S4ag Water

Water

Water management is a biological problem as much as an infrastructure problem. Before investing in hardware — pipes, pumps, tiles, tanks — ask whether the soil biology is working. A healthy food web builds aggregate structure that infiltrates water faster, and organic matter that holds it longer. In many cases, building soil OM by 1–2% solves an irrigation problem more cheaply than installing a new drip system. Start with the biology, then invest in infrastructure for what biology cannot fix.

How this skill works: Each sub-tool pauses at a Checkpoint to confirm the assumptions it is about to build on before producing output. A recommendation built on a wrong assumption wastes time and money — confirm the checkpoint before acting. Each sub-tool ends with Next steps — the skills worth running once you have acted on this one.

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Expert Lineage

The thinkers whose frameworks underpin this skill — and what they specifically discovered that changes how you farm.

P.A. Yeomans — Keyline Design Yeomans spent thirty years on his New South Wales properties developing a systematic method for reading how water moves across any landscape. His core finding: water in an agricultural landscape defaults to the lowest point and exits the farm. The Keyline system redistributes water laterally across the slope, saturating the landscape rather than draining it. His specific tool — the keyline point, located just below the valley floor where slope transitions — allows a farmer to design water distribution across an entire property from a single correctly placed line. Before spending money on any water storage or irrigation infrastructure, map how water actually moves on the property.

Brad Lancaster — Rainwater Harvesting for Drylands Lancaster demonstrated in Tucson, Arizona that a household and small farm could meet most of its water needs from rainfall alone through systematic earthwork and vegetation design — in a place that receives less than 300mm annually. His specific contribution: every drop of rain that falls on the property should be considered a resource to capture before it becomes runoff. The sequence he established — slow it, spread it, sink it, store it, use it — applies equally to farm-scale water management. The least expensive water is rain you keep on your land.

Gary Zimmer — Biological Farmer Zimmer connected soil biology directly to farm water economics in quantifiable terms. His specific finding: every 1% increase in soil organic matter adds approximately 170,000 litres of plant-available water per hectare. In practical terms, a farm at 1% OM irrigating 50mm per week can, at 3% OM, irrigate 30mm per week for the same crop response. The soil improvement pays the irrigation bill. Before adding infrastructure, build the water-holding capacity in the soil.

Judith Schwartz — Water in Plain Sight Schwartz documented the farm-scale connection between land management and water cycle function. Her key finding: degraded landscapes with bare soil, compacted ground, and absent perennial vegetation are net exporters of water — rainfall runs off rather than infiltrating. Farms that restore ground cover and soil biology become net importers of water — rainfall infiltrates, recharges groundwater, and supports plant growth through dry periods. The direction of the water cycle on your farm is determined by your management decisions.

Elaine Ingham — Soil Food Web and Water Ingham's structural finding: fungal hyphae and bacterial biofilms physically bind soil particles into aggregates — the macro-pores between those aggregates are the channels through which water infiltrates and air circulates. A degraded, low-biology soil collapses its aggregate structure and becomes compacted and impermeable. Restoring the food web physically rebuilds infiltration capacity. Fungicide application — even at labelled rates — measurably reduces fungal hyphal length in soil, directly reducing aggregate stability and therefore water infiltration.

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Which tool fits

| You need to... | Tool | |---|---| | Choose between irrigation system types | irrigation-selection | | Know when and how much to irrigate | irrigation-scheduling | | Prepare for or manage drought conditions | drought-planning | | Fix a drainage problem | drainage | | Collect and store rainwater on the farm | water-harvesting | | Test water or address water quality concerns | water-quality |

Routing Decision

• Building or replacing an irrigation system → irrigation-selection
• System exists, unsure when to run it or how long → irrigation-scheduling
• Facing a dry season or want to drought-proof the farm → drought-planning
• Fields stay wet too long after rain, poor crop establishment → drainage
• Want to capture rainfall and reduce dependency on bore or mains → water-harvesting
• Using water from a dam, bore, or river and unsure if it's safe → water-quality
• Unclear → start with irrigation-selection to establish system context, then routing becomes obvious

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Irrigation Selection

Matches an irrigation system type to the crop, soil, and site conditions.

The right irrigation system is the one that puts water where roots are, when roots need it, without wetting foliage or compacting soil. Each system type has a different cost profile, labour demand, and water efficiency. The table below allows a direct comparison; the decision sequence follows.

