Necessity is the mother of invention” says the old adage, and it’s certainly true here in the Far West where we are in a drought. Like it does in most crises, the chance to learn presents itself in a big way. People like myself, who know little about soil science, meteorology or hydrology are realizing that some knowledge about these topics is the key to making every drop of water count.
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Unfortunately, there are no “one size fits all” answers. We grow grapes and the way we manage water, given our site and soils, differs from the techniques used by my neighbors who grow annual vegetables for their CSA. But we both determine the most efficient way to utilize our water by following these rules of thumb.
Plant & Soil Pointers
When choosing which varieties of any plant to grow, but especially the food producers, do your homework and find out what their ideal growing requirements are. Choose hardy cultivars developed to thrive in drought conditions. If possible, buy seed from local nurseries and grow plants with the same watering needs together. Dense planting will give you a bigger bang per gallon of water delivered.
Your soil’s field capacity will determine how much water it can deliver to plant roots. This is the amount of water left in soil after water has drained off via gravity. The rub is that only about half of the water left in the soil is available to plants. How much depends upon soil type. As Gary Zimmer writes in his excellent book The Biological Farmer, “When the available water is gone, the soil has reached its wilting point, which is the point at which a plant begins to wilt and cannot recover.”
Whether in a drought or not, you do not want this to happen. To avoid it, the first step is to have your soil analyzed for nutrients and its field capacity tested. Your local Extension Service can recommend a lab.
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If, like most people, you have too much clay or too much sand, the long-term fix is to add organic matter by applying mulch, compost, well-rotted animal manure, planting cover crops and using applicable permaculture techniques. These will create humus, which will improve your soil’s ability to absorb and hold water but also increase the supply of nutrients available, important because a healthy plant is more drought-resistant.
But what do you do until all that organic matter has decomposed? It’s critical to keep the growing area hydrated. Clay soils dry out slowly but are the devil to rehydrate once they do dry out, so water them more frequently but apply less water per irrigation. Do the same with sandy soils, which drain and dry out quickly. Be careful not to give sandy soils too much water. You’ll just waste it, since it will pass on through and go somewhere else. With both clay and sandy soils, the idea is to let water soak in gently, and keep it in the soil by taking measures to prevent evaporation and runoff. How much water to apply is the next question.
To know how much moisture is in the ground at a specific point in time you can buy inexpensive soil moisture sensors (less than $100) or dig down a couple of feet and see what the soil feels like. Ideally, it will have enough moisture in it to feel damp and form a loose ball that crumbles easily.
Your local NOAA weather station is an invaluable source of information. From it you can get the short- and long-term forecast and the relative humidity, which will give you an idea about the evapotranspiration (ET) rate for your area. ET refers to the movement of water into the atmosphere from surfaces including soil (evaporation) and from vegetation, such as leaves (transpiration). The higher the ET, the more water plants will need. Wind, heat and other factors contribute to the ET rate, as does the leafy surface of a plant. The larger the canopy, the greater the transpiration.
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You can buy atmometers for a few hundred dollars to measure ET, but for more most of us, paying attention to the weather data available for our area, observing our crops and checking the soil condition will tell us if it’s time to water. If so, the water should be delivered as efficiently as possible, and that takes know-how.
The Drop On Drip
It’s true that drip is the most efficient way for most of us to irrigate, although for some crops sprinklers may be the answer. Your site, how you get your water and how much you have available for irrigation at a given time will determine the system that makes the most sense for you.
Installing a system is not that difficult; it’s fun assembling the parts. The hard part is designing a system that has adequate pressure to send water where it needs to go, targets only the plants you want to water and delivers just the amount of water needed to keep them healthy.
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The best place to get advice is from a firm specializing in agricultural irrigation. Sales people at your local big box store are simply not up on the latest equipment developed for drought situations, nor is the equipment as well made. True, you will pay a little more, but believe me, you will not regret it. A couple of lessons learned: Putting a system on timers saves water, because it eliminates the “I forgot to turn it off” scenario. So does spending money on enough valves to give you the flexibility to water individual rows or blocks separately as needed.
This article was originally published in The NEW PIONEER™ Fall 2015 issue. Subscription is available in print and digital editions here.