Mixed Straw Research Articles

Straw recycling in rice paddy: Trade-off between greenhouse gas emission and soil carbon stock increase

A two-year field study was conducted in rice paddy to determine how straw incorporation influences net global warming potential (GWP) using the sum of methane (CH4) and nitrous oxide (N2O) fluxes and net ecosystem carbon budget (NECB), and greenhouse gas intensity (GHGI) using net GWP per unit of grain yield. Straw was applied by spreading over soil or mixing with soil during the dry fallow season and plowed right before flooding. In the control treatment, straw was removed for comparison. Soil organic carbon (SOC) stock changes were estimated by NECB, which means the difference between C input and output. Net primary production and applied straw were considered as C input source, and harvest C removal and heterotrophic respiration C loss were counted as C output. Straw removal depleted SOC stock at a range of 0.24–1.12 Mg C ha−1 yr−1, but straw application significantly increased SOC stock with the rate of 1.48–2.82 Mg C ha-1 yr-1. Straw spreading over soil was more effective than straw mixing with soil to increase SOC stock. However, straw application markedly increased GHG emission, in particular, CH4 emission by 27–263 % over straw removal. Between two straw treatments, annual CH4 fluxes were 25–50 % higher in straw spreading over soil than straw mixing with soil. However, the net GWP did not largely differ between straw spreading and straw removal, due to increased SOC stock. In comparison, straw mixing with soil could reduce the net GWP by 50–55 % over straw removal. Straw application increased grain yields by 7–26 % over straw removal. As a result, GHGI did not differ between straw spreading and straw removal, but was significantly lower in straw mixing with soil. Conclusively, straw application could be essential to increase SOC stock without GWP increase in rice paddy. In particular, the aerobic decomposition of straw during the dry fallow season by mixing with soil could reduce the net GWP by approximately 50–52 % over straw removal.

Structural Analysis of Humic Acid in Soil at Different Corn Straw Returning Modes through Fluorescence Spectroscopy and Infrared Spectroscopy.

The purpose of this study is to analyze the effects of different straw returning modes on the structure of humic acid (HA) in soil by fluorescence spectroscopy and infrared (IR) spectroscopy. Four different straw returning modes, including straw returning to topsoil (St), straw returning to subsoil (Ss), straw mixing with topsoil (Smt), and straw mixing with subsoil (Sms), were used in this study; the soil HA was analyzed after 12 months of corn straw returning by a combination of fluorescence spectroscopy and IR spectroscopy. Based on the results, it was established that IR spectroscopy can estimate the complication and oxidation degree of soil HA and also evaluate its aliphaticity and aromaticity. Monodimensional fluorescence spectroscopy could preliminarily determine the changes in the humification of HA through the fluorescence intensities. The intensity ratio of I456/I380 calculated from synchronous-scan fluorescence spectra could be used to evaluate the humification degree of soil HA. The total luminescence spectra of HAs provided more information on the fluorophores in the structure, including the amount and peak position of lignin-like structures and phenol-like or naphthol-like structures. Among the four straw returning modes, Ss is the most beneficial for reducing the oxidation degree and increasing the aromatization and humification degree of subsoil HA. It is believed that fluorescence spectroscopy and IR spectroscopy are relatively simple and sensitive methods for analyzing soil HA.

Revealing the alkaline characteristic evolution of bauxite residue under biomass fermentation

Biomass fermentation has been proposed as a simple and economical strategy to alleviate the high alkalinity of bauxite residue. This study investigates the neutralization of bauxite residue following the application of biomass as an alkali modifier by natural fermentation. Fresh bauxite residue samples were collected from Pingguo refinery (Aluminum Corporation of China). Samples were treated with straw mulching (SC), straw mixing (SM), bagasse mulching (BC), and bagasse mixing (BM), respectively. Treatments were analyzed for pH, EC, metal cations, and soluble alkali (OH−, Al(OH)4− and CO32−). The mineral phase and Na speciation were analyzed by X-ray diffraction (XRD) and near-edge X-ray absorption fine structure (Na-XANES). Optimum application rate for either straw or bagasse was 20% (w/w), reducing leachate pH from 10.26 to 8.56. During biomass transformation, the alkaline mineral grossular was completely dissolved, while calcite and cancrinite were dissolved to a lesser degree. No treatment changed the spatial distribution of Na+, but the basic anions (OH−, CO32−, and Al(OH)4−) were significantly reduced. Following treatment application, soluble alkali in the residues was significantly reduced while the alkaline minerals were slightly dissolved. This was determined as the main cause for the decrease in residue pH.

Effects of mixing maize straw with soil and placement depths on decomposition rates and products at two cold sites in the mollisol region of China

Crop straw is often retained on the ground as mulch or incorporated into soil through tillage practices. These straw management practices may affect straw decomposition rates and subsequently decomposition products due to mixing straw with soil, straw placement depths and experimental sites. Using litterbags containing maize (Zea mays. L) straw only (STO) or straw-soil mixture (SSM), this study aimed to determine the influence of mixing straw with soil and straw placement depths on decomposition rates and decomposition products, and to understand the relation of chemical composition of straw residues with straw decomposition rates. The litterbags were placed at three soil depths (0, 15 and 30 cm) in the fields at two cold sites (Hailun and Harbin), Northeast China, which had similar precipitations but different temperatures. During the 17-month experiment, the decomposition rate constants were higher by 60 %–160 % at a comparable depth in SSM than in STO. The mixing straw with soil was a more important factor in controlling straw decomposition rates than placement depths and experimental sites at the studied region. The relative abundances of O–alkyl C groups in straw residues decreased during the experimental period, even in the winter, while those of aromatic groups increased profoundly. The relative abundances of O–alkyl C groups in straw residues were lower by 0.4 %–6.9 % and those of aromatic groups were higher by 0 %–4.6 % in SSM than in STO. These findings suggest that the conventional litterbag method underestimated straw decomposition rates. Incorporating straw into soil could enhance maize straw decomposition and the formation of more stable soil organic matter (SOM) in the cold high-latitude studied region.

Effect of straw incorporation on methane emission in rice paddy: conversion factor and smart straw management

Straw incorporation is strongly recommended in rice paddy to improve soil quality and mitigate atmospheric carbon dioxide (CO2), via increasing soil organic carbon (SOC) stock. However, straw application significantly increased methane (CH4) emission during rice cultivation, and then its incorporation area was not expanded effectively. To find the reasonable straw management practice which can reduce CH4 emission without productivity damage, the effect of straw incorporation season and method on CH4 emission was investigated at six different textured paddy fields in South Korea for 2 years. A straw was applied right after rice harvesting in autumn, and the other right before rice transplanting in spring. In the autumn application, straw was applied with two different methods: spreading over soil surface or mixing with soil. Straw application significantly increased seasonal CH4 flux by average 28–122% over 197–590 kg CH4 ha−1 of the no-straw, but its flux showed big difference among straw applications. Fresh straw application before transplanting increased seasonal CH4 flux by approximately 120% over the no-straw, but the autumn application reduced its CH4 flux by 24–43% over 509–1407 kg CH4 ha−1 of the spring application. In particular, the seasonal CH4 flux was approximately 24% lower in straw mixing with soil after autumn harvesting than 423–855 kg CH4 ha−1 in straw spreading over surface. However, CH4 fluxes were not significantly discriminated by soil and meteorological properties in the selected condition. Straw application slightly increased rice grain yield by approximately 4% over the no-straw, but rice productivity was not statistically different among straw applications. Spring straw application increased CH4 intensity which means seasonal CH4 flux per grain yield by the maximum 220% over the no-straw. Autumn straw application significantly decreased CH4 intensity by average 24–65% over the spring straw application. In particular, CH4 intensity in straw mixing with soil treatment was not statistically different with the no-straw. Therefore, autumn straw application with mixing inner soil could be a reasonable straw management practice to decrease CH4 emission impact with improving soil productivity.

Effects of fertilization and straw return methods on the soil carbon pool and CO2 emission in a reclaimed mine spoil in Shanxi Province, China

Reclaimed soil is similar to an “empty cup” with a large carbon (C) sequestration potential. Agricultural management practices strongly influence C storage and soil carbon dioxide (CO2) emission. The objective of this study was to identify the effects of fertilization and straw return methods on the soil C pool and CO2 emission in a reclaimed mine spoil. Thus, we studied the effects of four fertilization treatments [chemical fertilizer (NP), manure (M), 50% M plus 50% NP (NPM), and unfertilized control (CK)] and three straw return methods [no straw return (no straw), return of straw mixed with soil (straw mixing), and return of straw to the surface of the soil (straw mulching)] in a mine reclamation region by examining changes in the soil C pool and CO2 emission. The soil C pool was evaluated by acid hydrolysis, considering three pools: (a) labile pool I (LP I), obtained by hydrolysis with 5 N H2SO4 at 105 °C for 30 min; (b) labile pool II (LP II), obtained by hydrolysis with 26 N H2SO4 at room temperature overnight, followed by 2 N H2SO4 at 105 °C for 3 h; and (c) the recalcitrant pool, measured as the unhydrolyzed residue. The CO2 emission/C sequestration and CO2 emission/grain yield ratios were used as indicators of C emission. Compared with the CK, the NPM treatment was the most efficient among the fertilization treatments in increasing grain yield (136%) and C sequestration (311%) and reducing the CO2 emission/C sequestration (62%) and CO2 emission/grain yield (32%) ratios. The straw mixing treatment had more soil organic carbon (SOC), a larger LP I and LP II, and more C sequestration than the other straw return treatments. The addition of manure resulted in a higher distribution rate of new organic C to the labile C pool (73–78%) than the addition of inorganic fertilizer (45%). Soil C emissions were mainly concentrated in the maize growing season, accounting for more than 80% of the total annual C emissions. LP I, LP II and CO2 emission were significantly positive correlated with SOC and yield. Therefore, soil C pools and CO2 emissions are significantly influenced by fertilization regimes and straw return methods, which should be used to important indicators to estimate the C balance in agro-ecosystems during the process of mine spoil reclamation.

Changes in the number of the species and fungal populations colonizing decomposing wheat crop residues

The present study investigated the changes in the number of the species and the fungal population colonizing the decomposing wheat crop residues. There was a slight increase in the number of species in decomposing wheat internodes on 30th day followed by substantial decline on 90th day. On the 150th day a sharp rise was observed followed by a sharp decline on 210th day. From decomposing wheat leaves the number of species isolated was exactly similar to that internode. However on 90th day moderate increase was observed. There was no change in number of species isolated from decomposing chaff on 30th day. On 90th day there is a negligible increase followed by a slight increase on 150th days. The number of fungal species isolated from the mixed straw remain unchanged till 30th day followed by moderate increase on 150th day when it reached almost double the number of species isolated in the beginning.

The role of roughage provision on the absorption and disposition of the mycotoxin deoxynivalenol and its acetylated derivatives in calves: from field observations to toxicokinetics.

A clinical case in Belgium demonstrated that feeding a feed concentrate containing considerable levels of deoxynivalenol (DON, 1.13mg/kg feed) induced severe liver failure in 2- to 3-month-old beef calves. Symptoms disappeared by replacing the highly contaminated corn and by stimulating ruminal development via roughage administration. A multi-mycotoxin contamination was demonstrated in feed samples collected at 15 different veal farms in Belgium. DON was most prevalent, contaminating 80% of the roughage samples (mixed straw and maize silage; average concentration in positives: 637 ± 621µg/kg, max. 1818µg/kg), and all feed concentrate samples (411 ± 156µg/kg, max. 693µg/kg). In order to evaluate the impact of roughage provision and its associated ruminal development on the gastro-intestinal absorption and biodegradation of DON and its acetylated derivatives (3- and 15-ADON) in calves, a toxicokinetic study was performed with two ruminating and two non-ruminating male calves. Animals received in succession a bolus of DON (120µg/kg bodyweight (BW)), 15-ADON (50µg/kg BW), and 3-ADON (25µg/kg) by intravenous (IV) injection or per os (PO) in a cross-over design. The absolute oral bioavailability of DON was much higher in non-ruminating calves (50.7 ± 33.0%) compared to ruminating calves (4.1 ± 4.5%). Immediately following exposure, 3- and 15-ADON were hydrolysed to DON in ruminating calves. DON and its acetylated metabolites were mainly metabolized to DON-3-glucuronide, however, also small amounts of DON-15-glucuronide were detected in urine. DON degradation to deepoxy-DON (DOM-1) was only observed to a relevant extent in ruminating calves. Consequently, toxicity of DON in calves is closely related to roughage provision and the associated stage of ruminal development.

