Who (or what) is this eddy you keep talking about?

Efficient water management has never been more critical for agriculture and specifically for viticulture. High-end viticulture needs to manage water to not only cut costs, but to keep quality high in a market of oversupply and buyers who hold the upper hand over the grower. High production viticulture may not need the water management finesse for quality that high-end viticulture does, but regulatory demands for groundwater protection as well as limitations on water deliveries push growers into making the most out of every gallon.

Here at AV, we’ve made use of impactful technologies to help growers irrigate efficiently and control vine stress to improve wine quality from their vineyards. Our primary tools have been the soil moisture probe and, more recently, the Florapulse microtensiometer. Both tools have been indispensable and even more so now that we have our own data portal to view and analyze these data streams. More recently, we’ve been working with a new tool, an eddy covariance device, for direct measurement of ET, which gives us another approach for irrigation management that we didn’t have before. Before I introduce this new tool, let me explain what direct measurement of ET is and how it differs from other ET measurements.

Eddy Covariance – who is this guy?

Eddy is not just your buddy down the road with whom you share a good laugh occasionally. Eddy or more meaningful, eddies, are swirls of turbulent air which we experience daily but don’t give a lot of thought. Unless you’re a micro-meteorologist like I am. Yes, I am one of those. I did my Ph.D. in micrometeorology of the vineyard environment so I know a thing or two about it. Let me give you the nickel tour of micrometeorology (let’s call it micromet for short), eddies, and how eddy covariance is used to measure ET.

Wind does not blow in a straight line. As air flows across the earth’s surface, or on a micromet-scale, the surface of a field, forest, desert, or whatever, it experiences friction from that surface. Air flow at the very surface of the earth is zero, because wind cannot penetrate the earth. So, as the wind blows across the surface, the portion closer to the ground experiences drag from the friction, which is enhanced by objects, such as buildings, trees, and of course grapevines. This friction causes a shear force in the air flow field, which creates the turbulent eddies. And these eddies swirl and interact with other masses of air, creating more eddies. These wind shear eddies are smaller than the primary eddies, and these smaller eddies interact with other packets of air, creating their own eddies. And so on and so on. So, indeed air does not flow in a straight line, with some exceptions like katabatic wind during the very still night when cold air sinks. Those flows are not turbulent, but during the day, you can count on turbulent eddies all over the place. You can see this if you look at smoke rising and then swirling: initially it rises quickly because of convection from the heat, but as it cools, it gets taken by the air and you can then see what the eddies look like.

So, now that you know what an eddy is, let’s discuss why It’s important to us, not only for agriculture, but as humans. Without air movement, everything that is generated at the earth’s surface (e.g. dust, CO₂, farts, and yes water vapor) would have to rely on diffusion from high concentrations at the surface to lower concentrations in the atmosphere above. Thankfully, that is not the case. The wind, with its turbulent eddies, facilitates the movement of gases and suspended particles (called aerosols) from the surface to the sky.

In the case of water vapor, the water vapor concentration (when it is not raining) is higher within and just above a plant canopy than it is in the air above the canopy. Turbulent eddies mix the moister air below with the drier air above (Fig. 1). In the portion that is swirling upward, vapor is brought upward. In the portion that is swirling downward, drier air is brought downward.

We can measure this! Eddies can be measured using high-speed anemometers. A sonic anemometer looks like a stethoscope, but it is really a pair of speakers and microphones. Several times per second the speakers emit an ultrasonic pulse, which is captured by the microphone on the other end. The time it takes for the sound wave to reach the microphone on the other end is measured and the difference in time between the two directions is a measurement of instantaneous wind speed. We can measure the turbulent air field this way and meteorologists can measure this in 3-D. For us, we only care about one axis – the vertical one. Because movement horizontally just moves vapor across the field and we only care about what is moved upward. So, the 1-dimensional sonic anemometer measures the fluctuations in vertical air movement. Over time, the net air movement is zero because the earth blocks vertical air movement. So, we only care about the fluctuations in the vertical direction.

We can also measure water vapor, or humidity, at the same high frequency. When air swirls upward, the moisture air registers an increase in humidity and when it swirls downward the drier air brought in registers a decrease in humidity. If we record the instantaneous vertical air velocity along with the instantaneous humidity, and take the covariance of the two over a time interval, we get a direct reading of water vapor flux. This is what eddy covariance is!

If it sounds complicated, you’re right it kind of is, but fortunately this is established technology and the covariance is computed on the fly by either the device itself or the equipment used to log the data. In my graduate research, and in my early professional career, I used eddy covariance equipment. The cost back then was about $30,000 in today’s dollars. You can find them now for that or much higher for use in micromet research. So, while eddy covariance equipment has long been the gold standard for ET measurements, its high cost has rendered it primarily a research tool, though developers of other ET methods have and are still using it as a standard to calibrate their approach.

That’s nice, but the gold standard is too expensive to use to directly measure ET

That’s right, equipment for eddy covariance has been just too costly to use as a source of daily ET measurements. Until recently, at least. Last year Li-COR, a company out of Nebraska who have been making plant and environmental research equipment for decades, released their LI-710 Evapotranspiration Sensor (Fig. 2), which is a simplified, but still effective, eddy covariance sensor in a small and rugged package. The best thing about it is the price tag, which is a fraction of the cost of a traditional eddy covariance system and puts it right into the cost-effective range for commercial agriculture. The device computes eddy covariance internally and communicates digitally to a datalogger.

Last year, overjoyed with this new technology, we entered into a reseller agreement with Li-COR and purchased some units to get more familiar with and to do some design for the best data logging and telemetry solutions. We’ve made substantial progress and have also developed an app to track ET and to help growers make determinations of irrigation from the information (Fig. 3).

Why use this over other ET measurement methods?

Our motivation for this blog post is to announce this new technology and not to disparage other technologies out there, but we should at least briefly discuss why it is such an exciting development for us and for agriculture in general.

Probably the most common way to obtain ET measurements is by using weather stations and using that information to determine reference ET (ETo) using the modified Penman equation. Weather inputs of solar radiation, wind speed, temperature and humidity are used to determine Daily ETo. Almost all weather stations will provide values for ETo, as this is a standard and common method. That said, ETo itself has limited utility, as it is based on the theoretical ET of a hypothetical reference crop (a mixed grass mowed to a certain height) and does not indicate the ET of the crop (ETc). For many crops, including grape vineyards, ETc is a fraction of ETo.

To determine ETc, ETo is multiplied by a crop coefficient (Kc). These crop coefficients are basically a “fudge factor” to represent the fraction of ETo that the actual crop experiences. Kc values will vary during the growing season as the canopy develops and then senesces, usually peaking around veraison, holding steady and then dropping near or after harvest. Kc values have been computed and published by many researchers for many different crops, including grape vineyards. However, they are prone to error and we have found, using soil moisture as our guide, that we can irrigate far less than the amount ETo*Kc produced without long-term loss of soil moisture. So, actual Kc is likely substantially lower than published values of Kc are telling us based on our experience.

In fact, last year we ran some REAL ET eddy covariance measurements and compared them with ETo computed from nearby weather stations and found effective Kc values of around 0.35 for a full canopy in three vineyards, compared with published values of around 0.6. That’s a big difference!

Surface renewal has been a popular method of ET determination in recent years. While surface renewal is a valid micromet method, we should caution that it is not a direct ET measurement. Rather, it is based on a surface energy budget (Fig. 4). Let me explain. The energy budget of a field (or any other part of the Earth’s surface) is comprised of four basic flux components:

1) Net radiation flux, Rn, which is the amount of solar radiation that provides energy to the surface (downwelling radiation minus reflected radiation)

2) Ground heat flux, G, which is energy that warms the surface of the soil and penetrates into deeper levels

3) Sensible heat flux, H, which is energy dissipated into the air by heating of the air from soil and leaves and is transported into the ambient environment by turbulence, just like water vapor is

4) Latent heat of evaporation flux, LE, which is energy used to evaporate water from liquid into vapor, which is then transported into the ambient environment by turbulence, just like sensible heat is.

