Immobilization Of Soil Nitrogen Research Articles

Manipulating soil resource availability to alter microbial communities for weed management in agroecosystems

The growing resistance of weeds to herbicides demands innovative strategies that harness soil biology for effective weed control. We examined the use of carbon amendments to stimulate microbial immobilization of soil nitrogen for weed control. We hypothesized that increased carbon availability will stimulate soil microbial growth, leading to greater nitrogen immobilization, which consequently decreases plant-available nitrogen and suppresses the growth of nitrogen-responsive weed species. We buried 80 19-L pots in a research farm field and added sawdust and sucrose to soils as a high carbon treatment and used unamended soils as a control. We examined eight different weed species separately, and measured plant growth, soil carbon, available nitrate, microbial carbon and nitrogen, and microbial community composition after 11 weeks of treatment. The carbon amendments altered plant-microbial competition for nitrogen, resulting in reduced biomass for most weed species. The carbon-amended soils had higher microbial biomass carbon and nitrogen, slower nitrogen cycling, and less available soil nitrogen, indicating enhanced nitrogen immobilization. The carbon treatment altered the beta diversity of soil fungi and bacteria and reduced fungal alpha diversity estimated by the Shannon index. The study results indicate that high carbon substrates can be used to modify plant-microbial competition for soil nitrogen with important implications for developing sustainable weed management practices.

Drive soil nitrogen transformation and improve crop nitrogen absorption and utilization - a review of green manure applications.

Green manure application presents a valuable strategy for enhancing soil fertility and promoting ecological sustainability. By leveraging green manures for effective nitrogen management in agricultural fields can significantly reduce the dependency of primary crops on chemical nitrogen fertilizers, thereby fostering resource efficiency. This review examines the current advancements in the green manure industry, focusing on the modulation of nitrogen transformation in soil and how crops absorb and utilize nitrogen after green manure application. Initially, the influence of green manure on soil nitrogen transformation is delineated, covering processes such as soil nitrogen immobilization, and mineralization, and losses including NH3, N2O, and NO3 --N leaching. The review then delves into the effects of green manure on the composition and function of soil microbial communities, highlighting their role in nitrogen transformation. It emphasizes the available nitrogen content in the soil, this article discussing nitrogen uptake and utilization by plants, including aspects such as nitrogen translocation, distribution, the root system, and the rhizosphere environment of primary crops. This provides insights into the mechanisms that enhance nitrogen uptake and utilization when green manures are reintroduced into fields. Finally, the review anticipates future research directions in modulating soil nitrogen dynamics and crop nitrogen uptake through green manure application, aiming to advance research and the development of the green manure sector.

Vital roles of soil microbes in driving terrestrial nitrogen immobilization.

Nitrogen immobilization usually leads to nitrogen retention in soil and, thus, influences soil nitrogen supply for plant growth. Understanding soil nitrogen immobilization is important for predicting soil nitrogen cycling under anthropogenic activities and climate changes. However, the global patterns and drivers of soil nitrogen immobilization remain unclear. We synthesized 1350 observations of gross soil nitrogen immobilization rate (NIR) from 97 articles to identify patterns and drivers of NIR. The global mean NIR was 8.77±1.01mgNkg-1 soilday-1 . It was 5.55±0.41mgNkg-1 soil day-1 in croplands, 15.74±3.02mgNkg-1 soilday-1 in wetlands, and 15.26±2.98mgNkg-1 soilday-1 in forests. The NIR increased with mean annual temperature, precipitation, soil moisture, soil organic carbon, total nitrogen, dissolved organic nitrogen, ammonium, nitrate, phosphorus, and microbial biomass carbon. But it decreased with soil pH. The results of structural equation models showed that soil microbial biomass carbon was a pivotal driver of NIR, because temperature, total soil nitrogen, and soil pH mostly indirectly influenced NIR via changing soil microbial biomass. Moreover, microbial biomass carbon accounted for most of the variations in NIR among all direct relationships. Furthermore, the efficiency of transforming the immobilized nitrogen to microbial biomass nitrogen was lower in croplands than in natural ecosystems (i.e., forests, grasslands, and wetlands). These findings suggested that soil nitrogen retention may decrease under the land use change from forests or wetlands to croplands, but NIR was expected to increase due to increased microbial biomass under global warming. The identified patterns and drivers of soil nitrogen immobilization in this study are crucial to project the changes in soil nitrogen retention.

Organic-C quality as a key driver of microbial nitrogen immobilization in soil: A meta-analysis

Microbial nitrogen (N) immobilization in soil can be enhanced by increasing carbon (C) bioavailability, yet the response of microbial N immobilization to the addition of organic matter is uncertain. In the present study, we investigated the effect of organic matter quality on microbial N immobilization. The response ratio (ln R), i.e., the ratio of microbial N immobilization in organic-C amended soil to that in control treatments, was calculated using data from 51 published studies. Overall, the addition of organic-C increased significantly microbial N immobilization by 105% relative to unamended soil. The type of organic-C affected the response of microbial N immobilization to organic-C addition. Glucose (classified as a labile compound) was more effective in stimulating microbial N immobilization than cellobiose and cellulose (classified as intermediately decomposable compounds). Tannin and oxalic acid (classified as recalcitrant compounds) did not significantly affect microbial N immobilization. The C/N ratio of organic materials did not affect the response of microbial N immobilization in the short-term (≤280 d); differences in the effect size (ln R+) were not significant among different C/N ratio groups. The effect of the form of inorganic-N (ammonium [NH4+] or nitrate [NO3−]) on the response of microbial N immobilization to organic-C addition was not significant, with a mean ln R+ of 0.838 (confidence interval [CI]: 0.590–1.099) for NH4+ and 1.642 (CI: 0.951–2.452) for NO3−. Moreover, the ln R of microbial NH4+ immobilization showed a significant positive relationship (P < 0.01) with that of microbial NO3− immobilization. The ln R+ for the experimental period decreased in the order of <30 d, 60–120 d, ≥120 d, and 30–60 d. The chemical quality of organic-C defined by three C pools (i.e., labile, intermediate, and recalcitrant) rather than the C/N ratio is a critical factor regulating the response of microbial N immobilization to organic-C addition.

Biotic and abiotic nitrogen immobilization in soil incorporated with crop residue

Incorporating crop residue favors biotic and abiotic nitrogen (N) immobilization, which can effectively conserve active N in soil. Here we summarize the occurrence characteristics of biotic and abiotic N immobilization and affecting factors, and then identify a general pattern of the relative importance of the two processes in soil incorporated with crop residue. When microorganisms decompose crop residue for a source of energy and carbon (C) to support their metabolism, they need N to build cellular components, resulting in N immobilization in biomass. Alternatively, N can be incorporated into soil organic matter (SOM) through the following known mechanisms: ammonium (NH4+) fixation by clay minerals, condensation of ammonia (NH3) with phenol or quinone rings, and nitrosation of nitrite (NO2-) with phenolic compounds. The biotic and abiotic contribution to N immobilization is significantly controlled by soil properties and crop residual quality. When a large fraction of C is in the form of labile organic compounds, biotic N immobilization may be important. In contrast, high fraction of lignin-derived phenolic compounds or other recalcitrant organic compounds facilitates abiotic N immobilization. In the N-limited soil, the increase in N availability contributes to microbial activity, which would stimulate biotic processes. However, when microbial metabolism switches from N-limited to C-limited due to the increase in N availability, abiotic processes become important. Abiotic processes even predominate over biotic processes under N-enriched conditions. The relative roles of biotic or abiotic N immobilization in soil incorporated with crop residue are dependent on the availability of C relative to N and soil N availability. Carbon and N availability in turn is related to their forms. Moreover, N availability is affected by soil pH. The mechanisms by which N is immobilized determine the fate of immobilized N and are of vital importance for the management of N availability and losses through combining N fertilizer with crop residue. More investigation is necessary to quantify the contribution of biotic and abiotic processes during the decomposition of crop residue and to determine the factors affecting N immobilization in the field.

The Influence of Organic Amendment Source on Carbon and Nitrogen Mineralization in Different Soils

