Knifing versus Injecting Phosphoric Acid with Subsurface Drip Irrigation Systems

ABSTRACT

Some subsurface drip irrigation (SDI) farmers have observed big increases of cotton lint yields just by the addition of small amounts of phosphorus (P). Several questions arise regarding these applications, such as what are the most appropriate rates, whether to split the rates between the phenological stages, and what is the most efficient method to apply P. Nutrients can be either knifed into the soil or injected through the irrigation system. A field experiment was conducted during 2004, 2006, and 2007 to evaluate the effect of knifing versus injecting the phosphorus in the irrigation system, and injecting it in one or two applications. The experimental design was a completely randomized with four treatments consisting of: 1) no P application, 2) knifing the P into the soil, 3) injecting P as phosphoric acid in one application, and 4) injecting P as phosphoric acid split into two applications. In two out of three years higher cotton lint yields were obtained by P application compared to where no P was applied. Knifing vs. injecting P with SDI system showed no significant effect on lint yield, gross return or cotton quality characteristics during three years of the study. Applying P in only one application or splitting the same amount of phosphorus in two applications resulted in no differences on lint yield, gross return, and cotton quality.

Keywords:

• phosphorus
• cotton yield
• subsurface drip irrigation

Notes

¹Delta Pine 458 Bollgard® Roundup Ready®.