We need dry weather to work the ground, but the plants need water all the time. So how does it work for sporadic rain events to nourish our (your) crops? How does the water get to the plants? And what if it doesn’t?
The genesis of water supply to the plant is the structure of the soil particles and the amount of organic matter among those particles. When we get a good soaking rain, some of the water percolates down into the soil through the worm holes and ant trails, but mostly it moves through the tiny channels and collection of cavities between the soil particles. If you have ever had a septic field installed, a trained technician will perform a “perk” test, to see how fast a given soil will drain away water. Every square foot of soil in Kentucky has been classified and mapped as to its capability to drain or hold water, along with dozens of other attributes considered in farming or construction.
While plants certainly need water, there can also be too much of a good thing. In fact, it is helpful to have the water drain away from the surface of the soil, so the roots can also have access to air. If the soil has too much clay, the water will “perch” on the surface, asphyxiating roots. But at the same time, you also want the soil to hold water for the plants as they wait for the next rain. The organic matter (OM) content of the soil has a direct correlation to the water holding capacity of a soil as it acts like a sponge, and breaks up the tight clay areas. Here at Elmwood Stock Farm, soils are running between 3-4% OM, and the research has shown that each percentage point of OM will hold 20,000 gallons of water. For reference, a one-inch rain over an entire acre (43,560 square feet) is 27,154 gallons. With our organic cropping systems, we are incrementally building soil by increasing the OM content of our soils, thus protecting our crops from the impact of short term dry spells.
Soil water can be lost by draining downward out of the root zone, pulled upward and out of the soil through capillary action, the chimney effect, or via plant transpiration. The combination of sun and wind will pull moisture from the topsoil in a dramatic fashion. The water that moves from the roots up through the plant and out the leaves as it grows, is called transpiration, which is a combination of translocation of water and respiration of the plant. Transpiration rates are higher in hot weather as the plants attempt to stay cool. Some fruits may taste sweeter in dry weather since there is less water available to fill the fruit.
To conserve precious rain water, we mulch some crops with hay or straw. Other places we plant living mulches between rows to keep the sun off the soil. The plants making up the living mulch are well-suited to the job because they grow slowly and don’t use much water themselves. We also use thin strips of plastic sheeting to hold moisture in the soil and keep the weeds from growing along the base of the plant rows.
Since we often have dry spells in Kentucky, at Elmwood Stock Farm we employ mechanical irrigation techniques to ensure the soil, and then the crop, have access to water to produce the food we all love to eat. The southern border of the farm is the Elkhorn Creek, at a location above an historic mill dam, which forms a deep pool of water to draw from. With electric or tractor driven pumps, we can send water through a series of underground and above ground pipes to the edge of each field. From there we have two options, t-tape or traveler. T-tape comes on a 4000’ roll, is laid under the plastic sheeting when the plastic is put down or is walked out by hand along the plant row. It has little holes that allow a single drop of water to drip out every 12 inches over a long period of time. This is a very efficient means of providing water directly to the crop. Home-garden-sized kits are available. The traveler is a big gun sprinkler attached to a large reel. The sprinkler gun is pulled to the end of the field. As the pump pushes water out of the sprinkler, which covers a 90’ diameter, the water pressure turns a crank that slowly winds the hose around the reel, thus moving the gun the length of the field. This applies a lot of water to the field in a fairly short amount of time.
So tillage, mulching, and crop rotations are the basis of our moisture management plan, but we leave nothing to chance to ensure a good crop will be harvested. No amount of irrigation beats a good soaking rain.
Mac Stone