Tag: nitrogen

Managing Nitrogen in Hay and Pasture Crops

This article is part of our Summer 2021 Newsletter by Kirsten Workman.

Perennial crops can be hard to target for nitrogen (N) applications, as the decision often depends on stage of establishment and species composition. Both factors change over time and adjustments should be made from season to season, or even within the same season. Below are factors to consider when trying to target the most efficient use of manure-based and purchased nitrogen in your perennial crops.

Species
Grass and legumes (alfalfa, clovers, trefoil) each have very different nitrogen needs. Grass crops will respond readily to both manure-based and fertilizer-based nitrogen. Grass species not only reward adequate N supply with increased yield, but also increased quality. Applying up to (and sometimes over) 200 pounds of nitrogen per acre on grasses almost always yields an economically viable response. Legumes, on the other hand, do not need additional nitrogen from manure or fertilizer. Legumes have a fascinating symbiotic relationship with a soil-borne bacteria known as rhizobia. Rhizobia fixes atmospheric nitrogen in nodules on the roots that it colonizes, and then transforms it into plant-available nitrogen. As a result, a clear stand of clover or alfalfa would not need additional nitrogen fertilizer or manure to reach maximum yield or quality. However, very few hay or pasture stands in Vermont are 100% grass or legume, and most farmers want a combination to maximize the benefits of species diversity and production. In these cases, we adjust the recommended nitrogen application rate to maximize production but still encourage the legumes in the stand to fix nitrogen. Fixing nitrogen is a trade-off for the plant, which shares carbohydrates with the rhizobia. This means that if extra nitrogen is available, plants can become “lazy” and not invest energy in that association. Additionally, a mixed stand with legumes that is treated with N up to the grass rates will encourage a shift of dominant species towards grasses as the grasses begin to outcompete the legumes.The table below shows how the nitrogen recommendations change depending on the legume content of the stand. In this case, grass is defined as any stand with less than 30% legume.

Split Applications
Because N is mobile (both in the soil and the plant), it is important to split applications to maximize uptake by the plant and reduce losses. With hay and pasture, fortunately, we take multiple harvests and have the opportunity to split applications into reasonable amounts to be utilized by the crop over the course of the season:
• Grass: split applications into 50 to 75 pounds per acre increments, ideally following each harvest.
• Mixed stands (30-60% legume): one single 40-pound application; if applied in early spring, a second 40-pound application may be beneficial.

N During Establishment (New Seedings)
Nitrogen fertility is not recommended for establishing legumes and mixtures. The exception is when a small grain is seeded with the legume or mixture. In this case, a 30 pound per acre application is recommended to get the companion crop up and growing ahead of the weeds. For a new grass seeding, the following recommendations apply:
• 50 pounds per acre for a spring seeded crop.
• If more than one harvest occurs in the seeding year, a second application of 40 to 50 pounds should be applied.
• Late summer seedings only need 30 pounds per acre.

Reducing Needed N With Maintenance of Legumes
If nutrients are limited and you are trying to reserve manure-based nitrogen for crops like corn or pure grass, take steps to maintain legumes in your stand. This will reduce or eliminate the need for manure or purchased nitrogen. Strategies to help maintain legumes include:

Maintain higher soil pH (6.8).
• Leave adequate crop residual between cuttings, but especially after your last cutting.
• Consider a less intensive cutting schedule to ensure adequate regrowth between harvests. Time your last harvest to allow for adequate regrowth before frost.
• Monitor and maintain adequate potassium and boron levels in the soil.

At the end of the day, managing nitrogen resources on hay and pasture crops will pay off. A well-fertilized grass crop will pay you back in most years. However, manure is especially tricky, as it is easy to overapply N on mixed stands and this can contribute to legumes becoming less competitive, leaving the stand open to weeds. If you want to maintain legumes, back off on N and manage for legumes. Split applications for the best effect and, if possible, utilize low disturbance injection to really make the most of N in manure applications.

Making nutrient management decisions systematically on your farm and keeping good records is all part of having a nutrient management plan. Even without a formal plan, you can make informed decisions based on these basic principles. We are here to help farmers optimize yields and manage their inputs wisely.

*All recommendations are from “Nutrient Recommendations for Field Crops in Vermont” (September 2020, https://go.uvm.edu/br1390). For specific recommendations, consult your crop adviser or call Kirsten for more information. If you would like help managing nutrient application rates, or have other related nitrogen questions, contact Kirsten at kirsten.workman@uvm.edu or 802-338-4969 ext. 347.

Keeping the Nitrogen in Manure

By Kirsten Workman (as published in our Spring 2021 Newsletter)

While manure often gets a bad rap, it gives farmers who raise livestock a valuable resource to meet the nutrient needs of crops and supplies organic matter to the soil in a way unmatched by commercial fertilizers. Utilizing manure effectively maximizes fertility, reduces runoff, and economizes spreading costs. Manure’s nutrient content varies with on multiple factors such as moisture, livestock, bedding, storage and feeding strategies. You should analyze manure annually to value these nutrients, including nitrogen (N).

Nitrogen in manure comes in two forms: organic and inorganic. The organic is a slow release N, broken down by soil organisms into plant-available forms, a process called mineralization. Most mineralization happens in the first year of manure application, and will continue slowly for one or more additional years. The inorganic portion (expressed as ammonium-N or NH4+ on your test results) is readily plant available, acting like a fertilizer application. Like fertilizer, it can be prone to losses. Liquid manure has much more readily available N, meaning it has the benefit of being available but also must be managed accordingly. Well-timed and incorporated manure optimizes N for your crop and minimizes losses, both to the air and water.

Timing. Spreading manure on living plants is the simplest way to retain available N. Spreading in the fall instead of spring can drop the amount of N available to a crop by as much as 55%, depending on dry matter content and incorporation. Manure applied in the fall has far more opportunity for loss before utilization, than manure applied in May. Volatization (loss to the air), leaching and runoff are all more likely to occur when applying on bare soil between annual crops, or even when hay/pasture is dormant, particularly with rain and snowmelt. This is not only an environmental issue, but also a farm profitability issue. Purchased nitrogen is a significant cost, so the more efficient use of manure the better.

Incorporation. Getting manure below the soil surface and into the root zone is key to retaining N. The longer the delay in time between application and incorporation, the greater the loss of ammonia volatization (NH3+). There are several ways to incorporate, but timing is critical. Incorporation methods include tillage, injection with specialized equipment, and even gentle rainfall (as long as it does not cause runoff).

Other considerations for retaining nitrogen from manure include high soil organic matter and cation exchange capacity, both the pH of soil and manure below 7, little or no wind, cool temperatures (but not frozen soils), moist but not saturated soils, and applying to a living crop including a cover crop. This chart illustrates the relationship between broadcast, incorporation, and nutrient loss:

Highest Loss to Lowest Loss in order –

Broadcast on surface without incorporation Broadcast; Incorporation 1 to 7 days after application Broadcast; Incorporation < 24 hours after application; Immediate incorporation or injection.

Manure Math. Using the book value for liquid dairy manure 8,000 gallons applied in the spring, immediate incorporation = 100 lbs. of available N 8,000 gallons applied in the fall with no incorporation = 52 lbs. of available N for your crop.

Book value – See “Nutrient Recommendations for Field Crops in Vermont” (http://go.uvm.edu/nutrecs; PDF, revised 2018, University of Vermont). Book values for manure are on page 24, Tables 15 and 16. Manure N availability changes with timing and incorporation are on page 25, Tables 17 and 18.

Need to test your manure? Visit the UVM Agricultural and Environmental Testing lab website (http://pss.uvm.edu/ag_testing) for forms and sampling instructions. You can also call us at 802-388- 4969 if you would like a manure jar sampling kit. Kits will be left in a box outside our office doors and can be resubmitted there. You must let us know ahead of time when you plan to drop it off because manure samples have to be frozen in a timely manner to retain N content. The best time to sample manure is at or near spreading.

Citations:

1. Nutrient Recommendations for Field Crops in Vermont (BR 1390.2). University of Vermont Extension, 2020. https://www.uvm.edu/sites/default/files/Northwest-Crops-and-Soils-Program/2021%20Events/NMP%20Class/NutrientRec_BR1390.3_Sept2020.pdf

2. Manure application methods and nitrogen losses. University of Minnesota Extension (2018). https://extension.umn.edu/manure-management/manure-application-methods-and-nitrogen-losses

3. Conserving Ammonia in Manure (CDLE Pub. 09-50). UMass Extension (2009). https://ag.umass.edu/crops-dairy-livestock-equine/fact-sheets/conserving-ammonia-in-manure

Resources:

 Taking a Manure Sample: https://www.uvm.edu/sites/default/files/media/Manure3.pdf

UVM Manure Sampling Analysis at the Agriculture and Environmental Testing Lab: https://pss.uvm.edu/ag_testing/

More information about manure sampling in Vermont for 2021: https://cvfc-vt.com/2021/03/nutrient-management-minute-manure-sampling/

Add Some Spring in Your Step with Our Spring Newsletter (2021)

Read the whole newsletter as a pdf.

In this Issue:

Nitrogen: An Overlooked Macronutrient

By Kirsten Workman, Agronomy Specialist

This article was originally printed as part of our Fall-Winter 2020 Newsletter.

In the Champlain Valley, we spend a lot of time and effort managing phosphorus (P). Rightfully so, as it is the pollutant behind algae blooms in Lake Champlain. Our clay soils often bind to it tightly, making it less available to plants when they need it most, and it isn’t perfectly balanced with crop needs in our manure applications. All of this makes it a tricky nutrient to manage. However, we have taken our eye off another primary macronutrient as a result.

