Hardpan

Hardpan can be the bane of a farmer’s existence.

Once a layer of hardpan forms, no water can penetrate the soil beyond that level. Any moisture that reaches the hardpan layer will simply run off.

Furthermore, roots cannot enter the hardpan, either. Once a probing root tip feels the hardpan, it will turn aside, directing root growth horizontally. Or, worse yet, the plant will give up growing roots altogether.

This phenomenon can have two very detrimental effects:

Shallow-rooted plants with poor drought tolerance.
Wet fields that collect water on the surface, drowning plants.

Causes of Hardpan

Hardpan can form in a number of ways. Sometimes it is a natural occurrence, while other times it is a manmade event.

Deposits are a major cause of hardpan in some areas. Hardpan-forming deposits can include:

Sodium.
Dissolved silica.
Rust/limestone combinations.

Clay soils are particularly prone to hardpan problems because their particles carry strong negative charges, thus inviting bonding with other substances. Acidic soils, which have a positive charge, have similar problems.

Any factor which tends to promote soil compaction can also help create hardpan. Two common factors include:

Heavy machinery or livestock traffic.
Repeated plowing, particularly at the same depth every year.

However, soils can form hardpan without help from compaction.

Now What?

If you have discovered that hardpan is a problem in your soils, never fear. The solution will take time, but there is hope nevertheless.

Your goal is to restore a capillary structure to the soil. This can be done in a number of ways:

Break up the hardpan layer. On a small scale, this is typically done with a broadfork. On a larger scale, a variety of animal- or tractor-powered tools are available, such as rippers and subsoilers.
Plant a strong-rooted cover crop. The ideal crop for this job will have the strength to force its roots into the hardpan and start to break it up. Good choices for deep compaction include chicory, tillage radishes, sweet clover, medium red clover, and fall mustard crops. For hardpan closer to the surface, consider annual ryegrass, hairy vetch, white clover, and forage turnips.
Work to build the level of organic matter in the soil. Organic matter separates soil particles, preventing compaction.

Again, curing soils of hardpan takes time. The more aggressively you pursue your soil improvement program, the faster you will begin to see results.

An Ounce of Prevention…

The key to avoiding hardpan is to preserve a lighter soil structure, and the key to preserving a lighter soil structure is to maintain soil health.

Healthy soils are well aerated. Plant roots burrow through the soil, keeping it loose and setting up a flow of nutrients. Organic matter keeps soil particles apart and retains just the right amount of moisture. Earthworms build tunnels, improving aeration still further.

The soil is a wonderful ecosystem. Fortunately, there are many ways that farmers can maintain that ecosystem:

Grow cover crops to keep soil particles spaced with roots.
Spread manure to add bulk to the soil and promote earthworm activity.
Keep livestock and vehicles out of soggy fields to prevent soil compaction.
Practice no-till farming to avoid disrupting the existing soil capillary structure.

Preventing and dealing with hardpan doesn’t have to be complicated. The same principles that apply to maintaining soil health in any other situation apply here.