FloraPulse vs ET Scheduling

FloraPulse vs ET Scheduling

Evapotranspiration (ET) scheduling is the most widely used scientific method for irrigation management. It estimates crop water use from weather data — temperature, solar radiation, humidity, and wind — using the FAO-56 Penman-Monteith equation. The formula is straightforward: ETc = ET0 × Kc, where ET0 is reference evapotranspiration and Kc is a crop coefficient. Growers calculate how much water the atmosphere “pulled” from the crop and replace it.

FloraPulse takes a fundamentally different approach. Instead of estimating what the atmosphere demands, our microtensiometers measure what the plant actually experiences — stem water potential (SWP), the water tension inside the tree’s vascular system. Both approaches are scientifically grounded. The question is which gives you better irrigation decisions.

Side-by-Side Comparison

Feature	FloraPulse (SWP)	ET Scheduling (ETc)
What It Measures	✅ Water tension inside the plant (bars)	⚡ Atmospheric water demand (inches/day)
What It Tells You	✅ How stressed the plant actually is right now	⚡ How much water the crop likely used
Site Specificity	✅ Measured on your actual trees	❌ Generic crop coefficient (Kc) applied to weather station data
Deficit Irrigation	✅ Direct stress thresholds for each growth stage	❌ Guessing: “apply 70% of ETc” — but is the tree stressed or fine?
Accounts for Root Problems	✅ Sees all stress — soil salinity, root disease, compaction	❌ Blind to anything below ground
Kc Calibration Needed	✅ None — direct measurement	❌ Must estimate Kc by crop, age, canopy, trellis, rootstock
Data Source	Sensor in tree trunk, 24/7 automated	Weather station (CIMIS, on-farm, OpenET)
Cost	⚡ ~$1,800/year per sensor	✅ Free (CIMIS) or low (on-farm station)
Best For	Precision irrigation timing and deficit management	Baseline water budgeting and SGMA accounting

The Crop Coefficient Problem

ET scheduling relies on a critical assumption: that a published crop coefficient (Kc) accurately represents your orchard. In practice, Kc values vary far more than most growers realize.

Research from UC Davis and the USDA has documented that Kc for apple trees ranges from 0.42 for 3-year-old trees to 1.10 for 13-year-old trees — a 2.6× difference driven by canopy size alone. For grapevines, Williams et al. found that the Kc for a Lyre trellis at the same row spacing was nearly double that of a VSP trellis (0.96 vs 0.49). Tree age, variety, rootstock, pruning, and canopy management all shift Kc — but the generic tables most growers use don’t capture any of this.

This means a published Kc value for “almond” or “walnut” could be off by 30–50% for your specific block. You might be applying 70% of ETc thinking you’re running a controlled deficit — when you’re actually drowning or starving the trees. Without measuring the plant directly, you simply can’t know.

FloraPulse bypasses this entirely. Instead of estimating water use from weather and hoping the coefficient fits, you measure the plant’s actual water status. No Kc tables. No canopy estimation. No guessing.

Why Growers Are Moving Beyond ET Alone

ET-based scheduling was a major advance over calendar-based irrigation. But as water becomes scarcer and allocations tighten under SGMA, growers need more precision than “replace what the weather says you lost.” Here’s where ET falls short:

• Invisible stress: A tree with damaged roots, salt buildup, or compacted soil can be severely stressed even when ET says it should be fine. ET-based scheduling sees none of these below-ground problems — it only models the atmosphere. SWP captures the plant’s integrated response to all factors affecting water uptake.
• Deficit irrigation is a guess: Many growers apply a percentage of ETc (e.g., 70% during hull split in almonds) to impose controlled stress. But without measuring the plant, you don’t know if 70% is producing mild stress, severe stress, or no stress at all — it depends on your soil, root health, and whether the Kc even fits. Goldhamer & Fereres (2011) showed that SWP-based regulated deficit irrigation in almonds saved ~5 inches of water per year with no significant yield loss over five years — precision that ET alone cannot deliver.
• Station distance: Most growers pull ET data from a CIMIS station that may be miles from their orchard. Microclimates — valley floors vs. hillsides, coastal influence, urban heat islands — can make published ET0 significantly different from conditions at the tree. FloraPulse measures your specific tree, in your specific block.
• No feedback loop: ET scheduling is open-loop: you estimate use and irrigate, but never confirm whether the plant actually needed it. SWP closes the loop — you see how the tree responded to your last irrigation and adjust accordingly.

