Evidence of rich microbial communities in the subsoil of a boreal acid sulphate soil conducive to greenhouse gas emissions

The largest areas of acid sulphate (AS) soils in Europe are located in Finland, where 67,000–130,000 ha of AS soils are in agricultural use. In addition to their acidifying effects on waters, AS soils might be a significant source of greenhouse gases. In this pilot research, carbon and nitrogen content and microbial activity were studied in an AS and a non-AS soil. Large carbon and nitrogen stocks (110 Mg C_org ha^?1 and 15 Mg N_tot ha^?1) as well as high substrate induced respiration (33 μg CO₂–C g^?1h^?1) were found in the C horizons of the AS soil but not in the non-AS soil. High microbial activity in these horizons of the AS soil was further confirmed by the measurement of dehydrogenase activity, basal respiration, the numbers of culturable bacterial cells, and the ratio of culturable to total numbers of cells. Still, the denitrifying enzyme activity was very low in the anaerobic horizons of the AS soil, indicating the prevalence of microbes other than denitrifiers. We suspect that the microbial community originated with the genesis of AS soil and has been supported by the large stocks of accumulated carbon and mineral nitrogen in the C horizons. If these permanently water-saturated subsoils are exposed to oxygen and their microbial activity consequently increases, large carbon and nitrogen stocks are likely to be mobilised, resulting in increased emission of greenhouse gases. Additional studies of boreal AS soils are needed to assess their potential contribution to increases in greenhouse gas fluxes at the local, regional, and global scales.     

Agricultural management affects earthworm and termite diversity across humid to semi-arid tropical zones

Earthworm and termite diversity were studied in 12 long-term agricultural field trials across the sub-humid to semi-arid tropical zones of Eastern and Western Africa. In each trial, treatments with high and low soil organic C were chosen to represent contrasts in long-term soil management effects, including tillage intensity, organic matter and nutrient management and crop rotations. For each trial, a fallow representing a relatively undisturbed reference was also sampled. Earthworm taxonomic richness decreased in the direction fallow > high-C soil > low-C soil and earthworm abundance was higher in fallow than under continuous crop production. Termite abundance was not significantly different between fallow and high and low-C treatments and termite taxonomic richness was higher in fallow soil than in the two cropping systems. We concluded that fewer species of earthworms and termites were favored under agricultural management that led to lower soil C. Results indicated that the soil disturbance induced by continuous crop production was more detrimental to earthworms than to termites, when compared to the fallow.     

Grass–legume mixtures can yield more nitrogen than legume pure stands due to mutual stimulation of nitrogen uptake from symbiotic and non-symbiotic sources

Concerted use of legumes and of functional diversity in grassland forage systems can provide major contributions to the challenges of agricultural systems being productive yet environmental friendly. Acquisition and transformation of nitrogen (N) resources by legumes and grasses were studied in a temperate grassland experiment near Zurich (Switzerland) to investigate mechanisms driving effects of functional diversity in mixed swards and to optimise mixtures for efficient resource use.Grass–legume interactions and N availability were varied by manipulating legume percentage of the sward (0–100%) and N fertiliser application (50, 150 or 450 kg of N ha^?1 year^?1). ¹⁵N technology quantified N derived from symbiotic (Nsym) and non-symbiotic (Nnonsym) sources.Generally, acquisition of Nsym by the entire mixture was stimulated by grasses. As a result, strong overyielding of Nsym occurred (e.g. 75 and 114% for year 1 and 2 at N150) and mixtures with only 60% and 37% legumes (year 1 and 2) already attained the same Nsym yield as pure legume stands. Legumes stimulated Nnonsym acquisition by the entire mixture, largely via increased uptake by the grass component. Thus, overyielding of Nnonsym of 31% occurred in year 1 (N150).Mutual grass–legume interactions stimulated acquisition of Nsym, acquisition of Nnonsym and efficient transformation of N into biomass compared to either monocultures. These effects of functional diversity can substantially contribute to productive and resource efficient agricultural grassland systems and were maximised in mixtures with 40–60% legumes.     

‘Formiguers’, a historical system of soil fertilization (and biochar production?)

‘Formiguers’ are structures similar to charcoal-kilns that were used to burn piles of biomass with a soil cover in order to produce fertilizers for agricultural plots. Their use was widespread in Spain up to the 1960s and similar structures are still in use in India and Bhutan. Our objective was to study the effects of the ‘formiguer’ on its soil cover in terms of changes in nutrient availability. We built an experimental 0.5-m³ ‘formiguer’ with 68 kg of plant material with a 12% moisture content and 550 kg of soil with a 16% moisture content. The content of organic carbon and mineral nitrogen decreased in the soil cover as a result of burning. After aerobic incubation all samples had a similar content of mineral nitrogen. Exchangeable potassium and total and labile phosphorus increased after burning as a result of the soil cover mixing with the ashes of the biomass as the ‘formiguer’ collapsed during burning in the first two cases, while mineralization of organic compounds produced the increase in labile phosphorus. This input of nutrients for the agricultural plots occurs at a net loss of 0.4–2.5 Mg organic C ha^?1. Very small amounts of charcoal were produced and this may be the reason for their low occurrence in soils today. Burning of ‘formiguers’ required the harvest of vegetation from a considerable forest area (10–25 ha per hectare of agricultural land) and represented a significant disturbance of these systems.     

Long-term impact of a gliricidia-maize intercropping system on carbon sequestration in southern Malawi

Tree/crop systems under agroforestry practice are capable of sequestering carbon (C) in the standing biomass and soil. Although studies have been conducted to understand soil organic C increases in some agroforestry technologies, little is known about C sequestered in simultaneous tree/crop intercropping systems. The main objective of this study was to determine the effect of agroforestry practice on C sequestration and CO₂-C efflux in a gliricidia-maize intercropping system. The experiment was conducted at an experimental site located at the Makoka Agricultural Research Station, in Malawi. The studies involved two field plots, 7-year (MZ21) and 10-year (MZ12), two production systems (sole-maize and gliricidia-maize simultaneous intercropping systems). A 7-year-old grass fallow (Grass-F) was also included. Gliricidia prunings were incorporated at each time of tree pruning in the gliricidia-maize. The amount of organic C recycled varied from 0.8 to 4.8 Mg C ha⁻¹ in gliricidia-maize and from 0.4 to 1.0 Mg C ha⁻¹ in sole-maize. In sole-maize, net decreases of soil carbon of 6 Mg C ha⁻¹ at MZ12 and 7 Mg C ha⁻¹ at MZ21 in the topsoil (0–20 cm) relative to the initial soil C were observed. After 10 years of continuous application of tree prunings C was sequestered in the topsoil (0–20 cm) in gliricidia-maize was 1.6 times more than in sole-maize. A total of 123–149 Mg C ha⁻¹ were sequestered in the soil (0–200 cm depth), through root turnover and pruning application in the gliricidia-maize system. Carbon dioxide evolution varied from 10 to 28 kg ha⁻¹ day⁻¹ in sole-maize and 23 to 83 kg ha⁻¹ day⁻¹ in gliricidia-maize. We concluded that gliricidia-maize intercropping system could sequester more C in the soil than sole-maize.     

Changes in soil respiration across a chronosequence of tallgrass prairie reconstructions

Close relationships among climatic factors and soil respiration (R_s) are commonly reported. However, variation in R_s across the landscape is compounded by site-specific differences that impede the development of spatially explicit models. Among factors that influence R_s, the effect of ecosystem age is poorly documented. We hypothesized that R_s increases with grassland age and tested this hypothesis in a chronosequence of tallgrass prairie reconstructions in central Iowa, U.S.A. We also assessed changes in root biomass, root ingrowth, aboveground net primary productivity (ANPP), and the strength of soil temperature and moisture in predicting R_s. We found a significant increase in total growing season R_s with prairie age (R² = 0.79), ranging from 714 g C m^?2 in the youngest reconstruction (age 4) to 939 g C m^?2 in the oldest prairie (age 12). Soil temperature was a strong predictor of intra-seasonal R_s among prairies (R² = 0.78–0.87) but mean growing season soil temperature and moisture did not relate to total R_s. The increase in R_s with age was positively correlated with root biomass (r = 0.80) and ANPP (r = 0.87) but not with root ingrowth. Our findings suggest that growing season R_s increases with tallgrass prairie age, root biomass, and ANPP during young grassland development.     

Use of life cycle assessment methodology for determining phytoremediation potentials of maize-based cropping systems in fields with nitrogen fertilizer over-dose

Using the life cycle assessment (LCA) method, we analyzed the effects of different cropping systems (sole maize (CK), maize + soybean (CST) and maize + groundnut (CGT)) on the environment. The comprehensive index of environmental impacts varied in the order, sole maize > maize + groundnut > maize + soybean, with corresponding intercropping values of 0.1295, 0.1229 and 0.0945, respectively. The results showed that intercropping maize with suitable plants (e.g., groundnut and soybean) could reduce the adverse effects of over-application of nitrogen fertilizer on the environment. The study further showed that the LCA method may be a convenient and effective approach for analyzing the environmental impact of fertilizer management in agricultural fields.     

Inequality,agro-pastoral exchanges,and soil fertility gradients in southern Mali

Nutrient balances aggregated at the continental, national, or regional levels for African farming systems are usually reported as strongly negative. At the landscape or farm scale, the most commonly reported variability is the gradient of decreasing soil fertility from intensively managed “home” fields to more extensively managed “bush” fields. Case study evidence from an agro-pastoral community of southern Mali’s cotton zone showed that “home” and “bush” fields differed significantly in nutrient balances and soil fertility status but that inter-household differences related to household practice and social factors were even more important.Plot and household-level soil nutrient balances were calculated in 1996–1997 from participatory exercises such as resource flow mapping, participant observation, and soil sampling. The overall community-level nutrient balances averaged −9.2 kg N ha⁻¹, +0.8 kg P ha⁻¹, and −3.4 kg K ha⁻¹, with significant inter-household variation. Soil analysis confirmed significant variation in soil nutrient status at both the landscape and plot levels. Comparing the scale and patterns of input use inequality using Gini coefficients showed the range of coefficients attributable to household behaviours matched or surpassed those attributable to distance factors alone. Input use intensity declined with increasing distance from nutrient sources but field level nutrient balances were better explained by household practice than by distance. Systemic differences in household asset ownership, use, and resource allocation behaviour suggested that much of the diversity seen in the nutrient balances and soil analyses was due to persistent inter-household inequality and the consequent exchanges of agro-pastoral resources. Inter-household negotiations for inputs (such as exchanges of manure and carts) and household-level decisions about input allocation created, exploited, and reinforced a mosaic of soil fertility “hotspots” surrounded by less fertile and less intensively managed patches.     

Changes in functional structure of soil bacterial communities due to fungicide and insecticide applications in canola

The fungicide vinclozolin and insecticide λ-cyhalothrin are widely used to control canola (Brassica spp.) diseases and insect pests, respectively, in Canada. We investigated non-target effects of these pesticides, applied at recommended rates, on soil microbial biomass, functional bacterial diversity and functional community structure of soil bacteria (by evaluating patterns of C substrate utilization) in canola rhizosphere and bulk soil at three locations in Alberta from 2002 to 2004. Experimental treatments were (a) untreated control, (b) vinclozolin fungicide foliar application, (c) λ-cyhalothrin insecticide foliar application, and (d) vinclozolin and λ-cyhalothrin applications. No significant pesticide effects on soil microbial biomass or functional bacterial diversity were observed, but the functional structures of soil bacteria were altered. In 1 of 12 cases, the control treatment had a different soil bacterial community structure from the 3 pesticide treatments. The fungicide treatment had different bacterial community structures from the control or insecticide treatments in 3 of 12 cases, the insecticide treatment had different community structures from the control or fungicide treatments in 4 of 12 cases, and the combined fungicide and insecticide treatment had different community structures from the other treatments in 3 of 12 cases. Therefore, evaluating soil bacterial functional structures revealed pesticide effects that were not detected when bacterial diversity or microbial biomass were measured in canola rhizosphere or bulk soil.     

Effects of different diets on utilization of nitrogen from cattle slurry applied to grassland on a sandy soil in The Netherlands

Dietary adjustments have been suggested as a means to reduce N losses from dairy systems. Differences in fertilizing value of dairy slurry as a result of dietary adjustments were evaluated in a 1-year grassland experiment and by long-term modelling. Slurry composition of non-lactating dairy cows was manipulated by feeding diets with extreme high and low levels of dietary protein and energy. C:N_total ratio of the produced slurries ranged from 5.1 to 11.4. To evaluate their short-term fertilizer N value, the experimental slurries (n = 8) and slurries from commercial farms with variable composition (n = 4), were slit-injected in two grassland fields on the same sandy soil series in the north of The Netherlands (53°10′N, 6°04′E), with differences in sward age and ground water level. The recently established grassland field (NEW) was characterized by lower soil OM, N and moisture contents, less herbs and more modern grass varieties compared to the older grassland field (OLD). Slurry was applied in spring (100 kg N ha⁻¹) and after the first cut (80 kg N ha⁻¹) while in total four cuts were harvested. Artificial fertilizer N treatments were included in the experiment to calculate the mineral fertilizer equivalent (MFE) of slurry N. The OLD field showed a higher total N uptake whereas DM yields were similar for the two fields. Average MFE of the slurries on the OLD field (47%) was lower than on the NEW field (56%), probably as a result of denitrification of slurry N during wet conditions in spring. Slurries from high crude protein diets showed a significantly higher MFE (P < 0.05) compared to low crude protein diets. No significant differences in MFE were observed between slurries from high and low energy diets. On both fields, MFE appeared to be positively related to the ammonium content (P < 0.001) and negatively to the C:N_total ratio of the slurry DM (P = 0.001). Simulation of the effect of long-term annual application of 180 kg N ha⁻¹ with highest and lowest C:N_total ratio suggested that both slurries would lead to an increase in annual soil N mineralization. Both soil N mineralization and SOC appeared to be substantially higher in equilibrium state for the slurry with the highest C:N_total ratio. It is concluded that in a situation with slit-injection, the reduced first-year N availability of slurry with a high C:N_total ratio as observed in the grassland experiment will only be compensated for by soil N mineralization on the very long term.     

Emissions of N2O and NH3, and nitrogen leaching from direct seeded rice under different tillage practices in central China

Tillage practices affect the fate of fertilizer nitrogen (N) through influencing transformations of N, but few studies have examined N₂O and NH₃ emissions, and N leaching from different rice tillage systems. Thus the objective of this study was to assess N₂O emission, NH₃ volatilization and N leaching from direct seeded rice in conventional tillage (CT) and no-tillage (NT) production systems in the subtropical region of China during the 2008 and 2009 rice growing seasons. Treatments were established following a split-plot design of a randomized complete block with tillage practices as the main plot and N fertilizer level as the sub-plot treatment, and there were four treatments: NT + no fertilizer (NT0), CT + no fertilizer (CT0), NT + compound fertilizer (NTC) and CT + compound fertilizer (CTC), respectively. Results showed that N fertilization significantly increased (p < 0.01) N₂O emissions, NH₃ volatilization and N leaching from rice fields in both years. In general, there was no significant difference in N₂O emissions and NH₃ volatilization between NT0 and CT0 in both years, while NTC had significantly higher (p < 0.05) N₂O emissions and NH₃ volatilization compared to CTC. Over the two rice growing seasons, NTC showed 32% and 47% higher N₂O emissions, and 29% and 52% higher NH₃ losses than CTC. Higher (p < 0.05) N₂O emissions from NTC than CTC were presumably due to higher soil organic C and greater denitrification. Total N and NO₃^? concentrations were higher (p < 0.05) in CTC than NTC, but larger volumes of percolation water in NTC than CTC resulted in no significant difference in leakage of total N and NO₃^?. Hence, application of N fertilizer in combination with NT appeared to be ineffective in reducing N losses from N fertilizer in paddy fields.     

Soil C storage as affected by tillage and straw management: An assessment using field measurements and model predictions

Soil tillage and straw management are both known to affect soil organic matter dynamics. However, it is still unclear whether, or how, these two practices interact to affect soil C storage, and data from long term studies are scarce. Soil C models may help to overcome some of these problems. Here we compare direct measurements of soil C contents from a 9 year old tillage experiment to predictions made by RothC and a cohort model. Soil samples were collected from plots in an Irish winter wheat field that were exposed to either conventional (CT) or shallow non-inversion tillage (RT). Crop residue was removed from half of the RT and CT plots after harvest, allowing us to test for interactive effects between tillage practices and straw management. Within the 0–30 cm layer, soil C contents were significantly increased both by straw retention and by RT. Tillage and straw management did not interact to determine the total amount of soil C in this layer. The highest average soil C contents (68.9 ± 2.8 Mg C ha^?1) were found for the combination of RT with straw incorporation, whereas the lowest average soil C contents (57.3 ± 2.3 Mg C ha^?1) were found for CT with straw removal. We found no significant treatment effects on soil C contents at lower depths. Both models suggest that at our site, RT stimulates soil C storage largely by decreasing the decomposition of old soil C. Extrapolating our findings to the rest of Ireland, we estimate that RT will lead to C mitigation ranging from 0.18 to 1.0 Mg C ha^?1 y^?1 relative to CT, with the mitigation rate depending on the initial SOC level. However, on-farm assessments are still needed to determine whether RT management practices can be adopted under Irish conditions without detrimental effects on crop yield.     

