Acetylene and N-serve effects upon N2O emissions from NH4+ and NO3− treated soils under aerobic and anaerobic conditions

N₂O emissions from soils treated with NH₄⁺-N under aerobic conditions in the laboratory were 3- to 4-fold higher than those from controls (no extra N added) or when NO₃^?-N was added. Although the emission of N₂O-N in these field and laboratory experiments represented only 0.1–0.8% of the applied fertilizer NH₄⁺-N and are therefore not significant from an agronomic standpoint, these studies have conclusively demonstrated that the oxidation of applied ammoniacal fertilizers (nitrification) could contribute significantly to the stratospheric N₂O pool.Like N-serve, acetylene was shown to be a potent inhibitor of nitrification as it stopped the oxidation of NH₄⁺-N to (NO₃⁺-N + NO₂^?)-N and hence reduced the evolution of N₂O from nitrification within 60 min after its addition.Although high amounts of NO₃^?-N were present, the rate of denitrification was very low from soils with moisture up to 60% saturation. The further increase in the degree of saturation resulted in several-fold increase of denitrification which eventually became the predominant mechanism of gaseous N losses under anaerobic conditions.     

Nitrous oxide production at different soil moisture contents in an arable soil in China

Abstract

Laboratory incubations were conducted to investigate nitrous oxide (N₂O) production from a subtropical arable soil (Typic Plinthodults) incubated at different soil moisture contents (SMC) and with different nitrogen sources using a 10% (v/v) acetylene (C₂H₂) inhibitory technique at 25°C. The production of N₂O and CO₂ was monitored during the incubations and changes in the contents of KCl-extractable NO^? ₃-N and NH⁺ ₄-N were determined. The production of N₂O increased slightly with an increase in SMC from 40% water-holding capacity (WHC) to 70% WHC, but increased dramatically at 100% WHC. After incubation the NO^? ₃-N content increased even at a SMC of 100% WHC. At a SMC of 100% WHC, the addition of NH⁺ ₄-N promoted the production of N₂O and CO₂, whereas the addition of NO^? ₃-N decreased N₂O production. Compared with the incubation without C₂H₂, the presence of C₂H₂ increased NH⁺ ₄-N content, but decreased NO^? ₃-N content, and there was no significant difference in N₂O production. These results indicate that heterotrophic nitrification contributes to N₂O production in the soil.     

NH3 Volatilization,N2O Emission and Microbial Biomass Turnover from 15N-Labeled Manure Under Laboratory Conditions

On irrigated agricultural soils from semi-arid and arid regions, ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission can be a considerable source of N losses. This study was designed to test the capture of ¹⁵N loss as NH₃ and N₂O from previous and recent manure application using a sandy, calcareous soil from Oman amended one or two times with ¹⁵N labeled manure to elucidate microbial turnover processes under laboratory conditions. The system allowed to detect ¹⁵N enrichments in evolved N₂O-N and NH₃-N of up to 17% and 9%, respectively, and total N, K₂SO₄ extractable N and microbial N pools from previous and recent ¹⁵N labeled manure applications of up to 7%, 8%, and 15%. One time manured soil had higher cumulative N₂O-N emissions (141 µg kg^?1) than repeatedly manured soil with 43 µg kg^?1 of which only 22% derived from recent manure application indicating a priming effect.     

Effect of ammonium-, nitrite- and nitrate nitrogen on anaerobic nitrogenase activity in soil

