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

Final report for LNE14-338

Project Type: Research and Education
Funds awarded in 2014: $249,576.00
Projected End Date: 10/31/2018
Grant Recipient: University of Maryland
Region: Northeast
State: Maryland
Project Leader:
Dr. Ray Weil
University of Maryland
Co-Leaders:
Dr. Sarah Hirsh
University of Maryland
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Project Information

Summary:

Problems addressed and solution pursued

Sufficient nitrogen (N) is essential for growing productive, profitable crops; however, N not used by crops can cause environmental problems (e.g., eutrophication in bodies of water). Summer cash crops such as corn and soybean typically take up N for only four months out of the year—May through August. Cover crops growing in the fall and spring months can extend the period during which N is being scavenged from the soil. Several cover crop species (e.g., brassicas, cereal grasses) can grow roots over 1 m deep during the fall months, which allows them to recover deep soil N[1],[2]. Our research objectives included:

  1. Assess how much mineral N remains in the soil profile from 0-210 cm deep following corn or soybean senescence
  2. Determine the effectiveness of various cover cropping systems to capture mineral N from the 0-210 cm profile in the fall and spring

Measure corn yield and N requirements following various cover crop systems

Research approach, educational approach, farmer learning outcomes

In order to assess how much N remained after growing summer crops, we took deep (210 cm) soil cores in August-September in transects on 14 farms in 2014 and seven farms in 2015. In 2016, we took the soil cores from side-by-side corn and soybean fields on four farms to compare the soil profile for soybean and corn fields. During the three years, deep soil cores were taken in 29 fields across the Piedmont, Ridge and Valley, and Coastal Plain regions of Maryland and southeast Pennsylvania, including 14 fields with Coastal Plain sediments parent materials, six fields with calcareous rock parent materials, and 9 fields with acidic rock parent materials.

Between the 2014-15 and 2015-16 growing seasons, 28 farmers set-up replicated plots of cover crops. Most of these included four cover crop treatments: 1) forage radish, 2) winter cereal (e.g., rye, triticale, wheat, oats), 3) mixed cover crops (radish + winter cereal + usually clover), and 4) no cover control; each treatment was replicated 3-4 times. We collected biomass samples within replicated treatments from 11 cover crop trials in the 2014-15 season and eight cover crop trials in the 2015-16 season. We collected deep soil cores within replicated treatments from seven cover crop trials in the 2014-15 season and six cover crop trials in the 2015-16 season.

We assessed corn growth and yield following cover crop treatments for various fertilizer rates. In 2015, three farms planted cover crops into corn with various N fertilizer rates; corn yield was measured for each plot/subplot. In 2016, six farms planted cover crops into corn, four had various N fertilizer rates. On five farms (corn failed on one farm due to deer pressure), corn biomass samples and height measurements at the V5 stage, PSNT soil samples, and yield was measured for each plot/subplot.

In addition, in order to investigate methods of establishing cover crops earlier in the season, in 2014, two farms employed aerial seeding of cover crops, one farm experimented with irrigating after planting, and eight farms experimented with using low rates of N fertilizer after planting. In 2015 three farms experimented with inter-seeding cover crop trials, three farms experimented with irrigating after planting, two farms experimented with early vs. late planting date for cover crops, and two farms experimented with using low rates of N fertilizer after planting.

The SARE graduate student grant, “On-farm and isotopic evaluation of deep soil nitrogen capture and cycling by cover crop mixtures” allowed us to expand the N tracer work. Through using 15N isotope tracer, we investigated the ability of cover crops to capture residual N and recycle it for subsequent corn. The 15N tracer was buried at 60, 120, or 180 cm, and we investigated cover crops treatments of forage radish, rye, radish + rye, and radish + rye + Crimson clover, and cover crop planting date treatments of early-September and early-October. The treatments were replicated three times at each of two sites, for a total of 172 plots. We took fall and spring cover crop biomass samples from the plots. Corn was planted on the plots after the cover crops were chemically terminated, and V5 and harvest grain samples were collected from the plots. Deep soil cores (210 cm) were taken in February or April, in June, and in October in select plots in order to investigate the rate of 15N leaching.

The Deep N SARE project has led to follow-on research on collaborating farms and on research stations. In late summer 2016 and in late summer 2017, we set-up a cover crop planting date and termination date experiment at two sites per year, which investigated 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 shared our research findings through Extension meetings and field-days, professional conferences, a webinar and several videos, publications and newsletters, and articles featuring our research in farm magazines. Our intended farmer learning outcomes included:

  1. Understand the benefits and disadvantages of various cover crop species and planting dates, in regards to N conservation and cash crop yield and profit.
  2. Have ideas for ways in which cover crops can be planted by mid-September for various cropping systems, including conventional corn-soybean rotations that are often not harvested until October.

Research conclusions

We found that after growing a summer crop, there remained on average 253 kg/ha mineral N in the soil profile (115 kg/ha of NO3-N; 138 kg/ha of NH4-N). Fifty-five percent of the mineral N was found from 90–210 cm deep. There were higher levels of NO3 (but not NH4) in soil after growing soybean than after corn. In the experiments in which we buried 15N isotopic tracer, we found that rye, radish, or mixed species cover crops captured NO3 from 120 cm and even trace amounts from 180 cm deep by December. For fall growth, early-planted cover crops captured on average 14.5% of the buried 15N from 60 cm, 2.67% of the buried 15N from 120 cm, and 0.31% of the buried 15N from 180 cm. Late-planted cover crops captured on average 1.36% of the buried 15N from 60 cm and 0.07% of the buried 15N from 120 cm. For the early-planted rye, the percent recovery was higher in the fall than the spring for 60 cm, 120 cm, and 180 cm burial depths. For the late-planted rye, the spring percent recovery (6.58%) was higher than the fall (1.45%) for the 60 cm burial, although not significantly (p = 0.1042), and the spring percent recovery (0.31%) was significantly (p = 0.0318) higher than the fall (0.09%) for the 120 cm burial, although by a very small amount.

From the 25 on-farm trials, we found that while variable due to differences in soil fertility and weather, if cover crops were planted by early September, they significantly reduced the amount of N in deep soil layers (0.5–2 m deep) by December. By April, the radish cover crop released NO3 on soil surface layers, while the triticale cover crop immobilized the NO3. While corn N fertilizer response is variable based on site fertility, in our study, corn following winter cereal tended to have lower yields and/or higher fertilizer requirements than corn following no cover crop or a radish or mixed cover crop.

The Deep N SARE project has led to follow-on research on collaborating farms and on research stations that indicates that early-planting also has a marked effect on the reduction of nitrate in leaching water (measured at three feet deep). We found that corn following radish or mixed species (containing radish and/or legume) cover crop had less N requirements or higher yield than corn following a winter cereal cover crop.

Overall, our research found 1) large pools of mineral N remain after summer crops, 2) if planted early, cover crops can capture residual N from deep soil layers, and 3) radish or mixed cover crop species can clean up deep soil N without immobilizing it.

Farmer adoption actions that resulted from the education program

From the start of the project we had an exceptional interest and response to our call for cover crop farm trial collaborators, with over 30 farmers interested in participating. Between 2014 and now, a large local and national audience of farmers have learned about the basic early cover crop-planting nitrogen-capture concepts of our project via 18 presentations at extension meetings and events, 5 presentations at professional meetings, 3 field-days, 1 webinar, 4 productions of online videos, 5 publications in Newsletters or journals, and through being featured in 4 farm magazine articles. There were a total of approximately 2,070 people who attended our presentations at Extension meetings and field-days. This does not include people who watched our webinar or videos, attended our talks at professional conference meetings, or read about our work in newsletters and farm magazines.

We have numerous personal communication accounts that farmers are adapting earlier plated cover crops as a results of our research. In addition, we conducted a survey after our 1-Nov 2017 field-day. For the statement “This field-day increased the chances that I will aim to plant cover crops by early September in future growing seasons or encourage others to do so”, 23/27 survey responders indicated that they “agree” or “strongly agree”, while the remaining 4 survey responders did not write a response. In order to determine state-wide potential impacts of our research, we looked at the statistics for the number of Maryland acres that had early-planted forage radish alone or in a mix. We used this proxy since our research has been encouraging farmers to include early-planted forage radish as a cover crop to capture deep soil N and help prevent immobilization of N in the spring. The Maryland Department of Agriculture Cover Crop Program statistics indicate that the total number of radish planted alone or in mix by 15-September planting date is trending up: 2014-2015 = 13,248 acres, 2015-2016 = 13,055 acres, 2016-2017 = 16,117 acres, 2017-2018 = 18,456 acres. (Note, that in 2017-2018 the radish alone or in mix cover crop planting date was by 1-Oct, not 15-Sept as in the three previous years.)

[1] Dean, J.E. and R.R. Weil. 2009. Brassica cover crops for nitrogen retention in the Mid-Atlantic Coastal Plain. Journal of environmental quality 38: 520-528.

[2] Thorup-Kristensen, K. 2006. Effect of deep and shallow root systems on the dynamics of soil inorganic N during 3-year crop rotations. Plant and Soil 288: 233-248.

 

Performance Target:

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.

Introduction:

Winter cover crops are considered one of the most cost-effective means of reducing agriculture’s contribution to nitrogen nutrient loading to local groundwater and to the Chesapeake Bay. However, we propose that improved management could make cover crops much more beneficial for both the farmer and the environment than is currently the case. Under typical current practice, a winter-hardy cereal cover crop such as rye or barley is planted after cash crop harvest sometime in October or November. With this practice, fall growth and N accumulation are insignificant and the main part of the N capture that occurs takes place in spring during about 4-6 weeks between green-up in mid-March and burn-down in April/May. Using Maryland Department of Agriculture data for recent years, the amount of N captured (leaching loss prevented) is only about 8 lbs N/acre. In addition, no fertilizer savings or yield boost is credited to the typical cover crops. The low N-load reduction credited to cover cropping in MD indicates that most of the cover crop systems currently used under the state subsidy programs (winter cereals planted in mid-October) cannot root deeply enough, soon enough to capture the large pool of residual soil N that we believe exists. Also, many cover crops actually tie-up or immobilize N in spring after they are killed. In fact, some cover crops may actually require increased N application in spring to avoid yield reductions. This may explain why despite subsidies up to $105/A, less than half of MD cropland has cover crops, whereas in neighboring non-subsidy states (like PA) estimates suggest only about 5% of cropland has cover crops. There is now evidence that some early-planted cover crops are able to absorb sub-soil N effectively and release it so that large amounts of N can be taken up by the following crop. This could reduce N leaching losses and N-fertilizer applications to summer crops and hence make cover crops more environmentally beneficial and economically attractive. Cover crop adoption would increase and be less reliant on subsidies.

Our proposed research has the potential to convert cover cropping from a lose-lose (little benefit to farmers or taxpayers) into a win-win situation (with both taxpayers and farmers benefiting from cover crop). We propose to develop and promote systems of early deep-rooted cover crops that help farmers profit from N already on (or under) their farms while addressing environmental impacts and regulatory pressures. We predict that new cover crop practices can pay (instead of cost) $50/acre by 1) capturing 50-150 lbs N/acre in fall, 2) increasing yields, 3) releasing N in spring to allow reduced fertilizer use, while at the same time meeting regulatory requirements to substantially reduce water quality impacts. The project will utilize deep soil N by getting rapid-growing, deep-rooted, non-immobilizing cover crops established early. This will involve a number of strategies, including using early-maturing crop cultivars, changing crop rotations, using aerial seeding (possibly with irrigation) into standing crops and assuring sufficient startup nutrients.

Cooperators

Click linked name(s) to expand
  • Dr. Sjoerd Duiker
  • Stanley Fultz
  • Jeffrey Graybill
  • Steve Groff
  • Sarah Hirsh
  • Jim Lewis
  • Sudeep Mathew
  • Kelly Nichols

Research

Hypothesis:

a. Significant after-harvest mineral-N exists deep in subsoils on farms with manuring history.

b. Early-planted but not late-planted cover crops capture deep-N.

c. Where topsoil nitrate-N <10 mg/kg, fertilization of early-planted cover crops with 20 kg/ha N will increase deep-N capture by > 20 kg/ha.

d. Rapidly decaying cover crops (eg. radish) release captured N in time for spring cash crop use, allowing fertilizer N reduction.

e. Early-planted, winter-killed cover crops reduce N leached by > 100 kg N/ha and increase yields of following spring crops.

Materials and methods:

Cropland soil profile N

We sampled soil to 210 cm deep on a total of 29 farm fields, on a wide range of commercial farm row-crop fields, in August-September during a three year period (2014-2016). The timing of the samples was chosen to determine the amount of N left in the profile after summer cash crop N uptake had ceased.  Soil was sampled in this survey across the main agricultural regions in MD and southeast PA, in the Piedmont, Ridge and Valley, and Coastal Plain physiographic regions (figure 1). The 29 sites were classified into three soil parent material groups: 1) coastal plain sediments, 2) acidic rock parent materials, and 3) calcareous rock parent materials. Most farms practiced no-tillage or limited-tillage, there was a range of manure histories, and sampling on most farms followed corn or soybean crops, although other crops were included, which were common to particular counties (e.g., tobacco). Eight of the 29 fields were selected as four pairs of side-by-side corn and soybean fields, in order to evaluate the effect of previous crop on residual N.

Soil cores 210 cm deep were collected using hand-driven probes (Dean and Weil, 2009; Veihmeyer, 1929) from 14 fields between 20-Aug and 20-Sep in 2014, from seven fields between 17-Aug and 25-Sep in 2015, and from eight fields between 24-Sep and 29-Oct in 2016. In 2014 and 2016 two soil cores were collected at five points along a straight transect; in 2015 three soil cores were collected at four points within the field. Points were 20 to 50 m apart, depending on the size and shape of the field; cores at a point were less than 1 m apart. In 2014 and 2016, soil was divided into 15 cm increments and two soil cores taken from each point along the transect were composited for each depth increment. In 2015, soil was divided into 30 cm increments, and the values of the three cores per point were averaged after soil analysis.

 

On-farm cover crop trials

Cover crop experiments were conducted on 19 farm sites, two of which were at Central Maryland Research and Education Center (Clarksville, MD), with the other 17 on private commercial farms. Experiments were located throughout the main agricultural areas in MD and Southeastern PA. Depending on the farmers’ preferences, situation and facilities, the cover crop experiments varied somewhat among sites, with regard to plot size, specific cereal species used, tillage practices and planting dates. In general, the experiments followed a randomized complete block design with three to four blocks. Plot size was dependent on the equipment and land available on a given farm, and were on average 409 m2, ranging from 45 m2 to 2128 m2. Cover crop treatments typically included 1) forage radish (radish), 2) winter cereal (cereal), 3) a multi-species cover crop comprised of forage radish + winter cereal + crimson clover (Trifolium incarnatum L.) (mix), and 4) a control of winter weeds only with no-cover crop planted (control). The winter cereal species and species in the cover crop mix varied according to farmer preference.

On nine of the farms with cover crop experiments, corn was planted following cover crop termination to test for cover crop effects on V5 corn growth and/or corn yield. On five farms the fall cover crop treatment main plots were split at corn planting into multiple N fertilizer rate sub plots, and the response of corn to N fertilization was measured.

Cover crop biomass samples and soil cores from 0-210 cm deep were obtained in late-fall, prior to the cover crop species dying or becoming dormant for the winter, and in late-spring, shortly before cover crop termination. Biomass was collected from two to five 0.25 m2 quadrats per plot. Growing degree days (GDD) and precipitation available to cover crops were determined between cover crop planting date and fall or spring cover crop sampling, based on the precipitation and temperature data from the closest weather station to the study site. Soil cores were taken with hand-driven Veihmeyer probes (Veihmeyer, 1929) from 0 to 210 cm deep when possible, or until the probe reached groundwater or an impenetrable layer of rock. Two to five soil cores were taken per plot.

 

Soil samples were dried, sieved to 2 mm, and NO3-N and NH4-N was extracted (2 g soil in 20 mL solution) with 0.5 M potassium sulfate (K2SO4) and filtered. A Lachat QuikChem 8500 Automated Ion Analyzer (Hach Company, Loveland, CO) was used to analyze the filtrate for NH4–N (salicylate method) and for NO2-N + NO3-N (cadmium reduction method). Stocks of NO3-N and NH4-N (kg ha-1) were calculated from concentrations of NO3-N and NH4-N using soil bulk density values (core method). Soil particle size analysis was performed by the modified pipette method (Gavlak, et al., 2005). Total C and N analysis was performed at University of Maryland Department of Environmental Science and Technology Analytical Lab on LECO CN628 Elemental Analyzer (LECO Corp., St. Joseph, MI); (Nelson and Sommers, 1996); (Matejovic, 1993).