Soil organic matter is one of the largest stores of carbon and nitrogen in various ecosystems that can crucially improve plant nutrition. The present study was conducted to investigate the effect of organic matter sources on carbon and nitrogen mineralization and also the contemporary comparison of carbon and nitrogen mineralization and nitrogen immobilization in soils amended with different organic treatments. Accordingly, six types of organic amendments were applied to three types of soils, under a constant temperature and moisture at the laboratory scale. The treated soils were incubated 60 and 120 days for nitrogen and carbon mineralization study, respectively. Results showed two decomposition stages, an initial rapid increase in decomposition in the first 20 days followed by a slower stage reaching a steady state condition. The amount of mineralized carbon ranged from 980 to 6860 mg/kg of dry soil for soils incorporating with different types of organic matters. The carbon mineralization kinetic data was well fitted to a second-order kinetic model showing the differences in microbial decomposition resistance of residues contents. The kinetic of carbon and nitrogen mineralization fluctuated similarly but in different scales. Net ammonification of fertilizer group, sheep manure, cow manure, and vermicompost was decreased, whereas in plant residue group, plane tree leaves, corn leaves, and wheat straw was increased. Two nitrification periods (first 10 days and 35 to 60 days) and an immobilization period (10 to 35 days) were observed. After 60 days of incubation of amended clayey soil, the nitrification values in plane tree leaves, corn leaves, wheat straw, municipal waste vermicompost, cow manure, and sheep manure were − 13.98, 14.06, 13.22, 34.88, − 12.25, and − 12.15 mg kg−1, respectively. The carbon and nitrogen mineralization trends fluctuated due to probably different resistance of substance components to microbial decomposition. Since the nitrate is the main part of inorganic N, therefore, net N mineralization had a similar trend as nitrification in different soils. Those organic residues with high ratios of C/N immobilized the mineral nitrogen, due to the presence of more carbon and a higher nitrogen decomposition rate, resulting in suppressed levels of nitrogen in the amended soil.

Rolled Winter Rye–Hairy Vetch Cover Crops for Weed Control in No-till Pumpkin

AbstractWeed control is a challenging aspect of pumpkin production. Winter rye mulches may offer growers a means to manage weeds in pumpkin; however, rye degradation leads to an immobilization of soil nitrogen. Combining winter rye with a nitrogen fixing legume such as hairy vetch is an interesting option that may solve this problem. Twelve combinations including three hairy vetch seeding rates, two termination dates and the use or not of glyphosate before rolling cover crops were studied during the 2013 and 2014 growing seasons at the Laval University Agronomic Station in Saint-Augustin-de-Desmaures, Quebec, Canada to evaluate weed control and effects on pumpkin production. Adding hairy vetch to winter rye provided no benefits because of severe winterkill of the legume. Using glyphosate was necessary to prevent rye regrowth. Pumpkin growth was better and yields were higher than in the plots were no glyphosate was used. Mulches established at flowering (Zadoks 69) provided about 2,000 kg ha−1 more aboveground dry biomass than at early heading (Zadoks 51). This high biomass was essential in glyphosate treated plots in order to maintain excellent weed control throughout the growing season. When compared with the no-mulch weed-free control, yield in Zadoks 69+glyphosate treatment was lower in 2013 but comparable in 2014.

Establishing the relationship of soil nitrogen immobilization to cereal rye residues in a mulched system

Background and aimsSoil nitrogen (N) immobilization from cover crop residues may help suppress weeds. We established a gradient of cereal rye shoot biomass to determine the extent that soil N can be immobilized and its effect on redroot pigweed (Amaranthus retroflexus L.).MethodsA microplot study was conducted in no-till cereal rye (Secale cereale L.)—soybean (Glycine max L. (Merr.)) systems at two sites in eastern USA. Microplots received 0, 2000, 5000, 8000, 12,000 or 15,000 kg ha−1 of cereal rye shoot biomass, and were injected with two mg 15N kg−1 soil 5 cm below the soil surface. Pigweeds were sown and allowed to germinate.ResultsMaximum rates of cereal rye shoot decomposition were observed at ≥5000 kg ha−1. Although cereal rye shoot N declined, shoots became enriched with 15N, indicating fungal transfer of soil N to shoots. Soil inorganic N declined by an average of 5 kg N ha−1. Pigweed tissue N and biomass were reduced in the presence of cereal rye. The magnitude of pigweed N reduction was similar across all shoot application rates.ConclusionsWe found weak evidence for a cereal rye shoot-based N immobilization mechanism of weed suppression. Our results indicate N immobilization may be primarily due to root residues.

Biochemical characteristics of cover crop litter affect the soil food web, organic matter decomposition, and regulation of plant-parasitic nematodes in a banana field soil

Suppression of plant-parasitic nematodes and decomposition of organic matter are important soil food web functions. The availability and nature of carbon substrates in soil drive the structure, dynamics, and activities of soil food webs and may alter the way they function in the ecosystem. In this study, we assessed the effects on nematode communities of incorporating litter from three cover crops with contrasting biochemical characteristics into soil taken from a banana field. The litter type influenced nematode taxa and functional guilds during the 90-day assay. The cellulose- and hemicellulose-rich litters of Crotalaria zanzibarica and Paspalum notatum induced similar nematode successions, causing bacterivorous and fungivorous nematode populations to increase early in the study period and promoting a fungal decomposition pathway at the end of the trial. These two litters were the most effective at decreasing the soil’s nematode infective potential with regard to major banana plant-parasitic nematodes, such as Pratylenchus coffeae, Helicotylenchus multicinctus, and Rotylenchulus reniformis. C. zanzibarica showed good potential as a green manure plant, as it increased the soil mineral nitrogen content during the 45 days following incorporation of litter. By contrast, litter from Acacia auriculiformis, which had high lignin content, induced immobilization of soil nitrogen and did not significantly increase microbivorous nematodes before day 45. This treatment failed to reduce the soil’s nematode infective potential for H. multicinctus and R. reniformis populations. Our study also showed that the dynamics of nitrogen mineralisation in soil were related to the C:N ratio of litters but not to the decomposition pathway. The biochemical characteristics of litters appear to be critical drivers of nematode ecological successions and decomposition pathways following plant litter amendments to soil taken from a banana field.

Long‐term outcome of nitrogen immobilization to restore endemic sand grassland in Hungary

Summary Soil nitrogen immobilization by carbon amendment is a management technique used for conservation purposes to increase the competitive ability of late‐seral plant species over early‐seral species based on their different tolerance of low soil nitrogen content. We immobilized nitrogen over six growing seasons on three ex‐arable fields with poor sandy soils in the Hungarian lowland in order to restore endemic sandy grassland. Sucrose and sawdust were applied at rates based on previous laboratory experiments using local soils. We tested the efficacy of long‐term carbon amendment for lowering soil nitrogen availability and favouring late‐seral native species over early‐seral weed species. Carbon amendments resulted in significant increase in soil microbial biomass C and reduced soil nitrogen availability after 2 years. Total vegetation cover was reduced by reducing soil nitrogen availability, but total species richness was not impacted. Cover of early‐seral species decreased, and species richness and cover of late‐seral species increased irrespective of nitrogen immobilization. However, after 4–6 years reducing soil nitrogen availability hampered the spread of moss under vascular vegetation. Synthesis and applications. This study supports the efficacy of carbon amendment as a tool to immobilize available soil nitrogen in the upper soil layers. However, the desired impact on vegetation was not fully achieved despite application over several years. Nitrogen immobilization was most relevant to bryophytes, lacking deep root systems, which may explain the responsiveness of this group to N limitation. The different impact of N availability on the complex of early‐seral, late‐seral vascular species and that of the bryophyte layer provides opportunity for directing state transformations in arid grasslands. Bryophyte cover can be suppressed through carbon amendments in order to enhance the germination and establishment of grassland species. The advantage of the method is that it opens bryophyte cover gradually without disturbing the soil surface, possibly avoiding the establishment of invasive species. However, further studies are required for deeper insight.

Nitrogen, phosphorus and sulfur mineralization as affected by soil depth in rangeland ecosystems

The potential mineralization and immobilization of soil nitrogen (N), phosphorus (P) and sulfur (S) are relatively high in natural ecosystems. This study was conducted to investigate the changes in essential plant macronutrients; N, P, and S status in response to different soil depth in rangeland ecosystems in vitro. The net nutrient mineralization was measured during 90 days at different depths (0–15, 15–30, 30–45 and 45–60 cm), using kinetic models to estimate the release rate. The net ammonification and mineralization of P and S were described using parabolic diffusion equation, while the power function equation was used to describe the net nitrification. The results indicated that the amount of released ammonium (NH4+) decreased with time and depth and the rates of net ammonification were negative in all samples. Conversely, nitrification increased with time and depth and the rates were all positive. The net mineralization for both P and S reduced with time. The concentration of mineralized SO42− increased with depth like nitrate (NO3−). Accumulation of SO42− and NO3− in subsurface soils and NH4+ and P at surface horizons can increase the potential of their loss by leaching or volatilization.

