Effects of Cover Crop combinations and Fertilizer Application Timing on Nitrogen Leaching

Effects of Cover Crop combinations and Fertilizer Application Timing on Nitrogen Leaching

Summary

Introduction

            Nitrogen (N) pollution from fertilizer is a serious concern in Illinois and the North Central Region as well as the rest of the United States. Studies have shown that agriculture fields dominated by tile drained row crop management can cause increased nitrate loss via tile water (Baker, 1975) (Gast, 1978)(Jaynes, 2001)(Dinnes, 2002)(Smiciklas, 2008).   Nitrate loading has impaired drinking water supplies locally in Illinois, making it more expensive to treat and provide safe drinking water to the public.  On a national scale, N loading in the Mississippi River has led to the development of a hypoxic zone (dead zone) in the Gulf of Mexico. Little progress has been made to reduce N loading into the Mississippi River and to the Gulf of Mexico.  One study found that over a ten year period (1998-2008) attempts to reduce N flux into the Mississippi river have not significantly reduced N concentrations (Sprague, 2011).  In Illinois, best management practices (BMPs) such as grassed water-ways, stream buffers, and strip-till farming have been introduced to reduce nitrate loading in surface runoff.   However, these BMPs were found to be ineffective at reducing nitrate concentrations in surface water (Lemke, 2011).  The authors of this study concluded that tile drainage provided a pathway nitrate to bypass surface BMPs and flow directly to waterways.  Nitrate leaching to tile water is a non-point source problem.  Fall applied N (common in Central Illinois) has been shown to leach below the root zone of corn (Hubbard, 1991), where it becomes susceptible to leaching into tile water.  Planting of cover crops offers a non-point source solution, to this non-point source problem.  Cover crop roots can intercept fall applied N that otherwise would percolate below the root zone of corn (Dean, 2009). In the Northeast forage radish has been shown to reduce nitrate leaching deep in the soil profile.  In theory, cover crop mixtures including forage radish should reduce the amount of nitrate in tile water and escape into the environment.

            This project is an attempt to evaluate the impact of cover crops and N fertilizer timing on N loss from agriculture fields in Central Illinois.  To do this a split plot design was created with multiple cover crop treatments receiving both spring and fall fertilizer. Treatments also included spring control (no cover crop), fall control (no cover crop) and zero control (no fertilizer and no cover crop) plots (Figure 1). 

Materials and Methods

The treatment plots was be located at the Illinois State University Farm Lexington, Illinois.  The dominant soil within the experimental field is the Drummer silty clay loam soil series.  The Drummer series is poorly drained and requires tile drainage, and is typical of soil in Central Illinois and the North Central Region. With the help of the Natural Resources Conservation Service; soil samples were taken from each plot to a depth of 80 inches.  These samples have been analyzed by the graduate student in the Illinois State University (ISU) Research Laboratories in Normal, IL and at United Soils, Inc. soil and plant testing facility located in Fairbury, Il.  Inorganic N analysis was determined by selective membrane diffusion (TL-2800 Ammonia Analyzer, Timberline Instruments) and plant tissue analysis was done by dry combustion (Rapid N analyzer, Elementar Americas, Mt. Laurel, NJ).

Cover crops were planted into standing soybeans on September 20^th, 2012 (Table 1) by a PTO driven broadcast seeder.  Cover crops failed to establish in the fall of 2012 and no substantial cover crop biomass accumulated in the spring of 2013.  It is possible that by allowing soybeans to senesce and leaves to drop before planting cover crops seed was prevented from creating good seed to soil contact and resulted in lack of establishment.  It should also be noted that weather plays a large role in the successful establishment of broadcasted cover crop seed.   It is important that cover crop seeding is followed by significant rainfall and warm weather; otherwise seeds will remain dominant or rot and fall establishment is negatively impacted.  A new broadcast cover crop planter was created to plant cover crops in the fall of 2013 (Figure 2). By dropping cover crop seed between corn rows, in controlled bands better establishment in the second cover crop growing season will hopefully occur. Treatments that called for fall N received 200 kg N/ha as anhydrous ammonia on November 19^th, 2012. Spring applied N was side-dressed into V4 corn on June 20^th, 2013.  Both the fall and the spring N applications included nitrification inhibitor.

Results and Discussion

In the spring of 2013, soil nitrate was significantly greater (P<0.05) at all depths, in plots that received fall applied N when compared to spring applied N and zero control treatments (Figure 3).  Though it should be noted that at this point no spring fertilizer had been applied, as a result soil nitrate in spring application and zero control plots were not significantly different.  No significant differences were detected in soil ammonium. However, there was a biological trend for fall applied N plots to have more soil ammonium at the 5-20cm depth (P = 0.12).  As a result of greater soil nitrate and ammonia, fall N application plots also significantly increased total soil inorganic N at the 0-5, 5-20, and 20-50cm depths by 8.4, 21.6 and 7.5 kg N/ha respectively.   Grain was hand harvested to measure yield and corrected to 15.5% moisture content.  Grain yield for both spring and fall N application plots did not differ but both resulted in significantly greater (P<0.05) yield then the zero control plots (Figure 5).

Fall N application resulted in greater soil inorganic N compared to both the spring application and zero control treatments.  Increased soil inorganic N at the upper depths (0-5 and 5-20cm) in fall application plots compared to other treatments was likely caused by anhydrous ammonia application. These depths correspond directly with the injection region of knifed anhydrous ammonia. Increased soil nitrate at lower depths (20-50 and 50-80cm) in fall application plots relative to spring application and zero control treatments was likely caused by leaching of nitrified anhydrous ammonia applied in the fall. 

Despite the fact that the fall application plots had greater spring inorganic N before corn was planted grain yield of the spring applied treatments were no different from that of the fall applied treatments.  Several weeks passed between the soil sampling date and the point at which corn began N uptake.  During this time additional inorganic N in fall application plots was susceptible to loss via nitrate leaching and denitrification.   Therefore, it is likely that a portion of the additional inorganic N from fall applied N was not available to the corn crop once it began to take up N from the soil.  In contrast, N side-dressed at the V4 corn growth stage was less susceptible to loss relative to fall applied N because it was only applied after corn N uptake had begun.

Preliminary Conclusions

The preliminary data indicate that, from an environmental perspective, spring N application is favorable to fall applied N because it results in less fertilizer loss to the environment and does not reduce corn grain yield.  However, this may not be true from an economic perspective because the risks associated with spring applied N might outweigh environmental benefits to many Central Illinois farmers.  To better understand the benefits to farmers, additional treatments that include different N rates, N application timing, and cover crops have been added to this project.  This will strengthen the project’s ability to help provide advice to Central Illinois famers about how to improve N fertilizer management.  Data from these additional treatments will be included in the final project report.

• Figures and Graphs for Project

Objectives/Performance Targets

Objectives and Performance Targets

There are 3 objectives of this project:

1)      Evaluate the environmental benefit of cover cropping by quantifying the ability of each treatment to reduce nitrate leaching below corn root depth.

2)      Cost analysis of the benefit of using cover crop combination to Central Illinois farmers.

3)      Compare the benefits of cover crop treatments following fall fertilizer and spring fertilizer applications.

The project thus far has not been able to address these objectives due to the lack of cover crop establishment in the first year. However, with improved planting equipment there is potential for an improved cover crop establishment and spring biomass accumulation in the projects second year.   However, an unstated objective of this project was to compare fall and spring N fertilizer applications without cover crops. This is important, because in Central Illinois the many farmers continue to apply nitrogen in the fall.  After two years of data is collected we will be able to complete a cost analysis comparing spring and fall applied N and use that data to help provide N management advice to Central Illinois farmers.

Accomplishments/Milestones

Accomplishments/Milestones

This project has succeeded in creating an advisory group that includes farmers, members from the agriculture industry, government and non-profit organizations to give advice and help promote cover crop research in Central Illinois. Farm members include Jeff Bender a Central Illinois farmer, Steve Groff a cover crop expert and Indiana farmer, Russell Derango Illinois State University Farm Manager.  Industry contributors include ProHarvest Seed, United Soils, Inc. and members of the Illinois Council of Best Management Practices and the U.S.D.A Natural Resources Conservation Service.  These individuals and groups have come together to give advice and help promote the newly created Illinois State University Cover Crop Research Program founded by Dr. Shalamar Armstrong. 

Impacts and Contributions/Outcomes

Impacts and Contributions/Outcomes

Once the project is complete findings from this research will be disseminated throughout the scientific community via publications in refereed journals and professional presentations at an appropriate international annual meeting.  Data from this study will be used by Illinois Extension, NRCS, and SWCS for outreach about cover crop cost-share programs. The data will also be presented to trade journals such as Prairie Farmer, Successful Farmer and Corn and Soybean Digest.  Research findings will be published on websites of sustainable agriculture research groups such as Sustainable Agriculture Research and Education, and Midwest Cover Crops Council.

In addition, a field day at the ISU Farm will be held offering morning seminars in the conference center facilitated by National Resource Conservation Service and Soil Water and Conservation District professionals.  Afternoon field tours will allow farmer and extension educators to see cover crop stands in the field and scientific posters that illustrate the analysis of each cover crop planted. 

Impacts that have already been achieved

              Data from this project and other projects at the Illinois State University Cover Crop Research Program have been used to advise farmers about cover crop management and performance at multiple growers meetings and presentations in Central Illinois.  Additionally, innovative cover crop planting techniques have been demonstrated to famers and used at cover crop training days as examples of how cover crops can be planted into standing cash crops.

Collaborators: