Unfertilized Plots Research Articles

Short-term nitrogen fertilization decreased root and microbial respiration in a young Cunninghamia lanceolata plantation

Aims As the primary pathway for CO_2 emission from terrestrial ecosystems to the atmosphere, soil respiration is-estimated to be 80 Pg C·a1- to 100 Pg C·a1, equivalent to 10 fold of fossil fuel emissions. As an important management practice in plantation forests, fertilization does not only increase primary production but also affects soil respiration. To investigate how nitrogen(N) fertilization affects total soil, root and microbial respiration, a N fertilization experiment was conducted in a five-year-old Cunninghamia lanceolata plantation in Huitong, Hunan Province, located in the subtropical region. Methods One year after fertilization, soil respiration was monitored monthly by LI-8100 from July 2013 to June 2014. Soil temperature and water content(0–5 cm soil depth) were also measured simultaneously. Available soil nutrients, fine root biomass and microbial communities were analyzed in June 2013. Important findings Total soil, root and microbial respiration rates were 22.7%, 19.6%, and 23.5% lower in the fertilized plots than in the unfertilized plots, respectively. The temperature sensitivity(Q10) of soil respiration ranged from 1.81 to 2.04, and the Q10 value of microbial respiration decreased from 2.04 in the unfertilized plots to 1.84 in the fertilized plots. However, neither the Q10 value nor the patterns of total soil respiration were affected by N fertilization. In the two-factor model, soil temperature and moisture accounted for 69.9%–79.7% of the seasonal variations in soil respiration. These results suggest that N fertilization reduces the response of soil organic carbon decomposition to temperature change and may contribute to the increase of soil carbon storage under global warming in subtropical plantations.

A reassessment of the contribution of soybean biological nitrogen fixation to reactive N in the environment

The expansion of soybean (Glycine max (L.) Merr) acreage, increasing yields, and recent nitrogen (N) fertilization recommendations could have a major effect on the contribution of biological N fixation (BNF) in soybeans to reactive nitrogen (Nr) in the environment. We used 15N natural abundance to separate fixed N into grain, aboveground vegetative biomass, and roots along a 9-point N-fertilizer gradient to ask: 1) is the belowground BNF contribution sufficiently different from aboveground to affect regional estimates of soybean Nr production based on harvested biomass, and 2) how does N fertilizer affect soybean yield and BNF’s contribution to different tissues? The contribution of root and vegetative biomass to overall plant BNF was five times lower than that for grain. Including this difference in BNF extrapolations translates to 3.5 ± 0.5 Tg Nr yr−1 for total US soybean production, ~37 % lower than earlier estimates that did not differentiate tissue source. Production of Nr ranged between 35 ± 11 and 73 ± 5 g Nr kg−1 grain and was affected by both fertilization and irrigation. In all cases N credits to the next rotational crop were minor. N-fertilization at even very low levels (17–50 kg N ha−1) did not affect yield, but grain N content increased with fertilizer level. The percent BNF contributed to plant N decreased linearly with increasing fertilization, in grain from 49 ± 8 % in unfertilized plots to a plateau of 16 ± 6 % at fertilization ≥85 kg N ha−1; in aboveground vegetative biomass from 77 ± 4 % to a plateau of 11 ± 11 % at 146 kg N ha−1; and in roots from 88 ± 12 % to a plateau of 41 ± 6 % at 146 kg N ha−1. The average whole-plant BNF contribution decreased from ~84 % in unfertilized plots to a plateau of ~34 % at fertilization rates greater than 84 kg ha−1. Results underscore the unnecessary expense and environmental burden of adding N fertilizer to modern soybean varieties, and provide a refined lower estimate for the contribution of soybean N fixation to the US and global Nr budgets of 3.5 and 10.4 Tg Nr yr−1, respectively.

