Evaluating Scale-appropriate Technology for Organic No-till Vegetable Production

View the project final report

Commodities

Practices

• Crop Production: no-till
• Production Systems: organic agriculture
• Soil Management: soil quality/health

Because the majority of vegetable farms in North Carolina are less than 5 acres, with many not relying on herbicides for weed control, it would be useful to understand how organic no-till vegetable production systems perform based on a variety of scale-appropriate equipment, and to define the spatial scale at which each system is profitable. During the 2020 growing season we evaluated the performance (cover crop termination success, weed pressure, and crop yield) of three small-scale, organic no-till vegetable production systems, using equipment appropriate for smaller scales (walk-behind tractor and associated equipment, and two manual methods), alongside their larger-scale counterparts (tractor-based) to determine the spatial thresholds that make no-till production feasible for small-scale vegetable growers. The cover crop was cereal rye (Secale cereale var. ‘Wrens Abruzzi’) and the cash crop was butternut squash (Cucurbita moschata var. ‘Atlas F1’). Cover crop termination equipment included a roller-crimper and a flail mower, drawn or powered by a tractor or walk-behind tractor, as well as a manual crimper and landscape fabric. A tilled and bedded treatment (with plastic mulch) was implemented as a reference using either a tractor or walk-behind tractor. Additionally, rye was crimped at two growth stages (late-flower and late-milk) to test termination success across crimping equipment (tractor, walk-behind tractor and manual), which vary substantially in weight per linear foot. All treatments were replicated four times at CFSA’s Elma C. Lomax Research and Education Farm (Concord, NC) and medium/small-scale no-till treatments (walk-behind tractor and manual) were implemented at Red Scout Farm (Black Mountain, NC; unreplicated). One additional farm, Living Web Farm (Mills River, NC) volunteered to replicate treatments but could not establish sufficient cover crop biomass for weed suppression. Treatments were discontinued at this site.

Cover crop biomass was adequate to suppress most early season weed species across treatments, but was not adequate to suppress ryegrass (Lolium species), brome (Bromus species) and crabgrass (Digitaria species)  at Lomax Farm. Cover crop termination was successful (>90%) across all treatments, suggesting that larger-scale (heavier) equipment is not necessary for successful termination via crimping. Weed pressure was lowest in the landscape fabric treatment, and much higher in other treatments (mowed treatments were numerically but not statistically the highest). Butternut squash yield, collected only at Red Scout Farm due to crop failure at Lomax Farm, averaged 27,280 lbs/acre across treatments. Differences in yield were not tested at Red Scout Farm because treatments were not replicated, but average yield across treatments was higher than breakeven yields and therefore profitable. 

Production costs, standardized for one acre of production, were driven by the combination of labor, equipment and materials costs, which varied substantially among treatments. Because weeding was performed manually in all treatments, production costs were highest overall in the mowed treatments, where weed pressure was high. In general, however, one-acre production costs were driven by equipment (tractor, walk-behind tractor or manual), with tractor treatments highest, followed by walk-behind tractor treatments, and manual treatments. One-acre cost of production at Red Scout Farm was somewhat higher than at Lomax Farm due to more time spent weeding, but followed the same pattern. 

Analysis of spatial thresholds indicated that, at larger acreages (>3 acres), cover crop management method was more important for production costs than the equipment used, with mowed treatments being the most expensive, tilled treatments the least expensive, and crimped and landscape fabric treatments intermediate. At smaller acreages (<3 acres), equipment type was more important than cover crop management method, with tractor treatments the most expensive, followed by walk-behind tractor, followed by manual. The transition from equipment determining total production cost to method determining cost occured between 0.8 and 2.8 acres, depending on the method. Analysis of per-acre production cost, which accounted for economies of scale in tractor and walk-behind tractor treatments, indicated that per-acre costs decreased with increasing acreage in tractor and walk-behind tractor treatments, but not manual treatments. Additionally, per-acre production costs were highest in mowed treatments (above 1 acre), and lowest in tilled treatments (above 2 - 2.5 acres), and intermediate in crimped treatments. Per-acre production costs were lowest in the manual treatments among no-till methods up to at least 5 acres. Finally, maximum farmable acreage as a function of available labor hours was lowest in mowed treatments, highest in tilled treatments, intermediate in crimped and landscape fabric treatments. 

Overall, among no-till methods compared, crimping was preferable to mowing, as weed pressure and associated labor cost were high in mowed treatments. It is likely that if no-till-specific cultivation equipment (high-residue cultivator) were used with a tractor and walk-behind tractor, total production costs would decrease dramatically, making these methods more competitive with manual methods at smaller acreages (<5 acres). Finally, the fact that tilled treatments out-performed no-till treatments by most metrics - owing to the efficiency with which plastic mulch can be applied for season-long weed suppression - highlights the need for improvements to organic no-till production systems. We recommend that soil testing should be routine practice before sowing cover crops in order to identify potential soil fertility issues that will impact cover crop biomass. We advocate that, in addition to adopting existing technology for high-residue cultivation, a new technology is developed to mechanize the application of landscape fabric or similar material, which could bring per-acre production costs for landscape fabric use down substantially to costs that are comparable to tilled with plastic mulch. We believe that without this technology, organic no-till vegetable production will always be limited by weed pressure and the labor required to address it, and will never be cost-competitive with tillage-based systems. 

This research project tested the performance of three organic no-till cropping systems alongside a conventional-tilled one at two on-farm locations, using equipment appropriate for three spatial scales: tractor, walk-behind tractor, and manual equipment for large, medium and small scales, respectively.

Our objectives were to quantify:

1) cover crop termination success,

2) weed pressure (dry lbs/acre and/or time spent weeding),

3) butternut squash yield,

4) total production costs ($/acre spent),

5) profitability (net $/acre earned), and

6) spatial thresholds of production costs, profitability, and farmable acreage across equipment types and methods.