System comparison:

| System | Water efficiency | Capital cost | Labour | Best for | Avoid when | |---|---|---|---|---|---| | Drip (subsurface) | Very high | High | Low | Vegetables, perennials, orchards | Rocky soils; heavy clay that blocks emitters | | Drip (surface tape) | High | Medium | Medium | Row vegetables, annual crops | Rodent pressure; perennial plantings | | Overhead sprinkler | Medium | Medium | Low-medium | Pasture, establishing cover crops, frost protection | Foliar disease-prone crops; windy sites | | Micro-spray / wobbler | Medium-high | Medium | Low | Orchards, wide-row perennials | High-pressure systems without filtration | | Flood / border | Low | Low | High | Pasture, rice; only where water is abundant | Water-scarce conditions; soils with poor infiltration | | Hand-held / manual | Low | Very low | Very high | Small beds, nursery, establishment watering | Any scale beyond a home garden |

Decision sequence:

1. Identify the crop type. Vegetables and row crops: drip is usually correct. Orchards and perennial systems: micro-spray or subsurface drip. Pasture: overhead or flood where water is available. Mixed systems: zone the property by crop type and match systems per zone.

1. Assess the soil. Heavy clay: slow infiltration rate means slow application rates prevent runoff — drip or micro-spray. Sandy soils: water moves fast and deep — subsurface drip or frequent short overhead cycles. Loam: most systems work.

1. Assess water source and pressure. Town/mains pressure: any system. Gravity-fed dam or tank: check head pressure before selecting — drip requires minimum 1 bar. Bore or pump-fed: calculate flow rate and match system to available volume.

1. Consider the food web. Overhead irrigation wets foliage and can suppress foliar fungi (a secondary benefit in some diseases, a problem in others). More critically, flood and overhead irrigation can compact soil surface under heavy application — soil aggregate destruction reduces future infiltration. Drip irrigation preserves surface aggregates and concentrates biological activity around emitter zones.

Transition note: Moving from flood to drip irrigation is the most impactful single water-saving change on most vegetable and orchard operations. The capital cost can be recovered in water savings in 2–5 years in water-scarce regions.

Checkpoint — confirm before finalising:

• What crop or enterprise is this system serving? The crop type determines the system type.
• What is the water source — mains, bore, dam, river — and what is the pressure and flow rate available?
• Is organic certification a consideration? Some emitter cleaning chemicals are not permitted.

Recommending a drip system without confirming available pressure, or an overhead system on a disease-prone vegetable crop, creates an expensive problem.

Output:

IRRIGATION SYSTEM RECOMMENDATION

Farm context: [crop type / enterprise]
Water source: [source, pressure, flow rate]
Soil type: [soil]

RECOMMENDED SYSTEM: [system type]
  Configuration: [layout description — drip tape spacing, sprinkler spacing, etc.]
  Filtration required: [yes/no — type]
  Approximate capital cost range: [low/medium/high, or $/ha estimate]
  Labour requirement: [hours/week during irrigation season]

ALTERNATIVE IF BUDGET IS CONSTRAINED: [alternative system]

WHAT TO AVOID: [system type and reason]

NEXT DESIGN STEP: [what to measure or confirm before purchasing]

Next steps:

• Run irrigation-scheduling (within this skill) to set run times and frequency for the selected system.
• /s4ag-soil — improving OM before installing irrigation reduces the system capacity needed.
• /s4ag-earthworks — if the site has water storage potential, design catchment before finalising supply infrastructure.

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Irrigation Scheduling

Determines when to irrigate and how much to apply — without over- or under-watering.

Over-irrigation is at least as common as under-irrigation on most farms. Saturated soil drives out oxygen, anaerobic conditions kill aerobic biology, and roots suffocate. Under-irrigation creates crop stress at critical growth stages and reduces yield. The goal is to keep soil moisture in the range roots can access — typically field capacity to around 50% plant-available water depleted.

Reading soil moisture — three methods in order of cost:

1. Feel and look test (free). Take a soil sample from root zone depth. Squeeze a handful.

• Leaves wet hands, ribbon easily: at or above field capacity. Do not irrigate.
• Forms a ribbon but does not wet hands: in range. Irrigate only if forecast is dry.
• Falls apart, does not ribbon, dusty: below 50% depletion. Irrigate now.

2. Tensiometer or gypsum block (low cost). Install at root zone depth (typically 20–30cm for vegetables, 40–60cm for perennials). Read daily.

• Tensiometer 0–10 kPa: field capacity — too wet to irrigate.
• 10–30 kPa: ideal range for most crops. Irrigate when approaching upper end.
• 30–60 kPa: drying out — irrigate now for most vegetables; some deficit irrigation crops (olives, grapes) can go to 60–80 kPa.
• Above 60 kPa: stress zone. Irrigate immediately for most crops.

3. Evapotranspiration (ET) scheduling (moderate cost). Use local weather station ET data (many irrigation authorities publish this). Replace the previous day's ET minus any effective rainfall.

• Typical summer ET: 4–8mm/day depending on temperature, humidity, and wind.
• Effective rainfall: rain events above 5mm count; below 5mm, assume most evaporates before infiltrating.