Sandy loam soil, with added glucose, was incubated anaerobically under N₂ and subjected to repeated 1-h C₂H₂ reduction assays. In the presence of 1% glucose the addition of 50 μg NH₄⁺ ?N/g or of 20 μg NO^?₃ N/g (untreated soil contained 1.2 μg NH⁺₄?N and 7.10 μg NO^?₃-N/g) caused at least some suppression of nitrogenase activity. Activity developed when the KCl-extractable soil inorganic nitrogen concentration dropped below 35 μg/g. In the presence of 0.1 or 0.05% glucose the addition of 5 μg NH⁺₄?N/g caused some suppression of nitrogenase activity. However, activity developed when the soil NH₄⁺-N concentration dropped below about 4 μg/g. With 0.1% glucose and 5 μg added NO^?₂ N/g, activity did not develop until the soil NO^?₂ -N concentration dropped to zero. Added NO^?₃ N was rapidly reduced and denitrified to NO^?₂- N, N₂O-N and NH⁺₄ N and furthermore caused some inhibition of CO₂ evolution. The data from NH₄^?-addition experiments are consistent with a nitrogenase repression/ derepression threshold of 4 and 35μg NH⁺₄-N/g at 0.05 and 1% glucose concentrations, respectively. The data from NO^?₂- and NO^?₃-addition experiments suggest a combination of repression and toxicity effects in the presence of added NO^?₃ N.     

Effects of application of lime nitrogen and dicyandiamide on nitrous oxide emissions from green tea fields

Abstract

The aim of this study was to assess the mitigating effects of lime nitrogen (calcium cyanamide) and dicyandiamide (DCD) application on nitrous oxide (N₂O) emissions from fields of green tea [Camellia sinensis (L.) Kuntze]. The study was conducted in experimental tea fields in which the fertilizer application rate was 544 kg nitrogen (N) ha^?1 yr^?1 for 2 years. The mean cumulative N₂O flux from the soil between the canopies of tea plants for 2 years was 7.1 ± 0.9 kg N ha^?1 yr^?1 in control plots. The cumulative N₂O flux in the plots supplemented with lime nitrogen was 3.5 ± 0.1 kgN ha^?1, approximately 51% lower than that in control plots. This reduction was due to the inhibition of nitrification by DCD, which was produced from the lime nitrogen. In addition, the increase in soil pH by lime in the lime nitrogen may also be another reason for the decreased N₂O emissions from soil in LN plots. Meanwhile, the cumulative N₂O flux in DCD plots was not significantly different from that in control plots. The seasonal variability in N₂O emissions in DCD plots differed from that in control plots and application of DCD sometimes increased N₂O emissions from tea field soil. The nitrification inhibition effect of lime nitrogen and DCD helped to delay nitrification of ammonium-nitrogen (NH₄⁺-N), leading to high NH₄⁺-N concentrations and a high ratio of NH₄⁺-N /nitrate-nitrogen (NO₃^–-N) in the soil. The inhibitors delayed the formation of NO₃^–-N in soil. N uptake by tea plants was almost the same among all three treatments.     

Zusammensetzung und Eigenschaften von Sickerwasser aus Stallmiststapeln

Composition and properties of leachates from farmyard manure heaps Besides some rheological characteristics, the N_total, NH₄⁺-N, NO₃^? -N, P, K⁺, dry matter and ash content, as well as chemical oxygen demand and conductivity of farmyard manure leachates were examined. The K⁺ concentration was highest with an average of 5921 mg l^?1, followed by N_total (1139 mg l^?1, 66% of it as NH₄⁺-N and 4% NO₃^?-N) and P (334 mg l^?1). All parameters were highest in leachates of fresh manure and lowest at the end of a 6 months storage period. During the storage, the P concentration in leachates showed a decrease of 67.7%, followed by a decrease in N_t (-57.3%) and K⁺ (-24.0%). In leachates from a manure with an relatively high initial N_t content of 0.51% and a low C:N ratio of 16.8 the N_t concentration was 0.5–1 times higher than that of a manure with 0.44% N_t and a C:N ratio of 19.9. The viscosity and the thixotropy of leachates were both relatively high at the beginning of the manure's storage period, which led to a strongly developed blocking of porous systems. These properties that contribute to explain the high retention rate of nutrients in the top soil layer at manure storage sites, decreased with an increase in storage time.     

Rates and pathways of mineral nitrogen transformation in a soil from pastures

Short-term metabolic activities, including ammonincation, nitrification, denitrification and the release of CO₂, with and without added substrate, and most probable numbers of ammonifiers, nitrifiers and denitrifiers were measured on stored topsoil from pasture over 140 days in the absence of growing plants. Parallel samples of irradiated and untreated soil were examined. Release of mineral-N, chiefly as NH⁺₄N, was greater from the irradiated soil. In the untreated soil there was a slight increase in NO₃^?N. Microorganisms (estimated by MPN method) and microbial respiration in the untreated soil increased, and then diminished with time.The release of ¹³N₂O and ¹³N₂ was measured from intact soil cores amended with ¹³NO₃^?N and ¹³NH⁺₄N. The principal product from the treated soil when ¹³NO₃^?N was added was ¹³N₂, with little ¹³N₂O, whereas the irradiated soil evolved both ¹³N₂ and ¹³N₂O. Similarly, the irradiated soil continuously evolved ¹³N₂O from ¹³NH⁺₄N in contrast to the untreated soil.     

Effect of Adding Flue Gas Desulphurization Gypsum on the Transformation and Fate of Nitrogen during Composting

The objective of this study was to investigate the effect of adding flue gas desulphurization gypsum (FGDG) on the transformation and fate of nitrogen during co-composting of dairy manure and pressmud of a sugar refinery. The ammonia absorption of FGDG was investigated. The changes in compost temperature, pH, electrical conductivity (EC), moisture, organic matter, the C/N ratio, Kjeldahl N, NH₄⁺-N, NO₂^?-N, NO₃^?-N were assessed. The addition of FGDG did not significantly affect compost temperature, pH, EC, moisture, and organic matter degradation. However, the addition of FGDG significantly increased the NH₄⁺-N content in the compost during the thermophilic phase, and the NH₄⁺-N maximal content in the compost with FGDG (CP+G) was 59.9% more than that in the compost without FGDG (CP–G). FGDG was thought to create the formation of (NH₄)₂SO₄ and the cation exchange between NH₄⁺ and Ca²⁺. The NO₂^?-N content in the CP+G peaked on day 15, and was not observed in the CP–G. In the final compost products, the NO₃^?-N concentration in the CP–G was more than that in the CP+G, which was 1451 (CP–G) and 1109 mg·kg^?1 (CP+G) dry material. This might be due to the NO₂^? accumulation in the CP+G, which accelerated N loss in the form of N₂O. There is a strong correlation between N₂O emission and NO₂^?-N accumulation in the composting process. Compared with the original N content in the compost mixture, the N loss in CP–G and CP+G were 15.0 and 10.8%, respectively. These results revealed that NH₄⁺-N conservation effect was improved during the thermophilic phase and the total N loss was mitigated by adding FGDG into composting materials. FGDG could be utilized as a potential amendment to conserve nitrogen during composting.     

Greenhouse gas emissions and nutrient supply rates in soil amended with biofuel production by-products

