Managing nitrogen from swine and poultry manure in North Carolina.

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Title: Managing nitrogen from swine and poultry manure in North Carolina.
Author: Allen, Mark Benjamin
Advisors: Philip W. Westerman, Committee Member
Michael G. Wagger, Committee Member
Wei Shi, Committee Member
Robert L. Mikkelsen, Committee Chair
Abstract: With increasing pressure to regulate land application of animal manure, North Carolina faces a difficult dilemma, given the number of large-scale animal production facilities currently in operation. Poultry and swine industries in the state generate large volumes of animal manure that must be properly managed in order to avoid loss of N to ground water and surface water bodies. Using swine manure as an N source for soybean production is not commonly practiced due to soybean's ability to fix N, but recent research suggests that soybean may be a suitable receiver crop of anaerobic swine lagoon effluent. The objectives of this research were twofold: (1) determine the quantity of swine effluent-derived N taken up by soybean and estimate the degree of inhibition of symbiotic N-fixation and (2) determine how soil pH affects N mineralization, nitrification and immobilization when soil is amended with broiler litter. Swine effluent was spiked with (15NH4)2SO4 in order to attain a mean final 15N enrichment of 5.765 atom % 15N. The enriched effluent was applied 6 times at weekly intervals to nodulating and nonnodulating soybean growing in one-meter deep lysimeters at a rate of 185 kg PAN ha-1. Additional lysimeters with nodulating and nonnodulating soybean received no applications of effluent. Leachate was collected on a weekly basis and analyzed for 15N and total N. Soybean were harvested near maturity and analyzed for 15N and total N. Biological N-fixation in soybean was not completely inhibited when swine effluent was added and accounted for 55% of the total N in the shoot. Nodulated and nonnodulated soybean shoots recovered similar amounts of effluent N (36.6% and 33.4%, respectively). The addition of effluent and nodulation were both important sources of N for soybean growth, although the results suggest that nodulating and nonnodulating soybean behaved differently when they received effluent additions, as indicated by significant interactions. The experimental data showed that less than 1% of the added effluent N was accounted for in the leachate. An N budget of the plant-soil-water system showed that, of the effluent N added to nodulated soybean, 37% remained in the soil after the soybean were harvested, while 33% remained in the effluent-treated nonnodulated soybean. These results suggest that soybean can serve as an N receiver crop when swine effluent is the N source. To determine the effects of soil pH on N transformations in broiler litter amended soils, Wagram loamy sand with a pH of 4.4 was collected from a forested area near Clayton, NC, and sub-samples were limed to pH 4.8, 5.3, 5.8, 6.4, and 7.0. Broiler litter was added at a rate of 155 kg PAN ha-1 to the limed soils and incubated at 25°C and 60% of field capacity for 112 d. Total inorganic N was measured at 0, 7, 14, 28, 56, 77, and 112 d. Cumulative net N mineralized was fitted to a first order model to determine potentially mineralizable N. Although nitrification rates increased as soil pH increased, there were significant inverse relationships between soil pH and net N mineralized, as well as soil pH and potentially mineralizable N. Isotope dilution measurements showed that gross and net mineralization rates were equivalent, refuting the notion that relatively more NH4 immobilization had occurred in the high pH soils. The results indicate that N mineralization was enhanced at low soil pH, a phenomenon that presently is not fully understood.
Date: 2004-01-08
Degree: MS
Discipline: Soil Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/140


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