Everybody wants to grow nutrient dense food that is more nutritious, but what methods produce the best food? There is lots of talk online about organic gardening producing healthier food but is that really true? Are heirloom varieties better for you than hybrids?
In this post I’ll look at some interesting studies that try to answer these questions and the answers will surprise you.
What is Mineral Rich Food?
A number of terms are floated around in discussions about food quality. A very popular one is “nutrient density”. I have discussed nutrient density is some detail in a previous post; The Myth of Growing High Nutrient Density Food. The term is so poorly defined that it does not mean much.
Another term that is very ambiguous is “healthier” food. That can mean many things. Does it mean more nutritious? Or maybe it contains fewer toxins? Discussions that use this term, without a clear definition, are mostly useless.
In this post I am using the term mineral rich to mean food that has higher levels of basic minerals including phosphorus, potassium, calcium, magnesium, sodium, zinc, boron, manganese, copper, iron, and molybdenum. These are all minerals the body needs, so food with higher levels are healthier, provided they don’t reach toxic levels.
How do you grow mineral rich food?
Growing Mineral Rich Food Studies
I’ll have a closer look at two studies carried out by Allen Barker and his team, using tomatoes and cabbage, in multi-year field trials. I’ll also have a quick look at their study on lettuce.
The studies compared numerous cultivars of each vegetable and categorized them as either heirlooms (prior to 1950) or modern. In the case of cabbage, all moderns were F1 hybrids.
Three different fertilizer regimes were used; synthetic chemicals (10-4.4-8.3), organic with the same NPK (soybean meal, bone meal, and K2SO4) and compost. The synthetic and organic fertilizer provided 84–37–60 kg N–P–K/ha at planting and the compost provided about 280-60-40 kg/ha. The compost was made from cattle manure and crop residues.
The food produced was analyzed for mineral content, size and yield.
Heirloom vs Modern Varieties
On average, modern varieties produced a higher yield than heirlooms. But out of the top 6 producers, half were moderns and half were heirlooms.
Moderns also had larger fruit, but select heirlooms did produce the largest fruits.
Selecting the right cultivars is more important than selecting between modern or heirloom.
Yield Based on Different Fertilizer Regimes
Fertilizer regime had little effect on yield or fruit size.
Head weights with chemical or organic fertilizer were the same, but compost produced heads that were 72% smaller. This smaller size was probably due to lower levels of plant-available nitrogen.
It is a common belief that the smaller size of heirloom fruit means they contain higher levels of nutrients or worded another way, large fruit contains excess water which dilutes the minerals. On a weight basis, the minerals in modern and heirloom fruit were about the same. Larger fruit does not result in diluted nutrients.
Small fruit and large fruit contain similar amounts of nutrients on a weight basis. So it does not matter which size you eat; it’s the total amount of tomatoes that is important.
Fertilizer regimes had little effect on either macro or micro nutrients. The small variations that were observed would have no impact on diets.
“Differences among individual cultivars for each element were large. Cultivars with the highest accumulation of nutrients had about 20%–50% more of each nutrient than cultivars with the
lowest concentrations, with the exception of Fe, which was 100% higher. Considerable consistency occurred among cultivars that were the top accumulators of nutrients, but no cultivar ranked in the top five positions for all elements in each year.” What this means is that no single cultivar is the “most nutritious”, but some cultivars are better than others.
This study also looked at Brix values and confirms my previous conclusions, that Brix readings are not useful for measuring mineral concentrations.
Heirlooms and moderns had the same level of minerals. Larger heads did not dilute the minerals.
The fertilizer regime had no, or very little effect on mineral nutrient levels. Synthetic and organic fertilizer did produce higher yields.
The cabbage cultivars being tested had various maturity dates, but this had little effect on nutrient concentrations. Slow growing cultivars did not have increased nutrient levels.
Except for iron, the variation of nutrients in different cultivars was not dramatic.
The concentration of minerals in cabbage are considerably lower than in lettuce and it has been suggested that the closed heads of cabbage may limit nutrient absorption in the heads.
Minerals in Lettuce
Similar studies have been done on lettuce. Modern and heirloom selection had very little effect on mineral concentrations in lettuce. Yields were higher with synthetic and organic fertilizer, than with compost.
Conventional Agriculture vs Organic Agriculture
A meta-analysis of the yield performance of organic and conventional agriculture found that organic results in 5 – 35% lower yields. The above studies on cabbage and lettuce showed similar results when compost was used as a fertilizer.
This is one of the reasons scientists are skeptical that organic farming could feed the world.
What Does It Mean For the Gardener
Mineral nutrition in tomatoes is dependent on cultivar selection. Heirlooms and moderns are equally nutritious and the fertilizer regime has little impact. Organic fertilizer is not any better than synthetic, in this regard.
Similar results were found for cabbage. Heirlooms and moderns produce similar results and the type of fertilization has no effect on mineral content, provided enough nutrients are provided to the plant.
These results will be surprising to many because there is so much misinformation floating around about the benefits of heirlooms and organic gardening techniques. But consider this, heirlooms have been selected by gardeners mostly for flavor, and freedom from pests and diseases. How many gardeners analyze the mineral content of the fruit they select for seed harvesting? Not many. So it should be no surprise that heirlooms have not been selected for high nutrition.
Should modern day hybrids be more nutritious? Their development is focused on commercial needs such as shipping quality. There has been very little attention paid to nutrition.
As far as organic fertilizer goes, it all has to be decomposed into nutrient ions before plants can use it. Once in that form, the nutrients ions are identical to the ones found in synthetic fertilizer. The idea that the two are different, as far as fertilizing plants goes, has never made any sense to those who understand some basic chemistry.
Should you select cultivars for their higher mineral content? That depends on where you live. In countries that have access to lots of food, it really is not an issue. Select for taste and easy growing characteristics. If nutrition is an issue, then try some of the more nutritious cultivars, but keep in mind that switching from cabbage to lettuce may provide you with more mineral nutrients than trying to find the most nutritious cabbage.