The surface renewal approach measures not latent heat flux or water vapor flux, but it measures sensible heat flux. To determine latent heat flux, and from that, evaporation flux, the energy budget is used to net out that term. Usually, the other two terms, Rn and G, are estimated, and whether or not estimated or measured, each term in the energy budget equation represents a source of potential error. The net of it is that surface renewal is prone to error, unlike eddy covariance, which is a direct measurement of water vapor movement and does not require any assumptions or models.

Are there any limitations on where eddy covariance can be used?

Yes, there are limitations, which are pretty much the same limitations that surface renewal has. The field needs to be a decent size – large enough to provide a few hundred feet of upwind fetch to the sensor. This is to allow the flow field to stabilize and avoid edge effects, like from roads and ponds. And while the field should ideally be flat, sloped fields can be used as long as the slope is relatively consistent. We tested the LI-710 over some uneven and sloped vineyards last year and got good readings from those, but site selection is important and tiny little “island” vineyards are simply not candidates. This is true for both surface renewal and eddy covariance sensing techniques.

That said, most commercial-scale vineyards will be able to use this new device and we look forward to rolling them out to early adopters in this and upcoming growing seasons!

It's not for the faint of heart

Going no-till certainly has been picking up steam in recent years, and overall it’s a good thing. When I first got involved in viticulture back in 2010 I was living in Italy. Like a lot of Mediterranean viticultural areas, there was a tendency to disc everything all the time. If you didn’t have a barren wasteland with vines poking out of it, you weren’t a good farmer. Anything you couldn’t get to with a tractor you sprayed with herbicide. One of my first vineyard jobs in Italy was spraying glyphosate out of a backpack sprayer all spring. I felt like I was in the final scene of the Godfather! Minus the dying part.

Herbicide: the new four-letter word

Mentalities have shifted since then both in Europe and here in the states. All in all it’s a good shift. We’ve all seen places that have gone on for years and years using herbicide to a point where you don’t even need to spray it anymore because that soil is so dead. The only thing that grows on it is that weird reddish moss.

Percolation suffers. The soil forms a crust on top and water can’t infiltrate it. You’ll walk these vineyards and you see the water from the emitter just beads up and drips off the berm like Teflon. Then it pools in the tractor row. There is just no porosity to these soils and it makes irrigation almost impossible.

Aside from that, herbicides are gross. We’re lucky in vineyards to not use too many nasty chemicals but the ones that are nasty are all herbicides especially the pre-emergent ones.

Herbicides also have developed a bad rap among consumers especially roundup or glyphosate, which is ironic because it really isn’t that toxic compared to others. As an aside, there are a bunch of people out there who seem to think that glyphosate is the same thing as Agent Orange. For the record that is very not true. They are completely different chemicals. Commercial forms of glyphosate can be orangey in color. The resemblance ends there.

The trouble with tilling

Conventional tillage can also be problematic. Frequent tilling destroys soil structure. If you break a chunk of undisturbed soil apart, you’ll find that it breaks into aggregates of soil particles. Inside those aggregates you’ll find different sized pores, both big ones that hold air and tiny ones that hold water. Plants need both of these things to thrive. The aim of tillage is to break these aggregates up into smaller bits but long term that is going to negatively affect your plants.

Tillage also leads to compaction, again over time. Then the only way to break it up is with more tillage. It’s like one of those vicious things!

No-till coupled with covercropping helps build soil structure improving water-holding capacity and aeration of the soil by way of better porosity. It does this at the same time as it builds organic matter. Organic matter is a source of nutrients for the vines. Everything contained in the plant decomposes and becomes available to the vine. This is particularly important in the case of leguminous covercrops that fix nitrogen. Organic matter has a negative surface charge and so it holds onto all the positively charged cations your vine needs namely Ca, Mg, and K.

