10 Advantages of Organic Manure: What the Evidence Shows

The main advantages of organic manure are that it feeds crops slowly, adds organic matter that holds soil together, supports soil life and cuts some of the fertilizer you buy. Studies back each of these, but the size of the gain depends on the soil, the manure and the timing. A 2019 review of field studies found that yields of maize and wheat rise with soil organic carbon until it reaches about 2% (Oldfield et al., SOIL, 2019). This guide gives 10 advantages with dated numbers, the limits you need to know, and a calculator for your own spreading rate.

The 10 advantages of organic manure at a glance

The table shows what each advantage rests on and the catch to watch. Each one has its own section below.

What organic manure is and what it adds to soil

Organic manure is animal dung, farmyard manure, poultry litter, compost and similar material made from plant and animal residues. It gives the soil two things at once: plant nutrients and carbon-rich organic matter. The FAO soils bulletin on soil organic matter describes how soil organisms use this matter as food and, as they break it down, release extra nitrogen, phosphorus and sulphur in forms plants can take up.

Chemical fertilizer works the other way. It gives a fast, measured dose of nutrients but adds almost no carbon. Many farms use both, and the best mix comes from a soil test and local advice, not from a rule of thumb.

▶ Why organic matter matters in soil and in agriculture. · 7:33

1. It feeds crops slowly

Manure holds nitrogen (N), phosphate (P2O5) and potash (K2O). How much depends on the animal, the bedding and the moisture. The University of Kentucky lists about 11 pounds of N per ton for beef and dairy manure and 55 pounds for fresh broiler litter, all on an as-is moisture basis (Kentucky Cooperative Extension, AGR-146). Utah State University gives wide ranges for the same manure types and says a laboratory analysis should always be run (Utah State University Extension, 2004).

Chart

Nitrogen in solid manures

pounds of total N per ton, as-is moisture, manures used in Kentucky

Not all of that nitrogen reaches the crop in the first year. Kentucky counts 15 to 80% of manure N as available in year one (80% is for cool-season pasture or hay; 60% at most for corn), depending on the manure, the crop and when it is mixed into the soil. Some of the rest is released in later years.

Chart

Share of manure nitrogen a crop can use in year one

percent of manure N, selected Kentucky coefficients (corn, except the hay row)

2. It improves soil structure

Humus, the stable part of organic matter, increases soil aggregation and aggregate stability, according to the FAO. Sticky substances from earthworms, fungi and bacteria help bind particles together. Better aggregation means more pore space for air and roots. The effect builds over seasons, so one load of manure will not rebuild a compacted field.

3. It feeds soil life

Soil bacteria, fungi and earthworms live on organic matter. Adding manure or compost gives them food, and their work cycles nutrients back to the crop. No single figure for the boost in microbial activity holds across soils, so treat any “times more” claim with care. What the FAO source supports is simpler: more organic input gives soil organisms more to work with.

One risk goes with manure from animals that ate treated hay or pasture. Some herbicides, including aminopyralid, clopyralid and picloram, can pass through the animal and still harm sensitive crops such as tomatoes and beans when the manure is spread (NC State Extension). Ask the supplier what the animals ate, and follow the product label and local rules.

4. It helps soil hold water, but the gain is small

Many articles say organic matter lets soil hold 20% more water. The best global evidence gives a smaller number. A review of 60 studies and more than 50,000 measurements found that a 1% mass increase in soil organic carbon raises plant-available water by about 1.16 mm per 100 mm of soil, with larger gains in sandy soils than in clays (Minasny and McBratney, European Journal of Soil Science, 2018). University of Minnesota Extension cites 1.03 percentage points of available water capacity per 1% organic matter for medium-textured soil (University of Minnesota Extension, 2024).

Chart

Water held per 1% more soil organic carbon

extra mm of water per 100 mm of soil, average across 60 studies

In practice, raising soil carbon by a whole percentage point takes many years of added carbon, so manure is a slow way to add stored water.

5. It helps soil take in rain and resist erosion

The FAO describes soil with good porosity, plant cover and active soil life as one that lets water soak in and curbs erosion and runoff (FAO Soils Bulletin 80). Organic matter is part of how that structure forms, though this is general soil evidence and not a manure-specific trial. Manure left on the surface of sloping or frozen ground can itself run off, so spread it when the soil can take it in. Many places set closed periods for spreading; in England, for example, the rules apply in nitrate vulnerable zones (GOV.UK).