雪被斑块对川西亚高山两个森林群落冬季土壤氮转化的影响

为了解气候变暖情景下雪况变化对高寒森林冬季土壤氮转化的影响，测定了川西亚高山冷杉（<em>Abies faxoniana</em>）+红桦（<em>Betula albo-sinensis</em>）混交林（MF）和冷杉次生林（SF）三类雪被斑块（浅雪被、中厚度雪被和厚雪被）内冬季土壤氮矿化特征。结果表明:经过一个冬季（2011-2012），两个森林群落土壤净氮氨化量都为负值，净氮硝化量都为正值，且净氮硝化量显著高于净氮氨化量；冬季土壤氮氨化、硝化、矿化和固持量都是中度雪被厚度最高，但各雪被斑块之间都未达到显著水平。各雪被斑块下，冷杉次生林土壤氮矿化参数都显著高于针阔混交林，但雪被斑块和林型交互作用对冬季土壤氮矿化无显著影响。这表明，该区冬季土壤氮矿化以硝化过程为主，硝化和氨化过程可能受不同微生物群落调控；短时期内，未来气候变化所导致的雪被减少对该区森林冬季土壤氮转化影响可能不明显。;A consensus in global ecology is that climate change is profoundly altering the process of terrestrial ecosystem. In particular, more and more attentions have been focused on the effects of snow pack on soil process in cold biomes recently, since climate change characterized by winter warming and extreme is changing the pattern of seasonal snow cover and freeze-thaw cycles in the high-latitude and high-altitute regions. As yet, the results concerning the effects of seasonal cover and freeze-thaw cycles on soil process remain uncertainty, and little information has been available on the effects of snow pack on soil nitrogen tansformation in the subalpine forest of western Sichuan, China. In order to deeply understand the process of soil nitrogen transformation in the subalpine forest of western Sichuan under climate change scenarios, therefore, wintertime net nitrogen mineralization, net nitrogen ammonification, net nitrogen nitrification and microbial nitrogen immobilization in soils under three depths of snowpacks (deep snowpack, middle snowpack and shallow snowpack) were measured in two subalpine forests of western Sichuan, which locates at the upper reaches of Yangtze River and the eastern Qinghai-Tibet Plateau. The top of soil columns sampled from<em> Abies faxoniana </em>+ <em>Betula albo-sinensis</em> mixed forest and secondary fir forest were closed, and then <em>in-situ</em> incubated in the forest floor under deep snowpack, middle snowpack and shallow snowpack of the corresponding forest from November 2011 to April 2012, respectively. The results indicated that wintertime soil net nitrogen ammonification ranged from -2.37mg/kg to -2.22 mg/kg under different snowpacks in the mixed forest, and from -7.73 mg/kg to -7.10 mg/kg under different snowpacks in the secondary fir forest. Wintertime soil net nitrogen nitrification varied from 71.98 mg/kg to 82.69 mg/kg under different snowpacks in the mixed forest, and from 101.56 mg/kg to 124.89 mg/kg under different snowpacks in the secondary fir forest. Net nitrogen nitrification was significantly (<em>P</em> < 0.05) higher than net nitrogen ammonification. The highest rates of soil nitrogen ammonification, nitrification, mineralization and microbial nitrogen immobilization were observed in the middle snow pack, but no significant (<em>P</em> > 0.05) differences were observed among snow packs. Meanwhile, all measured indexes in each snow pack were significantly (<em>P</em> < 0.05) higher in the secondary fir forest than those in the fir-birch mixed forest. However, the interaction of snow pack and forest type was not significant on wintertime soil nitrogen transformation. The results suggested that soil nitrogen nitrification be a major process of wintertime soil nitrogen mineralization, and the process of soil nitrogen nitrification and ammonification be regulated by different microbial communities in the subalpine forests of western Sichuan, China. The result also implies that the decline of snowpack caused by climate change, in the short-run, has little effects on soil nitrogen mineralization in our study area.

Effect of seasonal freeze–thaw cycle on net nitrogen mineralization of soil organic layer in the subalpine/alpine forests of western Sichuan, China

