Microbial Biomass N Research Articles

Differential effects of raw and composted manure on nematode community, and its indicative value for soil microbial, physical and chemical properties

The impacts of two organic soil amendments on nematode abundance, community structure and soil characteristics were studied in field grown tomatoes. We hypothesized that as the raw (labile form) and composted (non-labile form) manures differ in their chemical composition and effect on microbial activity. Also they will have different effects on soil properties and directly and indirectly affect nematode community structure. Experiments were conducted during 2001–2002 in Wooster, Ohio on a silt loam soil. Treatments [raw or composted dairy cow manure in 2001 and beef calf manure in 2002, and an untreated control] were arranged in a randomized complete block design. Amendments were applied in the spring at a rate estimated to deliver 95–100 kg N ha −1, and incorporated prior to planting. Soil samples were collected in the spring (before adding amendments) and autumn (after crop harvest) to determine nematode abundance, community structure and soil characteristics: Shannon–Weiner ( H′), Simpson ( λ), Pielou ( J′) and combined maturity indices were used to compare nematode community structure in amended and non-amended plots. Spring incorporation of both organic amendments increased the abundance of bacterial feeding, fungal feeding, omnivorous and predatory nematodes, but decreased plant parasitic nematode populations. Plots treated with raw manure had the lowest number of plant parasitic nematodes while increases in non-plant parasitic nematodes were similar in both treatments. Shannon diversity ( H′) and combined maturity (∑MI) indices of soil nematodes were reduced in plots receiving raw but not composted manure. Application of raw manure increased total organic matter, microbial biomass-N, potentially mineralizable-N and C over composted manure in 2001, while both raw and composted manure increased particulate organic matter in both years. The effect of raw and composted manure on community indices was different in 2001 and 2002. We found a strong negative relationship ( r = −82, p < 0.0001) between the abundance of non-plant parasitic and plant parasitic nematodes across all treatments and sampling times, thus supporting the utility of the ratio between non-plant parasitic and plant parasitic nematodes as a useful soil quality indicator.

Soil Management for Better Nutrition of Lowland Rice

Some experiments were conducted in field conditions at Rampur, Nepal between 2001 and 2003 to assess the potential of wheat straw management with grain and green manure legumes in the lowland areas on soil N dynamics, crop yields and systems’ N balances. Two levels of wheat straw incorporation (0 and 2 Mg ha-1) with four types of land management (bare fallow control, mucuna, mungbean and maize) treatments were randomly allotted in the 10 m2 plots in the fields. When the land was left bare during the transition season, Nmin was initially building up of 50-80 kg of nitrate-N and subsequently lost by nitrate leaching and denitrification, resulting in low N uptake of rice. The application of wheat straw during DWT significantly reduced soil Nmin at the same rate as soil microbial biomass-N increased and resulted in &lt;1 kg ha-1 of nitrate leaching and minimal nitrous oxide emissions from the soil. Growing cover crops during transition period reduced leaching losses by half and nitrous oxide emissions by two thirds of those in the bare fallow control, and BNF-N additions by legumes ranged from 27 to 56 kg ha-1. Depending on the type of legume, this resulted in increased crop N uptake and grain yield. The lower N benefits were associated with the grain legume because about 50% of the N assimilation was removed by grain harvest, while the high benefits were obtained with green manures. When DWT is sufficiently long, the cultivation of legumes appears economically and ecologically beneficial and should be encouraged. Combinations of straw amendment and green manure use during DWT provide the largest benefits in terms of grain yield, and N balance with possible long-term benefits for system’s productivity. &#x0D; &#x0D; Key words: Soil, nutrient management, lowland rice &#x0D; &#x0D; J. Inst. Agric. Anim. Sci. 27:139-147 (2006)

Soil carbon pool and effects of soil fertility in seeded alfalfa fields on the semi-arid Loess Plateau in China

The dynamics of the soil organic carbon pool and soil fertility were studied in soils with different number of growing years of alfalfa ( Medicago sativa L.) in the semiarid Loess Plateau of China. The soil water content and soil water potential decreased and the depth of desiccated layers grew with the number of growing years of alfalfa. The soil organic C (SOC) cannot be enhanced on short timescales in these unfertilized and mowed-alfalfa grasslands in the topsoil, but the light fraction of organic C (LFOC), soil microbial biomass C (MBC) and microbial biomass N (MBN) all increased with the number of growing years. When alfalfa had been growing for more than 13 yr, the soil MBC increased slowly, suggesting that the MBC value is likely to reach a constant level. SOC, soil total P (STP), available P (AvaiP) and the ratio of SOC to soil total N (C/N) all decreased monotonically with the growing years of alfalfa up to 13 yr and then increased. SOC was significantly positively correlated with STP, AvaiP, soil total C (STC) and soil total N (STN) ( R=0.627**, 0.691**, 0.497*, 0.546*, respectively). MBC and LFOC were significantly positively correlated with the number of growing years of alfalfa ( R=0.873*** and 0.521*, respectively), and LFOC was more sensitive to vegetation components, degree of cover and landform than to the number of years of growth. SOC showed a significant negative correlation with LFOC/SOC and MBC/SOC ( R=−0.689**, −0.693**, respectively). A significant positive correlation exists between MBC and soil inorganic C (SIC). LFOC, MBC, LFOC/SOC and MBC/SOC were all significantly positively correlated with each other. Therefore, practices that involve water-harvesting technologies and add residues and phosphate fertilizer to soils should be promoted to improve soil nutrients and hydration and to postpone the degradation of alfalfa grasslands under long-term alfalfa production.

Seasonal changes in microbial function and diversity associated with stubble retention versus burning

The long-term (16-year) effect of stubble management (i.e. retained or burnt) on the size of the microbial community (microbial biomass-C and -N), microbial community structure (PLFA), and function (CO2-C evolution, gross N transformation rates, enzymatic activity, and community level physiological profiles) was investigated on 4 occasions during a single wheat-growing season using soil collected from the low-rainfall (&lt;250 mm) region of Western Australia. Significant differences (P &lt; 0.001) in microbial community structure and function were determined for different sampling times by phospholipid fatty acid (PLFA) analyses and community level physiological profiles (CLPP). However, neither PLFA nor CLPP analyses identified differences between stubble treatments. In contrast to total soil organic matter-C, for which no treatment differences were evident, microbial biomass-C was 34% and CO2-C evolution 61% greater in stubble-retained treatments than in burnt-stubble treatments in the 0–0.05 m soil layer. Seasonal increases in microbial biomass-C (P &lt; 0.001) were on average twice as large and CO2-C evolution (P &lt; 0.001) nearly 4 times greater in September during crop flowering compared with other sampling times. In contrast, microbial biomass-N remained constant throughout the entire sampling period. Stubble-retained treatments also demonstrated significantly greater (P &lt; 0.05) levels of arginine ammonification, acid phosphatase and β-glucosidase enzyme activity on average compared with burnt-stubble treatments. However, the effect (P = 0.05) of stubble treatment on gross N mineralisation, nitrification, or immobilisation rates was seasonally dependent with burnt-stubble treatments demonstrating lower gross N mineralisation rates than retained-stubble treatments in November. Gross N mineralisation was lower (37–83% on average) than potential gross nitrification rates (estimated in the presence of excess NH4+) measured from May to September. The rate of potential gross nitrification was observed to decline significantly (P = 0.06) in November and as a result, more closely matched gross N mineralisation rates. Potential gross nitrification rates were also up to 6 times greater than microbial immobilisation of NH4+, indicating that this would be the primary consumptive process in the presence of NH4+. Whilst potential nitrification rates in the presence of excess NH4+ were high, low soil NO3– concentrations indicate that plant/microbial demand for NO3– and NH4+ exceeded the supply capacity. For example, actual gross nitrification rates (determined in the presence of 15N-labelled NO3-) were only greater than gross N mineralisation in May, indicating N supply constrained nitrification at other sampling times. Findings illustrate that increased wheat yields of 31% in this study were associated with the retention of stubble. Further they demonstrate that changes in stubble management significantly influenced the mass and activity of microorganisms (and in some cases N cycling), whilst having little influence on community diversity.

Soluble Organic Nitrogen Pools in Forest soils of Subtropical Australia

Soil soluble organic N (SON) plays an important role in N biogeochemical cycling. In this study, 22 surface forest soils (0–10 cm) were collected from southeast Queensland, Australia, to investigate the size of SON pools extracted by water and salt solutions. Approximately 5–45 mg SON kg−1, 2–42 mg SON kg−1 and 1–24 SON mg kg−1 were extracted by 2 M KCl, 0.5 M K2SO4 and water, on average, corresponding to about 21.1, 13.5 and 7.0 kg SON ha−1 at the 0–10 cm forest soils, respectively. These SON pools, on average, accounted for 39% (KCl extracts), 42% (K2SO4 extracts) and 43% (water extracts) of total soluble N (TSN), and 2.3% (KCl extracts), 1.3% (K2SO4 extracts) and 0.7% (water extracts) of soil total N, respectively. Large variation in SON pools observed across the sites in the present study may be attributed to a combination of factors including soil types, tree species, management practices and environmental conditions. Significant relationships were observed among the SON pools extracted by water, KCl and K2SO4 and microbial biomass N (MBN). In general, KCl and K2SO4 extracted more SON than water from the forest soils, while KCl extracted more SON than K2SO4. The SON and soluble organic C (SOC) in KCl, K2SO4 and water extracts were all positively related to soil organic C, total N and clay contents. This indicates that clay and soil organic matter play a key role in the retention of SON in soil.

The effects of understorey dwarf bamboo (Sasa kurilensis) removal on soil fertility in a Betulaermanii forest of northern Japan

AbstractWe investigated the changes in soil microbial biomass C (MBC), microbial biomass N (MBN) and N mineralization in Sasa kurilensis‐present (SP) and S. kurilensis‐removed (SR) stands in a Betula ermanii forest. The mean levels of MBC and MBN were significantly higher in the SR stand than in the SP, which may have positively influenced the N‐mineralization rate as depicted by a significant positive correlation between these variables and the N‐mineralization rate. N immobilization and subsequent N release along with decreased use of available soil N due to S. kurilensis removal may have ensured greater N availability in the SR stand.

Influences of vermicomposts on field strawberries: Part 2. Effects on soil microbiological and chemical properties

The effects of applications of food waste and paper waste vermicomposts on some soil chemical and biological properties were evaluated in field plots planted with strawberries. Six-week old strawberries ( Fragaria ananasa, var. Chandler) were transplanted into 4.5 m 2 raised beds under a plastic tunnel structure measuring 9.14 × 14.6 × 3.6 m. Vermicompost were applied at rates of 5 or 10 t ha −1 supplemented with inorganic fertilizers to balance fertilizer recommendations for strawberries of 85–155–125 kg NPK ha −1. Effects of vermicomposts on strawberry growth and yields have been reported previously [Arancon, N.Q., Edwards C.A., Bierman P., Welch, C., Metzger, J.D., 2004. The influence of vermicompost applications to strawberries: Part 1. Effects on growth and yield. Bioresource Technology 93:145–153]. Total extractable N, NH 4-N, NO 3-N and orthophosphates did not differ significantly between treatments, except on the last sampling date (harvest date) in which significantly greater amounts of NH 4-N, NO 3-N and orthophosphates ( P ⩽ 0.05) were recorded in vermicompost-treated soils than in the controls. Two major results of vermicompost applications to soils were increases in dehydrogenase activity and microbial biomass-N which were not dose-dependent. Increased dehydrogenase activity and microbial biomass-N was correlated positively with the increased amounts of NH 4-N, NO 3-N and orthophosphates in the vermicompost-treated plots than in the controls. Increases in microbial populations and activities are key factors influencing rates of nutrient cycling, production of plant growth-regulating materials, and the build-up of plant resistance or tolerance to crop pathogen and nematode attacks.

