Best Soil for Agriculture: Why the Midwest Is So Fertile

The best soil for agriculture is a deep, well-drained loam or silt loam with plenty of organic matter. The University of Idaho soil orders guide calls Mollisols, the dark grassland soils of the US Midwest, among the most important and productive farm soils in the world. The rich lands of the Upper Midwest and the Mississippi River come from two sources: glacial and wind-blown deposits in the north, and river flood deposits in the valley.

This guide explains what makes a soil good, how the main soil types compare, and why these two American regions became so fertile. It also answers a common question: what happens to a river valley when a dam stops the floods? Use the calculator to work out how many days of water your own soil can hold for a crop.

What makes the best soil for agriculture

No single soil is best for every crop. Rice grows well on heavy clay that holds a flood. Carrots prefer a loose, sandy soil. Still, the soils that support the widest range of field crops share five traits.

• Depth. Roots can reach more water and nutrients. North Dakota State University notes that a layer of sand and gravel less than 3 feet down cuts rooting depth and available water.
• Medium texture. Loams and silt loams hold more plant-available water than sands.
• Organic matter. It binds particles into aggregates, which let water enter and then hold it for roots.
• Drainage. Roots need air as well as water. A soil that stays wet in spring delays planting.
• Good structure. Stable aggregates leave large pores for water entry and small pores for storage.

A typical silt loam topsoil is about 45% mineral matter and 5% organic residue by volume, and the rest is pore space, according to North Dakota State University Extension. That pore space is what stores water and air, so a soil’s structure matters as much as its chemistry.

Why texture matters: water held per foot of soil

Texture sets how much water a crop can draw on between rains. In the NDSU table, loams and silt loams hold 2.0 to 2.8 inches of available water per foot of soil. Sands hold 0.5 to 1.1 inches. Clays hold a lot of water in total, but they grip part of it too tightly for roots, so silty clays and clays offer 1.6 to 2.2 inches.

Why organic matter matters, and where it stops helping

Organic matter does more in some soils than others. University of Minnesota soil health specialist Anna Cates explains that the gain in plant-available water is larger in coarse soils than in finer loams and clays. Coarse soils need organic matter to build small pores, while fine soils already have them.

For yield, a global meta-analysis in the journal SOIL (2019) found maize and wheat yields were on average higher with more soil organic carbon, but the gains leveled off at about 2% organic carbon. The same study estimated that about two-thirds of the world’s cultivated maize and wheat land sits below that level. Organic carbon is not the same measure as organic matter, so read your lab report carefully.

Chart

Plant-available water by soil texture

Inches of water per foot of soil, low and high of each range

Best soil types for farming compared

Soil scientists in the US sort soils into 12 orders. The table covers the ones farmers ask about most often, with the wider US and world pattern where the source gives it.

Mollisols cover about 7% of the world’s ice-free land and about 21.5% of the US land area, which makes them the most extensive soil order in the country, according to the University of Idaho. Alfisols cover about 10.1% of ice-free land worldwide and about 13.9% of the US, and the same guide describes them as very productive for both farming and forestry.

These soils are not only American. An FAO country report on Ukraine, prepared around 2009, puts black soil, or chernozem, at 60.6% of the country’s arable land. Which biome has the richest soil? For farming, temperate grassland is the usual answer, because grass roots add organic matter deep into the profile year after year.

The FAO lecture notes on major soils describe soils in alluvial lowlands as young and marked by long wet periods. Stratified Fluvisols form where sediment is still arriving. That is the international name for the kind of soil a flooding river builds.

Chart

Share of world ice-free land by soil order

Estimated percent, selected orders

How much water can your soil hold for a crop?

Soil texture and root depth decide how long a crop can go between rains or irrigations. Enter two soil layers from your own soil survey or test pit. NDSU’s method adds the water held in each foot of the root zone. Its worked example of fine sandy loam over loamy sand over sand comes to 3.75 inches across 3 feet.

A crop cannot use all of that water without stress, so the calculator also asks what share you are willing to let the crop draw down. Your agronomist or local extension office can suggest a figure for your crop and stage.

Try the numbers for your own farm below.

Why the Upper Midwest has such rich soil

Why is the Midwest so fertile? Iowa State University gives a short answer for Iowa: glaciation, prairie vegetation and loess deposition shaped the state’s soils. Much of Iowa is covered by deep Mollisols with thick, dark, organic-rich surface layers. The same three forces work across the wider Upper Midwest, in different mixes from place to place.

