Exceedance of modern ‘background’ fine-grained sediment delivery to rivers due to current agricultural land use and uptake of water pollution mitigation options across England and Wales

Excessive loss of fine-grained sediment to rivers is widely recognised as a global environmental problem. To address this issue, policy teams and catchment managers require an estimate of the ‘gap’ requiring remediation, as represented by the excess above ‘background’ losses. Accordingly, recent work has estimated the exceedance of modern ‘background’ sediment delivery to rivers at national scale across England and Wales due to (i) current agricultural land cover, cropping and stocking, and (ii) current land use corrected for the uptake of on-farm mitigation measures. This sectoral focus recognises that, nationally, agriculture has been identified as the principal source of fine sediment loss to the aquatic environment. Two estimates of modern ‘background’ sediment loss, based on paleolimnological evidence, were used in the analysis; the target modern ‘background’ (TMBSDR) and maximum modern ‘background’ (MMBSDR) sediment delivery to rivers. For individual (n = 4485) non-coastal water bodies, the sediment ‘gap’ in excess of TMBSDR and MMBSDR, due to current land cover, cropping and stocking, was estimated to range up to 1368 kg ha⁻¹ yr⁻¹ (median 61 kg ha⁻¹ yr⁻¹) and 1321 kg ha⁻¹ yr⁻¹ (median 19 kg ha⁻¹ yr⁻¹), respectively. The respective ranges in conjunction with current land cover, cropping and stocking but corrected for the potential impact of on-farm sediment mitigation measures were up to 1315 kg ha⁻¹ yr⁻¹ (median 50 kg ha⁻¹ yr⁻¹) and 1269 kg ha⁻¹ yr⁻¹ (median 8 kg ha⁻¹ yr⁻¹). Multiplication of the estimates of excess sediment loss corrected for current measure uptake, above TMBSDR and MMBSDR, with estimated maximum unit damage costs for the detrimental impacts of sediment pollution on ecosystem goods and services, suggested respective water body ranges up to 495 £ ha⁻¹ yr⁻¹ and 478 £ ha⁻¹ yr⁻¹. Nationally, the total loss of sediment in excess of TMBSDR was estimated at 1,389,818 t yr⁻¹ equating to maximum environmental damage costs of £523 M yr⁻¹, due to current structural land use, compared to 1,225,440 t yr⁻¹ equating to maximum damage costs of £462 M yr⁻¹ due the uptake of on-farm sediment control measures. The corresponding total loss of sediment in excess of MMBSDR was estimated at 1,038,764 t yr⁻¹ equating to maximum damage costs of £462 M yr⁻¹, compared with 890,146 t yr⁻¹ and £335 M yr⁻¹ correcting excess agricultural sediment loss for current implementation of abatement measures supported by policy instruments. This work suggests that the current uptake of sediment control measures on farms across England and Wales is delivering limited benefits in terms of reducing loadings to rivers and associated environmental damage costs.     

Reconnecting crop and cattle farming to reduce nitrogen losses to river water of an intensive agricultural catchment (Seine basin,France): past,present and future

Nitrate and pesticide contamination of surface and groundwater has become a major problem in intensive farming regions in Europe, with nitrate concentrations reaching values above the standard defined in 2000 by the European Water Framework Directive. In the Seine basin, a major issue is the closure and abandonment of drinking-water wells, which force water managers and drinking-water producers to explore solutions for water resource protection. Organic farming has appeared as a credible alternative to conventional farming, and this study explores the potential of organic farming to reconcile agricultural production and water quality. On the basis of agricultural statistics, survey questionnaires and experimental data, the nitrogen soil surface balance (N-SSB) has been established at the scale of a small 104-km² catchment (The Orgeval sub-basin), representative of the intensive cash crop farming in the Seine basin. The N-surplus for arable land in specialized organic cash crop systems has been found to be half that of current conventional systems (15 kg N ha⁻¹ yr⁻¹ versus 30 kg N ha⁻¹ yr⁻¹, respectively). The N-yield in organic systems is 21% lower than in conventional systems, but total fertilization (mostly symbiotic N fixation) is also 26% lower. Whereas 2–3 years of forage legume (e.g., alfalfa) as a starter crop of the typical 7- to 10-year diversified rotation builds up N soil fertility and helps prevent weeds without pesticides, the existence of an outlet for this fodder production is a limiting factor for the economic sustainability and the environmental benefits of these farming systems. Therefore, we explored the possibility of a reconnection of livestock and crop farming systems in the Orgeval catchment, a traditional dairy farming and Brie cheese production region. We calculated the N-SSB for this type of a reconnected livestock and cropping system and found a value very close to the specialized organic cash crop system with full utilization of fodder production, leading to profitable animal production, essentially as milk in this farm design. This reconnected system is compared with the estimated situation in 1955 before separation of plant and livestock production. Furthermore, the N-SSB values were converted into infiltrating sub-root concentrations and used as a boundary condition to a biogeochemical model. Organic cropping and organic reconnected livestock cropping systems result in a 50% reduction of surface water nitrate concentrations, a surface water quality 20% better than that reconstructed for 1955, with an overall higher protein production.     

