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

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, 15 N 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 15 N 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.