GDD — growing degree days
GDD (growing degree days) accumulates daily by how much the mean temperature exceeds a base (here 0 °C). Turf grows by warmth, not calendar — the heat sum predicts growth and e.g. PGR longevity.
Glossary
Greenkeeping terms in plain language.
The same explanations Turfgrass Mastery OS shows beside its tool headings — the platform teaches while it works. Finnish terminology follows the greenkeeping glossary; Swedish follows the STERF vocabulary.
Core agronomic figures
ET₀ — reference evapotranspiration
ET₀ (reference evapotranspiration, FAO-56) is the water the turf and surface lose per day (mm). Irrigation is sized to replace it.
Growth potential
Growth potential (0–100 %) shows how close the temperature is to the grass's optimum. A low value means growth is limited by temperature, not by your practices.
Tool concepts
Agronomic Growing Degree Days (GDD)
GDD (growing degree days) accumulates daily by how much the mean temperature exceeds a base. Agronomic uses time PGR re-applications, disease risk and germination by heat sum — the plant lives by warmth, not the calendar.
Tool →Agronomic Planner
MLSN (Minimum Levels for Sustainable Nutrition) is a research-based guideline for the lowest sufficient soil nutrient levels for healthy turf. Fertilise to soil-test need — often well below traditional tables, with no loss of quality.
Tool →Cost per Round
Cost per Round divides total maintenance spend by rounds played. It is the course's key efficiency figure: compare seasons, justify budgets and see investment impact per golfer.
Tool →Disease Pressure Model
Disease-pressure models forecast turf disease risk from weather: temperature, leaf wetness and humidity determine when conditions for e.g. microdochium or dollar spot are met. The forecast times prevention to risk, not routine.
Tool →DU Calculator · Distribution Uniformity
DU (Distribution Uniformity) measures how evenly the irrigation system applies water: a catch-can test compares the driest quarter with the average. Low DU means overwatering most of an area so the driest spot gets enough — uniformity saves water and nerves.
Tool →ESG Reporting
ESG (Environmental, Social, Governance) covers environmental, social and governance responsibility. For a golf course an ESG report gathers measurable actions — water use, emissions, biodiversity, working conditions — in the form owners, municipalities and financiers ask for.
Tool →ET Calculator
ET (evapotranspiration) is the water the turf and soil surface lose to the air in a day (mm/day). Irrigation is sized to replace what evaporated — the FAO-56 ET₀ calculation does that from weather data instead of habit.
Tool →Grow-in Programme
Grow-in is the phase where a new or renovated surface is raised from seed or turf to full playing condition. It is its own programme — frequent feeding, watering and first cuts — whose discipline sets surface quality for years.
Tool →Growing Degree Days (GDD)
GDD (Growing Degree Days) is an accumulating measure of season warmth: each day adds the amount by which the mean temperature exceeds a base (often 0 °C). Turf grows by heat sum, not by calendar — so GDD predicts things like plant-growth-regulator wear-off and mowing demand better than a date does.
Tool →Irrigation Calibration
A water budget compares water in (rain + irrigation) with water out (ET) and shows whether a deficit or surplus is building. It reveals irrigation need before the turf shows it — and documents water use for permits.
Tool →Long-Term Property Plan (PTS)
A long-term plan (PTS) is the course's multi-year maintenance and investment programme: what gets renewed, when, and at what cost. It makes deferred maintenance visible and governable for the board.
Tool →Moisture Mapping
VWC (Volumetric Water Content) is the rootzone's water content by volume in percent — the number a moisture meter (e.g. TDR) reads. Moisture mapping turns a green into a map of dry and wet zones for targeted watering.
Tool →Natural Capital
Natural capital values the course's nature — meadows, woods, waters, carbon sinks — as visible assets. It translates environmental work into the language decision-makers and financiers understand.
Tool →Organic Matter Management (OM246)
OM246 measures rootzone organic matter at three depths: 0–2, 2–4 and 4–6 cm. Surface organic matter (thatch) drives green firmness, infiltration and disease pressure — OM246 tracking shows whether aeration and topdressing are keeping it in check.
Tool →Playing Quality Dashboard
Playing-quality metrics describe how the course plays: green speed (stimpmeter), surface firmness, moisture and trueness. Numbers make playing quality manageable — targets, measurement, adjustment.
Tool →Time-in-Motion (TiM)
Time-in-Motion is work-time analysis: measuring where greenkeeping hours actually go. Once the real hours behind mowing, bunkers and greens are known, rosters, machine purchases and budgets can be sized on measurements instead of gut feel.
Tool →Turf Doctor · Biostimulants
Biostimulants (seaweed extracts, humic substances, amino acids and the like) are neither fertilisers nor pesticides — they support the plant's own stress tolerance and rooting. Effects are real but condition-dependent, so choose by diagnosis, not sales pitch.
Tool →Turf Doctor · Wetting Agents
Wetting agents are surfactants that help water infiltrate water-repellent rootzones (dry patch) evenly. Product and programme are chosen by problem: penetrant, re-distributor or retainer.
Tool →Turf Economics
ROI (Return on Investment) shows whether a purchase pays itself back: yearly savings or income relative to price, and the payback period in years.
Tool →Weather-station parameters
WBGT — wet bulb globe temperature
WBGT (wet bulb globe temperature) combines heat, humidity, wind and solar radiation into one heat-stress figure. Used in occupational safety: at high values (above ~28 °C) heavy outdoor work needs breaks.
Wet bulb temperature
Wet bulb is the lowest temperature air reaches through evaporation. On a course it indicates e.g. syringing cooling power and frost-protection conditions.
Air temperature
Air temperature at 2 m. Drives growth (growth potential), disease pressure and GDD accumulation.
Relative humidity
Relative humidity is the share of moisture the air holds versus its maximum. Long spells of high RH plus leaf wetness create fungal disease conditions.
Absolute humidity
Absolute humidity is the actual water content of the air (g/m³) regardless of temperature — useful for judging dew and overnight moisture.
Rainfall
Rainfall (here 24 h). With ET it forms the water balance: rain − evapotranspiration = irrigation need.
ET₀ — reference ET
Reference ET (24 h) is calculated evapotranspiration in millimetres — the water the turf and surface lose in a day. Irrigation is sized to replace it.
Dew point
Dew point is the temperature at which air moisture condenses. When night temperature reaches it, leaves get wet — and leaf wetness hours are the key variable in disease models.
VPD — vapour pressure deficit
VPD (vapour pressure deficit, kPa) is the air's 'pulling power' for water. High VPD = fast drying and irrigation demand; very low VPD = transpiration stalls and disease pressure grows.
Delta T
Delta T is the gap between air and wet-bulb temperature — the spraying-conditions gauge. The ideal window is roughly 2–8 °C: lower means droplets drift, higher means spray evaporates before it works.
Heat index
Heat index is the 'feels like' temperature combining heat and humidity. A worker-safety gauge in hot spells.
Solar radiation
Solar radiation (W/m²) drives photosynthesis and evapotranspiration. Low radiation in shade explains weaker growth; high radiation plus drought = stress spike.
Wind gust
Gust is the momentary peak wind. Spraying stops when gusts exceed ~5–6 m/s because of drift.
Wind speed
Mean wind speed. Affects evapotranspiration, sprayability (ideally under ~4 m/s) and irrigation uniformity.
Wind
Wind affects evapotranspiration, sprayability and irrigation uniformity.
Soil temperature
Soil temperature drives root growth and germination — cool-season roots grow best in cool soil, and many operations (seeding, aeration) are timed by it.
Soil moisture
Soil moisture shows rootzone water status at sensor depth — the base metric for targeted irrigation.
Soil oxygen
Soil oxygen (%) shows whether roots can breathe. A well-aerated rootzone sits near the atmosphere's ~20 %; values falling clearly lower (compaction, waterlogging, ice cover) suffocate roots — in winter oxygen sensors track ice-damage risk.
Salinity (EC)
Salinity reflects the salt content of the rootzone (conductivity-based). Elevated salinity hampers water uptake and burns roots — watch it especially with recycled water or near the coast.
Water balance
Water balance (sensor-derived) compares water received with losses at the sensor — positive accumulates moisture, negative dries.