I had a fun morning last week working with my fellow Rockwall County Master Gardeners to look at their problem soils under the microscope. I’d done a brief class about the Soil Food Web at the February meeting. Last week’s session was to put what had been discussed into action by looking at the health of the soil samples they brought in.
Most of the gardeners brought in soil from problem areas which included existing vegetable beds and two lawn samples. Vegetables and bermuda grass require a fungal to bacteria ratio in the 0.3-0.75:1 range. Most of the samples had no fungal component at all, which leads to poor aggregation in the soil, less fertility and plants that require you to feed them instead of relying on the soil food web.
All of these soils would benefit from increased fungal mass, except for the one exceptional soil sampled. No protozoa were observed so that means natural nutrient cycling is not occurring except for those soils that had a few nematodes. You can increase protozoa by using good compost, a compost tea or a protozoa drench.
Interested in learning more about soil biology and how it affects your plants? We’ll be teaching a full day seminar in September in Fort Worth, stay tuned for details. If you want to know how the Master Gardeners sampled, you can see our instructions here. If you want your soil examined, you can read more about what we do here.
Sample 1 Fannin County Native Soil
Sample 1 was native soil from Fannin County. There was poor aggregation, no fungi, no predators (protozoa and nematodes) present. There was poor diversity of bacteria in the sample. Diversity is key in the soil food web. It’s important to add foods from different sources to build diversity. To get a clearer picture of the bacterial situation, this soil needs to be resampled and the bacteria counted to determine if it is so bacterial that it will be difficult to establish a fungal component. Alternately, you can look at what is currently growing in this soil. If it is primarily weeds, then it’s highly bacterial. Using a protozoa infusion or drench will help reduce bacteria levels (see instructions at end). Also adding fungal foods such as wood chips, oats, or fish hydrolysis will help establish a fungal component. Inoculate the soil before covering with wood chips with a good compost such as Texas Worm Ranch Vermicompost. You can also take a small amount of soil from underneath healthy trees to inoculate the wood chips. Another interesting way to increase fungi in your garden is to use Wine Cap Mushroom spawn. You’ll grow your fungal mass in your soil as well as edible mushrooms for your table. We’re about to start a “mother” bed of wine cap mushrooms to use to inoculate our composts and growing areas. We’ll write about that as it progresses!
Sample 2 Crab Grass
Sample 2 was from a clay soil growing crab grass. There was one bacterial feeding nematode present, which is encouraging that a predator in the soil food web was present. Predators eat fungi & bacteria, making nutrients available to plants. There wasn’t much fungi present and no protozoa were observed. When I looked at this sample, I didn’t have the original bag to look at the texture of the soil. Under the microscope, it looked less compacted than most clay soils I’ve seen. Add organic matter and fungal foods to shift this soil towards turf grass. A protozoa drench/spray would be helpful as would lightly top dressing with a good compost.
Sample 3 Dandelions
This was a heavier clay from the same gardener, currently growing dandelions. There were no predators nor fungi observed in the sample. Same recommendations as for Sample 2.
This soil had a potting soil appearance. It was much looser, and had perlite in it. It had low bacterial diversity, no fungi, no protozoa, a nematode and some aggregates. This was the first soil I looked at among these samples that had aggregation of the soil. Soil aggregates indicate increased structure due to the presence of bacteria. Bigger aggregates are formed when fungi is present giving that nice crumbly soil texture, and meaning that nutrients and water are retained better in the soil. I’m not sure what the target plants for this soil are, but to avoid weed issues, the fungal component definitely needs to be increased. A protozoa drench is not necessary for this soil as you can see in the photo below that there is not a huge amount of bacteria present (the smaller specks & bubbles).
Sample 5 Annuals in Pot
This was the best soil sample of the day. There was a large amount of fungus present in multiple fields. However, there were no predators observed. Since this is a small area, inoculating with a good compost would be the best way to introduce predators. There was low bacterial diversity, so diversify your food sources. This soil had good aggregation.
Sample 6 Garden
This sample was from a raised bed garden from the same gardener. This soil is not a good as the soil in sample 5. However, there was a nematode observed and decent aggregation. There is low bacterial diversity, some fungi but not enough, and no protozoa. Use the suggestions given previously for increasing fungi. Adding a good compost or making a compost tea will help increase the biology.
This soil had decent aggregates, but had little fungi, so the aggregation has room for improvement. There were no nematodes or protozoa observed. The bacterial diversity was poor. Follow the suggestions previously given to increase fungi biomass and diversity.
To make a protozoa infusion you’ll need:
5 G bucket
20 G aquarium pump
Alfalfa meal, pellets or hay
It’s preferable to use non-chlorinated water which includes water treated with chloramine. Place a thin layer of the alfalfa on the bottom of the bucket, just enough to cover it. Insert the plastic tubing, you may want to use suction cups to hold them down. Don’t use air stones though! Fill the bucket 3/4 full with water and connect the tubing to the pump. Run the pump for about 48 hours. Be sure to check on it periodically to make sure it hasn’t overflowed. Apply sparingly to the target area. This can be added to compost teas and extracts.
There’s work to do on most of these soils to build fungal biomass and increase diversity. Always use different sources in your compost, and in the foods you feed the soil to build diversity.
DISCLAIMER: Being a Master Gardener can lead you into unexpected areas. I was a Rockwall County Master Gardener before we started the farm in 2004. It’s a slippery slope folks! If you’re interested in becoming a Texas Master Gardener, applications will be accepted soon. Check with your local county extension office for more information. For Rockwall County, you can check www.rockmga.org.