Dirt. It’s arguably a farmer’s most valuable natural resource. But what makes some soils more productive than others? That’s a complicated question to answer, but we do know that the healthiest soils share some common characteristics. While some of these are difficult to change, there are management practices you can employ to improve soil quality.
Soil health 101
When you think about soil, you probably don’t consider that it is alive. In fact, there are more microorganisms in a teaspoon of healthy soil than there are people on Earth. Roots, earthworms, bacteria, fungi, actinomycetes, algae, protozoa, nematodes, mites and small insects work together to help build soil aggregates (sand, silt and clay). Some of the characteristics of healthy soils are inherent, while others are dynamic and can be influenced by management decisions.
Inherent soil characteristics
Examples of inherent soil characteristics include soil texture, drainage class and cation exchange capacity (CEC). These things are a result of the process of soil formation over time and are influenced in part by vegetation, topography and climate.
Dynamic soil characteristics
Many soil characteristics are amendable depending on the way soils are managed. Farmers looking to improve their soil health and crop productivity should focus on doing things to change the soil characteristics in this category. Soil organic matter content, microbial populations, bulk density, infiltration rate, soil water and nutrient holding capacity are examples of dynamic soil characteristics that change over a shorter time period with or without human intervention.
Measure your soil’s health
You have to measure soil health to manage it. A combination of field and laboratory testing can give you a comprehensive analysis of your soil’s health.
You can take core soil samples and send them off to a lab for analysis of total carbon, total nitrogen, phosphorus, potassium, CEC and soil pH. Soil testing labs can measure soil microbial biomass carbon and other biological indicators. Soil testing can give you a benchmark level of other micronutrients in the soil as well.
You can use visual field analysis to survey physical soil properties, like soil structure, compaction and water infiltration. Some biological analysis can also be done by examining plant and root health or counting earthworm numbers. Iowa State University offers a soil health field guide that includes a health assessment checklist for evaluating and scoring soil characteristics in the field.
Audit your management practices
Once you have done laboratory and in-field soil analysis, you can make changes to your management practices to improve soil health. Here are some recommendations:
- Consider no-till. Tillage can be very detrimental to physical and biological soil properties. Intensive tillage can result in the loss of organic matter and less water infiltration and can cause soil pores to collapse, leading to excessive ponding in fields. Research conducted by the National Association of Conservation Districts and Datu Research found that using cover crops and/or no-till can result in an economic return of over $100 per acre as a result of less fertilizer and erosion repair costs and higher yields.
- Rotate crops. Monoculture cropping systems are the worst for soil health. Adding different crops in the rotation can improve soil aggregation and organic matter. Organic matter content influences a number of soil characteristics, including soil bulk density (a measure of compaction), soil water holding capacity, cation exchange capacity and nutrient availability.
- Try a cover crop. Similar to the benefits of crop rotation, planting cover crops adds physical and biological diversity to the soil. In addition, cover crops protect topsoil erosion and soil stability. Adding grass, barley, legumes or wheat to your rotation can increase carbon availability in soil. Other cover crops with deep rooting systems, like radishes, can improve gas flow in soil and help with compaction.
- Manage crop residue. Crop residue can help retain soil moisture and reduce soil erosion. But it’s essential to manage the carbon to nitrogen (C:N) ratio to get the most benefit from crop residue. Soil microbes require carbon and nitrogen to remain viable in the soil. Their diet requires approximately 24 units of carbon for every unit of nitrogen metabolized. When there is too much carbon in the soil, the microbes need more nitrogen to compensate and extract it from the soil. This ties up nitrogen and makes it unavailable to crops. If C:N ratios are high, residue decomposes slowly, and the nutrients from that decomposition aren’t cycled back to plants as quickly. On the other hand, when the C:N ratio is low, soil microbes consume all of the carbon, but leave the excess nitrogen in the soil for plants and other microorganisms to use. In this case, residue decomposition happens quickly, and the benefits of the residue cover may be lost. Finding the right C:N balance makes a big difference when it comes to soil health. The Natural Resources Conservation Service recommends a 24:1 carbon to nitrogen ratio in crop residue to maintain microbe, soil and plant health. The C:N ratios of common field crops are shown in the table below.
Adapted from NRCS, Carbon to Nitrogen Ratios in Cropping Systems
- Limit traffic. Multiple trips through a field with heavy equipment is the leading cause of compaction. Compaction limits root growth, resulting in a number of crop production problems, including loss of standability, limitations on nutrient and water uptake and gas exchange in the soil. Limit field traffic during wet conditions and try to use the same paths when planting, fertilizing, applying pesticides and harvesting to minimize compaction.
There’s still a lot to learn, but we do know that management practices can have a significant impact on soil health. Since it’s your most valuable natural resource, it pays to protect your dirt. Use soil sampling every few years along with in-field surveys to make management adjustments to improve soil health. Small changes over short periods of time can improve farm productivity.