Mineralization Of Organic Nitrogen Research Articles

Microbial Mineralization of Organic Nitrogen Forms in Poultry Litters

Ammonia volatilization from the mineralization of uric acid and urea has a major impact on the poultry industry and the environment. Dry acids are commonly used to reduce ammonia emissions from poultry houses; however, little is known about how acidification affects the litter biologically. The goal of this laboratory incubation was to compare the microbiological and physiochemical effects of dry acid amendments (Al+Clear, Poultry Litter Treatment, Poultry Guard) on poultry litter to an untreated control litter and to specifically correlate uric acid and urea contents of these litters to the microbes responsible for their mineralization. Although all three acidifiers eventually produced similar effects within the litter, there was at least a 2-wk delay in the microbiological responses using Poultry Litter Treatment. Acidification of the poultry litter resulted in >3 log increases in total fungal concentrations, with both uricolytic (uric acid degrading) and ureolytic (urea degrading) fungi increasing by >2 logs within the first 2 to 4 wk of the incubation. Conversely, total, uricolytic, and ureolytic bacterial populations all significantly declined during this same time period. While uric acid and urea mineralization occurred within the first 2 wk in the untreated control litter, acidification resulted in delayed mineralization events for both uric acid and urea (2 and 4 wk delay, respectively) once fungal cell concentrations exceeded a threshold level. Therefore, fungi, and especially uricolytic fungi, appear to have a vital role in the mineralization of organic N in low-pH, high-N environments, and the activity of these fungi should be considered in best management practices to reduce ammonia volatilization from acidified poultry litter.

Municipal Biosolids as an Alternative Nutrient Source for Bioenergy Crops: II. Decomposition and Organic Nitrogen Mineralization

High‐yielding biomass crops remove significant quantities of soil nutrients, and nutrient replacement using inorganic fertilizers may not be sustainable. Municipal biosolids (MBS) are an alternative nutrient source. Organic N is the primary N form in MBS, and patterns of N mineralization can determine the effectiveness of MBS as an N source. The objectives of this experiment were to: (i) determine the effect of season of application on organic N mineralization rate and dry matter (DM) decomposition of Class A MBS measured in the field with litter bags and (ii) compare N mineralization measured using a field‐based technique with that predicted from the DECOMPOSITION model. Treatments were season of MBS application (spring and summer) during 2 yr. Organic N mineralization measured using litter bags followed the same pattern and arrived at a similar endpoint as predicted by the DECOMPOSITION model in three of four seasons. Lower spring temperatures and rainfall were associated with lower rates of N mineralization and DM decomposition during the 50 d following spring vs. summer application of MBS. When MBS were applied in summer, organic N mineralization leveled off approximately 50 d after application compared with 150 to 250 d following spring application. Seasonal weather conditions and N mineralization patterns should be considered when determining whether to apply MBS as the source of N, the timing of MBS application, and if single or split applications are best.

Pack rats ( Neotoma spp.): Keystone ecological engineers?

The potential role of two species of pack rats ( Neotoma albigula and Neotoma micropus) as keystone ecological engineers was examined by estimating the species diversity of invertebrates living in the nest middens, and nitrogen mineralization rates in soils associated with the middens. Although pack-rat middens in tarbush ( Flourensia cernua) shrublands were smaller than those in creostebush ( Larrea tridentata) shrublands, they housed a higher abundance and diversity of arthropods. The Neotoma spp. middens were an important microhabitat for crickets ( Gryllus sp.), wolf spiders ( Lycosa spp.), and lycid beetle larvae (Lycidae) in all of the shrub habitats. There were five arthropod taxa that occupied all middens in the creosote-bush shrubland, and 12 arthropod taxa that occupied all middens in the tarbush shrubland. Soils associated with pack-rat middens had significantly higher soil organic-matter content than reference soils. Nitrogen mineralization was significantly higher in soils associated with pack-rat middens than in reference soils. Neotoma spp. create habitats with moderate microclimates that are essential for several invertebrates, thus contributing to maintenance of biodiversity. The effects of middens on soil organic matter and nitrogen mineralization create nutrient-rich patches. Neotoma spp. affect biodiversity and critical ecosystem processes, thus supporting the designation of keystone ecological engineers.

