Saturday, August 08, 2015
Farm Bulletin: The Dirt on Dirt
The human brain has a deep affinity for names. Soon we will start harvesting the nameless grape which we call a "grape with no name," what a surprise. A nod to both a song and a restaurant from decades past located on Commonwealth Pier in Boston. Run and staffed by descendants and family of Portuguese fishermen, the restaurant had no name, no sign and no menu. Enter the only blue doorway on the pier, and when it is your turn in the line, look for an opening among the long tables covered with checked oil cloth. Two choices for lunch, the day's seafood chowder and the day's fried seafood. It was the toughest choice ever put before us.
Our nameless grapes (green grapes in top photo, center), so named, elicit opposite reactions. At Higgins, Greg and Patrick gamely put it on the menu as a "grape with no name" whereas Josh and his staff at Food Front display them as "Boutard grapes." Despite our entreaties that food should be defined by how it falls on the palate, Josh told us a nameless grape is just too much for people to swallow. Heidi's son, Jack, calls them Anthony grapes. We will leave them nameless, but we appreciate the dedications.
Human brains have a similar affinity for measurements. One such measurement that draws the attention of farmers is soil pH. It is a number that comes with a decimal point. Attach a decimal point to any number and it immediately takes on a hypnotically greater significance than one without. It is also a logarithm, but that never grabs people to the same degree as a decimal. The other alluring quality of soil pH is that it can be changed simply and reliably if deemed not optimal, typically raised at little cost by the application of agricultural lime. Synthetic fertilizers tend to acidify the soil, reducing nutrient availability, and lime acts as an antacid of sorts, as well as providing the element calcium. Plop, plop, fizz, fizz…
Under certified organic agriculture, synthetic nutrient sources with their acidifying behavior, as well as synthetic disease and pest controls, are prohibited. Indigestion solved? Not if you consider pH alone. On occasion we have had our soil tested, and the test results always included the pH as a perfunctory service. The results are all over the map, from 4.9 to about 7.1. It is a labile character of the soil, shifting with the seasons and crops, and its measurement is generally not particularly informative. In an organically managed soil, the bacteria, fungi, microfauna and the crops themselves all influence pH. So our soil might be acidic enough to warrant adjusting in a synthetic regime, but not under organic management.
But what about the calcium? Don't we need to add lime anyway, and the pH will tell us how much is safe to add because excess lime can damage the soil and inhibit plant growth? There are six elements plants need in substantial quantities: nitrogen, phosphorus, potassium, sodium, calcium and sulphur. We have to amend our soils to maintain sufficient levels of these elements; this is especially important on a commercial farm where we are hauling into market substantial quantities of these elements in the form of food.
On an organic farm, calcium and sulphur are especially important because they are the building blocks for the plant's defenses against diseases and insects. Calcium is a key element for cell wall strength—most of the plant's calcium actually resides in its cell walls—and sulphur is a building block for the crop's internal chemical defenses. On a farm where the crops have external chemical defenses against disease and insects, that is, synthetic fungicides and insecticides applied by the farmer, the cultivator need only provide just enough calcium and sulphur for basic biological functions. Organic farms have spiders, dragonflies and a host of other predaceous arthropods helping to control the insect populations, as well as beneficial bacteria, yeast and fungi that ward off disease, but we need strong plants as well. Consequently, crops grown under organic management need more calcium and sulphur available in the soil, in fact nearing an excess under conventional nutrient interpretations.
As mentioned above, agricultural lime, calcium carbonate (CaCO3), is problematic as a calcium source. It can damage the soil's structure and chemistry. Although it is cheap, a 50# bag of lime costs about $4.15, it is not the best deal. Another good source is gypsum, but it does cost about 50% more, at $6.05 for a 50# bag. Even though it is nominally more expensive, we use gypsum exclusively, and never use lime. Generous applications of gypsum do not harm the soil, in fact the mineral improves the soil's texture, nor does it change the pH significantly. This is important because many fungi and bacteria thrive in certain pH levels, and changing the pH suddenly and significantly without a very good reason can alter the microbial ecology of the soil unproductively.
Gypsum is calcium sulphate (CaSO4). The best reason for using gypsum from the perspective of an organic grower is that you get both important elements, calcium and sulfur, and pay just 50% more. A very good a deal, especially when you factor in the costs of transportation and spreading the amendment. The other problem with lime is that the carbonate anion is at best valueless, possibly harmful, absent terrestrial indigestion; plants fix their own carbon from the air through photosynthesis so it is completely non-nutritive. We use gypsum for all our crops, annual and perennial, and buy more of it than any other amendment.
A cautionary note on gypsum sources. It is best to avoid recycled gypsum because some older wallboard contained trace amounts of mercury as an anti-fungal agent, or fungicides. The Organic Materials Review Institute (OMRI) tests and certifies materials used in organic agriculture. On bags of gypsum and other amendments, it is best to look for the statement "OMRI Approved" or "OMRI Listed." We also use a small bucketful of gypsum to mark yellow jacket nests so no one walks into them. We toss it over the hole and they dig their way out unharmed. They are valuable predators and scavengers, worth keeping so long as we know where they are.
Too often, organic agriculture is characterized in the negative, especially the absence of synthetic pesticides. Once you settle in as an organic farmer, success comes with managing the soil ecology so that you build strong crops that coexist with the benefits and the challenges that nature delivers. Book 18 of Pliny's Natural History is his discussion of farming. The book opens with a rambling plea regarding stewardship of the earth—he was no Homer or Sappho—but as you read it the fundamental spirit of organic agriculture is apparent. He laments the tendency of farmers to treat their fields like a battlefield, deploying poisons and other measures against nature. He urges us to farm in a manner that thanks nature for bringing us into world, and treats her as our benefactor in a shared enterprise with the full measure her creation. It is apt advice 2,000 years later.