by Sanne Kure-Jensen
How can growers raise higher quality crops, bring tomatoes and cucumbers to market early and reduce costs while raising profits? Andy Radin of the University of Rhode Island (URI) Extension offered production tools at URI Extension’s mid-summer 2015 Twilight Meeting. Over 30 growers attended the workshop. Radin led a tour of the University of Rhode Island’s research high tunnels discussing soil fertility, tomato production techniques and cucumber variety trials. Dr. Rebecca Brown, URI Associate Professor, led a tour of the agronomy fields discussing cover crop trials.
Many growers regularly add manure-based compost to their high tunnels. This can lead to excess levels of phosphorous in soils. Radin said, “Organic nitrogen sources become available gradually over the course of the season and loss through volatilization and leaching is less likely.”
Plant-based mulch adds less phosphorous to soils. The carbon to nitrogen ratio in plant-based mulch can be as high as 80:1. These mulches improve soil tilth, provide small amounts of many plant nutrients and help store carbon in soils. Plant-based mulches can offer modest levels of critical macronutrients like nitrogen, potassium, phosphorus, calcium, magnesium and sulfur. Plant-based mulches may also supply small amounts of essential micronutrients such as boron, chlorine, iron, manganese, zinc, copper and molybdenum.
Last fall, Dr. Rebecca Brown arranged for URI grounds crew to bring leaves from the campus to the research farm. Contrary to popular belief, oak leaves and pine needles make great additions to any leaf mulch without affecting soil pH. To minimize trash among the leaves, grounds crews did not bring leaves from along campus paths and sidewalks. Leaves were spread in high tunnels four weeks after planting to allow maximum soil warming.
Tomatoes and cucumbers like a steady supply of nitrogen all season. Radin suggest growers take a pre-side-dress nitrate soil test in June. This test offers growers a sense of how much nitrogen the soil has a potential to release over the remainder of the growing season. Radin said high tunnels could allow for a particularly long growing season. He recommended assessing leaf nutrient concentrations. Radin sampled the most recently mature leaf – 5 to 6 leaves down from the growing tip. The research team dried these leaves, ground them up and sent the powder for analyses. Results can take 7 – 10 days, or longer.
In 2015, Radin and student researchers are running parallel petiole tests in-house to compare results with lab analyses for tomatoes grown in high tunnel soil conditions. Researchers crush tissue samples with a garlic press and test the sap for levels of nitrate and potassium. If the results track parallel with lab tests, this technique could help growers obtain fast, accurate results at lower costs. Growers using on-site tests could respond quickly to plant nutrient needs with side-dressing or fertigation (fertilizing through irrigation systems).
Plant tissue levels of potassium and nitrate fluctuate over the season. When developing and ripening fruits, plants use especially large amounts of potassium. Watch potassium levels carefully or plants and fruit can suffer ripening disorders like blotchy ripening or yellow shoulders.
Healthy soils should deliver steady supplies of nitrogen. In June, URI’s tomato and cucumber plants were healthy and vigorous. This season, URI researchers are comparing sources of slow release nitrogen: peanut meal, cottonseed meal and blood meal. These amendments, as well as potassium and phosphorous, were added at rates indicated by late fall / early winter soils tests. Soil amendments were applied a week before transplanting. Thanks to these slow-release fertilizers and the plant-based mulches, no additional nitrogen was needed until Aug. 1.
Tomatoes are most productive when managed to a single stem. Indoor tomatoes can yield as much as 30 – 40 pounds of fruit per plant with a longer growing season and some cucumber varieties yield up to 30 pounds per plant. At URI, staff and student researchers pluck side shoots off tomato plants twice a week. They also pull lower leaves to 12” off the ground, enabling good air circulation to minimize fungal disease and pest pressure. Cucumber pruning is performed similarly. These plants generally stop producing 8 to 10 weeks after planting. Well maintained indeterminate tomatoes, can produce right up to a hard freeze inside the tunnel.
Healthy productive tomato plants typically grow three leaves and then a flower bud/fruit cluster. To get large fruit, growers will thin clusters to 3 – 4 blossoms. Cherry and grape tomato cultivars are typically the most vigorous plants and may need additional pruning.
For convenient harvest without ladders, URI high tunnels use the “Lower and Lean” trellising system for tomatoes and cucumbers. The URI team secures 12’ to 18’ strings near the base of each plant. Growers wind the top of the string on a spool or Tomahook. That spool is secured to the hoop house or greenhouse rafter or collar tie. Each time the plants grow 8” – 12”, growers secure plants to their string supports. When the plants near the rafters, growers unwind lines and move the Tomahook along the rafter. The lower stem is allowed to lie on the ground. Growers remove lower leaves as necessary to maintain 12” air of space above the ground. Stems with ripening fruits move down for easy access and harvest.
Radin recommended leaving a light leaf canopy over ripening fruit. This dappled sunlight protects fruit from sunscald.
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