The Effects of Varying Salinity on Ammonium Exchange in Estuarine Sediments of the Parker River, Massachusetts

We examined the effects of seasonal salinity changes on sediment ammonium (NH4+) adsorption and exchange across the sediment–water interface in the Parker River Estuary, by means of seasonal field sampling, laboratory adsorption experiments, and modeling. The fraction of dissolved NH4+ relative to adsorbed NH4+ in oligohaline sediments rose significantly with increased pore water salinity over the season. Laboratory experiments demonstrated that small (∼3) increases in salinity from freshwater conditions had the greatest effect on NH4+ adsorption by reducing the exchangeable pool from 69% to 14% of the total NH4+ in the upper estuary sediments that experience large (0–20) seasonal salinity shifts. NH4+ dynamics did not appear to be significantly affected by salinity in sediments of the lower estuary where salinities under 10 were not measured. We further assessed the importance of salinity-mediated desorption by constructing a simple mechanistic numerical model for pore water chloride and NH4+ diffusion for sediments of the upper estuary. The model predicted pore water salinity and NH4+ profiles that fit measured profiles very well and described a seasonal pattern of NH4+ flux from the sediment that was significantly affected by salinity. The model demonstrated that changes in salinity on several timescales (tidally, seasonally, and annually) can significantly alter the magnitude and timing of NH4+ release from the sediments. Salinity-mediated desorption and fluxes of NH4+ from sediments in the upper estuary can be of similar magnitude to rates of organic nitrogen mineralization and may therefore be important in supporting estuarine productivity when watershed inputs of N are low.

No-till banana planting on crop residue mulch: effect on soil quality and crop functioning

Introduction. Aux Antilles francaises, les planteurs considerent generalement qu'il est necessaire d'effectuer periodiquement un travail du sol pour regenerer la porosite du sol et maintenir un fort rendement. Cependant, dans les bananeraies perennes d'altitude, le sol qui n'est jamais travaille presente de meilleures proprietes physiques et biologiques que dans bananeraies conduites de maniere conventionnelle. Pour determiner si le travail du sol avant la plantation est necessaire au bon fonctionnement d'une culture de bananiers et pour evaluer l'effet du labour sur la qualite du sol, une plantation de bananiers apres travail du sol classique a ete comparee a la plantation directe de bananiers sur un paillis de residus de recolte en parcelle experimentale. Materiel et methodes. La qualite du sol a ete evaluee par des indicateurs tels que la porosite, le statut organique, la biomasse microbienne et la structure des populations de nematodes. Le fonctionnement de la culture a ete evalue par la croissance de la plante, la distribution des racines, et la disponibilite de l'eau et de l'azote du sol. Resultats. Nous avons constate que le travail du sol a reduit la biomasse microbienne du sol et le nombre de guildes fonctionnelles de nematodes. Le travail du sol a eu seulement un effet a court terme sur la porosite du sol et n'a pas permis un enracinement plus profond. Bien que la mineralisation de l'azote organique du sol ait ete plus elevee avec le travail du sol conventionnel, la nutrition en azote des bananiers n'a pas ete meilleure, probablement parce que la fertilisation azotee elevee a compense les variations de la disponibilite de l'azote d'origine organique. Nous avons constate que la croissance des bananiers etait meilleure dans le traitement sans travail du sol. Cela a pu etre explique par un plus faible dessechement du sol du au paillis de residus de recolte laisse sur la surface du sol pour le traitement sans travail du sol. Conclusion. Par rapport au travail du sol classique, une plantation sans labour a ameliore la qualite du sol et les performances de la culture.

Photocatalytic degradation of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution using UV/TiO 2 and UV/H 2O 2/TiO 2 photocatalysis

Degradation of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution by TiO 2 photocatalysis under UVA (365 nm) irradiation was studied. Enhancement of photocatalysis by addition of H 2O 2 was also evaluated. The results showed that no significant degradation occurred by 300-min UVA irradiation per se and pH had a great effect on antibiotic degradation. Photocatalytic reactions approximately followed a pseudo-first order kinetics and the rate constants ( k) were 0.007, 0.003 and 0.029 min − 1 for amoxicillin, ampicillin and cloxacillin, respectively. Addition of H 2O 2 at ambient pH ∼ 5 and TiO 2 1.0 g/L resulted in complete degradation of amoxicillin, ampicillin and cloxacillin in 30 min. Dissolved organic carbon (DOC) removal, and nitrate (NO 3 −), ammonia (NH 3) and sulphate (SO 4 2−) formation during degradation indicated mineralization of organic carbon, nitrogen and sulphur. UV/H 2O 2/TiO 2 photocatalysis is effective for degradation of amoxicillin, ampicillin and cloxacillin in aqueous solution.

In situEvaluation of Net Nitrification Rate inTerra RossaSoil Using a Fourier Transform Infrared Attenuated Total Reflection15N Tracing Technique

Nitrification and mineralization of organic nitrogen (N) are important N transformation processes in soil, and mass spectrometry is a suitable technique for tracing changes of (15)N isotopic species of mineral N and estimating the rates of these processes. However, mass spectrometric methods for tracing N dynamics are costly, time consuming, and require long and laborious preparation procedures. This study investigates mid-infrared attenuated total reflection (ATR) spectroscopy as an alternative method for detecting changes in (14)NO(3)-N and (15)NO(3)-N concentrations. There is a significant shift of the nu(3) absorption band of nitrate according to N species, namely from the 1275 to 1460 cm(-1) region for (14)NO(3)(-) to the 1240-1425 cm(-1) region for (15)NO(3). This shift makes it possible to quantify the N isotopes using multivariate calibration methods. Partial least squares regression (PLSR) models with five factors yielded a determination error of 6.7-9.2 mg N L(-1) for aqueous solutions and 5.9-7.8 mg N kg(-1) (dry soil) for pastes of a Terra rossa soil. These PLSR models were used to monitor the changes of (15)NO(3)-N and (14)NO(3)-N content in the same Terra rossa soil during an incubation experiment in which [(15)NH(4)](2)SO(4) was applied to the soil, allowing the estimation of the contributions of applied N and mineralized N to the net nitrification rate, the potential losses of the applied (15)NH(4)-N, and the net mineralization of soil organic N.

Method and timing of grassland renovation affects herbage yield, nitrate leaching, and nitrous oxide emission in intensively managed grasslands

Managed grasslands are occasionally ploughed up and reseeded in order to maintain or increase the sward productivity. It has been reported that this renovation of grassland is associated with a flush of soil organic nitrogen (N) mineralization and with a temporary increase in soil mineral N contents. Here, we report on the effects of method and time of grassland renovation on herbage yield, nitrate (NO3−) leaching and nitrous oxide (N2O) emission. Field experiments were carried out at three sites (two sandy soils and a clay soil) in the Netherlands for three years. Renovation of grassland increased the percentage of Perennial ryegrass from 48–70% up to more than 90%. However, averaged over three years, dry matter yields were higher for the reference (not reseeded) swards (on average 13.6 Mg ha−1 for the highest N application rate) than for the renovated grasslands (12.2–13.1 Mg ha−1 dry matter). Grassland renovation in April did not increase N leaching in comparison to the reference. However, renovation in September increased the risk of leaching, because mineral N contents in the 0–90 cm were in November on average 46–77 kg N ha−1 higher than in the reference. Contents of dissolved organic N (DON) in the soil were not affected by renovation. Renovation increased N2O emissions by a factor of 1.8–3.0 relative to the reference grassland. Emissions of N2O were on average higher after renovation in April (8.2 kg N2O-N ha−1) than in September (5.8 kg N2O-N ha−1). Renovation without ploughing (i.e. only chemically destruction of the sward) resulted in a lower percentage of perennial ryegrass (60–84%) than with ploughing (>90%). Moreover, N2O emissions were higher after renovation without ploughing than with ploughing. Clearly, farmers need better recommendations and tools for determining when grassland renovation has beneficial agronomic effects. Losses of N via leaching and N2O emission after renovation can probably not be avoided, but renovation in spring in stead of autumn in combination with ploughing and proper timing of fertilizer application can minimize N losses.

