Nitrogen Mineralization Potential Research Articles

Root Parameters Show How Management Alters Resource Distribution and Soil Quality in Conventional and Low-Input Cropping Systems in Central Iowa.

Plant-soil relations may explain why low-external input (LEI) diversified cropping systems are more efficient than their conventional counterparts. This work sought to identify links between management practices, soil quality changes, and root responses in a long-term cropping systems experiment in Iowa where grain yields of 3-year and 4-year LEI rotations have matched or exceeded yield achieved by a 2-year maize (Zea mays L.) and soybean (Glycine max L.) rotation. The 2-year system was conventionally managed and chisel-ploughed, whereas the 3-year and 4-year systems received plant residues and animal manures and were periodically moldboard ploughed. We expected changes in soil quality to be driven by organic matter inputs, and root growth to reflect spatial and temporal fluctuations in soil quality resulting from those additions. We constructed a carbon budget and measured soil quality indicators (SQIs) and rooting characteristics using samples taken from two depths of all crop-phases of each rotation system on multiple dates. Stocks of particulate organic matter carbon (POM-C) and potentially mineralizable nitrogen (PMN) were greater and more evenly distributed in the LEI than conventional systems. Organic C inputs, which were 58% and 36% greater in the 3-year rotation than in the 4-year and 2-year rotations, respectively, did not account for differences in SQI abundance or distribution. Surprisingly, SQIs did not vary with crop-phase or date. All biochemical SQIs were more stratified (p<0.001) in the conventionally-managed soils. While POM-C and PMN in the top 10 cm were similar in all three systems, stocks in the 10–20 cm depth of the conventional system were less than half the size of those found in the LEI systems. This distribution was mirrored by maize root length density, which was also concentrated in the top 10 cm of the conventionally managed plots and evenly distributed between depths in the LEI systems. The plow-down of organic amendments and manures established meaningful differences in SQIs and extended the rhizosphere of the LEI systems. Resulting efficiencies observed in the LEI grain crops indicate that resource distribution as well as abundance is an important component of soil function that helps explain how LEI systems can maintain similar or greater yields with fewer inputs than achieved by their conventional counterparts.

Modeling nitrogen mineralization at surface and deep layers of sandy soils

ABSTRACTWe evaluated potential soil nitrogen mineralization of 46 sandy fields of the Pampas for determining the contribution of deep layers to mineralization and modeling its trend in depth as a possible tool for improving current existing mineralization models based on surface data. Mineralization, total and mineral nitrogen decreased with depth. A potential model fitted well to these variables (R2 = 0.95–0.99), but mineralization showed a more stratified profile. Consequently, the fraction of total nitrogen mineralized decreased with depth despite soils had constant texture across the profile. Potential mineralization to 1 m depth could be estimated using data from the 0–0.2-m soil layer and the average curvature of the potential model (R2 = 0.60) or linear regression methods (R2 = 0.71). Another estimation of potential mineralization could be performed by developing a pedotransfer function which used as predictors total nitrogen and depth (R2 = 0.62), without the need of laboratory incubations. Our results showed that for sandy soils, deep nitrogen mineralization account for 40% of soil mineralization and can be assessed using surface data or the total nitrogen content of the soils. Because surface soil mineralization and whole profile mineralization were highly correlated, it is improbable that field mineralization modeling may be improved using deep data in these soils.

Evaluation of Cool-season Vegetable Rotations in Organic Production

Certified organic production is challenging in the southeastern United States due to high weed, insect, and disease pressure. Maintaining and building soil organic carbon in midscale organic production systems can also be difficult due to the warm, moist conditions that promote decomposition. Focusing on cool-season cash crops paired with warm-season cover crops may help alleviate these production problems. This 3-year study (2011–13) evaluated two vegetable rotations of cool-season crops with cover crops for their productivity, disease management, and soil building potential in Watkinsville, GA. In the first rotation, cool-season cash crops included onion (Allium cepa), strawberry (Fragaria ×ananassa), and potato (Solanum tuberosum). These crops were rotated with green bean (Phaseolus vulgaris), oats/austrian winter pea (Avena sativa/Pisum sativum ssp. arvense), southernpea (Vigna unguiculata), and sunn hemp (Crotalaria juncea). In the second rotation, cool-season cash crops included onion, broccoli (Brassica oleracea Italica group), lettuce (Lactuca sativa), and carrot (Daucus carota ssp. sativus). These were rotated with millet (Urochloa ramosa), sunn hemp, egyptian wheat/iron clay pea (Sorghum sp./Vigna unguiculata), and sorghum × sudangrass (Sorghum bicolor × S. bicolor var. sudanese)/iron clay pea. Onion yields in both rotations were at least 80% of average yields in Georgia. Lettuce yields were at least double the average yields in Georgia and were comparable to national averages in the 2nd and 3rd years of the study. Strawberry yields in these rotations were lower than Georgia averages in all 3 years with a trend of lower yields over the course of the study. By contrast, potato, although lower than average yields in Georgia increased each year of the study. Broccoli yields in the first year were substantially lower than average Georgia yields, but were comparable to average yields in the 2nd year. Carrot remained less than half of average Georgia yields. Green bean were half of average Georgia yields in the 2nd year and were comparable to average yields in the 3rd year. As expected from what is observed in cool-season organic vegetable production in Georgia, disease pressure was low. Cover crops maintained soil organic carbon (C) with a small increase in active C; however, there was a net loss of potentially mineralizable nitrogen (PMN). Active C averaged across both rotations at the beginning of the study at 464 mg·kg−1 and averaged 572 mg·kg−1 at the end of the study. On the basis of this study, using cover crops can maintain soil carbon without the addition of carbon sources such as compost. Finally, longer term work needs to be done to assess soil management strategies.

Potential nitrogen mineralization responses of urban and rural forest soils to elevated temperature in Louisville, KY

Soil nitrogen (N) mineralization is an important process determining terrestrial N availability, and evidence suggests elevated temperatures will enhance N mineralization rates. Along a 40 km urban-rural gradient of chestnut oak forest stands in Louisville, KY, we expected N mineralization rates would be higher in urban than in rural forests in part due to increased temperatures caused by the urban heat island. However, a 12-month field study along this Louisville gradient showed that annual N mineralization rates were lower in urban than in rural stands. Since variation in precipitation inputs and other factors across this land-use gradient may be influencing soil N mineralization rates, we conducted a three-month soil incubation experiment in the lab to determine the extent to which a + 2 °C temperature difference could affect soil N mineralization in urban and rural soils. Across the range of temperatures tested, rural soils mineralized N at twice the rate of urban soils under base (7.86 vs. 3.65 mg N kg−1 AFDW soil d−1) and elevated (9.08 vs. 4.76 mg N kg−1 AFDW soil d−1) temperatures (p < 0.01). A 2 °C temperature difference, did not significantly alter total inorganic N production in urban (p = 0.272) or rural soils (p = 0.293). The proportion of nitrate produced was lower in the urban (15.1 %) than in the rural soils (72.3 %; p < 0.01). These results suggest that differences in soil organic matter quality and potentially decomposer community composition are the primary explanatory factors for forests along this Louisville gradient.