 

15N study

The study was located at the Central Maryland Research and Education Center—Beltsville Facility (Laurel, MD). The year one study was performed from September 2014 to November 2014 during the fall cover crop growing season. The study contained six blocks, three at each of two sites, located 1.30 km away from each other. The study included 12 treatments in a split-split plot design with three replications at both sites. Plots were 3 m x 3 m in size. Experimental factors that defined the treatments included cover crop planting date, cover crop species, and 15N burial treatments. The treatments were in a complete factorial combination of these factors with cover crop planting date as the main plot factor, cover crop species as the split-plot factor, and 15N burial depth as the split-split plot factor. The cover crop treatment included: 1) forage radish (radish) and 2) cereal rye (rye). Rye is a common cover crop grown in Maryland and the cover crop with the largest monetary incentives under the Maryland cover crop program (Maryland Department of Agriculture, 2018). Radish is a cover crop increasingly being used in Maryland, which has shown much potential for quick root growth and deep N scavenging. The cover crop planting date included: 1) an early-planted date of 28 Aug and 2) a late-planted date of 29 Sep. The 15N burial depth treatments included: 1) 100 cm burial, 2) 200 cm burial, and 3) control treatment in which no 15N was applied. Solution of 0.5 g KNO3 isotopic tracer 99% enriched in 15N and 250 ml DI (deionized) water were made. Each solution contained 0.07345 g 15N. The 15N solution was buried at one point in the center of each plot. Cover crop biomass was harvested 25 Nov 2014.

The year two experiment was performed from September 2015 to October 2016 during the cover crop-cash crop cycle. The study contained six blocks, three at each of two sites, located 1.06 km away from each other. The study included 29 treatments in a randomized complete block design with six replications. Plots were 3 m x 3 m in size. Experimental factors that defined the treatments included cover crop, cover crop planting date, and 15N burial depth. The treatments were in an incomplete factorial combination of these factors. The cover crop treatment included: 1) radish, 2) rye, 3) radish + rye (two-way mix), 4) radish + rye + crimson clover (three-way mix), and 5) control treatment in which no cover crop was planted. The cover crop planting date treatments included: 1) an early-planting date of 3 Sep and 2) a late-planting date of 8 Oct. There was no late-planting date treatment for the two-way mix, as we did not expect an interaction between planting date and the influence of clover on the cover crop mixture. The 15N burial depth treatments included: 1) 60 cm burial, 2) 120 cm burial, 3) 180 cm burial, and 4) control treatment in which no 15N was applied. Solutions of 0.5 g KNO3 isotopic tracer 99% enriched in 15N and 250 ml DI (deionized) water were made. Each solution contained 0.07345 g 15N. The 15N tracer was divided among five burial points per plot. Fall cover crop biomass was sampled between 14 Dec 2015 and 31 Dec 2015, and spring biomass was sampled between 30 April 2016 and 7 May 2016. Samples were taken using minimally destructive techniques so the cover crops could decompose in the plots. Corn was planted on the plots after the cover crops were chemically terminated, and V5 and harvest grain samples were collected from the plots. Deep soil cores (210 cm) were taken in February or April, in June, and in October in select plots in order to investigate the rate of 15N leaching.

Soil samples were taken beside 15N burial points in year one and year two studies, in order to evaluate 15N leaching patterns. Biomass and soil samples were analyzed for 15N at Cornell University Stable Isotope Laboratory using an isotope ratio mass spectrometer (ThermoFinnigan Delta Plus) integrated with an elemental analyzer (Carlo Erba NC2500) through an open split interface (Conflo II). The concentration of 15N in the sample is reported as atom percent (at%) 15N.

Research results and discussion:

Cropland soil profile N

Following summer crop senescence, on average 253 kg ha-1 of Nmin remained in the upper 210 cm of soil, with 22% located at 0-30 cm, 23% at 30-90 cm, 27% at 90-150 cm, and 28% at 150-210 cm depth. Across the 29 fields, 115 kg ha-1 of the total Nmin was NO3-N and 138 kg ha-1 was NH4-N. Nitrate-N levels for Coastal Plain sediments fields were lower than acidic rock fields in the 90-150 cm depth and than calcareous rock fields in the 150-210 cm depth (p < 0.10; Table 1). Across the 29 fields, sand percentage was negatively correlated with NO3-N concentration (p < 0.10) at 0-30 cm, 90-150 cm, and 150-210 cm depths, but neither sand nor clay percentage was correlated with NH4-N concentration. Within-field CV of 0-210 cm total stock of NO3-N was on average 35% (standard error (SE) = 5.1, N = 19) and of NH4-N was on average 44% (SE = 5.0, N = 19). The CVs for the two N species were uncorrelated.

Based on the four pairs of adjacent corn and soybean fields sampled in 2016, there was significantly more soil NO3-N following soybean than corn at 30-60 cm, 120-150 cm, 150-180 cm, and 180-210 cm. Levels of soil NH4-N differed between corn or soybean only at 180-210 cm (figure 2). 

The large pools of residual N represent both fertilizer N unused by summer crops (Wang and Weil, 2018) and N mineralized from soil and plant organic matter (Dahnke and Johnson, 1990; Weil and Brady, 2017). Residual soil N is often assumed to be a result of N fertilizer over-application, or low N uptake during drought years (Forrestal, et al., 2012); hence, N management and policies to reduce N loading primarily focus on N fertilized fields (Maryland Department of Agriculture, 2014). However, we believe that large pools of residual Nmin are more universal. Our data, in agreement with previous studies (Gentry, et al., 2001; Jaynes, et al., 2001; Kessavalou and Walters, 1999; Pantoja, et al., 2016; Rembon and MacKenzie, 1997) indicates soybeans without N fertilizer can leave even more residual nitrate in the soil profile than corn receiving fertilizer. Compared to corn, soybean creates a high N environment with less (and lower C/N ratio) residues, and therefore less N is immobilized (Angle, 1990; Gentry, et al., 2001; Green and Blackmer, 1995).

While stocks of NO3-N and NH4-N in the soil profiles were similar, our results suggest that NO3-N is more transient, leaching through the soil, whereas NH4-N is accumulating through cation exchange sorption. For example, crop (corn versus soybean) affected NO3-N levels much more than NH4-N levels. Similar results were found in Wisconsin (Bundy, et al., 1993) for the upper 90 cm of soil in spring. Kristensen and Thorup-Kristensen (2004) and Bergström (1986) also found that crop species affected residual NO3-N more than residual NH4-N. The negative correlation between sand and soil NO3-N concentration (but not NH4-N concentration) supports the expected faster NO3-N leaching in sandier soils. The lack of correlation between clay and NH4-N concentration is not surprising as the NH4-N ions measured would occupy only a small fraction of the cation exchange sites on any of the soils.

Importance of vertical location of N

Many studies report how soil N is affected by cover crops (Chu, et al., 2017; Ebelhar, et al., 1984; Kuo and Jellum, 2002; Ladoni, et al., 2015; Ruffo, et al., 2004; Sainju, et al., 2006) or other cropping practices (Anderson and Peterson, 1973; Poudel, et al., 2002; Rice, et al., 1986; Scalise, et al., 2015) after sampling only 15 to 30 cm of soil. However, it is the deeper N (1-2 meters deep) that is most at-risk for leaching to groundwater before plants can take it up. Across all our fields, 57% (65 kg N ha-1) of NO3-N and 55% (138 kg N ha-1) of total Nmin to 210 cm was at 90-210 cm.

In regions, such as the mid-Atlantic, with year-long rainfall, favorable mineralization conditions during much of the “off-season” and permeable soil types, scavenging residual N as soon as possible after crop harvest will be important to prevent N from leaching beyond rooting depth. We suggest that early-planted, deep-rooted cover crops could be a tool to accomplish such N conservation.

 

On-farm cover crop trials

In late-fall, across six farms, for the 0-30 cm and 30-60 cm deep soil increments, the NO3-N (kg ha-1) was significantly higher in the control treatment than the radish, winter cereal, or mix treatments, and for the 60-90 cm soil increment, NO3-N (kg ha-1) was significantly higher in the control treatment than the radish treatment. In late-fall, for the 0-30 cm deep soil increment, the NH4-N (kg ha-1) averaged across six farms was significantly lower in the control treatment than the mix treatment (table 2).

In the spring, across 11 farms, in every 30 cm soil increment from 0-210 cm, soil in the winter cereal treatment had significantly lower NO3 than soil in the control treatment. In soil increments from 30-210 cm deep, soil in the mix treatment had significantly lower NO3 than soil in the control treatment and the same level of NO3 as soil in the winter cereal treatment; from 0-30 cm deep, soil in the mix treatment had the same level of NO3 as soil in the control and radish treatments and higher NO3 than soil in the winter cereal. From 0-30 cm deep, soil in the radish treatment had significantly higher NO3 than soil in control or winter cereal. From 30-60 cm deep, soil in the radish treatment had significantly higher NO3 than soil in winter cereal or mix treatments (and the same level as control). In each 30 cm increment from 60-150 cm deep, soil in the radish treatment had significantly higher NO3 than soil in the winter cereal, the same level of NO3 as soil in mix, and lower NO3 than soil in control. In each 30 cm increment from 150-210 cm deep, soil in radish had significantly higher NO3 than soil in control and the same level of NO3 as soil in mix and winter cereal. Across 11 farms, the soil NH4-N (kg ha-1) did not differ at any soil depth increment (table 2). Figure 3 depicts soil NO3-N levels per depth per farm.

Radish, winter cereal, and mix cover crops each performed differently in terms of reducing deep soil NO3 in the fall and spring and increasing surface soil NO3 in the spring. Radish was the most effective cover crop at reducing the soil NO3 in the fall from the deeper soil layers and ensuring available NO3 on the soil surface (0-30 cm) in the spring. Other studies have also found radish to be more effective than rye at reducing levels of soil NO3-N by late-fall, especially in deep layers (> 1 m) (Thorup-Kristensen, 2001); (Thorup-Kristensen, et al., 2009); (Kristensen and Thorup-Kristensen, 2004a). However, in the spring, radish was less effective than winter cereal at reducing soil NO3 from 30-150 cm deep. Winter cereal was the most effective at reducing soil NO3 in the spring throughout the entire soil profile. Mix was more effective than winter cereal and as effective as radish at ensuring available NO3 on the soil surface (0-30 cm) in the spring, and was as effective as winter cereal in reducing soil NO3 from 30-210 cm soil.

In the fall, across the 13 farms, radish biomass was significantly higher than mix, which was significantly higher than winter cereal. The N content was significantly higher for radish and mix than for winter cereal. The C/N ratio did not differ between radish, mix and winter cereal cover crop treatments. In the spring, across the 10 farms, winter cereal biomass was higher than mix. There were no significant differences between the N uptake of winter cereal and mix. The C/N ratio was greater for winter cereal than mix. When comparing radish to winter cereal prior to their termination (i.e., naturally winter-killing for radish or oat (Avena sativa L.) and chemically terminated with herbicide for rye (Secale cereale L.) and triticale (x Triticosecale Wittm. ex A. Camus), biomass was not significantly different between radish and winter cereal (p = 0.9251). The N content was significantly higher for radish (80.1 kg ha-1) than winter cereal (58.7 kg ha-1) at a significance level of p = 0.0013. The C/N ratio was significantly lower for radish (14.2) than winter cereal (22.6) at a significance level of p < 0.0001 (Table 3).

Radish winter-killed at all farm sites. For samples taken shortly before winter-kill, the average C/N ratio was 14.2. When C/N ratios are < 25/1, N will generally be plant available and not immobilized (Weil and Brady, 2017). Therefore, N released from the dead radish biomass was likely available for plant uptake and not immobilized. The cover crop biomass shortly before termination for radish and winter cereal did not differ, but on average radish had accumulated 21.4 kg ha-1 more biomass N than winter cereal, and radish biomass had a C/N ratio of 14.2 while the winter cereal C/N ratio was 22.6. Therefore, the radish cover crop had both greater N accumulation in the biomass and a lower likelihood of N immobilization due to the lower C/N ratio. Winter cereal cover crops commonly have C/N ratios higher than mixes.

The number of GDD was positively correlated to fall radish biomass (r = 0.43; p = 0.094) and spring winter cereal biomass (r = 0.63, p = 0.012). Precipitation was positively correlated to spring winter cereal biomass (r = 0.58; p = 0.025). Topsoil (0-30 cm) NO3-N was positively correlated to fall winter cereal biomass (r = 0.77; p = 0.001) and to fall radish biomass (r = 0.48; p = 0.080). The percent sand in the topsoil was negatively correlated to fall winter cereal biomass (r = -0.52; p = 0.056), fall radish biomass (r = -0.47; p = 0.092), and spring winter cereal biomass (r = -0.74; p = 0.002). Topsoil nitrate was negatively correlated with topsoil percent sand in fall radish plots (r = -0.50; p = 0.070), fall winter cereal plots (r = -0.53; p = 0.050), and spring winter cereal plots (r = -0.57; p = 0.026). The topsoil percent silt was positively correlated to fall winter cereal biomass (r = 0.52; p = 0.0582), fall radish biomass (r = 0.56; p = 0.0381), and spring winter cereal biomass (r = 0.70; p = 0.004).

Across the six farms on which PSNT soil samples were taken, the soil NO3-N concentration for radish was significantly higher than for winter cereal and mix. The soil NH4-N concentrations did not differ among any of the cover crop treatments. Across the six farms, the V5 corn biomass plant-1 and shoot N plant-1 were significantly affected by the previous cover crop treatment in the order radish > mix = control > winter cereal. Averaged across six farms at the farmers’ standard N fertilizer application rate, corn yield from radish or control was higher than winter cereal. Corn yield from radish was higher than mix. Averaged across six farms at the 0 fertilizer N rate, corn yield for radish > control = mix > winter cereal (Table 4). Figure 4 depicts corn N response curves per farm.

Nitrogen fertilizer response curves can help determine if more or less fertilizer is required for optimal corn yields. At Howard IB farm, the N response plateaued for corn following radish cover crop, mix cover crop, or control cover crop at 135 kg ha-1 N applications (farmer’s normal rate), but the N response continued to increase for corn following rye cover crop even at 202 kg ha-1 (150% of farmer’s normal rate). The Lancaster IA farm exhibited exceptionally high soil fertility and corn yields were high and minimally responsive to N fertilization in any of the cover crop treatments. The Howard IA corn also showed minimal responses to N. On Frederick I farm, the interaction between corn yield and fertilizer rate was not significant, although corn following radish and control had yields around 10 Mg ha-1 that leveled off at 112 kg ha-1 N fertilizer application (100% farmer’s normal rate), while corn following winter cereal had maximum yields of 7600 kg ha-1 at 168 kg ha-1 N fertilizer application (150% of farmer’s normal rate). While corn N fertilizer response is variable based on site fertility, in our study, corn following winter cereal tended to have lower yields and/or higher fertilizer requirements than corn following no cover crop or a radish or mixed cover crop.

Through performing on-farm trials of early-planted cover crop systems, we were able to observe a range of cover crop responses. Cover crops are affected by soil type, management, and weather. Furthermore, site-by-site results of residual soil NO3-N and NH4-N were often highly variable. Soil sampling can be challenging due to the heterogeneity of soil, more so in deep soil layers. Even with the variability among sites and soil samples, there were clear trends showing that early-planted forage radish and rye cover crops (monoculture or mix) can scavenge soil N from 1+ m. This is expected to reduce NO3-N leaching.

 Overall it can be concluded that winter cereal had a negative impact on the following corn. Either extra fertilizer will need to be added, which is contrary to the goal of improving the overall cropping system’s nutrient use efficiency, or farmers’ yields will be reduced, which is contrary to the goal of “making cover crops pay”. On the other hand, a mixed species cover crop has no negative (or positive) impact on the cropping system, and a radish cover crop has a neutral or sometimes positive impact on the cropping system, in terms of improving the overall nutrient use efficiency. Cover cropping is a practice that is already widely adopted in Maryland, and planting cover crops earlier in the fall can greatly increase their ability to scavenge and potentially release deep soil N.

 

15N study

In year one, at the clayey site and at the sandy site, for early-planted cover crops, the 15N percent recovery was higher when 15N was buried at 100 cm than 200 cm, but there was no difference between radish and rye cover crops. At the clayey site, for late-planted cover crops, the 15N percent recovery did not differ between 100 cm and 200 cm placement or between radish and rye cover crops. At the sandy site, for late-planted cover crops, the 15N percent recovery was higher when 15N was buried at 200 cm than 100 cm. The 15N percent recovery was higher by the radish cover crop than the rye (figure 5).

