How can animal manure help my soils be healthier and more productive?

Agustin Olivo – Graduate Research Assistant, University of Nebraska, Lincoln

Do you have ponding, crusting, poor soil structure, low water retention or erosion in some of your fields?

Animal manure, when correctly applied, can help to solve several of these issues.

The purpose of this article is to explain how manure application can help improve your soil health and productivity. It is easier to understand soils when we split their characteristics into their chemical, physical, and biological properties. However, these property classes are part of a whole system and are all important.

Soil Chemical Properties

What are the soil chemical properties important to soil health? How are they affected by manure?

Soil chemical properties are necessary for well-functioning soils to support development and functions of plant and soil organisms. Of the many soil chemical properties the following are affected by manure application:

Property	Description	How can manure help?
Soil Organic Matter	Composed of all organic components of the soil. It affects all soil physical, chemical, and biological properties. It has a direct correlation with soil fertility, plant nutrition, water holding capacity, bulk density, and aggregate stability.	Increase soil organic matter
Nutrients Content	Mainly nitrogen, phosphorous and other micronutrients, available in the soil to be absorbed by plants.	Provide nutrients to crops
Cation Exchange Capacity (CEC)	The ability of the soil to hold nutrients and release them through chemical reactions for plant uptake.	Increase CEC
pH	A measure of the level of acidity or alkalinity in the soil. Essential for plant nutrition, growth and soil’s biological and chemical activity.	Keep pH in normal levels

What problems are associated with soil chemical properties?

• Crops with nutrient deficiencies (Figure 1a).
• Crops with nutrient deficiencies (Figure 1b).
• Low soil organic matter level.

How can manure improve soil chemical properties?

Animal manures, when integrated into a crops fertility program, will benefit soil chemical properties and reduce the concerns illustrated above. Those benefits vary depends on the composition of the amendment. In general, the most important immediate effect is the addition of nutrients. Manure can fulfill a significant amount of the crops nutrient requirements for nitrogen, phosphorus, potassium and micro-nutrients. One has to manage manure so that when applying sufficient quantities of one nutrient, another nutrient is not over-applied or is utilized in future years. Usually manure recommendations are made based on the chemical content of the manure, so it is important that a complete analysis be made. While generally not a problem, excess salt can affect soils negatively, and the salt levels of the manure should be monitored by soil testing to avoid problems. Over the long term, when manure with high carbon content is applied, such as beef manure, soil organic matter increases. As organic matter increases, more nutrients come available due to a larger pool of nutrients.  The benefits from increased soil organic matter are exhibited by an improvement in other physical and biological properties as well. Furthermore, additional organic matter in the soil due to manure applications can increase our soil Cation Exchange Capacity. Manure can also contain components with potential liming effects on the soil. This particular contribution can help keep soil pH in normal levels, maximizing nutrients availability for crops.

Soil Physical Properties

What are the soil physical properties important to soil health? How are they affected by manure?

Generally, the soil physical properties demonstrate how well the soil can provide physical stability and support for soil organisms and plants. Some of the physical properties affected by manure application are:

Property	Description	How can manure help?
Bulk Density	Amount of solid particle weight per volume of such mass of soil. It reflects the level of porosity (void space in the soil that can be filled by air or water) and compaction of the soil. Compacted soils (higher bulk density) have less porosity, lower air content, lower water infiltration, and poor plant growth.	Reduce bulk density
Soil Aggregate Stability	The strength of the soil structure to resist the impact of an external force, like rainfall, wind and water erosion. An enhanced soil aggregate stability benefits crop growth and prevents erosion.	Increase aggregate stability
Water Infiltration	Movement of water through the soil surface into the soil profile. Increasing infiltration reduces water and nutrients runoff and enhances availability for plants.	Increase water infiltration
Water Holding Capacity	The capability of the soil to hold water that can then be available for crops.	Increase water holding capacity

What problems are associated with soil physical properties?

• Wind and water erosion (sheet, gully erosion, Figure 2a).
• Field difficult to till and with lots of clods.
• Presence of crusting on the field after tillage or heavy rain, what can generate slow and uneven emergence.
• Frequent crop stress, due to the soil’s limited capacity for water retention (Figure 2b).
• Detectable compaction on the field, with limited penetration and horizontal root growth.
• Ponding on the field surface due to infiltration problems (Figure 2c).

How can manure improve soil physical properties?

In general, reductions in bulk density have been demonstrated mainly with long-term manure applications across different kind of soils. Incidentally, as bulk density decreases, soil compaction also diminish and the soil porosity increases. According to a study, manure and compost application also result in a quick and  significant increase in water-stable large macro aggregates after  the application. Rising aggregate stability generates a better environment for plant development since it facilitates root growth, water infiltration, and retention. All these positive effects together lead to less ponding, runoff and erosion problems in wet years. Likewise, they make it more tolerant to droughts in drier ones. Furthermore, these features also make soils more resistant to compaction and erosion effects.

Soil Biological Properties

What are the soil biological properties important to soil health? How are they affected by manure?

Soil biology is composed of all live organisms within the soil (plant roots, earthworms, fungi, bacteria, actinomycetes, algae, protozoa, nematodes, mites, springtails, and small insects). All of them play an important role in building soil health, facilitating soil organic matter decomposition, nutrient cycling and soil particles aggregation. For these reasons, their abundance and activity have a direct impact on the availability of nutrients that plants can absorb to grow. Some of the most important biological properties affected by manure applications are:

Property	Description	How can manure help?
Earthworms Population	Earthworms help accelerate biomass decomposition, nutrient cycling and building a better pores system for water infiltration and retention.	Increase soil biological activity
Microbial Biomass Carbon and Microbial Respiration	Laboratory measurement used as an indicator of the microbial abundance in the soil. Both are directly related to the general biological activity, which influences the nutrients availability for crops and the generation of the substances that act as a “glue” to help build more stable soil aggregates.

What problems are associated with soil biological properties?

• No visible signs of casts or earthworms.
• No or stagnant smell.
• Slow residue decomposition.

How can manure improve soil biological properties?

Several studies demonstrated the positive effects of manure on soil biological properties, and its impact in microbes and larger fauna. When compared with inorganic fertilizer applied at the same nutrient rates, manure has a more significant effect on soil biological activity. In terms of organisms’ abundance and activity, a recent review concluded that “manure and biosolid application increases abundance of soil fauna, such as bacteria, fungi, and earthworms.” The same paper indicated the microbial respiration rate was increased between 10% and 135% with the application of manure, as well as microbial biomass carbon, both indicators of microorganism’s abundance on the soil. Another publication also points out that “carbon and other nutrients in manure can increase microbial biomass by two to three times.” Regarding larger organisms and its crucial role on nutrient cycling, the same report indicates that grazing on microbes by microarthropods and nematodes releases much of the nitrogen that afterward is available during crops’ growing season. This last example clearly shows the positive impact of an augmented activity of the soil food web on plants’ development.

Additional reading:

Do you want to know more about soil health and/or conduct a more precise assessment of your fields’ soil health? Check: https://store.extension.iastate.edu/product/Iowa-Soil-Health-Management-Manual

Do you want to start applying manure in those fields where soil properties do not perform well?

Check: https://water.unl.edu/category/animal-manure-management or https://soilhealthnexus.org/category/manure/

References:

• Al-Kaisi, M., Kwaw-Mensah, D. (2016). Iowa Soil Health Field Guide- Crop 3089A, 1–90.
• Edmeades, D. C. (2003). The long-term effects of manures and fertilizers on soil productivity and quality: a review. Nutrient Cycling in Agroecosystems, 66, 165–180.
• Eghball, B. (2002). Soil Properties as Influenced by Phosphorus- and Nitrogen-Based Manure and Compost Applications. Agronomy Journal, 94(1), 128–135. https://doi.org/10.2134/AGRONJ2002.1280
• Graham, E., Grandy, S., Thelen, M. (2012). Emerging Issues in Animal Agriculture Manure effects on soil organisms and soil quality OVERVIEW. Retrieved from http://msue.anr.msu.edu/uploads/files/AABI/Manure effects on soil organisms.pdf
• Schott, L., Millmier Schmidt, A. (2017). SOIL HEALTH, Synthesis of Short-and Long-term Studies Reporting Soil Quality Metrics under Agricultural and Municipal Biosolid Applications 2016. Manure and Soil Health Working Group Report Synthesis of Short-and Long-term Studies Reporting Soil Quality Met. Retrieved from https://soilhealthnexus.org/files/2018/02/ncrwn-synthesis-of-short-long-term-studies-reporting-soil-quality-metrics-report-FINAL.pdf
• Wortmann, C. S., Shapiro, C. A. (2008). The effects of manure application on soil aggregation. Nutrient Cycling in Agroecosystems, 80(2), 173–180. https://doi.org/10.1007/s10705-007-9130-6

Other resources:

• Interview with Dr. Charles Wortmann (Agronomy and Horticulture, UNL).
• Manure and soil health testing. Presentations and discussions hosted by the North Central Region Water Network in February and March 2017, addressing manure and soil health topics. (https://lpelc.org/manure-and-soil-health-testing/).
• https://lpelc.org/animal-manures-impact-on-soil-properties/