Manure and Composted Manure Use in Arizona Agriculture

Not all manures are the same. Before discussing application practices, it is important to distinguish between the different forms of animal-based soil amendments.

Raw manure

Raw manure refers to animal waste that has not been treated. It contains readily available nutrients, but also weed seeds, salts, and potentially harmful pathogens such as E. coli, Salmonella, and Listeria. Due to these risks, raw manure must be applied with caution and in accordance with food safety guidelines.

Composted manure

Composted manure is treated animal waste that has been managed through a controlled biological process where heat, moisture, and microbial activity break it down into a stable product. Proper composting reduces pathogens, weed seeds, and odors, and produces a soil amendment that is safer and easier to handle than raw manure. The composting process also helps balance the carbon-to-nitrogen (C:N) ratio and offers opportunities to incorporate plant-based bulking materials (USDA-NRCS, 2010).

USDA definitions for achieving treated compost

• Aerated enclosed composting maintains aerobic conditions at ≥131 °F (55 °C) for 3 consecutive days, followed by adequate curing.
• Turned windrow composting maintains aerobic conditions at ≥131 °F (55 °C) for 15 days with a minimum of 5 turnings, followed by adequate curing.
• After the required hot phase, compost is cured until temperatures fall and stabilize near ambient levels below 131 °F. This ensures biological stability and maturity.

When animal-based manure or composted manure is applied to soil, it is legally defined under the Food Safety Modernization Act (FSMA) as a Biological Soil Amendment of Animal Origin (BSAAO) (U.S. Food and Drug Administration, 2015). FSMA is a federal law administered by the U.S. Food and Drug Administration (FDA) that sets food safety standards for growers. While the law’s requirements apply specifically to commercial produce farms with annual sales exceeding $25,000, its guidelines represent good agricultural practices that are useful for all growers, including home gardeners and small farms.

It is also helpful to distinguish between animal-based and plant-based composts. Plant-based composts (made from yard 2 The University of Arizona Cooperative Extension trimmings, food scraps, or crop residues) are not considered BSAAOs. They play a crucial role in soil health, but their use involves a distinct set of considerations and falls outside the scope of this publication.

The nutrient content of manure varies by animal species, feed, bedding, and storage. Because of variability, laboratory testing of manure or composted manure is strongly recommended for accurate nutrient management.

Salinity

Manure or composted manure, depending on its animal source, can be high in soluble salts, including sodium (Na⁺), calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺), chloride (Cl⁻), and sulfate (SO₄²⁻). Excessive salt applications can raise soil electrical conductivity beyond thresholds for sensitive crops, reducing germination, stunting growth, and mimicking the symptoms of drought stress (Arp et al., 2025).

pH and micronutrients

Most manures have neutral to slightly alkaline pH (7–8.5). In already alkaline Arizona soils, this can worsen micronutrient deficiencies, particularly of iron, zinc, and manganese. High pH can also slow the mineralization of organic nitrogen (University of Minnesota Extension, 2018).

Soil moisture

Adequate water promotes microbial activity that drives nutrient mineralization. In dry soil, decomposition slows, and nutrients remain tied up in organic matter. Conversely, overly wet soils may increase nitrogen losses through leaching or denitrification. Nutrients, especially nitrogen, can also migrate away from fields through runoff, reducing fertilizer value for crops and contributing to water quality issues in streams, rivers, and groundwater.

Weed seeds

Manure can contain viable weed seeds that pass through the digestive systems of livestock, particularly horses and cattle, whose digestive systems do not fully destroy them. These seeds can germinate when manure is applied to the soil. Composting manure, according to USDA standards for treated compost, is an effective method for killing most weed seeds before use on crops.

Residual herbicides

Certain persistent herbicides, particularly those containing aminopyralid, clopyralid, or picloram, can persist after digestion and remain active in manure. When this manure is applied to gardens or fields, herbicide residues can injure sensitive crops such as tomatoes, peppers, and legumes. This risk varies with animal diet and feed source; producers should be aware of feed additives or hay treated with long-residual herbicides.

Soil chemistry

Soil chemistry plays a key role in how nutrients from manure or composted manure are released and taken up by crops. For this reason, monitoring soil chemistry through regular testing is essential to ensure amendments provide the intended benefits without creating new challenges.

It is essential to acknowledge that the results from manure and composted manure applications vary by region. In Arizona’s arid, alkaline soils, challenges such as salinity buildup and micronutrient availability are more common than in humid, temperate regions like the Midwest. Recommendations from other regions should be adapted to local soil and water conditions for the best results.

Not all nutrients in manure or composted manure are immediately available to plants. Here is how the compositions of each compare. 

Raw Manure

• Approximately 40-70% of the total nitrogen (N) in raw manure is available to plants during the first year after application, with an additional 10% or so released in each of the next two years as organic matter breaks down (Mallarino & Sawyer, 2023).
• Most phosphorus (P) and potassium (K) are readily available in the first season.
• Raw manure contains higher concentrations of soluble salts and ammonium, largely from animal urine and feed supplements. These salts can quickly raise soil salinity if applied in excess or without adequate irrigation to leach salts below the root zone.
• Rapid increases in nutrient concentrations from manure applications can create an imbalance or unhealthy buildup of one nutrient, such as phosphorus, leading to long-term accumulation in soil. 

Composted Manure

• During composting of the manure, nutrients become more stabilized through microbial decomposition and the conversion of ammonium to organic nitrogen. Only about 10–30% of total nitrogen is plant-available in the first year, with gradual mineralization over time.
• Most phosphorus (P) and potassium (K) are readily available in the first season.
• Composting also lowers the soluble salt content because moisture and microbial activity drive off ammonia and leach salt from the pile. The addition of plant-based bulking materials, such as straw, leaves, or wood shavings, further dilutes salts (University of Minnesota Extension, 2018).

By comparison, composted manure provides a steadier nutrient supply and is generally safer for maintaining soil health over time, while raw manure offers quicker nutrient availability but requires careful management to prevent salt and nutrient accumulation

Applying manure or composted manure can improve the physical, chemical, and biological qualities of soil in ways that support long-term crop productivity.

• Provides essential plant nutrients. Manure and composted manure contain most of the 14 essential plant nutrients, including both macronutrients (such as nitrogen, phosphorus, and potassium) and micronutrients (such as iron, zinc, and manganese). These nutrients are released gradually through decomposition and microbial activity, supporting crop growth while also replenishing soil fertility.
• Increases organic matter and improves soil structure. Organic matter in manure and composted manure coats soil particles and binds them into stable aggregates, which improve tilth, reduce compaction, and enhance root growth.
• Enhance water infiltration, holding capacity, and aeration. In sandy soil, manure or composted manure helps retain water and nutrients, while in heavy soil, it improves drainage and aeration. These changes increase the soil’s ability to store and deliver water to crops between irrigation or rainfall.
• Boosts CEC (cation exchange capacity). CEC is the soil’s ability to hold onto positively charged nutrients such as potassium, calcium, and magnesium. Adding organic matter, manure, and composted manure increases CEC, making more nutrients available for crop uptake and reducing losses to leaching.
• Supports microbial diversity and nutrient cycling. Manure and composted manure provide food sources for soil microbes. These organisms facilitate the breakdown of organic matter, releasing nutrients in plant-available forms and supporting disease suppression. Composted manure in particular supplies stable carbon that promotes long-term microbial activity and enzyme function.

Because manure and composted manure originate from animals, they may contain pathogens such as E. coli, Salmonella, and Listeria. These pathogens can pose risks to human health if soil amendments are not applied correctly. The Food Safety Modernization Act (FSMA) Produce Safety Rule requires specific interval standards for untreated manure use for commercial produce farms.

• 120-day interval between the application of untreated manure and harvest if the edible portion of the crop comes into direct contact with soil or soil particles (e.g., carrots, lettuce).
• 90-day interval between the application of untreated manure and harvest if the edible portion does not come into direct contact with soil (e.g., corn, apples).

Even for small farms and home gardens that are not legally required to follow FSMA, adopting these waiting periods is considered best practice to reduce food safety risks.

Runoff is another important consideration. Rainfall or irrigation soon after manure application can move pathogens from the field into adjacent production areas or surface water. Likewise, livestock housed or pastured near cropland can be a source of pathogens. Even if untreated manure is not applied directly, runoff from areas where animals live or graze can contaminate nearby crops.

Composting is an effective measure for controlling pathogens. Properly managed composting reaches high temperatures that kill most pathogens and weed seeds, producing a more stable and safer soil amendment. In contrast, simply curing or aging manure does not reliably reduce pathogens (USDA-NRCS, 2010).

Worker hygiene and harvest timing are also critical. Anyone handling manure or composted manure should wash their hands thoroughly before working with crops. Tools and equipment should be cleaned regularly to avoid crosscontamination.

Timing

Applications should be made close to planting and avoided in fall or winter when crops are not actively growing. This reduces the risk of nutrient losses through leaching or runoff. Applying nutrients as close as possible to the time when plants need them ensures efficient uptake. Incorporating manure or composted manure into the soil within a few days of application reduces nitrogen losses from volatilization and minimizes odors.

Avoid manure or composted manure applications during seed germination, as high levels of ammonia can inhibit seed emergence and damage young seedlings. Allow at least several weeks between application and direct seeding to prevent injury and ensure salts and ammonia have dissipated.

Application method

Manure and composted manure can be applied by broadcasting across the field or banding along crop rows. Incorporation depth should place nutrients within the active root zone (4–6 inches) but not so deep that nitrogen is lost below rooting depth. Solid manures are best incorporated mechanically, while liquid manures can be injected or applied with irrigation water where permitted.

Rate determination

Application rates should be based on:

• Manure or composted manure nutrient analysis (total N, P₂O₅, K₂O, & moisture content)
• Soil test results
• Crop nutrient requirements and expected yield 

Do not apply more nitrogen than the crop can take up. In many cases, application rates are limited by phosphorus rather than nitrogen, as phosphorus is relatively immobile and can accumulate in soil over time. When soil test phosphorus levels are high, calculate manure rates based on P to avoid environmental losses.

Understanding crop nutrient requirements is essential for balancing manure or compost applications. Each crop removes different amounts of nitrogen, phosphorus, and potassium from the field, so matching application rates to these needs prevents over- or under-fertilization, protects water quality, and ensures long-term soil fertility. A pre-application soil test is crucial for determining existing nutrient levels—especially potassium, which is often already elevated in Arizona soils— before adding amendments. In addition, many Arizona soils are alkaline and may require supplemental micronutrients such as iron and boron, which could be affected by large-scale additions of organic amendments and should be managed accordingly (University of Arizona, Desert Ag Solutions, 2025).

Example calculations

Nitrogen-based application

120 lb. of N/ac for sweet corn using raw dairy manure. From manure analysis,0.8% total N on a fresh-weight basis, estimated 50% first-year N availability.

1. Convert total N to pounds per ton: 0.8% × 2000 lb. = 16 lb. N/ton
2. Adjust for first-year availability (50%): 16 lb. × 0.5 = 8 lb. plant-available N/ton
3. Determine application rate based on the crop demand: 120 lb. N needed ÷ 8 lb. N/ton = 15 tons manure per acre

If the manure contains 0.5% P₂O₅, 15 tons × 10 lb./ton = 150 lb. P₂O₅/ac applied. This exceeds the crop need of P (60 lb./ ac), so the rate may need to be limited by phosphorus or manure diluted with low-P material. The example below calculates the manure addition rate by P and the shortfall of N for additional supplementation.

Phosphorus-based application

60 lb. of P₂O₅/ac for sweet corn using raw dairy manure. From manure analysis, 0.5% total P₂O₅ on a fresh-weight basis, estimated 100% first-year P availability.

1. Convert manure P to pounds per ton: 0.5% × 2000 lb. = 10 lb. P₂O₅/ton (note: the majority of P and K are available in the first year of application)
2. Determine application rate based on the crop demand: 60 lb. P₂O₅/ac ÷ 10 lb./ton = 6 tons/ac of manure
3. Estimate how much N comes along for the ride: Total N per ton = 0.8% × 2000 = 16 lb. N/ton. First-year plant-available N ≈ 50% 8 lb. N/ton. At 6 tons/ac: 6 × 8 = 48 lb. available N/ac supplied by the application of 6 tons/ac
4. Calculate N shortfall and plan a separate N source Crop N requirement for sweet corn = 120 lb. N/ac. Shortfall = 120 − 48 = 72 lb. N/ac still needed (supply this with a separate N application (e.g., applied soluble N or another low-P amendment))

When no soil or manure analysis is available, use Table 3 as rough preplant ranges for composted manure worked 4–6 inches into the soil. Rates target about 0.1 lb. plant-available N per 100 sq ft, which is appropriate for most mixed vegetable beds. Start at the low end if you have saline water or alkaline soil and avoid high-salt materials in seedbeds. Remember to follow the FSMA manure application timing guidelines to reduce food-safety risks. Avoid using fresh manure on actively growing crops or within 90–120 days of harvest for edible crops.