In year two, September-planted cover crops recovered significantly more 15N than October-planted cover crops from the 60 cm depth and from the 120 cm depth. For fall growth, early-planted cover crops captured on average 14.5% of the buried 15N from 60 cm, 2.67% of the buried 15N from 120 cm, and 0.31% of the buried 15N from 180 cm. Late-planted cover crops captured on average 1.36% of the buried 15N from 60 cm and 0.07% of the buried 15N from 120 cm (figure 6). There were no significant difference in 15N recovery between radish and rye for any planting-date by depth combination, across planting-dates, across-depths, or across planting-dates and depths.

For the late-planted rye, the spring percent recovery (6.58%) was higher than the fall (1.45%) for the 60 cm placement, although not significantly (p = 0.1042), and the spring percent recovery (0.31%) was significantly (p = 0.0318) higher than the fall (0.09%) for the 120 cm placement, although by a very small amount. The location of 15N in soil cores taken beside 15N burial points indicated that the tracer was leaching downward over time.

Figure 1. Locations in Maryland and Pennsylvania of the 29 crop fields in which a transect of 0-210 cm deep soil cores were taken.

 

Table 1. Soil NO3-N, NH4-N, and mineral N (Nmin) (kg N ha-1) for 0-30 cm, 30-90 cm, 90-150 cm, 150-210 cm, and 0-210 cm. Values are means with standard error (SE) in parenthesis for all fields (N=29), Coastal Plain sediments fields (N=14), calcareous rock fields (N=6), and acidic rock fields (N=9). Within a mineral N type and depth increment, values followed by the same letter do not differ significantly among Coastal Plain sediments, acidic rock, and calcareous rock fields. The symbols * and † indicate p < 0.05 and 0.1, respectively.

 

 

Figure 2. NO3-N and NH4-N (kg N soil layer-1 ha-1) in four pairs of adjacent corn and soybean fields. The symbols **, *, †, ns indicate p < 0.01, 0.05, 0.1, and not significant.

 

Table 2. Soil NO3-N and NH4-N (kg ha-1) in radish, winter cereal (cereal), mixed species (mix), and control cover crop treatments for six farms for late-fall sampling and for 11 farms for spring sampling. Means for cover crop treatments and depth increments followed by the same letters do not differ statistically. Farms sampled in late-fall include Dorchester IB, Frederick IV, Huntington IA, Lancaster IA, Lancaster II, and Lancaster V. Dorchester IB cores only to 180 cm deep, Frederick IV did not have soil core samples from mix treatment. Farms sampled in spring include Dorchester IB, Frederick I, Frederick III, Howard IB, Huntington IA, Lancaster IA, Lancaster IB, Lancaster II, Lancaster III, Lancaster V, and Kent II. Dorchester IB and Kent II soil cores were to only 180 cm deep. Lancaster V did not have soil core samples from mix treatment.

 

Table 3. Cover crop biomass (kg ha-1), N content (kg N ha-1), and C/N ratio for fall cover crop growth (late-fall sampling), fall and spring cover crop growth (spring sampling), and cover crop growth prior to termination (late-fall radish, prior to winter-kill, and spring winter cereal, prior to herbicide termination. Different letters indicate statistically significant differences between cover crop treatments.

 

Table 4. Percent of maximum corn yield following cover crop treatments for standard fertilizer application or no fertilizer application. Cover crop treatment values for percent of maximum corn yield, within the same fertilizer N level, followed by different letters are significantly different (p < 0.05).

 

Figure 3. Amount of NO3-N (kg ha-1) in 0-210 cm soil profile for seven farms at fall sampling and 10 farms at spring sampling. 1Spring samples from 120-150 cm and 150-180 cm depths are the average values from 120-180 cm.

 

Figure 4. Corn grain yield associated with various N fertilizer rates and preceding cover crop treatments. Error bars show standard error of mean.
Figure 5. Experiment #1, 15N percent recovery for early- and late-planted cover crops on sandy site and clayey site.
Figure 6. Experiment #2, December 15N percent recovery from each 15N burial depth for early- and late-planted cover crops (across all cover crops). The 15N burial depth values for log10 15N percent recovery within the same cover crop planting date treatment followed by the different letters are significantly different (p < 0.05).

 

Research conclusions:

Overall conclusions

We found there were often trade-offs between scavenging residual N and releasing the N for the subsequent crop. Radish was very effective at scavenging N in the fall; however, it sometimes led to increased levels of NO3-N in the spring soil in shallow as well as deep soil layers. The 15N tracer study indicated that radish, rye, and two-way or three-way mixes of radish + rye + (crimson clover) all performed equally well in scavenging residual N from deep soil layers. Winter cereal cover crops caused a yield loss and/or increased N fertilization needs for a subsequent corn crop. Utilizing mixed cover crop species may be optimal in terms of N scavenging and release. Mixed cover crops were very effective at scavenging residual N in the fall and spring, and typically did not cause a yield gain or loss for subsequent crops. Radish may also be a good choice, in terms of being able to reduce subsequent corn N fertilizer application amounts.

The effect of cover crops on the cropping system may take more than one growing season to become apparent. Furthermore, it is important to keep in mind that cover crop effects are expected to be highly variable from site-to-site and year-to-year, according to soil and weather patterns. Thus, while the on-farm proponent of our study was not as precisely controlled as the research station trials, we believe it was very valuable for considering the range of cover crop responses that we would expect to see across practitioners.

In conclusion, we found substantial levels of inorganic soil N remained in the soil profile (0-210 cm deep) following summer crops. On average, there was more residual inorganic N in the soil profile than the amount of N fertilizer that a farmer would typically apply to a corn crop. This provides both a risk and an opportunity. The residual N is at risk to leach into bodies of water and cause eutrophication and associated environmental problems. However, the pool of residual N also could serve as a valuable resource to farmers, if they utilize it and reduce their fertilizer use. Cover crops were able to access deep pools of N, but only if the cover crops were planted by the first week in September in our study region. If planted early, forage radish and winter cereal cover crops were very effective at scavenging deep soil N from 1+ m deep and in some cases even up to 2 m deep. The radish cover crop was sometimes effective at recycling N to subsequent crops. We expect radish and mixed species may have greater positive effects on subsequent crops after several years of use.

 

Policy Implications—improving efficiency of cover crop program through deep rooted cover crops

Currently the State of Maryland has an incentive program in which landowners are paid to grow cover crops. The incentive payment amounts vary, depending on cover crop species, cover crop planting date, previous cash crop, and field management practices. Farmers are eligible for cover crop payments if they plant the cover crop by 5 Nov and kill after 28 Feb. The program gives “early planting” bonus payments if the cover crop is planted before 15-October (Maryland Department of Agriculture, 2018). We found in the current study that cover crops planted after 30-September will have minimal biomass accumulation and soil N uptake and will not capture subsoil N in the fall. Under the current cover crop program, planting rye alone is given a bonus incentive over planting rye within a mix. However, we found in the current study that rye monocultures typically require additional spring N fertilization or decrease subsequent corn yields. If planting cover crops leads to increased N fertilizer requirements, it is counterproductive toward the goal of using cover crops to reduce residual soil N and risks of N leaching from cropland.

The EPA Interim Evaluation of Maryland’s 2016-2017 milestones reports that the Agriculture sector in Maryland was not on-track to reach its 2017 N target, which is a 60% reduction of the 2009 N loads into the Bay to achieve water quality standards (EPA, 2017). While this failure may be partly a result of legacy N effects due to the slow flow of groundwater (Ator and Denver, 2015), it may also be partly a result of conservation practice implementation. For example, cover crops will not perform to their full potential if they are planted too late. Due to the extent of cover crops on the landscape (e.g., 478,000 acres in Maryland in 2014), improvements in the ability of cover crops to reduce N leaching from the land through incorporating earlier planting dates and more deep-rooted species could foster a more sustainable, cycling crop system and greatly reduce the N load into bodies of water. We therefore suggest that incentives be increased for earlier cover crop planting, especially for planting prior to mid-September. We recognize that such early cover crop planting may require additional adaptations of a farm system, such as earlier maturing crop varieties, interseeding into standing crops, or changes in crop rotations.

Participation Summary
27 Farmers participating in research

Education

Educational approach:

We shared our research findings through Extension meetings and field-days, professional conferences, a webinar and several videos, publications and newsletters, and farm magazine articles featuring our research. Our intended farmer learning outcomes included:

  1. Understand the benefits and disadvantages of various cover crop species and planting dates, in regards to N conservation and cash crop yield and profit.
  2. Have ideas for ways in which cover crops can be planted by mid-September for various cropping systems, including conventional corn-soybean rotations that are often not harvested until October.