Crop-specific adjustments:

| Crop stage | Water demand relative to ET | |---|---| | Germination / establishment | High — keep surface moist until established | | Vegetative growth | 70–90% ET replacement | | Flowering / fruit set | 100% ET replacement — most critical period | | Fruit fill | 80–100% ET | | Ripening / harvest | 60–70% ET — some deficit increases Brix in many fruits | | Cover crop / fallow | 0% — rely on rainfall |

Food web note: Soil biology requires air as well as water. The pore spaces in well-aggregated soil hold both — but if soil is irrigated past field capacity and held saturated, aerobic bacteria and fungi die and anaerobic bacteria dominate. Schedule irrigation to allow the soil to breathe between events. The 24–48 hours of drying between irrigations is not wasted time — it is oxygen replacement that the food web needs.

Checkpoint — confirm before finalising:

• What crop and growth stage are we scheduling for? Demand varies by stage.
• What is the soil type? Sandy soils need more frequent, shorter runs; clay needs longer intervals and slower application.
• Is there a functioning soil moisture monitoring tool in place, or are we relying on visual assessment?

Scheduling without knowing growth stage or soil type produces a number that may be correct or dangerously wrong.

Output:

IRRIGATION SCHEDULE

Crop: [crop name]
Growth stage: [stage]
Soil type: [soil]
System type: [drip / overhead / other]

CURRENT SOIL MOISTURE: [reading or assessed status]

IRRIGATION EVENT
  Frequency: [every X days]
  Run time: [minutes/hours]
  Volume per event: [mm or litres/m2]
  Best time of day: [morning recommended to reduce evaporation and foliar disease]

ET REPLACEMENT TARGET: [mm/day]
  Effective rainfall this week: [mm]
  Irrigation required this week: [mm]

NEXT SOIL MOISTURE CHECK: [date]

SIGNS TO WATCH FOR
  Under-watering: [crop indicator]
  Over-watering: [crop indicator]

Next steps:

• Run drought-planning (within this skill) if the season ahead is forecast dry and the schedule needs to become a rationing plan.
• /s4ag-soil — building OM reduces the volume and frequency of irrigation required.
• /s4ag-vegetables or /s4ag-orchards — crop-specific water demand at each growth stage.

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Drought Planning

Builds drought resilience before dry conditions arrive, and manages water rationing once they do.

Drought planning has two phases: preparation (before the dry season or dry period begins) and rationing (once soil moisture is depleted and supply is constrained). These require different actions. Preparation is about soil and system; rationing is about prioritisation and loss minimisation.

Phase 1: Preparation — do these before the dry season.

1. Increase soil water-holding capacity. Every 1% of soil OM holds approximately 170,000 litres/ha of additional plant-available water. A farm at 1% OM and a farm at 3% OM receive the same rainfall but the 3% OM farm has twice the buffer to draw on. Increasing OM is the most cost-effective drought-proofing investment available — cheaper than any tank or bore deepening.

Actions to increase OM: compost additions (3–5 t/ha/year moves OM measurably over 3–5 years), permanent cover crops in fallow periods, reduced tillage (every tillage event oxidises OM), and deep-rooted species that add OM at depth.

2. Mulch exposed soil. Bare soil loses water to evaporation at a rate of 3–6mm/day in summer. A 10cm organic mulch layer reduces this to 0.5–1mm/day. For market gardens and orchards, mulching between rows is the fastest way to reduce irrigation demand. Suitable mulches: wood chips (feeds fungal food web), straw, compost, living mulch (low-growing cover crop between rows).

3. Shade the soil surface. High plant canopy cover reduces soil temperature, which reduces evaporation. In vegetable systems, close plant spacing and tall neighbours reduce exposed soil. In orchard and perennial systems, understorey plantings serve the same function and build food web biology.

4. Improve catchment efficiency. Check that every rainfall event is being captured and infiltrating. Clear any areas of compaction that cause runoff. Install or improve water harvesting infrastructure before the dry season (→ run water-harvesting sub-tool). Fill storage capacity before the dry season begins — do not wait.

5. Know your minimum viable water needs. List enterprises by water demand and decide in advance which ones get priority if supply is constrained. This decision is emotionally difficult in crisis — make it now.

Phase 2: Rationing — during drought conditions.

Prioritise by enterprise and growth stage:

| Priority | Enterprise / stage | Rationale | |---|---|---| | 1 | Perennials at fruit set or fruit fill | Loss at this stage is permanent yield loss | | 2 | Transplanted annuals in establishment | Stress now means poor season; transplant investment wasted | |

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Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: human-avatar
• Source: human-avatar/skills-for-agriculture
• License: MIT
• Homepage: https://www.npmjs.com/package/@human-avatar/skills-for-agriculture

Install and usage instructions live in the source repository linked above.