Earthworms differentially modify the microbiome of arable soils varying in residue management

Earthworms are among the most important soil ecosystem engineers. Their effects on soil structure have been well documented, however, there is limited knowledge on how earthworms in the long term affect the soil microbiome, especially in arable soils. We investigated the soil microbiome of rice (cultivated under aerobic condition) and wheat fields in two consecutive seasons after manipulating earthworms and organic amendments for 14 years. Composition of soil prokaryotes and eukaryotes were analyzed by Illumina sequencing. Molecular network analysis suggest that in mulched rice fields earthworms foster species interlinked with many others and shift the dominance of prokaryotes from Planctomycetes to Proteobacteria. In contrast, in fields where residues were incorporated into the soil earthworms shifted the dominance of prokaryotes from Proteobacteria to Planctomycetes. Further, earthworms significantly increased the Proteobacteria-to-Acidobacteria ratio, a putative indicator of high nutrient turnover. Further, the ratio of prokaryote-to-eukaryote abundance was increased by earthworms when straw was incorporated into the soil. In conclusion, the results suggest that in the long term earthworms mainly modify the structure and functioning of prokaryote rather than eukaryote communities in arable fields. The effects of earthworms on the structure of microbial communities and microbial interactions are closely linked to resource management practices. The more pronounced effects of earthworms in treatments with residues mulched as compared to incorporated into the soil suggest that earthworm effects in part were due to bioturbation, i.e. mixing straw with mineral soil.

Optimization of acetyl xylan esterase gene expression in Trichoderma reesei and its application to improve the saccharification efficiency on different biomasses

Abstract Trichoderma reesei is an important microbe in biomass hydrolysis but is characterized by its inability to remove acetylated glucomannan. To improve the saccharification efficiency of T. reesei , an acetyl xylan esterase (AXE) gene from Aspergillus oryzae was successfully overexpressed by fusing with xynlanase 2 (Xyn2) from T. reesei as a carrier protein. The production of AXE in the selected transformant T2 was 11.04 U/ml, which was approximately 74% higher than that of the parent strain. The molecular mass of recombinant AXE (rAXE) on SDS-PAGE was about 35 kDa. The saccharification efficiency of rAXE from T. reesei Rut-C30 was better than that of the parent strain and resulted in approximately 23.2%, 22.7%, and 19.4% higher yield of reducing sugar in paddy straw, corn stover plus paddy straw mix (1:1 ratio), and corn stalk (delignified) hydrolysis, respectively. This result demonstrates that the expression of heterogenic accessory enzymes in T. reesei may be an alternative approach to improve the ability of the enzyme complex to decompose lignocellulose.

Feasibility of using straw in a strong, thin, pulp moulded packaging material

Packaging is a ubiquitous commodity that is being used in increasing quantities. This increased use has led to a problem with disposal, with increased quantities of used packaging being sent to landfill. One sustainable solution suggested is the use of biobased, biodegradable packaging. An example of this is paper based pulp moulded products which have been used previously for a number of packaging applications. In this paper the feasibility of replacing paper fibre with waste cereal straw fibre is examined. The aim was to produce materials that could be used to form flat, round trays, such as those used in supporting shrink wrapped food items. The material was required to have properties that matched existing alternatives, such as expanded polystyrene, in terms of physical and mechanical characteristics but with an enhanced level of biodegradability. The data showed that the pulp moulded material containing up to 80% straw performed significantly better compared to expanded polystyrene in tensile properties (modulus of 0.47MPa for an 80% straw mix compared to 0.16MPa for EPS). Modulus under bending was shown to be lower for straw based materials compared to EPS (0.015MPa compare to 0.035MPa). Adjustments in product thickness allowed performance parameters to be met. Wet end addition of chemicals was successfully used to provide water resistance without affecting other variables. In addition to exhibiting good performance characteristics the pulp moulded material was shown to be biodegradable, exhibiting 20% mass loss after only 4 weeks covered in unsterile soil.