Milestones

Milestone #1 (click to expand/collapse)
What beneficiaries do and learn:

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.

Proposed number of farmer beneficiaries who will participate:
1350
Actual number of farmer beneficiaries who participated:
1000
Actual number of agriculture service provider beneficiaries who participated:
200
Proposed Completion Date:
October 31, 2018
Status:
Completed
Date Completed:
October 31, 2018
Accomplishments:

Between 2014 and 2018, a large local and national audience of farmers have learned about the basic early cover crop-planting nitrogen-capture concepts of our project via 24 presentations at extension meetings and events, 8 presentations at professional meetings, 3 field-days, 2 webinars, 6 productions of online videos/podcasts, 9 publications in Newsletters or journals, and through being featured in 6 farm magazine articles. There were a total of approximately 2,070 people who attended our presentations at Extension meetings and field-days. This does not include people who watched our webinar or videos, attended our talks at professional conference meetings, or read about our work in newsletters and farm magazines.

 

Primary products sharing results of project:

Hirsh, S.M., and R.R. Weil. 2019. Deep soil cores reveal large end-of-season residual mineral nitrogen pool. Agricultural & Environmental Letters doi: 10.2134/ael2018.10.0055. Deep-soil-cores-reveal-large-end-of-season-residual-mineral-nitrogen-pool-Hirsh-Weil-2019

Weil, R., and S. Hirsh. 27 February 2017. Go deep, go early—effective cover cropping for nitrogen capture. On-line Webinar. 1 hour. Agricultural Nutrient Management Program, University of MD, https://www.youtube.com/watch?v=yCXoh7BqxNw&feature=youtu.be

Duiker, S.W., R.R. Weil, and S.M. Hirsh. Reaping benefits from early-fall planted cover crops. https://psu.app.box.com/s/korodwzeq4lrr8mpc92r5zcmvqlxs54q/file/363276764145.

Hirsh, S., R. Weil. Fall 2016. Getting cover crops planted in September, despite late crop harvests. University of Maryland Extension Ag Newsletter. Volume 7, Issue 6. pp. 10-11. Agronomy News September 8,2016

Hirsh, S., R. Weil. Fall 2015. It’s August—are your cover crops growing yet? University of Maryland Extension Ag Newsletter. Volume 6, Issue 5. pp. 2-4.  Agronomy News Aug 13, 2015

Dr. Ray Weil on SARE deep nitrogen study with cover crops. North East Sustainable Agriculture and Research and Education. Video on line. USDA/NESARE, 6:56. 
https://drive.google.com/file/d/13M4ziArYZesiOnZTYnThBLMhWWDecyAW/view?usp=sharing

 

Complete list of educational outreach below:

Farm magazine articles

Lancaster Farming— “the leading Northeast and mid-Atlantic farm newspaper” with 60,000 paid subscribers in Pennsylvania and 15 other states (http://www.lancasterfarming.com/site/about.html)

  1. Bravo, M. 2017. Cover crop researchers converge in New York. Lancaster Farming North Edition, p. A2. Press coverage of Hirsh’s talk at Northeast Cover Crop Conference at Cornell University.
  2. Gruber, 2014. Getting to the roots of cover crop benefits. Lancaster Farming, Lancaster Farming .com, Lancaster, PA. http://www.lancasterfarming.com/results/Getting-to-the-Roots-of-Cover-Crop-Benefits#.VGEFsPnF-Sp. Press coverage of Weil’s field day talks at Groff Farm. Getting-to-the-Roots-of-Cover-Crop-Benefits-_-Main-Edition-_-lancasterfarming

Farm Journal –the leading US farm magazine with 250,000 unique users and 1,000,000 visits per month 

  1. Weil, R. 2017. Planting green? Best practices to make it work. Farm Journal – High Yield Conservation Vol. 7. No. 4. http://harvestingthepotential.org/wp-content/uploads/HGBF-Vol7No4-FJ-EarlySpring2017-Hill-Weil-LRtrim-FINAL.pdf
  2. Weil, R. 2017. Love the residue. Farm Journal – High Yield Conservation. Volume 8, No. 7 http://harvestingthepotential.org/wp-content/uploads/HGBF-Vol7No8-FJ-Nov2017-Hill-Weil-FINAL-LRtrim.pdf
  3. 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
  4. 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

 

Publications and Newsletters

  1. Hirsh, S.M., and R.R. Weil. 2019. Deep soil cores reveal large end-of-season residual mineral nitrogen pool. Agricultural & Environmental Letters doi: 10.2134/ael2018.10.0055. Deep-soil-cores-reveal-large-end-of-season-residual-mineral-nitrogen-pool-Hirsh-Weil-2019

  2. Wang, Fang, Ray R. Weil, Lei Han, Mingxin Zhang, Zhaojun Sun and Xiongxiong Nan. 2019. Subsequent nitrogen utilization and soil water distribution as affected by forage radish cover crop and nitrogen fertilizer in a corn silage production system. Acta Agriculturae Scandinavica, Section B — Soil & Plant Science. DOI: 10.1080/09064710.2018.1498911

  3. Wang, F., and R.R. Weil. 2018. The form and vertical distribution of soil nitrogen as affected by forage radish cover crop and residual side-dressed N fertilizer. Soil Science 183:22-33. doi: 10.1097/SS.0000000000000224
  4. Wang, F., R.R. Weil, and X. Nan. 2017. Total and permanganate-oxidizable organic carbon in the corn rooting zone of US coastal plain soils as affected by forage radish cover crops and N fertilizer. Soil and Tillage Research 165:247-257.
  5. Hirsh, S., R. Weil. Fall 2016. Getting cover crops planted in September, despite late crop harvests. University of Maryland Extension Ag Newsletter. Volume 7, Issue 6. pp. 10-11. https://extension.umd.edu/sites/extension.umd.edu/files/_docs/AgronomyNewsSeptember82016.pdf
  6. Hirsh, S., R. Weil. Fall 2015. It’s August—are your cover crops growing yet? University of Maryland Extension Ag Newsletter. Volume 6, Issue 5. pp. 2-4. https://extension.umd.edu/sites/extension.umd.edu/files/_docs/AgronomyNews6-5.pdf
  7. Nutrient Management Annual Report. 2015. Nutrient management research for agronomic and vegetable crops. Page 9. https://extension.umd.edu/sites/default/files/_docs/programs/anmp/NMAR_2015.pdf. Circulated in print to 2,000 famers and ag professionals on line.
  8. DeVore, B. 2015. King of the cover crops: An Indiana initiative has made the state a national leader in getting continuous living cover established on crop acres. Can it change the way farmers view soil? The Land Stewardship Letter 33(4):24-27. Features Ray Weil’s week-long visit to Indiana’s Conservation Cropping Initiative.
  9. Graybill, Jeffrey S. December 2015. Is excessive growth affecting the winter survival of small grains? Penn State Field Crops Newsletter. Is-Excessive-Growth-Effecting-the-Winter-Survival-of-Small-Grains_-Forage-and-Food-Crops

 

Field-days (approx. 295 total attendees)

  1. Hirsh, Sarah and Ray Weil. 2017. Field-day: Getting the most from cover crops. Laurel, MD. 1 November 2017. 40 in attendance (17 MD Dept of Ag or USDA, 16 University of Maryland, 4 farmer, 3 other).
  2. Graybill, Jeffrey. 2014. Field day at a Lancaster County cooperator’s. Quarryville, PA. 12 November 2014. 15 in attendance.
  3. Weil, Ray and Natalie Lounsbury. 2014. Field day at Cedar Meadow Farm. Lancaster, PA. 30 October 2014. 240 in attendance (40 min field day talks to 8 groups of 30 farmers, professional and reporters).

