Maximizing Nutrition in Backyard Gardens
by Ben Grosscup
(forthcoming) Massachusetts Organic Food Guide, 2009-10
Is it possible to grow food with exquisite flavor, beautiful shine, extraordinary nutrition, and extended shelf-life? According to growers who have done it, not only can farm-sized growing operations do it, but with the right tools and knowledge, people can do it in their own backyards. Practitioners of this kind of growing say their goal is to maximize crop nutrient density – the amount of nutrition per volume of crop – and that this can be done in a manner entirely consistent with certified organic growing practices.
Nutrition Starts in the Soil
The difference in what these growers are doing lies in their soil fertility management and the soil science that informs them. Crops, they say, grow best in the presence of healthy communities of micro-organisms in the soil, and this microbial life crucially depends on the nutrition provided by a wide variety of properly balanced minerals. A healthy plant has microbes living all over its roots and leaves that digest minerals for their own nutritional needs while symbiotically transforming the minerals into available nutrition for the plant. As this process functions more effectively, the nutritional value of the crops we eat increases.
Nutrition enables photosynthesis – the process by which plants combine carbon dioxide and water in the presence of light and enzymes to produce sugar. Simple sugar (glucose) is the immediate product of photosynthesis, and depending on the availability of a full complement of nutrition, plants normally convert glucose into more complex sugars, proteins, fats, and carbohydrates. Without adequate nutrition in the soil, however, photosynthesis is compromised and the sugars in the plant sap will be degraded at the molecular level.
A cheap and highly indicative instrument for assessing crop quality is the refractometer. It uses a calibrated prism to measure how much the dissolved solids in a plant’s sap refracts light; the higher the light refraction index, the higher the presence of large molecules — primarily complex sugars — in the crop. The refractometer’s unit of measurement is called “brix”. A high-brix level at harvest time generally suggests a healthy plant. High-brix is also consistently correlated with high mineral content, because many enzymes that aid in photosynthesis require a wide range of mineral nutrients to function.
Making it Happen
One Central Massachusetts grower and Director of the Real Food Campaign, Dan Kittredge, outlines three interlocking soil management strategies, each corresponding to a branch of science:
- Balancing minerals in the soil (chemistry)
- Activating soil microbiological communities (biology)
- Maintaining the electrical conductivity of the soil (physics)
First, for the soil to attain an optimal level for crop growth, mineral nutrients are made present in certain quantities and balanced in certain ratios to each other – for instance, 7:1 calcium to magnesium and 1:1 phosphorous to potassium. Certain soil tests, such as the Ream’s Test, provide well-measured estimates of the availability of various minerals to plants. A consultant can then calculate recommended quantities (in pounds per acre) of various amendments needed for a more optimal balance. To incorporate most applications of minerals into the soil’s living system, a source of carbohydrate that is readily available as food for microbes — such as powdered humates, molasses, or sugar — is always added.
Second, microbial inoculations, which can be ordered and then brewed in a tank with a simple bubbler (to provide oxygen) or bought from a supplier, are applied alongside the mineral amendments. These inoculations jumpstart the biological process in the soil. As with the mineral applications, the goal is to feed the microbes with sufficient energy and nutrition in order to digest the mineral nutrients. To accomplish this, growers add substances such as fish emulsion, sugar, and/or kelp to the microbial cocktails they spray on their crops.
Third, steps are taken to monitor and maintain soil electrical conductivity, which is easily measurable (in microsiemens or µS) using an electrical conductivity meter. The measurement is important, because soil mineral levels and microbial activity affect conductivity. Steady conductivity is indicative of a healthy microbiological community, but a dip in conductivity is followed by diminished brix levels within 24-48 hours. This dynamic provides growers with a useful early warning system to help maximize yield and nutrition. A wide variety of stresses on plants, including functional nutrient deficiencies or a fast approaching storm front, will diminish soil conductivity. One way to increase soil conductivity – before plant brix reductions – is to apply a nutrient drench along each bed, because doing so provides soluble nutrients. Another approach, which requires base minerals (e.g. calcium) to be well established in order to be beneficial, is to apply a very low concentration of sea minerals (e.g sea water), vinegar, and sugar in a foliar spray (too much easily burns a crop). This can also help restore conductivity by stimulating plants to release carbon exudates into the soil that stimulate microbes, which in turn, digest nutrients for plants. Taking conductivity readings 30-120 minutes after making various interventions helps to refine one’s approach, because it provides almost immediate information on what techniques are working best.
Scaling From Farm to Garden
For some farmers, what’s more challenging than the soil science is figuring out how to physically deliver the various mineral and microbiological amendments to the soil. Ari Kurtz of Lindentree Farm in Lincoln, Massachusetts has been experimenting with these new management techniques for a whole season on a portion of his 11-acre farm. “It is a major practical challenge to properly spread 2,000 lbs of rock dust across two acres. You’re trying to spread this material evenly, and you need to carefully calibrate the spreader so that it releases just the right amount,” he says. One recommended management strategy Kurtz still has in the plans is spraying microbiological inoculants. That step has been held up mostly for lack of a boom sprayer – an infrastructural investment that may take time to implement.
When growing on a garden scale, it becomes easier to apply materials by hand. A number of companies provide products primarily for gardeners striving for nutrient density.
Jon Frank manages International AgLabs’ gardening division – High Brix Gardens in Fairmont, Minnesota. He began by reformulating some of the products that another division of the company, Fertilizer Brokerage, had been selling to large scale farmers for many years – but this time with backyard gardeners in mind. Frank, whose company performs soils tests, says they are important for revealing what’s in the soil already. Gardens are different from each other, and you want to avoid over-applying minerals. He finds that in gardens where compost has been routinely applied without a corresponding mineral fertilizer program, soils often contain excessive phosphorous and potassium and insufficient calcium, which he says should be at about 3,000 lbs per acre.
Frank says that after working with clients for three years, he often sees yields double, triple, and even quadruple, while brix levels increase as well. The vast majority of what Frank recommends is organically-certifiable. There are alternatives to the few that are not, although he says the alternatives are slower at achieving high brix, which according to Frank, is the most reliable indication of plant health.
Thomas Giannou of T&J Enterprises in Spokane, Washington is another purveyor of products for backyard gardeners striving for high brix crops. He offers an Organic Garden Kit with multiple soil amendments as well as a microbe tea brewer, but his program doesn’t normally include soil tests. He recommends roughly the same soil treatment regardless of pre-existing conditions, saying that he’s been able to get consistently excellent brix in the first year with his program. It includes large applications of dry minerals and foliar sprays that contain numerous minerals, fungal and bacterial inoculants, and food sources for beneficial microbes.
One important part of this overall program is applying 1 cup per square foot of a mineral mixture that provides, among other necessary nutrients, a concentration of 7,600lbs calcium per acre. His website shows reports of numerous crops grown with the soil fertility program he recommends that matured in less time than expected and attained high brix, sweet taste, and vastly extended shelf life. Giannou readily acknowledges that his approach is not for everyone, because the short-term cost of minerals for a large acreage may exceed the short-term income received from it.
Nutrient Dense Crops
While awareness of nutrient dense crops is growing, most people have not yet heard of it. Even as people evaluate a wide range of food labels – “organic,” “fair trade,” “sustainable,” and “local,” – there remains no widely recognizable certification system to assess what foods are nutrient dense. People can’t find this food in most grocery stores, including natural foods stores. The reality is that most of agriculture has not yet made it a priority to maximize nutrition in produce. Still, there’s no reason to despair, because people can ask for this food from producers they know and/or start growing it themselves.
This article is a reprint from the NOFA 2009 Organic Food Guide
Northeast Organic Farming Association, Massachusetts Chapter
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(forthcoming) Massachusetts Organic Food Guide, 2009-10