Nitrogen (N)

Nitrogen is the dominant macronutrient in agriculture. While it hasn’t had top billing here lately, it is probably the most important and studied nutrient from a crop production standpoint. Without adequate nitrogen, yield and quality can be compromised. Nitrogen drives vegetative growth and protein content, having a direct correlation with forage value in livestock systems and nutrition in food crops. In watersheds where the receiving surface waters are marine (e.g., the Connecticut River which drains to Long Island Sound, or the Mississippi River which drains into the Gulf of Mexico), nitrogen causes water quality issues like eutrophication and algae blooms – the same problems that phos-phorus causes in Lake Champlain. Generally, N is much more mobile than P in soil. Because of this, it is often prone to loss. The primary pathways for N loss are:

• Volatilization – N turns into ammonia gas and dissipates into the atmosphere. (Applying nitrogen when temperatures are cool, a light rain is expected to facilitate incorporation, or by physically mixing it with the soil can reduce volatilization risk. Nitrogen stabilizers can also inhibit this reaction.)

• Denitrification – Occurs in saturated soil conditions when nitrate turns into N2 and N2O gas. (Good soil drainage, high soil organic matter and proper pH, split N applications and nitrogen stabilizers can help prevent excessive denitrification.)

• Runoff – Carries nitrogen from manure, fertilizer and eroded soil off the field into ditches, creeks, rivers and streams. (Field buffers, reducing erosion, properly timed nutrient applica-tions can reduce N runoff.)

• Leaching – When N can’t attach to soil particles or be taken up by plants, it easily leaches downward with soil water toward groundwater and even out tile drain outlets. This is much more common in sandier soils that do not have the water holding capacity of heavier soils like clay and loam. (Applying manure and nitrogen fertilizer during the growing season, proper nutrient management, avoiding fall-killed sod, and utilizing cover crops to increase nutrient uptake can decrease the amount of N leaching.)

A primary reason nitrogen is analyzed so much, is that farms can often see immediate impacts from over or underutilizing nitrogen. In addition, good N management can also save a farm a significant amount of money in fertilizer savings. This often gets overlooked when N prices are low (as they have been recently), and farms are prone to “insurance applications” of N to make sure they aren’t shorting their crops. With prices averaging between $0.28 to $0.41 per pound of N¹ (depending on the type of fertilizer), it can seem like a cheap way to ensure good yields and quality. However, in a time of tight margins and increasing environmental regulation this can be an unsustainable way to operate. And if you are an organic producer, the $3 to $5 per pound cost of N fertilizer means you probably already understand the value of farm-produced nitrogen, and being as efficient as possible with those homegrown and purchased sources of N². In 2018, Vermont agricultural producers utilized almost 10,000 tons of nitrogen fertilizer, with another 7,000 tons of multi-nutrient fertilizers that likely had some portion of nitrogen³. In comparison, during this same time period, 15 tons of phosphate fertilizer was sold for agricultural use.

In the coming months, we’ll dig deeper into the world of nitrogen and see where we can do a better job providing our crops with adequate nitrogen without breaking the bank or causing unintended environmental consequences. We will consider:

– Corn and Nitrogen: Managing N in corn silage crops and how do we know if we’ve overdone N applications? A Caring Dairy Prove-It Project case study on Corn and Nitrogen.

– Managing N in hay and pasture crops and letting nature pay your fertilizer bill.

– Manure and N management – how do we make the most of the nitrogen in our manure?

– HomegrowN – taking credit for all the nitrogen on your farm, not just the stuff you purchase outright.

If you have a question about N fertilizer or manure management you can also contact Kirsten at kirsten.workman@uvm.edu.

One tool available to producers to evaluate N management strategies is the Corn Stalk Nitrate Test (CSNT), seen here on the Gosliga Farm (Addison, Vt.). It is designed to be a report card assessment at the end of the season to help modify and improve N management strategies on the farm in future years. The CSNT is a useful tool that indicates whether the nitrogen supply for that year was low, marginal, optimal, or in excess of what the corn needed this year. Corn that has received inadequate N will remove N from the lower cornstalk and leaves during the grain filling period. Plants that have received more N than needed to attain maximum yields tend to accumulate nitrate-N in the lower stalks at the end of the season.

Citations:

¹ August 2020 (Progressive Farmer by DTN), https://www.dtnpf.com/agriculture/web/ag/crops/article/2020/08/12/fertilizer-prices-remain-lower-first

² Organic N price based on estimated costs of bulk sodium nitrate (a.k.a. Chilean nitrate)

³ VAAFM, 2018-2019 Vermont Fertilizer Analysis Report https://agriculture.vermont.gov/sites/agriculture/files/documents/PHARM/Fertilizer/Annual%20Report%20Fertilizer%202018-2019.pdf

RESOURCES: https://extension.missouri.edu/publications/wq252 http://cceonondaga.org/resources/nitrogen-basics-the-nitrogen-cycle