Reduced tillage in organic systems: a soil and water quality imperative

Final Report for LS08-210

Project Type: Research and Education
Funds awarded in 2008: $190,000.00
Projected End Date: 12/31/2011
Region: Southern
State: North Carolina
Principal Investigator:
Dr. J. Paul Mueller
North Carolina State University
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Project Information


To date we have found that total C and N were increased by 10-20% in systems using conservation tillage versus conventional tillage. Microbial respiration, microbial biomass N and net N mineralization were much lower in the conventional system than in other systems. Increased total N and microbial biomass N imply enhanced N holding potential in the systems, and improved net N mineralization means enhanced ability of the systems to meet plant N needs. All these findings suggest that compared to the conventional system all other systems show greater potential in improving water quality and sequestering carbon. We are documenting the weed seed bank in the various systems and monitoring weed seed emergence. Although the organic system had concentration of nitrate slightly exceeding 10ppm, drainage was lowest in this system. Soil water content differed between systems at soil depths below 60cm.

Project Objectives:

General: To provide the preliminary data necessary for the implementation of effective weed control
strategies based on conservation tillage practices and light, surface cultivation suitable for organic grain
production systems in the southeastern USA. Based on initial experimental data, the most promising
practices will be integrated into the existing long-term farming systems experiment located at The Center
for Environmental Farming Systems (CEFS).

1. To compare alternative organic weed management systems: one with major emphasis on cultivation and tillage and another with major emphasis on conservation tillage.

2. To monitor the impacts of the weed management strategies in objective 1 on water quality (NO3, PO4,
DOC), soil physical properties, soil C and N dynamics, microbial activities associated with the organic
systems under comparison and with non-organic systems which are part of the existing experimental
design at CEFS.

3. Use The Organic Farm Panel comprised of farmers, county agents, non-profit partners and researchers
and meets twice annually to set the agenda for organic research and extension activities conducted by


This project was designed to examine effects of organic weed management on crop productivity and soil and water quality variables.Two fundamentally different approaches are being attempted by North Carolina farmers: a conventional tillage, cultivation intensive approach, and a reduced tillage system utilizing weed suppressive cover crops and mulches. Conventional tillage is raising serious concerns over soil health, erosion and water quality. However, reduced organic tillage systems are unproven and the growers engaged in these practices are concerned about their ability to control weeds over the long-term. The use of strip-tillage and the arrival of new equipment that make light cultivation tillage a reality will energize this approach.

When surveyed and in focus groups organic farmers cite weed pests as their most serious and intractable problem. Current weed management strategies in organic production systems are centered on cultivation. This has been shown to be effective in many cases (Smith, et al. 2000 ), but loss of soil carbon, the importance of particulate organic matter fraction and the potential for soil erosion and water quality issues must be addressed if organic grain systems are to be sustainable(Marriot and Wander, 2006). Quality data from infiltrating water collected below the root zone of organic systems is of particular interest do to the paucity of data in the literature and because of the ability to directly compare these data with data collected from other systems located on the Farming Systems Research Unit at CEFS. Conservation tillage approaches that rely on allelopathic smother crops, and strategic, light, surface cultivation has the potential to drastically reduce reliance on tillage for weed control (NRCS, 2002). These practices, combined with recent advance in conservation tillage implements and high residue cultivation tools, are redefining organic weed management.


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  • Shuijin Hu
  • Charles Raczkowski
  • Chris Reberg-Horton


Materials and methods:

Weed management in organic grain production is difficult with limited options available. Crop rotational effects and cover crop management are important tools for effective weed management. In addition, the impact of these systems of management on water quality compared with conventional systems is helpful in verifying best practices for organic grain production.

Several rotational strategies for organic grain production will be studied:

1.) Perennial/Annual Rotation: 3 years of hay followed by 3 years of crops. This system will use cultivation and tillage for weed control.

The 6-yr rotation is as follows: 3-yrs of hay (fescue, orchard-grass and red clover mix) followed by wheat/soybean. A mixture of crimson clover, hairy vetch and rye will be seeded over the top of the soybeans prior to harvest and followed by sunflower, a fall cover of crimson clover and vetch spring disked for corn.

2.) Fallow/Annual Rotation: 1-yr fallow-stale seed bed/summer cover crop followed by 2-yrs crop. This system will use cultivation and tillage for weed control.

The 6-yr rotation is as follows: early spring disking of fall planted rye followed by 1 or 2 cycles of stale seedbed. A summer cover of sudangrass, which can be mowed mid summer if needed to reduce biomass prior to fall rye. Field will be disked for rye allowing the incorporation of compost or manure followed the next year by soybean and a rye cover crop. A mixture of legumes will be seeded over the top of the soybeans prior to harvest. Spring disking for corn will allow another opportunity for the incorporation of compost or manure if desired.