Investigation of Soil Legacy Phosphorus Transformation in Long-Term Agricultural Fields Using Sequential Fractionation, P K-edge XANES and Solution P NMR Spectroscopy

Understanding legacy phosphorus (P) build-up and draw-down from long-term fertilization is essential for effective P management. Using replicated plots from Saskatchewan, Canada, with P fertilization from 1967 to 1995 followed by either P fertilization or P cessation (1995-2010), soil P was characterized in surface and subsurface layers using sequential fractionation, P K-edge X-ray absorption near-edge structure (XANES) and solution (31)P nuclear magnetic resonance (P NMR) spectroscopy. Legacy P from a 28-year build-up was sufficient for 15 years of wheat cultivation, resulting in no significant differences in crop yield in 2010. In surface soils, soil test (Olsen) P decreased significantly in unfertilized plots compared with 1995, which was reflected in declining aluminum (hydr)oxide-associated inorganic P by fractionation and XANES. Furthermore, XANES analysis revealed a decrease of calcium-associated P in 2010-unfertilized soils at both depths and an increase of Fe (hydr)oxides-associated P in the 2010-fertilized and -unfertilized surface soils relative to the 1995 soils. Increased total organic P and orthophosphate diesters by P NMR and accumulated inositol hexaphosphate by XANES were observed in surface soils with P fertilization cessation. In subsurface soils, few legacy P transformations were detected. These results provide important information about legacy P to improve agricultural sustainability while mitigating water quality deterioration.

Willow Root Development and Morphology Changes Under Different Irrigation and Fertilization Regimes in a Vegetation Filter

Determining the appropriate wastewater dose to supply nutrients while avoiding overirrigation is essential for achieving more balanced above- and belowground development of the plants, thereby ensuring high filtering functionality of a willow vegetation filter system. Aboveground biomass and root development of a 3-year-old willow vegetation filter in response to three increasing doses of secondary-treated urban wastewater under both fertilized and unfertilized conditions were evaluated. Fine, coarse and total root biomass, fine root length density (FRLD), specific fine root length (SFRL) and specific root area (SRA) were assessed in soil core samples collected at four different depths (0–20, 20–40, 40–60 and 60–80 cm) in all treatments. While aboveground biomass increased as wastewater amounts and fertilization increased (from 23.89 Mg ha−1 in non-irrigated condition to 47.07 Mg ha−1 in the highest wastewater dose, from 31.5 Mg ha−1 in unfertilized plots to 40.1 Mg ha−1 in the fertilized), total and fine root biomass decreased when willow was irrigated with the highest wastewater dose (i.e. total root biomass is 2.54 Mg ha−1 in non-irrigated condition—1.36 Mg ha−1 in the highest wastewater dose). The root biomass did not follow the same development pattern, and a significant decrease in fine root biomass was observed when the highest irrigation dose was applied. In these circumstances, we believe that the supply in water and nutrient is sufficient to the development of the willows which react by diminishing the amount of roots proportionally to the aboveground parts. This may lead to a higher transpiration rate and allow willows to avoid a surplus of water in the soil.

Heterotrophic respiration in drained tropical peat is greatly affected by temperature—a passive ecosystem cooling experiment

Vast areas of deforested tropical peatlands do not receive noteworthy shading by vegetation, which increases the amount of solar radiation reaching the peat surface. Peat temperature dynamics and heterotrophic carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes were monitored under four shading conditions, i.e. unshaded, 28%, 51% and 90% shading at experiment sites established on reclaimed fallow agricultural- and degraded sites in Central Kalimantan, Indonesia. Groundwater tables on the sites were at about 50 cm depth, the sites were maintained vegetation free and root ingrowth to gas flux monitoring locations was prevented. Half of the four shading areas received NPK-fertilization 50 kg ha−1 for each of N, P and K during the experiment and the other half was unfertilized. Increases in shading created a lasting decrease in peat temperatures, and decreased diurnal temperature fluctuations, in comparison to less shaded plots. The largest peat temperature difference in the topmost 50 cm peat profile was between the unshaded and 90% shaded surface, where the average temperatures at 5 cm depth differed up to 3.7 °C, and diurnal temperatures at 5 cm depth varied up to 4.2 °C in the unshaded and 0.4 °C in the 90% shaded conditions. Highest impacts on the heterotrophic CO2 fluxes caused by the treatments were on agricultural land, where 90% shading from the full exposure resulted in a 33% lower CO2 emission average on the unfertilized plots and a 66% lower emission average on the fertilized plots. Correlation between peat temperature and CO2 flux suggested an approximately 8% (unfertilized) and 25% (fertilized) emissions change for each 1 °C temperature change at 5 cm depth on the agricultural land. CO2 flux responses to the treatments remained low on degraded peatland. Fertilized conditions negatively correlated with N2O efflux with increases in temperature, suggesting a 12–36% lower efflux for each 1 °C increase in peat temperature (at 5 cm depth) at the sites. Despite the apparently similar landscapes of fallow agricultural land and degraded peatland sites, the differences in greenhouse gas dynamics are expected to be an outcome of the long-term management differences.