Soil quality response to long-term nutrient and crop management on a semi-arid Inceptisol

The soil quality concept provides a tool to help quantify the combined biological, chemical and physical response of soil to crop management practices. Our objective was to quantify effects of 10 fertilizer and farm yard manure (FYM) treatments applied for 31 years to a rotation that included maize (Zea mays), pearl millet (Pennisetum americanum), wheat (Triticum aestivum) and cowpea (Vigna unguiculata) on an Inceptisol at the Indian Agricultural Research Institute in New Delhi, India. A soil quality index (SQI) based on six soil functions (i.e. the soil's ability to: accommodate water entry, facilitate water movement and storage, resist surface degradation, resist biochemical degradation, supply plant nutrients and sustain crop productivity) was derived for each treatment using bulk density, water retention, pH, electrical conductivity (EC), plant-available nutrients, soil organic matter (SOM), microbial biomass, soil enzymes and crop yield. SQI ratings ranged from 0.552 (unfertilized control) to 0.838 for the combined NPK fertilizer plus manure treatment. Comparisons among treatments indicated that SQI increases associated with the combined (NPK + manure) treatment were distributed as follows: N (7.1% increase), P (7.8%), K (14.4%), Zn (4.8%) and manure (15%). The control (−11.4%) and N alone (−5.1%) resulted in degradation compared to a reference soil (no fertilizer/manure, no crop), and NP alone or sub-optimal rates of NPK were on the verge of degradation. Hand weeding and sulphur application had no measurable effect on SQI. High K fixing capacity was a limiting factor for these soils, even when FYM was applied. The lower SQI rating associated with N or NP-only treatments suggests that two of the most common fertilizer management practices in India may not be sustainable. The SQI was calculated without the weighting factors too, which revealed that the weighting factors did not affect the relative ranks of individual treatments.     

Agroforestry associating coffee and Inga densiflora results in complementarity for water uptake and decreases deep drainage in Costa Rica

The shade impact by Inga densiflora on water use and drainage in a coffee agroforestry system (AFS) was compared to coffee monoculture (MC) in Costa Rica. Rainfall interception, transpiration, runoff and soil water content were monitored during 3 years. Runoff was lower in AFS than MC (5.4 and 8.4% of total rainfall, respectively) and a higher water infiltration was observed under AFS. Still, the higher combined rainfall interception + transpiration of coffee and shade trees in AFS resulted in a lower drainage than in MC. No coffee water stress was recorded either in AFS or MC as relative extractable soil water remained above 20% during the dry seasons. Time course of soil water content showed enhanced access to soil water between 100 and 200 cm depth in AFS. This suggests complementarity for soil water between coffee and shade trees. The model HYDRUS 1D predicted that drainage at 200 cm depth accounted for a large fraction of annual rainfall (68% for MC and 62% for AFS). Climatic scenario simulations showed (1) a potential competition for water between coffee and shade trees when the dry season was extended by 4–6 weeks compared to actual, and (2) a severe reduction in annual drainage, but without competition for water when rainfall was reduced down to 40% of the actual.     

Monitoring and verifying agricultural practices related to soil carbon sequestration with satellite imagery

The Kyoto Protocol entering into force on 16 February 2005 continues to spur interest in development of carbon trading mechanisms internationally and domestically. Critical to the development of a carbon trading effort is verification that carbon has been sequestered, and field level measurement of C change is likely cost prohibitive. Estimating C change based on agricultural management practices related to carbon sequestration seems more realistic, and analysis of satellite imagery could be used to monitor and verify these practices over large areas. We examined using Landsat imagery to verify crop rotations and quantify crop residue biomass in north central Montana. Field data were collected using a survey of farms. Standard classification tree analysis (CTA) and boosted classification and regression tree analysis (BCTA) were used to classify crop types. Linear regression (LM), regression tree analysis (RTA), and stochastic gradient boosting (SGB) were used to estimate crop residue. Six crop types were classified with 97% accuracy (BCTA) with class accuracies of 88–99%. Paired t-tests were used to compare the difference between known and predicted mean crop residue biomass. The difference between known and predicted mean residues using SGB was not different than 0 (p-value = 0.99); however root mean square error (RMSE) was large (1981 kg ha⁻¹), implying that SGB accurately predicted regional crop residue biomass but not local predictions (i.e., field or farm level). The results of this study, and previous research classifying tillage practices and estimating soil disturbance, supports using satellite imagery as an effective tool for monitoring and verifying agricultural management practices related to carbon sequestration over large areas.     

