Real-Time Soil CO2 Respiration Rate Determination and the Comparison between the Infrared Gas Analyzer and Microrespirometer (MicroRes®) Methods

Soil carbon dioxide (CO₂) respiration is one of the important soil health parameters that provides a general assessment of soil microbial activity and soil quality. Soil respiration rates, however, have not been widely applied in soil testing protocols mainly because the traditional methods are either inconvenient, technically cumbersome or too expensive. Currently, only two methods are available for a true real-time soil respiration rate determination (<2 h): the infrared gas analyzer (IRGA) and the microrespirometer (MR or MicroRes^®) methods. We analyzed the real-time soil respiration rates of 20 soil samples from fifteen states after various periods of incubation using the IRGA method and the MR method. The measured soil respiration rates ranged from 0.4 µL CO₂/h/g to 9.0 µL CO₂/h/g. Both methods show precision in soil respiration determinations (CV = 12.7% and 11.9%, respectively). Comparison of the results between the IRGA and MR methods indicates high degrees of agreement (r² = 0.914). This study shows that the MR method is a simpler and more cost-effective alternative for real-time soil respiration rate determinations.     

Potential effect of conservation tillage on sustainable land use: A review of global long-term studies

Although understood differently in different parts of the world, conservation tillage usually includes leaving crop residues on the soil surface to reduce tillage. Through a global review of long-term conservation tillage research, this paper discusses the long-term effect of conservation tillage on sustainable land use, nutrient availability and crop yield response. Research has shown several potential benefits associated with conservation tillage, such as potential carbon sequestration, nutrient availability, and yield response. This research would provide a better perspective of the role of soil conservation tillage and hold promise in promoting application of practical technologies for dryland farming systems in China.     

Effects of Surface Application of MSW Compost On Cotton Production – Soil Properties,Plant Responses,And Nematode Management

Equipment was modified and/or developed for broadcast and banded applications of municipal solid waste (MSW) compost at selected rates to agricultural land for cotton production. Replicated tests were conducted for four years to determine the effects of compost on soil properties, crop yield, and nematode populations. Soil type in the test field was Faceville loamy sand. Broadcast application of compost significantly reduced soil compaction in the top 30 cm of soil in cotton rows and row-middles compared to no compost application. Banded application did not affect compaction in the row middles. Columbia lance nematode densities decreased in all compost-treated plots during all four years of study. Several plots treated with compost had nematode densities comparable to those found in the plots treated with Temik 15G nematicide. Compost application significantly increased the soil organic matter content and soil nitrogen content at six and 14 weeks after planting. However, the compost did not affect the leaf nitrogen content of the cotton plant during the same sampling periods. In 1996, 1997, and 1998, all rates of added compost significantly increased seed cotton yield. Yield increase was proportional to application rate. There were very few carry-over compost effects from each previous year's treatments on either soil organic matter, soil nitrogen, or seed cotton yield.     

Comparison of Yield Potential and Herbicide Program Cost Between Herbicide‐Resistant and Conventional Soybean

Abstract

Using the results of seventy‐one soybean (Glycine max) variety performance trials, the existence of a yield drag (YD) of herbicide‐resistant varieties when compared to conventional varieties is verified. The trials were conducted from 1996 to 2000 at five locations, on 569 varieties covering three maturity groups in irrigated and dryland conditions using conventional tillage. Trend analysis of YD suggests that it (i) is magnified by irrigation; (ii) has declined to negligible levels; (iii) is not significantly different across maturity group; and (iv) exhibits some locational differences. An analysis of six herbicide programs revealed that glyphosate programs are generally more expensive than reduced‐rate conventional programs but are comparable to or cheaper than full‐rate conventional herbicide regimes. It is further conjectured that seed/technology and herbicide cost differences across seed/herbicide systems will adjust to competitive conditions in the long run.     