Comparing intensive,extensified and organic grassland farming in southern Germany by process life cycle assessment

To reduce the environmental burden of agriculture, suitable methods to comprehend and assess the impact on natural resources are needed. One of the methods considered is the life cycle assessment (LCA) method, which was used to assess the environmental impacts of 18 grassland farms in three different farming intensities — intensive, extensified, and organic — in the Allgäu region in southern Germany. Extensified and organic compared with intensive farms could reduce negative effects in the abiotic impact categories of energy use, global warming potential (GWP) and ground water mainly by renouncing mineral nitrogen fertilizer. Energy consumption of intensive farms was 19.1 GJ ha⁻¹ and 2.7 GJ t⁻¹ milk, of extensified and organic farms 8.7 and 5.9 GJ ha⁻¹ along with 1.3 and 1.2 GJ t⁻¹ milk, respectively. Global warming potential was 9.4, 7.0 and 6.3 CO₂-equivalents ha⁻¹ and 1.3, 1.0 and 1.3 CO₂-equivalents t⁻¹ milk for the intensive, extensified and organic farms, respectively. Acidification calculated in SO₂-equivalents was high, but the extensified (119 kg SO₂ ha⁻¹) and the organic farms (107 kg SO₂ ha⁻¹) emit a lower amount compared with the intensive farms (136 kg SO₂ ha⁻¹). Eutrophication potential computed in PO₄-equivalents was higher for intensive (54.2 kg PO₄ ha⁻¹) compared with extensified (31.2 kg PO₄ ha⁻¹) and organic farms (13.5 kg PO₄ ha⁻¹). Farmgate balances for N (80.1, 31.4 and 31.1 kg ha⁻¹) and P (5.3, 4.5 and −2.3 kg ha⁻¹) for intensive, extensified and organic farms, respectively, indicate the different impacts on ground and surface water quality. Analysing the impact categories biodiversity, landscape image and animal husbandry, organic farms had clear advantages in the indicators number of grassland species, grazing cattle, layout of farmstead and herd management, but indices in these categories showed a wide range and are partly independent of the farming system.     

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.     

Life-cycle environmental and economic impacts of energy-crop fuel-chains: an integrated assessment of potential GHG avoidance in Ireland

This paper combines life-cycle analyses and economic analyses for Miscanthus and willow heat and electricity fuel-chains in Ireland. Displaced agricultural land-uses and conventional fuels were considered in fuel-chain permutations. Avoided greenhouse gas (GHG) emissions ranged from 7.7 to 35.2 t CO₂ eq. ha⁻¹ a⁻¹. Most fuel-chain permutations exhibited positive discounted financial returns, despite losses for particular entities at a farm-gate processed-biomass price of €100 t⁻¹ dry-matter. Attributing a value of €10 t⁻¹ CO₂ eq. to avoided GHG emissions, but subtracting financial returns associated with displaced fuel supplies, resulted in discounted annual national economic benefits (DANEBs) ranging from −457 to 1887€ ha⁻¹ a⁻¹. Extrapolating a plausible combination of fuel-chains up to a national indicative scenario resulted in GHG emission avoidance of 3.56 Mt CO₂ eq. a⁻¹ (5.2% of national emissions), a DANEB of 167 M€, and required 4.6% of national agricultural land area. As cost-effective national GHG avoidance options, Miscanthus and willow fuel-chains are robust to variation in yields and CO₂ price, and appear to represent an efficient land-use option (e.g. compared with liquid biofuel production). Policies promoting utilisation of these energy-crops could avoid unnecessary, and environmentally questionable, future purchase of carbon credits, as currently required for national Kyoto compliance.     

