Field trial, 24 farms, one season

Environmental science poster

A season of battery free soil moisture sensors on 24 smallholder farms, laid out as an A0 landscape broadsheet. It is a field trial rather than a laboratory study, so the board reports the things field work actually turns on: whether the device survived, where it was weakest, and what it saved.

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The poster at full size, exactly as it prints. Every number, citation and caption on it was written for this example, so the layout is being judged on real content.

BU
Battery free soil moisture sensors for smallholder irrigation: field performance over one growing season
K. Osei ¹, L. Marchetti ¹ ², F. Ndlovu ²
1 Department of Agricultural Engineering, Brightwater University · 2 Regional Water Management Institute
ABSTRACT
Soil moisture sensors are sold to smallholders and then abandoned, usually when the battery dies and no replacement is available within a day of travel. We built a passive sensor that harvests its power from the reader and holds no battery at all, and we ran 96 of them across 24 farms in three soil types for one growing season.
INTRODUCTION
Irrigation on the farms in this district is scheduled by feel and by habit. Water is not metered and the cost of over watering is paid later, in pumping fuel and in nutrient washed below the root zone, so the feedback that would correct the habit never arrives. Where sensors have been introduced, the failure mode is consistent and it is not accuracy: the coin cell runs out after a season or two, the nearest replacement is a bus journey away, and the unit is left in the ground. Extension officers in this district could point us to buried sensors on nine of the first ten farms we visited. A sensor that never needs a battery removes that failure.
METHODS
Device. Passive LC resonator, no battery, read at 13.56 MHz by a handheld unit at up to 90 mm depth.
Sites. 24 farms across three soil types, 4 sensors per farm at 15 and 40 cm depth in two plots.
Reference. Gravimetric sampling fortnightly at each sensor location, oven dried at 105 degrees for 24 hours.
Comparison. Each farm irrigated one plot on sensor readings and one on its usual schedule.
Outcome. Agreement with gravimetric sampling, unit survival, water applied per hectare, and yield at harvest.
PARTICIPANT FLOW
Farms approached
31
Declined
7
Farms enrolled
24
Sensors installed
96
Units lost
5
Units read at harvest
91
NovDecJanFebMar0200400600800
Figure 1. Water applied per hectare by month, sensor scheduled plots against usual practice.
Source: plot water records, 24 farms, one season, 2026.
RESULTS
Across 24 farms and one season the sensors tracked gravimetric sampling to a mean absolute error of 3.4 volumetric percent, which is inside the band that separates the irrigation decisions farmers actually make. Agreement was best in the loam sites, where the error was 2.6 percent, and worst in the two heavy clay sites, where it rose to 5.1 percent in the fortnight after heavy rain and recovered as the profile drained. Depth mattered less than soil type: the 15 and 40 centimetre sensors differed by 0.4 percent on average. Ninety one of 96 units were still readable at harvest, a survival rate of 94.8%. Of the five lost, three were struck during ploughing and two were dug up by hand and not replaced. No unit failed electrically, which is the outcome the design was aimed at, and no unit drifted enough over the season to need recalibration.
DISCUSSION
The saving came mostly from not irrigating in the week after rain, which is the decision farmers told us they found hardest to judge by feel. That is worth noting, because it means the value of the device is concentrated in a handful of decisions each season rather than spread evenly across it. A reader shared between four farms would capture most of the benefit at a quarter of the cost. The clay sites are where the device is weakest and also where the decision is hardest, which is the wrong way round. The error there is not a calibration problem: bound water in clay shifts the resonant response in a way a single frequency cannot separate from free water, so the next iteration needs a second frequency rather than a better curve.
FUTURE WORK
A three season trial across two districts is planned, with metered water, independently weighed yield at harvest, and enough farms to detect a yield difference rather than only rule out a large one. We will add a second resonant frequency to separate bound from free water in heavy clay, which is the one condition where the current device is not good enough to schedule on.
18%
less irrigation water applied
95% CI 11 to 25, n=24 farms
Key finding
A sensor with no battery survived a season in the ground, tracked laboratory sampling closely enough to schedule irrigation, and cut water use by 18% with no measured yield penalty.
Mean absolute error 3.4 volumetric percent
91 of 96 units readable at harvest, no electrical failures
Water use down 18%, 95% CI 11 to 25
Weakest on heavy clay after rain
REFERENCES
1.Dobriyal P, et al. A review of methods for soil moisture measurement. Journal of Hydrology 2012;458:110-117.
2.Kashyap B, Kumar R. Sensing methodologies in agriculture for soil moisture. IEEE Access 2021;9:14095-14121.
3.Vereecken H, et al. On the value of soil moisture measurements. Water Resources Research 2008;44:W00D06.

Block by block

What each block on the board is for, in the order a reader walks it.

Title band and authors
The study title across the band with the university mark and three authors with generated superscripts.
Abstract
Two sentences: the failure the device is designed around, a dead battery with no replacement nearby, and the trial size of 96 passive sensors on 24 farms across three soil types for one season. The agreement, survival and water figures are left to the results, stat and key finding blocks.
Introduction
Why the habit persists, what happens to sensors that need batteries, and the trade a passive device makes in return.
Methods as a labelled protocol
Device, sites, reference standard, comparison and outcome. The paired plot design is stated in the comparison entry rather than left to be inferred.
Participant flow
Farms approached, declined, enrolled, sensors installed, units lost and units read at harvest, with the counts reconciling at every step.
Water figure and key number
Water applied per hectare by month for both schedules, beside a stat block carrying the 18% reduction with its interval.
Results and discussion
Agreement by soil type, survival with the failure modes, the water saving, and why the saving concentrates in the week after rain.
Future work and references
The three season trial across two districts and the second resonant frequency for heavy clay, then three references in journal style. The three references are invented for this fictional study, because the reference block is required on this layout; on your board, replace them with your sources.
How to adapt this board
Sites go into the second entry of the methods protocol, with how many and how they were chosen, because that is the first thing a field study is judged on. Seasons or sampling rounds go into the flow, where deployed, lost and analysed replace the participant path without changing the block. Sensor survival is a result in its own right and belongs in the results text rather than a footnote, since a reader has to know how much of the series is real before they read the chart. The key number block takes the single measurement that answers the question, and everything else stays in the figure.

What makes this board work

Survival is reported as a result

Ninety one of 96 units readable at harvest, with the five losses broken into three struck by ploughing and two dug up. For a device meant to live in a field, that is the finding, not a footnote.

The weakness is named and explained

Heavy clay after rain is where the error rises to 5.1 percent, and the board says why a single resonant frequency cannot separate bound from free water. Naming the failure mode makes the future work section mean something.

The claims are sized to the design

The water saving is metered and stated with an interval. The yield difference is called what it is, inside the noise for a single season, rather than being reported as a gain.

Questions people ask

What goes on an environmental science poster?

The problem in its setting, the sites and how they were chosen, the measurement and its reference standard, the results with intervals, and the limits of a single season or a single region. This board adds unit survival as a result, 91 of 96 sensors readable at harvest, because for a device left in a field that is part of the finding.

How do I show field results without a control group?

Pair the plots so every site is its own control. Each of the 24 farms here irrigated one plot on sensor readings and one on its usual schedule, so the comparison sits within a farm rather than between farms. That design is stated in the comparison entry of the methods block, and it is why the 18% water saving can carry an interval.

Should equipment failure go on the poster?

If the study is about equipment in the field, yes. This board puts the losses in the flow, 96 installed, 5 lost and 91 read at harvest, and the results give the causes: three struck during ploughing and two dug up by hand. It also says no unit failed electrically, which is the outcome the battery free design was built for.

Can I use landscape for a field study?

Landscape suits a study with several short columns and one wide figure, which is common for field work. This broadsheet sets abstract, introduction and methods down the left, the flow and figure in the middle, and the key finding and checked points on the right. Check the conference specification first, since some stands only take portrait.

Can I put a photo of the site on the board?

Not yet. Four of the forty layouts carry image figures, but those slots cannot be filled in the current builder, so every figure on a poster is a chart. Describe the site in the second methods entry and say where the photographs are published.

How do I show a season of water use on one chart?

Plot one bar per month for each schedule, as Figure 1 does here with water applied per hectare from November to March, sensor plots against usual practice. Two series keep the legend short and the months readable. Put the season total and its interval in the stat block, here 18% less water with a 95% interval of 11 to 25, rather than asking readers to sum bars.

What goes in the flow when there are no participants?

Whatever units the study counts. This board runs farms approached 31, declined 7 and enrolled 24, then sensors installed 96, units lost 5 and units read at harvest 91, so each step follows from the one before. The causes of the five losses sit in the results text rather than in the flow, which keeps each box to a label and a number.

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Sources

Written and checked by the OneCraft team. Last checked .