Changes in the soil C and N contents, C decomposition and N mineralization potentials in a rice paddy after long-term application of inorganic fertilizers and organic matter

ABSTRACTA long-term experiment on combined inorganic fertilizers and organic matter in paddy rice (Oryza sativa L.) cultivation began in May 1982 in Yamagata, northeastern Japan. In 2012, after the 31st harvest, soil samples were collected from five fertilizer treatments [(1) PK, (2) NPK, (3) NPK + 6 Mg ha−1 rice straw (RS), (4) NPK + 10 Mg ha−1 rice straw compost (CM1), and (5) NPK + 30 Mg ha−1 rice straw compost (CM3)], at five soil depths (0–5, 5–10, 10–15, 15–20 and 20–25 cm), to assess the changes in soil organic carbon (SOC) content and carbon (C) decomposition potential, total nitrogen (TN) content and nitrogen (N) mineralization potential resulting from long-term organic matter addition. The C decomposition potential was assessed based on the methane (CH4) and carbon dioxide (CO2) produced, while the N mineralization potential was determined from the potassium chloride (KCl)-extractable ammonium-nitrogen (NH4+-N), after 2, 4, 6 and 8 weeks of anaerobic incubation at 30°C in the laboratory. Compared to NPK treatment, SOC in the total 0–25 cm layer increased by 67.3, 21.0 and10.8%, and TN increased by 64.2, 19.7 and 10.6%, in CM3, RS and CM1, respectively, and SOC and TN showed a slight reduction in the PK treatment by 5.2 and 5.7%, respectively. Applying rice straw compost (10 Mg ha−1) instead of rice straw (6 Mg ha−1) to rice paddies reduced methane production by about 19% after the soils were measured under 8 weeks of anaerobic incubation at 30°C. Soil carbon decomposition potential (Co) and nitrogen mineralization potential (No) were highly correlated with the SOC and TN contents. The mean ratio of Co/No was 4.49, lower than the mean ratio of SOC/TN (13.49) for all treatments, which indicated that the easily decomposed organic matter was from soil microbial biomass and soil proteins.

Modeling soil organic carbon dynamics in an Austrian long-term tillage field experiment

An assessment of soil management impacts on carbon dynamics requires easily applicable tools. The carbon balance model CCB was applied to quantify the impact of different tillage systems on soil organic matter (SOM) dynamics. The model was able to describe the observed dynamics of SOM for conventional tillage (CT), but the correct simulation of ploughless soil management in the minimum tillage (MT) treatment required an adaptation of the calculation of the specific turnover conditions that are quantified as Biologic Active Time (BAT). We hypothesized a texture dependent reduction of the turnover activity with depth and calculated a site specific correction factor for the BAT of minimum-tilled soils where the topsoil is not mixed by ploughing. Without additional calibration we evaluated this approach using the data set of the field experiment in Fuchsenbigl (Austria) that was started in 1989 on a fine-sandy loamy Haplic Chernozem (FAO, 2006). The model predicted a reduced turnover activity with a BAT of 13dyr−1 for the MT treatment versus 23dyr−1 for the CT treatment having significant correlations between the modeled pool size of active SOM and the microbiological properties substrate induced respiration and potential nitrogen mineralization.

Soil water and mineral nitrogen content as influenced by crop rotation and tillage practice in the Swartland subregion of the Western Cape

Adoption of conservation agricultural practices, reduced tillage and crop rotation in the grain-producing areas of the Western Cape, South Africa, resulted in a gradual build-up of organic matter on the soil surface. It was expected that the increase in organic matter cover would influence soil water content and nitrogen mineralisation potential of the topsoil. The effect of crop rotation and tillage practice on soil water (g g−1) and mineral-N content (mg kg−1) in the 0–200 mm soil layer during 2010 and 2011 was assessed. Crop rotation, wheat monoculture (WWWW), lupin–wheat– canola–wheat (LWCW) and wheat–medic rotation (McWMcW) and tillage, conventional-till (CT), minimum-till (MT), no-till (NT) and zero-till (ZT) were studied. Crop rotation did not influence soil moisture content. Soil water content in CT tended to be lower compared with the other tillage treatments tested. A tendency of higher mineral-N in CT was observed, although not for all sampling dates. Mineral-N content did not differ between ZT, NT and MT. It is concluded that tillage influenced soil water and mineral-N content, whereas crop rotation only influenced mineral-N if the system included a legume crop (medic). Results obtained could be valuable in developing management strategies for wheat grown under different production systems.

Soil biochemical properties in brown and gray mine soils with and without hydroseeding

Abstract. Surface coal mining in the eastern USA disturbs hundreds of hectares of land every year and removes valuable and ecologically diverse eastern deciduous forests. Reclamation involves restoring the landscape to approximate original contour, replacing the topsoil, and revegetating the site with trees and herbaceous species to a designated post-mining land use. Re-establishing an ecosystem of ecological and economic value as well as restoring soil quality on disturbed sites are the goals of land reclamation, and microbial properties of mine soils can be indicators of restoration success. Reforestation plots were constructed in 2007 using weathered brown sandstone or unweathered gray sandstone as topsoil substitutes to evaluate tree growth and soil properties at Arch Coal's Birch River mine in West Virginia, USA. All plots were planted with 12 hardwood tree species and subplots were hydroseeded with a herbaceous seed mix and fertilizer. After 6 years, the average tree volume index was nearly 10 times greater for trees grown in brown (3853 cm3) compared to gray mine soils (407 cm3). Average pH of brown mine soils increased from 4.7 to 5.0, while gray mine soils declined from 7.9 to 7.0. Hydroseeding doubled tree volume index and ground cover on both mine soils. Hydroseeding doubled microbial biomass carbon (MBC) on brown mine soils (8.7 vs. 17.5 mg kg−1), but showed no effect on gray mine soils (13.3 vs. 12.8 mg kg−1). Hydroseeding also increased the ratio of MBC to soil organic C in both soils and more than tripled the ratio for potentially mineralizable nitrogen (PMN) to total N. Brown mine soils were a better growth medium than gray mine soils and hydroseeding was an important component of reclamation due to improved biochemical properties and microbial activity in mine soils.

On farm production of compost from nursery green residues and its use to reduce peat for the production of olive pot plants

The increasing environmental concerns about the use of peat as a non-renewable resource in growing substrates has led to the search for alternative materials. The aim of the present work was to develop a circular chain system model based on the “on farm” production of green compost in nursery from residues of pruning of woody plants and of grass mowing to replace peat in the composition of potting mixes. Composting process, carried out in a nursery located in Central Italy, was evaluated by the analysis of the succession of microbial communities and monitoring of temperature. The potential of green nursery compost in the replacement of different percentages of peat in potting mixes used for the cultivation of olive pot-plants was assessed by the estimation of the nitrogen mineralization potential and the detection of olive tree growth parameters. Results showed that initial mesophilic phase of composting occurred within three weeks followed by the thermophilic phase, which lasted for about 26 weeks and then by the second mesophilic phase. The potential of N mineralization varied with decreasing amount of peat present in the substrate. Plants cultivated in mixes obtained with reduced percentage of peat showed a regular development of growth parameters (plant height and stem diameter) during the whole cultivation cycle. Our results show that the widespread production and use of this renewable resource can provide the partial substitution of peat in potting mixes with the potential to consistently reduce the economic and environmental costs of nursery industry.

Nitrogen Dynamics Associated with Organic and Inorganic Inputs to Substrate Commonly Used on Rooftop Farms