 

Webinars

  1. Dawson, N., and S. Hirsh. 11 July 2018. Building soil health: Deep N and Cover Crops. On-line Webinar. 1 hour. University of MD.
  2. Weil, R., and S. Hirsh. 27 February 2017. Go deep, go early—effective cover cropping for nitrogen capture. On-line Webinar. 1 hour. Agricultural Nutrient Management Program, University of MD, https://www.youtube.com/watch?v=yCXoh7BqxNw&feature=youtu.be

 

Videos and podcasts

  1. Duiker, S.W., R.R. Weil, and S.M. Hirsh. Reaping benefits from early-fall planted cover crops. https://psu.app.box.com/s/korodwzeq4lrr8mpc92r5zcmvqlxs54q/file/363276764145.
  2. Weil, R. 2015. The science of soil health: Going deeper, In B. Koots, (ed.) Unlock the Secrets in the Soil. USDA/NRCS. https://www.youtube.com/watch?v=XzfFFNG5mnQ
  3. Weil, R. 2015. The science of soil health: Going Deeper, part 2, In B. Koots, (ed.) Unlock the Secrets in the Soil. USDA/NRCS.https://www.youtube.com/watch?v=Qo6zvBBROL0Weil, R.
  4. Weil, R. 2015. Dr. Ray Weil on sare deep nitrogen study with cover crops. North East Sustainable Agriculture and Research and Education. Video online. Univ. Md & Cedar Meadow Farm, 6:56 minutes. https://drive.google.com/file/d/13M4ziArYZesiOnZTYnThBLMhWWDecyAW/view?usp=sharing
  5. Weil, R. 2015. A soil scientist compares Indiana’s ‘bottom up’ approach to advancing soil health to Maryland’s ‘top down’ system. Ear to the Ground, Episode 174, Land Stewardship Project, http://landstewardshipproject.org/posts/podcast/787
  6. Baragona, S. 2017.Farmers find healthy soils yield healthy profits.SCIENCE & HEALTH, Voice of America, https://www.voanews.com/a/farmers-health-soils-profits-conservation-agriculture/3952583.html

 

Extension meetings (approx. 1895 total attendees)

  1. Virginia Crop Production Association Crops Summit. 50 minute talk: Scavenging and recycling deep soil nitrogen with cover crops. Richmond, VA. Anticipated 24 January 2019.
  2. Hirsh, S.M. and R.R. Weil. Poster presentation- Early-planted cover crops to scavenge and recycle deep soil nitrogen. University of Maryland AGNR Open House. 6 October 2018. Ellicott City, MD.
  3. 2018 Virginia Ag Expo. Poster presentation: Early-planted cover crops to scavenge and recycle deep soil nitrogen. 2 August 2018. Champlain, VA. 
  4. Digging Deeper into Soil Organic Matter. Presentation at National Cover Crop Conference. Indianapolis, IN Dec. 8 2017. 120 mainly farmers and farm advisors in attendance.
  5. Mid-Atlantic Crop Management School. 1 hour workshop: How strategic cover cropping doesn’t cost- it pays. 14 November 2017. Ocean City, MD. 2 workshops with 45 attendees each, 90 total.
  6. Mid-Atlantic Crop Management School. 1 hour workshop: Capturing nutrients with early planted cover crops. 15 November 2017. Ocean City, MD. 2 workshops with 100 attendees each, 200 total.
  7. Weil, R. Soil Carbon: Major Player in Maryland’s Greenhouse Gas Balance. Maryland Commission on Climate Change Mitigation Work Group, Baltimore, MD, Maryland Commission on Climate Change Mitigation Work Group http://www.mde.state.md.us/programs/Air/ClimateChange/MCCC/MWG/Pres1_Weil_updated.pdf. May, 2017. 
  8. Spoke and served as resource person during Future Harvest/SARE/Extension field day on “Delay the Burn” cover crop field day Caroline Co. 20 May, 2017. 20 farm advisers and farmers in attendance.
  9. Northeast Cover Crops Council. 30 minute presentation: Using cover crops to scavenge and recycle deep soil N. 8 November 2017. Ithaca, NY. 50? attendees.
  10. Delaware Agriculture Week Soil Health Workshop. Soil Health and On-Farm Research in the Mid-Atlantic Region. 12 January 2017. Harrington, DE. 163 attendees.
  11. 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. 1 November 2016. Two hour discussion with 200 members of Eastern Shore of Maryland agriculture community in attendance.
  12. Hirsh, Sarah and Ray Weil. 2016. Deep Soil Nutrients- a Neglected Resource for Profitability and Environmental Stewardship. Presentation at Commodity Classic Field Day. Centreville, Md. 28 July 2016. 50 farmers and agric. professionals in attendance.
  13. Weil, Ray. 2016. Creativity in Cover Cropping Systems for Farm Profitability and Clean Water. Invited Presentation to Howard County Extension Winter Ag Meeting. 17 February 2016. Glenwood, Md. 60 farmers and agric. professional in attendance.
  14. Weil, Ray. 2015. Invited paper: The Soil Health Revolution in American Agriculture and What It’s Success Could Mean for the Planet. 9th Annual Meeting of Pesticides and the Chesapeake Bay Watershed Project. Maryland Pesticide Network and The Johns Hopkins Center for a Livable Future. Pearlstone Conference Center. Reisterstown, MD. 8 October 2015. http://www.mdpestnet.org/wp-content/uploads/2015/11/Dr-Ray-Weil-presentation-10.28.2015.pdf. 50? attendees.
  15. Hirsh, Sarah M. “Planting Early Cover Crops to Capture and Recycle Deep Soil Nitrogen: an Untapped Resource for Profitability and Environmental Stewardship”. Presentation at Soil Health Field Workshop for Agricultural Service Providers.  Leonardtown, MD. 16 September 2015. 20 agric. service providers in attendance.
  16. Weil, Ray. 2015. Lessons Learned from Chesapeake Bay- Soil Organic Matter Management for Nutrient Cycling and Agricultural Sustainability. Keynote talk. The Conservation Cropping Systems Initiative and Bartholomew County Soil and Water Conservation District. Columbus, IN. 20 August 2015. 80 farmers and agric. professionals in attendance.
  17. Weil, Ray. 2015. Lessons Learned from Chesapeake Bay- Soil Organic Matter Management for Nutrient Cycling and Agricultural Sustainability. Keynote talk. The Conservation Cropping Systems Initiative, Moody Farms. Fremont, IN. 19 August 2015. 100 farmers and agric. professionals in attendance.
  18. Weil, Ray. 2015. Soil Health Systems. Keynote talk. The Conservation Cropping Systems Initiative and Purdue University. Covington, IN. 18 August 2015. 180 farmers and agric. professionals in attendance.
  19. Hirsh, Sarah and Ray Weil. 2015.  “Planting Early Cover Crops to Capture and Recycle Deep Soil Nitrogen: an Untapped Resource for Profitability and Environmental Stewardship”. Presentation at Commodity Classic Field Day. Centreville, Md. 23 July 2015. 50 farmers and agric. professionals in attendance.
  20. Graybill, Jeffrey S. “Successful integration of manure cover crops and no-till”. Presentation at PA Dairy Summit. Lancaster, PA. 4 February 2015. 57 attendees.
  21. Patches, Kelly. 2015. 2014: Franklin County in Review. “Cover crops”. Franklin Crops Day. Chambersburg, PA. 28 January 2015. 80 attendees.
  22. Weil, Ray. 2014. Getting Creative with Cover Crops as Tools for Soil Health and Nutrient Cycling. Mid Atlantic Crop Management School in Ocean City, MD. 19 November 2014. Two 1 hour sessions with a total of 145 agric. professionals in attendance.
  23. Weil, Ray. 2014. Panel on Innovations in Cover Crops. Meeting of the Minds. Lancaster, PA. 29 October 2014. 100 farmers and agric. professionals and press reporters in attendance.
  24. Weil, Ray. 2014 Impacts of Cover Crops of Yields. Invited Keynote talk at the 19thAnnual Cover Crop Field Day at Groff Farm, Lancaster, PA. 29 October 2014. 100 farmers, professionals and reporters in attendance.

 

Professional meetings

  1. Hirsh, Sarah M. and Ray Weil. 2018. Deep soil nitrogen capture and recycling by early planted, deep-rooted cover crops. American Society of Agronomy. Annual International Meetings. Baltimore. 6 Nov 2018.
  2. Weil, Ray. 2018. Taking Cover Crops to the Next Level to Maximize Multiple Benefits Invited Keynote Address. Annual Conference of the North East Cover Crop Council. November 14-15, 2018. State College, PA.
  3. Hirsh, S.M. and R.R. Weil. Poster presentation- Early-planted cover crops to scavenge and recycle deep soil nitrogen. University of Maryland AGNR Cornerstone Event Global Challenges: Building Healthy Food Systems. 4 October 2018. College Park, MD.

  4. Hirsh, Sarah M. and Ray Weil. 2017. Tracking deep soil nitrogen in cover crop systems: a N-15 isotope study. Soil Science Society of America/American Society of Agronomy. Annual International Meetings. Tampa. 23 Oct 2017.

