Influencing Cotton Health
Balanced nutrient supply, adequate moisture availability and the absence of insects and disease support healthy plant growth. The nutritional health of cotton refers to various plant tissues containing adequate and balanced concentrations of nutrients to support development at particular growth stage. A reduction in performance will occur if imbalance exists, both with respect to deficiency (deficiency imbalance) and excess (excess imbalance).
Nutrient removal from fields through harvest export, leaching and water runoff needs to be replaced to maintain soil fertility. Nutritional status management generally involves the supply of mineral nutrients in correct proportions and at opportune times using the 4Rs; right source, right nutrient rate, right time and right place. Nutritional balance is important as nutrient excess or deficiency may increase the plant’s susceptibility to diseases.
The effect of some nutrients on development and maturity of plants may support plant health. Phosphorus, for instance, supports rapid root growth and helps plants tolerant Black Root Rot. The opposite is observed with high nitrogen levels, which increase the shoot growth and delay plant senescence, creating conditions for pathogens attack.
Some nutrients “strengthen” plant tissues, such as calcium and potassium, while others make them more tender and juicy, and thus more sensitive (e.g., high nitrogen rates).
Mechanisms of physiological resistance by nutrients has been related to the amino acids regulation and protein synthesis. Nitrogen normally determines amino acids composition, whereas zinc and others interact with nitrogen to regulate amino acids, amides and protein concentration.
Some contradictory aspects, according to the literature, might be associated with indirect effects of nutrients and its interaction. An example would be Fusarium wilt in cotton, which decreases by increasing organic nitrogen, despite of temperature effect.
Cotton resistance to Fusarium wilt is also associated with zinc, that causes increase on ascorbic acid and carbohydrates.
Premature senescence in cotton is mainly related to potassium and phosphorus nutrition, regardless of potassium and phosphorus supply. This disturbance is caused mainly due to environmental stress, such as flooding, cold, cloudy days and soil compaction. These factors interfere with the plant’s capacity to absorb potassium and phosphorus, which is required in large amounts between flowering and boll filling. As a consequence of premature senescence, the bolls open earlier, providing smaller fibers, and lower quality than normal bolls. This risk can be reduced by foliar applications of potassium and phosphorus where low levels of soil K and plant tissue concentrations are detected.
