Cotton Root System and Fruit Load Characteristics Impacting Potassium Responses

Pima and Upland cotton varieties were evaluated at multiple sites where there was a history of visible symptoms of potassium deficiency and low to moderate soil potassium levels.  In furrow irrigated sites, two rates of supplemental potassium were shanked in approximately 8 inches from the plant row about 35-45 days after planting, and in two drip irrigated trials, supplemental potassium was injected either one time at 35 days after planting, or in three separate injections at 35, 56, and 87 days after emergence.  Soil potassium levels were determined in 15 cm increment depths to 45 cm and 30 cm increments to 105 cm prior to planting to determine baseline conditions. Root systems were evaluated on plants dug out of the soil at cutout by assessing: (a) primary tap root diameter by depth; (b) number of root laterals of target diameter from the 0 to 30 cm depth; and (c) primary root number if tap root damaged or not existent.  Leaf blade K was assessed at 2 week intervals from first bloom through cutout, and plant fruit load was determined using plant mapping.  Timing and severity of potassium deficiency symptoms was evaluated visually using an index rating.