Assessing soil chemical and physical property responses to deforestation and subsequent cultivation in smallholders farming system in Ethiopia

In Ethiopia land degradation in the forms of soil erosion and declining soil fertility are serious challenges to agricultural productivity and economic growth. Despite the general recognition of the threat from land degradation on agricultural productivity, few studies have been made to quantify the extent, rate and process of soil fertility depletion under various land use systems and management practices in the country. In this study we assessed soil chemical and physical property responses to deforestation and subsequent cultivation along a chronosequence of closely located farmlands of different ages (7, 10, 26, 34 and 53 years) since conversion from a tropical dry Afromontane natural forest in Ethiopia. These properties were compared with soil properties under an adjacent natural forest. The changes were used as indicators to evaluate the sustainability of the farm management. All the soils in the study were Mollic Andosols/Humic Haplustands. Soil bulk density (g cm⁻³) in the 0–10 and 10–20 cm soil layers increased significantly while percent pore space decreased significantly in a continuum with increasing cultivation period. Soil C and total N contents (g kg⁻¹) in the 0–10 cm soil layer declined significantly and exponentially with increasing years under cultivation. However, in the 10–20 cm soil layer both soil C and total N on the farmlands were significantly higher until after 34 years of continuous cultivation compared to the same soil layer under the natural forest. Consequently, the soil C stock (g m⁻²) of the upper 0.20 m mineral soil was not significantly lower on the farmlands until after 26 years of continuous cultivation compared to the natural forest soil. Available P and K (mg kg⁻¹) in the 0–10 cm layer were higher in the soils of the farmlands throughout the 53 years of continuous cultivation compared to the soil under the natural forest. Exchangeable Ca, CEC and base saturation in the 0–10 cm soil layer declined more or less throughout the cultivation period while in the 10–20 cm soil layer they followed the patterns of soil C of that depth. Generally, the magnitudes and rates of degradation of the soil properties following conversion and subsequent cultivation were lower than expected for a low input tropical farming system as the one investigated. Nevertheless, almost all soil quality attributes showed overall declining trends in the long perspective. This continuous decline, albeit slowly, in soil quality with increasing cultivation period indicated that the present land management is not sustainable. Therefore, improved management is imperative to sustain the soil quality and maintain long-term productivity of the farmlands.     

Modelling soil phosphorus decline: Expectations of Water Framework Directive policies

Depletion of plant-available soil phosphorus (P) from excessive to agronomically optimum levels is a measure being implemented in Ireland to reduce the risk of diffuse P transfer from land to water. Within the Nitrates and Water Framework Directive regulations the policy tool is designed to help achieve good status by 2015 in water bodies at risk from eutrophication. To guide expectation, this study used soil plot data from eight common soil associations to develop a model of Soil Test P (STP) (Morgan's extract) decline following periods of zero P amendment. This was used to predict the time required to move from excessive (Index 4) to the upper boundary of the optimum (Index 3) soil P concentration range. The relative P balance (P balance : Total soil P) best described an exponential decline (R² = 63%) of STP according to a backwards step-wise regression of a range of soil parameters. Using annual field P balance scenarios (?30 kg P ha^?1, ?15 kg P ha^?1, ?7 kg P ha^?1), average time to the optimum soil P boundary condition was estimated from a range of realistic Total P and STP starting points. For worst case scenarios of high Total P and STP starting points, average time to the boundary was estimated at 7–15 years depending on the field P balance. However, uncertainty analysis of the regression parameter showed that variation can be from 3 to >20 years. Combined with variation in how soil P source changes translate to resulting P delivery to water bodies, water policy regulators are advised to note this inherent uncertainty from P source to receptor with regard to expectations of Water Framework Directive water quality targets and deadlines.     

