Hard pan

Hard pans, plough pans or soil structure faults are terms used to describe a soil layer that is hard, compacted and roughly horizontal.

To make it simpler, we will just use one term for all of them: hard pans. Hard pans restrict root growth and make it difficult for water, air and other gases plus soil organisms to move up and down. They are caused by tilling to a particular depth or by several other factors.

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Hard pans restrict root growth and make it difficult for water, air, other gases plus soil organisms to move through the soil. They are often caused by tilling or ploughing to a particular depth.

A hard pan can occur at any depth.

The hard pan is more likely to cause severe problems if it is:

closer to the surface
thicker and/or
harder
and particularly if it is
- present during a dry time
- present during any other period that stresses plants

The more severe the problems, the more likely you are to get benefits from dealing with the pan.

Effects of hard pans

Hard pans show up in plants as

lack of drought tolerance, plants
- die off earlier in dry times
- are more affected by drought
and in restricted growth. Plants
- grow slower
- are stunted, they don't get to normal size for the same plants nearby or in years gone by
- slow down from lack of moisture before other similar plants slow down without a hard pan under them.

The stunting can be because of

a lack of soil moisture
a lack of nutrients
inability to grow a suitable-sized root mass.

The effect of all this on the soil keeps biological activity low.

These effects are the result of restricted effective soil depth.

The situation can be improved by increasing the effective depth of the soil. There is more info on improving conditions in soils that have hard pans in Non-inversion tillage

Detecting hard pans

Look for areas showing symptoms and save yourself some time. Look for areas where plants

die off earlier in dry times
are more affected by drought
grow slower or
don't get to normal size for the same plants nearby or in years gone by.

Many other factors can cause problems such as these, but this should help you narrow your search. On your land, with your management you may find hard pans more:

On the high part of slopes
Or on low parts
Or on the flats
Or on particular soil types.
Or in some other particular situation related to
- your land's conditions or
- your past management.

As a result, you can get a good understanding of the effects of your management from looking for hard pans.

You can dig for hard pans, but it is quicker to walk and use a steel rod to help you find them. A rod of around 6 mm or ¼ inch diameter with a teardrop or rounded point and a handle or knob on top to push against. This technique works well in most conditions, but definitely works better where there is enough moisture in the ground.

You push the rod in gently but firmly until it stops. Then dig down and find out whether this is a hard pan. Try a few more areas until you get a feel for it and then you should be able to use just the rod with less need for digging.

If the soil is dry, you may need to use a trowel, fork, mattock or shovel. The mattock is not generally as effective as the rod, because it cuts straight through some hard pans without you noticing. But if you get down close to the mattock hole you should be able to see and feel the hard pans on the vertical sides of the cut.

Some things that contribute to hard pans

Soils may have hard pans naturally: They are just hard at certain places because that is how they were laid down
Tillage methods: Some implements are more likely to cause pans. The worst are probably rotary hoes, disk harrows and disk ploughs, particularly if used when the soil moisture is not just right. Almost any mix of tillage tools used often enough at around the same depth will help create a hard pan.
Inappropriate species: Using shallow-rooted species means little use of and little opening up of deeper layers of the soil. As a result, a hard pan can develop just below the root zone
Inappropriate grazing management: Repeatedly giving only a short rest interval - grazing plants too soon after the previous grazing - can contribute to the development of a hard pan. This can also happen under set stocking, particularly in areas or on species favored by the stock. These plants will usually be undersized as a result of the grazing even before the pan develops and that is how a pan develops - these are now shallow-rooted plants, even if that is not their normal form
Poor infiltration: Water doesn't go very deep and as a result the plants growing in that soil can't and won't go deep. This concentrates biological activity in a shallow zone and as a result a hard pan often develops below it. And then infiltration will be even worse because the soil will fill up more quickly because it is effectively shallower
Lack of earthworking earthworms and other macrobes: Because these animals are not passing up and down through this zone, the pan can develop unimpeded
Overstocking: High weight of animals can lead to a compaction layer a little below the level of greatest biological activity. Soils can take months or even years to recover
Weather conditions: Such as lots of light rains but few good soaking rains. Can be worse with high evaporation soon after rain. Summer rainfall areas can be particularly prone to this problem
Shallow irrigation: Can do similar things but much quicker.

Dealing with hard pans

Plants with long taproots

Some plants have long taproots and can push through some hard pans, loosen compacted soil and bring up nutrients from lower layers. Some of these are

trees
alfalfa (lucerne)
safflower
some of the radishes

Conventional tillage

You may need to do this deeper than you have been, particularly if your tillage practices have contributed to the development of a hard pan

Non-inversion tillage

This is an extremely effective way to deal with hard pans and slow their development

Change in grazing practices

By grazing harder then resting the field for longer and particularly using Grazing shock, you may be able to stimulate the biological activity in the soil as well as open up channels through the pan

Related info:

Pastures that are rotationally grazed and green manures that are slashed can extend the benefits (think about how this works). One way to make this work is to Return a third to the soil

Selective grazing shapes your weed and pasture populations whether you like it or not.

Grazing shock has some similar effects if managed well.

Non-inversion tillage

Pastures that are slashed can reduce the problem (think about how this works). There's more about bringing this into effect in Return a third to the soil

By choosing a green manure mix that maximizes the impact on a hard pan, you can achieve a benefit over time.

Take particular care if the hard pan is over a dispersible clay.

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This page was updated on December 27, 2007