Explore other soil management options before using deep tillage.

Oct. 7, 2003 - If poor crop rotation caused the problem in the first place and you're not going to change it by deep ripping.

By Thom Steyn

Deep tillage can be an effective way to break up a layer of compacted soil. It can also be a recipe for disaster. For a lot of farmers, deep ripping may sound like a good way to solve a drainage problem or persistently poor root development. Deep tillage used under the right conditions and the right time can give a land a fresh start, but used on the wrong depth and/or way, when the compacted area is still wet it can and will be a waste of money, time and effort.

Remember that a ripper is a prescription tool for compaction and must be used accordingly. It is important to assess the problem first before doing anything. A soil probe from a penetrometer, pushed down slowly into the soil can reveal the depth and thickness of the compacted layer. You can also dig down (a profile hole) and find the area where plant roots seem to stop or branch out laterally.

Compaction is found regularly in South Africa. Work done by researchers of the ARC - Small Grain Institute on farms in different regions showed that up to 80 percent of the soils tested had some form of compaction. Of these soils, 20 percent were severely compacted. Compacted soils have a significant negative effect on crop yields in a stress year like the wheat season of 1999/2000. When conditions are more favorable the impact is less but still significant. It must be remembered that the advantages of deep ripping usually last for only a year or two, depending on the soil texture, structure and organic carbon.

Compaction is not limited to sand or clay texture soils and can form in all types of soils. It is caused by the equipment used, the weight and the amount of vibration that it exerts on the soil, as well as the soil moisture content during tilling. The following aspects are important when compaction occurs:

• Determine what has caused the compaction in the first place, so that a natural part of the soil structure is not mistaken for a compacted layer.
• Use longer crop rotations and deep-rooted crops in rotation to avoid or alleviate compaction.
• Incorporate manure/stubble into the soil to rebuild the soil structure.
• Use minimum or No Till practices to minimize the deterioration of soil structure.
• Make sure tillage is done when the soil moisture content is optimum.
• Vary the primary depth and angle of tillage each year.

When you do till, check the soil moisture content at the tooth depth. Unless the soil is dry enough to shatter, the tooth will only drag through and perhaps cause more serious sideways compaction. Continuous tilling at the same depth only enlarges the thickness of the layer and the compacted layer shifts down. Remember that aspects like crop rotation and timely tillage are the key to getting the most out of deep tillage.