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Micronutrients for increased crops yields and nutrition

If you could increase your yields and your markets demanded more produce, would you spend money on soil amendments? Derek Christianson of Brix Bounty Farm in Dartmouth, MA has long recommended farmers pay attention to soil micronutrients. He said soil amendments or foliar sprays are easy to justify with increased yields in healthier plants.

Derek Christianson mixing foliar spray to feed beets at Brix Bounty Farm in Dartmouth, MA.
Sanne Kure-Jensen
Derek Christianson of Brix Bounty Farm
Brix Bounty Farm

Christianson described the benefits of improving micronutrient availability in an Advanced Growers Workshop for the Northeast Organic Farming Association of RI (NOFA/RI). His program explored the nutritional needs of different crop families, key minerals needed to support healthy growth and the role of fertility management in achieving optimum yields. Christianson covered five crops, their fertility needs, cost and expense considerations and growing season management. Crops included beets, onions, spring cabbage, tomatoes and winter squash.

Thorough, accurate soil tests are critical for any grower. Christianson combines a mehlich-3 test from Logan Labs with a modified Morgan test from UMass for thorough soil testing. Site analysis and test results help determine ideal crops for a particular site as well as appropriate amendments.

Vigorous production happens under optimal chemical, biological and physical processes. Basic nutrients are needed for plant growth and health: Nitrogen, Phosphorous, Potassium (or Nitrogen, Phosphate, Potash). Humans and plants also need varying trace amounts of Carbon, Hydrogen, Oxygen, Sulfur, Calcium, Magnesium, Silicon, Boron, Chlorine, Molybdenum, Selenium, Cobalt, Copper, Iron, Manganese, Nickel, Sodium and Zinc.

Christianson urges growers to understand their site’s limiting factors. Is fertility adequate for anticipated yields? Will deficiencies affect plant health and increase diseases and/or pest pressure? Growers should maximize their Energy Return (Energy Returned on Energy Invested - ERoEI) just as they would any other Return on Investment (ROI) to maximize profitability.

Christianson recommends spending 5 to 15% of gross sales on fertility. Farm practices might include these tools:

  • Field Sprays - low concentration of traces minerals in late winter/spring
  • Bio-Builder Sprays - 1 - 3 times in spring and/or fall
  • Biodynamic Preps #500 and barrel compost - 1 – 2 times in spring and fall
  • Fall mineral applications - as budget and time allows
  • Pre-plant Mineral Mix and Energy Mix
  • Nutrient Drench/Inoculation at planting time and as needed
  • Sidedressing - 1 - 3 times as needed for high requirement crops
  • Foliar sprays - once/week (to once/month)


Beets must have adequate Calcium and Boron. They need Nitrogen for early season growth and less Nitrogen when nearly ready for harvest. Phosphorous is key to sugar production. Potassium and Boron are essential to moving the sugars into the roots.

Farm practices used are pre-planting fertilizer, row covers and sidedressing once or twice at 2 - 6 weeks after planting (WAP) including Potassium. They use weekly foliar sprays and/or fertigation. Adequate spacing and thinning are critical to good yields. Transplanting offers an opportunity for earlier harvests.

Brix Bounty Farm plants six successions to spread labor costs and broaden harvest windows. Customer favorite varieties include ‘Boro’,’ Kestrel’, ‘Merlin’ and ‘Zeppo.’


Top yields for onions come with vigorous early season growth. Minerals needed include available Nitrogen, Phosphorous, Sulfur (impacts pungency), Calcium and Copper.

Ensure sufficient Nitrogen and water for transplants. “Weeds are the enemy and will diminish onion size,” said Christianson. Ensure adequate water and cultivate regularly all season. Sidedress in May and June. Plant seedlings at the proper depth. Avoid late season Nitrogen application or release to improve storage life.

Farm practices used are pre-planting fertilizer, row covers and sidedressing once at 2 - 3 WAP and again at 4 - 6 WAP. Christianson says not to add Nitrogen after mid-June. They use weekly foliar sprays and/or fertigation. Adequate spacing and thinning are critical to good yields. Transplanting allows earlier harvests.


Spring cabbages need strong early season growth for maximum yields. Critical nutrients are Zinc, Nitrogen (for early ‘season’ growth not early ‘stage’ growth), Molybdenum, Sulfur, Boron and Calcium. Ensure adequate cell size and nutrition for transplants while in the greenhouse and spacing in fields.

Brix Bounty Farm ensures adequate Zinc early and Calcium throughout the growing season. Transplants are cultivated and sidedressed in May and June. They receive Boron and Calcium in July to prevent tip burn in high heat and humidity.

Farm practices used are pre-planting fertilizer, row covers against flea beetles and sidedressing once at 2-3 WAP and again at 4-6 WAP. They use weekly foliar sprays and/or fertigation.

‘Farao’ and ‘Super Red 80’ are favorite spring cabbage varieties at Brix Bounty Farm.


Intensive tomato management can yield more and better crops than large plantings. Tomatoes need Calcium, Phosphorous, Boron, Copper and Sulfur. Nitrogen and Potassium are needed for high yields.

Brix Bounty Farm uses pre-planting fertilizer, row covers and sidedressing in early June and again in early July. Farmers make a final cultivation in early July and plants clover as a cover crop between plants and rows. They use weekly foliar sprays and/or fertigation.

Brix Bounty Farm starts three successions of tomatoes in their high tunnel. The early ones are ready in case of warm spring. The main succession will have three times as many plants. A late succession will include late blight resistant varieties (same quantity as early succession). Plants are set out at 100 plants/1,000 square feet with 2’ spacing in rows. To maximize yields, shift plants’ focus from vegetative grown to fruit and ripening once fruit has started to set.


Winter Squash need adequate Calcium, Phosphorous, Silicon (one option is calcium silicate or Wollastonite), Boron, Copper, Zinc and Sulfur. During long, sunny June days, ensure adequate Silica, and Sulfur. Manage for Striped Cucumber Beetles. Variety selection will affect yield and fruit size. Be sure to match crops and size to your markets.

Strong fruit production and yield can be achieved with either direct sowing or transplant production. A vigorous start is important. “Be sure to cultivate one last time before the canopy closes and undersow with clover,” said Christianson. Manage for leaf diseases like powdery mildew. The canopy is critical for optimal fruit production and maturation.

Farm practices used are pre-planting fertilizer, sidedressing and weekly foliar sprays and/or fertigation. Brix Bounty Farm plants two successions, 10-14 days apart in 50-cell trays. Transplants go out 14 to 21 days after seeding (depending on variety). Popular varieties include ‘Sweet Dumpling’ and ‘Delicata.’ They start enough extra transplants for 2 to 3 beds (15% extra on top of usual 110%).

Christianson recommends selling butternut squash by the unit instead of by the pound: Small at $2-3, Medium at $4 and Large at $5 to $6. He only puts out a few medium squash and cabbages at a time in his unmanned stand. “Unfortunately, the extra large ones sometimes take a walk,” Christianson explained.

Christianson shared these experiences at an Advanced Growers Workshop called “Soil Fertility in Focus – Moving beyond N, P, K – Meeting the Nutritional Needs of Crops with Minerals, Microbes, & Management.” The workshop was organized by the Northeast Organic Farming Association of RI (NOFA/RI) and held at the University of Rhode Island.

Learn More

Christianson recommended these resources:

View Christianson’s Soil Fertility Workshop presentation here. His Soil Fertility Recommendation Worksheet here contains key resources, calculation guides, soil test guidelines as well as mineral supplement options and sources. See videos of Christianson demonstrating soil structure here.


Learn more about Brix Bounty Farm and Christianson’s upcoming workshops at or Email Derek Christianson at or call 508-992-1868. Visit Brix Bounty Farm’s self-service farm stand on Bakerville Road in Dartmouth, MA May through November.

Derek Christianson’s program was one of two Advanced Grower Workshops in 2013. Rhode Island organic farmers shared their expertise with other farmers, farm workers, apprentices and gardeners consumers. CRAFT workshops are organized by the Northeast Organic Farmers Association of Rhode Island (NOFA/RI) and supported by a grant from the RI Department of Environmental Management’s Division of Agriculture.

For a schedule of future workshops and other NOFA/RI events click here.

A similar story ran in the April, 2014 Eastern edition of Country Folks Grower.

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