Recognizing Good Soil Health

 

Dr. Alan Franzluebbers, North Carolina Extension has a YouTube video showing farmers how to look for healthy soils and then improve it. There are several obvious soil health indicators like looking for earthworms, earthworm burrows, and their middens. Also, remove surface residue and look for white spiderweb like matts which are beneficial fungi. Crop fields with small mushrooms growing are a good sign because those are beneficial fungi just spreading their spores. However, the hardest to see are the soil bacteria which can be over 1 billion per teaspoon of soil. Soil Biology has been understudied and is extremely important. 

Soil biology can be measured by looking at the soil biological activity, measuring the total biomass of living organisms, and by looking at the diversity of these organisms. The biology has four main functions: decomposers of crop residue, cycling of water and nutrients, controlling gasses like carbon dioxide for photosynthesis and oxygen for root respiration, and diversity of organisms (think reduce diseases, release nutrients, etc.) and to keep the soil in balance. 

There are four main soil processes to consider when evaluating soil biology which can be compared to a bee hive. The chemical process is how many nutrients (like fertilizer, N-P-K, micro nutrients, lime) are available which is like nectar or harvested pollen. The physical portion (like a hive) is how many soil aggregates (soil that crumbles) are produced. Good healthy soils have good water infiltration and less water runoff and allow the soil gasses to move freely. Poor soil structure looks more like concrete. Crops and beneficial microbes struggle to grow in these type soils. Biological activity is like the bee’s in a hive. They are the workers who process everything. And where all three processes interact, that is where soil organic matter (SOM) is formed which is like the honey in a hive. 

Dr. Alan showed graphs of grassland, cropland, and forested soils. In all cases, the majority of biological activity occurs in the top 4 inches. Going deeper dilutes the biological effect. Taking a sample with a core sampler is usually the best method. Usually, the sample is dried, crushed and sieved. This can destroy some biology, but it is the most common method of soil sampling. When soils are rewetted in a lab, the best soils with the best soil health wet easily, quickly absorb the water, and the water is not muddy. Poor soils with poor soil health have difficulty absorbing water and tend to stay muddy just like crop fields with poor soil structure. 

Lab researchers will check the soil for carbon dioxide bursts. The higher the bursts, the better the soil health. Microbes give off carbon dioxide which the plants can recycle to make crops. Here is where many labs differ in their procedures. Some labs do a quick burst, other a 24 hour or 1 day burst, 3 days, and even 10-day bursts of carbon dioxide. The Haney test, Solvita test (Woods), Cornell Cash test all use slightly different methods. 

Dr Alan likes a 3-day burst and uses a larger soil sample to get more uniform results. He found that the amount of soil diversity is highly associated with good soil health activity. He also found that the amount of Nitrogen (N) mineralized or recycled is also associated with the highest soil health. Interesting point, while sand, silt and clay (soil texture) are important, they have little effect on N recycling (mineralization) if soil health is high. 

Here is Dr. Alan’s bottom line. Inorganic nutrients (like fertilizer) are easy to test for but only represent about 50% of the total soil N that a plant takes up. The other organic N is associated with the microbes and the SOM and is harder to measure. Since soil N for plants is associated with high biological activity, farmers need less costly N fertilizer on healthy soils to get the same yield. 

A standard recommendation for N is around 0.9# to 1.2# of N per bushel of corn. For a 200- bushel corn crop, that’s 180-240# of N fertilizer needed for soils with poor soil health. For soils that have some or intermediate soil health, only 0.6-0.9# of N fertilizer are needed or 120-180# of N fertilizer. Only healthy soils (think virgin soils or fence row type soils), only 0.3-0.6# of N fertilizer or 60-120# of N fertilizer are needed. 

Many companies are now exploring the biological side of agriculture. There are many biological products out there but not all work on every farm. Using no-till, cover crops, and manure have been proven to improve soil biology and soil health. 

 

For more information, go to Dr. Alan Franzluebber’s youtube: