Improving Cotton Production Efficiency With Phosphorus and Potassium Placement At Multiple Depths in Strip Tillage Systems.

The use of starter fertilizers in the southeast U.S. upland cotton (Gossypium hirsutum) production is relatively new, and methods of applying starter fertilizers are currently being evaluated in many areas. A research trial to evaluate placement of phosphorus (P) and potassium (K) in upland cotton systems was conducted at two locations in Virginia and North Carolina during 2013. The objectives of this research were 1) determine the impact on of placing a fluid P and K fertilizer at multiple depths below the seed during strip-till cultivation and 2) selected combinations of P and K placed at multiple depths in the strip-till process in combination with subsurface banding of P and K fertilizer at planting on crop establishment, early season development, and nutrient status throughout the bloom period. Fluid P and K fertilizers were placed 15, 23, and 30 cm below the row during strip-till cultivation and banded 5 cm to the side and 5 cm below the seed at planting using a fertilizer injection coulter.  The rates of P and K chosen to evaluate placement were 22, 45, and 67 kg/ha of P₂O₅ and K₂O. Fertilizer placement combinations were tested at 45 kg/ha for both P₂O₅ and K₂O. Fertilizer placement was compared to conventional broadcast and starter fertilizer systems as well as a non-fertilized control. Emergence and plant populations were not affected by P and K placement or rate. Plant heights from the 5^th week after planting (WAP) through the 10^th WAP were significantly different among fertilizer management systems where 45 kg/ha P₂O₅ and K₂O was applied. Petiole and tissue analyses indicate nitrogen deficiencies elevate petiole P levels as the unfertilized checks contained the highest levels of P in cotton petioles each week during the bloom period. As the bloom period progressed nutrient levels dropped and were less responsive to nutrient management systems. The efficacy of using petiole and tissue testing programs throughout the bloom period in cotton needs to be further evaluated before producers implement such programs in Virginia.