Degradation of the antibiotics amoxicillin, ampicillin and cloxacillin in aqueous solution by the photo-Fenton process

The study examined degradation of the antibiotics amoxicillin, ampicillin and cloxacillin in aqueous solution by the photo-Fenton process. The optimum operating conditions for treatment of an aqueous solution containing 104, 105 and 103 mg/L amoxicillin, ampicillin, and cloxacillin, respectively was observed to be H 2O 2/COD molar ratio 1.5, H 2O 2/Fe 2+ molar ratio 20 and pH 3. Under optimum operating conditions, complete degradation of amoxicillin, ampicillin and cloxacillin occurred in 2 min. Biodegradability (BOD 5/COD ratio) improved from ∼ 0 to 0.4, and COD and DOC degradation were 80.8 and 58.4%, respectively in 50 min. Photo-Fenton treatment resulted in the release and mineralization of organic carbon and nitrogen in the antibiotic molecule. Increase in ammonia and nitrate concentration, and DOC degradation were observed as a result of organic carbon and nitrogen mineralization. DOC degradation increased to 58.4% and ammonia increased from 8 to 13.5 mg/L, and nitrate increased from 0.3 to 14.2 mg/L in 50 min.

Carbon-to-nitrogen ratio is a poor predictor of low molecular weight organic nitrogen mineralization in soil

Carbon-to-nitrogen ratio (C:N) has frequently been shown to be a good predictor of the speed of organic residue decomposition and N mineralization in soil. While this relationship appears to work well for complex organic materials (e.g. plant litter), its applicability to smaller organic substrates containing N remains unknown. Here we evaluated whether the intrinsic properties of amino acids and peptides could be used to predict their rate of microbial uptake and subsequent N mineralization. In an agricultural grassland soil we found that C:N, molecular weight, aromaticity and sulphur content provided poor indicators of amino acid bioavailabilityand subsequent NH 4 + release into soil. We therefore hypothesize that the position of amino acids along microbial biosynthetic pathways together with internal demand for individual amino acids rather than their C or N content is the primary determinant of N mineralization.

Optimization of Fenton process for treatment of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution

The study examined the effect of operating conditions of the Fenton process on biodegradability improvement and mineralization of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution. In addition, degradation of amoxicillin, ampicillin and cloxacillin under optimum operating conditions were evaluated. The optimum operating conditions for an aqueous solution containing 104, 105 and 103 mg/L amoxicillin, ampicillin, and cloxacillin, respectively were observed to be COD/H 2O 2/Fe 2+ molar ratio 1:3:0.30 and pH 3. Under optimum operating conditions, complete degradation of amoxicillin, ampicillin and cloxacillin occurred in 2 min. In addition, biodegradability improved from ∼0 to 0.37 in 10 min, and COD and DOC degradation were 81.4% and 54.3%, respectively in 60 min. Maximum biodegradability (BOD 5/COD ratio) improvement was achieved in 10, 20 and 40 min at antibiotics concentration 100, 250 and 500 mg/L, respectively for each antibiotic in aqueous solution. Increase in nitrate and ammonia concentration were observed due to mineralization of organic nitrogen, concentration of nitrate increased from 0.3 to 10 mg/L and concentration of ammonia increased from 8 to 13 mg/L in 60 min. The study indicated that Fenton process can be used for pretreatment of amoxicillin, ampicillin and cloxacillin wastewater for biological treatment.

Comparação entre modelos para predição do nitrogênio mineralizado: uma abordagem bayesiana

Neste trabalho, desenvolveu-se uma abordagem bayesiana para predizer as quantidades de nitrogênio mineralizados por intermédio de modelos não lineares. Os modelos não lineares considerados para avaliar a dinâmica da mineralização do nitrogênio e para ilustrar o procedimento bayesiano foram: modelo de Cabrera, Marion, Stanford e Smith. A comparação dos modelos foi feita por meio do Fator de Bayes (FB) e do Critério de Informação Bayesiano (BIC). A inferência sobre os parâmetros realizou-se por intermédio do Amostrador de Gibbs e do Metropolis Hastings. O modelo de Cabrera (1993) foi o que proporcionou melhor qualidade de ajuste ao conjunto de dados de mineralização de nitrogênio, sendo seguido pelo modelo de Stanford & Smith (1972) e, por último, o de Marion et al. (1981).