Gross nitrogen mineralisation rates in pastural soils and their relationships with organic nitrogen fractions, microbial biomass and protease activity under glasshouse conditions

In this study, gross nitrogen (N) mineralisation rates were determined in six pasture soils (Fleming, Kairanga, Karapoti, Lismore, Templeton and Waikoikoi) from three different regions of New Zealand. The soils were kept under controlled soil water potential (−10 to −30 kPa) and temperature (12–20°C) conditions in a glasshouse. The gross N mineralisation rates ranged from 0.76 to 5.87 μg N g−1 soil day−1 in the six soils and were positively correlated with the amount of amino acid-N (AA-N), ammonia-N (NH3-N), total hydrolysable-N (TH-N), microbial biomass-carbon (MB-C), microbial biomass-N (MB-N), protease activity and organic C and N. A stepwise regression was used to generate equations that could best describe gross N mineralisation rates. Microbial biomass-carbon and AA-N were included in the equation that best described the gross N mineralisation rate: $$ \begin{aligned} {\text{Gross}}\,{\text{N}}\,{\text{mineralisation}}\,{\text{rate }}{\left( {\mu {\text{g}}\,{\text{N}}\,{\text{g}}^{{ - {\text{1}}}} \,{\text{soil day}}^{{ - {\text{1}}}} } \right)} & \\ = - 0.566 + 0.001{\left( {{\text{MB - C}}\,\mu {\text{g}}\,{\text{C}}\,{\text{g}}^{{ - {\text{1}}}} \,{\text{soil}}} \right)} + 0.002{\left( {{\text{AA - N}}\,\mu {\text{g}}\,{\text{N}}\,{\text{g}}^{{ - 1}} \,{\text{soil}}} \right)}{\text{.}} & \\ \end{aligned} $$

The microbial biomass properties of a savanna soil under improved grass and legume pastures in northern Nigeria

Abstract A strategy for rehabilitating degraded or unproductive native grassland is the establishment of improved pastures to sequester organic carbon (OC) in the soil. Microbial biomass C, N and P are the most biologically active fraction of soil OC, and are thus, useful indices for assessing the health of soil ecosystems. The impact of improved grass pastures and a legume pasture on microbial biomass C, N and P in a savanna soil at Shika (Lat. 11°11′ N and Long. 7°38′ E), in northern Nigeria, was studied. The objective was to determine the pasture plant that best improved the microbial properties of the soil. Five managed pasture fields, consisting of Andropogon gayanus Kunth., Brachiaria decumbens Stapf., Chloris gayana Kunth., Digitaria smutsii Stent. and Stylosanthes guianensis (Aubl.) Sw., were sampled for the study. The concentration of OC in the field under B. decumbens was nearly twice (23.9 g kg−1) the concentration in other fields (13.1–14.6 g kg−1). The field under D. smutsii had significantly higher microbial biomass C (MBC) than other fields as determined by fumigation–extraction method, and MBC accounted for between 1.5 and 3.9% of OC in the soil. Microbial biomass N (MBN), ranged from 41 to 119 mg kg−1 and microbial biomass P (MBP) from 22 to 113 mg kg−1. The fields under S. guianensis and D. smutsii had significantly greater MBN and MBP than the other fields. The MBN accounted for between 3 and 10% of total N, while MBP accounted for between 19 and 75% of organic P (Po). D. smutsii and S. guianenesis had the most significant impact on microbial C, N and P, whereas B. decumbens sequestered more OC in the soil. Thus, D. smutsii and B. decumbens are two promising grass pastures that can be established to rehabilitate degraded or unproductive savanna lands.

The contribution of soil organic matter fractions to carbon and nitrogen mineralization and microbial community size and structure

The aims of this study were to: (i) assess the impact of hay and fertilizer application on organic matter (OM) fractions (dissolved organic matter (DOM), light fraction organic matter (LFOM, <1.0 g cm −3), heavy fraction OM (HFOM, <1.7 g cm −3)), carbon (C) and nitrogen (N) cycling processes and microbial community size and structure, and (ii) quantify the role of OM fractions to C and N cycling. Soil was collected in 2001 from a field experiment to which grass hay (1996) and/or fertilizer (1995 and 1999) had previously been applied. DOM-C ( P<0.05) and DOM-N ( P=0.07) were significantly higher in control and fertilized soil than hay and hay+fertilized soil. LFOM and HFOM C and N contents and C/N ratios were significantly ( P<0.05) higher in hay+fertilized and hay amended soil than in control and fertilized soil. Potentially mineralizable-N (PMN), microbial biomass-C (MB-C), microbial biomass-N (MB-N) and microbial respiration (CO 2) were not affected by fertilizer and/or hay application. Gross N mineralization (Gross Min) and gross nitrification (Gross Nit) rates were significantly ( P<0.05) higher in fertilized, hay, hay+fertilized soil than control soil. However, there was no significant difference between treatments in gross N immobilization rates. Results reported here highlight the importance of a labile fraction of the DOM pool to N and C cycling as its removal significantly ( P<0.05) reduced PMN, MB-N, Gross Min and Gross Nit compared with whole soil in most or all treatments. In soil where DOM+LFOM were removed PMN was significantly ( P<0.05) lower, but MB-C, Gross Min and Gross Nit was significantly ( P<0.05) higher than in DOM removed soil. This suggests that LFOM plays an important role as a sink for mineral-N. Total soil phospholipid fatty acid (PLFA) concentration was significantly ( P<0.05) higher in hay amended than control, fertilized and hay+fertilized soil. Principal components analysis was able to clearly discriminate between control, fertilized, hay+fertilized and hay amended soil. Soil amended with hay or fertilizer had a microbial community structure which differed from that of the control or hay+fertilized soils. Redundancy analysis with Monte Carlo permutation tests revealed that PLFA profiles were strongly correlated to differences in Gross Min, Gross Nit, MB-N, MB-C, MB-C/N ratio, total soil C and total soil C/N ratio. The results of this research suggest that changes in microbial structure are related to aspects of soil C and N pools and cycling.

Nitrogen Balance as Affected by Application Time and Nitrogen Fertilizer Rate in Irrigated No‐Tillage Maize

High N requirements of no‐tillage maize (Zea mays L.) make it imperative to develop management strategies that optimize crop production and N use efficiency (NUE). A 4‐yr field experiment was conducted at Balcarce (37°45′S, 58°18′W), Argentina, on a Typic Argiudoll and a Petrocalcic Paleudoll. The objective was to evaluate the effect of urea rate (0, 70, 140, and 210 kg N ha−1) at planting (FPL) or six‐leaf stage (FV6) on NH3 volatilization, denitrification, soil residual nitrate, soil microbial biomass N (MBN), N uptake, grain yield, and unaccounted N (UN). Grain yield was 10.5 and 11.2 Mg ha−1, and N uptake at physiological maturity was 168 and 192 kg N ha−1 (average of N rates) for FPL and FV6, respectively. Gaseous N losses ranged from 7.6 to 13.8% of applied N and were not affected by the fertilizer time. Relative to unfertilized control, fertilized treatments increased MBN (13.4 kg N ha−1) similarly for both fertilization times. For FPL, UN was 55, 69, 86, and 103 kg N ha−1 for 0, 70, 140, and 210 kg N ha−1, respectively. For FV6, UN was 55, 46, 49, and 34 kg N ha−1 for 0, 70, 140, and 210 kg N ha−1, respectively. The losses were attributed to nitrate (NO3) leaching. Results of this experiment show that high fertilizer NUE in combination with economically competitive grain yields can be obtained when N is applied at V6 because gaseous N losses are low (less than 13.8%) and NO3 leaching would be reduced.

Tillage, crop residue and crop sequence effects on nitrogen availability in a legume-based cropping system

A field study was conducted to determine the effects and interactions of crop sequence, tillage and residue management on labile N pools and their availability because such information is sparse. Experimental treatments were no-till (NT) vs. conventional tillage (CT), and removal vs. retention of straw, imposed on a barley (Hordeum vulgare L.)-canola (Brassica rapa L.)-field pea (Pisum sativum L.) rotation. 15N-labelling was used to quantify N uptake from straw, below-ground N (BGN), and fertilizer N. Straw retention increased soil microbial biomass N (MBN) in 2 of 3 yr at the four-leaf growth stage of barley, consistent with observed decreases in extractable soil inorganic N at seeding. However, crop yield and N uptake at maturity were not different between straw treatments. No tillage increased soil MBN, crop yield and N uptake compared to CT, but had no effect on extractable soil inorganic N. The greater availability of N under NT was probably related to soil moisture conservation. Tillage effects on soil and plant N were mostly independent of straw treatment. Straw and tillage treatments did not influence the uptake of N from its various sources. However, barley following pea (legume/non-legume sequence) derived a greater proportion of its N from BGN (13 to 23% or 9 to 23 kg N ha-1) than canola following barley (nonlegumes) (6 to 16% or 3 to 9 kg N ha-1). Fertilizer N constituted 8 to 11% of barley N uptake and 23 to 32% of canola N uptake. Straw N contributed only 1 to 3% of plant N uptake. This study showed the dominant influence of tillage on N availability, and of the preceding crop or cropping sequence on N uptake partitioning among available N sources. Key words: Crop residue, crop sequence, labile nitrogen, nitrogen uptake, pea, tillage

Quantifying the contribution of dissolved organic matter to soil nitrogen cycling using 15N isotopic pool dilution

Dissolved organic matter (DOM) has been recognised as a key carbon and nitrogen (N) pool involved with soil–plant–microbe interactions. Yet few studies have quantified this contribution in agricultural soils. In this study we leached DOM from a sandy loam and sandy clay loam soil under either grassland or arable cropping. Two weeks after DOM removal microbial respiration from soils was not altered. However, a significant ( P<0.05) decline in microbial biomass-N, potentially mineralizable-N, gross N mineralization and gross nitrification occurred after leaching. This data illustrate that whilst DOM is a small component of the soil OM it contributed up to 25% of microbial N supply within these agricultural soils.

Microbial biomass in a soil amended with different types of organic wastes.

Application of different types of organic wastes may have a marked effect on soil microbial biomass and its activity. The objective of this study was to quantify the amount of microbial biomass in a loamy-clayey soil, amended with different types of organic waste residues (composts of municipal solid waste of different ages, sewage sludge and farmyard manure) and incubated for 8 weeks at 25 degrees C and two-thirds of field capacity, using the fumigation-extraction method. Both microbial biomass-C and -N (BC and BN, respectively) appeared to be dependent on the type of organic waste residues, on their degree of stability, and on their chemical characteristics. In general, organic wastes increased the microbial biomass-C content in the soil and the microbial BC was positively correlated with the organic C content, the C/N, neutral detergent fibre/N (NDF/N) and acid detergent fibre/N (ADF/ N) ratios. The microbial biomass content decreased according to the period of incubation, especially when the compost used was immature. The microbial biomass-N was positively correlated with the total N and percentage of hemicellulose. The microbial biomass-C was linearly related with the microbial biomass-N and the ratio BC/BN was exponentially related with the BC.

Effects of vermicomposts produced from food waste on the growth and yields of greenhouse peppers

Vermicomposts, produced commercially from food wastes, were substituted at a range of different concentrations into a soil-less commercial bedding plant container medium, Metro-Mix 360 (MM360), to evaluate their effects on the growth and yields of peppers in the greenhouse. Six-week-old peppers ( Capsicum annum L. var. California) were transplanted into 100%, 80%, 60%, 40%, 20% or 10% MM360 substituted with 0%, 10%, 20%, 40%, 60%, 80% and 100% vermicompost. All plants were watered three times weekly with 200 ppm Peter's Nutrient Solution from the time of transplanting up to 107 days. Peppers grown in potting mixtures containing 40% food waste vermicomposts and 60% MM360 yielded 45% more fruit weights and had 17% greater mean number of fruits than those grown in MM360 only. The mean heights, numbers of buds and numbers of flowers of peppers grown in potting mixtures containing 10–80% vermicompost although greater did not differ significantly from those of peppers grown in MM360. There were no positive correlations between the increases in pepper yields, and the amounts of mineral-N and microbial biomass-N in the potting mixtures, or the concentrations of nitrogen in the shoot tissues of peppers. Factors such as: an improvement of the physical structure of the potting medium, increases in populations of beneficial microorganisms and the potential availability of plant growth-influencing-substances produced by microorganisms in vermicomposts, could have contributed to the increased pepper yields obtained.

