Influence of surface‐applied poultry manure on topsoil and subsoil acidity and salinity: A leaching column study

It has been suggested that surface applications of animal manure can ameliorate both top and subsoil acidity. For that reason, the effects of surface incorporation (0–5 cm) of a high rate of poultry manure to an acid soil on pH and exchangeable and soluble Al in the top‐ and subsoil were investigated in a leaching column study. During the experimental period of 108 d, columns received a total of 875 mm with leaching events occurring after 9, 37, 58, and 86 d. Incorporation of poultry manure into the surface 5 cm resulted in a large rise in pH measured in both 1M KCl and in soil solution. This liming effect was attributed primarily to the substantial CaCO₃ content of poultry manure. In the 15–45 cm layer, pH_KCl was not significantly different between poultry manure and control treatments but surprisingly, soil‐solution pH was substantially less in the poultry‐manure treatments. Exchangeable Al was significantly less in poultry manure than in control in all soil layers although the effect was most marked in the 0–5 cm layer. However, although concentrations and activities of monomeric Al (Al_mono), and the proportion of total Al present as Al_mono, in soil solution were lower under poultry manure than in control in the 0–5 cm layer, the reverse was, in fact, the case in lower soil horizons. This was attributed to a soluble‐salt effect, originating from the large cation content of poultry manure, displacing exchangeable Al³⁺ and H⁺ back into soil solution. Indeed, electrical conductivity and concentrations of Ca²⁺, Mg²⁺_, K⁺, and Na⁺ in soil solution were substantially higher in the poultry‐manure than in the control treatments at all soil depths. Poultry‐manure applications also resulted in substantial increases in the concentrations of Ca²⁺_, Mg²⁺_, K⁺, Na⁺, Al_mono, NH , and NO in leachates, particularly at the fourth leaching. It was concluded that although surface application of poultry manure can raise soil pH in the topsoil, increases in soluble‐salt concentrations in soil solution can greatly modify this effect in the subsoil.     

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.     

Assessing Tillage Systems for Reducing Ammonia Volatilization from Spring-Applied Slurry Manure

The effect of tillage management on NH₃-N volatilization and its influence on succeeding corn (Zea mays L.) silage production were studied at the University of Massachusetts Agricultural Experiment Station (South Deerfield, MA) during 2010–2012 growing seasons. Tillage treatments consisted of disking before and after manure application, solid-tine aeration before and after manure application, and no-till management. The greatest NH₃-N loss (61 percent) occurred within the first 8 h after slurry manure application regardless of tillage management. The greatest NH₃-N emission occurred with surface application (no-till), which ranged between 5.2 and 10.3 kg NH₃-N ha^?1 (9–20 percent of NH₃-N applied) over the 3 years of the study. Immediate incorporation of manure into soil through disking reduced NH₃-N loss by 66 to 75 percent. Ammonia loss abatement with aeration before or after manure application ranged from 13 to 41 percent compared with surface manure application. Tillage management did not influence corn silage yield or quality.     

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.     

Transformations of nitrogen-15-labelled urea in a flooded soil as affected by floodwater algae and green manure in a growth chamber

 The effects of floodwater algae and green manure on transformations of ¹⁵N-urea were studied in columns of a sandy loam soil in a growth chamber. The columns were flooded and either kept in the light, to allow algal growth, or in the dark (control) for 17 days before adding the labelled urea. Changes in urea-, NO₃ ^–- and NH₄ ⁺-N levels and the pH of the floodwater were measured over the subsequent 41-day period, during which the control column remained in the dark and those containing algae were maintained either in the dark to cause the death of the algae or in the light. Volatilized NH₃ was monitored, and on termination of the experiment the distribution of ¹⁵N between NO₃ ^–, NH₄ ⁺ and organic forms was measured in the soil. Urea hydrolysis was most rapid in the presence of both living algae and green manure, followed by dead algae, and was slowest in the control. The concentration of NH₄ ⁺-N in the floodwater was, however, reduced in the presence of algae due to assimilation and NH₃ volatilization owing to the raised day-time pH in the floodwater. NH₃ volatilization for the first 10 days was rather high in the columns kept in the light compared to those in the dark. Total volatilization plus denitrification losses were greatest where dead algae were present, owing to the absence of live algae which assimilated more than half of the applied N. Algal growth in floodwater increased the depth of the aerobic soil layer present at the soil-water interface. Subsequently, under dark conditions, stimulated algal growth reduced the depth of the aerobic layer causing less nitrification, which resulted in lower losses of N due to denitrification, i.e. 17% of the applied urea-N as compared to 39% in the light treatments. Although the presence of green manure caused a marked increase in the rate of hydrolysis, algal assimilation prevented excessive N losses via volatilization, indicating that the retention of higher quantities of NH₄ ⁺-N may have increased fertilizer-N use efficiency. Received: 22 January 1999     

Application of hydrochar and pyrochar to manure is not effective for mitigation of ammonia emissions from cattle slurry and poultry manure

Nitrogen (N) loss as ammonia (NH₃) from agricultural systems is one of the major sources of atmospheric pollutants and is responsible for more than 50% of global NH₃ emissions. Ammonia volatilization from animal manures may be altered by amendment with chars derived from pyrolysis (pyrochars) or hydrothermal carbonization (hydrochars) by providing exchange sites for ammonium (NH₄⁺) or changing the pH of manure. Pyrochar and hydrochar differ in chemical and structural composition, specific surface area, and pH and therefore may affect NH₃ volatilization differently. In a laboratory incubation experiment, we investigated the effect of pyrochar (pH 9.0) and hydrochar (pH 3.8) from Miscanthus on NH₃ emission after addition to poultry manure and cattle slurry. We analyzed manure treatments with and without char addition and acidification and determined the effect of char addition on immobilization of manure-derived NH₄⁺. Ammonia emission from pure poultry manure amounted 84% of the applied NH₄⁺-N, while 67% of the applied NH₄⁺-N was lost as NH₃ from cattle slurry. Addition of pyrochar or hydrochar had no or only marginal effects on NH₃ emissions except for a reduction in NH₃ emissions by 19% due to hydrochar application to CS (p?<?0.05), which seems to be primarily related to the char pH. Sorption of NH₄⁺ by admixture of chars to manure was generally small: between 0.1- and 0.5-mg NH₄⁺-N g^?1 chars were sorbed. This corresponds to between 0.1 and 3.5% of the NH₄⁺ applied, which obviously was not strong enough to reduce emissions of NH₃. Overall, our results do not provide evidence that addition of pyrochar or hydrochar to cattle slurry and poultry manure is an effective measure to reduce NH₃ volatilization.     

Presubmergence and green manure affect the transformations of nitrogen‐15‐labeled urea under lowland soil conditions

The effect of presubmergence and green manuring on various processes involved in [¹⁵N]‐urea transformations were studied in a growth chamber after [¹⁵N]‐urea application to floodwater. Presubmergence for 14 days increased urea hydrolysis rates and floodwater pH, resulting in higher NH₃ volatilization as compared to without presubmergence. Presubmergence also increased nitrification and subsequent denitrification but lower N assimilation by floodwater algae caused higher gaseous losses. Addition of green manure maintained higher NH₄⁺‐N concentration in floodwater mainly because of lower nitrification rates but resulted in highest NH₃ volatilization losses. Although green manure did not affect the KCl extractable NH₄⁺‐N from applied fertilizer, it maintained higher NH₄⁺‐N content due to its decomposition and increased mineralization of organic N. After 32 days about 36.9 % (T₁), 23.9 % (T₂), and 36.4 % (T₃) of the applied urea N was incorporated in the pool of soil organic N in treatments. It was evident that the presubmergence has effected the recovery of applied urea N.     

Simultaneous nitrification and diffusion in soil. III. The effects of the addition of ammonium sulphate

The simultaneous nitrification and diffusion of NH₄⁺, applied as ammonium sulphate to laboratory columns, was followed experimentally and with a simulation model. Ammonium was applied as a fertilizer band at levels equivalent to 69 kg N ha^?1 to a 1 cm depth. The concentration profiles of NH₄⁺, NO₃^?, SO^2?₄ and pH were measured in two columns for incubation times of 214 and 286 h. The simulation model provided for the precipitation and ion pair formation of CaSO₄, the adsorption equilibria of NH₄⁺ and soil acid with the soil solid phase, and nitrifier growth and activity. In general, good agreement was found between the experimental and simulated concentration profiles. The effect of CaSO₄ precipitation on the diffusion of N was investigated using model simulations of the diffusion of NH₄⁺ in the absence of nitrification. The simulations suggested that the reactions of SO^2?4 in the soil could markedly affect the spread of NH₄⁺ from a band of (NH₄)₂SO₄.     

