It is not nitrogen, but water, that is the most limiting factor in crop production. Soil texture, structure, percent organic matter (OM) and management practices also influence the amount water and nutrients a soil can retain for crop use. You can better understand your farmland’s strengths and weaknesses by digging deeper into the physical characteristics of your soil and where different soil types are located on your farm.
Soil Texture
Soil texture refers to the feel of soil. Soils are made up of different amounts of sand, silt, and clay. There are 12 soil textural classes according to the USDA classification system. Each soil texture has varying responses to water, affecting major crops like corn, soybeans, wheat, and alfalfa differently. Here’s a general overview:
1. Sand: Sandy soils have the largest particle size, which allows water to drain quickly. As a result, sandy soils tend to dry out faster. Sandy soils have low water and nutrient-holding capacity and struggle to retain sufficient amounts for crops. Shallow-rooted crops are more susceptible to drought stress in sandy soils, as they may experience water deficits that hinder their growth and yield.
2. Silt: Silty soils have medium-sized particles, providing better water retention than sandy soils. They have moderate water-holding capacity and drainage characteristics. During drought, silty soils can retain moisture for longer periods compared to sandy soils. Silty soils have more plant-available water capacity than clayey soils.
3. Clay: Clay soils have lots of small fine particles with many inner layers creating lots of surface areas that hold water and nutrients tightly. They have higher water and nutrient holding capacity but lower drainage, resulting in slower water movement and potential waterlogging. Also, they have lower plant available water capacity than silty soils because clays hold water tightly as they dry. During drought, clay soils can retain moisture relatively well, which benefits crops like corn, soybeans, and wheat. However, excessive water retention in clay soils can also lead to root oxygen deprivation and negatively impact crop growth in wet years. Any crop with a deeper root system may perform better in clay soils during drought as it can access the stored water.
How to quickly estimate your soil texture
There are several ways to determine the texture of the soil. Quick methods that can be used include: the jar method, or hand texturing( A 3588 Table 2.2) But you may already have some clues on the farm:
1. Hand texture by feel is another option. Instructions can be found here https://www.nrcs.usda.gov/sites/default/files/2022-11/texture-by-feel.pdf or get help from a crop consultant, county land and water, or NRCS personnel to help.
2. SnapPLus nutrient management software provides each field’s dominant soil type. The soil names themselves can give you clues, for example, Wisconsin’s State Soil- Antigo Silt Loam. Just like a food product ingredient list, they are listed in order of quantity. Antigo Silt loam is mainly silty, followed by loamy. Loam is an even mixture of sand, silt, and clay.
3. Online Soil Maps- visit WebSoil Survey zoom into your location or enter your address to see overlaying soil type. https://websoilsurvey.nrcs.usda.gov/app/
Soil texture’s influence on water
Water infiltration speed and plant water availability are dependent on soil texture. In coarse sandy soils the bigger pore spaces increase the rate of water movement and have higher infiltration rates than fine textured soils. Coarse soils can “soak” up a drenching rain or recharge quickly but is unable to hold as much water as finer textured soils. A coarse sand infiltrates very fast, up to 10 inches per hour, while a clay is the slowest can be less than 0.05 inches per hour. However, sandy soils have a low water holding capacity compared to loamy or clayey soils. On the opposite end, soils with very high clay contents hold water tightly and provide less water storage for plants than loamy soils. The table below illustrates the water that can be absorbed by soil that is available to plants, which varies with soil texture.
| Soil Texture | Plant Available Water (Inches of water per foot of soil depth |
|---|---|
| Coarse Sand | 0.25-0.75” |
| Fine Sand | 0.75-1.0” |
| Loamy Sand | 1.1” |
| Sandy Loam | 1.2-1.4” |
| Loam | 1.95” |
| Fine Sandy Loam | 1.40-2.00” |
| Silt Loam | 2.00-2.50” |
| Silty Clay Loam | 1.8-2.0” |
| Silty Clay | 1.5-1.7” |
| Clay | 1.2-1.5” |
Organic matter increases water retention
Typical Wisconsin soils have 1.5- 4% organic matter, peat or muck soils can be over 20%. The organic portion of soil is important, it improves soil properties that help plants grow by promoting structure, pore space, and a home and source of food for soil life. Yet anytime you till and mix oxygen into the soil, organic matter is burned off a bit. Over time this can decrease the amount of organic matter in soil. Increasing soil organic matter can take 5 to 8 years depending on soil type, climate, and management.
Organic matter has a natural attraction to water. Organic matter acts as a sponge in the soil, capable of holding and storing water. It has a high water-holding capacity due to its porous structure and ability to absorb and retain moisture, plus it helps aggregation and pore space where water can be stored. Here are some general examples of the impact of organic matter on soil water:
- For each 1 % increase in soil organic matter helps soil hold 20,000 gallons more water per acre.
- An ideal soil with 4-5% organic matter can soak up a 4-6” rain event.
- A 1994 study by Hudson showed that a silt loam soil with 4% organic matter holds more than twice the water of a silt loam with 1% organic matter.
Understanding the role of soil texture in water-holding capacity, and that organic matter significantly improves water-holding capacity can help us understand the strengths and weaknesses of a field during rainfall, irrigation, and during flood or drought conditions. Wisconsin has a wide range of soil textures. The challenge in managing sandy soils is to improve water retention or water holding capacity. In fine texture soils, however, the challenge can be to remove excess water depending on drainage conditions. Both goals can mean increased profit. Farmers cannot change the soil texture that mother nature has provided them. Although increasing organic matter content takes time, practices such as adding compost or manure, using cover crops, and practicing organic farming methods can enhance the soil’s ability to retain water and support healthy soil and healthy plant growth.
More info
More detail on soil water can be found in A3588 http://corn.agronomy.wisc.edu/Management/pdfs/A3588.pdf
Soil and Water Management Presentation https://soilsextension.webhosting.cals.wisc.edu/wp-content/uploads/sites/68/2014/02/CCA_Soil_Water_Mgmt.pdf Soil Moisture Management https://fyi.extension.wisc.edu/cropirrigation/soil-moisture-management/
