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SOIL FERTILITY & PLANT NUTRITION

Cotton Nitrogen Management in a High-Residue Conservation System: Cover Crop Fertilization

^a Virginia Polytechnic Inst. and State Univ., Eastern Shore Agric. Research and Ext. Center, 33446 Research Dr., Painter, VA 23420
^b USDA-ARS, J. Phil Campbell Sr. Natural Resource Conserv. Center, 1420 Experiment Station Rd., Watkinsville, GA 30677
^c Auburn Univ., Agronomy and Soils Dep., 202 Funchess Hall, Auburn University, AL 36849
^d USDA-ARS, National Soil Dynamics Lab., 411 South Donahue Dr., Auburn, AL 36832

^* Corresponding author (mreiter{at}vt.edu).

Nitrogen is required for adequate residue production from cereal cover crops used in no-till cotton (Gossypium hirsutum L.) production, but residues can immobilize N needed by cotton. We conducted a 3-yr field study on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudult) in northern Alabama to test N fertilizer practices for cotton grown with a rye (Secale cereale L.) cover crop and conservation tillage. Nitrogen rates applied to the rye cover crop were 0, 34, and 67 kg N ha^–1 and cotton N rates were 0, 45, 90, and 135 kg N ha^–1. Additionally, ¹⁵N microplots were established in cover crop N treatments of 34 kg N ha^–1 and in cotton treatments of 90 kg N ha^–1. Data collected included cover crop aerial biomass, cover crop C/N ratios, cotton leaf N at first flower, lint yield, lint quality, and ¹⁵N in plant and soil samples. Cotton grown in unfertilized rye treatments needed 57 to 60% (38–40 kg N ha^–1) more N to maximize yields above median conventional tillage N recommendations (67 kg N ha^–1). Cover crop N rates of 67 kg N ha^–1 maximized cover crop biomass production for soil protection and soil organic matter aggradation. If the cover crop was fertilized, minimum cotton N applications of 70 and 76 kg N ha^–1 were needed for economic optimum and maximum lint yield, respectively. We speculate that cotton N rates may be decreased in the future as new N and C pool equilibria are reached.

Abbreviations: FUE, fertilizer nitrogen use efficiency • SOM, soil organic matter