Ethanol production results in distiller grain, and biodiesel produces glycerol as by-product. However, there is limited information on effects of their addition on evolution of N₂O and CO₂ from soils, yet it is important to enable our understanding of impacts of biofuel production on greenhouse gas budgets. The objective of this study was to evaluate the direct effects of adding wet distillers grain (WDG), thin stillage (TS), and glycerol at three rates on greenhouse gas emissions (N₂O and CO₂) and nutrient supply rates in a cultivated soil from the Canadian prairies. The WDG and TS application rates were: 100, 200, or 400 kg N ha^?1, whereas glycerol was applied at: 40, 400, or 4,000 kg C ha^?1 applied alone (G???N) or in a combination with 300 kg N ha^?1 (G?+?N). In addition, conventional amendments of urea (UR) and dehydrated alfalfa (DA) were added at the same rates of total N as the by-products for comparative purposes. The production of N₂O and CO₂ was measured over an incubation period of 10 days in incubation chambers and Plant Root Simulator? resin membrane probes were used to measure nutrient (NH ₄ ⁺ -N, NO ₃ ^? -N, and PO ₄ ^?3 -P) supply rates in the soil during incubation. Per unit of N added, urea tended to result in the greatest N₂O production, followed by wet distillers grain and thin stillage, with glycerol and dehydrated alfalfa resulting in the lowest N₂O production. Cumulative N₂O production increased with increasing the rate of N-containing amendments and was the highest at the high rate of UR treatment. Addition of urea with glycerol contributed to a higher rate of N₂O emission, especially at the low rate of glycerol. The DA and WDG resulted in the greatest evolution of CO₂ from the soil, with the thin stillage resulting in less CO₂ evolved per unit of N added. Addition of N fertilizer along with glycerol enhanced microbial activity and decomposition. The amendments had significant impacts on release of available nutrient, with the UR treatments providing the highest NO ₃ ^? -N supply rate. The TS treatments supplied the highest rate of NH ₄ ⁺ -N, followed by WDG compared to the other amendments. The WDG treatments were able to provide the greatest supply of PO ₄ ^?3 -P supply in comparison to the other amendments. Microbial N immobilization was associated with glycerol treatments applied alone. This study showed that the investigated biofuel by-products can be suitable soil amendments as a result of their ability to supply nutrients and N₂O emissions that did not exceed that of the conventional urea fertilizer.     

Short-term effects of ammonium nitrogen in upland pasture soil affected or not affected by cattle

The short-term effects of excessive NH₄⁺-N on selected characteristics of soil unaffected (low annual N inputs) and affected (high annual N inputs) by cattle were investigated under laboratory conditions. The major hypothesis tested was that above a theoretical upper limit of NH₄⁺ concentration, an excess of NH₄⁺-N does not further increase NO₃⁻ formation rate in the soil, but only supports accumulation of NO₂⁻-N and gaseous losses of N as N₂O. Soils were amended with 10 to 500 μg NH₄⁺-N g⁻¹ soil. In both soils, addition of NH₄⁺-N increased production of NO₃⁻-N until some limit. This limit was higher in cattle-affected soil than in unaffected soil. Production of N₂O increased in the whole range of amendments in both soils. At the highest level of NH₄⁺-N addition, NO₂⁻-N accumulated in cattle-affected soil while NO₃⁻-N production decreased in cattle-unaffected soil. Despite being statistically significant, observed effects of high NH₄⁺-N addition were relatively weak. Uptake of mineral N, stimulated by glucose amendment, decreased the mineral N content in both soils, but it also greatly increased production of N₂O.     

Determination of kC and kNin situ for calibration of the chloroform fumigation-incubation method

¹⁴C-labelled glucose and ¹⁵N-labelled KNO₃ were added to soil and the microbial biomass during 42 days' incubation was estimated using the chloroform fumigation-incubation method (CFIM). By day 1, most of the glucose (1577 μgCg^?1 soil) was metabolized and 110 μg NO^?₃-Ng^?1 soil were immobilized. In situ values for the proportions of biomass C (k_C) and biomass N (k_N) mineralized during the 10 days after CHCl₃ fumigation were determined on the basis that the immobilized labelled C and N remaining in the soil at this time were present as living microbial cells and their associated metabolites. The tracer data indicated that biomass C could be calculated by applying a k_c value of 0.41 to the CO₂-C evolved from the fumigated sample without subtraction of an unfumigated “control”. Biomass N was estimated from the net NH₄^?-N accumulation during the fumigation-incubation. The problem of reimmobilization of NH⁺₄-N where organisms of wide C:N ratio occur was overcome by adjusting the value of k_N according to the ratio of CO₂-C evolved: net NH₄⁺-N accumulated during the fumigation-incubation (C_F:N_F).A C_F:N_F ratio of 6:1 resulted in a k_N of 0.30 whereas a ratio of 13:1 indicated a k_N of 0.20.     

