Poultry litter and tillage influences on corn production and soil nutrients in a Kentucky silt loam soil

Broiler chicken (Gallus gallus) manure, a rich source of plant nutrients, is generated in large quantities in southeastern USA where many row crops, such as corn (Zea mays L.), are also extensively grown. However, the use of broiler manure as an economical alternative source of nutrients for corn production has not been extensively explored in this region. This study was conducted to examine the use of broiler litter as a source of nutrients for corn production, as influenced by tillage and litter rate, and any residual effects following application. In addition, the consequence of litter application to soil test nutrient levels, particularly P, Zn and Cu, was explored. The treatments consisted of two rates of broiler litter application, 11 and 22 Mg ha⁻¹ on a wet weight basis, and one rate of chemical fertilizer applied under no-till and conventional tillage systems. Treatments were replicated three times in a randomized complete block design. Corn was grown with broiler litter and inorganic fertilizer applied to the same plots each year from 1998 to 2001. In 2002 and 2003, corn was planted no-till, but only N fertilizer was applied in order to make use of other residual litter nutrients. Soil samples were taken yearly in the spring prior to litter application and 4 years after the cessation of litter application to evaluate the status of the residual nutrients in soil. Two years out of the 4-year experiment, broiler litter application produced significantly greater corn grain yield than equivalent chemical fertilizer application and produced similar grain yield in the other 2 years. Corn grain yield was significantly greater under no-till in 1999, but significantly greater under conventional-till in 2000, and no difference between the two tillage systems were observed in 1998 and 2001. With 4 years of litter application, Mehlich-3 P increased from an initial 18 mg kg⁻¹ to 156 mg kg⁻¹ with 11 Mg ha⁻¹ litter and to 257 mg kg⁻¹ with 22 Mg ha⁻¹ litter. For every 6 kg ha⁻¹ of P applied in poultry litter Mehlich-3 P was increased by 1 mg kg⁻¹. Modest increases in Mehlich-3 Cu and Zn did not result in phytotoxic levels. This study indicated that an optimum rate of broiler litter as a primary fertilizer at 11 Mg ha⁻¹ applied in 4 consecutive years on a silt loam soil produced corn grain yields similar to chemical fertilizer under both no-till and conventional tillage systems and kept soil test P, Cu and Zn levels below values considered to be harmful to surface water quality or the crop.     

Phosphatase activities in soil after repeated untreated and alum-treated poultry litter applications

Repeated additions of untreated and aluminum sulfate (alum)-treated poultry litter to soil affect ecology and consequent nutrient dynamics. The objective of this study was to determine how repeated annual poultry litter additions affected phosphatase activities in concert with changes in soil phosphorus (P). Field plots were amended annually since 1995 with either 2.24 or 8.96 Mg ha⁻¹ alum-treated (AL-1 or AL-4, respectively) or untreated poultry litter (PL-1 or PL-4, respectively) or equivalent rates by N content of ammonium nitrate (AN-1 or AN-4, respectively). Soil pH, total C (C_Tot), microbial biomass C, double-stranded deoxyribonucleic acid (dsDNA), Mehlich-III P (M3P), water-soluble P (WSP), and acid and alkaline phosphatase activities were measured before and 10 days, 1 month, and 6 months after fertilizer applications in 2003 and 2004. M3P and acid phosphatase activities were higher in AL-4 soil than in all other treatments. Higher WSP in the untreated compared to the alum-treated litter resulted in higher WSP in the soil amended with untreated litter. At the same time, alkaline phosphatase activities were significantly higher in PL-4 compared to AL-4. In contrast, alkaline phosphatase activities were significantly lower in AN-4, the treatment with the lowest pH. Additionally, alkaline phosphatase activities expressed per unit C_Tot or dsDNA remained significantly greater in PL-4 and significantly lower in AN-4, than all other treatments. Thus, some factor beyond an increase in soil C or microbial biomass contributed to elevated alkaline phosphatase activities in PL-4, despite increased WSP in the treatment receiving the high rate of untreated litter.     

