The Hidden World of Roots

Just like icebergs, the above ground part of plants is only the tip of what is really going on. Recently, Dr. Richard Zobel of the United States Department of Agriculture spoke at the Southwest Ag Conference on Rhizobotany or the science of roots. Dr. Zobel is one of those rare researchers - the root physiologist.

Roots exist in a much more complex environment than the shoot or upper part of the plant. Makes sense, shoots deal with weather and are in the open air while roots still deal with daily weather but exist and grow in the soil, a complex arrangement of mineral particles, organic matter and air or water filled spaces. The density, pH, water content or nutrient content of the soil can vary greatly within the area exploited by a root system. That smooth soil surface hides a wealth of variability.

At one time it was believed that plants grew roots as the rest of the plant grew during the spring and the plant used those very same roots throughout the summer until it died in the fall. Gradually it came to be understood that roots generally need actively growing surfaces or root tips for nutrient uptake. Further careful measurements have shown that roots are constantly growing, dying and sloughing off the plant. For example the finest lateral roots only live about 2 weeks. This constant growing and dying of roots changes the soil close to the root system, creating a localized environment that is better for root growth and other living organisms like bacteria.

Roots are responsive to the environment. New roots can be started or initiated within 24 hours of a change in the soil environment. For example, think back to the dry conditions last summer. The root systems of most plants had stalled in growth but once the rain came the plants responded quickly. Roots only need 10 per cent of their root surface at any point in time. So why does the plant commit that many resources to roots? The extensive root system allows the plant to take nutrients and water from other areas within the soil profile, so once a location has been stripped of nutrients the root system can access them elsewhere.

Dr. Zobel shattered many of our beliefs about roots in his talk. Big in a root system is not necessarily better, in fact often this indicates a problem. A plant will grow a larger root system in reaction to stress, whether it is drought, compaction or other stressors. Really what he was getting at was that a good root system is consistent and well developed through the soil profile - you should not see a concentration or witches broom effect. A larger root system uses the plant resources reducing the amount available for building yield.

So make a plan for next summer to get to know your crop's roots better - they may be trying to tell you something.

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