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

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

Summary

This project is designed to examine effects of organic weed management on crop productivity and soil and water quality variables. 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. We are documenting the weed seed bank in the various systems and monitoring weed seed emergence.

Objectives/Performance Targets

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).
Specific:
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 CEFS.

Accomplishments/Milestones

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.
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 that will hopefully make for a successful sampling this fall, winter and spring. They are in the process of purchasing piezometers to sample the perched water table on all plots for nitrogen and phosphorus analysis.
During winter 2009 – 2010 Dr. Raczkowski and his team at NC A &T installed all pore water samplers to sample drainage. We (Melissa, Kenny, Marsha and I) used this time period to learn and become familiar with this type of technology. We learned that it is not easy to sample pore water drainage in coarse textured soils. However, I believe that it is doable but we need a very wet winter period.
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 also 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 – depending on soil conditions (hopefully not dry and hard):
• Install pore water samplers that were removed in tillage plots 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.

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 provides a summary of the mean difference in weed species densities among the treatments.

See Table 1 attachment

The stale seed bed treatment has so far proven the most effective treatment at controlling weed seed banks. This treatment had declining seedbanks for most weed species from 2009 to 2010. The hay 3/crop 3 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 seedbank 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.

• Table 1. Mean difference of weed seedbank densities by species as influenced by tillage system, 2009 to 2010

Impacts and Contributions/Outcomes

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 -1 of rye dry matter per acre.
• To assure the aforementioned level of biomass early planting of the rye cover crop is suggested. Chances of getting over 8,000 kg ha -1 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.

Collaborators: