Nitrogen and Water Use Effectiveness in Cotton-Based Cropping Systems.

The study is based on an evaluation of crop rotation ability to reduce irrigation and fertilizer nitrogen in cotton farming systems. The study was carried out at the University of Florida North Florida Research and Education Center in Quincy, Florida on an Ultisol (Dothan loamy sand). Nitrogen and water use effectiveness of cotton (Gossypium hirsutom L.) was assessed by evaluating seasonal responses to climatic and managerial changes in both conventional cotton-cotton-peanut (Arachis hypogaea L.) and peanut-cotton-bahiagrass-bahiagrass (Paspalum notatum Fluegge) rotations under non-irrigated and irrigated conditions with oats (Avena Sativa L.) grown as winter cover crop; the crops within each of the phases were grown every year. The field has been in conservation-strip tillage since 1980s with well-established experimental plots of 18.3 m wide (i.e. 20 rows, 10 fertilized with N versus 10 without N fertilization) and 45.6 m long with non-irrigated and irrigated sub-plots being perpendicular to the rows.

Cotton from both rotations responded to cumulative precipitation with a trend of stable yields. Without N fertilization non-irrigated cotton from sod rotation yielded higher than both 1^st-yr and 2^nd-yr cotton from conventional rotation. A trend of increased water use efficiency was observed for cotton from sod rotation compared to conventional rotation. In dry years, cotton in the sod rotation is not reaching the stress level for initiating irrigation as often as cotton in the conventional rotation. Without irrigation, cotton from sod rotation yielded higher than cotton from conventional one. Nitrogen leaching tended to occur during wet periods with N losses up to 22 kg ha^-1 from conventional system versus 13 kg ha^-1 from the sod-rotation system.