Nitrogen mineralization, a main way that soil organic nitrogen converts to mineral nitrogen, is one of the key processes in soil nitrogen cycle. The mineral nitrogen has an important role in plant growth in the growing season. It has been widely accepted that soil freezing in winter can kill a number of microorganisms, weakening soil nitrogen mineralization. However, more and more recent studies have documented that soil microorganisms still have high activity during the deep freezing period, and obvious nitrogen mineralization in winter. Seasonal freeze–thaw cycle is a common phenomenon in the subalpine/alpine forest region, which may have a strong effect on soil ecological processes. Furthermore, the changing pattern of seasonal freeze–thaw cycles might have a significant influence on soil nitrogen mineralization in this region in the scenarios of global warming. As yet, little attention has been given to nitrogen mineralization of soil organic layer as affected by changed seasonal freeze–thaw pattern, although the increasing studies have demonstrated that winter warming might give strong effects on the litter decomposition and microbial activity in the subalpine/alpine forest regions. Therefore, a method of intact soil core incubation in combination with natural environmental gradient was employed by transferring forest soils from 3582m (A1) of altitude to 3298m (A2) of altitude and 3023m (A3) of altitude in the subalpine/alpine forests of western Sichuan, respectively. The amounts and rates of net nitrogen mineralization in soil organic layer were measured. The incubation period included the growing season and the freeze–thaw season from May 24, 2010 to April 19, 2011. The results suggested that significant net nitrogen mineralization was only observed in soil organic layer at low altitude (A3) during the whole incubation period. Forest soils at higher altitudes (A1 and A2) showed obvious soil nitrogen immobilization. In comparison with the growing season which showed remarkable nitrogen immobilization characteristic, the freeze–thaw season showed obvious nitrogen mineralization at lower altitudes (A2 and A3). In contrast, the nitrogen immobilization amounts at high altitude (A1) in freeze–thaw period were less than those in the growing season. Besides, the maximum of net nitrogen mineralization amounts and rates at high altitude (A1) in soil organic layer mainly occurred in the late stage of growing season and the onset of freezing, soil nitrogen mineralization at the middle altitude (A2) mainly occurred in the onset of freezing and the deep freezing period, while the highest amount and rate of net nitrogen mineralization at low altitude (A3) occurred in the early stage of thawing and the late stage of growing season. Furthermore, the amount and rate of soil net nitrogen mineralization during the freeze–thaw season were increasing with the decrease of altitude, which correlated with soil freeze–thaw cycle and freezing process at different altitudes. These results indicated that increasing soil temperature in the future could not only significantly enhance soil nitrogen mineralization in the freeze–thaw season, but also improve soil nitrogen mineralization by increasing freeze–thaw cycle times and shortening freeze–thaw period. However, the processes were significantly influenced by soil micro-environment of subalpine/alpine forest regions.

Promoting microbial immobilization of soil nitrogen during restoration of abandoned agricultural fields by organic additions

Application of organic materials to soils to enhance N immobilization into microbial biomass, thereby reducing inorganic N concentrations, was studied as a management option to accelerate the reestablishment of the native vegetation on abandoned arable fields on sandy soils the Kiskunsag National Park, Hungary. Sucrose and sawdust were used at three different topographic sites over 4 years. N availability and extractable inorganic N concentrations were significantly reduced in all sites. Soil microbial biomass C and microbial biomass N increased significantly following C additions, but the microbial C to microbial N ratio remained unaffected. It is concluded that the combined application of the rapidly utilized C source (sucrose) promoted N immobilization, whereas the addition of the slowly utilized C source (sawdust) maintained the elevated microbial biomass C and microbial biomass N in the field.

Adubação orgânica da batata com esterco e, ou, Crotalaria juncea: II - disponibilidade de N, P e K no solo ao longo do ciclo de cultivo