The breakdown of old plant matter into organic matter is driven by microbes and this is what people mean when they talk about the “living soil”. Herbicides and tillage disrupt the lifecycles of soil microbes and limit their ability to do this. No-till is supposed to leave these little guys alone to do the work we need to free up nutrients and make them plant available. In theory anyway.

Mismeasure of microbes

I say in theory because this is really hard to measure. I think this is one of those areas where agriculture lapses into the religious. Basically, it’s a hard thing to sample for and we see this all the time sampling for nematodes. You may have one pocket over here that has this number of some kind of microorganism and a few feet over you have a different one. It’s hard to establish scientifically that one tillage treatment or another favors diversity of microorganisms or how numerous they are. Many of the papers out there come up inconclusive even if it makes total sense that if you mess with something’s environment they aren’t going to thrive as much as if you left it alone.

But there are some shining examples of work that support this idea. Chen et al. found that conservation tilling (i.e. no till and reduced till) increased total soil microbial biomass by 37% at least in the top 8” of the soil. They found that this only worked in loamy soils, and that sandier or coarser textured soils didn’t see the same effect. This is mostly because you need higher levels of soil carbon and sandy soils don’t have a whole lot of that. It showed what we expected that fewer disturbances allowed for more efficient use of that soil carbon. Basically, the microbes did a better job breaking things down if you didn’t run a plow through their house every couple of months.

Nunes et al. is another paper that explored this topic. They looked at seven different indicators for soil health:

• Soil organic content
• Microbial biomass carbon, which is a measurement of carbon contained in the living portion of the soil i.e. microbe bodies
• Nitrogen
• Soil respiration, which is proxy for microbial activity
• Active carbon, which is the carbon that is available to the microbes
• Beta glucosidase, which is the enzyme involved in the degradation of cellulose (plant bodies)
• Soil protein, which is the soil’s ability to store nitrogen

They found that every one of these measures was improved by reducing till. Again, this is usually something we see only in the top portion of the soil (top 8”).

The bigger picture

Now neither of these studies are on vines. If you’re looking for some reading material on no-till in vineyards, Richard Smart from UC Davis did some incredible ahead of his time work. I urge you to take a look at some of his papers. This one in particular puts no-till into the context of global warming, which if anything, is the real reason we all should be looking at moving in this direction.

Bottom line is that untilled land sequesters more carbon than tilled. ½ of all the carbon in the atmosphere is estimated to come microbial respiration of carbon on the surface of the soil. A lot of this comes from the large-scale repurposing of land that has occurred over the last 200 years. All nitrogen (nitrous oxide is also a greenhouse gas) comes from microbial activity on the surface of the soil.

Covercrops alone don’t help the problem. Yes, the covercrop sequesters a lot of carbon but if you then till that into the soil, the benefit is lost. All that carbon gets released and it gets released quickly.

This is a great study. They looked at one vineyard over seven seasons and found that going no-till sequestered 1.5 metric tons per acre. It also increased the oxidation of methane which is good even though that technically increases CO2. Methane’s global warming potential is 27 times that of CO2 so less methane is a good thing.

This study also took into account fuel burned up during tractor passes as well as N20 production. No-till is net negative. Even going to occasional tilling tipped the scales not just because it released sequestered carbon, but also just because it meant another tractor pass.

The limitations are numerous

From a practical standpoint, what does it mean to go no-till? The first limitation we face is that, you have another plant whether a covercrop or a weed, that competes with your vine for water and nutrients. This is going to be a lot more severe if you are going wall to wall no till i.e. where you leave the undervine row untilled as well. Most growers we work with if they do go no-till opt for just leaving the midrow or the tractor row untilled. Leaving the undervine untilled is a whole lot harder.

A lot of the studies that are out there on no till point out that going no-till significantly reduced yield in whatever crop they were working on. Grapes are a little different since, if you’re a fine wine maker, yield may not be your main target. Some of the growers I’ve spoken to about their experiences say that in the first year they noticed stunted growth. Keep in mind that the cover crop is growing in the spring, right when your shoots are trying to develop. It’s the worst timing, but there’s not a lot you can do about it. This is of particular importance in climates with wetter winters. In those cases, there’s a lot of spring nutrient uptake that goes on in the midrow since roots are active there due to all the rainfall. Other dryer areas go into the growing season with pretty dry soils so the only area where you have to worry about competition is right under the emitters.

There seem to be a lot of growing pains in the first year of switching to no-till as you’re suddenly without the easy button to deliver a slug of nutrients to your vines. The benefits that no-till provides are soil structure and organic matter. These things take some time to form. You may need to fertilize more than you normally do. If you’re an organic producer, which you may be if you’re considering no-till, that’s going to be a significant expense if you suddenly have to give everything a shot of expensive organic nitrogen.

On the flipside, if you have an overly vigorous vineyard, no-till can do a good job soaking up some of that extra vigor.

Plants don’t just compete they actively sabotage by way of what’s called “allelopathy”. If you’ve ever wondered why your vines look like crap around an oak tree, that’s allelopathy. Vines don’t play well with others and some weeds and covercrops especially if they’re in the vine row have a similar action.

Another limitation is that there is no ideal covercrop. Ideally you have a nice low-lying covercrop that you can seed once. It reseeds itself. It doesn’t take over. It gets tall and you cut it and it shades out all other growth. In the case of grasses, you have to cut before they seed otherwise they’ll be too tall. Leguminous cover crops aren’t nearly as assertive, but they also don’t provide nearly as much organic matter or ground cover.

The big problem that a lot of growers face when going no-till is rodents. That nice mulch you create by mowing is the perfect place for gophers and ground squirrels to hide. If you have untilled vine rows, voles can be a problem. I’ve seen new vineyards (and some fairly mature ones) scrapped entirely because voles girdled the trunk of every vine.

Tilling also does a really good job of getting rid of burrow systems, which is important if you struggle with ground squirrels and gophers. The occasional till chops those guys up and doesn’t allow them to build a city under your vineyard. I’ve seen infestations of ground squirrels so bad you can’t even take a step without falling through the ground into a burrow. They will eat the roots right out from under your vine.

Definitely not the easy-button

All of this boils down to the fact that going no-till is going to be more expensive and more time-consuming than conventional farming. The growers I’ve spoken to who have gone no-till have a worker whose specific job is trapping rodents for at least two to three days a week all season long. That adds up to a lot.

Another thing to consider when going no-till is that you’ll probably need some specialized equipment. If you’re just doing the tractor row no-till, a mower may suffice plus a weed knife…assuming you are also getting rid of herbicide. There are a lot of fun toys out there that you can check out for undervine weed control. The finger weeder is an interesting one. It’s actually a passive implement that doesn’t require any power from the tractor to work. It just rotates with the forward movement of the tractor. The Multiclean is another minimal-disturbance implement. Our farming company has one of these and they seem to like it. Timing is really everything. If you let the brush get too high, you will have a tangled mess on your hands. It’s especially hard in vineyards with high-water holding capacity as you may not be able to enter the vineyard with a tractor before the weeds have already taken over.

You’ll need to rethink how you reseed your cover crop. You can’t just broadcast seed over an untilled surface and assume they’re going to take root. There are some direct seeders out there specifically for this reality but again, it’s an investment.

The limitations to undervine weeding or tilling, if you’re still planning on tilling the vinerow are topography and vine spacing. These implements are always harder to use on a steep and/or uneven incline. If you have tight vine spacing, the tool may not have time to fully rebound and swing back in between vines. That will leave a lot of missed spots.

One thing to keep in mind when transitioning to a reduced or no-till system is to adjust your expectations. Nothing looks cleaner than an herbicided vineyard. You’re going to have missed spots here and there and you’re going to have some weeds. Getting over the mental block is a big one for some people.

Find what works for you

Even if you aren’t going hard core no-till, there are ways to simply reduce tillage, which is still a step in the right direction. A lot of vineyards we work with till alternate rows and switch every 3 to 5 years. As I mentioned, wall to wall no-till under the vines is a whole lot harder, so maybe you just want to keep your midrow non-tilled and use a weed knife undervine. That’s still good.