Employing rooftops for the cultivation of crops in limited urban space has garnered interest in densely populated cities in the United States, where there is a growing demand for locally sourced vegetable products. Fertility management recommendations for rooftop farming, however, are scant. With insufficient research on nutrient cycling within rooftop farming systems, which tend to use soilless substrates with low organic matter content, the potential tradeoffs between the negative impacts (e.g., nutrient runoff) and the benefits (e.g., increased locally produced vegetables, stormwater retention, etc.) associated with rooftop farms are unclear. The objective of this study was to evaluate the effects of organic and inorganic nitrogen (N) inputs on the N dynamics within substrate typically used on rooftop farms. Substrate without added N inputs (control) was compared with substrates receiving N sources that are both realistic for and/or reflective of amendments currently applied on urban rooftop farms: a synthetic fertilizer (Osmocote® 14N–4.2P–11.6K), and three organic N inputs—composted poultry manure, municipal green waste (MGW) compost, and vermicompost. Aboveground crop biomass and yields of Beta vulgaris (swiss chard), along with inorganic N availability (ammonium: and nitrate: ), potentially mineralizable nitrogen (PMN), leachate-inorganic N concentrations, and pH and electrical conductivity (EC) levels were measured during an 8-week greenhouse experiment. Despite differences in carbon-to-nitrogen ratios (C:N), few differences in N cycling and yields were found among the treatments receiving organic N inputs. Crop yields from the synthetic fertilizer and MGW compost treatments were higher than the other organic N input treatments. Inorganic N levels in the synthetic fertilizer treatment decreased from 129 mg N/L at the start of the season to 113 mg N/L at the end of the season, while nearly 10-fold decreases of inorganic N concentrations in the substrate of the control and organic N input treatments from week 0 (79.5–117.8 mg N/L) to week 8 (12.8–16.6 mg N/L) were observed. Greater N availability at critical periods during the season may have promoted greater crop N uptake efficiency and, therefore, higher yields in the system receiving synthetic fertilizer. However, the greatest losses of and via leachate were also measured from this treatment. Our results show that the type of N input influenced plant-available N and yields and that the MGW compost treatment best achieved the balance between higher yields and reduced N losses to potential roof runoff. Furthermore, additional N inputs to these systems, particularly to the treatments receiving organic composts, will likely be necessary if a high N-demanding crop (such as swiss chard) is to be grown in the same substrates for more than 8 weeks. Rooftop farming is an emergent component of urban agriculture; regulations and guidelines for nutrient management of rooftop farms are necessary to optimize productivity and long-term benefits and to minimize negative environmental impacts.

Plant species richness leaves a legacy of enhanced root litter-induced decomposition in soil

Increasing plant species richness generally enhances plant biomass production, which may enhance accumulation of carbon (C) in soil. However, the net change in soil C also depends on the effect of plant diversity on C loss through decomposition of organic matter. Plant diversity can affect organic matter decomposition via changes in litter species diversity and composition, and via alteration of abiotic and/or biotic attributes of the soil (soil legacy effect). Previous studies examined the two effects on decomposition rates separately, and do therefore not elucidate the relative importance of the two effects, and their potential interaction. Here we separated the effects of litter mixing and litter identity from the soil legacy effect by conducting a factorial laboratory experiment where two fresh single root litters and their mixture were mixed with soils previously cultivated with single plant species or mixtures of two or four species. We found no evidence for litter-mixing effects. In contrast, root litter-induced CO2 production was greater in soils from high diversity plots than in soils from monocultures, regardless of the type of root litter added. Soil microbial PLFA biomass and composition at the onset of the experiment was unaffected by plant species richness, whereas soil potential nitrogen (N) mineralization rate increased with plant species richness. Our results indicate that the soil legacy effect may be explained by changes in soil N availability. There was no effect of plant species richness on decomposition of a recalcitrant substrate (compost). This suggests that the soil legacy effect predominantly acted on the decomposition of labile organic matter. We thus demonstrated that plant species richness enhances root litter-induced soil respiration via a soil legacy effect but not via a litter-mixing effect. This implies that the positive impacts of species richness on soil C sequestration may be weakened by accelerated organic matter decomposition.