6. It can cut the fertilizer you buy

This is where the money saving is easiest to see. Kentucky’s worked example shows fresh broiler litter at 55 pounds of N per ton meeting the 172 pounds of net nitrogen need of a corn crop at about 6.9 tons per acre. The same load supplied 304 pounds of phosphate against a need of 70, an excess of 234 pounds. Repeated phosphate overapplication can limit how much manure you may spread in future years.

So manure often replaces nitrogen fertilizer, but it can overfill phosphate. A soil test tells you which nutrient to plan around.

▶ Mixed farming explained: manure from livestock as fertilizer for crops. · 2:55

7. It goes with higher yields, up to a point

The 2019 review by Oldfield, Bradford and Wood links higher soil organic carbon to higher maize and wheat yields, levelling off at about 2% (SOIL, 2019). About two-thirds of the world’s cultivated maize and wheat land is below 2% soil carbon. If carbon were raised to regional targets, the model gave a yield gain of 10 ± 11% for maize and 23 ± 37% for wheat, and a cut of 7% and 5% in nitrogen fertilizer. The authors warn that the data cannot prove cause: richer soils also grow better crops and return more residue. Treat these as modelled averages, not a promise for your field.

8. It can add soil carbon

Evidence here is for organic farming systems as a whole, which use manure, compost, cover crops and rotations together; it is not a manure-only trial. A meta-analysis of organic and non-organic farming systems found topsoil carbon stocks 3.50 Mg C per hectare higher under organic management (Gattinger et al., PNAS, 2012). That difference shrank when only zero-net-input systems were compared, and the yearly build-up rate was no longer significant in the highest-quality subset. A later model study found that converting all cropland to organic farming without cover crops and residue recycling could lower global soil carbon, while an optimal organic scenario preserved it (Nature Climate Change, 2023). The lesson is that carbon comes from the amount of carbon you put in, and manure is one source of it.

Chart

Extra topsoil carbon in organic farming systems

Mg C per ha, organic systems vs non-organic (not manure alone)

9. It steadies soil acidity

The FAO notes that humus is an important buffer, reducing swings in soil acidity and nutrient availability, and that about 35 to 55% of the non-living part of soil organic matter is humus. Buffering slows pH change. It does not fix acid soil, so keep testing pH and follow local liming advice.

10. It recycles farm and food waste

Composting turns food scraps, yard trimmings and farm residues into a soil amendment instead of landfill waste. The US EPA says composting returns nutrients and carbon to soil that would otherwise be thrown away (US EPA). On a livestock farm the same logic applies to manure: it is a nutrient source you already own.

Solid, liquid and composted manure compared

The form of manure changes both the nutrient load and the handling. Kentucky Extension lists dairy manure from a holding pit at 31 pounds of N per 1,000 gallons, but dairy lagoon liquid at only 4 pounds, because the lagoon is mostly water. Haul distance therefore matters: dry manures can be moved some distance economically, while liquid manures cannot.

Poultry litter is the richest per ton, and in the Kentucky example its phosphate ran far past crop need; other manures can do the same. Beef and dairy solids are lower in nutrients, so they suit fields that need organic matter more than a big nitrogen dose. The US EPA describes composting as recycling that turns organic material into a soil amendment. Compost still needs a test, since its nutrient level depends on the feed material.

Where the gains are likely to be largest

The evidence points to a few situations. Fields with low soil carbon have the most room to gain, which fits the 2019 yield review, where yields rose with soil carbon up to about 2%. Sandy soils gain more plant-available water per unit of added carbon than clays do. Farms with their own livestock already have the manure, so the cost is hauling and spreading, not purchase. Fields with a long history of heavy manure are the opposite case: they may already carry high phosphate, and the next step is a soil test, not another load.

It also helps to be patient. Soil carbon moves slowly. The PNAS meta-analysis found a mean build-up of 0.45 Mg C per hectare per year for organic systems against non-organic, with a wide range of ±0.21, and the figure fell in the stricter subsets. Plan for years of steady inputs, and judge progress with repeat soil tests at the same depth and time of year.

Limits and risks of organic manure

• Variable content. Nutrient levels change with animal, bedding, storage and moisture. Test the manure.
• Phosphate build-up. Spreading to meet nitrogen can overfill phosphate, as the Kentucky example shows.
• Nitrogen loss. Kentucky’s table shows only 15 to 20% of manure N still available to the next corn crop after a fall application with no cover crop.
• Legal limits. In England’s nitrate vulnerable zones, livestock manure is capped at 170 kg of N per hectare per year on average across the holding (GOV.UK).
• Herbicide residue. See advantage 3.

Rules on rates, timing and storage differ by state, province and country. Check your local rules and get advice from your extension service or agronomist before you change fertilizer plans.

Timing and method: how to keep the nitrogen

When and how you spread decides how much nitrogen the crop gets. Kentucky Extension gives three working rules. First, mix manure into the soil soon: if it is not incorporated within seven days of spreading, the nitrogen availability coefficient falls by 15 points. Second, apply close to the time of fast crop growth, because growing crops take up nitrogen best. Third, rain helps: as little as half an inch after spreading moves nitrogen into the soil, while heavy rain on wet or frozen ground can wash it away.

A cover crop changes the fall picture. In the Kentucky tables, a cover crop lifts first-year availability after fall spreading from 15 to 50% for poultry or liquid manure, and from 20 to 40% for other manures, because the cover crop holds the nitrogen until spring.

How to read a manure test

A lab report lists total nitrogen, ammonia nitrogen, phosphate and potash, usually per ton or per 1,000 gallons. Utah State University gives example ranges for solid manures in pounds per ton: poultry litter 40 to 80 of total N, 30 to 60 of P2O5 and 30 to 50 of K2O, against 5.8 to 7.4 of N, 1.8 to 2.4 of P2O5 and 2.4 to 3.6 of K2O in separated dairy solids. Those ranges are wide, so use your own test.

Work in four steps. Take the net nutrient need from your soil test. Multiply the manure’s total N by the availability share for your timing. Divide the need by that figure to get tons per acre. Then check phosphate and potash for the same load, because they can exceed what the crop needs. The calculator below runs these steps for nitrogen and phosphate.

Some nitrogen is released in later years. Kentucky puts the carry-over at 3 to 12% of the nitrogen applied the previous year for poultry or liquid manure and 5 to 25% for other manures, with the higher shares on fields that get manure often. Subtract this credit from the crop’s need.

How much manure to apply: a rate calculator

Use the calculator below to plan around nitrogen and check the phosphate that comes with it. It follows the Kentucky worksheet method: net N need divided by the N that is available per ton.

Try the numbers for your own farm below.

Ways to add more organic matter

Manure is one route. Composting farm and food waste, spreading well-rotted livestock manure, growing green manure and cover crops, mulching with crop residue and rotating diverse crops all add carbon. The FAO lists crop residue management, cover crops, compost and mulch among practices that increase soil organic matter. Move in steps and compost raw manure first, so you can see the effect on yield and soil test results before changing the whole farm.

▶ Seven sustainable farming practices that protect soil and water. · 4:34

Tracking the result from space

Satellite vegetation maps do not measure soil organic matter. They show how green and vigorous a crop is, field by field and week by week. Farmonaut Satellite + AI Farm Monitoring System draws these vegetation maps for your fields, so you can compare a manured block with an unmanured one over a season. Keep records of manure rates, dates and crops alongside the maps. Developers can use the Farmonaut API and its API developer documentation; managers of many sites can look at large-scale farm management tools. For a wider view of the field, read about an agritech company and how it supports farms.

FAQ

What are the advantages of organic manure?

It supplies nutrients slowly, adds organic matter, feeds soil organisms, improves structure, can cut bought nitrogen and adds some soil carbon. Size of the benefit depends on soil, manure type and timing.

Does organic manure raise crop yields?

Yields of maize and wheat rise with soil carbon up to about 2% in a 2019 global review, but the review cannot prove cause and the gains vary widely between fields.

Can manure replace chemical fertilizer?

It can replace some or all nitrogen on some farms. Kentucky’s example shows broiler litter meeting a corn crop’s nitrogen need. Check phosphate and potash with a soil test, and ask local advisers.

What are the disadvantages of organic manure?

Nutrient content varies, nitrogen can be lost, phosphate can build up, and herbicide residues or weed seed can arrive with it. Spreading rules may limit when and how much you apply.

How much water does organic matter add?

About 1.16 mm of plant-available water per 100 mm of soil for each 1% rise in soil organic carbon, on average, in a 2018 review of 60 studies.

How should I start?

Test the soil and the manure, apply to meet one priority nutrient, mix it in soon after spreading, and keep records.