Influence of green manuring with Sesbania rostrata and Aeschynomene afraspera or urea on dynamics and uptake of nutrients by wetland rice

Nutrient concentrations in the soil and crop uptake from incorporated green manure and urea in flooded rice was studied in field experiments. Release of plant-available nitrogen (NH₄ ⁺-N) from green manure was slightly delayed compared with that from prilled urea (PU) because Sesbania rostrata L. and Aeschynomene afraspera L. released the N gradually after their decomposition, whereas N became available immediately after PU application. Exchangeable NH₄ ⁺-N concentration in soil peaked at 163 mg kg^–1 in the transplanted rice (TPR) and 198 mg kg^—1 in broadcast-seeded rice (BSR) at 0 and 1 week after PU application. Broadcast-seeded rice depleted NH₄ ⁺-N faster than did TPR because of the crop‘s vigorous growth in the former during the early stage. Soil solution NH₄ ⁺-N followed a similar trend to that of soil NH₄ ⁺-N. Incorporation of S. rostrata and A. afraspera increased the concentration of P, K⁺, Fe²⁺ and Mn²⁺ in soil solution more than did the application of PU. However, zinc concentration decreased in all treatments. Both PU and green manure increased the N status of the rice plants and enhanced the uptake of P, K, Fe, Mn and Zn by the rice crop. This suggests that application of green manures improves the uptake of these nutrients by the crop. The highest apparent N recovery was obtained with PU followed by green manure. Received: 11 November 1996     

长期施肥对土壤固定态铵含量及其有效性影响

棕壤连续13年定位试验表明,长期施用化肥或低量有机肥对土壤固定态接含量均无显著影响;而施用高量有机肥区固定态接含量比试验前平均增加30.2％。这部分增加的固定态按主要来自土壤有机氮矿化补充。施肥后固定态铵的净增加量超过作物施氮量是土壤激发效应的结果。土壤原有固定态铵含量在113～116mg／kg,对作物无效,而新固定态按时作物有效。生长季耕层土壤固定态铵总释放量（N）对照区为43kg／hm2,化肥区平均为110kg／hm2;有机肥与化肥配合区平均为165kg／hm2。施钾对固定态铵的释放有一定抑制作用。     

Effects of 4-amino 1,2,4-triazole, dicyandiamide and encapsulated calcium carbide on nitrification inhibition in a subtropical soil under upland and flooded conditions

 Nitrification inhibition of soil and applied fertilizer N is desirable as the accumulation of nitrates in soils in excess of plant needs leads to enhanced N losses and reduced fertilizer N-use efficiency. In a growth chamber experiment, we studied the effects of two commercial nitrification inhibitors (NIs), 4-amino 1,2,4-triazole (ATC) and dicyandiamide (DCD), and a commonly available and economical material, encapsulated calcium carbide (CaC₂) (ECC) on the nitrification of soil and applied NH₄ ⁺-N in a semiarid subtropical Tolewal sandy loam soil under upland [60% water-filled pore space (WFPS)] and flooded conditions (120% WFPS). Nitrification of the applied 100 mg NH₄ ⁺-N kg^–1 soil under upland conditions was retarded most effectively (93%) by ECC for up to 10 days of incubation, whereas for longer periods, ATC was more effective. After 20 days, only 16% of applied NH₄ ⁺-N was nitrified with ATC as compared to 37% with DCD and 98% with ECC. Under flooded soil conditions, nitrates resulting from nitrification quickly disappeared due to denitrification, resulting in a tremendous loss of fertilizer N (up to 70% of N applied without a NI). Based on four indicators of inhibitor effectiveness, namely, concentration of NH₄ ⁺-N and NO₃ ^–-N, percent nitrification inhibition, ratio of NH₄ ⁺-N/NO₃ ^–-N, and total mineral N, ECC showed the highest relative efficiency throughout the 20-day incubation under flooded soil conditions. At the end of the 20-day incubation, 96%, 58% and 38% of applied NH₄ ⁺-N was still present in the soil where ECC, ATC and DCD were used, respectively. Consequently, nitrification inhibition of applied fertilizer N in both arable crops and flooded rice systems could tremendously minimize N losses and help enhance fertilizer N-use efficiency. These results suggest that for reducing the nitrification rate and resultant N losses in flooded soil systems (e.g. rice lowlands), ECC is more effective than costly commercial NIs. Received: 25 May 2000     

A standardized method for the determination of the intrinsic carbon and nitrogen mineralization capacity of natural organic matter sources

A new method was developed for the simultaneous determination of the intrinsic carbon and nitrogen mineralization capacity of organic matter (OM) sources by means of an aerobic incubation in suspension. The proposed method is based on determination of the oxygen consumption, monitored indirectly via pressure measurement, and on determination of nitrogen mineralization, through the periodical measurement of NH₄⁺-N, in a liquid suspension of the samples. The suspension is standardized in terms of nutrient composition and pH, and well-controlled incubation conditions that can be enforced as desired. This method rules out the effect of soil conditions and thus reflects the intrinsic properties of the OM. The method is faster and more reproducible than soil incubation tests that are currently used. In such a system, it is important that nitrification is inhibited to avoid oxygen consumption by nitrifiers and prevent the production of gaseous nitrogen compounds. Two nitrification inhibitors, N-allylthiourea and 2-ethynylpyridine, were tested at different concentrations for three reference samples, soil, bark and manure. Both inhibitors completely suppress NO₃⁻ formation without suppressing the heterotrophic microbial activity, thus allowing the correct determination of the oxygen uptake rate (OUR). When nitrification inhibitors were added, nitrous oxide could not be detected anymore in the gas phase of the system, which confirms that nitrification was inhibited and indicates that denitrification and nitrifier denitrification activity was negligible. N mineralization rates were determined by frequent sampling from the liquid phase of the system without disturbing the pressure measurement during the incubation and subsequent determination of NH₄⁺-N. The method presented allows for the reliable and relatively easy and cheap, simultaneous determination of carbon and nitrogen mineralization rates for a wide range of OM sources.     

Impact of nitrogen and phosphorus additions on soil gross nitrogen transformations in a temperate desert steppe

Nutrient addition has a significant impact on plant growth and nutrient cycling. Yet, the understanding of how the addition of nitrogen (N) or phosphorus (P) significantly affects soil gross N transformations and N availability in temperate desert steppes is still limited. Therefore, a ¹⁵N tracing experiment was conducted to study these processes and their underlying mechanism in a desert steppe soil that had been supplemented with N and P for 4 years in northwestern China. Soil N mineralization was increased significantly by P addition, and N and P additions significantly promoted soil autotrophic nitrification, rather than NH₄⁺-N immobilization. The addition of N promoted dissimilatory NO₃⁻ reduction to NH₄⁺, while that of P inhibited it. Soil NO₃⁻-N production was greatly increased by N added alone and by that of N and P combined, while net NH₄⁺-N production was decreased by these treatments. Soil N mineralization was primarily mediated by pH, P content or organic carbon, while soil NH₄⁺-N content regulated autotrophic nitrification mainly, and this process was mainly controlled by ammonia-oxidizing bacteria rather than archaea and comammox. NH₄⁺-N immobilization was mainly affected by functional microorganisms, the abundance of narG gene and comammox Ntsp-amoA. In conclusion, gross N transformations in the temperate desert steppe largely depended on soil inorganic N, P contents and related functional microorganisms. Soil acidification plays a more key role in N mineralization than other environmental factors or functional microorganisms.     

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.     

Variation in the relationship between nitrification and acidification of subtropical soils as affected by the addition of urea or ammonium sulfate

The effects on nitrification and acidification in three subtropical soils to which (NH₄)₂SO₄ or urea had been added at rate of 250 mg N kg⁻¹ was studied using laboratory-based incubations. The results indicated that NH₄⁺ input did not stimulate nitrification in a red forest soil, nor was there any soil acidification. Unlike red forest soil, (NH₄)₂SO₄ enhanced nitrification of an upland soil, whilst urea was more effective in stimulating nitrification, and here the soil was slightly acidified. For another upland soil, NH₄⁺ input greatly enhanced nitrification and as a result, this soil was significantly acidified. We conclude that the effects of NH₄⁺ addition on nitrification and acidification in cultivated soils would be quite different from in forest soils. During the incubation, N isotope fractionation was closely related to the nitrifying capacity of the soils.     

Ammonia volatilization following urea application at maize fields in the East African highlands with different soil properties