Soil compaction and poultry litter effects on factors affecting nitrogen availability in a claypan soil

Soil compaction may affect N mineralization and the subsequent fate of N in agroecosystems. Laboratory incubation and field experiments were conducted to determine the effects of surface soil compaction on soil N mineralization in a claypan soil amended with poultry litter (i.e., Turkey excrement mixed with pine shavings as bedding). In a laboratory study, soil from the surface horizon of a Mexico silt loam soil was compacted to four bulk density levels (1.2, 1.4, 1.6 and 1.8 Mg m⁻³) with and without poultry litter and incubated at 25 °C for 42 days. A field trial planted to corn (Zea mays L.) was also conducted in 2002 on a Mexico silt loam claypan soil in North Central Missouri. Soil was amended with litter (0 and 19 Mg ha⁻¹) and left uncompacted or uniformly compacted. Soil compaction decreased soil inorganic N by a maximum of 1.8 times in the laboratory study; this effect was also observed at all depths of the field trial. Compacted soil with a litter amendment accumulated NH₄⁺-N up to 7.2 times higher than the noncompacted, litter-amended soil until Day 28 of the laboratory incubation and in the beginning of the growing season of the field study. Ammonium accumulation may have been due to decreased soil aeration under compacted conditions. Application of litter increased soil N mineralization throughout the growing season. In the laboratory study, soil inorganic N in unamended soil was negatively correlated with soil bulk density and the proportion of soil micropores, but was positively related with soil total porosity and the proportion of soil macropores. These results indicate that soil compaction, litter application and climate are interrelated in their influences on soil N mineralization in agroecosystems.     

Soil fungal population levels in cotton fields fertilized with poultry litter and their relationships to soil nutrient concentrations and plant growth parameters

Application to land of large quantities of waste materials from concentrated animal production, without causing environmental pollution, presents a major challenge to agriculture in the 21st century. Effects of land-applied animal wastes on chemical contents of soil are well documented, but less is understood of their effects on microbial populations in soil. This study was undertaken to evaluate effects of commercial application of poultry litter (PL), as a fertilizer, on soil fungal population levels and components on cotton farms in Mississippi, and to determine relationships of fungal population levels to soil nutrient contents and cotton growth and yield. On each of two farms, soil fungal population levels were estimated by dilution plating from samples of soil collected at two sampling times during 2 years from replicated plots of four fertilization treatments: 0 fertilizer, conventional mineral fertilizer (CF), low PL, and high PL. Soil fungal population levels differed significantly (P = 0.05) according to years or seasons and fertilization treatments on both farms. Population levels often were higher in soils amended with low or high PL, or with CF, than in unfertilized controls. On one farm where PL was tilled into soil, fungal population levels increased significantly during the course of the experiment in PL and CF treatments, but not in unfertilized controls, as determined by linear regression. No such increases were observed on the second farm where PL was applied no-till. Population levels of Fusarium semitectum and Penicillium purpurogenum were significantly higher in PL-treated soils than in unfertilized controls in 1 or 2 of 4 sampling events at both farms, while levels of four other species or groups of fungi usually did not differ. Fungal population levels were significantly correlated (P = 0.05) with N concentrations of soils in 1–4 sampling events on each farm and less frequently correlated with concentrations of nine other elements. In 4 of 24 instances, soil fungal population levels were significantly correlated with leaf area index, chlorophyll content, or yield of cotton, and correlation coefficients with these plant parameters were always positive. Major conclusions derived from this study are (1) no deleterious effects on population levels of total or select soil fungi were observed with use of PL as a fertilizer for commercial cotton production; and (2) soil fungal population levels may increase over time in association with greater fertility and plant growth that is induced by both mineral fertilizer and PL applications.     

