| Poultry manure is a nitrogen (N) source applied at different rates and times in a multitude of crop and tillage scenarios in North Carolina. Although standard assumptions are that 50% of the total N is available to the first crop when surface applied and 60% when incorporated, soil type, application times, environments and tillage practices may all affect fertilizer N equivalence (FNE coefficients calculated from yield) or plant available N (PAN coefficients determined from plant N uptake). Therefore, information on the effect of manure type and management is required to strengthen the knowledge for profitable use of this resource and understand residual effects in the soil. The objectives of this study were to; (i) evaluate the effect of poultry manure source and management on yield and plant N uptake and to verify FNE and PAN coefficients for winter wheat (Triticum aestivum L.) and summer cotton (Gossypium hirsutum) -- corn (Zea Mays L.) rotation, (ii) evaluate the effect of poultry manure source and management on tiller density, yield, and yield components of wheat, and (iii) determine the availability of N remaining in soils following the intended crops. Two types of field experiments (wheat and cotton-corn) were established and a follow-up laboratory study was conducted. Wheat field experiments were established at two research stations, the Lower Coastal Plain Tobacco (LCPRS) on a Goldsboro loamy sand (Aquic Paleudults) and the Tidewater (TRS) on a Portsmouth fine sandy loam (Typic Umbraquults) using broiler litter (BL) and composted layer manure (CLM) applied at three times in 2008/2009 and 2009/2010 seasons. A cotton-corn rotation study was conducted in adjacent conventional and conservation tillage fields at two research stations, the Upper Coastal Plain (UCPRS) on a Norfolk loamy sand (Typic Kandiudults), and TRS on a Portsmouth fine sandy loam in 2008, 2009, 2010 and 2011 seasons using layer manure (LM), CLM and BL. Post-harvest soils from both studies were incubated at 10, 20 or 30 °C for 112 days with N mineralization monitored by periodic sampling. Results showed that wheat FNE and PAN values were much less than the standard assumption, with FNE values of 0.31 for CLM and 0.18 for BL, and PAN values of 0.25 and 0.14, respectively, when applied at a rate of 134 kg total N ha--1 . At a lower application rate, coefficient values were higher, but still well below 0.5 (i.e. 50% availability). For corn, a much higher proportion of the manure N became available than for winter wheat. First year FNE coefficients ranged from 0.59 to 0.68, while PAN coefficients ranged from 0.68 to 0.81. Due to the erratic nature of the responses of cotton to inorganic N, very little manure N efficiency data could be determined. Incubation of post-harvest soil samples found relatively large amounts of mineralizable N in all samples, typically 40 to 100 kg N ha--1, but net mineralization of less than 15 kg N ha--1 resulting from most manure N applications. Mineralization of soil and manure N was enhanced at higher temperatures, but much of the manure N was still unaccounted for in the crop N budgets. Nevertheless, 2nd and 3rd year summer crop growth trials detected residual manure effects, with 2nd year residual FNE coefficients ranging from 0.11 to 0.26 for corn and cotton, and 3rd year residual FNE coefficients ranging from 0.05 to 0.34 for corn. Poultry manure N is probably less available to winter crops than to summer crops due to temperature effects on mineralization; and although residual manure may supply N for at least an additional two crops, soil mineralization assays may not effectively quantify this due to the large background soil mineralizable N. |
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