Introduction: Increase in concentration of various greenhouse gases and their possible contributions to the hypothetical global warming is becoming a serious concern.  Agricultural practices, fossil fuel burning, deforestation, industrial emissions, and wetlands have contributed to atmospheric increases of carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons.  Some of these gases may contribute to “global warming”.  Significant amount of emission of methane and nitrous oxide are mainly coming from anthropogenic activities such as cultivation of wetland rice and application of various C and N rich soil amendments.  Organic soil amendments, including sewage sludge, are currently gaining increased attention for soil improving physical and chemical properties of agricultural soils for enhancing the yield and quality of various crops. Therefore, evaluation of flux of various greenhouse gases from soils amended with sewage sludge is essential to quantify the release of various greenhouse gases into the atmosphere. 

Materials and Methods:  Studies were initiated to evaluate the emission of greenhouse gases (CO₂, CH ₄ and N ₂O) from two soils with contrasting properties (Candler fine sand from Florida [FS] and Ogeechee loamy sand from Georgia [GS]) amended with varying rates (0, 24.7, 49.4, 98.8, and 148.3 Mg ha^-1) of two types of sewage sludge (industrial [ISS] and domestic [DS] origin). Domestic [DS] sewage sludge had 39.5 % C and 4.6 % N where as the industrial [ISS] sewage sludge used in this experiment had 27.8% C and 3.7% N.  Twenty grams of respective soil samples were amended with appropriate amount of sewage sludge, to attain the above per hectare rates, in 250 mL Qopak bottles and incubated, in static chambers, under anaerobic condition at field capacity soil water content for the respective soils.  Gas samples were extracted on a daily basis and injected to a gas chromatograph (GC 14) equipped with electron capture detector (ECD) and flame ionization detector (FID) to monitor CH₄, CO₂ and N₂ O.  Effect of acetylene on the emission of N₂O was also tested in this study.  Static chambers were flushed to remove all head space gases upon completion of each sampling event and the anaerobic condition was ensured for monitoring of gaseous emission for the next sampling event.  This procedure was adapted throughout the study period to facilitate the determination of emission rates at each sampling events.

Results and Discussion:   

Soil	Type of SS	Rates of SS	Mean cumulative emission per gram of soil with C2H2			Mean cumulative emission per gram of soil without  C2H2
		Mg ha-1	CO2	CH4	N2O	CO2	CH4	N2O
			mg	µg	µg	mg	µg	µg
FS	DS	0.0	9.44	159.84	6.27	12.08	59.42	4.19
		24.7	25.19	168.96	51.19	27.60	60.18	39.20
		49.4	38.37	169.35	216.21	40.71	62.19	76.28
		98.8	57.49	175.70	244.72	58.15	62.75	227.42
		148.3	72.74	191.25	349.57	71.77	65.18	280.51
	ISS	0.0	12.72	110.17	27.40	11.59	56.94	11.08
		24.7	23.02	124.12	40.97	24.29	58.12	29.78
		49.4	32.92	127.40	44.62	32.10	58.62	34.76
		98.8	41.41	141.94	45.19	47.61	62.10	37.74
		148.3	59.25	168.93	60.71	54.37	63.96	50.71
GS	DS	0.0	16.81	112.89	8.67	18.30	55.59	6.08
		24.7	31.58	115.04	44.24	26.13	55.69	29.60
		49.4	37.06	120.92	66.52	33.48	60.12	47.50
		98.8	52.65	129.23	217.31	53.00	60.21	159.68
		148.3	65.06	152.71	270.90	71.54	69.78	218.72
	ISS	0.0	18.30	86.69	29.20	20.49	54.58	9.72
		24.7	25.84	87.59	29.95	26.00	58.62	28.90
		49.4	27.30	102.05	31.52	30.43	59.13	31.36
		98.8	46.41	102.74	50.31	45.65	59.38	46.16
		148.3	53.68	118.66	69.21	55.07	75.50	51.16

Results of this study showed a very clear trend of increasing emission of various greenhouse gases with rates of amendment irrespective of the type of soils and amendments. Emission of gases was greater in both soils amended with sewage sludge from domestic origin rather than from industrial origin suggesting that either lower C and N content or possible harmful chemicals present in industrial sludge may hinder the microbial activity. Furthermore, results of this study indicated a greater amount of gaseous emission from a sandy soil amended with sewage sludge than those from a loamy sand soil.  Results also clearly depicted the inhibitory effect of acetylene in both soils by producing more nitrous oxide emission compared to the soils not receiving acetylene. 

Conclusion:Results of this study suggest the need to consider the greenhouse gas emissions from soils when amended with organic soil amendments such as sewage sludge, especially at high rates. Results also indirectly imply the importance of this evaluation due to the potential emission of various greenhouse gases in the event of accidental spills of sewage into wetland ecosystem.