Vermicompost as a fast-acting nitrogen amendment to mitigate nitrogen deficiencies in organic vegetable production

View the project final report

• 2013 annual report
• 2014 annual report

Commodities

• Vegetables: greens (leafy)

Practices

• Crop Production: organic fertilizers
• Education and Training: demonstration, on-farm/ranch research
• Production Systems: organic agriculture
• Soil Management: earthworms, nutrient mineralization, soil quality/health

Vermicompost (VC) is becoming an alternative to thermophilic waste composting (TC). Its application is however restricted to special applications by its high price. Because its high available nutrient content, specifically nitrogen and calcium, is generally greater than that of its thermophilic counterpart, it may be a good starter fertilizer. Earthworms bias nitrogen speciation towards mineral, available forms. VC may thus be an organic, fast acting amendment that remedies nutritional deficiencies in early growth, acting as an alternative to Chilean nitrate. Commercial vermicomposting is relatively new in Northern New England and little is known about the effectiveness and economics of field crops amended with vermicompost. We will carry out field trials to test the hypothesis that VC acts as a fast-acting nitrate amendment that can improve nitrogen deficiencies in early growth. Specifically, we will compare yields and quality of crops in treatments where starter VC, TC and no starter amendment are applied. We will also compare occurrence of nutrient deficiencies and yields of crops that were directly sown into beds with those of crops started in VC in greenhouses and subsequently transplanted into the field. An economic and leachate water quality assessment will also be carried out. Outreach will be done through a project blog, presentations at conferences, a field day and factsheets.

Our overarching goals are to show that VC may as a soil amendment prevent early season nutrient deficiencies; to measure nutrient leaching; to compare cost and benefits of using VC; to transfer this knowledge to organic farmers.
Performance Targets: 1. Establishing 24 research plots at Bella Farm.
2. Direct seeding and preparation of greenhouse starts.
3. Measurement of soil water NO3 and NH4, extracted from soil water samplers installed below the root zone, after storm events.
4. Estimate of plant nutrient deficiencies.
5. Estimate of early nutrient supply rates using Plant Root Simulator samplers.
6. Maintaining a project blog.
7. Presenting the project to 1 regional and 1 national conference.

Vermicompost will be obtained from our partners at VermiVision of Palo Alto California and compost from the Highfields Center of Composting in Wolcott, Vermont. Both products are quality controlled and fertility data is available although we will test their compost prior to using them in this study.

Field plots will be established at our collaborator’s farm. The study is designed to compare the effect on crop growth of VC with the effect of TC and the effect of doing nothing (C for control). These primary treatments will be implemented in two forms: directly seeded DS) and transplanted greenhouse starts (GS) to give a total of 6 treatments (VC X DS, TC X DS, C X DS, and VC X GS, TC X GS, C X GS). The design will have four replicates of each treatment. Two long, parallel seedbeds (1-m wide) will be prepared. 12 plots (2m by 2m) will be installed in each seed bed. Primary treatments VC, TC and C will be arranged in a stratified random fashion (four blocks of 3) along the seed beds. These will be arranged for a pairwise comparison of corresponding DS and GS treatments in the two parallel seed beds. DS and GS will be placed randomly in either the first or the second seed bed (Table 1). There will be a 1 m buffer between each plot and seedbed.

The soil will be characterized for texture, organic matter content, density and saturated hydraulic conductivity at 20 cm depth increments to a depth of 60 cm. Unsaturated conductivity will be estimated using the soil hydraulic properties calculator. In addition Watermark sensors will be used to log soil matric potential. These data will be used to parameterize, calibrate and validate a soil water flux model (Hydrus) for estimation of nitrogen leaching from the field.

Table 1: Randomized pairwise linear block design to compare compost treatment effects and seed starter method.
Plot 1 2 3 4 5 6 … 12
VCXDS TCXGS CXDS TCXDS CXGS VCXGS … TCXGS
VCXGS TCXDS CXGS TCXGS CXDS VCXDS … TCXDS

Crop: Swiss Chard (beta vulgaris, var: Large White Ribbed). Large White Ribbed was selected as it can withstand frost and does not bolt in the summer like some other varieties do when exposed to frost early in the season. This characteristic will make it easier to synchronize the plant growth stages of greenhouse started and directly seeded chard.

Greenhouse start production: A mixture of 50% compost (VC or TC) and 50% conventional organic growing medium (such as coir) will be placed into trays for starter plugs (5-cm deep, 1-inch wide wells). Plugs will be started in late April. For the control, only the conventional growing medium will be used. Seedlings will be planted by hand in the field after May 31when plants are 2 inches in size before transferring them to the field. In-row spacing will be 30 cm and between-row spacing will be 50 cm allowing 2 rows of crops in each seedbed.

Direct seeding: Direct seeding will be accomplished with a precision seeder placing seeds into rows prepared with VC, TC or no amendment. VC and TC rates will be calculated based on inorganic nitrogen analyses for the composts and soils to satisfy 20% of nitrogen as inorganic N. Prior to planting seedbeds will be prepared according to recommendations for swiss chard. Chard seeds will be spaced in the field at distances of 10 cm within the row with rows separated by 50 cm, and subsequently thinned to an in-row spacing of 30 cm. The seeds will be placed in the field in mid-May.