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.     

Nitrogen turnover in a repeatedly manured arid subtropical soil: Incubation studies with 15N isotopes

Under the hot and moist conditions of irrigated agriculture in the arid subtropics, turnover of organic matter is high, which can lead to considerable carbon (C) and nitrogen (N) losses. Therefore, sustainable use of these soils requires regular manure application at high rates. To investigate the contribution of consecutive manure applications to an arid sandy soil to various soil N pools, goat manure was isotopically labeled by feeding ¹⁵N‐enriched Rhodes grass hay and applied to the soil during a two‐year field experiment. In the first year, soils received ¹⁵N‐labeled manure to distinguish between soil‐derived and manure‐derived N. In the second year, these plots were split for the application of either ¹⁵N‐labeled or unlabeled manure to discriminate N derived from previous (first year) and recent (second year) manure application. Soil samples (of control and ¹⁵N‐manured soil) were collected at the end of the first and the second year, and incubated in two laboratory experiments with labeled or unlabeled manure. At the beginning of Experiment 1, 7% of total N, 11% of K₂SO₄ extractable N, and 16% of microbial biomass N were derived from previously field‐applied manure. While the application of manure during incubation increased microbial biomass N by 225% and 410% in the control soil and the previously field‐manured soil, respectively, N₂O emissions were more affected on the control soil, releasing considerable amounts of the soil N‐pool (80% of total emissions). In Experiment 2, 4% of total N, 7% of K₂SO₄ extractable N, and 7% of microbial biomass N derived from previously applied manure, and 4%, 8%, and 3% from recently applied manure, respectively. Microbial biomass N and N₂O‐N derived from manure declined with time after manure application, whereas in Experiment 1 this tendency was only observed for microbial biomass N.     

Role of soil drying in nitrogen mineralization and microbial community function in semi-arid grasslands of north-west Australia

We examined effects of wetting and then progressive drying on nitrogen (N) mineralization rates and microbial community composition, biomass and activity of soils from spinifex (Triodia R. Br.) grasslands of the semi-arid Pilbara region of northern Australia. We compared soils under and between spinifex hummocks and also examined impacts of fire history on soils over a 28 d laboratory incubation. Soil water potentials were initially adjusted to −100 kPa and monitored as soils dried. We estimated N mineralization by measuring changes in amounts of nitrate (NO₃⁻-N) and ammonium (NH₄⁺-N) over time and with change in soil water potential. Microbial activity was assessed by amounts of CO₂ respired. Phospholipid fatty acid (PLFA) analyses were used to characterize shifts in microbial community composition during soil drying. Net N mineralized under hummocks was twice that of open spaces between hummocks and mineralization rates followed first-order kinetics. An initial N mineralization flush following re-wetting accounted for more than 90% of the total amount of N mineralized during the incubation. Initial microbial biomass under hummocks was twice that of open areas between hummocks, but after 28 d microbial biomass was<2 μ g⁻¹ ninhydrin N regardless of position. Respiration of CO₂ from soils under hummocks was more than double that of soils from between hummocks. N mineralization, microbial biomass and microbial activity were negligible once soils had dried to −1000 kPa. Microbial community composition was also significantly different between 0 and 28 d of the incubation but was not influenced by burning treatment or position. Regression analysis showed that soil water potential, microbial biomass N, NO₃⁻-N, % C and δ¹⁵N all explained significant proportions of the variance in microbial community composition when modelled individually. However, sequential multiple regression analysis determined only microbial biomass was significant in explaining variance of microbial community compositions. Nitrogen mineralization rates and microbial biomass did not differ between burned and unburned sites suggesting that any effects of fire are mostly short-lived. We conclude that the highly labile nature of much of soil organic N in these semi-arid grasslands provides a ready substrate for N mineralization. However, process rates are likely to be primarily limited by the amount of substrate available as well as water availability and less so by substrate quality or microbial community composition.     