Which Approach Is Best For You?

Using Both Together

ET and SWP are not competing methods — they answer different questions. The most sophisticated irrigation programs use both:

• ET for the water budget: Track total consumption for SGMA reporting, allocation management, and seasonal planning. OpenET provides field-scale (30-meter) ET data across the U.S.
• SWP for irrigation timing: Decide when to irrigate and how much stress is acceptable at each growth stage. SWP provides the real-time feedback loop that ET cannot.

Think of it this way: ET is your fuel gauge (how much water was consumed). SWP is your engine temperature (how the plant is actually performing). You need both for optimal management — but if you had to choose one for irrigation decisions, the engine temperature tells you more.

When ET Scheduling Still Makes Sense

We’re advocates for plant-based sensing, but ET scheduling has clear strengths in certain situations:

• Annual row crops: For corn, cotton, tomatoes, and other annuals with well-calibrated Kc values and uniform canopies, ET scheduling works well. The Kc variability problem is far less severe when every plant in the field is the same age and size.
• Seasonal water planning: Before the irrigation season starts, ET projections help estimate total water needs, size pumps, and plan allocations. SWP is a real-time tool — it can’t predict next month’s demand.
• Regulatory compliance: SGMA groundwater sustainability agencies increasingly use ET (via OpenET) to measure on-farm water consumption. You may need ET data for reporting regardless of how you schedule irrigation.
• Zero-budget operations: CIMIS data is free, funded by California taxpayers. For growers who can’t invest in sensors, ET-based scheduling with published Kc tables is vastly better than irrigating by calendar or “feel.”

Frequently Asked Questions

Can I still use CIMIS/ET data alongside FloraPulse?

Absolutely. Many of our growers use ET for seasonal water budgeting and SGMA reporting while using FloraPulse SWP data for day-to-day irrigation decisions. ET tells you how much water left the system; SWP tells you whether the tree is happy with what it received. The FloraPulse dashboard already incorporates weather data — including VPD (vapor pressure deficit) — to calculate daily baseline water potential, so you get the atmospheric context alongside direct plant measurements.

Why can’t I just use ET at a lower percentage for deficit irrigation?

You can try, but you’re guessing. Applying “70% of ETc” assumes your Kc is accurate, your soil is uniform, your roots are healthy, and atmospheric demand is the only factor. In practice, 70% of ETc might produce no stress in a block with deep clay soil and aggressive roots, or dangerous stress in a sandier block nearby. Goldhamer et al. (2003) showed that SWP-based triggers produced up to 40% water savings in almonds because they responded to actual plant status rather than a fixed percentage of estimated demand.

How does SWP handle high-ET days differently than ET scheduling?

On a high-ET day (high temperature, low humidity, wind), ET scheduling says the crop used a lot of water and you should replace it all. But the plant may not be stressed — deep-rooted, well-irrigated trees can handle high atmospheric demand without trouble. Conversely, a moderate-ET day following a heat wave might show low ET but the plant is still recovering from accumulated stress. SWP captures these dynamics because it measures the plant’s actual physiological state, not just what the weather did.

What about OpenET and satellite-based ET? Isn’t that more accurate than CIMIS?

OpenET is a major improvement — it provides field-scale (30-meter resolution) ET estimates using an ensemble of six remote sensing models, with an accuracy of about ±15% for croplands. It’s excellent for water accounting and SGMA compliance. But even precise ET data still tells you consumption, not stress. Knowing that your almond block used 0.28 inches yesterday doesn’t tell you whether the trees need more water today. SWP answers that directly.

Does FloraPulse work for SGMA water reporting?

SGMA compliance requires water consumption accounting, which is ET-based. FloraPulse doesn’t replace ET for regulatory reporting. What it does is help you use less water within your allocation — by enabling precision deficit irrigation with published stress thresholds for each crop and growth stage. Growers facing tighter allocations find that SWP-based management is the most effective way to maintain yield while reducing water use. See our SGMA compliance page for more details.

Ready to Move Beyond Weather-Based Guessing?

ET scheduling is a solid starting point — but for tree crops and vineyards, measuring the plant directly unlocks a level of precision that weather data alone cannot provide. Contact our team to see how continuous SWP data compares to your current ET-based approach.