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.     

Biogas production from maize and dairy cattle manure—Influence of biomass composition on the methane yield

There is an increasing world wide demand for energy crops and animal manures for biogas production. To meet these demands, this research project aimed at optimising anaerobic digestion of maize and dairy cattle manures. Methane production was measured for 60 days in 1 l eudiometer batch digesters at 38 °C. Manure received from dairy cows with medium milk yield that were fed a well balanced diet produced the highest specific methane yield of 166.3 Nl CH₄ kg VS⁻¹. Thirteen early to late ripening maize varieties were grown on several locations in Austria. Late ripening varieties produced more biomass than medium or early ripening varieties. On fertile locations in Austria more than 30 Mg VS ha⁻¹ can be produced. The methane yield declined as the crop approaches full ripeness. With late ripening maize varieties, yields ranged between 312 and 365 Nl CH₄ kg VS⁻¹ (milk ripeness) and 268–286 Nl CH₄ kg VS⁻¹ (full ripeness). Silaging increased the methane yield by about 25% compared to green, non-conserved maize. Maize (Zea mays L.) is optimally harvested, when the product from specific methane yield and VS yield per hectare reaches a maximum. With early to medium ripening varieties (FAO 240–390), the optimum harvesting time is at the “end of wax ripeness”. Late ripening varieties (FAO ca. 600) may be harvested later, towards “full ripeness”. Maximum methane yield per hectare from late ripening maize varieties ranged between 7100 and 9000 Nm³ CH₄ ha⁻¹. Early and medium ripening varieties yielded 5300–8500 Nm³ CH₄ ha⁻¹ when grown in favourable regions. The highest methane yield per hectare was achieved from digestion of whole maize crops. Digestion of corns only or of corn cob mix resulted in a reduction in methane yield per hectare of 70 and 43%, respectively. From the digestion experiments a multiple linear regression equation, the Methane Energy Value Model, was derived that estimates methane production from the composition of maize. It is a helpful tool to optimise biogas production from energy crops. The Methane Energy Value Model requires further validation and refinement.     

Carbon stocks in Swiss agricultural soils predicted by land-use,soil characteristics,and altitude

Effects of agricultural land-use and land-use change on soil organic carbon (SOC) pools play an important role in the mitigation of the global greenhouse effect. To estimate these effects, baseline SOC data for individual regions or countries are needed. The aim of this study was to quantify current SOC stocks in Swiss agricultural soils, to identify meaningful predictors for SOC, and to estimate historical SOC losses. SOC stocks in mineral soils were estimated from combined georeferenced data for land-use, topography, and profile data (n=544) from soil surveys. Mean SOC density in the layer 0–20 cm ranged between 40.6±8.9 t ha⁻¹ (±95% confidence interval (CI)) for arable land and 50.7±12.2 t ha⁻¹ for favourable permanent grassland, and in the layer 0–100 cm from 62.9±15.2 t ha⁻¹ for unfavourable grassland to 117.4±29.8 t ha⁻¹ for temporary grasslands (leys). SOC stocks in organic soils were quantified separately for intact and cultivated peatlands using data from peatland inventories and current SOC densities calculated from average peat decay rates. Organic soils account for less than 3% of the total area but store about 28% (47.2±7.3 Mt) of the total SOC stock of 170±17 Mt. Land-use type, clay content, and altitude (serving as a climate proxy for grassland soils at higher altitudes) were identified as main SOC predictors in mineral soils. Clay content explained up to 44% of the variability in SOC concentrations in the fine earth of arable soils, but was not significantly related to SOC in grassland soils at higher altitudes. SOC concentration under permanent grassland increases linearly with altitude, but because soil depth and stone content limit carbon storage in alpine grassland soils, no relationship was found between altitude and SOC stock. A preliminary estimate suggested that about 16% of the national SOC stock has been lost historically due to peatland cultivation, urbanisation, and deforestation. It seems unlikely that future changes in agricultural practices could compensate for this historical SOC loss in Swiss agricultural soils.     

