Here’s a summary of some of what we know about critical N and K concentrations across various phenological stages.

The critical N and K level in the youngest mature leaf and its petiole typically declines as the cotton plants progress through their phenological stages. This reflects the plant’s changing N and K requirements throughout its growth cycle.

During vegetative growth (e.g., squaring and early bloom), the critical level tends to be higher than at later stages as the plant actively builds new tissues and demands more N for rapid growth.

As the plant enters peak flowering and boll development, the critical levels start to decline. This shift signifies the plant’s increased focus on reproductive processes and reduced need for vegetative growth.

As bolls mature and defoliation approaches, critical levels reach their lowest point. This reflects the efficient resorption from leaves to support boll development and seed filling.

The rate of decline is faster for petiole vs leaf critical levels, on the positive side, making petioles more able to quickly reflect the change in uptake but making them more prone to be affected by growing condition factors rather than soil nutrient supply.

If you like these brief cotton nutrition insights and want to learn more about cotton nutrition, contact us about joining one of our new Better Soils Management for Cotton Nutrition courses starting in 2024 that will be available in most Australian cotton growing regions.