Organic fertilization for greenhouses

Organic fertilization for greenhouses

Summary

Production of vegetable and herb transplants is an integral part of USDA certified organic farm and greenhouse operations. Little information is available on organic fertilization for greenhouse production systems. Preplant incorporated and liquid organic fertilizers are being evaluated as sources of nutrients for seedling and potted plant production in soilless potting mixes. Nitrogen and phosphorus availability are being determined by standard media extraction procedures and incubations of amended potting mixes. A wide variety of preplant-incorporated and liquid fertilizer formulations are being tested alone and in combinations to develop optimum strategies for fertilization and to maintain high productivity while meeting requirements for organic certification. This project has been extended until January 31, 2013 with a final comprehensive report to follow soon after. This study is being conducted in the greenhouses and laboratories located at the University of Connecticut.

Objectives/Performance Targets

• To evaluate nitrogen and phosphorus availability from organic pre-plant incorporated fertilizers (PPIF) and organic liquid fertilizers (LF) in soilless potting mixes (SPM). To evaluate combinations of PPIF and LF for commercial production in SPM.

Accomplishments/Milestones

I conducted 2 greenhouse trials this year. The first trial from March-May took a refined approach to preplant fertilizer + liquid fertilizer combinations based on our previous research and used representative products (high vs. low phosphorus release and low vs. high nitrogen release). In a randomized complete block factorial design six preplant fertilizers at a rate of 0.3 g N / L were combined with five liquid fertilizers at 150 ppm. A 1 peat: 1vermiculite soilless potting mix incorporating dolomitic lime and an organic wetting agent was amended with the preplant fertilizers. Liquid fertilizers were applied at every irrigation after emergence. Subirrigation was used to avoid nutrient leaching. Lettuce and mizuna were grown from seed to transplant stage in 6-cell packs of 30 cm3 plug cells. Saturated media extracts (SME) were used to evaluate pH, electrical conductivity (EC) and nutrient concentrations of SPM prior to planting and in conjunction with plant harvest. A solution displacement (pour-thru) extraction was used mid-way through the trial for non-destructive monitoring of pH and EC and nutrient concentrations with growing plants. Concentrations of ammonium, nitrate and phosphate were determined using standard colorimetric methods. A chromometer (CR-400, Konica Minolta Sensing, Inc., Ramsey, NJ) was used to quantify observed differences in lettuce leaf coloration seen in digital photos at plant harvest. Values were recorded as lightness/measure of light to dark (L*), chroma value/color intensity (C*), and hue angle/actual color (H*). Shoot fresh weight was measured after detaching the shoot at the cotyledonary node. Plant shoot tissue was dried for 24 hours at 90 – 95 C and ground to pass a 20-mesh screen for N and P analysis. The second greenhouse trial in May-June evaluated the response of tomato seedlings to six rates of a single preplant fertilizer in combination with three rates of two different liquid fertilizers. The goal was to find the optimal combination of preplant + liquid fertilizer rates. Saturated media extracts (SME) were used to evaluate pH, electrical conductivity (EC) and nutrient concentrations of SPM prior to planting and in conjunction with plant harvest. Concentrations of ammonium, nitrate and phosphate were determined using standard colorimetric methods. Shoot fresh weight was measured after detaching the shoot at the cotyledonary node. Plant shoot tissue was dried for 24 hours at 90 – 95 C and ground to pass a 20-mesh screen for N and P analysis

Additionally, a month-long incubation trial was conducted in the laboratory. Seven preplant fertilizers were mixed at a rate of 0.4 g N/L into two commercial potting mixes amended with lime and wetting agent. Pots 12 cm tall with a volume of 445 cm3 were filled with media and incubated at 20 C. Deionized water was applied to the surface twice weekly and the leachate was collected. The volume of leachate was estimated by weight. Standard colorimetric methods were used to measure ammonium, nitrate and phosphate in the leachate.

Analysis of these trials is nearly complete. Preliminary results indicate that fertilizer product choice caused significant differences in fresh weight and nutrient concentrations in media extracts in the March-May greenhouse trial. There was a positive fresh weight response to increased preplant fertilizer rate in the May-June greenhouse trial. The incubation trial shows that soilless media choice and fertilizer product choice affect nutrient concentrations in leachate. This project has been extended until January 31, 2013. A final report containing detailed results and conclusions will be submitted by March 31, 2013.

Impacts and Contributions/Outcomes

A poster summarizing this project was presented at the 1st Northeast Organic Research Symposium held in conjunction with the Northeast Organic Farming Association of New York’s Winter Conference in Saratoga Springs in January 2012. These two events attracted a total of about 1400 farmers, gardeners, and others interested in organic farming. A summary of the poster was also published in the conference proceedings.

A fact sheet will be compiled at the conclusion of this project and published on the University of Connecticut’s Cooperative Extension IPM website and the New England Greenhouse Update webpages as well as our SARE project page. When complete, this project will benefit greenhouse growers and farmers who are interested in improving their organic fertilization practices in potted plant and plug production. Extension personnel have expressed keen interest in disseminating this information. Additional research is being planned based on the results of this project.

• Organic Research Symposium poster

Collaborators: