By Porter Mitchell
Porter Mitchell is a Farmer Services Coordinator at Georgia Organics.
Biosolarization
Biosolarization is an organic method of weed control that uses heat from the sun to kill weeds. A farmer covers their growing area with clear plastic and keeps the soil underneath the plastic moist using drip irrigation. The sun heats the soil up to 140 degrees Fahrenheit which kills weeds and weed seeds.
Biosolarization Courtesy of Semantic Scholar
Biosolarization is also good for the soil. When the ground is thoroughly watered the water displaces the air in the soil. This creates an anaerobic (oxygen free) environment for helpful bacteria and fungi to grow and flourish. These fungi and bacteria help make nutrients more available for crops and can even kill many soil-borne diseases.
Research performed by our friends at ATTRA/NCAT shows that biosolarization is extremely effective on nutsedge, mustards, pigweed, thistle, and annual grasses. One study showed that biosolarization reduced weed coverage from 34 percent to four percent!
Tips for Using Biosolarization at Your Farm:
You must use clear plastic. Black plastic blocks the sun’s UV rays and keeps the soil from becoming hot enough to kill weeds and weed seeds. Try using old hoop house plastic to save on costs.
You must keep the soil under the plastic moist. Water thoroughly.
You must create a good seal on the plastic to keep air out and moisture in. Air coming in can cool the soil and hamper the process.
How long does biosolarization take?
It takes roughly four weeks to kill weeds and weed seeds through biosolarization but the time can vary on temperature, humidity, soil type, and weed type. It’s best practice to take notes on which area you laid the plastic, which weeds are a problem in that area, and how long it took kill the weeds. A temperature log can also be useful if you are using biosolarization during the fall, winter, and spring seasons when weather can be unpredictable.
Drawbacks of Biosolarization
Alas, there is no perfect method of weed control. Here are some drawbacks of biosolarization:
Biosolarization does not kill weeds that spread with deep rhizomes like Johnson grass.
Biosolarization is not a realistic method of weed control if you do not use drip irrigation.
Rolling out drip irrigation and plastic is time consuming, although some farmers have been successful at rolling drip irrigation lines and plastic mulch simultaneously using their plastic layers.
Keeping the edges sealed means weighing them down, and weighing them down means moving and managing heavy sandbags.
Removing the plastic, cleaning it, and storing it can be a time-consuming and messy process.
Biosolarization Courtesy of UC Davis
Biosolarization Pro-Tip
Do you know that a field or bed has the same weed pressure every year? Get a head start on weeds by using biosolarization right when weeds emerge!
Up the Ante with ASD!
ASD is short for anaerobic soil disinfestation (that’s a mouthful!). ASD causes bacteria in the soil to release compounds that act as pesticides, killing harmful soil-borne diseases and pests. ASD also accelerates breaking down organic matter.
The process for ASD is similar to biosolarization but with two important differences: the farmer spreads a thick layer of organic matter on the area before covering and the farmer uses permeable plastic mulch instead of clear plastic. Use whatever organic matter you have readily available like compost, used straw, or broken-down wood chips.
Have you tried biosolarization? Let us know your results and any helpful tips or lessons learned! Email Porter at porter [at] georgiaorganics.org