A Comparison of Super-Valid Restricted and Row–Column Randomization

In complete block experiments, treatments are often randomized within blocks without any other restrictions. When the blocks are rows of plots and the blocks are laid out in parallel so that also columns of plots are formed, there might be random effects of both rows and columns. In this situation, a row–column design is a natural choice. Super-valid restricted randomization is another option. This article compares these randomization procedures for small complete block experiments (5–10 treatments in 3–6 blocks). Validity of a randomization procedure is defined for mixed-effects models. The two randomization procedures are compared with regard to average variance in pairwise comparisons. Row–column randomization is recommended when either there are at least four replicates, or the number of replicates is three and intercolumn variance is not known to be small. These conclusions assume a model with fixed effects of treatments and random effects of rows and columns, and estimation using the REML method and the Kenward and Roger approximation.     

Utilization Potential of Peats – a Study on Peat Biodegradability Determined by Respirometric Method

The biodegradation of different peat types was studied with a manometric respirometric test. Compaction peat and sphagnum peat samples were analysed, and the effect of peat pH on biodegradation behaviour was evaluated. Only minor (BOD/ThOD?<?0.4%) biodegradation was observed with compaction peat samples, and the stable state, in which biodegradation stopped, was achieved during a two month period. As expected, sphagnum peat samples with a lower decomposition rate degraded more than compaction peat samples. Alkalinity (pH between ca. 4–9) of the peat was noticed to reduce the degree of biodegradation and accelerate the achievement of the stable state.     

Long-term effects of mineral fertilizers on soil microorganisms – A review

Increasing nutrient inputs into terrestrial ecosystems affect not only plant communities but also associated soil microbial communities. Studies carried out in predominantly unmanaged ecosystems have found that increasing nitrogen (N) inputs generally decrease soil microbial biomass; less is known about long-term impacts in managed systems such as agroecosystems. The objective of this paper was to analyze the responses of soil microorganisms to mineral fertilizer using data from long-term fertilization trials in cropping systems. A meta-analysis based on 107 datasets from 64 long-term trials from around the world revealed that mineral fertilizer application led to a 15.1% increase in the microbial biomass (C_mic) above levels in unfertilized control treatments. Mineral fertilization also increased soil organic carbon (C_org) content and our results suggest that C_org is a major factor contributing to the overall increase in C_mic with mineral fertilization. The magnitude of the effect of fertilization on C_mic was pH dependent. While fertilization tended to reduce C_mic in soils with a pH below 5 in the fertilized treatment, it had a significantly positive effect at higher soil pH values. Duration of the trial also affected the response of C_mic to fertilization, with increases in C_mic most pronounced in studies with a duration of at least 20 years. The input of N per se does not seem to negatively affect C_mic in cropping systems. The application of urea and ammonia fertilizers, however, can temporarily increase pH, osmotic potential and ammonia concentrations to levels inhibitory to microbial communities. Even though impacts of fertilizers are spatially limited, they may strongly affect soil microbial biomass and community composition in the short term. Long-term repeated mineral N applications may alter microbial community composition even when pH changes are small. How specific microbial groups respond to repeated applications of mineral fertilizers, however, varies considerably and seems to depend on environmental and crop management related factors.     

Carbon Monoxide in Ouagadougou, Burkina Faso – A Comparison between Urban Background, Roadside and In-traffic Measurements

Spatial variations of Carbon Monoxide (CO) are examined in the urban environment of Ouagadougou, Burkina Faso. Focus is given on the variations between urban background, roadside and in-traffic measurements. Results show significant differences between the three methods where average in-traffic values were 2–3 times higher than average roadside values and 10–12 times higher than average background values. During traffic congestions these differences extended up to 6 and 20 times respectively. Results are discussed in relation to human exposure assessments and WHO guidelines.     

Assessment of gross and net mineralization rates of soil organic phosphorus – A review

The quantification of net soil organic P mineralization rates is hampered by the potentially rapid sorption of released phosphate. Here, isotopic dilution approaches to assess gross and net organic P mineralization rates under steady-state conditions are reviewed, including different analytical and numerical solutions to assess P transformation rates based on incubation experiments with ³²P- or ³³P-labeled soils. Non-isotopic approaches are also commented on. Published isotopic dilution studies show that isotopically exchangeable P during incubation can partly or even predominantly (20–90%) result from biological and biochemical rather than physicochemical processes. The relative contribution of biological and biochemical processes tends to be lower in arable soils than under grassland and forests and is negatively related to the availability of inorganic P and positively to concentrations of soil organic carbon. Typical basal gross organic P mineralization rates range between 0.1 and 2.5 mg P kg⁻¹ d⁻¹, but rates up to 12.6 mg P kg⁻¹ d⁻¹ have been observed in grassland and forest soils. The further partitioning of gross organic P mineralization remains uncertain, but a dominance of microbial immobilization and remineralization is likely under most conditions, at least during the initial weeks of incubation. Over longer time periods, the relative importance of mineralization of non-living soil organic P increases, with the contribution of extracellular hydrolysis remaining to be elucidated. This requires other approaches than enzyme activity assays, since measurements of phosphomonoesterase activity in soil render organic P mineralization rates that are one to two orders of magnitude greater than those determined by isotopic dilution. The numerical modeling approach will enable assessment of soil P transformation rates under non-steady-state conditions, where P fluxes are likely to be greater than under steady-state conditions. Ultimately, an improved understanding of the biological and biochemical processes in soil P dynamics may help to improve P management in agroecosystems.     

A history of hubris – Cautionary lessons in ecologically sustainable forest management

Logging is one of the most important forms of native-forest exploitation and can have substantial impacts on biodiversity and key ecosystem services. Here we briefly contrast logging operations in temperate and tropical forests and then highlight several challenges for understanding the ecological impacts of logging. We argue that many logging studies are conducted at small spatial scales or over inadequate time periods, and are biased against finding significant negative impacts. This is because of confounding environmental differences between logged and unlogged forests as well as the prolonged nature of forest stand development. Human perceptions of logging also can be biased by the ‘shifting baseline’ phenomenon, and by an incorrect perception that logging operations approximate natural disturbance regimes. We argue that the ecological impacts of logging can be more challenging to detect than is often appreciated, and that forest managers and decision-makers should be cautious when weighing the arguments of pro-logging lobbies.     

A Comparison of the Elemental Composition of Leaf Tissue of Spartina Patens and Spartina Alternifora in Louisiana’s Coastal Marshes

Elemental concentrations in leaf tissue can identify limiting conditions in crops and can be useful in managing and restoring marshes. Coastal management and restoration plans frequently include Spartina spp. because they are common plants in coastal wetlands across North America. Researchers frequently compare results of stoichiometric studies among Spartina spp. to corroborate results, although their stoichiometry may not be comparable. We compare the stoichiometry of paired samples of Spartina patens and Spartina alterniflora collected across Louisiana. Overall differences in stoichiometry between species, seasonal changes, and effects of porewater chemistry were quantified. Manganese (Mn) concentrations and calcium (Ca) concentrations were higher in S. alterniflora and the difference in [Ca] increased seasonally. Sodium concentrations were similar, except during prolonged inundation. Short flooding durations decreased carbon (C):nitrogen (N) without increasing [Mn] or flooding stress in both species.     

Preliminary Study of Variable Rate Application – Organic Liquid Fertilizer by Using SPAD Chlorophyll Meter on System of Rice Intensification (SRI) Cultivation

Knowing actual nutrient requirements for rice plants is crucial in supplying the correct amount of fertilizer, especially nitrogen since nitrogen is one of the most key limiting nutrients in rice cultivation. A preliminary study of variable rate application (VRA) on System of Rice Intensification (SRI) planting by using organic foliar fertilizer was carried out to determine the effectiveness of precision fertilization. Foliar fertilizer was formulated based on actual nitrogen needed by rice plants using Soil-Plant Analyses Development (SPAD) chlorophyll meter measurements. The experiment was laid out in a randomized complete block design (RCBD) with four treatments (50% fixed rate, 100% fixed rate, 150% fixed rate and VRA) and four replications for each treatment. Plant growth performances (plant heights, number of tillers, number of panicle and flower) and yield performances (grain yield, number of grain, 1000-grain weight and number of spikelets) were recorded during the study. The results showed that foliar application of VRA resulted in significantly higher yield performances; grain yield (13.65 g), number of grain (807.50), 1000-grain weight (16.79 g), and number of spikelets (7.50) compared to uniform fertilizer applications. VRA treatments had the highest SPAD readings at every planting stage during the experiment; however, a high nitrogen supply was needed during the mid-tillering stages (35 DAT) compared to other fertilizer rates. Besides, VRA application shows the most savings in term of total nitrogen supply (415 µg) compared to uniform rates application; 50% fixed rate (400 µg), 100% fixed rate (810 µg), and 150% fixed rate (1210 µg).     