黄土丘陵沟壑区枯枝落叶层和土壤的光谱差异特征分析

枯枝落叶层在植被防止土壤侵蚀的功效中发挥着主导作用,枯落层的光谱特征分析将为遥感估算枯落层盖度提供重要依据。该文利用陕北延河流域典型植被群落土壤和枯落层样本的光谱测试数据,分析土壤和枯落层在在可见光-近红外波段(400~1 100 nm)和短波红外波段(1 100~2 500μm)的光谱差异特征及主要影响因素,并进一步评价归一化植被指数(NDVI,normalized difference vegetation index)和归一化衰败植被指数(NDSVI,normalized difference senescent vegetation index)、归一化差值耕作指数(NDTI,normalized difference tillage index)、纤维素吸收指数(CAI,cellulose absorption index)等植被指数区分土壤和枯落层的有效性。结果表明,在可见光-近红外波段土壤和枯落层的反射光谱特征相似,两者难以区分,但在短波红外波段的1 700和2 100 nm处因枯落层具有纤维素吸收特征而与土壤存在差异。含水量对土壤和枯落层反射光谱特征的影响强烈,水分的存在降低了土壤和枯落层在整个光谱范围的差异性。光谱空间中枯落线和土壤线的关系表明,NDVI指数难以反映土壤和枯落层的光谱差异特征;由于宽波段的影响,利用多光谱指数NDSVI和NDTI表征枯落层信息具有一定的局限性;高光谱指数CAI利用了枯落层与土壤在2 100 nm处的差异特征,能够较好地区分出土壤与枯落层,该研究为利用遥感技术有效提取枯落层等衰败植被信息提供了新的途径。     

Predicting soil erosion in conservation tillage cotton production systems using the revised universal soil loss equation (RUSLE)

Despite being one of the most profitable crops for the southeastern USA, cotton (Gossypium hirsutum L.) is considered to create a greater soil erosion hazard than other annual crops such as corn (Zea mays L.) and soybeans (Glycine max (L.) Merr.). Reduced tillage systems and cover cropping can reduce soil erosion and leaching of nutrients into ground water. The objectives of this study, which was conducted in north Alabama from 1996 to 1998, were to assess the impact of no-till and mulch-till systems with a winter rye (Secale cereale L.) cover crop and poultry litter on soil erosion estimates in cotton plots using the revised universal soil loss equation (RUSLE). Soil erosion estimates in conventional till plots with or without a winter rye cover crop and ammonium nitrate fertilizer were double the 11 t ha⁻¹ yr⁻¹ tolerance level for the Decatur series soils. However, using poultry litter as the N source (100 kg N ha⁻¹) gave soil erosion estimates about 50% below the tolerance level under conventional till. Doubling the N rate through poultry litter to 200 kg N ha⁻¹ under no-till system gave the lowest soil erosion estimate level. No-till and mulch-till gave erosion estimates which were about 50% of the tolerance level with or without cover cropping or N fertilization. This study shows that no-till and mulch-till systems with cover cropping and poultry litter can reduce soil erosion in addition to increasing cotton growth and lint yields, and thus improve sustainability of cotton soils in the southeastern USA.     

Influence of beech litter fragmentation and glucose concentration on the microbial biomass in three different litter layers of a beechwood

In February 1993 samples of litter from three different litter layers (upper, intermediate, and lower) were taken from a beechwood growing on basalt soil. Using the substrate-induced respiration method, we investigated the influence of fragmentation and glucose concentration on the maximum initial respiratory response. Glucose concentrations ranged between 0 and 160000 g g^-1 dry weight. The initial respiratory response reached a maximum at 80000 g glucose g^-1 dry weight. The addition of higher concentrations of glucose resulted in negligible changes in respiration. Litter materials of four different size classes (intact leaves, fragmented <100 mm², <25 mm², and <5 mm²) were amended with 80000 g glucose g^-1 dry weight. Substrate-induced respiration was at a maximum in the size class <25 mm². The addition of glucose to intact litter did not result in microbial growth. It is concluded that C is not the primary limiting element for the microflora in litter layers of the study site. Fragmentation of beech litter enabled the microorganisms to grow. Presumably, nutrients that limited microbial growth in intact litter were mobilized by the fragmentation procedure and enabled microorganisms to grow in fragmented litter materials.     

Phosphorus and trace metal dynamics in soils amended with poultry litter and granulates

Environmental sustainability of animal agriculture is strongly dependent upon development of approaches to minimize the potential environmental impacts of applying animal manures. The excess manure and its nutrients (primarily phosphorus) in intensive animal production regions may need to be exported to other areas to comply with increased regulations on manure management. In our previous study we generated a variety of granulated products from poultry litter to achieve export of excess litter from the southwestern Ozarks, AR, USA. Our objective in the present study was to determine the effect of the application of poultry litter and granulated litter products on phosphorus (P), arsenic (As), copper (Cu) and zinc (Zn) dynamics in two Arkansas soils (Dewitt silt loam and Hector sandy loam). Poultry litter and granulated products were mixed with the surface horizon (0–15 cm) of soils at two application rates: P‐based (100 kg total P per hectare) and N‐based (160 kg plant‐available N per hectare). Soil–litter mixtures were incubated at 25 °C for 21 days. Sub‐samples were removed at 1, 7 and 21 days to determine the solubility and availability of P, As, Cu and Zn in soils. Results suggest that when litter was applied at 100 kg total P per hectare, contents of P, As, Cu and Zn were significantly greater in the soils amended with litter and granulated products than in the control (soil alone). However, the contents of P, As, Cu and Zn did not significantly differ in the soils amended with either normal litter or granulated litter products at total P or plant‐available N‐based application rates. This suggests that poultry litter granulation is a sound management practice that can be used to reduce concerns with fresh litter transport and potentially improve P and trace element balances in intensive poultry production regions, especially when applied on a plant‐available N basis.     

Influence of leaf litter types on microbial functions and nutrient status of soil: Ecological suitability of forest trees for afforestation in tropical laterite wastelands

The impact of forest tree leaf litters on microbial activity and nutrient status of red laterite soil was tested for the ecological suitability of Cassia siamea, Shorea robusta, Acacia auriculiformes and Dalbergia sissoo, which are typically used for afforestation of wastelands in eastern India. The objectives were to compare seasonal variation in soil enzyme activity in 30-years old afforested sites, and to study nutrient status and microbial biomass and function during short-term in-situ incubation of litter in decomposition pits. In afforested soils, enzyme activities significantly varied between litters and seasons. All enzyme activity except invertase dominated in the soils containing Dalbergia and Cassia litters compared to the others. The seasonal effect was enzyme-dependent, with amylase and cellulase reaching peaks during the rainy season but invertase activity showed a reverse trend with lowest values in rainy season, except in Acacia soil, and protease activity was lowest in the soil containing Cassia and Dalbergia during the rainy season. Dehydrogenase activity was negligible in the soils containing Shorea and Acacia, but remained high with respect to Dalbergia and Cassia during all seasons. The decomposition pit study showed significant increase of soil nutrients with respect to litter types and intervals, except with respect to electrical conductivity. Cassia and Dalbergia litters enabled notable increase of soil nutrients than Shorea and Acacia. The soil enzyme activity, in general, increased with duration of litter decay, but microbial biomass C (MBC) decreased over time except in Shorea. Therefore, the enzyme rates normalized to the MBC indicated inverse relations for all enzymes, except in the soil containing Shorea. A positive relationship existed between MBC and soil respiration in Cassia, Acacia and Dalbergia. Analysis of variance revealed main effects of litter types for increasing protease, MBC and CO₂ output, and a main effect of intervals for enhancing enzymes other than cellulase. Rates of soil respiration were greater in soils contain Cassia and Dalbergia, and showed significant differences between litters and between intervals. All enzymes were significantly correlated with electrical conductivity, organic carbon and available phosphorus contents, and all enzymes except invertase were correlated with nitrate concentrations. The acidic soil pH did not affect enzyme activities, and soil nutrients exerted only weak effect on MBC and respiration. Our study showed that leaf litters of Cassia and Dalbergia trees improved the nutrient status and microbial activity in soil more so than Shorea and Acacia litters, and therefore, afforestation using Cassia and Dalbergia trees may be particularly suitable for soil restoration in tropical laterite wastelands.     