Grain legume effects on soil nitrogen mineralization potential and wheat productivity in a Mediterranean environment

The objective of this work was to provide evidence on the effects of faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) on the dynamics of soil N availability and yield parameters of wheat (Triticum turgidum L. var. durum) in a legume–wheat rotation in comparison with the effects of the more extensively studied common vetch (Vicia sativa L.). Soil samples were taken from field plots just before wheat sowing and incubated in the laboratory to assess N mineralization potential, soil respiration and N immobilization after incorporation of legume residues. Soil after vetch cultivation showed the highest residual N and mineralization potential (120 mg N kg−1 soil), the greatest CO2 release and the smallest N immobilization. Smaller mineral N release (80 mg N kg−1 soil) was shown by soil after faba bean cultivation, which, however, would be capable to support an average wheat production without fertilization. Soil after chickpea and wheat cultivation manifested no differences in residual N and mineralization or immobilization potential. Laboratory results were well correlated with grain yield and N uptake during the second season of rotation in the field. All legumes resulted in significant yield surpluses and provided N credit to the following unfertilized wheat.

Nitrogen Mineralization from Sugarcane Vinasse

Vinasse is a liquid residue applied as a fertilizer in sugarcane crops. However, in areas far away from sugarcane mills the cost of the distribution can be very high due, the large volume of water. So, one solution is to concentrate the vinasse by the evaporation process to reduce transport costs. Considering that the nitrogen mineralization kinetics is not known in concentrated vinasse, the objective of this study was to evaluate the net and potential nitrogen mineralization in soil that received vinasse concentrated and not concentrated. The treatments with concentrated vinasse provided the highest values of net mineralization and total nitrogen, which presented significant correlation each other, the same way as the potential mineralization values had a positive correlation with the doses and the amounts of total nitrogen. The total nitrogen values can be used as an index of nitrogen availability in soils that received concentrated vinasse.

Soil nitrogen mineralisation dynamics under long-term different irrigation methods in greenhouses

Irrigation is the only source of soil water in greenhouse cultivation. The objective of this study is to illustrate the differences in soil organic nitrogen mineralisation caused by irrigation volume and frequency, and provide theoretical bases for the process of nitrogen transformation and nitrogen fertiliser application under different irrigation methods. The soil nitrogen mineralisation process was studied by the long-term intermittent leaching aerobic incubation method which was used by Standford and Smith in 1972. Parameters of soil nitrogen mineralisation potential (N0), the mineralisation rate constant (k) and half-life period (t1/2) in different soil layers were studied in greenhouse tomato cultivation for seven years, irrigated in three ways: subsurface irrigation (SI), drip irrigation (DI) and furrow irrigation (FI). The results showed that the first-order reaction kinetic model can be used to predict the soil organic nitrogen mineralisation characteristics in a greenhouse. There were five soil layers (0–10, 10–20, 20–30, 30–40 and 40–50 cm) in this study. In 0–20 cm soil layers, the N0 value of DI was highest, then FI, and SI was lowest. Apart from 10 to 20 cm soil layer, the k values of SI and DI were higher than for FI in other soil layers, while the t1/2 value of FI was highest, then DI, and t1/2 of SI was the lowest. The main reasons were that large amounts of water in FI would lead to increased soil bulk density and reduced soil temperature. DI with property ratio of the temperature and moisture was beneficial to organic nitrogen mineralisation. For SI, due to the overall upward movement of water for many years, nitrate accumulated and the pH value decreased in 0–20 cm soil layers. DI could increase the proportion of N0 value to the soil's total nitrogen. Therefore, according to the results of this study, DI gives the best effect on soil fertility, followed by SI and then by FI.

Soil-Plant-Microbial Relations in Hydrothermally Altered Soils of Northern California