Glacial deposits gave the parent material

Ice sheets ground up rock as they moved. When they melted, they left behind till, a mixed deposit of clay, silt, sand and gravel. Meltwater sorted some of this into outwash plains, and the ice front left ridges called moraines. The result is a patchwork of soil structure and drainage, even within one county.

Wind added a blanket of loess

Loess is silt carried and dropped by wind. It is deep, easy for roots to explore, and has the medium texture that holds water well. In western Iowa, the Iowa Geological Survey reports loess generally more than 60 feet thick in the Loess Hills, with 150 to 200 feet recorded locally. Iowa State describes the soils of this belt as highly productive but prone to erosion, especially on steep slopes.

Prairie built the dark topsoil

Till and loess supplied the minerals. Prairie supplied the color. Grass roots died and regrew in the soil for thousands of years, and that steady addition of organic material formed the thick, dark layer that defines a Mollisol.

Rainfall and drainage finished the job

A USDA regional assessment (2015) credits deep, fertile soils and sufficient, reliable rainfall for the Corn Belt’s productivity. It also says about 40% of the region’s arable land has subsurface drainage. Many of the richest fields were once too wet to farm in spring, and tile made them workable.

Is glacial till good for farming?

It depends on its age. Iowa State’s summary shows the contrast within one state. North-central Iowa has young till with closed basins and poorly drained soils, which need drainage but produce well once drained. Southern Iowa has older, more weathered till that gives more acidic, clay-rich profiles. So till is a good starting point, but the age of the deposit and the drainage matter a great deal.

▶ Why soil matters in farming: soil as a living system that holds water and supplies nutrients. · 9:58

How floods built Mississippi River soil

In a natural valley, a flooding river brings new deposits of rich soil to the lands along its banks. When water spills over the banks, it slows down and drops its load. Coarser material settles first near the channel. Finer silt and clay travel further across the floodplain.

The US Geological Survey says sediment left on banks and floodplains is often mineral-rich and makes excellent farmland, and it names the Mississippi and the Nile as examples. So the Mississippi mattered twice for US farming: the same river that built the soil also carried the crop to market.

Valley soils differ from Midwest upland soils in useful ways. They are younger and vary in layers, so a sandy streak can sit next to heavy clay in the same field. Heavy clay areas suit rice, because they hold a flood. Lighter ridges near old channels suit cotton and soybeans. River-valley soils are fertile but, as Iowa State notes for its own alluvial soils, prone to flooding.

Glacial vs flood deposits at a glance

The two regions reached high fertility by different routes, and they need different care.

What rich soil is worth: cropland values by state

Land prices reflect many things, including rent, crop prices, irrigation, and demand from buyers outside farming. Soil quality is only one driver, so read the numbers as a market signal and not as a soil rating.

Chart

Average cropland value by state, 2026

US$ per acre, USDA survey averages, selected states

USDA NASS Land Values 2026 (survey averages, published July 2026) put the US average cropland value at $6,020 per acre. Iowa averaged $10,700, Illinois $10,200, and Ohio $10,100. The lower Mississippi states came in far lower: Mississippi at $4,060, Arkansas at $3,850 and Louisiana at $3,660 per acre.

Those are state averages. They do not say a Delta field is poorer than an Iowa one, since rented land, crop mix, flood risk and local demand all differ. For a state-by-state view of soils and yields, see our guide to the best state for farming by soil type.

Chart

Cropland value trend in four states

US$ per acre, USDA survey averages, 2022 to 2026

If a dam stops the floods, what happens to the valley?

This is a common exam question: every year a river floods, bringing new deposits of rich soil to the lands all along the river valley. Now, suppose a dam is built that prevents the flooding. How might that impact agriculture in the river valley?

The short answer: farms gain safety and steady water, but lose a natural supply of new sediment. Over time, farmers replace that with fertilizer and other soil care.

• Gains. Fewer flooded crops, more reliable planting dates, water for irrigation and transport, and often more land that can be farmed each year.
• Losses. No new layer of silt and clay on the fields. Harvests still remove nutrients, and floods no longer add any back.
• Costs. More fertilizer to keep yields up, which can raise the risk of nutrient runoff.
• Downstream effects. The dam traps sediment, so the delta and coast receive less of it.

What the Mississippi record shows

A study in Nature Geoscience (Blum and Roberts, 2009) reports that dams in the Mississippi basin have cut the river’s sediment load by 50%, and that 25% of the delta’s wetlands have been lost to the sea over the past few centuries. The authors estimated that a further 10,000 to 13,500 km² could be submerged by 2100 without sediment input, because of subsidence and sea-level rise.