Photoacceleration of plant litter decomposition in an arid environment

In arid ecosystems, abiotic processes facilitate the physical and chemical degradation of plant litter to the extent that decomposition models that use climatic and litter composition variables as surrogates for microbial activity are not predictive. The purpose of this study was to estimate the potential contribution of photodegradation to the decomposition of plant litters that varies in architecture and chemical composition. Litter of Pinus edulis, Juniperus monosperma and Populus deltoides were exposed to ambient and attenuated sunlight, with and without supplemental water additions, at a riparian forest site along the Middle Rio Grande (New Mexico, USA). Mass loss, elemental composition, and microbial extracellular enzyme activities (EEA) were measured over 639 days. The composition of the fungal communities associated with the decomposing litters was compared by analyses of fungal ITS nrDNA sequences. Litter exposed to ambient sunlight had greater mass loss rates than shaded litter, independent of the water treatment: Populus increased by 100%, Pinus by 86% and Juniperus by 46%. The increases were proportional to exposed litter surface area per g dry mass. EEA potentials, particularly oxidative activities, were low in comparison to those measured in mesic ecosystems. For Populus litter, the principal driver of photoacceleration appeared to be photodegradation of cellulose; for Pinus, it was photodegradation of polyphenols; for Juniperus accelerated mass loss was associated with photodegradation of both polysaccharides and polyphenols. Fungal community composition varied by litter type, but the dominant colonizers were yeasts and dark-septate hyphal taxa; a finding consistent with the low enzymatic oxidation potential. This study shows that photochemical oxidation can supplement enzymatic oxidation and increase decomposition rates. As a result, organic matter decomposition in arid ecosystems is not restricted to periods of high moisture availability as is plant production. This decoupling may partly account for the low soil organic matter content of these ecosystems.     

Do plant species encourage soil biota that specialise in the rapid decomposition of their litter?

Plants are often nutrient limited and soil organisms are important in mediating nutrient availability to plants. Thus, there may be a selective advantage to plants that alter the soil community in ways that enhance the decomposition of their litter and, hence, their ability to access nutrients. We incubated litter from three tree species (Fagus sylvatica, Acer pseudoplatanus and Picea sitchensis) in the presence of biota extracted from soil beneath a stand of each species to test the hypothesis that litter decomposes fastest in the presence of biota derived from soil where that species is locally abundant. We found that respiration rate, a measure of decomposer activity and carbon mineralisation, was affected by litter type and source of soil biota, whereas, mass loss was only affected by litter type. However, litter from each tree species did not decompose faster in the presence of indigenous soil biota. These findings, therefore, provide no support for the notion that woodland plants encourage the development of soil communities that rapidly decompose their litter.     

Effects of soil invertebrates on the survival of some genetically engineered bacteria in leaf litter and soil

Seven bacterial strains, most of them bearing natural or recombinant plasmids, were introduced in oak leaf litter or soddy-podzolic soil. In these substrata, which contained litter-dwelling diplopods and isopods, or endogenic earthworms, bacteria survival was followed. In the absence of the animals, the numbers of introduced strains gradually decreased. In the presence of the animals, plasmid-bearing strains of Pseudomonas putida survived at 10⁵–10⁷ CFUs g^-1 up to 1.5 months in both leaves and soil. The total numbers of bacteria found in excrements from the soil macrofauna were 5–15 times higher than in the food. The numbers of P. putida in the excrements were equal to or higher than in the food. The numbers of Pseudomonas stutzeri JM302 (pLV1013) and Azospirillum brasiliense ATCC29710 (pFACII) in the excrements were always 2–10 times lower than in the food. The digestive fluid taken from the middle part of the gut of the diplopod Pachyiulus flavipes showed a strong antibacterial activity. Those bacteria with lower survival in the gut appeared to be more sensitive to digestion by the midgut fluid. In contrast, the hindgut fluid did not suppress the viability of P. stutzeri JM302 (pLV1013). We postulate that the introduced bacteria partially survive the midgut passage and then multiply with a high growth rate in the hindgut of the animals. The environmental consequences of the interactions between soil invertebrates and the released bacteria are discussed.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

Correlation between earthworms and plant litter decomposition in a tropical wet forest of Puerto Rico

Earthworms are recognized to play an important role in the decomposition of organic materials. To test the use of earthworms as an indicator of plant litter decomposition, we examined the abundance and biomass of earthworms in relation to plant litter decomposition in a tropical wet forest of Puerto Rico. We collected earthworms at 0–0.1 m and 0.1–0.25 m soil depths from upland and riparian sites that represent the natural variation in soils and decomposition rates within the forest. Earthworms were hand-sorted and weighed for both fresh and dry biomass. Earthworms were dominated by the exotic endogeic species Pontoscolex corethrurus Müller; they were more abundant, and had higher biomasses in the upland than in riparian sites of the forest. Plant leaf litter decomposed faster in the upland than riparian sites. We found that earthworm abundance in the upper 0.1 m of the soil profile positively correlated with decomposition rate of plant leaf litter. Ground litter removal had no effect on the abundance or biomass of endogeic earthworms. Our data suggest that earthworms can be used to predict decomposition rates of plant litter in the tropical wet forest, and that the decomposition of aboveground plant litter has little influence on the abundance and biomass of endogeic earthworms.     

Effect of plant litter addition on element leaching in young sandy soils

The knowledge about element leaching and biogeochemical cycles during initial stages of soil development is very limited. Therefore, we studied the effects of parent material characteristics and plant litter addition on element leaching from young sandy soils in a microcosm experiment. Our objective was to evaluate the function of young soils as a source and/or sink for nutrients during initial pedogenesis and to identify main processes which are involved in the initial development of biogeochemical cycles. The main research questions were: (1) How do differences in parent material characteristics affect nutrient leaching?; and (2) How is nutrient leaching of young soils influenced by litter addition of different plant functional groups (e.g., legume and grass species)? Combined treatments of two minimally weathered parent materials (pure sand and loamy sand) with plant litter of two plant species (Lotus corniculatus L. and Calamagrostis epigejos L.) were investigated in a soil column experiment. In addition, control columns with parent material or plant litter only were included. Carbonate weathering as a main source for calcium leaching was induced by the moderately acidic irrigation solution used in the experiment. It was 7.5 fold greater for the loamy sand parent material compared to the pure sand despite lower carbonate contents in the loamy sand. Leaching of K was very low for both parent materials but greater for the loamy sand parent material, likely due to transfer processes from fixed to exchangeable potassium forms in the clay minerals of the loamy sand. Plant litter addition generally increased leaching losses. Carbonate dissolution was intensified by both plant litter types, especially by L. corniculatus, very likely due to H⁺ released during nitrification of N released from plant litter and an increase in partial pressure of CO₂ from microbial respiration. In contrast, K was largely retained in the soils, probably due to fixation by clay minerals and microbial immobilization. Only the pure sand treated with L. corniculatus litter leached K, resulting in 4–6 fold greater leaching losses compared to all other treatments. Nitrogen released from L. corniculatus litter was almost completely nitrified and was nearly doubled as compared to that from C. epigejos, resulting in greater N leaching. The results of our study allow identifying the general function and processes of vegetation patches in young ecosystems formed as a result of initial parent material characteristics and invading vegetation with respect to litter decomposition, soil solution composition, nutrient retention and leaching, and effects on the soil mineral phase. These patterns are not mere additive effects of parent materials plus plant litter, but reflect differences in biogeochemical process intensities and could result in an increasing heterogeneity of soil properties, nutrient availability, and element leaching fluxes with time.     

Nitrogen addition change soil N pools with litter removal or not in subtropical forest

ABSTRACT

There are many nitrogen (N) pools in soil, so their availability and different status can give information about bulk soil response to N deposition. However, the different size of N pools in forest soils and the relationship between them have not been well studied under N deposition when considering the role of litter. Here soil in an N-deposition experiment carried out for 5 years in a broad-leaved forest was used as an object to study the response of N pools to N deposition by stepwise extraction using water or solutions containing 0.5 M K₂SO₄, 2.5 M H₂SO₄ (LPI), or 13 M H₂SO₄ (LPII), and calculation of recalcitrant (RC) N pool. Under N control (CT), soil with the presence of litter had a higher N of 23.8–106.8% in the first four pools, but lower of 80.6% in recalcitrant N pool compared with soil with the absence of litter. In the absence of litter, N addition increased soil N in labile pool but decreased N in the RC pool compared to CT and these impacts were greater at high added N (HN) than low-added N (LN) rates. However, in the presence of litter, LN increased the amount of N in the K₂SO₄- extracted pool and HN reduced that in the water extracted pool. Additionally, LN and HN increased TN in the RC pool and HN increased the total soluble N (TSN) in the LPI and LPII pool. N changes in the water extraction pool were attributed to inorganic N, whereas they were NH₄ ⁺ and soluble organic N (SON) in the K₂SO₄-extracted, LPI, and LPII pools. In the presence of litter, HN increased the SON concentration in the K₂SO₄, LPI, and LPII extractions; thus, SON may be a potentially important N form for N availability. These results suggested that N additions improve the accumulation of N in RC pool with the presence of litter. The different effects of N additions on soil N pool or N form in each pool depend on litter present or not.     

