- Vegetables: broccoli, cabbages, tomatoes
- Crop Production: cover crops
This study investigated winter cover crops to improve soil quality and reduce nitrogen fertilizer inputs in organic high tunnel production systems. Cover crops included Austrian winter peas, bell beans, mustard, and Daikon radish, which were followed by summer tomatoes and fall broccoli. Winter peas contributed a greater amount of biomass nitrogen than all other treatments, which led to higher tomato leaf chlorophyll and a 48% increase in mean tomato yield compared to the control. Broccoli early-season leaf chlorophyll was also increased by the winter pea treatment and plant biomass was significantly increased.
Although cover crops have been well studied for field production systems, their application in in high tunnel vegetable production has had limited study. Available information on the subject was limited to extension bulletins, newsletters, conference presentations, and production manuals (Baldwin, 2010; Blomgren and Frisch, 2007; Evans et al., 2011; Melendez and Rabin, 2012; Rivard, 2013). Despite negative and dismissive reports on high tunnel cover crops from extension agents and farmers in the Northeast (Blomgren and Frisch, 2007), preliminary studies in New Jersey and Mississippi have shown opportunity for winter cover crops to provide benefits to high tunnel vegetable production, including the uptake of leachable excess nutrients, weed suppression, and spring nitrogen release (Evans et al., 2011; Melendez and Rabin, 2012).
Arguments have been made to dismiss the applicability of cover crops in high tunnel systems (Blomgren and Frisch, 2007; Melendez and Rabin, 2012). The risk of soil erosion is minimized in a high tunnel, so cover crops are not specifically required to prevent soil loss. Cover crops grown throughout the winter in a warm high tunnel could provide habitat for overwintering pests. Season extension in a high tunnel minimizes the windows of time between crops, which eliminates niches that cover crops usually fill. And lastly, the capital investment in a high tunnel makes growers reluctant to use valuable high tunnel ground to grow a crop that does not provide immediate economic return.
Despite these issues, the reported and potential benefits of high tunnel cover crops justifies further research on the subject. To begin with, the timing of cover cropping in a high tunnel can minimize the negative aspects of the practice. Local growers have said that the time-period between mid-November and mid-February was the least productive season for high tunnel vegetable growers in the South due to cold temperatures and lack of light (Dr. C. Rom, personal communication). During this period, tunnels are vacant or idle. By selecting this time period to grow a winter cover crop that can tolerate such environmental conditions, the lost revenue stream for the grower is minimized. The modified environment of a high tunnel, with increased soil and air temperatures (Wien, 2009), could also speed the growth of winter cover crops during the stated 90-day period in mid-winter, producing more green biomass than would be produced during the same time period in the field. It is thought that if a green manure crop were able to improve soil quality and decrease the requirement for purchased organic matter and fertilizer inputs, the cost savings for the grower could justify the additional management input.
Intensive vegetable production in a high tunnel requires inputs of organic materials to maintain soil organic matter, preserve soil quality, and ensure long-term productivity (Coleman, 1999; Lamont et al., 2003; Milner et al., 2009). Green manure cover crops have been shown to increase soil organic matter and nutrient cycling (Pieters, 1927; Powlson et al., 1987), and could replace purchased organic inputs in high tunnel production. Winter legumes have shown the potential to contribute significant amounts of nitrogen to subsequent vegetable crops in a field setting (Burket et al., 1997; Gaskell and Smith, 2007), which would reduce purchased fertilizer costs for high tunnel growers if similar rates of nitrogen contribution occurred in the high tunnel system. The deterioration of soil quality and the formation of hard pans due to frequent tillage is a documented problem in high tunnel production, which could be ameliorated by the ability of green manure cover crops to improve soil structure and aggregate formation (Hermawan and Bomke, 1997; Roberson et al., 1991; Tisdall and Oades, 1982) and improve the rooting depth of vegetable crops due to the “bio-drilling” effect of certain cover crops (Weil and Kremen, 2007). The ability of legume and brassica winter green manures to suppress soil-borne pathogens in vegetable crops (Monfort et al., 2007; Zhou and Everts, 2007) is another important benefit that winter cover crops could provide to high tunnel systems.
The ability of winter cover crops to improve the yield and performance of vegetable crops in field production systems have been well-documented in the scientific literature. It is the hypothesis of this study that short-season winter cover crops grown in a high tunnel, then mowed and incorporated, will improve the growth and yield of subsequent vegetable crops.
Project objectives:div style="margin-left:1em;">
- To evaluate four winter cover crop species for their ability to improve soil quality and supplement fertilizer requirements when grown as a green manure before a succession vegetable crops in a high tunnel system.
- To evaluate the effect of winter cover crops on vegetable crop growth and yield within a high tunnel production system. Vegetable crops will include tomato and broccoli.