Does the potential ammonium fixation of soils have an impact on the optimum nitrogen fertilizer rate?

Field experiments were conducted to determine the effect of nitrogen (N) fertilizer forms and doses on wheat (Triticum aestivum L.) on three soils differing in their ammonium (NH₄) fixation capacity [high = 161 mg fixed NH₄-N kg^?1 soil, medium = 31.5 mg fixed NH₄-N kg^?1 soil and no = nearly no fixed NH₄-N kg^?1 soil]. On high NH₄⁺ fixing soil, 80 kg N ha^?1 Urea+ ammonium nitrate [NH₄NO₃] or 240 kg N ha^?1 ammonium sulfate [(NH₄)₂SO₄]+(NH₄)₂SO₄, was required to obtain the maximum yield. Urea + NH₄NO₃ generally showed the highest significance in respect to the agronomic efficiency of N fertilizers. In the non NH₄⁺ fixing soil, 80 kg N ha^?1 urea+NH₄NO₃ was enough to obtain high grain yield. The agronomic efficiency of N fertilizers was generally higher in the non NH₄⁺ fixing soil than in the others. Grain protein was highly affected by NH₄⁺ fixation capacities and N doses. Harvest index was affected by the NH₄⁺ fixation capacity at the 1% significance level.     

DENITRIFICATION IN A VERY ACID TROPICAL SOIL

In a very acid upland clay surface soil and with glucose added to give initial C/N weight ratios (added glucose-C: NO₃-N) in the soil of 0, 2 and 5, the rates of evolution of N₂ and N₂O were maximum at C/N = 2 but were significantly less at 0 and 5. The total N₂ and N₂O production was highest at C/N = 0, confirming that increasing amounts of glucose immobilised more nitrate into the biomass. As with added NO^?₃-N, the time lag, preceding a maximum ‘steady state’ rate of N₂0 evolution, increased regularly with increasing glucose. Within this ‘steady state’ period, the gaseous CO₂-C/(N₂+ N₂O)-N weight ratio in the effluent gas are between 1.0 and 1.3, which corresponds well with the stoichiometric ratios of 1.07 and 1.29 for the reduction of NO^?₃ to N₂O and N₂ respectively. Before and after this period, this gaseous C/N ratio was much higher. Denitrification was not observed in subsurface soil even after adding 100 mg kg^?1glucose-C although it contained 4 times as much indigenous nitrate as the surface soil. Inoculating this soil with increasing amounts of the surface soil, up to 15 per cent by weight, induced substantial increases in the rates and amounts of denitrification. The effects of increasing the soil pH. of introducing increasing oxygen concentrations in the influent gas. and the fate of added NH⁺₄-N, are briefly reported here. In these experiments. NO^?₂-N did not accumulate in the incubated soil nor was there any NH₃in the effluent gas. Evolution of N₂ only occurred when N₂O evolution was in its final stages.     

Nitrification Inhibitor,Fertilizer Rate,and Temperature Effects on Nitrous Oxide Emission and Nitrogen Transformation in Loamy Sand Soil

An incubation study investigated the effects of nitrification inhibitors (NIs), dicyandiamide (DCD), and neem oil on the nitrification process in loamy sand soil under different temperatures and fertilizer rates. Results showed that NIs decreased soil nitrification by slowing the conversion of soil ammonium (NH₄⁺)-nitrogen (N) and maintaining soil NH₄⁺-N and nitrate (NO₃^?)-N throughout the incubation time. DCD and neem oil decreased soil nitrous oxide (N₂O) emission by up to 30.9 and 18.8%, respectively. The effectiveness of DCD on reducing cumulative soil N₂O emission and retaining soil NH₄⁺-N was inconsistently greater than that of neem oil, but the NI rate was less obvious than temperature. Fertilizer rate had a stronger positive effect on soil nitrification than temperature, indicating that adding N into low-fertility soil had a greater influence on soil nitrification. DCD and neem oil would be a potential tool for slowing N fertilizer loss in a low-fertility soil under warm to hot climatic conditions.     