Microbial biomass and mineralization-immobilization of nitrogen in some agricultural soils

Summary The chloroform fumigation-incubation method (CFIM) was used to measure the microbial biomass of 17 agricultural soils from Punjab Pakistan which represented different agricultural soil series. The biomass C was used to calculate biomass N and the changes occurring in NH₄ ⁺-N and NO₃ ^–-N content of soils were studied during the turnover of microbial biomass or added C source. Mineral N released in fumigated-incubated soils and biomass N calculated from biomass C was correlated with some N availability indexes.The soils contained 427–1240 kg C as biomass which represented 1.2%–6.9% of the total organic C in the soils studied. Calculations based on biomass C showed that the soils contained 64–186 kg N ha^–1 as microbial biomass. Immobilization of NCO₃ ^–-N was observed in different soils during the turnover of microbial biomass and any net increase in mineral N content of fumigated incubated soils was attributed entirely to NH₄ ⁺-N.Biomass N calculated from biomass C showed non-significant correlation with different N availability indexes whereas mineral N accumulated in fumigated-incubated soils showed highly significant correlations with other indexes including N uptake by plants.     

Mineralization and denitrification in upland, nearly saturated and flooded subtropical soil II. Effect of organic manures varying in N content and C:N ratio

 Nitrogen and carbon mineralization of cattle manure (N=6 g kg^–1; C:N=35), pressmud (N=17.4 g kg^–1; C:N=22), green manure (N=26.8 g kg^–1; C:N=14) and poultry manure (N=19.5 g kg^–1; C:N=12) and their influence on gaseous N losses via denitrification (using the acetylene inhibition technique) in a semiarid subtropical soil (Typic Ustochrepts) were investigated in a growth chamber simulating upland, nearly saturated, and flooded conditions. Mineralization of N started quickly in all manures, except pressmud where immobilization of soil mineral N was observed for an initial 4 days. Accumulation of mineral N in upland soil plus denitrified N revealed that mineralization of cattle manure-, pressmud-, poultry manure- and green manure-N over 16 days was 12, 20, 29 and 44%, respectively, and was inversely related to C:N ratio (R ²=0.703, P=0.05) and directly to N content of organic manure (R ²=0.964, P=0.01). Manure-C mineralized over 16 days ranged from 6% to 50% in different manures added to soil under different moisture regimes and was, in general, inversely related to initial C:N ratio of manure (R ²=0.690, P=0.05). Cumulative denitrification losses over 16 days in control soils (without manure) under upland, nearly saturated, and flooded conditions were 5, 23, and 24 mg N kg^–1, respectively. Incorporation of manures enhanced denitrification losses by 60-82% in upland, 52–163% in nearly saturated, and 26–107% in flooded soil conditions over a 16-day period, demonstrating that mineralized N and C from added manures could result in 2- to 3-fold higher rate of denitrification. Cumulative denitrification losses were maximal with green manure, followed by poultry manure, pressmud and cattle manure showing an increase in denitrification with increasing N content and decreasing C:N ratio of manure. Manure-amended nearly saturated soils supported 14–35% greater denitrification than flooded soils due to greater mineralization and supply of C.     

Responses of the bacterial and fungal biomass in a grassland soil to multi-year applications of dairy manure slurry and fertilizer

Plots of a tall fescue (Festuca arundinacea) sward in the south coastal region of BC, Canada, were treated with dairy manure slurry or fertilizer at 50 or 100 kg NH₄-N ha⁻¹ up to four times per year for six consecutive years; control plots received no manure or fertilizer. The length of fungal hyphae and abundance of bacterial cells were determined by direct counting at 19 sample dates during the fourth (1997), fifth (1998) and sixth (1999) application years. Bacterial abundance was significantly greater in manured soil than in fertilized and untreated soils. In contrast, hyphal length was significantly greater in untreated soil than in manured and fertilized soils. In subplots that ceased to receive manure in 1998, bacterial abundance remained greater through 1998 and 1999 than in previously fertilized plots, indicating that the 4 year cumulative effect of manure was detectable for at least two growing seasons after applications cease. The apparently negative effect of manure and fertilizer on fungal hyphae also appeared to persist through 2 years after applications ceased. Bacterial abundance increased after an initial application of manure for 1 year to previously untreated plots, but not to levels comparable to plots treated with manure continuously from 1994 to 1998.Increases in bacterial abundance, during the one to three week intervals immediately following individual applications of manure, were inconsistent and other factors, such as soil moisture, temperature and perhaps crop phenology appear to have had strong effects on the timing of these microbial responses. Annual means for bacterial abundance and total microbial biomass in the continuous manure treatment were similar for all 3 years. This suggested that the manure-induced increase in microbial biomass probably reached a plateau between one and 3 years after applications commenced. The large bacterial populations along with abundant carbon substrates in manured soil, relative to fertilized soil, were probably capable of immobilizing influxes of mineral N, explaining the observations that less leaching occured from manured than from fertilized soils.     

Conservation of mineral nitrogen in restored soils at opencast coal mine sites: II. The effects of inhibition of nitrification and organic amendments on nitrogen losses and soil microbial biomass

Soils stored in stockpiles during opencast mining operations accumulate significant quantities of ammonium (of the order of 200 μg NH₄⁺-N g^?1 soil) within the predominantly anaerobic cores of mounds. Upon stockpile dismantling and land restoration, this NH⁺₄-N is rapidly oxidized to NO^?₃-N, which is readily lost from newly restored soil ecosystems by leaching and denitrification. Experiments were set up to examine how these significant reserves of mineral N might be conserved in such situations. Application of the nitrification inhibitor dicyandiamide was successful in minimizing NO₃^?-N lost by leaching, though large concentrations of NH₄⁺-N were detected in drainage waters. Straw incorporation decreased nitrate leaching by up to 40%; biomass C was some 40% greater in straw-amended than in unamended soils after 14 weeks, though biomass N was similar in both. Addition of nitrogen-free organic materials (glucose, starch and cellulose) produced different results, with glucose amendment showing the greatest reduction in nitrate leaching in the short term (due to an apparent stimulation of denitrification) whereas addition of cellulose resulted in the most effective conservation of nitrogen over 14 weeks; this was due, at least in part, to uptake of mineral N by the soil microbial biomass.     

Effects of legume green-manuring on nitrogen mineralization and some microbiological properties in an acid rice soil

We studied N mineralization of legume green manures under laboratory and field conditions, and the effects of field green-manuring on the microbiological properties of an acid Alfisol soil. No significant differences were found in the mineralization rates of Sesbania (Sesbania cannabina), sunnhemp (Crotalaria juncea), and cowpea (Vigna unguiculata) green manure. Mineralization was higher in field-capacity moist soil than water-saturated soil. The decomposition of sunnhemp under field wetland conditions, in the absence of a rice crop, was a rapid as it was under in vitro conditions. The decomposition released considerable amounts of mineral N and the level of NH ₄ ⁺ -N was significantly higher than NO ₃ ^– -N. Significant improvements were observed in the microbial biomass, dehydrogenase activity, and bacterial populations in the field soil green-manured for rice for 3 years, compared with fertilized soil.     

土壤微生物体氮测定方法的研究

用熏蒸-0.5mol/LK2SO4 直接浸取NH4+-N法 (简称薰蒸 铵态氮法 ) ,熏蒸 淹水培养法和熏蒸 通气培养法测定了有机质、全氮和C/N比差异较大的 15种土壤的铵态氮增量 (FN)。结果表明 ,它们之间有极显著的正相关 ,在反映土壤微生物体氮上有相同趋势。两种培养方法测定的FN 近乎一致 ,由此而计算的微生物体氮也几乎相同。对红油土铵态氮法测定值仅为两种培养法的 1/ 10。把铵态氮法中的FN 校正后 ,其结果与 2种培养法测定的微生物体氮同样近乎一致。用 3种方法测定的微生物体氮均与土壤有机碳存在显著正相关性。淹水培养和铵态氮法水分条件易控制 ,又无NH3的挥发损失 ,比通气培养法更加优越。对培养试验和长期肥料定位试验的土样测定结果表明 ,土壤中易矿化新鲜有机物料也会使熏蒸 淹水培养法测定的FN 显著下降 ,由此而计算的微生物体氮也显著减少 ,但熏蒸 铵态氮法测定的FN 不受新鲜有机物质的影响。与土壤微生物数目进行比较后发现 ,土壤中含易分解有机物质少或微生物体氮含量低时 ,选用熏蒸 淹水培养法测定误差小 ;当土壤中富含新鲜有机物质时 ,熏蒸 铵态氮法测定的结果更加可靠。用这两种方法在同类土壤上测定的FN 的比值相对稳定 ,微生物体氮 (BN)的平均比值为 0.98～1.01,不受施肥的影响     

Mineralization of Three Organic Manures Used as Nitrogen Source in a Soil Incubated under Laboratory Conditions

Abstract

The rate and timing of manure application when used as nitrogen (N) fertilizer depend on N‐releasing capacity (mineralization) of manures. A soil incubation study was undertaken to establish relative potential rates of mineralization of three organic manures to estimate the value of manure as N fertilizer. Surface soil samples of 0–15 cm were collected and amended with cattle manure (CM), sheep manure (SM), and poultry manure (PM) at a rate equivalent to 200 mg N kg^?1 soil. Soil without any amendment was used as a check (control). Nitrogen‐release potential of organic manures was determined by measuring changes in total mineral N [ammonium‐N+nitrate‐N (NH₄ ⁺–N+NO₃ ^?–N)], NH₄ ⁺–N, and accumulation of NO₃ ^?–N periodically over 120 days. Results indicated that the control soil (without any amendment) released a maximum of 33 mg N kg^?1soil at day 90, a fourfold increase (significant) over initial concentration, indicating that soil had substantial potential for mineralization. Soil with CM, SM, and PM released a maximum of 50, 40, and 52 mg N kg^?1 soil, respectively. Addition of organic manures (i.e., CM, SM, and PM) increased net N released by 42, 25, and 43% over the control (average). No significant differences were observed among manures. Net mineralization of organic N was observed for all manures, and the net rates varied between 0.01 and 0.74 mg N kg^?1 soil day^?1. Net N released, as percent of organic N added, was 9, 10, and 8% for CM, SM, and PM. Four phases of mineralization were observed; initial rapid release phase in 10–20 days followed by slow phase in 30–40 days, a maximum mineralization in 55–90 days, and finally a declined phase in 120 days. Accumulation of NO₃ ^?–N was 13.2, 10.6, and 14.6 mg kg^?1 soil relative to 7.4 mg NO₃ ^?–N kg^?1 in the control soil, indicating that manures accumulated NO₃ ^?–N almost double than the control. The proportion of total mineral N to NO₃ ^?–N revealed that a total of 44–61% of mineral N is converted into NO₃ ^?–N, indicating that nitrifiers were unable to completely oxidize the available NH₄ ⁺. The net rates of mineralization were highest during the initial 10–20 days, showing that application of manures 1–2 months before sowing generally practiced in the field may cause a substantial loss of mineralized N. The rates of mineralization and nitrification in the present study indicated that release of inorganic N from the organic pool of manures was very low; therefore, manures have a low N fertilizer effect in our conditions.     

Clinoptilolite Zeolite Influence on Nitrogen in a Manure-Amended Sandy Agricultural Soil

Zeolite minerals may improve nitrogen availability to plants in soil and reduce losses to the environment. A study was conducted to determine the influence of clinoptilolite (CL) on nitrogen (N) mineralization from solid dairy manure (224 kg N ha^?1) in a sandy soil. Clinoptilolite was added to soil at six rates (0 to 44.8 Mg CL ha^?1), each sampled during 11 sampling dates over a year. Over time, nitrate (NO₃)-N increased, ammonium (NH₄)-N decreased, but total inorganic N increased. Clinoptilolite did not influence the nitrification rates of initial manure NH₄-N or mineralization of organic N (ON) over time. It is possible that adsorption of manure-derived potassium (K) outcompeted the NH₄-N for CL exchange sites. The ON concentration was constant up to 84 days and then decreased by approximately 18% over the remaining time of the study across all treatments. Clinoptilolite use in this sandy soil did not alter mineralization of N from dairy manure.     

Nitrogen Mineralization of Two Manures as Influenced by Contrasting Application Methods under Laboratory Conditions

The decomposition and the associated nitrogen (N) dynamics of organic N sources are affected by their contact with soil. While several authors have examined the effect of surface application or incorporation of crop residues on their decomposition rate, less information is available about the relationship between the placement of animal manure and their N mineralization rate. This study investigated the influence of chicken manure and cattle manure placement on soil N mineralization. The manures were incorporated or surface applied at 175 mg N kg^?1, and N release was periodically determined over 56 days by measuring inorganic N [nitrate (NO₃ ^?) N and ammonium (NH₄ ⁺) N] in a 2 M potassium chloride (KCl) extract at a ratio of 1:10 (w/v). Results indicated that the control soil released a maximum of 64 mg N kg^?1 soil at day 21, a sixfold increase over the initial concentration, which indicates its substantial mineralization potential. Manure treatments showed an initial increase in net NO₃ ^?-N content at the start of the experiments (until day 7) before an extended period of immobilization, which ended at day 21 of the incubation. A small but positive net N mineralization of all manures was observed from 28 days of incubation. At each sampling time, the mean mineral N released from the control was significantly less (P < 0.01) than surface-applied chicken manure, incorporated chicken manure, and surface-applied cattle manure. Treatments exceptions were at days 21 and 28 where N immobilization was at its peak. In contrast, incorporation of cattle manure showed a different N-release pattern, whereby the mineral N amount was only significantly greater than the control soil at days 42 and 56 with 84 and 108 mg N kg^?1 soil respectively. Incorporation of chicken manure and cattle manure did not favor nitrification as much as surface application and cattle manure caused a much greater immobilization when incorporated than when surface applied.     

Ammonia volatilization from poultry manure-amended soil

Summary Poultry manure (PM) is commonly applied to cropland as a fertilizer, usually at rates determined by the nitrogen content of the manure. Limited information is available, however, on the volatilization of ammonia from poultry manure-amended soils, despite the effect these losses may have on the fertilizer value of the manure. This study was initiated to determine the influence of incorporation and residue cover on NH₃ losses from PM-amended soils. In the first experiment, a dynamic flow technique was used to measure NH₃ losses from 18 manures applied to a bare soil surface at a rate of 12 Mg ha^-1. In the second experiment, 3 of the 18 manures were incorporated either immediately, 24 h or 72 h after application. The third experiment compared the same three manures applied to a bare soil surface or to corn or soybean residues. Surface application of the manures resulted in the loss of from 4 to 31% of the total N applied in the manures. Incorporation of the PM with soil significantly reduced NH₃ loss with the greatest decrease following immediate incorporation. Crop residues either had no effect or slightly reduced NH₃ volatilization losses relative to PM application to a bare soil surface. Ammonia volatilization was not well correlated with individual manure properties, but a multiple regression approach using manure pH and total N content offered some promise as a means to segregate manures of the basis of volatilization potential.     

A field study of gross rates of N mineralization and nitrification and their relationships to microbial biomass and enzyme activities in soils treated with dairy effluent and ammonium fertilizer

Abstract. Gross N mineralization and nitrification rates were measured in soils treated with dairy shed effluent (DSE) (i.e. effluent from the dairy milking shed, comprising dung, urine and water) or ammonium fertilizer (NH₄Cl) under field conditions, by injecting ¹⁵N-solution into intact soil cores. The relationships between gross mineralization rate, microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) as affected by the application of DSE and NH₄Cl were also determined. During the first 16 days, gross mineralization rate in the DSE treated soil (4.3–6.1 μg N g^?1 soil day^?1) were significantly (P 14;< 14;0.05) higher than those in the NH₄Cl treated soil (2.6–3.4 μg N g^?1 soil day^?1). The higher mineralization rate was probably due to the presence of readily mineralizable organic substrates in the DSE, accompanied by stimulated microbial and extracellular enzyme activities. The stable organic N compounds in the DSE were slow to mineralize and contributed little to the mineral N pool during the period of the experiment. Nitrification rates during the first 16 days were higher in the NH₄Cl treated soil (1.7–1.2 μg N g^?1 soil day^?1) compared to the DSE treated soil (0.97–1.5 μg N g^?1 soil day^?1). Soil microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) increased after the application of the DSE due to the organic substrates and nutrients applied, but declined with time, probably because of the exhaustion of the readily available substrates. The NH₄Cl application did not result in any significant increases in microbial biomass C, protease or urease activities due to the lack of carbonaceous materials in the ammonium fertilizer. However, it did increase microbial biomass N and deaminase activity. Significant positive correlations were found between gross N mineralization rate and soil microbial biomass, protease, deaminase and urease activities. Nitrification rate was significantly correlated to biomass N but not to the microbial biomass C or the enzyme activities. Stepwise regression analysis showed that the variations of gross N mineralization rate was best described by the microbial biomass C and N.     