3.) Annuals Only Rotation: 3-yrs crops. This system will use cultivation and tillage for weed control.

The 6-yr rotation is as follows: early spring disking of fall planted rye followed by 1 or 2 cycles of stale seedbed followed by soybean. A mixture of legumes will be seeded over the top of the soybeans prior to harvest and followed by sunflower. A cover crop mixture of crimson clover and vetch will be disked in the spring for corn.

4.) Rotational Tillage: 1-yr fallow-stale seed bed-summer cover crop followed by 2-yrs crop. This system will use conservation tillage-smother crops and rolling, no-till planting for weed control. No-till planting will occur in this system whenever there is a large amount of cover crop to use as mulch and when perennial weeds will allow. Anywhere between 1 and 3 crops will be planted no-till in the 3-yr sequence.

Water Quality: NO3, PO4, DOC- Drainage samples for NO3-N, NH4-N, PO4 and DOC analysis.
Sustainable agricultural systems need nutritional ecosystem balance with adequate plant nutrient availability and minimum to no losses in runoff and drainage waters. Studies in the southeastern coastal plain region need to quantify drainage chemical losses (e.g., nutrient losses below the root zone) in conventional farming systems and in systems that utilize alternative practices that foster system sustainability. Only with these results will we be able to prescribe growers sustainable nutrient management strategies for water quality protection and that ensure the sustainability of agricultural activities and protection of aquatic systems. To generate the desired chemical drainage information and to be able to evaluate system performance, comparisons will be made with other systems located on the Farming Systems Research Unit at CEFS.

The experimental site has nearly flat terrain and a sandy loam texture in the upper soil horizon. We have observed negligible to minimal runoff during rainfall events suggesting that runoff chemical losses during the study will be minimal. All soil profile layers at the site are coarse textured and thus the soil has a high percolation rate conducive to the leaching of chemicals below the root zone.
Chemical leaching (NO3-N, NH4-N, PO4 and DOC) will be measured using drain-gauges (DG). A DG measures water flux (drainage) and it also has a surface port through which samples are drawn to measure nutrient concentration. It sits below the root zone, collecting down-welling water into a duct and wick system. The collected water volume is recorded by a surface data logger. The drain-gauge data is used with the nutrient concentration data to determine the total amount of chemicals leached below the root zone on a per land area basis.
Three DG’s will be installed in each of 18 experimental plots (6 systems x 3 replications) at the Farming Systems Research Unit. Systems include the sucessional system, the BMP conventional tillage system, the BMP no tillage system, the organic cultivated system, the organic conservation tillage system, and the integrated crop/animal pasture system. We estimate the collection of biweekly drainage samples for a total of 468 samples (18 units x 26 weeks sampling/year). Water samples will also be drawn from the adjacent ditches at CEFS for comparison with samples collected in the DGs
Samples will be kept chilled at 4 ?C in a cooler. Then, water samples are stored at 4 ?C in a lab refrigerator. Three water quality indicators (NO3, PO4) are analyzed by automated flow injection (Lachat method) (Mulvaney, 1996). Dissolved organic carbon is measured on a TOC analyzer within one week following the sampling (Nelson and Sommers, 1996).

Research results and discussion:

Soil Measurements:
Soil sampling was completed in the fall of 2009. Microbial biomass carbon (MBC), Microbial biomass
nitrogen (MBN), microbial respiration, net nitrogen mineralization, and extractable nitrogen were analyzed
for all systems. After 10 years of management, compared to the conventional system, total C and N were
increased by 10-20% in all other systems, except woodlot that decreased by nearly 10%. Microbial
biomass C did not differ significantly among various systems, but microbial respiration, microbial biomass N and net N mineralization were much lower in the conventional system than in other systems. Increased
total N and microbial biomass N imply enhanced N holding potential in the systems, and improved net N
mineralization means enhanced ability of the systems to meet plant N needs. All these findings suggest
that compared to the conventional system all other systems show greater potential in improving water
quality. In 2010-2011, we continued to analyze soil samples collected in 2010. Total C and N, microbial
biomass C and N, microbial community structure as well as microbial activities (respiration and N
mineralization) were assessed. These results are being summarized in a manuscript draft. In addition, we
assessed how different microbial communities and their activities resulting from different management
practices affect the growth of two fungal pathogens (Pythium ultimum and Rhizoctonia solani) and their
disease activities.
In year 2011-2012, density fractionation of soil carbon was performed. Compared to the conventional control, carbon in light fraction (d?1.0 g cm-3) increased by 11-247% in sustainable managed systems, but carbon in both heavy (1.0 g cm -3 < d ? 1.6 g cm-3) and very heavy fractions (d > 1.6 g cm-3) did not show differences among these systems, implying more carbon loss in conventional system. Along with the results of previous years, soils under sustainable managements show enhanced potential to sequestrate carbon and to sustainably supply N for plant need while reduce soil N leaching to water environment.