Short rotation forestry – Earthworm interactions: A field based mesocosm experiment

Short rotation forestry (SRF) which consists of planting rapidly growing native and non-native tree species has been introduced to the UK to increase woody biomass production. A largely unknown aspect of SRF species is their interaction with soil fauna, of which the earthworm community is a major component. Earthworms have a pronounced impact on litter decomposition, nutrient cycling and tree growth. Conversely, tree litter and root chemistry can impact on the associated earthworm community development. The aim of this study was to determine direct interactions between SRF species and earthworms. A field-based mesocosm experiment was conducted using Betula pendula (birch) and Eucalyptus nitens (eucalyptus) with two earthworm species Lumbricus terrestris and Allolobophora chlorotica. The one year experiment revealed that native birch and non-native eucalyptus had a similar influence on L. terrestris population development. However, birch had a positive impact on A. chlorotica population establishment compared with eucalyptus. In the presence of earthworms, total tree biomass and leaf nitrogen concentration of eucalyptus were increased respectively by 25% and 27% compared with an earthworm-free control. In the presence of earthworms, surface litter incorporation was greater for both tree species (almost 5 times for birch and 3 times for eucalyptus) compared with controls. This work showed direct SRF-earthworm interactions which differed for tree species.     

Degradative Oxidation of 2,4,6 Trichlorophenol Using Advanced Oxidation Processes – A Comparative Study

In the present study, a comparative assessment of 2,4,6-T (2,4,6-Trichlorophenol) degradation by different AOPs (Advanced Oxidation Processes – UV, UV/ H₂O₂, Fenton, UV/Fenton and UV/TiO₂) in the laboratory scale is performed. The effects of different reactant concentrations and pH are assessed. 2,4,6-T removal, Total Organic Carbon mineralization (TOC) and dechlorination are monitored. Of all the AOPs, UV/Fenton process is more effective in degrading 2,4,6-T. The optimum conditions obtained for the best degradation with UV/Fenton are: pH?=?3, Fe⁺² concentration of about 5 ppm, and peroxide concentration of 100 ppm for an initial 100 ppm of 2,4,6 T concentration at room temperature. In these conditions, a pseudo first-order rate constant is evaluated. The degradation rate of 2,4,6 T followed the order: $$ {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{Feton}}}}} \right. \kern-\nulldelimiterspace} {{\text{Feton}}}} > {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{TiO}}_{\text{2}} > {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}} \right. \kern-\nulldelimiterspace} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}}}} \right. \kern-\nulldelimiterspace} {{\text{TiO}}_{\text{2}} > {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}} \right. \kern-\nulldelimiterspace} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}}} > {\text{UV}} $$      

Salinity effects on nitrogen metabolism in plants – focusing on the activities of nitrogen metabolizing enzymes: A review

Nitrogen (N) metabolism is of great economic importance because it provides proteins and nucleic acids which in turn control many cellular activities in plants. Salinity affects different steps of N metabolism including N uptake, NO₃^? reduction, and NH₄⁺ assimilation, leading to a severe decline in crop yield. Major mechanisms of salinity effects on N metabolism are salinity-induced reductions in water availability and absorption, disruption of root membrane integrity, an inhibition of NO₃^? uptake by Cl^?, low NO₃^? loading into root xylem, alteration in the activities of N assimilating enzymes, decrease in transpiration, and reduction in relative growth rate which results in a lower N demand. However, the effects of salinity on N metabolism are multifaceted and may vary depending on many plant and soil factors. The present review deals with salinity effects on N metabolism in plants, emphasizing on the activities of N metabolizing enzymes in a saline environment.     