Variations of soluble organic nitrogen and microbial nitrogen in deciduous forest soils along an urban–rural gradient

Soluble organic N and microbial N pools in terrestrial ecosystems have been less studied than those of inorganic N. Therefore, cross-system variation in their pool sizes and seasonal dynamics, both absolute and relative to inorganic N pools, needs to be quantified so that their ecological importance in different ecosystems can be evaluated. We measured extractable soil organic N (ESON), microbial biomass N (MBN), and the net production rates of ESON in red oak-dominated remnant forests, along an urban–rural gradient in the New York City metropolitan area. We were interested in (1) determining the seasonal dynamics of ESON and MBN, and (2) examining whether the contrasts in land use (urban, suburban, rural) surrounding these forest remnants were associated with different amounts of ESON and MBN. This field-based study was conducted continuously for 16 months. Yearly average ESON concentrations ranged from 60 to 140 mg kg −1 soil organic matter (SOM), 3–4 times those of inorganic N, and average MBN ranged from 600 to 1100 mg kg −1 SOM. There was a considerable MBN increase in spring in all plots across the gradient. The average increase expressed on an areal basis (to a depth of 7.5 cm) ranged from 1.75 to 4.19 g N m −2. The N incorporated into the microbial biomass in spring was gradually released later in the growing season (the mean MBN decrease ranged from 1.11 to 3.82 g N m −2). The spring MBN increase could be an important retention mechanism for conserving soil inorganic N when plant N uptake may be low. The amplitude in the seasonal dynamics of ESON was far less than that of inorganic N, as was that of net ESON production rates when compared to net N mineralization. These suggest a closer coupling of plant N uptake with inorganic N, much more than with ESON. Both ESON and MBN were significantly higher in rural soils than in urban soils, and both concentrations were positively correlated with SOM content. The variation in ESON, MBN, or SOM associated with this urbanization gradient suggests that the form of N exported, the plant N budget and soil N retention mechanisms may be differentially affected by urban, suburban and rural land uses.

Dynamics and plant uptake of nitrogen and phosphorus in soil amended with sewage sludge

Sewage sludge (SS) represents an inexpensive source of plant nutrients, but the fertilizer value can vary considerably. A field study was carried out, in which anaerobically digested sewage sludge (SS1) and activated sewage sludge (SS2) from the same treatment plant were applied to a crop of oat ( Avena sativa L.). Application rates with SS1 were around 120 kg ha −1 P, 20 kg ha −1 NH 4 +–N and 130 kg ha −1 total N. With SS2, inputs of P and NH 4 +–N were similar to SS1, but total N input was 50% higher. Soil inorganic N and resin-extractable inorganic phosphate (P i), microbial biomass N (MBN), microbial biomass P (MBP) and microbial biomass C (MBC), as well as crop uptake of N and P, were monitored between mid April and late June. Five weeks after sludge application, soil inorganic N had increased from 25 to >60 kg ha −1 in both treatments due to mineralization of sludge constituents. The soil microbial biomass N and biomass P increased temporarily with SS2, but by the end of June biomass N had decreased by 28–34 kg N ha −1 relative to the pre-amendment level. An increase in biomass P was observed after SS2 amendment, but in general P dynamics were obscured by a high background content of inorganic P in the soil. Both crop growth and crop nutrient uptake were increased with application of SS2 compared to SS1. Microbial biomass N decreased and biomass C:N increased during the period of crop N uptake, indicating competition for N between plants and microbes. The N fertilizer value of SS1 corresponded to 32%, and that of SS2 to 53% of total N in the sludge.

