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Because roots perform the important functions of water and mineral absorption, as well as provide the plant anchor, management decisions should be made with consideration given to the affect it will have on rooting depth. Some of the factors impacting root growth and development include:
Planting Conditions - Poor early root development resulting from chilling injury can continue to cause problems throughout the season with diminished feeding capacity and limited yield potential.
A root system reaches its maximum depth at first flower.
Water and Nutrients - Controlled water and nutrient applications encourage good root development and growth. Excessive water and nutrients can lead to shallow rooting with drought and deficiencies resulting in excessive root growth, both of which can negatively impact productivity of the aboveground parts of the plant.
Compaction - Soil compaction presents another problem to effective root function and development. With restricted root development, the frequency of irrigation impacts yield as the harmful affects of a shallow root system can be overcome by frequent applications of small volumes of water. To minimize compaction, it’s advisable to stay out of wet fields. Subsoiling prior to planting may be needed to improve root development.
Oxygen - Soil oxygen is necessary for root growth. Another key to oxygen reaching the root zone is good field drainage. Drainage keeps soil from saturating (which fills the soil air spaces with water).
Soil pH - Root development is also affected by soil pH, with normal growth occurring between pH levels of 5.5 to 8. Outside these ranges, root development is restricted.
The cotton plant attempts to balance growth between below- and aboveground parts. This is called the root-to-shoot ratio. The root-to-shoot ratio differs at various stages of growth and is influenced by environmental conditions. To understand the root-to-shoot relationship, it’s important to know roots supply the plant with the moisture and nutrients which enable growth. Shoots, or aboveground growth, supply the carbohydrates needed for continued root growth.
Research shows that root length and biomass reaches maximum at 1,000 DD60s or approximately one week after first flower. Peak vegetative dry weight reaches its maximum at approximately 1,530 DD60s. In the intervening 530 DD60s, fruit and vegetative dry weight increase dramatically, but total fine root length decreases to only 47 percent of its peak value. Root and vegetative growth is extremely sensitive to and slowed by initial boll set as competition for carbohydrates increases. Once flowering begins, root development cannot overcome prior development problems.
Water stress shifts growth from shoots to
roots and low solar radiation shifts growth
from roots to shoots. Shoot damage, whether
through environmental factors like hail or
mechanical like poor post-directed herbicide
applications, will slow root growth until the
plant can recover. Similarly, root pruning will
slow shoot growth until root growth recovers.
Most growers and consultants are aware that
cultivations damage roots and slow shoot
development. We are probably less aware that shoot damage retards root development.
This article is from the Cotton Management Guide, a publication with year-round advice on managing high-yielding cotton. Download the Deltapine Cotton Management Guide now or sign up for new content to be delivered to your email each month.
Click here to learn about branch development.