Soil Health

The cover story on my just arrived Crops and Soils magazine is "Soil Health".  I was interested because we assist with soil health.  The article starts out talking about the fact that in the past, soil health was most often related to soil fertility.  I would venture that a good balance of plant nutrients is still needed to maintain a healthy soil from the standpoint of crop production.  Maybe a bit of a definition is in order.  Susan Andrews of NRCS says in the article that soil health is the capacity to soil to do what it was intended to do.  She says that in the case of crop production, productivity, nutrient cycling to prevent nitrogen leaching, holding water for plant use, filtering contaminants, and resisting erosion.

I would contend that all of the listed functions start with soil fertility.  We cannot maximize productivity without maintaining proper fertility.  We need to have healthy crops to take up the nitrogen fertilizer we use.  Good plant root systems create macro pores that move and store water in the soil.  Healthy soil has healthy microbial populations that help break down contaminants, and healthy soil has good tilth which increases water infiltration and reduces soil erosion.

I tell my customers that in the realm of simple soil testing, the best indicator that you are maintaining healthy soil besides the nutrient levels is the organic matter content.  Organic matter test levels can vary a bit from year to year because of randomness, but over time we hope to maintain organic matter levels.  We maintain organic matter in two ways.  First we need to produce a lot of plant material so that as it decomposes, it replaces organic matter that has oxidized during the growing season.  In addition, we want to prevent excessive soil erosion.

Erosion prevention is pretty simple too.  Avoid burying more residue than necessary and avoid unnecessary tillage trips.  No-till is the most effective in reducing soil loss, but judicious tillage can be a useful soil management tool on less sloping soils.

Healthy soils tend to support aerobic microbes.  Drainage practices can help remove excess water and promote healthy microbes.  Proper soil pH can also support healthy microbes.  Avoiding field operations on wet soils avoids compaction.  Compaction reduces the air content in soils, reduces water movement in soils, reduces water holding capacity, and makes root penetration more difficult.

In the East and Midwest, cover crops are enjoying a surge of popularity.  Why?  Cover crops help with the issues that Ms. Andrews pointed out.  Cover crops can help with uptake of excess nitrogen and making that nitrogen available for future crops.  Cover crops open more pores improving uptake and transport of water.  More water entering the soil is less water to create erosion.  Cover crops can also help the soil recover from the effects of compaction and in some cases will even help prevent compaction.  All of the positive effects of cover crops generally translate into more productivity.  In arid and semiarid regions, cover crops may not be helpful because of water conservation issues.

Having healthy soils is not impossible even with high levels of productivity, but NRCS's Norm Widman cautions in Crops and Soils that "you can screw it up fast, but it takes a long time to fix it."