How Old School Technology is Helping Today’s Wineries Save Water
We have had a basic understanding of how water and sugars travel through the vine since the 1800s. It has been almost sixty years since an article first mentioned means of measuring these components (“Sap Pressure in Vascular Plants” Science Volume 148. April 16, 1965). In the mid 1970s Donald W. Grimes, based in the San Joaquin Valley, began using what are known as “pressure bombs” to help with irrigation strategies in cotton. The first mention of a pressure bomb in relation to vineyard management is credited to Robert Mondavi in the mid 1980s.
Today, Californians are living in the state’s driest period in history (LA Times; Sean Greene and Thomas Suh Lauder Feb 16, 2023). Water is a scarce commodity these days, yet is a necessary evil in vineyard management. Unfortunately, vines can’t tell us when they need water… or can they?
I had the pleasure of sitting down with Joe Nielsen of Ram’s Gate Winery in Sonoma, who has been using pressure bombs in the vineyard to help minimize the amount of irrigation needed to maintain the highest quality fruit.
Lori Budd:
What is the relationship of water to the vine? What is important about the progression in the vintage?
Joe Nielsen:
Grapevines are perennials and grape growing is a multi-year process. When we don’t have water, it not only affects the vigor of the vine this vintage, but affects the budwood being created, which impacts the following year. Water is a topic for today, a topic for tomorrow, and it is also a topic from yesterday.
LB:
What exactly is a pressure bomb? What is the benefit of using one?
JN:
A pressure bomb is very old technology. It is a tried and true technology that has been proven to work. It is a mobile device that, through looking at the leaf, can be brought into the vineyard and allows us to see the water pressure within the vine. Vines will show stress sooner than they truly need water.
LB:
How does a pressure bomb work?
JN:
There are scientific studies that show there are opportune times to take the measurements; either pre-dawn when the vines reset their water potential, or you can take it at solar noon (not true noon). This is when the maximum stress the vine is experiencing during the day [is occuring]. It is normally the hottest point of the day. The leaves are taken off the vine, both in the shade and in the sun. We then pressurize the chamber, so that turgor pressure can be measured. We look at the number and compare it to what we know are historical stress numbers. Every variety has a different stress point. We then learn how long after watering it takes the vine to return to stress level. Now we can create an irrigation schedule.
LB:
At what time during the vine’s lifecycle are you typically using the pressure bomb?
JN:
It definitely depends on where you are growing. The pressure bomb readings are done mostly pre-bloom, through bloom, and by the time we see the fruit set I want to know what my cycles are in order to maintain stress. I want to see that stress and know how long it takes to get back to non-stress levels.
LB:
How are you using pressure bombs to learn how the vines are developing from one vintage to the next and calculate how much to add?
JN:
Over time, it has been a bit of trial and error. We are tracking stress over a period of time. It is not one measurement; it isn’t doing things in isolation. The first time we go out, you may see no stress, so we’ll go back out in a week. We may see that the vine is beginning to enter stress, so we’ll shorten our window between our next reading. If we see the vine approaching stress levels, we’ll go back the next day. We will start with a little water and take an additional reading. If it resets to low stress the next day, I know it was too much water. If it takes about a week to return to stress, then that was probably the right amount of water.
LB:
Why is the use of pressure bombs so helpful in the pursuit of sustainability?
JN:
If we are only going on visual cues, we are probably going to water more frequently than we need to. When we talk about California conservation, I think this is an invaluable tool to create the gaps that we need to not only save water but also create the quality we desire. We can see that the plant is in a healthy spot even if it is 90o.
LB: Is there a certain time during the vine’s lifecycle that you want more or less stress?
JN:
We want to have pre-veraison or pre-set stress, not post-version stress; that’s when we just want to maintain. There are a lot of philosophies that watering post-veraison can lead to water berries or overly plump fruit, and I agree with that to an extent. I would say that if you are planning to allow for some dry-down and don’t over irrigate, you can figure out what is the right amount, but I am always trying to not do too much of anything.
LB:
We always hear that vines produce higher quality fruit when they are under stress. But how much stress is too much? How does the pressure bomb aid in this decision?
JN:
There is always a certain amount of subjectivity along with that objectivity. This is where experience and knowledge play a role in the decision. For example, the Sauvignon Blanc on our property is almost always in stress compared to the Pinot Blanc right next to it. It is a fairly vigorous plant and will take as much water as I am willing to give it. The pressure bomb lets me know when it drops into a stressful place for it vs. a stressful place for the Pinot that is right next to it.
LB:
Is there any special irrigation equipment necessary in order to water depending on the pressure bomb’s results?
JN:
No, the irrigation system is not dictated by the pressure bomb. It is an analog machine. It doesn’t feed a computer that turns on a system. It is old school. I like it because it is sort of foolproof, it is mobile, and it’s not expensive once you buy the equipment, yet gives us a lot of data.
LB:
What are your final thoughts on the use of the pressure bomb and how it relates to quality winemaking?
JN:
Water is a concern in California. Not only are you making a decision that impacts yourself and your wine quality, but also your neighbors’. It impacts sustainability. It is being thoughtful for a lot of other players, not just yourself. It’s not set it and forget it. Every year, different things happen in the weather, so if we are intent on making a wine of place and terroir, being stewards and being sustainable, like we are at Ram’s Gate, then understanding water is imperative.