Research components:
1. Survey Maryland cover crops in October of 2021 to determine growth-stage, biomass and degree of N-deficiency.
2. Split plot randomized design with 4 replications on two soils for 2 years; subplots are N at 0, 15 and 30 lbs/acre and main plots are cover crop types (weeds only, rye, radish, or mixture) inter-seeded into standing corn late-August/early-September (as proven successful in previous research).
3. On-farm strip trials with two treatments (no N v. 20 lbs N/acre) applied on early-planted farmer-choice cereal, brassica or mixed cover crops (inter-seeded into early corn hybrid). Measure soil nitrate (0-6 and 6-12 inches deep Aug. 20 and Sep. 20), percent groundcover (using CANOPEO), biomass and N uptake at end-of-November and end-of-April. Measure following soybean yields, using calibrated yield monitors. Data-loggers to monitor soil moisture at 6 and 30 inches depth to quantify water-conservation, nutrient cycling and compaction alleviation benefits to soybeans from enhanced cover crops growth.
4. Develop in-field nitrate-test to predict where cover crops nitrogen fertilization is justified. Data from cover crop nitrogen-response (biomass and nitrogen-capture) will be used to model relationship between late-summer soil-nitrate and biomass/nitrogen-capture responses by cover crops to N application and rate. Based on PSNT model, we expect there to be a threshold soil nitrate level below which N fertilization is justified.

Overall goal is greatly enhanced effectiveness of Northeast cover cropping, especially where manure application is rare and/or soil texture is coarse. We plan to determine extent of nitrogen-deficient cover crops and whether small nitrogen application in fall can increase cover crop benefits in winter and spring. Also develop a practical in-field nitrate-test determining where nitrogen fertilization of cover crops is justified. Results will be developed and shared with farmers, advisors and cover crop policymakers.

Update:
Fertilizing cover crops – do you have to put some in to get more out?
August 2021 Progress Report to the Maryland Soybean Board


As this is a winter cover crop-focused project, most of the activity will take place after the reporting period for this progress report. In the initial months of this funding cycle, we did analyze samples collected from last year's research. As mentioned in the final report from last year's project, the cover crops were fertilized rather late due to wet weather and insufficient growing degree days were available for the cover crops to respond to the applied nitrogen. This was reflected in both the small gain in the dry matter that was re[orted in the final report from last year, and now, in the small gain in nitrogen concentration in the tissue (from 1.9% N without fertilizer to only 2.1% N with 15 lbs N/acre). This year we plan to establish the cover crops earlier and apply the fertilizer much earlier so that there will be at least a month of good growing weather during which the cover crops can respond to the applied nitrogen if needed.
We have recently contacted farmers on the Eastern Shore in Caroline county who are willing to host research on their fields of soybean and corn on sandy soils where nitrogen limitations are most likely. Last year we found it was prohibitively complicated to ask farmers to apply strips of low levels of fertilizer onto their aerially-seeded cover crops before harvest. Therefore this year we will establish replicated small plots within the commercial farms’ established cover crops in cornfields before harvest. We will collect composite soil samples from 0 to 15 and 15 to 30 cm (1 ft) for analysis of soluble nitrate prior to applying any material. We will then apply the fertilizer by hand as urea dissolved in water to plots receiving either 0 or 15 lb of nitrogen per acre. The plots receiving zero N will receive the water without nitrogen in it.
These plots will be flagged and then the cover crop growth measured after corn harvest at the end of the cover crop growing season in November. The nitrogen in the tissue will be measured and the N uptake will be calculated to see if the added nitrogen resulted in a net increase in the capture of nitrogen that otherwise would have leached over winter.
Similar plots will be established at Central Maryland research and education center (CMREC) on both silty and sandy soils. We are aiming to have a total of 40 to 50 discreet sites that can be used to assess the N application practice.
If there is a significant impact on cover crop growth by the applied nitrogen we will mark these plots and follow up the following spring to determine if there is an early soybean seedling response to this enhanced nitrogen-containing cover crop.

Update:

View uploaded report

Update:
In this study at two sites on contrasting soils, we have been monitoring the leaching of nitrogen using suction lysimeters all winter long and into spring. We have overcome some issues with getting samples under some soil conditions by installing and modifying the lysimeters. The samples from the lace emitters are still being analyzed for nitrogen and phosphorus using the Auto analyzer in our lab. Cover crop biomass was sampled and measured in late November and early December of 2021 to document the fall nitrogen uptake. A peer-reviewed paper in the journal of environmental quality was recently published that shows that reductions in nitrogen loss during winter and spring are driven by the amount of nitrogen taken up in late fall.

This spring in plots slated to be planted to soybean, we are imposing early medium, and late cover crop termination dates. The early termination was accomplished on April 11th, 2022. The mid termination will be accomplished in early May simultaneous with soybean planting. And the late termination will be performed a week to 10 days after soybean planting.

Slugs can cause a great deal of damage to young seedlings of soybeans and corn. Some farmers are concerned that cover crops may make slug damage worse, especially the practice of planting green. As part of the planting green study, we are monitoring slug populations and damage in soil conditions that may affect these factors. In early April we installed 48 slug traps and collected soil moisture, soil surface temperature, and data on slug numbers on two dates. The slug monitoring activity will intensify as we get close to planting and for the two weeks following planting. We accept to complete our slug monitoring in early June and couple that with measurements of soybean stand density and growth in June as well as final yields next fall.

We propose that, under Maryland conditions, small fertilizer applications may stimulate cover crops to provide improved net water-quality, soil-conservation, carbon and soybean yield benefits. Currently, fertilizing cover crops in fall with N is not allowed by the MAC cover crop program, but if we produce sufficient data that showed the above hypotheses were true, then it’s likely that MDA would tweak the program to allow it under appropriate circumstances (e.g., below a certain topsoil nitrate threshold). The fall soil nitrate threshold may be similar to that proposed by Maryland research (Forrestal et al., 2014) on a pre-plant soil NO3–N test for winter wheat to help identify field where starter N will produce economic returns and reduce potential NO3–N leaching losses.

Knowledge gaps we propose to address include: 1) How widespread are poorly functioning nitrogen deficient cover crops? 2). Will a small application of nitrogen stimulate deeper root growth so cover crops can enhance the net nitrogen capture by an amount substantially larger than the nitrogen applied? 3). How can we determine where and how much nitrogen application to cover crops would be justified? Several papers documented successful use of a fall nitrate test for fall application of nitrogen to winter wheat showing that when nitrate-N in top foot of soil is less than 9 ppm, fall nitrogen will increase wheat yields. We hypothesize a somewhat similar but earlier nitrate test in late-August/early-September could predict the value of a small nitrogen application shortly after cover crop seeding, especially when interseeding early into high nitrogen uptake and high C/N ratio crops like corn.