Stabilisation of soil organic matter in invertebrate faecal pellets through leaf litter grazing

Soils were amended with either leaf litter or faeces from pill millipedes fed on the leaf litter, then incubated at 20 °C for 130 days whilst monitoring the respiration rates. Significantly more CO₂ was respired from soil containing leaf litter than that amended with an equivalent weight of faecal matter, whilst the unamended soil exhibited a respiration rate similar to soil amended with faecal material. Consideration of these findings with recently observed differences in biochemical compositions of litter and faeces suggests that processing of plant litter by detritivores leads to more stabilised forms of organic matter by removal of biochemical components essential to the nutrient requirements of the invertebrate and the soil microbial biomass.     

降尘、凋落物和生物接种对沙地土壤结皮形成的影响

土壤生物结皮广泛存在于干旱、半干旱地区,特别是沙漠地区。为了了解沙漠地区生物结皮的形成机制,2007年在科尔沁沙地对流沙进行了田间模拟降尘、添加凋落物和结皮生物接种的试验,研究了几种外界物质输入对沙漠结皮特性的影响。得到如下结果:降尘可以明显促进沙地土壤结皮的形成,但结皮盖度和厚度的增加与降尘量的多少并不存在线性关系,而是非线性关系。少量凋落物(100 g m-2)的存在可以增强降尘对结皮发育的促进作用,但输入较多的凋落物(250 g m-2)反而会抑制降尘的作用。结皮接种可以明显增强降尘对结皮形成的促进作用,其中干旱环境中接种地衣结皮的效果较好,在湿润环境中接种苔癣结皮的效果较好。结皮盖度对外来物质的输入较为敏感,结皮厚度随外来物质种类和数量的增加而变化较小。与光照、干旱环境相比,遮荫、湿润环境更有利于沙地结皮的形成和提高降尘等外来物质输入的效果。     

Long-term litter decay in Canadian forests and the influence of soil microbial community and soil chemistry

Long-term rates of litter decay have been shown to be primarily influenced by temperature, moisture and litter quality. However, while decomposition is a biological process, the relative importance of microbial communities and other soil chemistry factors is not well understood. Our analysis examined long-term litter decay parameters, microbial community composition via phospholipid fatty acid (PLFA) analysis, and soil organic horizon chemistry at 14 upland forested sites. Data were collected as part of the Canadian Intersite Decomposition Experiment (CIDET), a 12-year national litter decomposition experiment. Residual errors from a two-pool exponential decay model with decay rates modified by mean annual air temperature and moisture stress were compared to PLFA marker groups and chemistry variables. Residual errors were not well explained by soil PLFA marker group abundance or concentration, soil pH, nor soil C:N ratios. The best predictor of residual error was soil carbon percent (%C), with higher %C associated with slower than predicted decomposition.     

Decomposition and nutrient content of litter in a fertilized eucalypt forest

The decomposition and nutrient content of litter was studied for 2 years in regrowth Eucalyptus diversicolor forest to which N (0, 200 kg ha^-1 year^-1) and P (0, 30, 200 kg ha^-1) had been applied. The P addition increased, and the N addition decreased, the rate of dry weight loss of decomposing litter. Analysis of the coefficients of a double exponential decay model with components describing the release of labile and resistant fractions indicated that decomposition of the resistant component of litter was most affected by the fertilizer additions. Treatment with N reduced the rate of loss of this component and increased its half-life by approximately 30%, whereas P treatment increased its rate of decay and decreased its half-life by approximately 30%. P accumulated in litter during decomposition. P uptake and retention was greater in P-treated than untreated plots. The application of N reduced P accumulation in litter. An accumulation of N also occurred during decomposition, the amount of N imported into litter being greater on plots treated with N fertilizer. Treatment with N affected the amount of S in decomposing litter. Litter on N-treated plots either accumulated more S or released it more slowly than litter on plots not treated with N. The application of N as NH₄NO₃ decreased forest-floor litter pH, increased litter layer mass (by 15%), and increased the amount of N (by 34%) and S (by 32%) stored in the forest floor. Treatment with P reduced the amount of N (by 22%) stored in the litter layer. The application of 200 kg P ha^-1 in the absence of N increased the store of P in the litter layer by 80%, but when N and P were applied together the amount of P in the litter was not significantly different between P treatments.