Article Summary: Healthy soil underpins profitable grazing, so test it regularly, read the results, and target fertiliser to fill only the true gaps. Keep pH near neutral with lime, maintain phosphorus and sulphur for clover, apply nitrogen sparingly when growth will respond, and balance potassium and magnesium to protect both pasture and cow health. A paddock-specific plan that tracks nutrient removal and effluent returns turns every fertiliser dollar into stronger, more resilient swards.
Healthy pastures begin beneath the surface. The soil that feeds your ryegrass–clover sward is a living, dynamic system, and your grazing returns will never rise above its potential. By adopting a structured approach to soil fertility testing, interpreting, and acting you give your pasture the solid footing it needs to perform season after season.
Why Healthy Soil Matters
Think of soil as the farm’s silent workforce. It houses billions of microbes, stores moisture, and supplies every blade of grass with sixteen essential nutrients. When any one of these nutrients slips out of balance, you see it first in the paddock: uneven growth, less clover, and declining feed quality. Over time, those small slips erode stocking rates and milk solids.
A well‑balanced soil profile does more than push dry‑matter yields. It buffers pasture through climatic extremes, supports strong root systems that mine moisture in a dry spell, and reduces nutrient losses to waterways. In other words, good fertility underwrites resilience as well as production.
Reading Your Soil: Testing and Interpreting Results
Regular soil testing—every two to three years for most paddocks, annually on high‑input or effluent blocks remains the only reliable way to know what is happening below ground. A basic test reports pH and key macronutrients (P, K, S, Mg, Ca), while extended panels add trace elements and cation exchange capacity.
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Sampling: Walk a W‑shaped transect, take 15–20 cores to 75 mm depth, mix them in a clean bucket, and label clearly.
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Targets: For dairy pastures on most New Zealand soils, aim for pH 5.8–6.0, Olsen P in the mid‑20s to low 30s µg/mL, and exchangeable K and Mg within their respective “target” bands on the laboratory report.
Once you have the numbers, classify each paddock as maintenance (nutrients in the target range) or capital (nutrients below target). Maintenance blocks only need to replace what livestock remove. Capital blocks require a plan to lift levels gradually; raising P or K too quickly is costly and increases environmental risk.
Phosphorus – Setting the Foundation
Phosphorus is the engine oil of a clover‑based system. Adequate Olsen P supports rapid root growth in ryegrass and fuels the nitrogen‑fixing bacteria in clover nodules. When P is short, clover contribution falls, forcing greater reliance on purchased nitrogen fertiliser.
On most dairy platforms, applying single superphosphate each autumn or spring keeps P and sulphur ticking over. Split or late‑winter applications reduce the risk of runoff during heavy rain. Overshooting the target brings no production gain, so match the maintenance rate to your milk‑solids removal and effluent recycling. Effluent paddocks often need little or no additional P because the dairy shed is already shifting phosphorus back to the soil.
Nitrogen – A Powerful but Precise Lever
Nitrogen fertiliser works best when ryegrass is hungry for it. Apply 20–40 kg N/ha to paddocks with 1,600–1,800 kg DM/ha residuals and enough soil moisture for two to three weeks’ growth. In spring, responses of 10–15 kg extra dry matter per kilogram of N are common. In mid‑summer drought or cold winter, those responses collapse, and much of the N may leach or volatilise.
Many regions now enforce a cap of 190 kg N/ha/year. Working within that ceiling forces a sharper strategy:
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Use clover as the primary N source by keeping pH, P, S, and Mo in line.
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Target N to shoulder periods early spring and autumn when every extra kilogram of pasture has high feed value.
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Avoid back‑to‑back applications; give the sward time to respond before deciding on the next round.
With good grazing management and a strong legume base, you can often trim total N inputs without sacrificing production, lowering both cost and nitrate losses to water.
Potassium, Sulphur, and the Other Team Players
Potassium cycles quickly through a dairy farm. Large amounts leave the paddock in milk and dung that is then washed down the dairy shed and sprayed on effluent areas. If effluent returns are uneven, K can build to excess under the irrigator and slide below target in outer paddocks. High K immediately before calving also raises milk‑fever risk, so time dressings carefully.
Sulphur is the companion nutrient to nitrogen and phosphorus in clover metabolism. Elemental S products release slowly and suit high‑leaching pumice soils, while sulphate forms in superphosphate or ammonium sulphate provide a quick pulse where rainfall is lower.
Trace elements such as boron, zinc, and molybdenum rarely limit pasture growth but can influence animal health. Blood and liver tests, alongside herbage analysis, help you decide whether to correct these with fertiliser or supplement blocks.
Balancing pH, Calcium, and Magnesium
Soil pH is the master switch for nutrient availability. Below pH 5.5, aluminium starts to bind phosphorus and stunt root growth. Above pH 6.2 on some soils, trace elements like manganese become less available. Regular lime applications typically 1–2 t/ha every five to seven years keep pH in the sweet spot and supply calcium.
Magnesium plays a dual role, supporting chlorophyll in plants and preventing grass tetany in lactating cows. If soil Mg is low, consider dolomite lime or targeted Mg fertilisers in autumn, when grass tetany risk is highest.
Building a Practical Fertility Plan
A sound fertility plan joins the science of soil tests with the realities of cashflow and pasture demand. Work through the following steps with your agronomist or fertiliser adviser:
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Map the farm: Group paddocks by soil test status, effluent application, and production needs.
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Set priorities: Allocate capital nutrient spend to the lowest blocks first; keep maintenance blocks ticking over.
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Schedule applications: Fit around calving, mating, and local weather patterns. Avoid heavy dressings on saturated soils.
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Track removal: Update maintenance rates annually using milk‑solids production, silage movements, and effluent returns.
Keeping the plan visible on a whiteboard, in your farm management software, or both makes it easier to stick to and review each season.
Bringing It All Together
Managing soil fertility is less about pouring on product and more about fine‑tuning a complex system. By testing soils regularly, targeting nutrients where they give the best return, and respecting environmental limits, you ensure that every kilogram of fertiliser is working for you. Strong, balanced soils grow vigorous pastures, support healthy animals, and underpin the profitability of your dairy business for the long term.
Until we meet again, Happy Fertilisations!
- The Dedicated Team of Pasture.io, 2025-07-29