Modelling greenhouse gas emissions from European conventional and organic dairy farms

Agriculture is an important contributor to global emissions of greenhouse gases (GHG), in particular for methane (CH₄) and nitrous oxide (N₂O). Emissions from farms with a stock of ruminant animals are particularly high due to CH₄ emissions from enteric fermentation and manure handling, and due to the intensive nitrogen (N) cycle on such farms leading to direct and indirect N₂O emissions. The whole-farm model, FarmGHG, was designed to quantify the flows of carbon (C) and nitrogen (N) on dairy farms. The aim of the model was to allow quantification of effects of management practices and mitigation options on GHG emissions. The model provides assessments of emissions from both the production unit and the pre-chains. However, the model does not quantify changes in soil C storage.Model dairy farms were defined within five European agro-ecological zones for both organic and conventional systems. The model farms were all defined to have the same utilised agricultural area (50 ha). Cows on conventional and organic model farms were defined to achieve the same milk yield, so the basic difference between conventional and organic farms was expressed in the livestock density. The organic farms were defined to be 100% self-sufficient with respect to feed. The conventional farms, on the other hand, import concentrates as supplementary feed and their livestock density was defined to be 75% higher than the organic farm density. Regional differences between farms were expressed in the milk yield, the crop rotations, and the cow housing system and manure management method most common to each region.The model results showed that the emissions at farm level could be related to either the farm N surplus or the farm N efficiency. The farm N surplus appeared to be a good proxy for GHG emissions per unit of land area. The GHG emissions increased from 3.0 Mg CO₂-eq ha⁻¹ year⁻¹ at a N surplus of 56 kg N ha⁻¹ year⁻¹ to 15.9 Mg CO₂-eq ha⁻¹ year⁻¹ at a N surplus of 319 kg N ha⁻¹ year⁻¹. The farm N surplus can relatively easily be determined on practical farms from the farm records of imports and exports and the composition of the crop rotation. The GHG emissions per product unit (milk or metabolic energy) were quite closely related to the farm N efficiency, and a doubling of the N efficiency from 12.5 to 25% reduced the emissions per product unit by ca. 50%. The farm N efficiency may therefore be used as a proxy for comparing the efficiencies of farms with respect to supplying products with a low GHG emission.     

Evaluation of two soil carbon models using two Kenyan long term experimental datasets

RothC and Century are two of the most widely used soil organic matter (SOM) models. However there are few examples of specific parameterisation of these models for environmental conditions in East Africa. The aim of this study was therefore, to evaluate the ability of RothC and the Century to estimate changes in soil organic carbon (SOC) resulting from varying land use/management practices for the climate and soil conditions found in Kenya. The study used climate, soils and crop data from a long term experiment (1976–2001) carried out at The Kabete site at The Kenya National Agricultural Research Laboratories (NARL, located in a semi-humid region) and data from a 13 year experiment carried out in Machang’a (Embu District, located in a semi-arid region). The NARL experiment included various fertiliser (0, 60 and 120 kg of N and P₂O₅ ha⁻¹), farmyard manure (FYM—5 and 10 t ha⁻¹) and plant residue treatments, in a variety of combinations. The Machang’a experiment involved a fertiliser (51 kg N ha⁻¹) and a FYM (0, 5 and 10 t ha⁻¹) treatment with both monocropping and intercropping. At Kabete both models showed a fair to good fit to measured data, although Century simulations for treatments with high levels of FYM were better than those without. At the Machang’a site with monocrops, both models showed a fair to good fit to measured data for all treatments. However, the fit of both models (especially RothC) to measured data for intercropping treatments at Machang’a was much poorer. Further model development for intercrop systems is recommended. Both models can be useful tools in soil C predictions, provided time series of measured soil C and crop production data are available for validating model performance against local or regional agricultural crops.     

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.     

