Under high pH conditions (>pH 7.5) B becomes unavailable as it is strongly bound in the soil. Excessive use of lime can exacerbate the problem. Boron readily leaches, particularly from sandy soils and tropical soils with a low CEC.
Because of leaching in soils that have a poor ability to hold B, it is often difficult to build up and maintain levels in the soil. Drought stress may increase B deficiency simply because B uptake is in part determined by water uptake. High light intensity and long-day conditions also increase B deficiency.
Dicotyledon plants (e.g. cotton) have a higher B requirement than monocotyledons (grasses and cereals). Boron is needed for the production of nucleic acids and plant hormones as well as the movement of plant sugars. It is essential to maintain the structural integrity of the plant membranes and is found in large quantities in the leaves, growing points and fruit. Boron is important to pollen viability, and flower and boll development.
Boron aids in efficient utilization of other nutrients including nitrogen and potassium, and can help move nitrogen and carbohydrates from leaves to developing fruit. It in turn helps assimilate these into complex carbohydrates and proteins, making cotton fiber. Boron is critical for the uptake of calcium (Ca) and helping improve Ca movement through the plant. When high levels of Ca are being applied, additional boron may be needed to maximize Ca uptake.
Cotton needs B during all growth stages, but especially during boll development. Boron helps cotton to develop more fruiting sites, aids in pollination and boll retention, and contributes to quality fiber. Unfortunately B is least available during this time, especially in non-irrigated production.
The base B recommendation in cotton is 0.5 lb/A. On loamy Coastal Plain soils with normal rainfall and irrigation, soil applied B can be effective. However B readily leaches through the soil profile - especially on sandy soils, fields with excessive rainfall, or low CEC soils which are abundant throughout the U.S. cotton belt. Thus foliar applications are recognized to be the most effective and efficient method.
Foliar applications are made just prior to and during square development. The standard foliar recommendation is to apply B in two 0.25 lb/A foliar applications between first square and first bloom. Existing data suggests the most efficient method is to apply in increments of 0.10 lb/A. Foliar applications above the base recommendation of 0.5 lb B/A and up to 2 lb B/A is best determined by tissue or petiole testing. The use of a product formulated adjuvant is recommended.
Creating the right nutrient management strategy in Cotton production is not a “one-size-fits-all” prescription. Cotton is grown in vastly different environments with differing soil conditions and yield potentials. Any nutrient program needs to be designed for these variables. But where do you start? Find these answers and more in this free webinar by Cotton Grower.