Soils developed on relict hydrothermally altered soils throughout the Western United States present unique opportunities to study the role of geology on above and belowground biotic activity and composition. Soil and vegetation samples were taken at three unaltered andesite and three hydrothermally altered (acid-sulfate) sites located in and around Lassen Volcanoes National Park in northeastern California. In addition, three different types of disturbed areas (clearcut, thinned, pipeline) were sampled in acid-sulfate altered sites. Soils were sampled (0 to 15 centimeters) in mid-summer 2010 from both under-canopy and between-canopy areas within each of the sites. Soils were analyzed for numerous physical and chemical properties along with soil enzyme assays, carbon and nitrogen mineralization potential, microbial biomass-carbon and carbon-substrate utilization. Field vegetation measurements consisted of canopy cover by life form (tree, shrub, forb, grass), tree and shrub density, and above-ground net primary productivity of the understory. Overall, parameters at the clearcut sites were more similar to the unaltered sites, while parameters at the thinned and pipeline sites were more similar to the altered sites. We employed principal components analysis to develop two soil quality indices to help quantify the differences among the sites: one based on the correlation between soil parameters and canopy cover, and the second based on six sub-indices. Soil quality indices developed in these systems could provide a means for monitoring and identifying key relations between the vegetation, soils and microorganisms.

Effects of Red-Backed Salamanders on Ecosystem Functions

Ecosystems provide a vast array of services for human societies, but understanding how various organisms contribute to the functions that maintain these services remains an important ecological challenge. Predators can affect ecosystem functions through a combination of top-down trophic cascades and bottom-up effects on nutrient dynamics. As the most abundant vertebrate predator in many eastern US forests, woodland salamanders (Plethodon spp.) likely affect ecosystems functions. We examined the effects of red-backed salamanders (Plethodon cinereus) on a variety of forest ecosystem functions using a combined approach of large-scale salamander removals (314-m2 plots) and small-scale enclosures (2 m2) where we explicitly manipulated salamander density (0, 0.5, 1, 2, 4 m−2). In these experiments, we measured the rates of litter and wood decomposition, potential nitrogen mineralization and nitrification rates, acorn germination, and foliar insect damage on red oak seedlings. Across both experimental venues, we found no significant effect of red-backed salamanders on any of the ecosystem functions. We also found no effect of salamanders on intraguild predator abundance (carabid beetles, centipedes, spiders). Our study adds to the already conflicting evidence on effects of red-backed salamander and other amphibians on terrestrial ecosystem functions. It appears likely that the impact of terrestrial amphibians on ecosystem functions is context dependent. Future research would benefit from explicitly examining terrestrial amphibian effects on ecosystem functions under a variety of environmental conditions and in different forest types.

Carbon and nitrogen mineralization potential of biofuel crop (Jatropha curcas L.) residues in soil

Use and management ofjatropha residue is currently an important global issue for attaining sustainability in biofuel production from Jatropha curcas on wastelands. Perhaps, knowledge about the decomposition characteristics and nutrient release pattern from jatropha residues amended soils are lacking. Thus, the objective of present research was to characterize the carbon (C) and nitrogen (N) mineralization of jatropha residues during decomposition in soil. The chemical composition of the residues, in terms of C, N, cellulose, hemicelluloses, lignin and phenolics contents were determined. Laboratory incubation studies were carried out with two soils (inside and outside-canopy soil ofjatropha shrub) and four jatropha residues (1% w/w) amendments (cake, leaf, fruit shell or control soil only). The cumulative CO2 evolution of the added residues was in the magnitude of fruit shell>leaf>cake>control soil. Net C mineralized in soils were in the range of 46-50, 66-67 and 75-77% of C added by cake, leaf and fruit shell, respectively at the end of incubation study. Soils amended with leaf immobilized N during the first 64 days but subsequently released inorganic N. The addition of cake and fruit shell resulted in net N mineralization and net N immobilization, respectively throughout the incubation period. Cumulative N released by the end of incubation was in the order of cake>leaf>control>fruit shell. Net N mineralization in soils during the study was 75-92 and 21-27% of N added by cake and leaf, respectively whereas there was net N immobilization in fruit shell amended soil. Cumulative CO2 evolution as well as N mineralization during incubation were higher in inside-canopy soil compared with that of outside-canopy soil. Jatropha cake and leaf proved to be a potential source of mineral N, however leaf will take about 60-70 days as gestation period to mineralize the nitrogen. Similarly, leaf and fruit shell also exhibited a good potential of C mineralization.