Evaluation of Mechanical Parameters of Pellets

The paper dealt with the evaluation of mechanical properties of the cylinder wheat straw, rapeseed straw and 50/50 % mixed wheat and rapeseed straw pellet samples. The pellets were made by the granulating machine MGL 200 (Kovonovak). The compressive loading curves of dependencies of stress on strain were realised by the test stand Andilog Stentor 1000 (Andilog Technologies, Vitrolles, France). Certain mechanical parameters were determined, namely the initial force (force at 10 % of compress strain), force in maximum of loading curve, strain in maximum of loading curve, initial stress (stress at 10 % of compression strain), stress in maximum of loading curve and modulus of elasticity. Mean value of the initial force was maximal for mixed straw pellet samples 52.49 N. Mean values of the initial force of the wheat straw samples and the rapeseed straw samples were smaller and almost identical 43.58 N and 43.12 N. Mean values of the initial stress of loading curve, of the wheat straw samples reached 1.46 MPa, the rapeseed straw samples reached value 1.40 MPa and the mixed straw samples reached value 1.63 MPa. Mean value of the force in maximum of loading curve was also maximal for mixed straw pellet samples 213.26 N. Mean values of the force in maximum of loading curve of the wheat straw samples reached 178.11 N. The rapeseed straw samples reached value 95.95 N and the mixed straw samples reached value 213.26 N. Mean values of the stress in maximum of loading curve, of the wheat straw samples reached 5.93 MPa, the rapeseed straw samples reached value 3.11 MPa and the mixed straw samples reached value 7.10 MPa Mean values of the modulus of elasticity, of the wheat straw samples reached 18.27 MPa, the rapeseed straw samples reached value 13.08 MPa and the mixed straw samples reached value 14.97 MPa. Significant correlations of the mechanical parameters pellet samples were observed among initial force and initial stress and modulus of elasticity. Significant correlations of force in maximum with stress and strain in the maximum were observed.

Simulation of accumulation and mineralization (CO2 release) of organic carbon in chernozem under different straw return ways after corn harvesting

Straw return is the main way of fertility improvement of cultivated chernozem in Songnen Plain of Northeast China. To reveal the effect of “corn straw return mixed with soil or ploughing” (“straw mixing” for short) and “corn straw return to the surface of soil” (“straw mulching” for short) on fertility and environment of soil, we focused on the effects of different straw applications on the release of CO2 and accumulation of soil organic carbon. A laboratory simulative incubation experiment was conducted with chernozem, and corn stalk. Under the constant condition of 28°C, all curves of the emission rate of CO2 had appeared a peak of the emission of CO2 on the 4th or 6th day of the culture, and then stepped into the first slow emission platform on the 13th–52nd day and stepped into the second slow emission platform on the 52nd–91st day. With the same amount of straw, the peak value of CO2 emission rate of “straw mixing” (23.00, 43.64, 79.70mgkg−1d−1 for straw 2%, 4%, and 6%, respectively) was apparently greater than that of “straw mulching” (22.94, 39.76, 58.71mgkg−1d−1 for straw 2%, 4%, and 6%, respectively). However, after entering the slow emission platform, the average emission rate of CO2 of “straw mixing” would be less than that of “straw mulching”. There was an apparent intersection point (about 31d for straw 2%, 4% and 47d for straw 6%) on the curves of both the CO2 emission rate of “straw mixing” and “straw mulching”. Before the intersection point, the accumulated amount of CO2–C emission of “straw mixing” was greater than that of “straw mulching” and then lower than that of “straw mulching” gradually after the point. The analysis of the result about the soil organic carbon and the composition of micro-aggregate showed that with the same amount of straw addition, “straw mixing” could increase soil organic content and improve the composition of micro-aggregate better than “straw mulching”. The results indicated that it might have a better effect on fertility and environment of soil than the return of straw for surface of soil if the means of ploughing in autumn and rotary tillage, etc. could be used in the process of the returning of straw mixed with soil or cultivation.

Effects of Nitrogen Fertilizer and Planting Density on Yield Loss Percentage of Mechanical Harvesting in Rapeseed

In this study, Huayouza 62 was planted by direct-seeding with three nitrogen(N) fertilizer levels(120, 180, and 240 kg N ha–1) and three planting densities(15×104, 30×104, and 45×104 plant ha–1). The yield loss percentages of mechanical harvesting were investigated when the moisture contents in seeds ranged from 10.86% to13.17%. The results showed the total yield loss percentage was from 6.13% to 7.82% in different treatments. There existed differences in the ratio of the yield loss in different parts to the total yield loss. The ratio of the yield loss caused by shattering(SL) to the total yield loss was the least in different treatments, ranging from 2.41% to 3.90%. The ratio of the yield loss caused by combine header(CHL) to the total yield loss ranged from 17.99% to 21.99%. The ratio of the yield loss caused by cleaning and threshing(CTL) to the total yield loss ranged from 74.15% to 79.52%, among which the yield loss caused by mixed straw and shell(ML) was the main part(from 65.51% to 69.05%), and the yield loss caused by non-threshing pod(NTPL) was low with the range from 8.64% to 10.47%. The plot yield increased with increasing N application rates and planting densities. The total yield loss percentage had extremely significantly positive correlation with plot yield(r = 0.970**) and N fertilizer(r = 0.918**), and no significant correction with planting density(r = 0.358). The results of this study indicated that in the rapeseed mechanical production, appropriate N fertilizer and planting density should be applied for high yield, and then the yield loss percentage should be reduced on the basis of high yield.