Humic Acid–Like Substances Extracted from Compost Improve Fe Nutrition of Lemon Grown on Calcareous Soil: An Environmentally Safe Approach

The short-term effectiveness of soil-applied humic acid–like substances [naturally complexed or uncomplexed with iron (Fe)] extracted from composted poultry (HLSP) and sheep (HLSS) manures in preventing lime-induced Fe chlorosis in Eureka lemon (Citrus lemon L.) cuttings grafted on sour orange (Citrus aurantium L.) was investigated and compared with the commonly applied ethylenediamine di-2-hydroxyphenyl acetate ferric (FeEDDHA). Treatments were untreated plants and plants fertilized with FeEDDHA, HLSP, and HLSS injected into the soil at a total rate of 25 mg Fe per plant each. Chlorophyll concentration index (CCI) of the youngest fully expanded leaves, growth vigor, and leaf Fe concentration were measured. HLSP and HLSS, similar to FeEDDHA, resulted in significantly greater CCI values, growth vigor, and leaf Fe concentration compared to untreated plants. HLSP and HLSS offer potential alternative to FeEDDHA to prevent lime-induced Fe deficiency in Eureka lemon. Concentrates of HLSP and HLSS can be commercially prepared to offer an inexpensive and environmentally safe product.     

Potential environmental impact of technosols composed of gossan and sulfide-rich wastes from São Domingos mine: assay of simulated leaching

Purpose

The aim of this study was to evaluate (i) the ability of two Technosols, prepared with gossan or sulfide-rich wastes plus mixtures of organic/inorganic amendments, to improve the characteristics of the wastes by the analysis of the variation of elemental concentrations in their simulated leachates, and (ii) the potential environmental risk of these Technosols evaluated through the concentrations of the elements leached from the tailings containing the two wastes, considering their mass in the São Domingos mine.

Materials and methods

Composite samples of two São Domingos mining wastes (gossan wastes—GW; sulfide-rich wastes—SW) were collected. Amendment mixtures, containing different organic/inorganic wastes (from green agriculture, distillation of Ceratonia siliqua and Arbutus unedo fruits, and limestone quarry), were applied at 12, 30, and 60 g/kg. Two sets of microcosm assays were performed under controlled conditions in greenhouse and monitored during 7 and 13 months for GW and SW, respectively. Materials from each pot/treatment (<5 cm of depth) were collected after 1, 4, 7, and 13 months of incubation and used to obtain simulated leachates (DIN extraction). The analytical parameters evaluated in the leachates were pH, electrical conductivity, and element concentrations using flame atomic absorption spectrometry for cations and graphite furnace atomic absorption spectrometry, ionic chromatography, and UV-VIS for elements that normally occur as anions in aqueous solution.

Results and discussion

Simulated leachates from SW had lower pH and higher concentrations of potentially hazardous elements than leachates from GW. The concentrations of As in leachates from GW-Technosols were higher than those in leachates from GW-control but <0.6 mg/kg. In GW-Technosols leachates, the pH and the concentrations of some nutrients (e.g., Ca and phosphates) also increased when compared to the control. In the SW-Technosols, the pH of the leachates increased only in the first month as long as limestone was present. In these leachates, a general decrease of the concentrations of some elements was observed (e.g., As, sulfate, Fe, Pb), especially in the first month. A clear influence of the dose and type of amendments was not observed during the experimental time span for both wastes.

Conclusions

The concentrations of elements like Al, Ca, Fe, and Pb in the leachates are controlled by both the pH of the solutions and the concentrations of phosphates and sulfates. The extensive mass of the studied mine wastes contribute to the release to the neighboring environment of considerable amounts of potentially hazardous elements. The rehabilitation of the mine wastes by the conception of Technosols, especially with sulfide-rich wastes, can reduce significantly their environmental impact.