Microorganisms in sewage sludge added to an extreme alkaline saline soil affect carbon and nitrogen dynamics

There are plans to vegetate soil of the former lake Texcoco and use wastewater sludge to provide nutrients. However, the Texcoco soil is N depleted, so the amount of N available to the vegetation might be limited and the dynamics of C and N affected. We investigated how emissions of CO₂, N₂O and N₂, and dynamics of mineral N were affected when different types of N fertilizer, i.e. NH₄⁺, NO₃⁻, or unsterilized or sterilized wastewater sludge, were added to the Texcoco soil. An agricultural soil served as control. Sewage sludge added to an alkaline saline soil (Texcoco soil) induced a decrease in concentrations of NH₄⁺ and NO₃⁻. Addition of sewage sludge increased the CO₂ emission rate > two times compared to soil amended with sterilized sludge. The NH₄⁺ concentration was lower when sludge was added to an agricultural soil for the first 28 days and in the Texcoco soil for 56 days compared to soil amended with sterilized sludge. Production of N₂O in the agricultural soil was mainly due to nitrification, even when sludge was added, but denitrification was the main source of N₂O in the Texcoco soil. Microorganisms in the sludge reduced N₂O to N₂, but not the soil microorganisms. It was found that microorganisms added with the sludge accelerated organic material decomposition, increased NH₄⁺ immobilization, and induced immobilization of NO₃⁻ (in Texcoco soil). These results suggest that wastewater sludge improves soil fertility at Otumba (an agricultural soil) and would favour the vegetation of the Texcoco soil (alkaline saline).     

Effect of crop residue C:N ratio on N2O emissions from Gray Lowland soil in Mikasa,Hokkaido, Japan

Abstract

We studied the effect of crop residues with various C:N ratios on N₂O emissions from soil. We set up five experimental plots with four types of crop residues, onion leaf (OL), soybean stem and leaf (SSL), rice straw (RS) and wheat straw (WS), and no residue (NR) on Gray Lowland soil in Mikasa, Hokkaido, Japan. The C:N ratios of these crop residues were 11.6, 14.5, 62.3, and 110, respectively. Based on the results of a questionnaire survey of farmer practices, we determined appropriate application rates: 108, 168, 110, 141 and 0 g C m^?2 and 9.3, 11.6, 1.76, 1.28 and 0 g N m^?2, respectively. We measured N₂O, CO₂ and NO fluxes using a closed chamber method. At the same time, we measured soil temperature at a depth of 5 cm, water-filled pore space (WFPS), and the concentrations of soil NH⁺ ₄-N, NO^? ₃-N and water-soluble organic carbon (WSOC). Significant peaks of N₂O and CO₂ emissions came from OL and SSL just after application, but there were no emissions from RS, WS or NR. There was a significant relationship between N₂O and CO₂ emissions in each treatment except WS, and correlations between CO₂ flux and temperature in RS, soil NH⁺ ₄-N and N₂O flux in SSL and NR, soil NH⁺ ₄-N and CO₂ flux in SSL, and WSOC and CO₂ flux in WS. The ratio of N₂O-N/NO-N increased to approximately 100 in OL and SSL as N₂O emissions increased. Cumulative N₂O and CO₂ emissions increased as the C:N ratio decreased, but not significantly. The ratio of N₂O emission to applied N ranged from ?0.43% to 0.86%, and was significantly correlated with C:N ratio (y = ?0.59 ln [x] + 2.30, r ² = 0.99, P < 0.01). The ratio of CO₂ emissions to applied C ranged from ?5.8% to 45% and was also correlated with C:N ratio, but not significantly (r ² = 0.78, P = 0.11).     