Effect of integrating straw into agricultural soils on soil infiltration and evaporation

Soil water movement is a critical consideration for crop yield in straw-integrated fields. This study used an indoor soil column experiment to determine soil infiltration and evaporation characteristics in three forms of direct straw-integrated soils (straw mulching, straw mixing and straw inter-layering). Straw mulching is covering the land surface with straw. Straw mixing is mixing straw with the top 10 cm surface soil. Then straw inter-layering is placing straw at the 20 cm soil depth. There are generally good correlations among the mulch integration methods at p < 0.05, and with average errors/biases <10%. Straw mixing exhibited the best effect in terms of soil infiltration, followed by straw mulching. Due to over-burden weight-compaction effect, straw inter-layering somehow retarded soil infiltration. In terms of soil water evaporation, straw mulching exhibited the best effect. This was followed by straw mixing and then straw inter-layering. Straw inter-layering could have a long-lasting positive effect on soil evaporation as it limited the evaporative consumption of deep soil water. The responses of the direct straw integration modes to soil infiltration and evaporation could lay the basis for developing efficient water-conservation strategies. This is especially useful for water-scarce agricultural regions such as the arid/semi-arid regions of China.

Effects of partial replacement of barley with sugar beet pulp on pre- and post-partum performance of Zel ewes

Sixteen Zel ewes (BW = 37 ± 3.10 kg) were used in a completely randomized design to determine the effects of partial replacement of barley grain with beet pulp (BP), during late pregnancy and early lactation, on litter weight, lamb’s daily gain, milk yield and milk composition. Dietary treatments were initiated approximately three weeks prior to expected lambing dates, and continued for three weeks post-partum. Treatments consisted of 1) a basal diet + 330 g/kg of barley grain (BBG), and 2) a basal diet + 195 g/kg of barley + 135 g/kg BP (BBP). The basal diet contained 444, 117, 101 and 8 g/kg of wheat straw, wheat bran, canola meal and mineral-vitamin mix supplement, respectively. Both diets were offered as a total mixed ration twice daily. Partial replacement of BP increased feed intake. Diets did not affect milk compositions but feeding BBP increased milk yield (1084 vs. 737 g/d), litter weight (3453 vs. 2735 g) and lambs’ daily gain (218 vs. 156 g/d). The lambs’ live weight at 14 d (5992 vs. 4749 g) and 21 d (7553 vs. 5854 g) was affected by maternal nutrition and a higher BBP. The results of this study indicate that late gestation and early lactation ewes can be supplemented with BP without detrimental effects on milk production or milk composition, and feeding ewes with BP during this period resulted in increased litter weight and growth of lambs.

Compost: A Potential Value-Added Product for Dairy Operations?

The objective of this study was to evaluate the composting potential of various bedding materials that were previously used in experimental compost bedded packs for dairy cows. Each material was placed in windrows (1.8 m high, 9.1 m long, and 2.3 m wide) from April 2007 to September 2007 and managed as needed to promote composting. Materials included: sawdust (SD) (control), corn cobs (CC), wood chip fines/sawdust mix (WC/SD), soybean straw (SS), wood chip fines/soybean straw mix (WC/SS), and soybean straw/sawdust mix (SS/SD). Replicated samples were taken weekly and analyzed for dry matter (DM). Carbon:nitrogen ratio (C:N ratio), pH, total C, total N, NH4-N, and NO3-N were measured once monthly. Temperature was measured twice weekly. Total P, total K, and EC were measured at the beginning and end of the composting period. Windrow temperatures exceeded 55°C for 10 to 96 days, and coliform populations were reduced from 106 or 107 to 500 cfu/mL or fewer in all materials. CC, SS/WC, WC/SS, and SS were the only materials that decreased (P < 0.05) in moisture content from day 0 to day 138. Materials were similar when comparing day 0 and day 138 for NH4-N, total N, and inorganic N concentrations. SS, SS/SD, WC/SS, and WC/SD all decreased in total C and C:N ratio(P < 0.05) from day 0 to day 138. C:N ratios were below 20:1 at the end of the composting period, with the exception of SD and WC/SD. Based on these results, all materials composted during the time period and would potentially work as a soil amendment/mulch if proper composting takes place.

Heavy metals removal from mine runoff using compost bioreactors

Permeable bioreactors have gained both research and management attention as viable methods for treating mine runoff waters. We examined the operation of a field‐scale bioreactor (containing mixed compost, straw and gravel) for treatment of runoff from the Mother Load (ML) mine in northern Idaho, U.S. and compared it to an experimental laboratory‐scale reactor, containing a similar matrix and treating similar mine runoff water. In general both reactors were efficient in removing most of the metals assayed, Al, As, Cd, Fe, Ni, Pb and Zn, with the exception of Mn. Both systems showed evidence of bacterial‐mediated sulphate reduction and concomitant metal sulphide complexes. However, the experimental laboratory bioreactor showed greater proportions of immobile metals reductions than did the ML bioreactor, presumably due to the greater action of sulphate‐reducing bacteria. The major metal removal mechanism in the ML bioreactor was surmised to be adsorption. Differences in metal removal mechanisms between the reactors were hypothesized to be due to fluctuating hydraulic residence times at the ML site, in turn, due to unregulated runoff flow.

Hydraulic Properties of Soil-Straw Mixtures

Crop residue management at the soil surface controls C sequestration and soil erosion. The size and distribution of crop residues incorporated into the topsoil affect soil physical properties. The objective of this work was to analyze the immediate effect of straw incorporation on the hydraulic properties of soil. Laboratory experiments were performed to determine the retention and the hydraulic conductivity curves of soil and wheat (Triticum aestivum L.) straw mixtures. The samples consisted of 1-cm straw pieces mixed with loamy soil aggregates of 2 to 3 mm in diameter. Volumetric straw contents were 0, 0.1, 0.2, and 0.3 cm3 cm−3 Suction table and pressure extractor methods were used to measure the water retention curve. Hydraulic conductivity curves were obtained using Wind's evaporation method. At a constant water pressure head, gravimetric water content increased with increasing straw content. The relationship between water pressure and volumetric water content did not differ significantly between the treatments. An additive model based on the sum of the water retention of straw and soil measured separately gave a good estimation of the water retention measured in the mixture. Hydraulic conductivity decreased with increasing straw content for the same water pressure head. Tomographic images showed that mixing straw into the soil created new pores in the samples. Results from simulations of straw decomposition indicated that (i) the uptake of water by straw has to be taken into account when calculating how much water should be added gravimetrically in an incubation experiment and (ii) changes in hydraulic conductivity due to the presence of straw can have an impact on water and C dynamics.

Hydraulic Properties of Soil–Straw Mixtures

Crop residue management at the soil surface controls C sequestration and soil erosion. The size and distribution of crop residues incorporated into the topsoil affect soil physical properties. The objective of this work was to analyze the immediate effect of straw incorporation on the hydraulic properties of soil. Laboratory experiments were performed to determine the retention and the hydraulic conductivity curves of soil and wheat (Triticum aestivum L.) straw mixtures. The samples consisted of 1‐cm straw pieces mixed with loamy soil aggregates of 2 to 3 mm in diameter. Volumetric straw contents were 0, 0.1, 0.2, and 0.3 cm3 cm−3 Suction table and pressure extractor methods were used to measure the water retention curve. Hydraulic conductivity curves were obtained using Wind's evaporation method. At a constant water pressure head, gravimetric water content increased with increasing straw content. The relationship between water pressure and volumetric water content did not differ significantly between the treatments. An additive model based on the sum of the water retention of straw and soil measured separately gave a good estimation of the water retention measured in the mixture. Hydraulic conductivity decreased with increasing straw content for the same water pressure head. Tomographic images showed that mixing straw into the soil created new pores in the samples. Results from simulations of straw decomposition indicated that (i) the uptake of water by straw has to be taken into account when calculating how much water should be added gravimetrically in an incubation experiment and (ii) changes in hydraulic conductivity due to the presence of straw can have an impact on water and C dynamics.