If this is something you want to do, the best option is to design future blocks with no-till in mind. The above picture is from a ranch in Paicines managed by Kelly Mulville, who’s the viticulturist who thought this design up. He’s trained the vines on a high wire and the dripline is also really high. This allows him to run sheep all year long, which is great because normally you have kick your sheep out once your vines get tasty. The high dripline too is a really good idea. It makes a lot of undervine implements easier to use as a low dripline gets in the way. I know growers who have spent all winter raising the dripline wire 6 inches just so they can get a Multiclean to work.

There are some places where despite the benefits, we really don’t recommend no-till. Don’t plant a new vineyard on untilled soil. Your baby vines are not going to be able to handle the competition. Also ripping is the only way to break up any hardpans you have and incorporate any amendments that you’ve added.

Rodents can get out of hand and so can weeds. If you have an outbreak of star thistle or something else that is really aggressive or if you have an underground city of squirrels under your vines, just till. There’s no point in being a martyr.

The picture above is of a vineyard on Mount Etna in Sicily. The Etnean viticultural area is spectacular and it’s almost completely tilled, mostly because they have this one kind of wild chestnut that, if left alone for a season, will grow a tree right in the middle of your vineyard. Like Etna, there are some places where no-till just doesn’t work.

If this is something that interests you though. Go for it. Throw everything against the wall and see what sticks. Like everything, a one-size-fits-all mindset isn’t going to work. If you’ve been growing grapes for a while though, you already knew that.

Articles:

Chen, H., Dai, Z., Veach, A. M., Zheng, J., Xu, J., & Schadt, C. W. (2020). Global meta-analyses show that conservation tillage practices promote soil fungal and bacterial biomass. Agriculture, Ecosystems & Environment, 293, 106841.

Nunes, M. R., Karlen, D. L., Veum, K. S., Moorman, T. B., & Cambardella, C. A. (2020). Biological soil health indicators respond to tillage intensity: A US meta-analysis. Geoderma, 369, 114335.

Wolff, M. W., Alsina, M. M., Stockert, C. M., Khalsa, S. D. S., & Smart, D. R. (2018). Minimum tillage of a cover crop lowers net GWP and sequesters soil carbon in a California vineyard. Soil and Tillage Research, 175, 244-254.

Read this first!

As agricultural consultants in California, irrigation consulting during the growing season is our bread and butter. A lot of times, especially in vineyards with lighter soils where I recommend short and frequent irrigations, I know my desired schedule amounts to a tall order. Not everyone can feasibly do two hours, three times a week. No matter what’s best for the vines, I have to work with a human irrigator, who is still going to turn the valve on at 5 pm and turn it off at 7 am the next day.

In a lot of cases, this amounts to a vineyard that is both over- and under-watered: the 14-hour irrigation percolated past the rootzone in under 3 hours and the rest of the week (after the root zone water was depleted) the soil was dry as a bone.

So, I’m happy to see so much interest these days in valve automation.

I’m also apprehensive because I’ve automated valves and it’s not a silver bullet. It’s not any bullet. It’s a useful tool that needs to be applied to what is already a functioning irrigation system. And some of y’all don’t have that.

How does valve automation work?

To get why this is the case, you have to understand how automatic valves are automated. You may have a diaphragm or a bonnet valve in the vineyard already that you manually turn on and off. That valve is then automated via a solenoid, which is a small electromagnetic device with a plunger. When actuated, the plunger moves up to open the valve, or down to close it.

Given that very few farms have line power at valve locations to provide the constant AC power needed to hold open the solenoids, most ag valves use solenoids known as “DC latching solenoids”. They are actuated by ~12V pulses of electric current powered by a solar panel/battery, and held in that position by a mechanical latch. This can be reversed by applying a reverse polarity pulse, in which case the plunger is latched in the opposite state. These actions are triggered by the control system which is ultimately controlled by you via whatever app came with the automating system.