How to use the table

1. Find your manure type on the table.
2. Multiply the lb. per 100 sq ft by your bed size. Example: a 4×12 bed is 48 sq ft, which is roughly half of 100 sq ft.
3. Spread evenly and incorporate lightly. Water well after application. 

Note: a standard 5-gallon bucket holds ~0.67 ft³ and weighs ~20 lb. for typical composted manure. So, 3 buckets ≈ 60 lb. per 100 sq ft.

Square-foot examples

• 4×12 bed (48 sq ft) using dairy compost 
  45–65 lb. per 100 sq ft --> apply ~22–32 lb. (about 1–1.5 buckets).
• 10×10 plot (100 sq ft) using horse compost
  60–90 lb. per 100 sq ft --> apply 60–90 lb. (about 3–4.5 buckets).
• 4×8 bed (32 sq ft) using poultry compost
  10–20 lb. per 100 sq ft --> apply ~3–6 lb. (a light dusting mixed in, or blend 1 part poultry compost to 3–4 parts regular compost).

Manure and composted manure are valuable resources for improving soil health when used thoughtfully. They provide essential nutrients, organic matter, and long-term benefits to soil structure and fertility. However, they must be managed carefully to protect crops, water quality, and human health.

• Time applications to crop needs, applying the right rates, and considering environmental risks are all essential steps.
• Composting offers added benefits. Properly composted manure reduces pathogens and weed seeds while providing more stable, slow-release nutrients.
• Soil testing and record keeping are critical. Regular monitoring of soil chemistry and documentation of application rates help ensure amendments provide the intended benefits without creating new challenges

The Natural Resources Conservation Service (NRCS) has established Conservation Practice Standards, such as Nutrient Management (Code 590) and Waste Utilization (Code 633). These standards provide detailed guidance on balancing nutrient applications with crop needs while protecting water quality and should be consulted when developing nutrient management plans. In Arizona’s arid climate, careful timing, irrigation management, and monitoring of soil salinity are crucial for maximizing the benefits from manure and composted manure.

Arp, T., Francis, B., McLane, E., Lombard, K., & Sanyal, D. (2025). A soil health survey of agricultural lands in the southern Intermountain West (az2163). University of Arizona Cooperative Extension. http://hdl.handle.net/10150/678915 

Bliss, N. B. (2003). Soil organic carbon on lands of the Department of the Interior (Open-File Report No. 2003–0304). U.S. Geological Survey. https://pubs.usgs.gov/of/2003/0304/report.pdf 

Clemson University Cooperative Extension. (2001). Poultry manure production and nutrient content. https://www.clemson.edu/extension/camm/manuals/poultry/pch3b_00.pdf  

Mallarino, A. P., & Sawyer, J. E. (2023). Using manure nutrients for crop production (PMR 1003). Iowa State University Extension and Outreach. https://store.extension.iastate.edu/product/PMR1003 

University of Arizona, Desert Ag Solutions. (2025). Potassium (2.3). Retrieved November 13, 2025, from https://desertagsolutions.org/research-areas-and-initiatives/improve-plant-nutrition/fertilizer-guidelines-vegetablecrops-arizona/nutrients-required-2/potassium-2-3 

University of Minnesota Extension. (2018). Manure characteristics. https://extension.umn.edu/manuremanagement/manure-characteristics 

USDA-NRCS. (2010). Chapter 2: Composting. In National Engineering Handbook, Part 637 – Animal Waste Management (210–VI–NEH, Amend. 40, November 2010). U.S. Department of Agriculture, Natural Resources Conservation Service.

USDA Natural Resources Conservation Service. (2019). Conservation practice standard: Nutrient management (Code 590) (NRCS, NHCP, May 2019). U.S. Department of Agriculture.

USDA Natural Resources Conservation Service. (2017). Conservation practice standard: Waste recycling (Code 633) (NRCS, NHCP, October 2017). U.S. Department of Agriculture.

U.S. Food and Drug Administration. (2015). Biological soil amendments of animal origin (BSAAO): Fact sheet. https://www.fda.gov/files/food/published/Fact-Sheet--Biological-Soil-Amendments-of-Animal-Origin_Download.pdf