How to improve cotton health

A reduction in performance will occur if imbalance exists, both with respect to deficiency (deficiency imbalance) and excess (excess imbalance).

As a result of the general removal of mineral nutrients from the production site, via harvest, leaching and water runoff, nutrient replenishment is generally required. Thus, nutritional status management generally entails the supply of mineral nutrients in correct proportions and at opportune times. Nutritional balance is important, since nutrient excess may increase susceptibility to diseases. The interaction between host, nutrient and pathogen is not fully known, however it is nowadays accepted that diseases severity can be reduced by:

• Increasing crop "tolerance"
• Facilitating diseases evasion
• Increasing plant physiological resistance
• Reducing pathogen virulence

The effect of some nutrients on development and maturity of plants may lead to evasion. Phosphorus, for instance, can reduce shoot growth and therefore reduce susceptibility to rust. 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 phosphorus 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 (F. oxysporum f. sp. Vasinfectum) is also associated to zinc, that causes increase on ascorbic acid and carbohydrates.

Premature senescence

Premature senescence in cotton is related to potassium nutrition, regardless of potassium supply. This disturbance is caused mainly due to environmental stress, such as flooding, cold, cloudy days and soil compaction, which interferes in plant capacity to absorb potassium – required in large amounts - between flowering and boll filling. Due to 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 where low levels of soil K are detected.