Nitrogen Mineralization Potential as Influenced by Microbial Biomass, Cotton Residues and Temperature

Integrating information on nitrogen (N) mineralization potentials into a fertilization plan could lead to improved N use efficiency. A controlled incubation mineralization study examined microbial biomass dynamics and N mineralization rates for two soils receiving 56 and 168 kg N ha−1 in a Panoche clay loam (Typic Haplocambid) and a Wasco sandy loam (Typic Torriorthent), incubated with and without cotton (Gossypium hirsutum L.) residues at 10 and 25°C for 203 days. Microbial biomass activity determined from mineralized carbon dioxide (CO2) was higher in the sandy loam than in clay loam independent of incubation temperature, cotton residue addition and N treatment. In the absence of added cotton residue, N mineralization rates were higher in the sandy loam. Residue additions increased N immobilization in both soils, but were greater in clay loam. Microbial biomass and mineralization were significantly affected by soil type, residue addition and temperature but not by N level.

English

The objective of this work was to study the effects of tillage and liquid manure applications on some physical and chemical properties and also on the carbon and nitrogen mineralization potential from a meadow soil.&nbsp;Our results indicated that tillage and manure applications had no effect on the concentration of Cu, Mn, total N and organic C in the 0 - 15 cm layer of soil after 15 years of treatment. However soil P, Ca, Mg and Zn contents increased significantly with manure applications. Soil organic matter and total N significantly decreased in the 15 &ndash; 30 cm depth. No significant change could be detected in soil structural stability in both layers. Moreover, tillage affected significantly soil soluble C and the C/N ratio. Application of 100 t ha-1&nbsp;manure significantly increased soil soluble C. The results of this study suggest that tillage increased significantly the soil N mineralization rate. The potentially mineralizable nitrogen (N0) was higher in tilled than in no-tilled soil and was at its maximum in the 0 &ndash; 15 cm layer of the soil. Furthermore, a significant positive interaction was observed between tillage and manure application on N mineralized after 1.4 wk (Ne). No significant change was detected in both C mineralization rate (Cm) and potentially mineralizable C (C0). The total amounts of mineralizable carbon (Cm) and nitrogen (Nm) significantly decreased in 15 &ndash; 30 cm depth and were very closely correlated with the total amounts of C or N and mineralization rate constants (K). &nbsp; Key words:&nbsp;Carbon and nitrogen mineralization potentials, k constants, physical and chemical properties.

Will hydrologic restoration of Mississippi River riparian wetlands improve their critical biogeochemical functions?

Riparian wetlands are essential components of the landscape, providing critical functions including buffers for floodwaters, wildlife habitat and improvement of surface water quality. Many riparian wetlands have been hydrologically disconnected from the Mississippi River by a vast system of levees, altering the ecosystem services provided by these riparian zones. Efforts are underway to restore these ecosystem services, however previous research demonstrated that the statutory requirements guiding wetland restoration do not adequately consider soil biogeochemical cycling. We examined soil properties and biogeochemical indicators of nitrogen cycling to assess soil recovery in a recently hydrologically restored riparian wetland. This restored wetland, reconnected with the river for approximately two years, was compared to a nearby reference wetland where the river connection has been constant. Seasonal measurements included bulk density, total carbon, nitrogen and phosphorus, microbial biomass nitrogen, potentially mineralizable nitrogen (PMN) and potential denitrification. There were significant differences found for nearly all measured soil properties with higher bulk density and lower total C, total N, microbial biomass, PMN and potential denitrification at the restored compared to the reference site. The PMN and potential denitrification at the restored site plots were 27–46% and 2% (respectively) of the values measured at the reference site. This clearly demonstrates that while the regulatory indicators of success are improving, some critical biogeochemical functions of the restored sites are significantly lower than the reference site two years after hydrologic restoration.