Effect of Alum Treatment on the Concentration of Total and Ureolytic Microorganisms in Poultry Litter

Microbial mineralization of urea and uric acid in poultry litter results in the production of ammonia, which can lead to decreased poultry performance, malodorous emissions, and loss of poultry litter value as a fertilizer. Despite the fact that this is a microbial process, little is known about how the microbial populations, especially ammonia-producing (ureolytic) organisms in poultry litter, respond to litter amendments such as aluminum sulfate (Al(2)(SO(4))(3).14H(2)O; alum). The goal of this study was to measure the temporal changes in total bacterial and fungal populations and urease-producing microorganisms in nontreated litter or litter treated with 10% alum. Quantitative real-time polymerase chain reaction was used to target the bacterial 16S rRNA gene, the fungal 18S rRNA gene, or the urease gene of bacterial and fungal ammonia producers in a poultry litter incubation study. Nontreated poultry litter had relatively high total (2.8 +/- 0.8 x 10(10) cells g(-1) litter) and ureolytic (2.8 +/- 1.3 x 10(8) cells g(-1) litter) bacterial populations. Alum treatment reduced the total bacterial population by 50% and bacterial urease producers by 90% within 4 wk. In contrast, at 16 wk after alum treatment, the fungal population was three orders of magnitude higher in alum-treated litter than in nontreated litter (3.5 +/- 0.8 x 10(7) cells g(-1) litter and 5.5 +/- 2.5 x 10(4) cells g(-1) litter, respectively). The decrease in pH produced by alum treatment is believed to inhibit bacterial populations and favor growth of fungi that may be responsible for the mineralization of organic nitrogen in alum-treated litters.

Impacts of Land Use Change on Nitrogen Cycling Archived in Semiarid Unsaturated Zone Nitrate Profiles, Southern High Plains, Texas

Nitrate (NO3) profiles in semiarid unsaturated zones archive land use change (LUC) impacts on nitrogen (N) cycling with implications for agricultural N management and groundwater quality. This study quantified LUC impacts on NO3 inventories and fluxes by measuring NO3 profiles beneath natural and rainfed (nonirrigated) agricultural ecosystems in the southern High Plains (SHP). Inventories of NO3-N under natural ecosystems in the SHP normalized by profile depth are extremely low (2-10 kg NO3-N/ha/m), in contrast to those in many semiarid regions in the southwestern U.S. Many profiles beneath cropland (9 of 19 profiles) have inventories at depth that range from 28-580 kg NO3--N/ha/m (median 135 kg/ha/m) that correspond to initial cultivation, dated using soil water Cl. These inventories represent 74% (median) of the total inventories in these profiles. This NO3 most likely originated from cultivation causing mineralization and nitrification of soil organic nitrogen (SON) in old soil water (precultivation) and is attributed to enhanced microbial activity caused by increased soil wetness beneath cropland (median matric potential -42 m) relative to that beneath natural ecosystems (median -211 m). The SON source is supported by isotopes of NO3 (delta15N: +5.3 to +11.6; delta18O: +3.6 to +12.1). Limited data in South Australia suggest similar processes beneath cropland. Mobilization of the total inventories in these profiles caused by increased drainage/ recharge related to cultivation in the SHP could increase current NO3-N levels in the underlying Ogallala aquifer by an additional 2-26 mg/L (median 17 mg/L).

