Poultry Manure Nitrogen Availability to Corn and Cotton Under Conventional and Conservation Tillage.

Poultry manure application to North Carolina crops assumes 50% of the total N is available to the first crop when surface applied, and 60% when incorporated.  Since this might not hold constant for different crops, environments, and tillage practices, the objectives of this study were to (i) evaluate poultry manure N source, application rate, and residual N effects on yield and plant N uptake in a cotton-corn rotation under conservation and conventional tillage. Availability coefficients were calculated from crop yield responses (fertilizer N equivalence, FNE) or plant N uptake (plant available N, PAN) for the 1^st, 2^nd, and 3^rd crops.  Experiments were at the Upper Coastal Plain Research Station on a Norfolk loamy sand (Typic Kandiudults), and the Tidewater Research Station on a Portsmouth fine sandy loam (Typic Umbraquults) during 2008-2011. In adjacent conservation and conventional tillage fields, three sources (layer manure, composted layer manure, and broiler litter) were applied at two rates to each crop.   Yields and plant N uptake from these manure treatments were compared to N responses modeled from three inorganic fertilizer rates and a check treatment without N.  For corn fertilized with manure in 2009, analysis of variance found both manure source and application rate influenced crop yield and plant N uptake during the first year; only the manure source influenced the cotton crop yield in the second year; and there were no measureable differences the third year after application. The first year following manure application to corn, the FNE and PAN values exceeded 0.5 (50%), while in the 2^nd year following application FNE values ranged from 0.16 to 0.29, and in the 3^rd year FNE values ranged from 0.17 to 0.47. Thus, second and third year availability was highly variable, but indicated some contribution at lower levels than during the initial year of application.