研究采用1958年至2021年间收集的已公开与原创未公开数据集，分析了4个独立地貌分区内的牧草干物质（pasture dry matter, DM）产量分布与变异特征。达格维尔（Dargaville）的年均牧草干物质产量最高，达11900千克干物质/公顷；凯塔亚（Kaitaia）为9970千克干物质/公顷；凯科希（Kaikohe）与旺阿雷（Whangarei）的产量约为8400千克干物质/公顷。牧草水分利用效率（单位降雨量对应的干物质产量）的取值范围为10.8千克干物质/毫米/公顷（凯科希）至16.4千克干物质/毫米/公顷（达格维尔）。凯塔亚的年产量变异幅度最大，变异值超过2300千克干物质/公顷。本研究量化了牧草生长与温度之间的关联关系，以此估算这四个区域经温度校正后的生长速率。受夏季干旱条件影响，旺阿雷的春季牧草生长速率较低，为3.19千克干物质/度日（degree day, °Cd）；当累计度日达到2560°Cd（约合7630千克干物质/公顷）后，生长速率下降至1.85千克干物质/度日。上述结果表明，与新西兰其他区域相比，北地大区的牧草生产水平偏低。夏季干旱或冬季多雨时期难以获取充足的补充饲料，可能会进一步加剧产量偏低与牧草持久性不足的问题。这会提升过度放牧风险，进而降低植物储备与总光照截获量，最终造成牧草植株物理损伤，导致实际产量低于潜在产出水平。