Nitrogen mineralization and assimilation at millimeter scales

This study used inoculated, artificial soil microcosms containing sand, clay, cellulose, and localized “hotspots” of highly labile, organic N-containing dead bacteria to study N mineralization and assimilation at millimeter scales. Labeling with ¹⁵NH₄⁺ along with measurement of its assimilation into microbial biomass at the bulk scale allowed estimation of gross rates of ammonification and N assimilation using isotope dilution. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses of transects of organic-¹⁵N across Si wafers in contact with the microcosms indicated strong gradients of ¹⁵NH₄⁺ assimilation as a function of proximity to the hotspots that were not apparent using bulk analyses. This combination of bulk and ToF-SIMS analyses represents a powerful approach to explore the physical and biochemical factors that affect N process heterogeneities in soils.     

Gross nitrogen mineralization and nitrification rates and their relationships to enzyme activities and the soil microbial biomass in soils treated with dairy shed effluent and ammonium fertilizer at different water potentials

 Gross N mineralization and nitrification rates and their relationships to microbial biomass C and N and enzyme (protease, deaminase and urease) activities were determined in soils treated with dairy shed effluent (DSE) or NH₄ ⁺ fertilizer (NH₄Cl) at a rate equivalent to 200 kg N ha^–1 at three water potentials (0, –10 and –80 kPa) at 20  °C using a closed incubation technique. After 8, 16, 30, 45, 60 and 90 days of incubation, sub-samples of soil were removed to determine gross N mineralization and nitrification rates, enzyme activities, microbial biomass C and N, and NH₄ ⁺ and NO₃ ^– concentrations. The addition of DSE to the soil resulted in significantly higher gross N mineralization rates (7.0–1.7 μg N g^–1 soil day^–1) than in the control (3.8–1.2 μg N g^–1 soil day^–1), particularly during the first 16 days of incubation. This increase in gross mineralization rate occurred because of the presence of readily mineralizable organic substrates with low C : N ratios, and stimulated soil microbial and enzymatic activities by the organic C and nutrients in the DSE. The addition of NH₄Cl did not increase the gross N mineralization rate, probably because of the lack of readily available organic C and/or a possible adverse effect of the high NH₄ ⁺ concentration on microbial activity. However, nitrification rates were highest in the NH₄Cl-treated soil, followed by DSE-treated soil and then the control. Soil microbial biomass, protease, deaminase and urease activities were significantly increased immediately after the addition of DSE and then declined gradually with time. The increased soil microbial biomass was probably due to the increased available C substrate and nutrients stimulating soil microbial growth, and this in turn resulted in higher enzyme activities. NH₄Cl had a minimal impact on the soil microbial biomass and enzyme activities, possibly because of the lack of readily available C substrates. The optimum soil water potential for gross N mineralization and nitrification rates, microbial and enzyme activities was –10 kPa compared with –80 kPa and 0 kPa. Gross N mineralization rates were positively correlated with soil microbial biomass N and protease and urease activities in the DSE-treated soil, but no such correlations were found in the NH₄Cl-treated soil. The enzyme activities were also positively correlated with each other and with soil microbial biomass C and N. The forms of N and the different water potentials had a significant effect on the correlation coefficients. Stepwise regression analysis showed that protease was the variable that most frequently accounted for the variations of gross N mineralization rate when included in the equation, and has the potential to be used as one of the predictors for N mineralization. Received: 10 March 1998     

Comparison of Chemical Methods for Assessing Nitrogen Mineralization in Two Calcareous Soils Treated with Organic Materials

