Combining Alternative Cover Crop Strips, Living Mulches and Strip Tillage for Effective Weed and Nutrient Management in Organic Sweet Corn Production

View the project final report

• 2012 annual report

Commodities

• Vegetables: sweet corn

Practices

• Crop Production: conservation tillage
• Education and Training: display, extension, farmer to farmer, on-farm/ranch research
• Energy: energy use
• Farm Business Management: budgets/cost and returns
• Pest Management: competition, mulches - living, weed ecology
• Production Systems: agroecosystems, organic agriculture
• Soil Management: green manures, nutrient mineralization

Despite the benefits of reduced tillage for fuel savings and soil health, adoption by organic farmers has been limited due in part to the challenges created for weed and nitrogen management. The objective of our proposed research was to improve weed suppression and nutrient management in organic vegetable production by using a novel approach of alternating cover crop strips in zone tillage systems.  

In the first year of the study we tested various cover crop spatial arrangements in combination with strip-tillage. N-fixing hairy vetch (Vicia villosa Roth) was planted in a strip directly in-line with future sweet corn rows (IR) to supply N directly to the crop. This was compared to the standard practice of planting vetch across the whole plot.  Cereal rye (Secale cereale L.) was planted between crop rows and mowed and left on the soil surface to provide a mulch for weed suppression.  Additionally, white clover (Trifolium repens L.) was frost-seeded in the between-row area to act as a living mulch for additional weed suppression and increased N. We found that while white clover emergence in the spring was high, cereal rye suppression of the white clover living mulch resulted in little white clover survival into the summer.  In the preliminary trial, we did not see any significant differences due to hairy vetch arrangement, most likely due to poor vetch biomass.

In 2012 and 2013, we excluded the white clover living mulch to further examine how cereal rye and hairy vetch spatial arrangement impacts cover crop growth, as well as soil N, weeds, and sweet corn yields.  Treatments in the second year consisted of tillage (conventional vs. zone till), cover crop spatial arrangement (segregated vs. mixed), and weed management (high vs. low).  In both years, rye biomass was lower in the segregated spatial arrangement, but there was no significant difference in vetch biomass based on cover crop spatial arrangement. In 2012, total rye and vetch biomass was high, and when used as a mulch in the between-row of zone tillage, the rye and vetch mulch effectively suppressed weed growth.  This resulted in greater sweet corn yields within zone tillage under low weed management.  Under high weed management, in 2012 there was no significant difference in yields based on cover crop spatial arrangement or tillage. In 2013, we had lower cover crop biomass compared to 2012.  Winter annual weeds established within the cover crop and were not terminated when mowed, resulting in greater weed biomass within the between-row of zone tillage. In 2013, zone tillage resulted in lower sweet corn yields in zone tillage under high weed management. In both 2012 and 2013 we saw a greater proportion of early season inorganic N availability within the crop row compared to between-row when rye and vetch were segregated strips. Strip intercropping of rye and vetch showed promise for targeting N availability to the crop, and future work will examine whether this resulted in increased N uptake by the crop.

Introduction:

Reduced tillage systems can provide a number of agronomic benefits including improved soil health, decreased fuel and labor costs, and soil water conservation.  However, organic farmers rely heavily on tillage for weed control and increased nitrogen availability.  The goal of this project is to evaluate whether these challenges may be alleviated through strip intercropping of a grass and legume cover crop within a zone tillage (ZT) system. 

Zone (or strip) tillage is a form of conservation tillage that isolates soil disturbance to a narrow strip directly in row with crop establishment. This divides the cropping system into two distinct yet adjacent zones: tilled and untilled.  The tillage zone enhances soil aeration and creates a finer seedbed into which the crop will be planted (Licht and Al-Kaisi, 2005).  The untilled zone between-row (BR) maintains some of the benefits of no till, such as improved water infiltration, organic matter retention, and decreased erosion (Johnson and Hoyt, 1999). Zone-tillage enables a greater level of control over organic matter turnover.  Incorporating crop residue in-row (IR) enables faster decomposition and mineralization of organic matter to increase nutrient availability to the crop.  The between-row zone is left undisturbed, and when combined with a preceding cover crop, residue is preserved on the soil surface to provide a number of ecosystem services throughout the growing season, such as suppressing weed germination, reducing soil erosion and conserving soil moisture (Mohler and Teasdale, 1993; Unger and Vigil, 1998).  

Grass and legumes are two functionally diverse classes of cover crops that provide unique ecosystem services to the cropping system. Cereal grass cover crops are capable of providing a large amount of biomass to be used as a mulch for weed suppression, however the carbon rich residues can immobolize N and reduce yields due to N deficiency.  Legume cover crops are capable of providing large quantities of N via N fixation, but provide insufficient biomass for weed control. By segregating legumes and cereal grass cover crops into distinct zones (or strips), their functions can be targeted efficiently to maximize benefits to the crop.

Cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) are commonly used winter cover crops in northern climates, often planted in a uniform mixture.  When arranged as a strip intercrop, hairy vetch is planted directly in line with the future cash crop to concentrate the N-rich residue in close proximity to the crop rooting zone.  Cereal rye is planted between future cash crop rows to reduce the problem of N tie-up as well as potential interference with cash crop establishment. When combined with zone tillage, hairy vetch is incorporated prior to sweet corn planting, thereby reducing the potential for hairy vetch reemergence as a weed during the cropping season. Rye residue planted in the between-row area is mowed and left on the soil surface to reduce weed emergence and growth. We also proposed combining cereal rye and hairy vetch segregated strips with a white clover living mulch to provide N and additional weed suppression during the sweet corn growing season.

The objectives of this project were to evaluate the effect of vetch and rye alternating strips and zone-tillage on:

1. Weed suppression and community composition within the in- and between-row environments.
2. Cover crop contribution of N and soil N-dynamics.
3. Yield and quality of organic sweet corn.
4. Soil quality by utilizing short-term indicators of changes in soil health.