The influence of tillage, fertilization and meteorological conditions on the CO2 exchange rate in a loamy Cambisol

is no consensus worldwide concerning the effects of soil management practices on soil net CO 2 exchange rate (NCER). The main goal of the study was to determine soil NCER in different agricultural management systems under contrasting meteorological conditions. The evaluation of moisture and temperature (determined by frequency domain reflectometry (FDR) method) impact on total soil NCER was performed. A closed chamber (CC) method using an infra-red gas analyzer (IRGA) was applied. A two-factorial field experiment was established on an Endocalcari-Epihypogleyic Cambisol (CMg-p-w-can) at the Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry. A three-year (2009-2012) study revealed that rainy weather conditions suppressed NCER sharply: NCER was 15-fold lower under rainy meteorological conditions than under dry or normal conditions. Soil temperature in both unfertilized tillage systems (conventional tillage, no-tillage) was the main determinant for soil NCER, while this effect was suppressed by the total influence of soil water content, air temperature and amount of rainfall. Soil carbon dioxide flux was slightly (3%) higher under conventional tillage than under no-tillage during dry 2009 and normal 2012 years. In a wet year 2010, conventional tillage increased soil NCER by 70% compared to no-tillage. Fertilization with mineral NPK fertilizers increased soil NCER by on average 32% compared to unfertilized plots, but did not eliminate suppressive effects of meteorological conditions on soil NCER.

Root distribution and growth of cotton as affected by drip irrigation with saline water

The objective of this field experiment was to study the effects of irrigation water salinity and N rate on cotton (Gossypium hirsutum L.) growth and root distribution. A field experiment was established with a 3×2 factorial, completely randomized block design: i.e. three levels of irrigation water salinity (fresh water, brackish water, or saline water) and two rates of nitrogen (N) application (0 and 360kgN/ha). The results showed that cotton root biomass and distribution were significantly affected by water salinity and N fertilization, but not by N-salinity interaction. Between 85 and 90% of the root biomass was in the 0 to 20cm soil depth. Root biomass was higher in the fresh water (FW, 0.35dS/m) treatment than in the saline water (SW, 8.04dS/m) treatment, but was not significantly different from that in the brackish water (BW, 4.61dS/m) treatment. Nitrogen fertilizer increased total root biomass by 2 to 8% in the FW treatment, by 27 to 28% in the BW treatment and by 15 to 20% in the SW treatment. Most (83–95%) of the root length density was observed in the 0 to 60cm soil depth. Average root length density, root diameter, and root volume were not affected by water salinity, but decreased sharply as N rate increased. In the unfertilized plot, average root length density, root surface area, and root volume were all higher in the FW treatment than in either the BW or the SW treatments. In the fertilized plot, average root length density, root surface area and root volume were significantly higher in the BW and SW treatments than in the FW treatment. The root/shoot ratio increased significantly as irrigation water salinity increased. Application of N fertilizer increased N uptake, yield, and irrigation water use efficiency. However, saline water irrigation had a negative effect on N uptake, yield, and irrigation water use efficiency; moreover, N application exacerbated the negative effect. These results suggest that saline water irrigation inhibited cotton root growth, resulting in a reduction in shoot growth, N uptake, yield, and water and N use efficiency. Excessive fertilizer application may result in an increase in salt damage when cotton is irrigated with saline water.

Dynamics of Hedera helix L. in Central European beech forests on limestone: results from long-term monitoring and experimental studies

A spread of Hedera helix L. into beech forests has been observed during the last 20 years in Central Europe. As this species is susceptible to intensive frost, it is believed that climate change with mild winters is the responsible driver. Other factors can, however, be equally important including forest management, eutrophication, and browsing. We compared old (sampled 1955–1967) and recent (sampled 2000–2012) releves as well as managed/unmanaged, fenced/unfenced, and fertilized (N, P and a combination of both)/unfertilized plots sampled in two beech forest communities of the Gottinger Wald (Lower Saxony, Germany), and addressed these potential drivers and their effect on H. helix. The H. helix abundance significantly increased in the last 50 years, accompanied by a general temperature increase and a reduction in severe frost events suggesting an influence of climate change. Inter-annual changes in H. helix cover correlated with climate variables reveal an interplay between low minimum temperatures and snow cover. The spread of H. helix, however, also goes along with higher nitrogen availability and a reduction in browsing pressure. A fertilization experiment underlines a positive impact of N and P on the H. helix abundance, whereas fencing and management reduced it by promoting a competing shrub layer. Thus, climate change could not be identified as the main driver of a H. helix spread in the Gottinger Wald. It is rather caused by a complex interaction of changing abiotic (climate change and eutrophication) and biotic (browsing, competition) conditions, that is not fully understood yet.