  5. Weil, R. 2018. Keynote address: Roots run deep in cover crop science. Midwest Cover Crops Council Annual Meeting. Fargo, ND. https://www.dropbox.com/s/fj4jh9ho6ajb1jm/Roots%20Run%20Deep%20in%20Cover%20Crop%20Science_Ray%20Weil.pdf?dl=0
  6. Hirsh, Sarah M. and Ray Weil. 2017. Using cover crops to capture and recycle deep soil N: on-farm experiments. Soil Science Society of America/American Society of Agronomy. Annual International Meetings. Tampa. 24 Oct 2017.
  7. Hirsh, Sarah M. and Ray Weil. 2017. How much nitrogen is left in the soil profile after summer annual crops? A deep N survey on mid-Atlantic farms. Soil Science Society of America/American Society of Agronomy. Annual International Meetings. Tampa. 23 Oct 2017.
  8. Weil, Ray, Sarah Hirsh, and Fang Wang, 2016. Looking Deeper for Impacts of Soil Management. Soil Science Society of America/American Society of Agronomy. Annual International Meetings. Phoenix, Arizona. 7 Nov 2016.
  9. Hirsh, Sarah M. and Ray Weil. 2015. Isotopic Evaluation of Deep Soil Nitrogen Uptake by Cover Crop Systems. Soil Science Society of America/American Society of Agronomy. Annual International Meetings. Minneappolis, MN. 18 Nov 2015.
  10. Weil, Ray. R. 2014. Cover Crops – Tools for Sustainability in the NE USA. Invited paper (270-6) in Symposium–Cover Crops and Soil Health, Tuesday, November 4, 2014. International Meetings of the Soil Science Society of America, Long Beach , CA. 2-5 November 2014. https://scisoc.confex.com/scisoc/2014am/webprogram/Paper86657.html
Milestone #2 (click to expand/collapse)
What beneficiaries do and learn:

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.

Proposed number of farmer beneficiaries who will participate:
20
Actual number of farmer beneficiaries who participated:
19
Actual number of agriculture service provider beneficiaries who participated:
3
Status:
Completed
Date Completed:
October 29, 2016
Accomplishments:

In order to assess how much N remained after growing summer crops, we took deep (210 cm) soil cores in August-September in transects on 14 farms in 2014 and 7 farms in 2015. In 2016, we took the soil cores from side-by-side corn and soybean fields on 4 farms to compare the soil profile for soybean and corn fields. During the three years, 29 total deep soil cores were taken in 29 fields, including 11 fields with Coastal Plain parent material soils in MD and 18 fields with residual parent material soils in MD and PA.

Milestone #3 (click to expand/collapse)
What beneficiaries do and learn:

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.

Proposed number of farmer beneficiaries who will participate:
40
Actual number of farmer beneficiaries who participated:
28
Actual number of agriculture service provider beneficiaries who participated:
3
Status:
Completed
Date Completed:
June 2, 2016
Accomplishments:

Between the 2014-15 and 2015-16 growing seasons, 28 farmers set-up replicated plots of cover crops. Most of these included four treatments: 1) Forage radish, 2) a winter cereal (e.g., rye, triticale, wheat, oats), 3) Mixed cover crops (radish, winter cereal, usually clover), and 4) No cover control; each treatment was replicated 3-4 times. We were able to collect biomass samples within replicated treatments from 11 cover crop trials in the 2014-15 season and 7 cover crop trials in the 2015-16 season.

We were able to collect deep soil cores within replicated treatments from 7 cover crop trials in the 2014-15 season and 6 cover crop trials in the 2015-16 season.

Milestone #4 (click to expand/collapse)
What beneficiaries do and learn:

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.

Proposed number of farmer beneficiaries who will participate:
4
Actual number of farmer beneficiaries who participated:
7
Actual number of agriculture service provider beneficiaries who participated:
3
Status:
Completed
Date Completed:
October 31, 2016
Accomplishments:

We assessed corn growth and yield following cover crop treatments for various fertilizer rates. In 2015, three farms planted cover crops into corn with various N fertilizer rates; corn yield was measured for each plot/subplot. In 2016, 6 farms planted cover crops into corn, 4 had various N fertilizer rates. On 5 farms (corn failed on farm 6 due to deer pressure), corn biomass samples and height measurements at the V5 stage, PSNT soil samples, and yield was measured for each plot/subplot.

Milestone #5 (click to expand/collapse)
What beneficiaries do and learn:

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

Proposed number of farmer beneficiaries who will participate:
8
Actual number of farmer beneficiaries who participated:
3
Actual number of agriculture service provider beneficiaries who participated:
1
Status:
In Progress
Accomplishments:

Field-days (approx. 295 total attendees)

  1. Hirsh, Sarah and Ray Weil. 2017. Field-day: Getting the most from cover crops. Laurel, MD. 1 November 2017. 40 in attendance (17 MD Dept of Ag or USDA, 16 University of Maryland, 4 farmer, 3 other).
  2. Graybill, Jeffrey. 2014. Field day at a Lancaster County cooperator’s. Quarryville, PA. 12 November 2014. 15 in attendance.
  3. Weil, Ray and Natalie Lounsbury. 2014. Field day at Cedar Meadow Farm. Lancaster, PA. 30 October 2014. 240 in attendance (40 min field day talks to 8 groups of 30 farmers, professional and reporters).

Milestone Activities and Participation Summary

Educational activities:

4 Journal articles
4 On-farm demonstrations
11 Published press articles, newsletters
34 Webinars / talks / presentations
3 Workshop field days
6 5 videos, 1 podcast

Participation Summary:

1057 Farmers
110 Number of agricultural educator or service providers reached through education and outreach activities

Learning Outcomes

54 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
20 Agricultural service providers reported changes in knowledge, skills, and/or attitudes as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

We have had direct feedback from at least 15 farmers who have said they learned about the importance of getting cover crops established earlier than their used to and have applied this knowledge by planting early cover crops, often mixtures, to a total of 20,000 acres of land in the mid-Atlantic.

Performance Target Outcomes

Target #1

Target: number of farmers:
250
Target: change/adoption:

plant early radish/rye covercrops

Target: amount of production affected:

25,000 acres

Target: quantified benefit(s):

reduce N leaching by 2,000,000 lbs

Actual: number of farmers:
22
Actual: change/adoption:

Modified cropping systems to aim at earlier planting of cover crops by using early maturing crop cultivars and/or using methods of seeding earlier such as aerial seeding int standing crops.

Actual: amount of production affected:

more than 13,000 acres in Maryland and several 1000 acres in PA.

Actual: quantified benefit(s):

Early planted cover crops reduced overwinter and spring nitrate in leaching water compared to traditional timing of cover crop planting.

Performance Target Outcome Narrative:

From the start of the project we had an exceptional interest and response to our call for cover crop farm trial collaborators, with over 30 farmers interested in participating. Between 2014 and now, a large local and national audience of farmers have learned about the basic early cover crop-planting nitrogen-capture concepts of our project via 24 presentations at extension meetings and events, 8 presentations at professional meetings, 3 field-days, 2 webinars, 6 productions of online videos/podcasts, 9 publications in Newsletters or journals, and through being featured in 6 farm magazine articles. There were a total of approximately 2,070 people who attended our presentations at Extension meetings and field-days. This does not include people who watched our webinar or videos, attended our talks at professional conference meetings, or read about our work in newsletters and farm magazines.

 

We have numerous personal communication accounts that farmers are adapting earlier plated cover crops as a results of our research. In addition, we conducted a survey after our 1-Nov 2017 field-day. For the statement “This field-day increased the chances that I will aim to plant cover crops by early September in future growing seasons or encourage others to do so”, 23/27 survey responders indicated that they “agree” or “strongly agree”, while the remaining 4 survey responders did not write a response. In order to determine state-wide potential impacts of our research, we looked at the statistics for the number of Maryland acres that had early-planted forage radish alone or in a mix. We used this proxy since our research has been encouraging farmers to include early-planted forage radish as a cover crop to capture deep soil N and help prevent immobilization of N in the spring. The Maryland Department of Agriculture Cover Crop Program statistics indicate that the total number of radish planted alone or in mix by 15-September planting date is trending up: 2014-2015 = 13,248 acres, 2015-2016 = 13,055 acres, 2016-2017 = 16,117 acres, 2017-2018 = 18,456 acres. (Note, that in 2017-2018 the radish alone or in mix cover crop planting date was by 1-Oct, not 15-Sept as in the three previous years.)

10 Farmers changed or adopted a practice

Additional Project Outcomes

3 Grants applied for that built upon this project
2 Grants received that built upon this project
$285,000.00 Dollar amount of grants received that built upon this project
30 New working collaborations
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.