The contact between the solenoid plunger and the actual closing mechanism can be either direct, indirect, or semi-direct (see above video). Most situations you see in vineyards are indirect. The solenoid plunger basically just redirects water from moving on one side of the diaphragm to the other. This creates a pressure differential to open the valve or a pressure equalization to close the valve. The water pressure itself is used to both open the valve and to close it.

This is nice because you can open and close a high water flow valve using only a tiny solenoid plunger actuated with very little energy. The water pressure itself is doing all the work. This is why, for example, a 6-inch valve can be operated using the same solenoid as a 2-inch valve.

The million-dollar question: What if you don’t have enough pressure?

Long story short, your valve isn’t going to open or close the way it should.

To get a more complete answer, I got in touch with Saul Medrano over at AvidWater. Saul has a lot of experience with valve automation in everything from greenhouses to berry farms to vineyards. Vineyards tend to have more challenging topography than other growing situations, so I was interested to hear his opinion on some of the common culprits of dropping pressure in these cases. According to Saul:

“Incorrect usage and placement of air vents is a big one. Some people may think that just because there is an air vent, it’s going to work, but really it depends on what air vent you have and where. That and just not understanding what pressure losses you get across all the components like valves, air vents, filters, check valves. You need to understand what it takes for them to work properly.”

He added:

“You really have to stick to whatever the manufacturer says the valve can handle. If the manufacturer says, ‘Hey, this thing can operate properly at 10 PSI’, it should be able to operate at that.”

There are some creative work arounds out there. Anytime water passes through a filter, there's a drop in pressure whether it's clogged or not. You may have high pressure at your pump but low pressure at your valve, especially with changes in elevation.

And you may not even have that…

A few years ago, we installed 10 PSI (threshold) pressure switches wherever we had soil moisture probes we monitored to give us irrigation feedback for our weekly recommendations. This was effectively just to measure the duration of irrigations: switch turns on when irrigation starts and turns off when irrigation stops. We chose 10 PSI assuming that people would have at least that in their driplines. For the record, most pressure-compensating drip emitters are designed to function between 12 and 58 PSI. Below (or sometimes above) that range, the emitter output will be erratic and outside the specified flow.

We found in many blocks both hilly and flat, the irrigations failed to actuate the switch. This means that when irrigations get going, the line isn’t even being pressurized to 10 PSI. Aside from issues with distribution uniformity of water and fertilizer, a system like this would need to be automated specifically with valves that could function at low pressure. We’ve often seen automated valves that don’t work consistently because of low system pressure. This usually translates into a valve that doesn’t shut off once it’s turned on because the pressure is too low to impact the diaphragm. 

At the source, the pressure these growers are getting is probably adequate. That doesn’t mean that by the time it gets to the valve the pressure is the same. In fact, laws of physics dictate that it is not the same. Filters, fittings, pipes themselves and changes in elevation continually eat away at the pressure you have in your system and that will determine what your options are for automating.

I asked Saul what some of the reasons for poor pressure in vineyards are. He responded:

“Over the last three years, obviously, it’s been a tough market. There are a lot of designs out there that are just designed to be cheaper. Everyone has sacrificed some performance in the system to reduce cost. If your irrigation system isn’t designed properly and you’re not using the right equipment to handle that, low-pressure or high-pressure system, then it’s not going to work.”

And on the other hand,

“I’ve seen some sites where they have all the bells and whistles. They have a VFD (i.e. Variable Frequency Drive) at their pump. They have a pressure-regulating valve at the irrigation site. And then they have pressure-compensating emitters. The diaphragm valve with the pressure-reducing pilot is going to open and close to try to match the pressure that it needs. And in turn, the pressure-compensating emitters are going to do the same thing. You have three things that are trying to achieve this one common goal, and it just creates chaos.”

