Nitrogen contribution from cover crops for vegetable crop uptake

Final report for ONE16-281C

Project Type: Partnership
Funds awarded in 2016: $11,067.00
Projected End Date: 12/31/2017
Region: Northeast
State: Massachusetts
Project Leader:
Katie Campbell-Nelson
Cornell Cooperative Extension, Columbia and Greene Counties
Expand All

Project Information

Summary:

The goal of this trial was to find out if farmers could provide sufficient nitrogen for their cash crops using leguminous cover crops alone or with reduced nitrogen fertilizers and no additional phosphorus. We also hoped to increase the use of the soil nitrate test as a tool for monitoring nitrogen dynamics in vegetable fields. We planted cover crops on six MA farms in a randomized complete block design. In early September 2016 plots were seeded using different implements on each farm with the following treatments: 1) No Cover Crop, 2) Winter Rye (70lbs/A) and Hairy Vetch (20lbs/A), 3) Farmer Choice (Table 1).  The cover crops were sampled for biomass and incorporated using different implements in late May 2017. Two weeks later each plot was split with half receiving 60 lbs N/A in the form of Chilean Nitrate and the other half receiving none. Four weeks after incorporation, a cash crop of the farmer’s choice was planted on each farm. We sampled soil nitrate 6-12” deep every two weeks beginning on the day of incorporation in late May until eight weeks after in late July. Finally, we measured yield of the cash crop planted into each of these treatments. Results of the trial were shared at an on-farm Twilight Meeting in September, 2017 to 50 growers and agricultural service providers and at the New England Vegetable and Fruit Conference in December, 2017 to 200 growers and agricultural service providers. As a result of this project, the participating farmers implemented one or more of the following practices:

  • Transplant most crops 4 weeks after cover crop incorporation to match peak N release with peak N demand by the crop.
  • Direct seed most crops 2 weeks after cover crop incorporation to match peak N release with peak N demand by the crop.
  • Experiment with less nitrogen fertilizer and use no phosphorus fertilizer in soils with optimum P levels.
  • Plant new cover crop mixes including forage radish, crimson clover, and Fria annual ryegrass.
  • Take more soil Nitrate tests to monitor N-dynamics in vegetable fields.
  • Conduct their own research and participate in on-farm research.

 

Introduction:

Years of research on nitrogen contributions from cover crops to following cash crops have been conducted all over North America, but farmers still struggle to manage timely nitrogen (N) release in their soils to match cash crop peak demand because there is such great variability in soil type, microclimate, and farm cultural practices. Managing N demands of vegetable crops on diversified farms in New England is particularly challenging given the high crop diversity with different nutrient needs (amounts and timing). Prior research in the 1980's by Dr. Fred Magdoff resulted in the development of the Pre-sidedress Nitrate-nitrogen Test (PSNT) as a tool for nitrogen management in corn. The test has since then been applied to other vegetable crops such as cabbage, tomato, and pepper for making nitrogen sidedress decisions. Despite this additional research, the PSNT is still not often used by vegetable farmers in New England to manage N fertility.  We believe that the same test may be used effectively to monitor N mineralization from various cover crops to improve timing of N contributions to vegetable cash crops and reduce the use of commercial fertilizers even if it is not used to predict sidedress N applications. Because of the great variability in soil type, microclimate, and farm cultural practices, trials were conducted on multiple farms. There are over 1,400 vegetable farms in Massachusetts covering over 17,700 acres (USDA Agriculture Census, 2012) who could benefit from improved cover crop management, reducing N fertilizer use, and increase use of soil nitrate testing to monitor N release for cash crops. This project evaluated cover crop mixtures and reduced fertilizer applications with six diversified vegetable farmers to measure nitrogen availability in the spring to subsequent summer cash crops.

Project Objectives:

The main goals of this project are: 1) to expand evidence based N management for vegetable farmers who plant cover crops and 2) select cover crops with N mineralization rates that best match cash crop demands.

Project activities

Demonstration trials
Five farmers who participated in an August 2016 workshop conducted by the MA SARE state program titled “How to conduct an on-farm trial” were trained in implementing the specific trial for this project on their own farms in the Fall of 2016. The project team distributed cover crop seed at the beginning of the trial, assisted in cover crop establishment, and reviewed methods for rating % ground cover. At the time of cover crop incorporation in May of 2017, the team visited each farm again to collect biomass samples and provide training in PSNT sampling protocols to farmer collaborators. Experimental design was identical for all farms except for one “farmer choice” cover crop treatment in order to gather a large data set and to simplify implementation of this project.

Educational activities
Results of the trial were shared at an on-farm Twilight Meeting in September, 2017 to 50 growers and agricultural service providers and at the New England Vegetable and Fruit Conference in December, 2017 to 200 growers and agricultural service providers. Two collaborating growers shared their experiences with the trial. Events and results of this trial will be published in the Vegetable Notes Newsletter (2,700 subscribers). Event notifications were distributed to mailing lists such as: NRCS, Southeastern MA Agricultural Partnership (SEMAP) and the New England Vegetable and Berry Growers Association (NEVBGA). Trial results will be submitted to HortScience if conducted for 2 years.

Cooperators

Click linked name(s) to expand/collapse or show everyone's info
  • Samantha Corcoran
  • Julie Fine
  • Masoud Hashemi
  • Andrew Lawson
  • Kevin O'Dwyer
  • Kate Parsons
  • Paul Peckham
  • Edwin Matuszko
  • Laura Tangerini
  • Maria Topitzer
  • Ryan Karb

Research

Materials and methods:

We planted cover crops on six MA farms in a randomized complete block design. In early September 2016 plots were seeded using different implements on each farm with the following treatments: 1) No Cover Crop, 2) Rye (70lbs/A) and Vetch (20lbs/A), 3) Farmer Choice (Table 1). The cover crops were sampled for biomass and C:N ratios, and incorporated using different implements in late May 2017. Two weeks later each plot was split with half receiving 60 lbs N/A in the form of Chilean Nitrate and the other half receiving none. Four to six weeks after incorporation, a cash crop of the farmer’s choice was planted on each farm. We sampled soil nitrate 6 to12” deep depending on how rocky the field was every two weeks beginning on the day of incorporation in late May until eight weeks after in late July. Finally, at the end of the season in we measured yield of the cash crop planted into each of these treatments. Following is a detailed timeline of our project activities:

Appendix: 2016 Annual Report Nitrogen contribution from cover crops for vegetable crop uptake

Date Project Activities
September 2016 Plots were seeded between August 26th - September 8th, 2016 on 6 farms across MA (see Fig.1 map attached). A baseline soil sample was taken from all locations before seeding and we expected differences in pH, organic matter, and starting soil nitrate levels among locations to affect the mineralization of N in this trial next season (Table 1 in Appendix linked above).  
September 2016 – May 2017 Percent cover was rated visually by the farmers and project staff in October and November, 2016. Differences were observed among treatments within and between farms. Farmers guessed that their ‘Farmer Choice’ treatments often had better coverage or more biomass than the winter rye/ hairy vetch treatment and wondered how weed coverage would affect N mineralization next season. (Figure 3 a and b in Appendix linked above)
October 2017 Biomass samples were taken from all plots with any plant matter that would winter-kill: annual weeds, oat, pea, tillage radish. Biomass was weighed and analyzed for nutrient content to calculate C:N ratios and total N becoming available over winter.
May 2017 We incorporated cover crops using different implements on each farm and collected the following data with farmers (biomass, tissue analysis (C:N ratio), first soil nitrate samples).
May-July 2017 Farmers and project staff took soil nitrate samples from each treatment biweekly (4 times over a period of 8 weeks) and delivered samples to UMass for analysis.
June-July 2017 We planted cash crops at each farm and rated vigor: 2 weeks and 4 weeks after transplant or germination.
August-October 2017 We evaluated yield on 3 out of 6 locations due to limitations in the farmer's crop plan.  Crop yield was evaluated for sweet corn on one farm and cabbage on 2 farms.
September 2017 We presented results of these trials to 50 farmers and agricultural service providers at an on-farm Twilight Meeting.
December 2017 We presented results of these trials at the New England Vegetable and Fruit Conference to 200 people along with farmers and educators from other states who conducted similar trials. 
Research results and discussion:

 

Farm

Farmer Choice (lbs/acre)

Cover Crop $/acre1

Cash Crop

Crop N needs lbs/acre

% Soil Organic Matter

2016 Fall NO3 ppm

Soil Type

Langwater

Oat (90), Pea (50), Vetch (40)

$308

Winter Squash

110-140

6.8

105

Charlton-Paxton fine sandy loam

Lyonsville

Fria rye (15), Crimson clover (15), Vetch (18)

$136

Winter Squash

110-140

2.9

25

Occum fine sandy loam

Many Hands Farm Corp

Summer 2016 seeded:
Sorghum Sudan (90)

Spring 2017 Seeded:
Oat (100), Pea (100)

$234

 

$251

Cabbage

160

6.2

5

Pootatuck fine sandy loam

Tangerini

Oat (90), Crimson clover (15), Vetch (18)

$205

Chard

105-130

3.4

30

Merrimac fine sandy loam

Twin Oaks

Fria annual rye (6), Crimson Clover (4), Tillage Radish (10)

$52

Cabbage

160

2.2

28

Deerfield loamy fine sand

UMass

Rye (60), Vetch (20), Tillage Radish (5)

$96

Sweet corn

100-130

1.7

20

Winooski silt loam

[1] The Rye (70lbs/A) and Vetch (20lbs/A) treatment cost $90/A.

Biomass and Tissue Analysis
Among all farms, Langwater produced the most biomass and plant available N from the Rye/Vetch treatment (139 lbs N/A), while Tangerini farm produced the most from their Farmer Choice Treatment (100 lbs N/A). Langwater and Lyonsville produced the most available N in their weed biomass (about 40 lbs N/A) compared to other farms. Carbon content was highest in the Rye/Vetch treatments affecting their N-mineralization rates.

Soil Nitrate
Nitrogen Mineralization Figures
Not surprisingly, there were statistically significant additional amounts of nitrates (NO3) in plots with additional fertilizer compared to those without on all farms and in most cases there were statistically significant aditional amounts of nitrates in plots with cover crops than those without. Peak nitrate release rates in the soil were measured 4-6 weeks after cover crop incorporation in all locations. We did not find the 'sufficiency ranges' of 25-30ppm soil nitrate to predict 'good' to 'excellent' yields in all cases.

Yield
Yields were highest from farmer choice treatments on 2 out of 3 farms (UMass and Matuszko) though not statistically different from the Rye/Vetch treatment. On one farm (Many Hands), yield was highest from the No-Cover plots and lowest on the Farmer Choice plots. This was surprising to us, but we hypothesize that the 6.2% organic matter in the soil contributed to the higher yields in the no-cover plots, while wet soils, sorghum sudan grass in particular, and minimal tillage contributed to the slow mineralization rates in the Farmer Choice plots.  In all 3 locations where yield was measured, ‘good’ to ‘excellent’ cash crop yields according to those published in the New England Vegetable Management Guide were achieved with a combination of cover crops and less than half the required N rates applied or in some cases only with the use of cover crops.

Discussion
Despite the overall trends in the data, varying soil type, microclimate, and cultural practices all affected the great variability in nitrate release rates and amounts from treatments on each farm. Therefore, we found the soil nitrate test to be a useful tool for monitoring N-mineralization on a field basis if not to predict N sidedress needs. 25-30ppm NO3 is considered 'sufficient' soil nitrate for most crops at the time a Pre-sidedress soil nitrate test (PSNT) is taken, typically 4-6 weeks after crop emergence (New England Vegetable Management Guide 2016-2017, Nitrogen Management Section.) Some farms achieved sufficiency ranges for their cash crops (Fig 1. UMass and Fig 2. Twin Oaks). Some farms did not achieve the sufficiency range due to poor cover crop establishment, high soil organic matter but wet soils with low mineralization rates (Fig 3. Many Hands) or poor cover crop establishment, low soil organic matter, and sandy soils with high mineralization rates (Fig 4. Lyonsville). Some farms exceeded the sufficiency range of NO3 required for their cash crops because of prior compost applications earlier in 2016 (Fig 5. Langwater) and an early spring 5-4-3 chicken manure fertilizer application of 25 lbs N/acre to the entire plot (Fig 6. Tangerini). Ultimately, the PSNT 'sufficiency range' did not predict whether or not a cash crop would achieve greater yields. Rather, we found that the soil nitrate test was best used to track the rate of mineralization in a field and that many factor affect this rate including: soil type, cover crop vigor and species, cultural practices such as methods of incorporation, environment, or fertilizers.

Research conclusions:

In this parable of the three bears (too much N, not enough N, and just the right amount of N), it may seem challenging to walk away with clear conclusions due to the diversity of results on each farm. However, we did find the soil nitrate test to be a valuable tool for monitoring this diversity on a field by field basis.

We would like to make the following tentative conclusions:

  • Cover cropping takes practice and finesse, but will pay off in the end. At $4.00 per lb/N for organic fertilizer ($434-660 per acre) or $0.85 per lb/N ($89.25-136 per acre) for conventional fertilizer, a farmer is saving themselves money by planting a nitrogen fixing cover crop. The cost of 60lbs N/A in this trial was $248 while most cover crop treatments cost less than that per acre (Table 1).
  • On 2 out of 3 farms, statistically similar, good yields were achieved by the Farmer Choice cover crop treatments and the No-cover fertilizer treatments receiving 60 lbs/A of commercial fertilizer.  This indicates that a leguminous cover crop mix can reduce the need for fertilizer applications by at least half for many crops.
  • It is possible to meet or exceed "sufficiency ranges" for cash crop N requirements with the use of cover crops or compost applications and high soil organic matter; no commercial fertilizer necessary.
  • Peak NO3 was released 4-6 weeks after cover crop incorporation or 2-4 weeks after additional N application on all farms. Growers can take an inexpensive soil nitrate (PSNT) test 4-6 weeks after incorporating cover crops to determine if they are in the sufficiency range for their cash crop (25-30ppm NO3), then make additional N applications if necessary or adjust their N management practices for the following year.
  • The soil nitrate test can be used to monitor N mineralization from the time of cover crop incorporation through harvest to make future management decisions.  For example, if a field has relatively high soil nitrate through the season and after harvest (greater than 25ppm), the farmer may use a cover crop at the end of the season to carry over some of that nitrogen to the following year, or consider reducing their fertilizer N use.

 

Participation Summary
10 Farmers participating in research

Education & Outreach Activities and Participation Summary

6 On-farm demonstrations
1 Webinars / talks / presentations
1 Workshop field days

Participation Summary:

220 Farmers
30 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:
  1. We hosted an on-farm Twilight Meeting in September, 2017 at the UMass Crop and Animal Research and Education Center in South Deerfield, MA where we shared the results of the 6 trials with 50 growers and agricultural service providers.
  2. We presented results of the 6 on-farm trials at the New England Vegetable and Fruit Conference on December 14th, 2017 in Manchester, NH to 200 farmers and agricultural service providers.
    1. Growing Our Own Nitrogen Presentation
    2. Conference proceedings (pp. 280-282)

Learning Outcomes

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

Farmers reported the following changes in key areas: greater knowledge of and an increased awareness of how to conduct on-farm research, how nitrogen mineralizes in their fields, and increased skills in managing nitrogen and cover crops. Specifically, participating farmers made one or more of the following changes on their farms:

  • Transplants most crops 4 weeks after cover crop incorporation to match peak N release with peak N demand by the crop.
  • Direct seed most crops 2 weeks after cover crop incorporation to match peak N release with peak N demand by the crop.
  • Experiment with less nitrogen fertilizer and use no phosphorus fertilizer in soils with optimum P levels.
  • Plant new cover crop mixes including forage radish, crimson clover, and Fria annual ryegrass. A surprising results was the use of late August seeded tillage radish (10lbs/A) for managing spring weeds.
  • Take more soil Nitrate tests to monitor N-dynamics in vegetable fields.
  • Conduct their own and participate in on-farm research.

Project Outcomes

10 Farmers changed or adopted a practice
1 Grant applied for that built upon this project
1 Grant received that built upon this project
$2,000.00 Dollar amount of grant received that built upon this project
1 New working collaboration
Project outcomes:

The goal of this trial was to find out if farmers could provide sufficient nitrogen for their cash crops using leguminous cover crops alone or with reduced nitrogen fertilizers and no additional phosphorus. We also hoped to increase the use of the soil nitrate test as a tool for monitoring nitrogen mineralization.

Assessment of Project Approach and Areas of Further Study:

More on-farm research on cash crop demand of nutrients is needed to increase farmer's adaptation of evidence-based N-management.

Information Products

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.