16 minute read
Managing nutrients in cold climates
Opportunities to avoid manure application during winter months can minimize losses and improve nutrient uptake.
by Eric Young
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Crop production in Northern regions is characterized by short growing seasons and seasonally high runoff potential. Soils warm slowly in the spring with extended periods of wetness, posing crop production and environmental risks.
Nutrient use efficiency (NUE) is the relative amount of applied nutrient that ends up in a crop. It varies widely by crop, weather, fertilization methods, and others factors.
Applying manure to actively growing crops (after hay cuttings or to cover crops, for example) or immediately prior to planting annual crops like corn can improve NUE and reduce losses. Methods of application also impact manure NUE.
From an NUE standpoint, applying manure in late fall, winter, and early spring (often termed the nongrowing season) is not ideal. Soils are generally wetter with higher runoff potential and depressed soil biological activity. In addition, freeze-thaw transitions have a major impact on runoff potential and nutrient movement. Frozen soils allow minimal infiltration and can elevate dissolved phosphorus (P) mobility to surface water with rapid snow melting.
Surface runoff and erosion processes drive both topsoil and P loss in many places. Mitigating surface runoff from field nutrient source areas is critical to maintain soil organic matter and crop productivity and for reducing nutrient runoff risk, particularly for farms
Control 5% solids
8% solids 15.4% solids
Figure 1. Dairy manure applied at the same rate (2,852 gallons per acre) and source but at differing solids content spanning the range of liquid to semisolid manure. Small plots were used to isolate and measure snowmelt runoff. Pictures by Eric Young and Jessica Sherman.
adhering to water quality regulations.
Snowmelt accounts for a substantial amount of the annual water budget and surface runoff in cold climates. While manure application to frozen, saturated, or snow-covered soils is discouraged in general for agronomic and environmental reasons, manure is still routinely applied under a wide range of weather conditions, including close to the onset and during the nongrowing season.
Many dairy operations have a limited number of fields that can reasonably receive manure and often have a need to fall-apply manure to fields with or without a cover crop. Fall-applied manure remains close to the soil surface where it is exposed to freezing temperatures followed by variable melting events as spring approaches. Manure nutrients in surface soil interact with melting snow, releasing nitrogen (N) and P.
Applying manure to a growing crop (hayfield or cover crop) using low-disturbance methods can reduce both soilbound and soluble nutrients. However, some level of nutrient runoff is inevitable, depending on the amount of runoff and soil N and P concentrations. Large storm events during the growing season can contribute to annual runoff losses, but losses during the nongrowing season are important to recognize in cold climates.
Available surface area for sorption and other nutrient attenuation mechanisms are compromised in frozen or partially frozen soils. The how (what method, rate, and incorporation level) and when of manure application in relation to weather and soil conditions is a critical aspect of trying to better predict runoff nutrient loss risk from manure.
The manure matters, too
While multiple field-related factors (soil type and drainage, hydrology, manure application method, crop system, and tillage intensity) affect
actual runoff and manure nutrient loss, manure itself also plays a role.
Livestock manure varies in physical and chemical form. In general, liquid manures (less than 6% solids) have lower nutrient content and behave more like a liquid than a solid, making them vulnerable to runoff losses under wet conditions. Manure’s flow resistance (viscosity) goes up rapidly when a higher solids content exists with a marked difference in form and ease of flow (Figure 1).
Since dry matter mass rises with solids content for a given manure source, total N and P rate applications also go up (per unit of volume applied). With this logic, applying higher solids content manure raises total nutrient application, but in a form less vulnerable to runoff flows. It is important to determine how changes in manure solids affect manure nutrient mobility and runoff nutrient losses when applied in different conditions.
