Deep soil nitrogen: A resource for sustainability in the mid-Atlantic using early cover crops

Deep soil nitrogen: A resource for sustainability in the mid-Atlantic using early cover crops

Summary

In 2016, we continued monitoring the seven ongoing on-farm cover crop experiments. Before cover crop termination in the spring, we took biomass samples to investigate spring cover crop growth, and we took deep (0-210 cm) soil cores within the cover crop plots to investigate the N content throughout the soil profile. Our collaborating farmers planted corn on the cover crop plots in six of the experiments. Furthermore, on four of the experiments, the farmers applied N fertilizer at either two or four different rates in subplots within the cover crop species main plots. In each plot/subplot, we took corn biomass samples and height measurements at the V5 stage, took PSNT soil samples, and measured yield.

In late summer/early fall of 2016, we took 210 cm deep soil cores in straight transects across side-by-side corn and soybean fields on four cooperating farms. We will compare N levels throughout the soil profile for the side-by-side soybean and corn fields in order to further investigate our questions concerning the source of N pools in crop fields.

In addition to monitoring the on-farm cover crop trials, we continued the related research funded by the SARE graduate student grant, “On-farm and isotopic evaluation of deep soil nitrogen capture and cycling by cover crop mixtures.” In May 2016, we took spring cover crop biomass samples from the 172 plots (planted in the fall of 2015). Corn was planted on all 172 plots after the cover crops were chemically terminated. V5 and harvest grain samples were collected from the plots in order to investigate how cover crops capture residual N and recycle it for subsequent corn. Deep soil cores (210 cm) were taken in June and October in select plots at the clayey and sandy sites in order to investigate the rate of N leaching.

Furthermore, in late summer 2016, we set-up a cover crop planting date and termination date experiment at two sites, which is investigating four planting dates and four termination dates for a cover crop species mixture of radish, triticale, and crimson clover. Fall cover crop biomass samples were taken and lysimeters installed to monitor groundwater nutrient levels.

We have discussed our work through numerous presentations and publications, listed in the Impacts and Contributions/Outcomes section below.

Objectives/Performance Targets

250 farmers plant 25,000 acres of early radish/rye covercrops reducing N leaching by 2,000,000 lbs; 100 of them also reduce N application by 50 lbs. on 10,000 acres, saving $0.5 million annually. 20 advisers recommend early cover crops and 2 state agriculture departments include them in their N load reduction programs.

Accomplishments/Milestones

-1000 dairy, 250 grain and 100 vegetable farmers managing 250,000 acres will learn through newsletters, field days, farm newspaper stories and extension meetings about early cover crops to reduce N fertilizer needs and prevent water pollution. 

In 2015-2016 we collaborated directly with eight farmers who used early planted cover crops on approximately 5,000 acres, with some 100 acres in replicated trials, including mixed species cover crops. In addition, a very large national audience of farmers learned about the basic early cover crop-planting nitrogen-capture concepts of our project via columns published in Farm Journal (the leading US farm magazine with 250,000 unique users and 1,000,000 visits per month).

-In the first year, 20 farmers (10 dairy and 10 grain or vegetable each year) will collaborate by permitting us access to designated areas on their farms for us to assess deep N under their fields. 

In late summer of 2014 and 2015, we took deep soil cores to investigate N pools in the 0-210 cm soil profile after growing corn. In 2016, we expanded our investigation of the soil N pool to both corn and soybean fields. We collaborated with farmers to find four side-by-side corn/soybean fields. Between 9/24/16 and 10/29/16, we took transects of deep (0-210 cm) soil cores (10 cores per field), for a total of 4 soybeans fields paired with 4 corn fields. Time and labor restraints limited us to eight fields, because soil cores were taken using hand-driven Veihmeyer probes.

-In each of three years, 10 farmers will collaborate by planting replicated strips with and without cover crop (2 trts) on their farms so we to access the N uptake and/or soil profile N depletion by one selected species of early planted, deep-rooted, non-immobilizing cover crops.

-In each of two years, 5 farmers will collaborate by planting replicated strips with 4 cover crop treatments to evaluate N uptake by 2 species and a multi-species cocktail of early planted, deep-rooted, non-immobilizing cover crops. 

In 2016, we continued to collect samples from seven of the eight cover crop experiments that were set-up in 2015. We collected spring cover crop biomass and deep soil cores. We were particularly focused in 2016 on the impact of cover crops on the following corn crop, as outlined below.

-In each of two years, 2-3 farmers will help us design and conduct spring N response trials superimposed on late summer cover crop treatments. 

In 2016, six of the on-farm cover crop experiments were planted into corn. On four of the experiments, the farmers applied various rates of N fertilizer as a sub-plot treatment within the main-plot treatment (cover crop species). On one farm the fertilizer was applied at two rates (due to size restraints)—1) no fertilizer or 2) 100% of his normal application rate. On the other three farms, the fertilizer was applied at four rates—1) no fertilizer, 2) 50% lower rate than normal, 3) 100%, and 4) 50% higher rate than normal. Within each corn plot (or N rate subplot when applicable), we collected soil PSNT samples and corn V5 plants. Yield was collected on five of the farms, as the sixth farm had total crop failure on the field that contained the cover crop plots.  

-8 of the collaborating farmers host and speak at field days on their farms. 