Levees add a second effect. They hold floodwater in the channel, so the sediment the river still carries passes by fields it once covered. That protects farms and towns, and few growers would swap it for yearly floods. But the soil now depends on management and no longer on the river.

The nutrient cycle before and after

In a natural valley, floods bring sediment and plant material, roots hold the soil, and soil life recycles nutrients. In a protected valley, the harvest takes nutrients out each year and people must put them back. Doing that with care protects both yield and water.

Fertilizer that crops do not use can leave the field. The US EPA says excess nitrogen and phosphorus can wash into waterways in rain and snowmelt, or leach into groundwater. Further south, NOAA forecasts and measures a low-oxygen zone in the northern Gulf each summer, and the EPA’s hypoxia page explains that the forecast models rest on springtime nitrogen loads measured by USGS. So field decisions across the basin link to water quality far downstream.

▶ How soil and water work together to shape crop production. · 9:40

How to keep good farm soil productive

Rich soil can still be lost or worn down. The first four steps draw on the EPA list of farm nutrient practices. The last two are general soil care advice. Check local rules and get advice from your agronomist or extension office before changing fertilizer, drainage or tillage. Always follow product labels.

1. Test before you add. Sample by soil type or zone, not by whole farm. EPA advises applying nutrients in the right amount, at the right time, with the right method and placement.
2. Keep ground covered. EPA notes that cover crops or perennials prevent bare periods, when soil and nutrients are most exposed to loss.
3. Plant field buffers. Trees, shrubs and grasses along field edges matter most where a field borders water.
4. Manage tile water. Conservation drainage options include changing drainage design and operation, woodchip bioreactors and saturated buffers.
5. Build organic matter slowly. Manure, residues and cover crops all add material. Expect change over years, not one season.
6. Protect river land and wetlands. Where it is safe and permitted, restored wet areas slow water and reduce runoff. This needs local agencies and neighbors on board.

Our guide to sustainable water and soil management covers more options.

What the evidence says about cost and yield

These practices are not a sure win in year one. A USDA Economic Research Service report (June 2025), which reviewed earlier studies, found that less tillage can cut input costs while net profit varies, and that the short-term return on cover crops was often negative without cost-share. It also reports that cover crop use often stopped: more than half of the operations using them in the 2012 or 2017 census did not report them in the next one. Adoption and persistence rose in the Heartland region.

No-till needs the same honest view. A global meta-analysis in Nature (2014), covering 5,463 paired yield observations, found that no-till reduced yields overall, though the response varied with conditions. Run a trial strip on your own farm first, and compare it with your normal practice for several seasons.

Where satellite maps fit

Satellite images do not measure soil nutrients directly. They show how crop growth differs across a field and over a season. That helps you decide where to dig, sample or walk first, especially on valley fields where the soil changes over short distances. Farmonaut offers satellite vegetation maps for this kind of field check on web, Android and iOS, and they work best alongside a soil test.

▶ A light explainer on seven simple ways to protect soil and water on the farm. · 4:34

FAQ

What is the best soil for agriculture?

For the widest range of field crops, a deep, well-drained loam or silt loam with good organic matter. Among soil orders, Mollisols are widely rated as highly productive. The right soil still depends on the crop: rice, for example, suits soils that hold water.

Why is the Midwest so fertile?

Glaciers left mineral-rich till, wind added deep silt called loess, and prairie roots built thick, dark topsoil over thousands of years. Reliable rainfall and tile drainage then made the land highly productive for corn and soybeans.

Which US states have the best soil?

No official ranking exists. Iowa and Illinois are known for deep Mollisols, and the Mississippi Valley for alluvial soils. Local soil survey maps tell you far more than a state average, because soil quality changes within a county and even within a field.

What is the richest type of farmland along rivers?

Floodplain land made of alluvial soil, which is silt, sand and clay left by floods. The USGS describes this sediment as often mineral-rich. Its risks are flooding, wet spells and sharp changes in texture across a field.

What crops grow best in these soils?

Upper Midwest soils are known for corn, soybeans and wheat. The Mississippi Valley grows cotton, rice, soybeans and corn. Soil, climate, markets and water supply together decide what fits a given farm.

Can you make poor soil into good farm soil?

You can improve it, within limits. Organic matter helps most on coarse soils, and drainage can transform wet ones. You cannot easily change texture or depth across a whole field, so match the crop to the soil you have and test before spending on inputs.

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