Soil microbial biomass during the early establishment of hoop pine plantation: seasonal variation and impacts of site preparation

Site preparation can alter soil physical, chemical and biological properties, which in turn may have significant impacts on tree growth of the following rotation. The major objective of this study was to investigate the impacts of season, soil compaction by mechanical harvesting and soil cultivation on soil microbial biomass carbon (C) and nitrogen (N) during the early stages of a second-rotation (2R) hoop pine ( Araucaria cunninghamii) plantation. Soil (0–10 cm depth) was sampled for 14 consecutive months in an established factorial field trial at Yarraman, southeast Queensland. There were three compaction treatments (0 forwarder pass, 1 forwarder pass and 16 forwarder passes) and two cultivation treatments (zero cultivation and disc plough), which were randomly arranged in three blocks. There was seasonal and spatial variation in soil microbial biomass in mineral soils among the different compaction and cultivation treatments, with soil microbial biomass C (MBC) ranging from 167 to 1149 μg g −1, microbial biomass N (MBN) from 16 to 257 μg g −1, and microbial C:N ratios from 4.0 to 14.6. Fluctuations in soil microbial biomass were mainly driven by the seasonal changes in environmental conditions (including rainfall, temperature and soil moisture). The MBC was less variable with season than the MBN. In general, seasonal fluctuations in MBN were similar amongst the treatments with an apparent peak in August (late winter), followed by a sharp decrease to a lowest point in October (mid-spring), and then a second peak in December (early summer). Soil compaction did not significantly affect MBC and MBN, while soil cultivation significantly reduced MBC and MBN only in the 0 forwarder pass for the experimental period except February and March 2001 (summer–early spring) for MBC and January–March 2001 (summer–early spring) for MBN. The potential mechanisms for the diverse impacts of soil compaction and cultivation on soil microbial processes are discussed in relation to the seasonal environmental changes.

Effects of two species of earthworms ( Allolobophora spp.) on soil systems: a microfaunal and biochemical analysis : The 7th international symposium on earthworm ecology · Cardiff · Wales · 2002

Summary In this work we studied how earthworm digestion affects both soil biochemical and microfaunal characteristics. We sampled paired fresh casts and bulk soil of two earthworm species, Allolobophora caliginosa and A. molleri, inhabiting a pasture and a riverside, respectively. We focused on the differences in faunal composition and biochemical characteristics between cast and bulk soil. Ammonium and carbohydrate contents were higher in casts than in the surrounding soil. DON content was lower in the casts than in the surrounding soil. Microbial biomass (measured as microbial biomass-N, arginine ammonification and SIR) and microbial activity (measured as basal respiration, β-glucosidase, alkaline phosphatase, dehydrogenase and protease) were also higher in casts in the surrounding soil than. Flagellate protozoa and nematode numbers were lower in A. caliginosa casts and higher in A. molleri casts than in the surrounding soil.

Effects of land-use and management practices on soil ergosterol content in andosols

Ergosterol is a fungus-specific chemical component which has been extensively used to assess the fungal biomass and activity in soils. In the present study, we investigated the soil ergosterol content in a group of Japanese soils differing in management. In addition, the relationships among the soil ergosterol content (SEC), microbial biomass C (MBC), and microbial biomass N (MBN) were also tested in different seasons. Our results showed that the SEC was lower in intensively cropped soils than in pasture and forest soils. In general, no consistent trend was observed for SEC of pasture soils within the same sampling period. However, SEC tended to decrease in most of the soils in autumn, which may be ascribed to the effect of seasonal changes on fungal biomass. No strong evidence could be obtained for the effect of different fertilizers on SEC, which can be due to different management variables and interspecific variations between fungal communities at different soil sites. Our results did not suggest the presence of a noticeable correlation between SEC and MBC or MBN. The ratio of SEC in total biomass C was lower (0.20 and 0.11% in spring and autumn, respectively) compared with the values reported.