Interactive responses of grass litter decomposition to warming, nitrogen addition and detritivore access in a temperate old field.

Plant litter decomposition has been studied extensively in the context of both climate warming and increased atmospheric N deposition. However, much of this research is based on microbial responses, despite the potential for detritivores to contribute substantially to litter breakdown. We measured litter mass-loss responses to the combined effects of warming, N addition and detritivore access in a grass-dominated old field. We concurrently assessed the roles of litter treatment origin vs. microenvironment (direct warming and N-addition effects) to elucidate the mechanisms through which these factors affect decomposition. After 6 weeks, mass loss increased in N-addition plots, and it increased with detritivore access in the absence of warming. After 1 year, warming, N addition, and detritivore access all increased litter mass loss, although the effects of N addition and warming were non-additive in the detritivore-access plots. For the litter-origin experiment, mass loss after 6 weeks increased in litter from N-addition plots and warmed plots, but unlike the overall decomposition response, the N-addition effect was enhanced by detritivore access. Conversely, for the microenvironment experiment, detritivore access only increased mass loss in unfertilized plots. After 1 year, detritivore access increased mass loss in the litter-origin and microenvironment experiments, but there were no warming or N-addition effects. Overall, our results provide support for a substantial role of detritivores in promoting litter mass loss in our system. Moreover, they reveal important interactions between litter origin, microclimate and detritivores in determining decomposition responses to global change.

Root length, biomass, tissue chemistry and mycorrhizal colonization following 14 years of CO2 enrichment and 6 years of N fertilization in a warm temperate forest.

Root systems serve important roles in carbon (C) storage and resource acquisition required for the increased photosynthesis expected in CO2-enriched atmospheres. For these reasons, understanding the changes in size, distribution and tissue chemistry of roots is central to predicting the ability of forests to capture anthropogenic CO2. We sampled 8000 cm(3) soil monoliths in a pine forest exposed to 14 years of free-air-CO2-enrichment and 6 years of nitrogen (N) fertilization to determine changes in root length, biomass, tissue C : N and mycorrhizal colonization. CO2 fumigation led to greater root length (98%) in unfertilized plots, but root biomass increases under elevated CO2 were only found for roots <1 mm in diameter in unfertilized plots (59%). Neither fine root [C] nor [N] was significantly affected by increased CO2. There was significantly less root biomass in N-fertilized plots (19%), but fine root [N] and [C] both increased under N fertilization (29 and 2%, respectively). Mycorrhizal root tip biomass responded positively to CO2 fumigation in unfertilized plots, but was unaffected by CO2 under N fertilization. Changes in fine root [N] and [C] call for further study of the effects of N fertilization on fine root function. Here, we show that the stimulation of pine roots by elevated CO2 persisted after 14 years of fumigation, and that trees did not rely exclusively on increased mycorrhizal associations to acquire greater amounts of required N in CO2-enriched plots. Stimulation of root systems by CO2 enrichment was seen primarily for fine root length rather than biomass. This observation indicates that studies measuring only biomass might overlook shifts in root systems that better reflect treatment effects on the potential for soil resource uptake. These results suggest an increase in fine root exploration as a primary means for acquiring additional soil resources under elevated CO2.

