My Five Senses

How Do I Know my Soil is Good?

How do I know my soil is fertile? You can get a soil test kit. It will tell you whether you are deficient in nitrogen, phosphorous or potassium (NPK) and whether your soil is alkaline or base. Then a gardener is instructed to add N, P, or K or lime to balance the acid. Soil tests treat your garden as a chemistry problem that strips down the complexity of the earth to a few key minerals. But gardeners have become more aware since the microbial turn in biology of the last two decades that the earth is very much alive. Adding fertilizer will feed plants, but not microbes living in the soil.

You might ask, what is wrong with feeding plants minerals they need to grow? If you just feed crops NPK, then two things happen. Plants no longer need to be good neighbors exchanging sugar for mineral nutrients with bacteria and fungi. They start bowling alone, relying on the gardener to dump more nutrients. When that happens, plants fail to develop relationships with organisms in the soil that deliver a far wider range of nutrients and micro nutrients in exchange for sugar. Second, the soil microbiome gets out of whack because a few species of microbes that thrive on N, P, and K are likely to take over. They are like crusading knights invading a city who kill the men and boys and prey on women. When the knights gallop off, they leave behind traumatized women, the offspring they spawned, and a totally new genetic profile. When that happens in a field, soil scientists call it “soil dysbiosis.” Soils out of balance have trouble holding water and nutrients. Plants growing in them are less resistant to disease and stress. They grow fast at first, pumped up with salt in the chemical fertilizers, but then slow down and produce with less vigor.

So, how do I know that my garden beds have a healthy microbiome? That is where the five sense come in.

The first thing a gardener does on approaching a finished compost pile is to put a hand in, grab a fist of dirt and smell it. It should smell, well, earthy, which I can only best describe as a scent that conjures childhood, days rolling outside. Children are short, clumsy and curious. They spend a lot of time with their hands on the ground picking up things they find and inspecting them closely. That is what a gardener does with her soil.

When I raise the lid on my compost bin I often hear the collective munch of hundreds of worms enjoying kitchen scraps. After I spread the compost in a thin layer on the garden beds, I hear the rustle and chirps of our resident robins and morning doves pecking away at the worms and black soldier flies in the earth. The jays taunt them from a fence post. Sound is a sure way to know if my soil is healthy. There is nothing sadder than a silent garden in the growing season.

Happy with the rich earthy smell, I give the handful of compost a squeeze. I like it when it takes the shape of my grip and, in a shadowy way, retains it. But the earth shouldn’t be too much like playdo. Good tilth is most even in dry weather. It both holds its shape but does not bind into a clod into a clay figurine.

Microbially-rich soils draw the eye by its rich brown-black color. Other hues are cause for alarm. Orange and red are often clay subsoils, the topsoil missing, a sign of erosion. Light brown to gray earth tell me that the soil is not retaining water and is probably lacking life as it has been over exposed from too much plowing, too many pesticides, insecticides and chemical fertilizers. White soils speak of excessive irrigation, the salt in water remains on top soils as a fine, pale film. (I once flew over Kazahstan in early autumn. I was surprised to see the ground covered with a light dusting of snow. When the plane landed, I realized there had been no snow. Instead, salt covered the Earth.) Mike Duff at La Brughera in Catalonia, Spain did this soil test of different sites on his farm. The darker earth at the far corner came from his nicely composted beds. The lighter soils from an exhausted field.

So, there you have it. Microbioperception, a term coined by microbiologist Karen Guillemin, relies on the primary senses: touch, smell, hearing, and sight. But what about taste? Some people eat soil, and they say that they don’t eat just any scoop of earth, but they go back to same spot to harvest particular ground which has the taste they crave. I don’t eat earth but I do savor the minerals from my garden beds when I harvest from it. I feel I can taste a greater range of flavors in the brightly colored chard, kale, tomatoes, carrots, beets and peppers I pull from garden. I can taste too a flatness when the soil is not right, when I have pushed through too many crops in a season or crowded together plants that don’t complement each other. They are both less sweet and acidic. They can be sour or strangely pliable, like trying to chew cardboard.

The message is to put your senses to work. They are just as good as a lab test, while simpler and cheaper. But more important, your senses put you in place. ‘To know your place,’ ‘to be put in place’, those are expressions that connote hierarchies of class and race. It is strange that in the last few centuries we have denigrated our connection to place. How enriching it is to take it back and embrace it.