Encyclopaedia

Essential nutrients, beneficial elements, and toxic or stress agents affecting plant growth.

• Chill Unit Targets
  Many perennial and overwintering crops require exposure to cool temperatures to properly release dormancy and resume uniform growth in spring. These requiremen…
• Everbearer strawberry: GDD / GDH behaviour
  Everbearing strawberries do not behave like traditional June-bearing types. They have reduced dormancy dependence and a more temperature-driven flowering habit…
• GDH → BBCH indicative bands
  This page provides indicative relationships between accumulated thermal time (GDH or GDD) and phenological development (BBCH stages). These values are not fixe…
• GDH, chill & dormancy
  Plant development in temperate climates is governed by temperature over time, not calendar dates. Two key concepts describe this: - Chill accumulation (winter)…
• How To Identify Dormancy Release
  Dormancy release is a biological transition, not a calendar event. Knowing when it has occurred is critical for correctly using GDD / GDH models. This page exp…
• Spring frost risk by phenological stage
  Spring frost damage risk depends far more on crop development stage than on the absolute temperature alone. This page explains how frost sensitivity increases…
• Worked Winter Comparison
  This example illustrates how winter temperature patterns influence spring development, even when spring temperatures appear similar. It explains why two season…

• Bbch Scale
  The BBCH scale is a standardised numeric system used to describe plant growth stages across many crops. It provides a common language for: - Crop development -…
• Daily Weekly Checks
  This page is a practical routine checklist for maintaining stable crop performance. The goal is to catch drift early and avoid over-correction. - Minimum/maxim…
• Feed Recipe Targets
  This page provides baseline nutrient targets for common horticultural crops grown in fertigation or substrate systems. These values are intended as starting po…
• Glasshouse Climate Blueprints
  This page provides practical baseline climate setpoints for common glasshouse crops. It is designed as a starting blueprint, not a fixed prescription. - Setpoi…
• Substrate Management
  This page provides practical guidance for managing substrates and fertigation systems in real growing conditions. It focuses on measurement, interpretation, an…
• Troubleshooting Flowchart
  This page helps diagnose common problems using observed symptoms, not assumptions. Work from top to bottom. Do not skip steps. - Is irrigation volume normal? -…

• Growth stage-specific VPD targets
  Plant sensitivity to VPD varies with: - Leaf area - Root system development - Transpiration demand - Sink strength A single “ideal VPD” does not exist. - Small…
• Hormonal Signalling
  Plant hormones are signalling molecules that coordinate growth, development, and stress responses. They operate at very low concentrations and act as informati…
• Photosynthesis
  Photosynthesis captures light energy and converts CO₂ + water into sugars (assimilates), releasing O₂ as a by-product. Those assimilates power growth, yield, r…
• Respiration
  Respiration breaks down sugars to release usable energy (ATP) for growth, transport, nutrient uptake, and repair. It consumes O₂ and releases CO₂. - Runs 24/7…
• Solar Radiation
  Solar radiation is the total electromagnetic energy emitted by the sun and received at the Earth’s surface. It includes: - Photosynthetically active radiation…
• Source Sink
  Source–sink dynamics describe the balance between: - Sources: tissues that produce carbohydrates (mainly mature leaves) - Sinks: tissues that consume carbohydr…
• Stress Memory
  Stress memory refers to a plant’s tendency to retain physiological responses after stress has ended. Plants do not return instantly to pre-stress function. Str…
• Transpiration
  Transpiration is water loss from leaves (mainly via stomata). It cools leaves and drives water movement from roots to shoots, supporting nutrient transport. Hi…
• Vapour pressure deficit (VPD)
  Vapour Pressure Deficit (VPD) describes the difference between how much moisture the air can hold and how much it currently holds. It represents the drying pow…
• Artificial light & CO₂
  Light and carbon dioxide are the primary drivers of photosynthesis. In protected cropping, both can be manipulated — but only effectively when they are balance…

• Air Filled Porosity
  Air-filled porosity describes the percentage of pore space occupied by air after drainage. It represents the amount of oxygen available to roots and soil micro…
• Bulk Density
  Bulk density describes the mass of dry soil or substrate per unit volume, including pore space. It is typically expressed as: - g/cm³ - kg/m³ Bulk density refl…
• CEC
  CEC is the ability of a soil or substrate to hold and exchange positively charged ions (cations). It represents the nutrient buffering capacity of the root zon…
• Compaction Dynamics
  Compaction is the progressive reduction of pore space caused by pressure, settling, and structural collapse. It affects both soils and substrates. - Repeated t…
• Crop Sensitivity
  Crop sensitivity notes highlight how different crops respond to: - Salinity - Sodium and chloride - pH extremes - Nutrient imbalance - Root-zone stress This in…
• Decomposition & C:N ratio
  Decomposition is driven by microbes consuming: - Carbon as an energy source - Nitrogen to build proteins If a material is carbon-rich, microbes may temporarily…
• EC & TDS
  EC measures the total concentration of dissolved salts (ions) in the root zone. It does not identify which ions are present—only the overall ionic strength. -…
• Field Vs Container Capacity
  Field capacity describes the water content of a soil after excess water has drained freely under gravity in an open field. It reflects: - Soil texture - Struct…
• Irrigation Pulse Design
  Pulse irrigation applies water in short, controlled events rather than long continuous applications. The aim is to: - Re-wet the root zone - Restore water avai…
• Media Ageing Curves
  Media ageing describes how substrates change physically and chemically over time. Ageing is driven by: - Decomposition - Settling - Irrigation cycles - Root gr…
• Mulder
  Mulder’s Chart describes nutrient interactions through: - Synergism: one nutrient enhances uptake or function of another - Antagonism: one nutrient suppresses…
• Nitrogen Cycle
  The nitrogen cycle describes how nitrogen moves between the atmosphere, soil or substrate, microorganisms, plants, and water. Nitrogen is unique among nutrient…
• Osmotic Stress
  Osmotic stress occurs when dissolved salts reduce the plant’s ability to take up water, even when moisture is present. Water moves from low salt concentration…
• Oxygen Vs Temperature
  Root respiration is temperature-dependent. As temperature rises, roots consume oxygen faster. This means oxygen stress can occur even when air-filled porosity…
• Phosphorus Cycle
  The phosphorus cycle describes the movement of phosphorus between minerals, organic matter, soil solution, plants, and microorganisms. Unlike nitrogen: - Phosp…
• Ratios
  Uptake is governed by ion competition, CEC occupancy and root transport. A nutrient can be adequate in absolute terms but poorly available because another nutr…
• Root Respiration Curves
  Root respiration is the metabolic process by which roots consume oxygen to generate energy. Respiration rate varies with: - Temperature - Root age - Oxygen ava…
• Root Zone Oxygen Diffusion
  Oxygen diffusion is the movement of oxygen from the atmosphere into the root zone and toward respiring roots. It occurs primarily through air-filled pores, not…
• Sodium Adsorption Ratio (SAR)
  SAR describes the relative proportion of sodium (Na⁺) to calcium (Ca²⁺) and magnesium (Mg²⁺) in water or soil solution. It is calculated as: SAR = Na⁺ / √((Ca²…
• Soil Texture Classes
  Soil texture describes the relative proportion of: - Sand - Silt - Clay Texture strongly influences water, air, and nutrient behaviour. - Very low WHC - Rapid…
• Soil Types
  - Low bulk density - Low WHC - High drainage - Low nutrient buffering - Rapid nutrient leaching - Balanced particle size - Moderate WHC - Good structure - High…
• Substrates
  - Moderate CEC, often K-dominant - Responds quickly to fertigation chemistry - High K can suppress Ca and Mg uptake - Requires deliberate Ca and Mg supplementa…
• Sulphur Cycle
  The sulphur cycle links atmospheric deposition, organic matter, soil minerals, and plant uptake. Sulphur behaves similarly to nitrogen in some respects but is…
• Water
  Hard water contains higher concentrations of dissolved calcium (Ca²⁺) and magnesium (Mg²⁺), commonly associated with bicarbonate (HCO₃⁻). Key characteristics:…
• Water Holding Capacity
  Water holding capacity describes the amount of water a soil or substrate can retain against gravity after drainage. It is usually expressed as: - % by volume -…
• Wetted Weight
  Wetted weight (or wet bulk density) describes the mass of soil or substrate after water has filled its pore space. It reflects: - Water holding capacity - Pore…
• pH
  pH is a measure of acidity or alkalinity in the root zone, defined as the negative logarithm (base 10) of hydrogen ion activity: pH = −log₁₀(aH⁺) Because pH is…

• Disease Triangle
  Plant disease is rarely caused by a single factor. It develops when three conditions align at the same time: - A susceptible host - A viable pathogen - A favou…
• Environmental Infection Thresholds
  Most plant pathogens do not infect continuously. They require specific environmental conditions, often for a minimum duration, before infection can occur. Thes…
• Inoculum Pressure
  Disease risk is not determined by whether a pathogen is present, but by how much viable pathogen is present. This is known as inoculum pressure. Low inoculum p…
• Latent Infection
  In plant disease, infection and symptoms are not the same event. Many pathogens infect plant tissue and remain latent — present but not visible — until conditi…
• Modes Of Spread
  Once a pathogen is present, disease severity depends largely on how it spreads. Modes of spread determine: - How fast disease moves through a crop - Which mana…
• Primary Vs Secondary Cycles
  Not all infections contribute equally to disease outbreaks. Understanding the difference between primary and secondary infection cycles explains: - Why early c…
• Why Calendar Control Fails
  Calendar-based disease control assumes that disease risk follows predictable dates. In reality, disease risk follows environmental conditions, not the calendar…

• Heat Water Interaction
  Heat stress and water stress rarely occur in isolation. When they overlap, their effects are multiplicative, not additive. This interaction is one of the most…
• Induced Deficiencies
  Not all nutrient deficiencies result from low supply. Many deficiencies are induced by excesses of other nutrients or environmental conditions. This is one of…
• Low Oxygen High Temperature
  Low oxygen and high temperature form one of the most destructive hidden stress combinations in crop production. Damage often occurs below ground, while symptom…
• Recovery Lag And Yield Ceiling
  Visible recovery does not mean functional recovery. After stress, crops often regain appearance while suffering a permanent reduction in yield potential. This…
• Salinity Calcium Interaction
  Salinity stress and calcium deficiency are tightly linked. Many crops show calcium-related disorders without low calcium supply, because salinity interferes wi…
• Single Vs Stacked Stress
  Plants are adapted to tolerate individual stress events. Problems arise when stresses: - Overlap - Occur in sequence - Interact with each other This is known a…
• Stress Priming Vs Exhaustion
  Plants do not respond to stress in a simple “damage vs no damage” way. Low to moderate stress can sometimes improve resilience. Repeated or prolonged stress, h…

• Critical Periods
  A crop is not equally sensitive all season. Some stages are relatively forgiving. Others are yield-defining windows, where short periods of stress, weak rootin…
• Frost Sensitivity By Stage
  Frost risk is not just about how cold it gets. It is about when the crop is exposed. The same temperature can be harmless in deep dormancy and highly damaging…
• Heat Stress Risk Windows
  Heat stress is not constant through the crop cycle. The impact depends heavily on timing, duration, and crop stage. The same temperature event can be harmless…
• Irreversible Vs Compensable Damage
  Not all damage to a crop has the same long-term impact. Some stresses reduce growth temporarily and can be recovered. Others permanently reduce yield potential…
• Root System Commitment
  The root system is not built evenly over time. There are key phases where root structure, depth, and capacity are established. These phases strongly influence…
• Sink Establishment
  A “sink” is any part of the plant that draws energy and nutrients for growth. In many crops, yield is determined by how many sinks are established early in dev…

• Capillary Rise Containers
  In containers and slabs, water does not distribute evenly from top to bottom. Capillary forces dominate, creating predictable moisture gradients that strongly…
• Dry Down Curves
  After irrigation, water content does not decline linearly. It follows a dry-down curve shaped by medium properties, root uptake, and evaporation. Understanding…
• Infiltration Vs Percolation
  Water movement through soil or substrate occurs in two distinct phases: - Infiltration – water entering the medium - Percolation – water moving downward throug…
• Irrigation Method Physics
  Irrigation method is not just about how water is delivered. It determines how water moves through the root zone, how evenly it is distributed, and how the plan…
• Preferential Flow
  Water does not move evenly through soil or substrates. It follows preferential flow paths — routes of least resistance that bypass much of the root zone. Prefe…
• Rewetting Hysteresis
  Dry substrates do not behave the same way when rewetted. This phenomenon is known as rewetting hysteresis and explains why irrigation “stops working” after dry…
• Why Ec Readings Lie
  EC readings are often treated as objective truth. In reality, EC measurements are highly context-dependent and frequently misleading immediately after irrigati…