Look for opportunities
While complex, modeling runoff nutrient losses, snowmelt, and other factors in cold climates has had recent success. A surface runoff P model (SurPhos) developed by Peter Vadas (USDA-ARS) and collaborators is one model that aims to simulate the snowmelt process and how it affects soluble P loss. Using 108 site years of field data, Vadas and others showed that winter manure application had a 2.5 to 3.6-fold larger runoff P loss compared to nonwinter-applied manure.
Applying at least some manure on frozen or snow-covered fields is still a fairly typical practice, particularly for farms without adequate storage. Researchers at USDA-ARS and Melissa Wilson at the University of Minnesota are investigating the effect of manure solids content on runoff N and P losses when manure is applied to a snowpack.
Results generally indicate that higher manure solids applied correspond to greater snowmelt runoff N and P concentrations and loading. However, the fraction of manure total P lost to snowmelt runoff was lower for semisolid manure compared to liquid manure, suggesting some possible influence of solids content on manure-P mobility in the snowpack.
Handling manure in cold climates is an evolving science. Farms should focus on applying manure closer in time to crop growth and to unfrozen soils without snow cover to the extent possible. New ways of applying manure before planting or to growing crops should also be considered.
Reconsidering time windows and crops that can receive manure while avoiding manure application to high-risk fields at times of high runoff risk can ultimately increase NUE. As a result, we can reduce environmental risk associated with manure application in cold climates. ■
The author is a research soil scientist for the Institute for Environmentally Integrated Dairy Management, USDAAgriculture Research Service.
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A covered lagoon digester is put to use in Hanford, Calif.
Less methane by 2030
California agencies have programs in place to reduce methane emissions from livestock agriculture in the next decade.
by Geetika Joshi
Farmers and ranchers in California know that their Golden State is more than palm trees and beaches. It is the largest dairy producing state in the nation, and based on 2017 data, California housed 1.7 million cows and produced 39.8 billion pounds of milk on 1,331 dairies.
The overwhelming majority of our dairy cows — 91% — live in the Central Valley, while the remaining 9% reside in the northern coast and southern regions. These areas vary significantly in climate, water, and air quality, all of which play a role in on-farm animal and manure management methods. The cooler climates up north are well-suited to pasture-based operations, while larger feedlot-style, flush-based systems prevail in the Central Valley.
The methane challenge
California’s large number of cows contribute methane emissions, which result from the action of methanogenic bacteria that thrive in the cows’ guts. Methane from livestock comes from two main sources: enteric fermentation, such as cow belching, and storage of manure in anaerobic (wet) conditions, such as ponds and lagoons.
Methane is a potent greenhouse gas (GHG), and its emissions are responsible for about 20% of the global warming now driving climate change. In California, agriculture accounts for 8% of the total inventoried GHGs, and about 53%of that is from animal agriculture. Enteric fermentation contributes to 28% of our agricultural methane emissions, while 25% stems from manure storage.
State legislation passed in 2016, SB 1383, requires California’s dairy and livestock sector to reduce its methane emissions to 40% below 2013 levels by 2030. The statute requires the California Air Resources Board (CARB), in consultation with the California Department of Food and Agriculture (CDFA), to potentially adopt regulations beginning in 2024 to reduce methane from dairy and livestock manure management operations. SB 1383 also requires CARB
to work with a broad range of stakeholders to identify and address challenges and barriers to the development of dairy methane emissions reduction projects.
While reducing enteric fermentation methane emissions remains a challenge that needs additional research and development, methods of manure management are well-researched and commercially available. One such method is establishment of anaerobic digesters to capture the methane produced from stored manure, which can then be used to generate renewable energy. There are also several nondigester technologies and practices that focus on eliminating wet storage conditions of manure to realize methane emissions reduction.
Funding for projects
California currently offers voluntary financial incentives for implementing measurable methane reductions at dairy and livestock operations. These incentives are provided through two CDFA-administered programs: the Dairy Digester Research and Development Program (DDRDP) and the Alternative Manure Management Program (AMMP). These programs are funded through California Climate Investments, also known as the Cap-and-Trade program.
DDRDP was first developed and implemented in 2014-15 with an initial appropriation of $12 million. In its first year, the program funded six dairy digester projects in the Central Valley, where the captured methane was used to make renewable electricity. DDRDP to date has awarded approximately $181.6 million to implement 107 projects located on individual dairies throughout California. These projects generate renewable compressed natural gas (RCNG) fuel in addition to renewable electricity-generating projects. Thirteen dairy digester projects are now complete, and the remainder are in various phases of completion.
Funded dairy digester projects are located across seven counties in the Central Valley, and collectively they reduce approximately 2 million metric tons of carbon dioxide equivalents (MMTCO 2 e) annually, which equates to 420,000 cars
This biogas cleanup and electricity generation equipment was installed in Bakersfield, Calif.
being taken off the road each year.
AMMP was first developed and implemented in 2016-17 in response to stakeholder interest in non-digester management practices. The need for large amounts of digester feedstock, a 50% financial match, proximity to natural gas pipelines, and ease of connection to existing electric grids are some of the key factors attributed to successful digester projects. Subsequently, smaller or more remotely located dairy operations needed a menu of additional options to participate in California’s methane reduction efforts.
AMMP incentivizes nondigester-based manure management practices. This includes conversion from water flush systems to dry scrape systems; solid separation followed by drying or composting of manure solids; compost-bedded pack barns; and increasing the amount of time animals spend on pasture.
AMMP has funded 106 projects totaling $61.9 million. Of these, 28 projects are complete, and the remainder are in various phases of completion. Funded projects are located across 12 counties and collectively reduce approximately 200,000 metric tons of CO 2 e annually. This is equivalent to more than 42,000 cars being taken off the road each year.
In 2019, CDFA also funded three demonstration projects, totaling almost $2 million. The aim of these projects is to showcase new and innovative manure technologies as well as conduct outreach and educate dairy farmers.
Opportunities exist
With expectations for Cap-and-Trade funding to continue, California is
To make manure easier to handle, a solid separator was installed at a dairy farm in Escalon, Calif.
poised to meet its target within the next decade for early and measurable methane reductions. In addition, many co-benefits exist that dairy producers can expect with a digester or alternative manure management practices. For example, digesters can provide an important revenue stream from the sale of renewable energy, which also contributes to climate change adaptation. Similar benefits may also be provided through production of compost.
Methods such as anaerobic digestion and drying of manure solids can potentially help reduce impacts to water quality, since these projects transform manure into a stabilized, easier-to-handle form. The resulting dried manure compost can be moved and used as a soil amendment benefiting plant and soil health.
Most importantly, these voluntary initiatives provide California’s dairy families with the tools and capacity to engage in climate change efforts. Dairy agriculture is an important economic and food contributor, and it is also playing a key role in California’s efforts to lead the nation in practices to mitigate and adapt to climate change. ■
For more information on CDFA’s Dairy and Livestock Methane Reduction Programs, visit: DDRDP: bit.ly/JNM-ddrdp and AMMP: bit.ly/JNM-AMMP. Follow us on Twitter: @CDFAClimateNews.
The author is a senior environmental scientist with the California Department of Food and Agriculture, Office of Environmental Farming and Innovation.
Cover crops can be a bridge
Capture more nutrients from manure by utilizing a cover crop.
by Brian Dougherty
Manure is an excellent source of valuable nutrients. However, it is susceptible to nutrient loss and impacts to water quality when applied long before a crop is present to take up the nutrients that manure provides.
Cover crops can help to bridge this gap. With proper management, cover crops and manure can work together to improve soil and reduce nutrient losses.
Manure adds nitrogen and other nutrients needed for soil microbial activity and crop growth. Cover crops can help capture and recycle those nutrients to the following crop and reduce the potential for nitrogen loss.
Soil microbial activity is enhanced with both manure and cover crops. This microbial activity has the potential to help with decomposition of cash crop and cover crop residue. Cover crops also help to improve soil structure and water infiltration.
