Cover crop and poultry litter management influence spatiotemporal availability of topsoil nitrogen

Green and animal manures provide plant-available N (PAN) in annual cropping systems and contribute to improved soil quality. Our objectives were to determine the effects of cover crop residue type and pelletized poultry litter (PPL) application method on: (i) the spatiotemporal distribution of topsoil mineral N (N_min), (ii) the average topsoil N_min at four developmental stages of corn (Zea mays L.), and (iii) corn N uptake. We collected soil and plant samples from a factorial experiment that included three cover crop residues: hairy vetch (Vicia villosa Roth), cereal rye (Secale cereale L.), and a hairy vetch/cereal rye mixture; and four PPL treatments: no PPL and 3.5 Mg PPL ha^-1 either broadcast at planting, subsurface banded at the fifth-leaf stage, or broadcast and incorporated at planting. Most of the N_min in the broadcast treatment was concentrated near the soil surface, N_min associated with the subsurface band remained within 10 cm of the delivery location throughout the growing season, while N_min was distributed to a depth of 20 cm in the incorporated treatment. Average N_min to 30 cm was significantly greater in soil with hairy vetch residue than in soil with cereal rye residue at emergence and the fifth-leaf stage, while the cover crop mixture had average N_min levels intermediate between the monocultures or similar to cereal rye depending on the year. In both years, corn N uptake tended to be greatest with hairy vetch residue and broadcast or subsurface band PPL application, averaging 215 kg ha^-1 across years in these treatments.