The presence of compacted layers such as plowpans can significantly affect the growth of cotton roots.The depth of these layers or zones of high soil strength can range from a few inches to a few feet below the soil surface. Generally,as soil resistance increases,the root elongation rate decreases,which can cause the root system to extract water and nutrients from only a limited soil volume.Thus,the plant will be more susceptible to drought stress later in the season. Rooting density is also generally lower in the compacted zones. The pictures shown depict some of the responses of young cotton roots to zones of igh soil strength. These plants were grown under conditions of optimum temperature and moisture. In Figure A,the growth of the taproot was root stopped when the seedling system encountered the compacted zone. These zones are not always distinguishable by color changes,so it may be difficult to determine exactly where the compacted layer begins and ends. In Figure A there was an increase or “flush ”of lateral root growth along the surface of the compacted zone in both seedlings which severely limited growth to lower depths. A similar situation is shown in Figure B. Figure C shows that the taproot encountered a zone of high soil strength which deflected the growth of the root until the root tip encountered a nearby zone of lower strength and the root continued to grow downward.Other variations of these typical responses may be observed but in general the growth of the taproot will either stop or be deflected at the surface of the compacted zone.

Figure A


Figure B


Figure C