Production-ecological modelling explains the difference between potential soil N mineralisation and actual herbage N uptake

We studied two different grassland fertiliser management regimes on sand and peat soils: above-ground application of a combination of organic N-rich slurry manure and solid cattle manure (SCM) vs. slit-injected, mineral N-rich slurry manure, whether or not supplemented with chemical fertiliser (non-SCM). Measurements of field N mineralisation as estimated from herbage N uptake in unfertilised plots were compared with (i) potential N mineralisation as determined from a standard laboratory soil incubation, (ii) the contribution of groups of soil organisms to N mineralisation based on production-ecological model calculations, and (iii) N mineralisation calculated according to the Dutch fertilisation recommendation for grasslands. Density and biomass of soil biota (bacteria, fungi, enchytraeids, microarthropods and earthworms) as well as net plant N-uptake were higher in the SCM input grasslands compared to the non-SCM input grasslands. The currently used method in Dutch fertilisation recommendations underestimated actual soil N supply capacity by, on average, 102kg Nha−1 (202 vs. 304kgha−1=34%). The summed production-ecological model estimate for N mineralisation by bacteria, fungi, protozoa, and enchytraeids was 87–120% of the measured potential soil N mineralisation. Adding the modelled N mineralisation by earthworms to potential soil N mineralisation explained 98–107% of the measured herbage N uptake from soil. For all grasslands and soil biota groups together, the model estimated 105% of the measured net herbage N uptake from soil. Soil biota production-ecological modelling is a powerful tool to understand and predict N uptake in grassland, reflecting the effects of previous manure management and soil type. The results show that combining production ecological modelling to predict N supply with existing soil N tests using aerobic incubation methods, can add to a scientifically based improvement of the N fertilisation recommendations for production grasslands.

Changes of soil agrichemical characteristics in pastures influenced by mineral fertilizing

Grasslands fertilizing is used for increasing of forage yields and quality and simultaneously for soil fertility maintenance. The aim of this study was to evaluate the effect of mineral fertilizing on basic agrichemical soil characteristics (pH, available nutrients) and soil organic matter at grazing exploitation of grasslands. 60 kg N.ha−1 was applied in the year of experiment establishment and 90 kg N, 30 kg P a 90 kg K ha−1 in each of following four years. Significantly higher pH (+0.17), available P (+48.5%), K (+15.4%) and organic C (+8.8%) content was found at fertilized treatment. pH value varied significantly during experiment period (range 0.6) and correlated inversely with proportion of white clover in first cut (r = −0.499). Although available K in soil was only on satisfactory level (less than good), K concentration in the forage was even from unfertilized plots higher than physiological requirement of plants. Available nutrient content constitutes only small proportion of total nutrient content: 5.1% at P, 2.1% at K, 12.0% at Mg and 39.0% at Ca.

Phosphorus Reduction in Turfgrass Runoff Using a Steel Slag Trench Filter System

ABSTRACTExcessive concentrations of P can lead to the deterioration of surface waters through eutrophication. This study was conducted to test the effectiveness of a trench filter system for P removal from runoff and to determine the effect of P fertilizer on P losses in runoff from bermudagrass [Cynodon dactylon L. (Pers.)]. A total of 12 plots on a uniform 5% slope covered with ‘Astro’ bermudagrass mowed at 38 mm were used to collect pre‐ and postfiltered runoff from 14 natural or simulated precipitation events that occurred from March through September 2012. Runoff filtered by steel slag contained from 14.2 to 49.2% lower dissolved P concentrations than runoff filtered through an inert gravel control. The P concentrations in runoff from fertilized plots were always greater than unfertilized plots. The difference between P concentrations from the fertilized and unfertilized treatments tended to decline with each runoff event from 13.1 mg L–1 in an initial event after fertilization to 1.6 mg L–1, 133 d and nine runoff events later. Trench filter systems could be used to remove a portion of the P in runoff from turfgrass areas.

Long-term effect of fertilization on soil fertility

The surplus of the NPK balances of Hungarian agriculture, appearing in the nutrient balance sheet is a consequence of intensive fertilization in the past. Hungary had a positive P-balance between 1960 and 1990 for 30 years, and a positive NK-balance between 1970 and 1990 for 20 years during the 20th century.Studying the long-term effects of superphosphate in a field experiment on calcareous chernozem soil, it was found that the “half life time” of residual P was 5–7 years. The trial, i.e. the P after-effect lasted for 20 years.Liming and fertilization are the main soil fertility improving considerations for acidic sandy soils. These soils are often poor in all major nutrients. Mineral fertilizers, mainly NH4NO3, acidify soil, the pH values sink in comparison to the unfertilized plot. Liming and use of dolomite powder may counterbalance the acidification.