• Cold Pockets And Inversions
  Cold damage and frost injury are rarely uniform. They occur in cold pockets created by temperature inversions and poor air movement. Understanding cold air beh…
• Edge Vs Centre Effects
  Crop performance is rarely uniform across a block, tunnel, or glasshouse. One of the most consistent patterns is the difference between edges and centres. Thes…
• Managing Variability
  No crop is uniform. Even in controlled environments, there are always differences in temperature, humidity, airflow, light, water distribution, and root-zone c…
• Microclimate Fundamentals
  Crops do not experience the same environment that weather stations report. They experience a microclimate — the local conditions at the scale of leaves, canopi…
• Sensor Placement Bias
  Sensors do not measure “the climate”. They measure where they are placed. Poor placement creates a false sense of control and explains why “the data looks fine…
• Vent Shadowing
  Ventilation does not distribute air evenly. Structures, crop density, and layout create vent shadowing, producing persistent climate gradients. These gradients…

• Compost And Nutrient Lockup
  Compost and organic materials are often added to improve structure, biology, and long-term fertility. However, they can also temporarily reduce nutrient availa…
• Labile Vs Stable
  Not all organic matter behaves the same way. The key distinction is between labile (easily decomposed) and stable (resistant) organic matter. This difference d…
• Organic Matter And Disease
  Organic matter strongly influences disease — but not always in the way expected. It can: - Suppress disease - Promote disease - Or do both at different times T…
• Oxygen Demand Of Decomposition
  Microbial decomposition consumes oxygen. In root zones, this oxygen demand can compete directly with roots, leading to hypoxia even in moist, well-drained syst…
• Root Microbe Competition
  Plants are not the only organisms competing for nitrogen. Microbes in the root zone actively compete with roots for available nitrogen, especially during organ…
• Temperature Driven Mineralisation
  Nutrient release from organic matter is temperature dependent. As temperature rises, mineralisation accelerates — often faster than crop demand. This mismatch…

• Acidification Overshoot
  Acidification is commonly used to correct high pH or bicarbonate levels. Overshooting acidification creates acute chemical stress that can be more damaging tha…
• Flush Events And Ec Correction
  Flushing is often used to correct high EC or suspected salt build-up. While sometimes necessary, flushing is a major disturbance event that can create new stre…
• Media Changeovers
  Changing growing media introduces a new physical, chemical, and biological system. Even when nutrient targets are matched, crop response often changes dramatic…
• Recovery Timelines
  After any disturbance, crops require time to recover. Recovery is rarely immediate and often proceeds in stages that are easily misunderstood. Misjudging recov…
• Repotting And Transplant Shock
  Repotting and transplanting are necessary operations — but they are also major stress events. Even when done carefully, they disrupt root function and create a…
• Root Pruning Effects
  Root pruning occurs intentionally (e.g. transplanting, root trimming) or unintentionally (e.g. hypoxia, disease, salinity). Regardless of cause, root pruning h…

• Decision Making Under Uncertainty
  Agronomy is not about certainty. It is about making good decisions with incomplete information in complex, living systems. This is a skill — not a formula. Unc…
• False Precision
  Modern agronomy has access to more data than ever before. The danger is not lack of information — it is false precision: treating uncertain numbers as exact tr…
• Intuition Vs Numbers
  Modern agronomy relies heavily on data: - sensors - models - thresholds - dashboards These tools are powerful, but they do not replace experience. There are si…
• Lag Effects And System Memory
  Plants and growing systems remember past conditions. This system memory explains why crops respond today to events that happened days or weeks ago. Lag effects…
• What Models Assume
  Models are powerful tools — but they are not reality. Every model rests on assumptions about how systems behave. Understanding those assumptions is more import…
• Why Thresholds Are Fuzzy
  In agronomy, thresholds are often used to guide decisions. Examples include: - target EC ranges - temperature limits - humidity bands - pest thresholds - nutri…