Capture nutrients with cover
A research project at the Northeast Research and Demonstration farm near Nashua, Iowa, has been investigating the potential to use cover crops to capture manure nutrients for the last four years.
One aspect of the study is evaluating cereal rye cover crop growth and nutrient uptake in a corn-soybean rotation receiving swine manure. The manure was injected at a rate of 150 pounds of nitrogen per acre (lbs. N/ac). Cover crop aboveground biomass samples were collected in the spring just prior to termination and analyzed for nitrogen (N), phosphorus (P), and potassium (K) content.
Manure was typically applied in early to mid-October after soybean harvest, but before soils had cooled to 50°F. This type of manure application is common, yet highly susceptible to nitrogen loss. Research has found that biological activity in the soil slows considerably when soils are 50°F or cooler.
Bacteria in the soil convert ammonium-N from manure to nitrate-N, which is readily available to crops. The nitrate molecule carries a negative charge and is very soluble in water. It does not adhere well to negatively charged clay particles, so it can easily leach downward through the soil profile.
The warmer soils are when manure is applied, the more rapidly the ammonium will convert to nitrate. This raises the likelihood of losing the N prior to crop uptake the following year. For these reasons, cover crops can be especially beneficial in fields receiving fall-applied manure.
In the Nashua study, there were substantial differences in cover crop growth and nutrient uptake in the aboveground biomass directly over where manure had been injected (Figure 1, blue bars) com
140 120 100 80 60 40 20 0 Aboveground nutrient uptake (lb/ac) Over manure band Between manure band No manure Over manure band Between manure band No manure Over manure band Between manure band No manure N uptake P uptake K uptake
Figure 1. The figure shows aboveground nutrient uptake by a cereal rye cover crop directly over the manure injection band (blue bar), between the manure injection bands (gray bar), and before soybeans (tan bar — no manure applied).
pared to between the manure injection bands (gray bars). On average across the four-year study, the cover crop took up about 90 lbs. N/ac in plots receiving 150 lbs. N/ac from manure. The plots going to soybeans where no manure was applied took up about 60 lbs. N/ac.
These results suggest that the cover crop took up significant residual soil N following soybean and likely took up N from the manure itself. Cover crop N uptake in a previous eight-year study on these same plots was only 13 lbs./ac prior to soybeans and 21 lbs./ac prior to corn in a spring urea-ammonium nitrate (UAN) sidedress system with the same N application rate.
There was no significant difference in corn yield following the cereal rye cover crop in this study. The cover crop led to significantly lower nitrate-N concentrations in drainage water, thus helping to improve water quality. Plots with cover crops also tend to have more water flowing through the drainage system, suggesting that more water is infiltrating rather than running off the surface. This research demonstrates the potential for substantial benefits when adding a cover crop to fields receiving liquid manure.
Start simple
If you are new to using cover crops, it is a good idea to start with “easy” acres, such as corn silage or seed corn ground where you can get the cover crop established earlier. Starting with single-species cover crops like cereal rye or oats can simplify management.
Sampling both soil and manure will help determine where and how much to apply. Proper equipment setup and calibration will help to get manure and cover crop seed applied at a consistent rate and depth. Waiting until soil temperatures have cooled to below 50°F to apply manure will help to reduce N loss. The Nashua study has also shown a substantial corn yield benefit (an additional 40 bu/ac) from this approach.
Monitor carbon to nitrogen (C:N) ratios in both manure and cover crops to help fine-tune management. Generally, the higher the C:N ratio, the longer it will take for a cover crop to break down and release nutrients back to the soil.
Treat the cover crop like a cash crop and manage manure like you would commercial fertilizer. They are both valuable resources worth the investment of your time. Attention to detail, planning, and flexibility will help make manure and cover crops a success on your farm. ■
The author is an ag engineering field specialist with Iowa State University Extension.
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