Measuring Water Quality:
Dr. Raczkowski and his team collected undisturbed soil cores on the 5 sampling points in all original SARE project plots and measured numerous soil physical properties: bulk density, plant available water holding capacity, total water holding capacity, total porosity, pore-size distribution, and hydraulic conductivity. They installed pore water samplers and became acquainted with their use and made pertinent modifications.

During winter 2009 – 2010 Dr. Raczkowski and his team at NC A &amp;T installed all pore water
samplers to sample drainage. During the same period the team used the CEFS hydraulic probe truck and scouted the three replications of the FSRU for the depth to the perched water table. The water table was found to range from 5 to 10 feet deep. Based on this, 15 pyzometers were purchased to install 12 feet deep and sample the water table during the winter months. In this manner, we will ensure having data if the pore water sampling failed. The team also planned to sample soil to the 4 foot depth. The soil samples plus the water table samples will give us the information we are searching for.

The 2010 – 2011 Winter was extremely dry and the team was not able to find the water table or sample pore water drainage. An attempt was made to install a pyzometer under the dry conditions and although successful, it was very difficult. The team purchased (with other non-SARE project monies) 15 access tubes to install, one in each plot, to begin year-round bi-weekly measurements of soil water content with the neutron probe.

Immediate Plans – Beginning in September 2011:

• Install pore water samplers and begin monitoring drainage during wet periods.
• Install remaining pyzometers and begin sampling when water table is present.
• Install neutron access tubes and begin soil water content measurements.
• Collect soil samples.

During January 2012, pore-water samplers, piezometers, and neutron probe access tubes were installed in each experimental plot of five agricultural production systems (BMP conventional tillage and no-tillage, organic production, integrated crop-animal, and plantation forestry). Soil water content has been measured biweekly to the 120 cm depth in depth increments of 15 cm. Drainage samples have been collected from pore-water samples installed at the 45 and 105 cm soil depths. Drainage, drainage nitrate and phosphate concentrations have been measured. Samples were collected from piezometers and water table depth and water nitrate and phosphate concentrations were measured.
Results from water sample collection dates February 23, March 5, March 15, April 4 and April 12, 2012, were analyzed and presented at the CEFS field day on May 3, 2012. In summary, Drainage was highest in the tree system and lowest in the pasture and organic production systems. The concentration of nitrate in the organic production system slightly exceeded 10ppm but drainage was lowest in this system. Soil water content differed between systems at soil depths below 60cm (see figures 1-3).
Additional funding sources have been secured to: (1) install shallow lysimeters (60cm soil depth) to measure drainage volume, (2) collect root samples to measure maximum root depth, effective rooting depth, and root density, (3) measure soil water retention capacity in 15cm increments to the 120cm depth, and (4) collect soil samples in 15cm increments to the 120cm depth to measure inorganic nitrogen and soil phosphorus.

Weed Seed Bank Research:
One of the ways we are tracking the impact of each of these organic systems is by examining weed seed
bank changes over time. Weed seed counts were gathered in the Organic System plots during the 2009 and 2010 growing seasons. Each sample was collected and GPS referenced at CEFS. Samples were elutriated to separate the clay fraction and large soil aggregates. Following the elutriation, samples were screened under microscopes to discern the weed seed density. Weed species were identified in the elutriated samples. Table 1 from 2010 report provides a summary of the mean difference in weed species densities among the treatments.
The stale seed bed treatment has so far proven the most effective treatment at controlling weed seed- banks. This treatment had declining seed-banks for most weed species from 2009 to 2010. The hay crop
treatments had relatively stable numbers showing little change. The reduced till system had a
disturbingly high increase in the number of pigweed. In 2009, this treatment was planted to sorghum-sudan with a no-till drill. Pigweed was able to set seed in these plots before hay mowing. A combination of high seed-bank numbers and poor rye cover crop growth in 2010 made this system the worst performer for weed control in 2010. Our findings are similar to others in the region. More emphasis is being placed on a rotational tillage approach for organic farmers. With this system, some crops are planted without tillage, but tillage is used periodically to disrupt weed cycles.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Two peer reviewed publications are listed below. In addition, a major field day was held on 3 May 2012 with over 300 participants in attendance. Besides visiting the experimental site, several posters were presented summarizing findings.

Smith, A.N., S.C. Reberg-Horton*, G.T. Place, A.D. Meijer, C. Arellano, and J.P. Mueller. 2010. Rolled rye mulch for weed suppression in organic no-tillage soybeans. Weed Science, 59(2):224-231. 2011.

Raczkowski, C. W., Mueller, J. P., Busscher, W. J., Bell. M. C. and M.L. 2012. McGraw. Soil physical properties of agricultural systems in a large-scale study. Soil and Tillage Research, 119 (3): 50-59.

Project Outcomes

Project outcomes:

Research involving soil physical properties and water quality has resulted in article publishes in peer-reviewed journal.

As a result of this grant, soil water and water quality can now be monitored indefinitely on the Farming Systems Research unit at CEFS.

One of the weed management approaches studied has led to two journal articles and an extension bulletin from the university (listed below). Results to date suggest that rye mulches used in a conservation tillage system for organic soybeans are extremely effective and can be superior to current production practices. We generated the following recommendations that appeared in the Organic Grains Newsletter published by NCSU:

This system requires a large amount of cover-crop (rye) biomass. We are recommending at over 8,000 kg/ha of rye dry matter.

To assure the aforementioned level of biomass early planting of the rye cover crop is suggested. Chances of getting over 8,000 kg/ ha DM are greatly improved rye cover-crop is planted in September or early October. Occasionally sufficient biomass may be obtained from November plantings but that is rare.

Assure that enough nitrogen is available to grow the desired level of cover-crop biomass. Fertilizing the
rye and tissue testing for N may be in order. This may sound like overkill, but the roller-kill system
demands we think about the cover crop differently. The rye is not just and erosion preventive cover, rather it represents an entire weed control program; it will save all the costs associated with spring tillage and cultivation.

Delay rolling the rye until it is in the milk or soft dough stage. Rolling too soon will resulted in an
incomplete kill.

Rolling and planting on the same day makes it more likely that dry soil will be encountered at planting.
Rye cover crops are very effective at depleting soil moisture. Some states are recommending that planting occur about 2 weeks after rolling or after enough rain has fallen to recharge soil moisture. So far we have had remarkably good luck with same day planting, with only one stand out of 10 failing to emerge.

Weed control and yields in this system are higher than the standard organic practices being utilized in NC. Organic soybean yields are highly variable because of weed control issues. In years with wet springs, missed passes with a rotary hoe or spring tooth harrow have caused in-row weed problems.

Lodging is worse in the roller system. We have a lot of theories so far, and very little data. Lateral roots
on the soybeans appear to be shallower in the mulched system. Mulched soybeans were taller this year
with pod set higher on the stem. Both observations could be part of the problem. We will be trying some
new ideas on planting this spring to see if we can prevent the lodging.

Almost any type of roller seems able to kill the rye, though this has not been researched here yet. By
waiting until the rye is in milk or soft dough, the rye is well on its way to senescence. Several farmers have tried cultipackers with good success.

Legume mulches for corn are less clear with stand establishment problems continuing to be an issue.
When stands are adequate, yields can be equivalent to current practices.
Organic farmers throughout the Southeast have become increasingly interested in reduced tillage systems.

The Agronomy Society of America had a symposium on reducing tillage in organic systems in the fall of
2010. Chris Reberg-Horton was asked to give a talk on these systems in the Southeast and on the
research associated with this project (abstract listed below). Farmer impacts include three farms that have
used cover crop mulches in the last year to see if the system works on their farm.

In May 2012 a major Field Day was held at CEFS and over 300 participants visited the experimental site where summary posters were presented.

Economic Analysis

Although the publications listed below have examined various economic aspects of this long-term experiment, additional data is necessary for the analysis of the current phase of this this long-term study.

Wossink A, Kuminoff N. 2002, September-October. Organic Agriculture in North-Carolina, N.C. State Economics. Avail from:

Sydorovych O, Raczkowski C, Wossink A, Mueller JP, Creamer N, Hu S, Bell M, Tu C. A technique for assessing environmental impact risks of agricultural systems. Renewable Agriculture and Food Systems. 2009;24(3):234-243.

Sydorovych O, Wossink A. The meaning of agricultural sustainability: Evidence from a conjoint choice survey. Agricultural Systems. 2008;98(1):10-20.

Farmer Adoption

Organic grain farmers have expressed much interest in adopting the roller-kill methods studied in this experiment although we are still refining the methodology because timing and cover crop management have been found to be critical to success.


Areas needing additional study

This experiment is for the long term and it will be necessary to collect several more years of data concerning weed management practices for organic grain production and the impacts of the systems under study on water quality.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.