-200 dairy and 50 grain or vegetable farmers will plant 25,000 acres of early covercrops reducing N leaching by 2,000,000 lb. (avg. 80 lb N/acre reduction)

 -100 of these farmers will also reduce fertilizer N use by 50 lb on 10,000 acres, saving 500,000 lbs N or $1.0 million (cost of N = $0.70 to $9.00/lb; avg. $1.00/lb N, includes some high priced N for organic and vegetable farms).

 -20 crop advisers will make early covercrops part of their recommendations.

 -2 state Departments of Agriculture will include early covercrops in their N load reduction programs.

Impacts and Contributions/Outcomes

In 2015-2016 we collaborated directly with eight farmers who used early planted cover crops on approximately 5,000 acres, with some 100 acres in replicated trials, including mixed species cover crops. In addition, a very large national audience of farmers learned about the basic early cover crop-planting nitrogen-capture concepts of our project via columns published in Farm Journal (the leading US farm magazine with 250,000 unique users and 1,000,000 visits per month). 

Collaborating farms spanned across six counties in the Piedmont regions of Pennsylvania and the Piedmont and Coastal Plan regions of Maryland. In these on-farm experiments, we continued to take the cover crop biomass and the deep soil core samples in the various cover crop treatments. In 2016 we were strongly focused on investigating the impact of cover cropping on corn yields. We have received much inquiry from both our collaborating farmers and others about what effect cover crops have on the following corn crop. Six of our farms planted corn following the cover crops, and on four of those experiments, farmers applied various rates of N fertilizer to subplots within the main cover crop treatment plots. Among cover crop treatments, we saw visual differences in early season corn growth, which seemed to make an impression on our collaborating farmers. The research being performed under the SARE graduate student grant, “On-farm and isotopic evaluation of deep soil nitrogen capture and cycling by cover crop mixtures,” is also following the N taken up by the cover crops. Through the 15-N and bromide tracers, we are able to determine if the N (or Br) taken up by the cover crops is present in the following corn crop. Through the results of the on-farm and N tracer studies, we should be able to better answer farmer raised questions concerning if N taken up by cover crops is cycled to the following corn crop, and how much N fertilization is required following various cover crops.

The deep (0-210 cm) soil cores that we took in 2014 and 2015 in September (following corn senescence) provided evidence that large pools of inorganic N remain in the soil after a corn crop. In 2016 we expanded this research and took soil cores in both corn and soybean fields to test our hypothesis that there are pools of N remaining after a corn crop, which had N fertilizer applied, and also after a soybean crop, which had no N fertilizer applied.

In addition, we set-up two experiments in Aug 2016 investigating differences in cover crop growth and nutrient acquisition for various planting dates and termination dates. Due to perceived advantages, many of our farmers and are moving toward “planting green” (planting corn or soybean into a live cover crop stand). Through this planting and termination study, we hope to provide them with further data to support this practice. In addition, initial results of our N15 tracer study indicate that earlier planting dates allow cover crops to access N from deeper soil layers, which ties in closely to the planting date/termination date experiment.

In 2016, we shared results of this study through the following events and publications:

1. Hirsh, S., R. Weil. Fall 2016. Getting cover crops planted in September, despite late crop harvests. University of Maryland Extension Ag Newsletter. pp. 10-11.

2. Our research on deep N capture was featured in the Annual Report of the University of Maryland Nutrient management Program (page 9), circulated in print to 2,000 famers and ag professionals on line at: https://extension.umd.edu/sites/default/files/_docs/programs/anmp/NMAR_2015.pdf

3. Hirsh, Sarah and Ray Weil. 2015. Deep Soil Nutrients- a Neglected Resource for Profitability and Environmental Stewardship. Presentationat Commodity Classic Field Day. Centreville, Md. 28 July 2016. 50 farmers and agric. professionals in attendance.

4. Weil, R. 2016. Digging deeper: Using nitrogen in the entire soil profile. Farm Journal Vol 6 No 4. Howard G. Buffet Foundation. http://harvestingthepotential.org/wp-content/uploads/HGBF-HYC-Vol6No4-Hill-Weil-EarlySpring2016-LR-FINAL1.pdf

5. Weil, R. 2016. Cover crop trials reveal N reduction. Farm Journal Vol 6 No 8. Howard G. Buffet Foundation http://harvestingthepotential.org/wp-content/uploads/HGBF-Vol6No8-FJ-Nov2016-Hill-Weil-LR-FINAL.pdf

6. Weil, Ray, Sarah Hirsh, and Fang Wang, 2016. Looking Deeper for Impacts of Soil Management. Soil Science Society of America. Annual International Meetings. Phoenix, Arizona. Nov. 07, 2016.

7. Weil, Ray. 2016. Creativity in Cover Cropping Systems for Farm Profitability and Clean Water. Invited Presentation to Howard County Extension Winter Ag Meeting. 17 Feb. 2016. Glenwood, Md. 60 farmers and ag professional in attendance.

8. Invited member of the 2nd annual Panel on “Can food production and a clean Chesapeake Bay coexist?” sponsored by the Chester and Sassafras River Keepers Associations and the Washington College Center for Environment. Washington College. Chestertown, Md. November 1, 2016. Two hour discussion with 200 members of Eastern Shore of Maryland agriculture community in attendance.

Collaborators: