Farm-scale testing of site-specific irrigation and nitrogen fertilization for cotton production in the Southern High Plains of Texas, USA

Proper management of irrigation and nitrogen (N) fertilizer are two important aspects of cotton (Gossypium hirsutum L.) production in the Southern High Plains of Texas (SHP), USA. Sitespecific or precision manipulation of these two inputs has been hypothesized to further improve their management, and practices and technologies have been researched and developed in recent years to facilitate such site-specific management. During 2002, an inter-disciplinary farm-scale research project was initiated on a research/demonstration farm near Lamesa, Texas, to evaluate the feasibility of site-specific irrigation and N fertilization. It was hypothesized that redistribution of irrigation resources would improve water availability on the two side slopes and avoid excess application of water in the bottom slope area. It was also hypothesized that variable rate N application would be more efficient than blanket rate application within the slope defined management zones. Additional irrigation only significantly improved cotton lint yields on both side slope areas during 2002. Lower levels of irrigation in the bottom slope area reduced yields significantly in 2003 and 2004. Variable rate N application did not produce statistically higher lint yields than blanket rate application, but did produce a more consistent response to N fertilizer. Blanket application tended to under-fertilize in the bottom slope area and over fertilize in the southfacing side slope area. These data provide some evidence that variable rate N application can increase efficiency. However, these increases in efficiency are small, and would probably not indicate a significant economic benefit above blanket rate N application.