Use of nitrogen (N) fertilizer is underway to increase in Sub-Saharan Africa (SSA). The effect of increasing N rates on ammonia (NH₃) volatilization—a main pathway of applied-N loss in cropping systems—has not been evaluated in this region. In two soils (Alfisols, ALF; and Andisols, AND) with maize crop in the East African highlands, we measured NH₃ volatilization following urea broadcast at six rates (0–150 kg N ha^?1) for 17 days, using a semi-open static chamber method. Immediate irrigation and urea deep placement were tested as mitigation treatments. The underlying mechanism was assessed by monitoring soil pH and mineral N (NH₄⁺ and NO₃^?) concentrations. More cumulative NH₃-N was volatilized in ALF than in AND at the same urea-N rate. Generally, higher urea-N rates increased proportional NH₃-N loss (percent of applied N loss as NH₃-N). Based on well-fitted sigmoid models, simple surface urea application is not recommended for ALF, while up to 60 kg N ha^?1 could be adopted for AND soils. The susceptibility of ALF to NH₃ loss mainly resulted from its low pH buffering capacity, low cation exchange capacity, and high urease activity. Both mitigation treatments were effective. The inhibited rise of soil pH but not NH₄⁺ concentration was the main reason for the mitigated NH₃-N losses, although nitrification in the irrigation treatment might also have contributed. Our results showed that in acidic soils common to SSA croplands, proportional NH₃-N loss can be substantial even at a low urea-N rate; and that the design of mitigation treatments should consider the soil’s inherent capacity to buffer NH₃ loss.     

Nitrification and Denitrification after Direct Injection of Liquid Cattle Manure

Abstract

Soil cores were collected in and around an injection slit in each of two field plots on a coarse sandy soil. The plots received either raw or anaerobically digested liquid cattle manure at a rate of 240 kg NH₄ ⁺-N ha^?1. During the three week period of the experiment, concentrations of dissolved organic carbon and NH₄ ⁺ and the moisture content of cores from the injection slit were consistently above the background level in the soil. Denitrification activity was only registered in soil cores sampled in the injection slit. A dramatic increase occurred between Day 14 and Day 21, when the denitrification rate reached 3.5 kg N ha^?1day^?1 in cores from the plot treated with raw manure, while the rate was 20-fold lower in the plot treated with digested manure. Nitrate accumulated between Day 7 and Day 21, suggesting a coupling between nitrification and denitrification.     

Microbial immobilization of ammonium and nitrate in relation to ammonification and nitrification rates in organic and conventional cropping systems

Agricultural systems that receive high or low organic matter (OM) inputs would be expected to differ in soil nitrogen (N) transformation rates and fates of ammonium (NH₄⁺) and nitrate (NO₃⁻). To compare NH₄⁺ availability, competition between nitrifiers and heterotrophic microorganisms for NH₄⁺, and microbial NO₃⁻ assimilation in an organic vs. a conventional irrigated cropping system in the California Central Valley, chemical and biological soil assays, ¹⁵N isotope pool dilution and ¹⁵N tracer techniques were used. Potentially mineralizable N (PMN) and hot minus cold KCl-extracted NH₄⁺ as indicators of soil N supplying capacity were measured five times during the tomato growing season. At mid-season, rates of gross ammonification and gross nitrification after rewetting dry soil were measured in microcosms. Microbial immobilization of NO₃⁻ and NH₄⁺ was estimated based on the uptake of ¹⁵N and gross consumption rates. Gross ammonification, PMN, and hot minus cold KCl-extracted NH₄⁺ were approximately twice as high in the organically than the conventionally managed soil. Net estimated microbial NO₃⁻ assimilation rates were between 32 and 35% of gross nitrification rates in the conventional and between 37 and 46% in the organic system. In both soils, microbes assimilated more NO₃⁻ than NH₄⁺. Heterotrophic microbes assimilated less NH₄⁺ than NO₃⁻ probably because NH₄⁺ concentrations were low and competition by nitrifiers was apparently strong. The high OM input organic system released NH₄⁺ in a gradual manner and, compared to the low OM input conventional system, supported a more active microbial biomass with greater N demand that was met mainly by NO₃⁻ immobilization.     

The influence of nitrate and ammonium fertilization on N2O release and CH4 uptake of a well-drained topsoil demonstrated by a soil microcosm experiment

The effects of the application of KNO₃ and NH₄Cl (100 kg N ha^?1) on N₂O release and CH₄ uptake by a well-aerated topsoil (porosity: 55%, water-filled pore space: 67% of the total pore space) were studied in a laboratory incubation experiment over 50 days using a soil microcosm system with an automated registration of N₂O and CH₄ fluxes. The total N₂O-N losses over 50 days were low for all treatments and amounted to 0.9 mg m^?2 for the control, 1.2 mg m^?2 for the soil columns fertilized with KNO3, and 7.3 mg m^?2 for the soil columns fertilized with NH₄Cl. The slightly elevated N₂O release after the application Of NH₄Cl was associated with the nitrification of NH₄⁺ added. Only ?0.06% of the fertilized NH₄?N was lost as N₂O. This nitrogen fertilization reduced the CH₄ uptake of the soil columns by 43% (NH₄Cl) and 21% (KNO₃), respectively.     

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.