Scale‐ and time‐dependent effects of fertilization, mowing and dominant removal on a grassland community during a 15‐year experiment

Summary Multiple land‐use change drivers affect, in most cases negatively, the biodiversity in species‐rich meadows. Empirical data that can help to disentangle the effects of individual drivers and quantify the time required for a biodiversity response are seldom available. Management decisions are often based on short‐term experiments or observational data. A 15‐year field experiment, comprising a factorial combination of fertilization, mowing and removal of the dominant species Molinia caerulea, was established in an oligotrophic wet meadow in Czech Republic. Each of the eight factorial combinations was replicated three times. Percentage cover for all species was monitored annually in 1‐m2 plots and species' presence recorded in each cell of a continuous square grid of 25 cells (0·1 × 0·1 m each). These data enabled various scale‐dependent estimates of species richness. The species composition of individual treatment combinations diverged over time, particularly at the start of the experiment, and by the latter stages resembled various typical grassland communities from the surrounding landscape. Fertilization had the most pronounced effect, leading to a sharp decrease in species richness, most rapidly at the smallest spatial scale. Mowing had on average a positive effect on species richness and led in most cases to spatially homogeneous species composition. The removal of Molinia had a positive effect on species richness, especially in unmown unfertilized plots. The effects of each factor were dependent on the combination of the other two factors, and also on time, with some effects continuously increasing throughout and some diminishing by the end of the experiment. The process of competitive exclusion with fertilization and cessation of mowing was, in some treatment combinations, rather slow. Synthesis and applications. Land‐use change drivers act in combination, and their effects on the structure of species‐rich wet meadows are dependent on both the temporal and spatial scales considered. Short‐term experiments might underestimate the response of vegetation and thus provide erroneous conservation recommendations. Mowing was only effective in preventing species richness decline caused by fertilization in the short term. The presence of a single dominant species can modify the effectiveness of conservation measures.

Phosphorus and Potassium Transformations in Soil Amended with Enriched Compost and Chemical Fertilizers in a Wheat–Soybean Cropping System

India imports large amounts of rock phosphate (RP) and potassium (K) fertilizers from other countries; hence, research priorities have been directed toward finding alternative sources of phosphorus (P) and K fertilizers. This study focuses on the transformations of P and K in soil amended with RP and waste mica–enriched compost. The enriched compost had greater total P, K, calcium (Ca), magnesium (Mg), micronutrients, and biological properties than ordinary compost. In a wheat–soybean rotation, application of 5 t ha−1 enriched compost along with 50% of the recommended rate of inorganic fertilizer resulted in increased concentrations of saloid P, iron (Fe) P, aluminum (Al) P, Ca-P, occluded P, water-soluble K, exchangeable K, and nonexchangeable K over unfertilized plots. In addition, plots that received enriched compost had greater microbial biomass and phosphatase activities than unfertilized plots. Thus, enriched compost could be an alternative source of water-soluble P and K fertilizers for crop production.

The effects of urea fertilization on carbon sequestration in Douglas-fir plantations of the coastal Pacific Northwest

If long-term carbon (C) sequestration can be quantifiably attributed to forest plantation nitrogen (N) fertilization, the net C credits could be used to offset the rising cost of fertilization and C released during the production, transportation, and application of N fertilizer and the effect of NOx volatilized after application. The purpose of our study was to determine the net change in C sequestration following N fertilization of second-growth Douglas-fir (Psuedotsuga menziesii [Mirb.] Franco) plantations in the Pacific Northwest. The C content of the trees, understory vegetation, forest floor, and mineral soil was quantified at age 26–33 at five sites, each with a fertilized plot that received a total of 896–1120kgNha−1 as urea over 16years paired with an unfertilized control plot. Tree biomass was estimated using biometric equations and by subtracting the difference between treatment and control at the year of site establishment from the difference between treatment and control final measurement. Understory vegetation on the fertilized plots contained significantly more C than on the control plots (0.2MgCha−1, S.D. 0.2). Nitrogen fertilization significantly increased C sequestered per tree by 2.2MgCha−1 (S.D. 1.8), but there was no significant increase in C sequestered in trees per plot. No significant change was found in forest floor, A horizon, and subsoil C contents due to fertilization. These results indicate that, while there is a greater amount of C stored per tree after fertilization, there was more difficulty in accessing C sequestration in forest plantations due to tree mortality and assumed soil variability between plots.

