Sustainable management of high tunnel organic vegetable production with short-season winter cover crops

Sustainable management of high tunnel organic vegetable production with short-season winter cover crops

Summary

Research on the effect of winter cover crops on growth and performance of successional vegetable crops has led to significant results for the 2013-2014 season. Austrian winter peas yielded greater biomass and biomass nitrogen content than the other treatments. Tomatoes showed a response to the cover crop with increased leaf chlorophyll, though yield results were mixed. Broccoli also showed a response with increased leaf chlorophyll, total biomass, and average head weight yield. This indicates that Austrian winter peas have potential to supplement nitrogen fertilizer use in high tunnel production for vegetable crops like broccoli.

Objectives/Performance Targets

1. 1. To evaluate four winter cover crops for their ability to improve soil quality and supplement fertilizer requirement when grown as a green manure from mid-November to mid-February, before a succession vegetable crops in a high tunnel system.

1. 1. To evaluate the effect of short-season winter cover crops on vegetable crop growth, yield, and quality within a high tunnel production system. Vegetable crops will include pac choi, tomatoes, and broccoli.

Accomplishments/Milestones

A full year of research has been conducted, with the second research season underway.

Five winter cover crop treatments have been evaluated, including a nontreated control, Austrian winter peas (Pisum arvense), bell beans (Vicia faba), mustard (Brassica juncea cv. Kodiak), and Daikon radish (Raphanus sativus var. longipinnatus), for their effect on soil quality and ability to supplement fertilizer requirement when included in a vegetable crop rotation in a high tunnel system. After incorporation, the cover crops were followed by a succession of vegetable crops, including tomato (cv. ‘Plum Dandy’) and broccoli (‘Bay Meadows’), which were fertilized at a 0.5x rate (50 lbs N per acre) to determine the ability of the cover crop treatments to supplement fertilizer inputs. The pac choi crop that was planned for spring was eliminated from the rotation plan due to slow growth of the cover crops over winter and the need to allow more time for cover crop growth. This extended the cover crop season from 90 days to 145 days and demonstrated that there would be insufficient cover crop biomass during the planned 90-day window from mid-November to mid-February.

Cover crops were seeded in a completely randomized plot design in the experimental high tunnel on Nov. 16, 2013 and incorporated on April 10, 2014 with measurements taken on Mar. 28 and post-incorporation soil measurements taken on April 26. Austrian winter peas yielded significantly greater biomass (1,595 lbs. dry weight/acre) and greater biomass nitrogen content (60 lbs. N/acre) than the other cover crop treatments. This led to a significantly lower soil C/N ratio 30 days after incorporation compared to other cover crop treatments, with the winter pea soil C/N dropping from 10.5 before incorporation to 9.6 30 days after incorporation.

Yield and performance of vegetable crops were measured to determine the effects of the cover crop treatments. Tomatoes (cv. ‘Plum Dandy’) were transplanted into the high tunnel in plastic-mulch beds on May 6, 2014. Tomato leaf chlorophyll was measured on a weekly basis during growth and measurements were highest in winter pea plots, showing an increase in nitrogen uptake going towards leaf chlorophyll development. Tomatoes were harvested from June 26 to July 22, with no significant difference in yield between cover crop treatments. The winter pea treatment did yield numerically less than all other treatments, but we believe this is due to a delay in fruiting caused by increased vegetative growth indicated by greater whole plant dry biomass measurements taken from tomato plants grown in the winter pea plots.

Broccoli early-season leaf chlorophyll (45 days after planting) was also increased by the winter pea treatment, although mean chlorophyll measurements taken over the season showed no significance. Broccoli yield in average head weight was numerically larger in the winter pea treatment (25% greater than the control) and broccoli plant biomass was significantly greater in the winter pea plots (39% greater than the control). The data indicate that for a vegetable crop with a high N demand, like broccoli, a leguminous winter cover crop can improve yield despite reduced N fertilizer application.

Research results were presented to scientists and students at the Southern Region American Society for Horticultural Science meeting in Atlanta, GA in January 2015. The oral presentation given, titled “Effect of Winter Cover Crops on Growth and Performance of Successional Vegetable Crops” won second place in the graduate student paper competition.

The second research season is currently underway with data collected on cover crop performance and the soil currently being prepared for tomato planting. Tomato and broccoli research crops will be grown with data collected as in the year before. Data will be compiled and analyzed to compare the two years of results. Results will be presented at the American Society for Horticultural Science meeting in 2016.

Impacts and Contributions/Outcomes

This research will demonstrate role that winter cover crops can play in improving the sustainability of intensive high tunnel vegetable production. Cover crop species will be recommended based upon their performance in a high tunnel environment, being evaluated for biomass performance, nitrogen fixation, organic matter contribution, and soil quality improvement. The potential benefits for vegetable production will be investigated, including increased yield with less fertilizer inputs and improved soil quality. Results of the study will give high tunnel vegetable growers in the Southern Region biological management tools for sustainable production. Research results from year one have been shared with horticultural scientists and students at the Southern Region ASHS meeting in January 2015 and final project results will be shared at the national ASHS meeting in 2016.

Collaborators: