Soil Moisture: More Important Than You Think

As anyone with a green thumb—or the habit of killing houseplants—knows, soil moisture is extremely important for plant health.

But what’s less widely known is that soil moisture monitoring has use cases far beyond gardening. In this post, I’ll discuss how soil moisture monitoring improves agriculture, both ecologically and economically. Then, I’ll examine some of soil moisture monitoring’s less widely known—yet still extremely important—use cases. Finally, to aid you in your soil moisture monitoring goals, I’ll also investigate several different options for soil moisture monitoring.

Now let’s begin by looking at the most obvious use case of soil moisture monitoring: improving irrigation.

Waste Not, Want Not

In 2015, a flurry of articles appeared decrying the consumption of almonds.

The outrage was largely understandable—while nutritious and tasty, growing almonds requires a jaw-dropping amount of water. According to the California Almond Board, it takes 1,100 gallons of water to produce just one pound of almonds.

It takes 1,100 gallons of water to produce just one pound of almonds.

California Almond Board

Yet something was lost in all the almond-hype: the fact that almonds are merely one of hundreds of crops grown in the United States every year, crops that consume 118 billion gallons of water every day. So, while almonds are the poster child of water-guzzlers, it’s worth noting that they’re a child with a large extended family.

This chart, courtesy of UC Davis, provides a more comprehensive picture:

Pie chart describing the water usage of different crops
Alfalfa uses more water per acre than almonds—and many other crops aren’t particularly efficient, either. (Source)

This staggering water usage is something that should concern citizens for two reasons: first, using so much water results in ecological damage and exacerbates droughts. Second, a greater demand for water drives up the cost per gallon, and these prices are passed onto the consumer, resulting in costlier grocery shopping.

Take the following graph of the producer price of almonds from the St. Louis Fed, for example:

Chart showing the price of almonds
Almond prices have steadily risen, a trend which has been worsened by recent droughts. (Source)

So there’s a clear environmental and financial incentive for farms and citizens to find ways to improve irrigation methods and decrease water usage.

One of the ways this is being done is through smart soil moisture monitoring—the practice of using internet-connected sensors to monitor the amount of water in soil. But how does smart soil monitoring improve agricultural water usage? 

Most obviously, smart soil moisture monitoring allows for smart irrigation. Smart irrigation refers to scheduling irrigation so that water is going where it’s needed, when it’s needed. Put another way, there’s little point in oversaturating already watered earth; likewise, it’s vital to irrigate areas that are in desperate need of water. This is where soil moisture sensors come in—it’s difficult to know visually how dry soil is, particularly because ideal moisture levels change with factors like soil composition and crop type.

A survey of Florida growers—responsible for 85,000 acres in total—found that irrigation based on smart soil moisture monitoring allowed 89% of growers to save on water, fuel, soil and electricity. One grower said that they saved over 50,000 gallons of water a day, and 78% of growers reported a reduction in labor costs.

Such numbers are not the exception, but rather the rule. Tests run by the International Center for Water Technology found that, generally, “smart irrigation controllers save up to 20 percent more water than traditional irrigation controllers.”

Smart irrigation controllers save up to 20 percent more water than traditional irrigation controllers.

International Center for Water Technology

Agricultural water use comprises around ⅓ of total daily usage in the USA, and integrating smart soil moisture monitoring into agriculture is a boon for the environment and the consumer. But according to the USGS, around 214 billion gallons of water are used for non-agricultural purposes every day! 

Non-agricultural uses are obvious: bathing, drinking, watering lawns and houseplants, etc. What’s less obvious is the fact that soil moisture monitoring can play an important role in many of these non-agricultural fields! Let’s examine some of the other applications. 

Going Green—Now, with Infrastructure

Various labelled examples of green infrastructure
Examples of the many effective and aesthetically pleasing types of green infrastructure. (Source)

A less talked about benefit of soil moisture monitoring is the fact that it can help preserve existing green infrastructure, measure green infrastructure performance, test which types of green infrastructure are most effective, and inform us where new green infrastructure would best be located. 

But first, what is green infrastructure?

In short, “green infrastructure” is a catch-all term that refers to utilizing plant-based infrastructure—like bioswales, green roofs, and tree canopies—to manage the water cycle. The term contrasts with “grey infrastructure,” referring to infrastructure that has been engineered explicitly by humans. For more on green infrastructure, you can check out this informative EPA article or read my colleague Sarah’s excellent blog post. 

What are the advantages of green infrastructure over typical water management methods?

First, cost: as can be seen here, studies have found that green infrastructure typically has a significant, positive return on investment. For instance, one study notes that it costs “$13 to $65 annually” to plant trees, but that the benefits range from $31 to $89 per tree.” According to another study, “the Philadelphia Water Department estimates that it can afford to spend up to $260,000 per acre on green infrastructure projects (green roofs, bioswales, rain gardens, etc.) rather than continue to treat the stormwater that otherwise would flow from these project areas into their combined sanitary/stormwater system.” A large part of the cost savings stems from the fact that green infrastructure helps combat combined highly unsanitary combined sewage overflows, or CSOs. 

Further, investing in green infrastructure has non-monetary benefits. Green infrastructure is more aesthetically appealing than, say, concrete drainage systems; as such it can result in quality of life improvements. All else being equal, almost anyone would prefer the installation of a park, rather than a typical gutter.

Clearly, green infrastructure is important—and soil moisture monitoring is a key aspect of maintaining green infrastructure. One of the main goals of green infrastructure is stormwater management. Yet green infrastructure is only able to control storm water if it is able to absorb stormwater; that is, if it’s not totally saturated. Since saturation is highly associated with various, controllable factors, like whether people are stepping on or littering in tree beds, understanding what tree beds are reaching saturation levels helps organizations like the NYC DEP decide where to implement rain guards and other protective measures.

Further, because green infrastructure is comprised of living organisms (e.g. trees in tree beds), it has varying efficacy—certain tree types perform better than others. But cities often have little data on how green infrastructure assets like trees and tree beds are actually performing. When provided with this data, officials can make more informed decisions around budgeting.

Clearly, soil moisture monitoring goes a long way towards understanding how green infrastructure is performing, where changes need to be made, and future green infrastructure should be implemented. If you’re interested in an excellent case study centered on these benefits of soil moisture monitoring, please feel free to read about our work with the Gowanus Canal Conservancy here.

(Soil Moisture) Knowledge is Power

Map of the United States showing soil moisture estimates
Daily soil moisture estimates are available from the National Weather Service’s Climate Prediction Center. (Source)

Soil moisture monitoring is also vital for research purposes, particularly in regard to climate change.

According to researchers, soil moisture can “affect [earth] surface fluxes and can subsequently impact air temperature, boundary layer stability, and precipitation.” Essentially, when temperature rises, water evaporates from the ground, which counteracts the increase in temperature (similarly to how the ocean plays a major role in determining global temperatures).

There has been discussion centered around creating a national soil moisture measurement network so as to better understand these effects, and it seems likely that such a network will be developed in the near future. This type of network would be a boon to climate researchers.

Additionally, a national network would be useful because soil moisture monitoring is a key part of understanding soil erosion, another important environmental factor. After all, soil erosion played a large part in the Dust Bowl which has been called “The Worst Environmental Disaster in the United States.” During the Dust Bowl, a period of wet years led to what the History Channel describes as “intensive cultivation of increasingly marginal lands that couldn’t be reached by irrigation.” This was furthered by legislation like the Homestead Act, which encouraged farming increases. The resulting period of dust storms halted agriculture, destroyed arable land, and had negative health consequences for livestock and people. But when soil moisture is monitored, potentially dangerous policy can be avoided, and policy changes combating erosion can be implemented proactively, rather than reactively.

Dust storm in Texas in 1935 during the Dust Bowl
Dust storm in Texas, 1935. Photo via Wikipedia

Another way in which soil moisture monitoring can play an important role in ecological research is through helping to estimate the severity of floods, which is increasingly important as climate change continues. For instance, several articles have discussed how the National Flood Insurance Program is facing severe challenges due to antiquated methods risk calculation methods.

But other types of flooding than coastal flooding—which the NFIP predominately deals with—are also impacted by soil moisture. Flash floods are one example, and, since flash floods are the most dangerous type of flood, anticipating flash floods is vital for those living in potentially affected areas. Some papers show promise for developing a model of flash flood prediction that incorporates soil moisture monitoring.

In short, although many think of soil moisture monitoring as having a relatively limited—albeit important—application of informing irrigation practices, it is highly important for those trying to effectively utilize green infrastructure, or for those involved in understanding and preparing for ecological events. Of course, there are other important use cases too: turf and golf course management, biofuel research, and even archeology!

Soil Moisture Monitoring: Sensor Overview

At Temboo, we focus on environmental engagement: by using our no-code platform, citizens and organizations can easily gain insight into their environment, allowing them to live healthily, understand their surroundings, and affect data-driven change.

One of the best ways these goals can be achieved is by setting up a soil moisture monitoring station. Of course, doing so may seem difficult—though it needn’t be so hard, especially if you utilize Kosmos and follow our guide on building a soil moisture monitoring system. And, to further assist in this process, I’ve conducted research into the various soil moisture sensor options that are available.

Person installing a sensor for soil moisture monitoring
Installing a soil moisture sensor can be a fairly simple process. (Source)

What aspects should someone look for in a soil moisture sensor? Obviously, measurement metrics are a primary concern. Most soil moisture sensors arrive at volumetric water content through measuring electrical conductivity. Typically, soil moisture sensors have two or more prongs, and, by measuring the time it takes for electricity to travel between these prongs, can determine the amount of water in the soil. Electricity travels faster in moist soils and slower in dry soils (for those who are further interested in the technicals, this link provides a great explanation). 

Some sensors not only arrive at water content, but explicitly break out electrical conductivity. This can be useful, as electrical conductivity is not just a means to measure moisture. Rather, it’s correlated with soil properties that affect crop productivity, including soil texture, cation exchange capacity (CEC), drainage conditions, organic matter level, salinity, and subsoil characteristics, as is discussed by the Nevada Climate Change Portal. Electrical conductivity can therefore inform an understanding of these other characteristics. 

Users should also consider the “bonuses” included with soil moisture sensors. For instance, many soil moisture sensors also measure temperature, which, according to EcoChem, an environmental chemistry consulting company, “has a profound influence on seed germination, root and shoot growth, and nutrient uptake and crop growth.” As the climate continues to change, this effect will only increase. Sensors which also measure temperature therefore provide a more robust view of soil health. 

It’s also important to consider the physical attributes of soil moisture sensors. Unlike, say, indoor air quality sensors, soil moisture sensors are inherently going to be exposed to rough conditions. If sensors are outdoors, they’ll be exposed to wind, rain, and temperature fluctuations. Therefore, it’s important that soil moisture sensors are weatherproof and built to last—the industry standard is of a polycarbonate or durable plastic enclosure. 

Weatherproof soil moisture sensor enclosure
Weatherproof soil moisture sensor enclosure.

Further, because soil moisture sensors are often spread out over a large geographic distance, the power source and method of data output are of particular concern. Most soil moisture sensors have fairly long power cables, allowing for them to be located wherever is needed. Others are battery powered, which has obvious pros (ease of installation) and cons (the need to occasionally change the battery). Data output behaves similarly, in that data which is wirelessly can be transmitted more easily, but may also suffer from transmission / range issues compared to wired data. 

With these considerations in mind, I’ve looked into many of the soil moisture sensor options in order to present a variety of quality sensors, one of which I hope will be suited to your soil moisture monitoring needs!

NameUsagePower OptionsData OutputForm FactorPrice
Stephens HydraProbeSoil Moisture, Electrical Conductivity, Temperature9 V to 20 V (~12 V ideal); connects via a powercordRS485, SDI126in sensor, variable cable length (over 1000 ft), durable stainless steel tines$475
Metergroup Teros 12Soil Moisture, Electrical Conductivity, Temperature4 V to 15 VDDI Serial, SDI12Robust epoxy body, 5m standard cable length, 5cm tinesAvailable upon request
Metergroup EC-5Soil Moisture, Electrical Conductivity, Temperature2.5 V to 3.6 VMETER Data Loggers, 250–1,250 mV5cm tines, 5m standard cable length, plastic body$115
NCD Soil MoistureSoil Moisture4AA batteries 2-mile wireless transmission to PC or cloud, Temboo Kosmos compatibleIndustrial grade plastic case$220
Sensoterra Moisture ProbeSoil MoistureNon-replacable Lithium ion batteryLoRaWAN 1.0.2, Open RESTful API, SenML server push notifications, GeoRSS feedPlastic body, 15-90cm tines$243
DecentLab DL-TRS12Soil Moisture, Electrical Conductivity2 alkaline C batteriesLoRaWAN® wireless Class A5m cable, polycarbonate enclosureAvailable upon request

Getting Started with Temboo

Everyone—from farmers to gardners to citizen scientists—can benefit from soil moisture monitoring. Hopefully, after learning more about the diverse applications of this exciting technology, you’ve realized you can benefit, too!

When we understand our surroundings, we can better appreciate our environment, better utilize resources, and better advocate for change in our communities. If this excites you, please check out Kosmos or get in touch with us to learn more about how Temboo can help with environmental engagement.