Most modern irrigation installations I’ve seen have a VFD either installed in tandem or built into the pump control. In the past, VFDs have been incentivized via several government programs (e.g. EQIP, SWEEP). However, just having a VFD isn’t the end of the story. Saul reiterated:

“There’s a misconception that if you have a VFD, you’re going to have the most energy-efficient pumping system. That’s not always true. It may use less energy, but it’s not necessarily going to be the most efficient usage. All it’s going to do is vary the speed of the motor to ramp up or down based on whatever pressure you’re trying to achieve. You need to make sure your VFD is programmed properly in order to have the most efficient energy use that you can have.”

Don’t let me scare you

Saul and I agree that automation is a good thing. With rising labor costs, it’s becoming more of a necessity. It’s also more time efficient when you have to get water to a bunch of blocks in the course of a week. When asked if he had any advice for those thinking of automating, Saul said:

“I think the first thing anyone should do if they’re interested in automation, is do some remote monitoring. Put some sensors on your field and keep track of what’s going on. You can monitor flow, monitor pressure, monitor EC, pH, just know what’s going on now in your field. Then you go into valve control. Now you have control and monitoring. I think everyone should have good data based off a sensor, not from a person who’s subject to human error.”

Lumo valves contain a flowmeter and pressure switch to both automate irrigations and monitor flow and pressure. This allows the grower to quantify their water use on a block-by-block basis and detect problems in realtime.

The com-bi-nation valve control and flowmeter

Let’s talk about the new kid on the block, shall we?

Lumo seems to be the latest and greatest in irrigation Agtech and they certainly give us a lot of food for thought. For those who aren’t familiar with the product, Lumo offers an all-in-one valve with built-in flowmeter and telemetry for control and monitoring. Compare this to a more classic automation arrangement where the telemetry device is wired to an external solenoid and (hopefully) a pressure switch (or transducer) to determine whether the valve actually opened and closed when you told it to.

Instead of working via a solenoid, Lumo valves work via a worm drive mechanism that moves up or down when actuated and directs the flow of water over or under the diaphragm. I’ve worked with a couple devices that use this method in place of a solenoid and they seem to perform better in low-pressure systems. Regardless, these valves are specified to operate at between 15 and 80 PSI and I would stick to manufacturer’s specifications…always.

Lumo solves an issue we often see in viticulture where individual valves are spread throughout the vineyard. In the past, this arrangement made automation expensive given that each valve needed its own telemetry device, which typically starts at around $1800. If all your valves are located at one central location, you may have automated years ago because one device can service a handful of valves. Single Lumo valves clock in under half of this price tag, so it’s a good option for when you have valves scattered around the farm.

What Lumo hangs its hat on though is its continued monitoring of water usage and fluctuations in flow. This allows for precise applications of water to each block as well as keeping a lookout for leaks and blowouts. For a lot of growers who have used Lumo, there tends to be a big discrepancy between how much they thought their output would be and what it is.

The above photo showcases how Lumo can be used to detect problems in an irrigation system. If the reported GPM is much higher than what you expected, you may have a leak, or in this case, a malfunctioning air vent.

Kick the tires

Will automation work in your vineyard? The best way to determine that is to have a qualified irrigation professional assess your system. Here at Advanced Viticulture, we partner with irrigation specialists throughout California to ensure that you put your best foot forward in any project. As Saul said,

“Automation is not going to fix a poorly designed system. You need to understand how your system works and make sure that it’s designed properly to handle an automation system on it. We’re honest with customers. We’re not going to sell them a system if we know it’s going to fail. We’ll say, hey, you need some upgrades to do before any automation to work here. I would say that’s a really important thing that sounds like common sense, but I’ve seen some stuff out there that had no business being installed.”

For the most part, no automation company, Lumo or otherwise, wants the application of their equipment to fail. Dissatisfied customers are infinitely more vocal than satisfied ones. It’s one of the reasons Lumo works with companies like AvidWater and Advanced Viticulture to make sure their product is a good fit for each system prior to installation. Regardless of what company you go with, ask around. Ask the company selling you the devices to put you in touch with an irrigation expert. Then plan your budget accordingly. You may need to do some work on your infrastructure first and put off automation for a year or two. That’s still better than getting stuck with an expensive system that doesn’t work.