Bacterial Content in Runoff from Simulated Rainfall Applied to Plots Amended with Poultry Litter

To evaluate potential bacterial runoff from poultry litter, litter was applied to test plots and exposed to simulated rainfall 1, 8 or 15 d after litter application. Runoff samples were tested for Salmonella and Campylobacter, two bacterial pathogens commonly associated with poultry, as well as common fecal indicators such as coliforms, enterococci and Escherichia coli. The runoff samples were evaluated from treatments of no litter (control), or the equivalent of 1, 2 or 4 ton/acre of untreated poultry litter. Additionally, runoff samples from treatments of 2 tons/acre of alum-treated litter, 2 tons/acre composted litter and 2 ton/acre deep-stacked litter were compared for bacterial content. Three replicates of the treatments were performed, for a total of 21 test plots. No Campylobacter was isolated from any of the samples and the majority of samples tested negative for Salmonella. Although Salmonella was detected in runoff from many of the plots, it may have originated from sources other than the applied litter (rodents, birds, etc.) since it was detected in two of the unfertilized control plots.

Sustained effects of atmospheric [CO2] and nitrogen availability on forest soilCO2efflux

Soil CO2 efflux (Fsoil ) is the largest source of carbon from forests and reflects primary productivity as well as how carbon is allocated within forest ecosystems. Through early stages of stand development, both elevated [CO2] and availability of soil nitrogen (N; sum of mineralization, deposition, and fixation) have been shown to increase gross primary productivity, but the long-term effects of these factors on Fsoil are less clear. Expanding on previous studies at the Duke Free-Air CO2 Enrichment (FACE) site, we quantified the effects of elevated [CO2] and N fertilization on Fsoil using daily measurements from automated chambers over 10 years. Consistent with previous results, compared to ambient unfertilized plots, annual Fsoil increased under elevated [CO2] (ca. 17%) and decreased with N (ca. 21%). N fertilization under elevated [CO2] reduced Fsoil to values similar to untreated plots. Over the study period, base respiration rates increased with leaf productivity, but declined after productivity saturated. Despite treatment-induced differences in aboveground biomass, soil temperature and water content were similar among treatments. Interannually, low soil water content decreased annual Fsoil from potential values - estimated based on temperature alone assuming nonlimiting soil water content - by ca. 0.7% per 1.0% reduction in relative extractable water. This effect was only slightly ameliorated by elevated [CO2]. Variability in soil N availability among plots accounted for the spatial variability in Fsoil , showing a decrease of ca. 114 g C m(-2) yr(-1) per 1 g m(-2) increase in soil N availability, with consistently higher Fsoil in elevated [CO2] plots ca. 127 g C per 100 ppm [CO2] over the +200 ppm enrichment. Altogether, reflecting increased belowground carbon partitioning in response to greater plant nutritional needs, the effects of elevated [CO2] and N fertilization on Fsoil in this stand are sustained beyond the early stages of stand development and through stabilization of annual foliage production.

Influence of mineral fertilization on edaphic fauna in Acacia auriculiformis (A. Cunn) plantations

Fertilization and/or the accumulation of organic matter from plant residues can influence the composition of soil and litter community. The goal of this study was to evaluate the effects of P and K fertilization on total faunal and nematode faunal composition and richness in plant litter and soil for 360 days in an area reforested with Acacia auriculiformis (A. Cunn), located in the municipality of Conceição de Macabu in the State of Rio de Janeiro. For each treatment (fertilized and unfertilized plots), samples of litter and soil (to a depth of 5 cm) were collected and transferred into a Berlese-Tüllgren funnels for the extraction of fauna. Mesofauna and macrofauna were quantified, and the major taxa identified. Nematodes were extracted by centrifugal flotation in sucrose solution and identified according to feeding habits. Density (number of individuals m-2) of total fauna, microphages, social insects and saprophages varied significantly per treatment and sampling time in both litter and soil. The total number of individuals collected was 5,127, and the total number of nematodes 894. Phosphorus and potassium fertilization resulted in an increase in total fauna density and richness in the litter due to an increased abundance of social insects, saprophages and herbivores. In the soil, fertilization increased the saprophage and predator densities. Saprophages were the predominant taxa in the litter, while social insects (Formicidae) prevailed in the soil. Litter nematode populations were favored by mineral fertilization. Bacteriophages were the predominant nematode group in both litter and soil.