Soil organic matter and microbial community structure in set-aside and intensively managed arable soils in NE-Saxony, Germany

The effects of set-aside and intensive management of agricultural soils on soil organic carbon (SOC) and nitrogen (N) mineralisation rates (gross and net rates), microbial biomass (chloroform-fumigation extraction method) and microbial community structure (phospholipid fatty acid analysis, PLFA) were assessed during one growing season (June and September). A former arable soil which has been set-aside as fallow with natural succession vegetation (“fallow land”) was compared to a soil under intensive agricultural management (“intensive”) with site conditions typical of NE-Saxony, Germany. The soil type was a sandy Cambisol. Six years of intensive agricultural management significantly decreased SOC and TN contents as well as pH and increased NO 3-N contents in the topsoil (0–10 cm) compared to fallow soil. As indicated by higher gross N mineralisation rates, the potential to deliver N increased during the fallow period. However, the substrate use efficiency of microorganisms and the turnover of the microbial biomass were higher in the intensively managed soil. Independent of management system SOC mineralisation, net N mineralisation, gross NH 4 consumption and gross NO 3 transformation rates increased with increasing water content from June to September. Principal component analysis of PLFA data indicated differences in the microbial community composition between the sites. However, in total the soil microbial community was more stable against land-use changes than against seasonal changes. The PLFA profiles of both sites changed into the same direction from June to September. Only the relative abundances of PLFA marker characteristic of Gram − bacteria and fungi showed a site × time interaction as did the MBC/MBN ratio and the MBN content. In total, the influence of land-use on most examined parameters of the sandy Cambisol was less pronounced than seasonal changes. Therefore, set-aside and taking set-aside land back into intensive agricultural production seem to be a reasonable management practice for sites on sandy Cambisols in NE-Saxony, Germany.

Nitrogen Mineralization in Soils Treated with Fly Ash–Amended Wastewater Sludges

Alkaline‐treated wastewater sludges with varying doses of fly ash were added to a clay soil at rates equivalent to 100 t (dry weight) raw sludge ha−1 soil, and the variations in ammonium, nitrate, and total nitrogen contents were monitored throughout an incubation period of 360 days at 28°C. The results showed that inhibition of organic nitrogen mineralization occurred in soil amended with fly ash–containing sludge during the first 90 days of incubation. After the total incubation period of 360 days, the inhibition effects of alkaline sludge amendments totally disappeared. In fact, mineralization was enhanced in alkaline pasteurized sludges containing 80% and 120% fly ash. The overall results indicated that application of sludges amended with fly ash may prolong the use (3 to 6 months) of nitrogen from the organic nitrogen pool in sludge.

The Effects of Soil Pollution Originated from Irrigation on Nitrogen Mineralization in Sludge Amended Soils

In this research, three wastewater sludges which were different in origin were amended to soil samples taken from Bursa-Ozluce region at rates equivalent to 100t/ha and an incubation study was performed during a period of 12 months. Soil samples which have similar physical properties were taken from two agricultural lands: nonirrigated and irrigated from polluted Nilufer-Ayvalý stream. Total and anorganic nitrogen forms and nitrogen mineralization ratios in sludge amended soils were compared and probable differences which might occur due to irrigation were studied. The results of the study indicated that wastewater sludge amendments apparently increased the total nitrogen contents of both soil samples. The nitrogen mineralization occurred during the first three months were significantly differentiated with respect to the origin of wastewater sludge (p<0.05). At the end of the total incubation period, 48- 66% of the sludge organic nitrogen was mineralized in all amended pots. When the results of the study were evaluated with respect to irrigated and nonirrigated soil samples, it was determined that the nitrate nitrogen concentrations in nonirrigated soils were significantly higher than those in irrigated soils for all sludge amendments (p<0.001). The calculated percentages of organic nitrogen mineralization at the end of 12 months in irrigated and polluted soils (average 54%) were significantly (p<0.05) different from calculated values in nonirrigated soils (average 64%) for all sludge amendments.

Effects of Soil Texture, Carbon Input Rates, and Litter Quality on Free Organic Matter and Nitrogen Mineralization in Chilean Rain Forest and Agricultural Soils

Nitrogen (N) mineralization in soil depends on carbon (C) input of plant materials, site environmental conditions, and soil texture. Empirical correlates of N mineralization can be difficult to interpret, however, because of interactions among these factors. A multiple regression model relating N mineralization to C input rates, litter quality, and soil texture in Chilean temperate rain forest soils was developed. Nitrogen mineralization rates ranged from 3.0 to 5.7 mg kg−1 soil d−1 depending on C input rate and soil texture but were not influenced by litter quality. We compared C storage of both forest and long‐term‐cropped soils with the protective capacity (i.e., the expected maximum C pool associated with the clay and silt fractions). Soil organic C associated with the fine fraction of forest soils was significantly greater than the calculated protective capacity, with clay‐rich soils averaging 141% more C than this limit and coarser soils having 56% more than predicted. In contrast, C content of cropped soils was well below the calculated protective capacity, averaging ∼32–60% less than this limit, showing the potential of these soils for sequestering C. The results were consistent with the finding that N mineralization was positively correlated with the amount of free organic matter associated with the sand‐size fraction in forest soils. The study illustrates that (i) the capacity of soils to preserve soil organic C in clay‐ and silt‐sized particles was greater than that of agricultural soils and (ii) in highly saturated soils, the N mineralization is a function of the quantity of organic‐matter input, which in turn accumulates as free organic C in the sand‐size fraction.

Transformation and mineralization of soil organic nitrogen by the humivorous larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

We studied transformation and mineralization of nitrogenous soil polymers by the humivorous larva of the scarabaeid beetle Pachnoda ephippiata, using 14C-labeled peptides, peptidoglycan, and chitin, both native and stabilized by co-polymerization with synthetic humic acids. The results indicated that these materials were solubilized mainly in the alkaline midgut. The solubilization rate of peptides to TCA-soluble products was higher than those of peptidoglycan and chitin. Solubilization rates were lower when the polymers were stabilized in humic acids. Incubation of soil with midgut fluid released amino acids, which explains the high in vivo concentrations of amino acids observed in the midgut fluid. The large amounts of \( {\text{NH}}^{ + }_{4} \) in the fresh fecal pellets indicated that at least 1.7% of the total nitrogen (7% of the acid-hydrolyzable peptides) in the ingested soil was mineralized during gut passage; also the amount of soluble protein and the solubility of humic substances increased. The combined evidence supports the hypothesis that not only microbial biomass but also the nitrogen-rich components of humus are important dietary components for humivorous insects, and that feeding activities of soil macroinvertebrates strongly impact transformation and mineralization of soil organic matter.

Long-term effects of continuous direct seeding mulch-based cropping systems on soil nitrogen supply in the Cerrado region of Brazil

In the Cerrado region of Brazil conventional soybean monoculture is since the 1980s being replaced by direct seeding mulch-based cropping (DMC) with two crops per year and absence of tillage practices. The objective of this study was to assess the long-term impact of DMC on soil organic matter accumulation and nitrogen (N) mineralization. Measurements of soil organic carbon (C) content, soil total N content and soil N mineralization, both under laboratory conditions using disturbed soil samples and under field conditions using intact soil cores were conducted on a chronosequence of 2-, 6-, 9- and 14-year-old DMC fields (DMC-2, DMC-6, DMC-9 and DMC-14, respectively). The average increase of organic C in the 0–30 cm topsoil layer under DMC was 1.91 Mg C ha−1 year−1. Soil total N increased with 103 kg N ha−1 year−1 (0–30 cm). The potential N mineralization rate under laboratory conditions (28°C, 75% of soil moisture at field capacity) was 0.27, 0.28, 0.39 and 0.36 mg N kg soil−1 day−1 for, respectively, the DMC-2, DMC-6, DMC-9 and DMC-14 soils. The corresponding specific N mineralization rates were 0.16, 0.15, 0.22 and 0.17 mg N g N−1 day−1. There was no obvious explanation for the higher specific N mineralization rate of soils under DMC-9, given the similar soil conditions and land-use history before DMC was introduced. Results from the in situ N incubation experiments were in good agreement with those from the laboratory incubations. We estimated that soil N mineralization increases with about 2.0 kg N ha−1 year−1 under DMC. The increase was mainly attributed to the larger soil total N content. These results indicate that even in the medium term (10 years), continuous DMC cropping has limited implications for N fertilization recommendations, since the extra soil N supply represents less than 20% of the common N fertilization dose for maize in the region.