Effect of Inorganic N Composition of Fertilizers on Nitrous Oxide Emission Associated with Nitrification and Denitrification

We studied the effect of repeated application (once every 2 d) of a fertilizer solution with different ratios of NH₄ ⁺ - and NO₃ ^?-N on N₂O emission from soil. After the excess fertilizer solution was drained from soil, the water content of soil was adjusted to 50% of the maximum water-holding capacity by suction at 6 × 10³ Pa. Repeated application of NH₄ ⁺- rich fertilizer solution stimulated nitrification in soil more than NO₃ ^?-rich fertilizer. Although the evolution of N₂O through nitrifier denitrification tended to increase with the repeated addition of a fertilizer solution rich in NH₄ ⁺ rather than in NO₃ ^?, the contribution of nitrifier denitrification remained at levels of 20 to 36% of the total emission regardless of the inorganic N composition. The total emission of N₂O also tended to increase with the application of NH₄ ⁺- rather than NO₃ ^?-rich fertilizer. It was suggested that the coupled process of nitrification and denitrification at micro-aerobic sites became important when fertilizer rich in NH₄ ⁺ was applied to soil under relatively aerobic conditions.     

Comparison of Factors Affecting Soil Nitrate Nitrogen and Ammonium Nitrogen Extraction

Extraction of soil nitrate nitrogen (NO₃ ^?-N) and ammonium nitrogen (NH₄ ⁺-N) by chemical reagents and their determinations by continuous flow analysis were used to ascertain factors affecting analysis of soil mineral N. In this study, six factors affecting extraction of soil NO₃ ^?-N and NH₄ ⁺-N were investigated in 10 soils sampled from five arable fields in autumn and spring in northwestern China, with three replications for each soil sample. The six factors were air drying, sieve size (1, 3, and 5 mm), extracting solution [0.01 mol L^?1 calcium chloride (CaCl₂), 1 mol L^?1 potassium chloride (KCl), and 0.5 mol L^?1 potassium sulfate (K₂SO₄)] and concentration (0.5, 1, and 2 mol L^?1 KCl), solution-to-soil ratio (5:1, 10:1, and 20:1), shaking time (30, 60, and 120 min), storage time (2, 4, and 6 weeks), and storage temperature (?18 ^oC, 4 ^oC, and 25 ^oC) of extracted solution. The recovery of soil NO₃ ^?-N and NH₄ ⁺-N was also measured to compare the differences of three extracting reagents (CaCl₂, KCl, and K₂SO₄) for NO₃ ^?-N and NH₄ ⁺-N extraction. Air drying decreased NO₃ ^?-N but increased NH₄ ⁺-N concentration in soil. Soil passed through a 3-mm sieve and shaken for 60 min yielded greater NO₃ ^?-N and NH₄ ⁺-N concentrations compared to other treatments. The concentrations of extracted NO₃ ^?-N and NH₄ ⁺-N in soil were significantly (P < 0.05) affected by extracting reagents. KCl was found to be most suitable for NO₃ ^?-N and NH₄ ⁺-N extraction, as it had better recovery for soil mineral N extraction, which averaged 113.3% for NO₃ ^?-N and 94.9% for NH₄ ⁺-N. K₂SO₄ was not found suitable for NO₃ ^?-N extraction in soil, with an average recovery as high as 137.0%, and the average recovery of CaCl₂ was only 57.3% for NH₄ ⁺-N. For KCl, the concentration of extracting solution played an important role, and 0.5 mol L^?1 KCl could fully extract NO₃ ^?-N. A ratio of 10:1 of solution to soil was adequate for NO₃ ^?-N extraction, whereas the NH₄ ⁺-N concentration was almost doubled when the solution-to-soil ratio was increased from 5:1 to 20:1. Storage of extracted solution at ?18 °C, 4 °C, and 25 °C had no significant effect (P < 0.05) on NO₃ ^?-N concentration, whereas the NH₄ ⁺-N concentration varied greatly with storage temperature. Storing the extracted solution at ?18 ^oC obtained significantly (P < 0.05) similar results with that determined immediately for both NO₃ ^?-N and NH₄ ⁺-N concentrations. Compared with the immediate extraction, the averaged NO₃ ^?-N concentration significantly (P < 0.05) increased after storing 2, 4, and 6 weeks, respectively, whereas NH₄ ⁺-N varied in the two seasons. In conclusion, using fresh soil passed through a 3-mm sieve and extracted by 0.5 mol L^?1 KCl at a solution-to-soil ratio of 10:1 was suitable for extracting NO₃ ^?-N, whereas the concentration of extracted NH₄ ⁺-N varied with KCl concentration and increased with increasing solution-to-soil ratio. The findings also suggest that shaking for 60 min and immediate determination or storage of soil extract at ?18 ^oC could improve the reliability of NO₃ ^?-N and NH₄ ⁺-N results.     