Os solos do Agreste paraibano têm baixa fertilidade e a prática usual de adubação é a incorporação de esterco na época do plantio. Entretanto, dependendo da qualidade do esterco, essa prática pode causar a imobilização de nutrientes do solo durante os primeiros meses de cultivo. É possível que o cultivo e incorporação de Crotalaria juncea, combinado com o esterco, possa promover mineralização mais sincronizada com a demanda de nutrientes pelas plantas. No presente estudo, realizado em 2003, foram conduzidos experimentos de campo e em casa de vegetação para testar essa hipótese. As parcelas de campo foram previamente cultivadas com batata no período de 1996 a 2002 e submetidas anualmente aos seguintes tratamentos: plantio e incorporação da crotalária na época da floração (C); adição de 15 t ha-1 de esterco (E); plantio e incorporação de crotalária + 7,5 t ha-1 de esterco (CE); e testemunha, sem esterco ou crotalária (T). Em 2003, foram aplicados os mesmos tratamentos de adubação orgânica e foi avaliada a dinâmica da decomposição e liberação de nutrientes pelo material vegetal e esterco contidos em sacolas de náilon incorporadas ao solo das parcelas de campo. Também se avaliou a dinâmica da disponibilidade de N, P e K no solo das parcelas de campo, por meio de coletas periódicas de solo. No ensaio em casa de vegetação, foram realizados cultivos sucessivos de capim-buffel (Cenchrus ciliaris L.) por um período de 300 dias, utilizando-se amostras do solo das parcelas de campo. As perdas de massa e nutrientes do material incorporado ao solo foram maiores nos primeiros 30 dias da incubação, em todos os tratamentos. No final do ensaio, as proporções de matéria seca e nutrientes remanescentes foram maiores nos tratamentos E e CE que nos tratamentos C e T. No solo das parcelas de campo, o tratamento E aumentou os teores de P e K extraíveis (Mehlich-1) do solo ao longo do período do estudo, porém provocou a imobilização de N do solo nas primeiras semanas. O tratamento C aumentou o teor de N mineral do solo no período imediatamente após a incorporação, mas não aumentou o teor de P e K extraíveis. No ensaio em casa de vegetação, o capim-buffel acumulou mais biomassa aérea e nutrientes no primeiro corte, 35 dias após o transplantio do capim, no solo do tratamento CE. Nos cortes subseqüentes, o tratamento E levou à maior produção de biomassa e acumulação de nutrientes, indicando que a limitação de N no período inicial após a incorporação de esterco ao solo prejudicou o crescimento do buffel. Os resultados corroboram a hipótese de que o plantio e incorporação da crotalária, combinado com a aplicação de apenas a metade da dose usual de esterco caprino, promoveu mineralização de nutrientes mais sincronizada com as necessidades das culturas agrícolas, pois foi capaz de evitar a imobilização de N do solo no período inicial de cultivo e elevou os teores de P e K disponíveis ao longo de todo o período.

New evidence for covalent coupling of peptides to humic acids based on 2D NMR spectroscopy: A means for preservation

Nitrogen immobilization in soils and sediments involving the preservation of peptides is an important yet not well-understood process. Several hypotheses have been proposed for the preservation of peptides in these systems; however, to date, there is no direct molecular-level evidence for any one of several hypotheses. In this study, a synthesized peptide with 15N-labeled amino acid residues was utilized to examine the mechanism by which humic substances from a peat might chemically interact with peptides to induce preservation. Two-dimensional 15N- 1H HSQC NMR experiments were performed to evaluate the bonding and nonbonding interactions between 15N-labeled peptide and an Everglades peat humic acid. The observed changes in cross peaks provide the first direct spectroscopic evidence for what we believe to be covalent binding between these substances. Noncovalent interactions between the 15N-labeled peptides and humic acid molecules are also observed in the spectra. Quinone structures in humic acids are suggested to be the important reactive groups, based on reaction of the labeled peptide with a model quinone which shows similar nitrogen–proton correlated peak patterns as is observed in the HSQC NMR spectra of humic acids reacted with the peptide. The Michael reaction with quinone structures is proposed, and this type of reaction provides a mechanism that is consistent with previous observation for the chemistry of sedimentary nitrogen species.

Net nitrogen immobilization in soil induced by small additions of energy sources

This study investigated whether small additions to soil of primary paper-mill sludge, a wood fibre residue from paper production (fibre sludge), caused temporary N immobilization and thereby reduced the amount of inorganic nitrogen leached from agricultural land. This was achieved by measuring respiration and immobilization of N in incubation studies at 8°C, with fibre sludge added at rates varying from 63 to 1000 mg C kg−1 soil. Glucose added at rates of 63–250 mg C kg−1 soil was used as a reference. Respiration in soil after glucose addition followed an exponential course with the highest rates on days 2–4. During this period maximum peaks of net N immobilization were measured. Even addition of only 63 mg glucose-C kg−1 soil caused significant immobilization of N in soil. Fibre sludge additions to soil caused lower respiration activities, characterized by two initial peaks followed by somewhat higher respiration rates during the remaining incubation than for glucose. It was likely that hemicellulose, which amounted to 14% of the total C, was the initial available energy source in the sludge as concentrations of water-soluble C were very low. Addition of at least 250 mg C kg−1 soil as fibre sludge was required to cause significant N immobilization in soil corresponding to 5 kg N ha−1. Both nitrate and ammonium were immobilized. Relating maximum N immobilization data during days 2 to 10 to corresponding respiration data for glucose and fibre sludge revealed that microbes utilised similar amounts of C per unit N immobilized. On average, 175.6±74.8 mg CO2-C were respired to immobilize 1 mg N and the relationship between C respiration and N immobilization was linear (R 2=0.984). To make soil application of fibre sludge a realistic counter-measure against N leaching from agricultural soils, pre-treatment is necessary to increase the content of energy readily available to microbes.

Alterações microbianas no solo durante o ciclo do milho nos sistemas plantio direto e convencional

A disponibilidade de resíduos de aveia-preta, com relação C:N elevada, resulta em imobilização microbiana de nitrogênio no solo, exigindo cuidados no manejo da adubação nitrogenada da cultura subseqüente. O objetivo deste trabalho foi avaliar as alterações na estrutura da comunidade microbiana ao longo do ciclo do milho, na presença de resíduos de aveia-preta e da aplicação de nitrogênio. Foram coletadas amostras de um Argissolo Vermelho distrófico no dia da semeadura do milho e 46, 62, 88 e 112 dias após a semeadura. O nitrogênio foi aplicado 25 dias e 49 dias após a semeadura. As alterações na comunidade microbiana foram avaliadas mediante relações entre carbono (C) e nitrogênio (N), nitrogênio reativo com ninidrina (N-Nin) e carboidratos (CHO) da biomassa microbiana, além da análise do rDNA fúngico e bacteriano. As diferenças na composição da comunidade microbiana, reveladas pela análise do rDNA, relacionaram-se mais com as relações C:N e C:N-Nin do que com a relação C:CHO. As relações C:N-Nin e C:N e as avaliações do rDNA mostraram um predomínio inicial de população fúngica. Com a aplicação de N, a população bacteriana tornou-se preponderante e, ao final do ciclo do milho, retornou para uma condição semelhante à inicial.

The effect of diesel fuel on common vetch (Vicia sativa L.) plants.

When petroleum hydrocarbons contaminate soil, the carbon:nitrogen (C:N) ratio of the soil is altered. The added carbon stimulates microbial numbers but causes an imbalance in the C:N ratio which may result in immobilization of soil nitrogen by the microbial biomass, leaving none available for plant growth. As members of Leguminosae fix atmospheric nitrogen to produce their own nitrogen for growth, they may prove more successful at growing on petroleum hydrocarbon contaminated sites. During a wider study on phytoremediation of diesel fuel contaminated soil, particular attention was given to the performance of legumes versus other plant species. During harvesting of pot experiments containing leguminous plants, a recurring difference in the number and formation of root nodules present on control and contaminated Common vetch (Vicia sativa L.) plants was observed. The total number of nodules per plant was significant reduced in contaminated plants compared to control plants but nodules on contaminated plants were more developed than corresponding nodules on control plants. Plant performance of Common vetch and Westerwold's ryegrass (Lolium multiflorum L.) was compared to illustrate any difference between the ability of legumes and grasses to grow on diesel fuel contaminated soil. Common vetch was less affected by diesel fuel and performed better in low levels of diesel fuel contaminated soil than Westerwold's ryegrass. The total amount of diesel fuel remaining after 4 months in Common vetch planted soil was slightly less than in Westerwold's ryegrass planted soil.

Immobilization of soil nitrogen as a possible method for the restoration of sandy grassland

Abstract.Experiments were designed to test the applicability of nitrogen immobilization as a means of accelerating the recovery of an endemic open sandy grassland (Festucetum vaginatae danubiale) on old fields in the Great Hungarian Plain. Effects of various carbon sources (sucrose, starch, cellulose and sawdust) and their combinations in different quantities were studied in laboratory microcosms. Carbon addition decreased nitrogen availability in all cases, the intensity and timing of change being dependent on the type of carbon source applied. The combination of 2 g each of sucrose and polysaccharides (starch, cellulose, sawdust) per kg soil was found to be the most effective, as sucrose decreased available nitrogen content of soil intensively and the polysaccharides maintained the immobilized nitrogen for a longer period. In a follow‐up experiment, sucrose and sawdust were selected for field application to test their effectiveness in immobilizing N and accelerating restoration. The field experiment was established to test the importance of abiotic site differences in the immobilization of soil nitrogen. Selected sites were located along an elevation, moisture and productivity gradient. Soil organic matter, microbial biomass‐C and decomposition rate varied between sites depending on the elevation gradient. At two sites with lower soil moisture and organic matter levels carbon addition increased microbial activity and nitrogen immobilization significantly.