Disaggregated greenhouse gas emission inventories from agriculture via a coupled economic-ecosystem model

Estimates of regional greenhouse gas emissions from agricultural systems are needed to evaluate possible mitigation strategies with respect to environmental effectiveness and economic feasibility. Therefore, in this study, we used the GIS-coupled economic-ecosystem model EFEM–DNDC to assess disaggregated regional greenhouse gas (GHG) emissions from typical livestock and crop production systems in the federal state of Baden-Württemberg, Southwest Germany. EFEM is an economic farm production model based on linear programming of typical agricultural production systems and simulates all relevant farm management processes and GHG emissions. DNDC is a process-oriented ecosystem model that describes the complete biogeochemical C and N cycle of agricultural soils, including all trace gases.Direct soil emissions were mainly related to N₂O, whereas CH₄ uptake had marginal influence (net soil C uptake or release was not considered). The simulated N₂O emissions appeared to be highly correlated to N fertilizer application (R² = 0.79). The emission factor for Baden-Württemberg was 0.97% of the applied N after excluding background emissions.Analysis of the production systems showed that total GHG emissions from crop based production systems were considerably lower (2.6–3.4 Mg CO₂ eq ha⁻¹) than from livestock based systems (5.2–5.3 Mg CO₂ eq ha⁻¹). Average production system GHG emissions for Baden-Württemberg were 4.5 Mg CO₂ eq ha⁻¹. Of the total 38% were derived from N₂O (direct and indirect soil emissions, and manure storage), 40% were from CH₄ (enteric fermentation and manure storage), and 22% were from CO₂ (mainly fertilizer production, gasoline, heating, and additional feed). The stocking rate was highly correlated (R² = 0.85) to the total production system GHG emissions and appears to be a useful indicator of regional emission levels.     

Soil-profile organic carbon and total nitrogen during 12 years of pasture management in the Southern Piedmont USA

Soil organic C (SOC) and total soil N (TSN) sequestration estimates are needed to improve our understanding of management influences on soil fertility and terrestrial C cycling related to greenhouse gas emission. We evaluated the factorial combination of nutrient source (inorganic, mixed inorganic and organic, and organic as broiler litter) and forage utilization (unharvested, low and high cattle grazing pressure, and hayed monthly) on soil-profile distribution (0–150 cm) of SOC and TSN during 12 years of pasture management on a Typic Kanhapludult (Acrisol) in Georgia, USA. Nutrient source rarely affected SOC and TSN in the soil profile, despite addition of 73.6 Mg ha^?1 (dry weight) of broiler litter during 12 years of treatment. At the end of 12 years, contents of SOC and TSN at a depth of 0–90 cm under haying were only 82 ± 5% (mean ± S.D. among treatments) of those under grazed management. Within grazed pastures, contents of SOC and TSN at a depth of 0–90 cm were greatest within 5 m of shade and water sources and only 83 ± 7% of maximum at a distance of 30 m and 92 ± 14% of maximum at a distance of 80 m, suggesting a zone of enrichment within pastures due to animal behavior. During 12 years, the annual rate of change in SOC (0–90 cm) followed the order: low grazing pressure (1.17 Mg C ha^?1 year^?1) > unharvested (0.64 Mg C ha^?1 year^?1) = high grazing pressure (0.51 Mg C ha^?1 year^?1) > hayed (?0.22 Mg C ha^?1 year^?1). This study demonstrated that surface accumulation of SOC and TSN occurred, but that increased variability and loss of SOC with depth reduced the significance of surface effects.     

The transport of Cu and Zn from agricultural soils to surface water in a small catchment

Long-term manure-borne copper and zinc inputs (18–324 mg Cu m⁻² yr⁻¹ and 100–800 mg Zn m⁻² yr⁻¹) to grassland soils resulted in their catchment in water concentrations that often exceeded the surface water quality criteria (2 μg Cu l⁻¹ and 5 μg Zn l⁻¹). This paper compares retention and release of Cu and Zn by two types of soil, a mineral soil (MS) and a dark colored soil rich in organic matter (OS). On the basis of dry soil mass, the OS has a higher retention/affinity for Cu and Zn than the MS, but much less Zn accumulated in the MS when compared on an areal basis. This is largely because of the much smaller bulk OS density and larger dissolved metal concentrations in the OS drainage than that for the MS. However, because of the greater water retention capacity of the OS, elevated metal concentrations in the soil solution do not necessarily cause greater loss to water. It is concluded that artificially drained OS can contribute significantly to the observed elevated Cu and Zn concentrations of the river, especially during relatively dry weather conditions when the contribution of water seeping from OS to the total river water discharge becomes increasingly important.