Identifying the Growth Limiting Physiochemical Parameter for Chives Grown in Biologically Treated Graywater

Plants can play an important role in wastewater treatment and water reuse in terrestrial and space systems. Chive growth in biologically treated graywater, simulating the anticipated early planetary base graywater, was evaluated in this study for NASA. Phytotoxicity due to physiochemical parameters such as ammonium-nitrogen (NH₄ ⁺-N), nitrite-nitrogen (NO₂ ^?-N), pH, and sodium (Na⁺) was assessed using a series of hydroponic experiments in an environmentally controlled growth chamber. Nitrification in wastewater was observed in all graywater treatments, which converted NO₂ ^?-N (a toxic form of nitrogen) and NH₄ ⁺-N (toxic at high concentrations) to nitrate-nitrogen (NO₃ ^?-N) (preferred N form for plant uptake). Irrespective of the increase in the NO₃ ^–-N concentration due to nitrification, chives in the wastewater treatments typically had poor or no growth. The high levels of Na⁺ present in the graywater treatments affected potassium uptake and may have affected other nutrient uptake. The impact of nitrification on wastewater pH and NO₂ ^?-N toxicity is believed to be the critical factor affecting chive growth and may hinder the use high nitrogen waste streams for plant growth unless NO₂ ^?-N concentrations are controlled during biological treatment of graywater.     

Nitrous oxide emissions from an irrigated sandy-clay loam cropped to maize and wheat

 Nitrous oxide (N₂O) emissions were measured from an irrigated sandy-clay loam cropped to maize and wheat, each receiving urea at 100 kg N ha^–1. During the maize season (24 August–26 October), N₂O emissions ranged between –0.94 and 1.53 g N ha^–1 h^–1 with peaks during different irrigation cycles (four) ranging between 0.08 and 1.53 g N ha^–1 h^–1. N₂O sink activity during the maize season was recorded on 10 of the 29 sampling occasions and ranged between 0.18 and 0.94 g N ha^–1 h^–1. N₂O emissions during the wheat season (22 November–20 April) varied between –0.85 and 3.27 g N ha^–1 h^–1, whereas peaks during different irrigation cycles (six) were in the range of 0.05–3.27 g N ha^–1 h^–1. N₂O sink activity was recorded on 14 of the 41 samplings during the wheat season and ranged between 0.01 and 0.87 g N ha^–1 h^–1. Total N₂O emissions were 0.16 and 0.49 kg N ha^–1, whereas the total N₂O sink activity was 0.04 and 0.06 kg N ha^–1 during the maize and wheat seasons, respectively. N₂O emissions under maize were significantly correlated with denitrification rate and soil NO₃ ^–-N but not with soil NH₄ ⁺-N or soil temperature. Under wheat, however, N₂O emissions showed a strong correlation with soil NH₄ ⁺-N, soil NO₃ ^–-N and soil temperature but not with the denitrification rate. Under either crop, N₂O emissions did not show a significant relationship with water-filled pore space or soil respiration. Received: 11 June 1997