Reliable and quick methods for measuring nitrogen (N)–supplying capacities of soils (NSC) are a prerequisite for using N fertilizers. This study was conducted to develop a routine method for estimation of mineralizable N in two calcareous soils (sandy loam and clay soils) treated with municipal waste compost or sheep manure. The methods used were anaerobic biological N mineralization, mineral N released by 2 M potassium chloride (KCl), ammonium (NH₄ ⁺) N extracted by 1 N sulfuric acid (H₂SO₄), NH₄ ⁺-N extracted by acid potassium permanganate (KMnO₄), and NH₄ ⁺-N released by oxidation of soil organic matter using acidified potassium permanganate. The results showed that oxidizable N extracted by acid permanganate, a simple and rapid measure of soil N availability, was correlated with results of the anaerobic method. Oxidative 0.05 N KMnO₄ was the best method, accounting for 78.4% of variation in NSC. Also, the amount of mineralized N increased with increasing level of organic materials and was greater in clay soil than sandy loam soil.     

The influence of nitrogen on atrazine and 2,4-dichlorophenoxyacetic acid mineralization in grassland soils

The influence of fertilizer N on the mineralization of atrazine [2-chloro-4(ethylamino)-6(isopropylamino)-s-triazine] and 2,4-D (2,4-dichlorophenoxyacetic acid) in soils was assessed in microcosms using radiometric techniques. N equivalent to 0, 250, and 500 kg N as NH₄NO₃ ha^-1 was added to three grassland soils. Compared to the control, the 250- and 500-kg treatments suppressed mineralization of atrazine by 75 and 54%, respectively, and inhibited mineralization of 2,4-D by 89 and 30%, respectively. Active fungal biomass responded to the N treatments in an opposite manner to herbicide mineralization. Compared to the control, the 250- and 500-kg treatments increased the active fungal biomass by more than 300 and 30%, respectively. These results agree with other observations that N can suppress the decomposition of resistant compounds but stimulate the primary growth of fungi. The degree of suppression was not related to the amount of N added nor to the inherent soil N levels before treatment. The interaction between the N additions and the active fungal biomass in affecting herbicide mineralization suggests that N may alter microbial processes and their use of C sources and thus influence rates of herbicide degradation in the field.     

Absorption of nitrogen by Japanese mint from mineralization and immobilization by the soil microbial biomass

Abstract

Laboratory incubation and greenhouse experiments were conducted with two soils having contrasting physico‐chemical characteristics to evaluate nitrogen (N) mineralization, immobilization in soil microbial biomass, and accumulation in Japanese mint (Mentha arvensis L.) using labeled (¹⁵NH₄)₂SO₄, applied at 0, 50, and 100 mg#lbkg^‐1 soil. Rate of mineralization in soils varied from 0.08 to 2.21 μg#lbg^‐1#lbday^‐1. Fertilizer application increased the mineralization of native soil N. About 22 to 60% of the applied ¹⁵N was recovered in the soil microbial biomass during the growth period of mint (January‐June). Relative contribution of fertilizer ¹⁵N towards total N uptake by mint at maturity was 42–54% in soil I and 35 to 55% in soil II. Contribution of soil N towards total N accumulation increased with the doses of ¹⁵N application.     

Nitrogen Inputs with Different Substrate Quality Modified pH,Eh, and N Dynamics of a Paddy Soil Incubated under Waterlogged Conditions

Synthetic fertilizer, livestock manure, and green manure are the typical nitrogen (N) sources in agriculture. This study was conducted to investigate the effects of different N sources on soil chemical environment and N dynamics. Changes in pH, redox potential (Eh), and concentration and δ¹⁵N of dissolved N [ammonium (NH₄⁺), nitrate (NO₃^?), organic N, and total N] of soils treated with urea (U), pig manure compost (PMC), and hairy vetch (HV) were investigated in an incubation experiment under waterlogged conditions. The patterns of pH, Eh, and N concentration reflected both a greater mineralization potential of N derived from U than that from HV and PMC and easier decomposability of HV than PMC. The δ¹⁵N further suggested that nitrification was more active for U than for HV- and PMC-treated soils and that N loss via NH₃ volatilization and denitrification would be greater for HV than U and PMC treatments.