Pasture eaten (t DM/ha) is known to be a primary driver of profitability in New Zealand pastoral dairy farm systems. However, locally relevant estimates of achievable home-grown feed eaten (the “pasture potential”) are difficult to derive at industry scale. This study used a multi-stage hybrid methodology to estimate farm-specific pasture potential across a large industry dataset. Each farm was spatially enriched with environmental covariates to assign it to a farm typologysystem. Within each farm type, a local nitrogen response slope was estimated based on pasture eaten values for nearby farms within an expanding radius (5-120 km); local pasture eaten was then estimated as a nominal zero-N figure, to remove the confounding impact of fertiliser usage. The pasture potential value was defined as the 90th percentile of home-grown feed eaten within farms of the same type, estimated via quantile regression. A machine learning model (XGBoost) was then developed to impute values for sparsely populated typologies. The analysis identified an average distance from pasture potential of 2.5-3.5 t DM/ha across the different regions. These findings highlight the potentialbenefit to farms having land-specific insights into their pasture potential and support the identification of pathways for improving farm performance in terms of profitability and emissions footprint.
Phosphorus (P) is a key nutrient recommended for optimal nitrogen fixation by legumes in New Zealand pastoral systems. However, few field studies have examined the response of legume monocultures to soil P levels. This research aimed to quantify how phosphorus affects lucerne growth and development in an irrigated cut and carry system with a starting Olsen P of 9 mg/L. A randomized complete block design with five superphosphate treatments (0, 50, 100, 200, 400 kg/ha/y) and four replicates was established within a stand of ‘Kaituna’ lucerne. All herbage was cut-and-carried to ensure no nutrient transfer or return from livestock. Lucerne stem height and annual yields (12000–20000 kg DM/ha) were not different among treatments over four years even when the Olsen P in the Control declined to ~3 mg/L in the top 150 mm. Herbage phosphorus use efficiency was consistently highest in the 50 kg superphosphate/ha treatment with eight times the quantity of applied phosphorus extracted from the soil profile. The 400 kg superphosphate/ha treatment was the only P application rate that was sufficient to fully replace P removed in herbage. These findings suggest lucerne growth was not limited at Olsen P levels below current recommendations, which suggests lucerne was acquiring P below the measured depth and/or accessing P not measured by the Olsen P test.
In the 2023/24 season New Zealand dairy farms are producing more milksolids per cow and per farm than ever before, but sector total factor productivity has been broadly flat since 2012/13.• The difference reflects input intensity. Since 2012/13, additional output has increasingly been supported by increasing reliance on purchased feed, fertilisers and labour resulting in flat productivity trend.• Flat productivity is better read as robustness through a difficult decade, but future competitiveness will depend on lifting pasture utilisation and input efficiency rather than simply spending more to produce more.
Carbon (C) markets are well established for aboveground woody vegetation domestically, and for soil organic C overseas. By reviewing published literature, this project aims to provide a scientifically defensible framework and dataset for estimating the vegetation C stocks in New Zealand grassland ecosystems. New Zealand currently uses IPCC Tier 1 values for biomass and root-to-shoot ratios derived from global vegetation types that do not align well with our intensively managed grassland systems. Shifting the High and Low producing grassland types used in the Land Cover Database to a Tier 2 approach requires inclusion of New Zealand-specific values of aboveground and belowground biomass. From the literature search of field measurements, the overall mean root-to-shoot ratio was 1.35 ± 1.86 and 3.64 ± 2.91 for High and Low producing grassland, respectively. These differ substantially from those root-o- shoot ratios (4.0 and 2.8) currently used in National Inventory calculations. There is good reason to challenge the Tier 1 assumptions, as a higher proportionof the C fixed by the plant is allocated belowground in environments where nutrients are scarce, such as in Low producing grassland, compared with High producing grassland. The review also identified an overall lower C concentration in plant tissue than that used in the inventory. This might be contributing to an overestimation of vegetation C stocks in grassland. We suggest the replacement of Tier 1 with Tier 2 values. Doing so provides a more accurate assessment of theC stocks in New Zealand grassland for the purpose of inventory reporting.
Environmental models deployed as software at scale require governance across science, data, code, release management, user enablement, and security. This extends beyond core scientific rigour without replacing its essential relevance.• A practical governance framework can be organised around governance domains, explicit trade-offs, and records that support accountability, learning and improvement.• The Overseer case is presented as an illustrative account of how these ideas are being explored in Aotearoa New Zealand. It is not offered as evidence that the approach is complete or effective in every respect.• An important corollary is that stewardship funding must extend beyond scientific research publication to include software development, quality assurance, documentation, support, and ongoing governance.