Reducing phosphorus in dairy diets improves farm nutrient balances and decreases the risk of nonpoint pollution of surface and ground waters

Reducing phosphorus (P) in dairy diets may result in different types of manure with different chemical composition. Application of these manures to soils may affect the soil P solubility and lead to different environmental consequences. A laboratory incubation study determined the impact of 40 dairy manures on P dynamics in two soil types, Mattapex silt loam (Aquic Hapludult) and Kalmia sandy loam (Typic Hapludult). The manures were fecal samples of lactating cows, collected from commercial dairy farms located in Northeastern and Mid-Atlantic United States, with a wide range of dietary P concentrations (from 2.9 to 5.8 g P kg⁻¹ feed dry matter, DM). Dried and ground fecal samples were mixed with surface horizon (0–15 cm) of soils at 150 kg P ha⁻¹ and the mixtures were incubated at 25 °C for 21 days. At the end of incubation, water soluble P (WS-P) and Mehlich-3 P (M3-P) in the soil–manure mixtures were substantially higher than the control (soil alone) but were lower than the soils receiving fertilizer KH₂PO₄ at 150 kg P ha⁻¹. Similarly, the relative extractability of P in soils amended with low- and high-P manures was always lower (<93%) than KH₂PO₄ suggesting that fertilizer P is more effective at increasing soil solution P in the short-term. Concentrations of WS-P or M3-P in soil–manure mixtures did not differ regardless of the source of manure (i.e. different farms and different diets). This suggests that when the same amount of P is added to soils through manure applications, the solubility or bioavailability of P in soils will be the same. However, P concentrations in feces correlate significantly with that in diets (r = 0.82^**); and when the manures were grouped into high-P diets (averaging 5.1 g P kg⁻¹) versus low-P diets (3.6 g P kg⁻¹), manure P was 40% greater in the high-P group (10.6 g kg⁻¹ DM) than the low-P group (7.6 g kg⁻¹ DM). Thus, lowering excess P in diets would reduce P excretion in manures, P accumulation in soils, improve P balance on farms, require less area for land disposal, and decrease potential for P loss to waters.     

Nutrient flows in small-scale peri-urban vegetable farming systems in Southeast Asia—A case study in Hanoi

In many peri-urban areas of Southeast Asia, land use has been transformed from rice-based to more profitable vegetable-based systems in order to meet the increasing market demand. The major management related flows of nitrogen (N), phosphorus (P), potassium (K), copper (Cu) and zinc (Zn) were quantified over a 1-year period for intensive small-scale aquatic and terrestrial vegetable systems situated in two peri-urban areas of Hanoi City, Vietnam. The two areas have different sources of irrigation water; wastewater from Hanoi City and water from the Red River upstream of Hanoi. The first nutrient balances for this region and farming systems are presented. The main sources of individual elements were quantified and the nutrient use efficiency estimated. The environmental risks for losses and/or soil accumulation were also assessed and discussed in relation to long-term sustainability and health aspects.The primary source of nutrient input involved a combination of chemical fertilisers, manure (chicken) and irrigation water. A variable composition and availability of the latter two sources greatly influenced the relative magnitude of the final total loads for individual elements. Despite relatively good nutrient use efficiencies being demonstrated for N (46–86%) and K (66–94%), and to some extent also for P (19–46%), high inputs still resulted in substantial annual surpluses causing risks for losses to surface and ground waters. The surplus for N ranged from 85 to 882 kg ha⁻¹ year⁻¹, compared to P and K which were 109–196 and 20–306 kg ha⁻¹ year⁻¹, respectively. Those for Cu and Zn varied from 0.2 to 2.7 and from 0.6 to 7.7 kg ha⁻¹ year⁻¹, respectively, indicating high risk for soil accumulation and associated transfers through the food chain.Wastewater irrigation contributed to high inputs, and excess use of organic and chemical fertilisers represent a major threat to the soil and water environment. Management options that improve nutrient use efficiency represent an important objective that will help reduce annual surpluses. A sustainable reuse of wastewater for irrigation in peri-urban farming systems can contribute significantly to the nutrient supply (assuming low concentrations of potential toxic or hazardous substances in the water). Nutrient inputs need to be better related to the crop need, e.g. through better knowledge about the nutrient concentrations in the wastewater and improved management of the amount of irrigation water being applied.     

Monitoring GHG from manure stores on organic and conventional dairy farms

Organic farming methods are claimed to be more environmentally friendly than conventional methods and the EU MIDAIR project had an overall aim to compare emissions from organic dairy farming with conventional methods of milk production. Manure stores are the second largest source of methane emissions (after enteric fermentation) on European dairy farming.The aim of this project was to measure green house gas (GHG) emissions from manures in covered and uncovered slurry stores and farm yard manure (FYM) heaps. The chosen method for measuring these emissions was the tracer ratio method, using sulphur hexafluoride (SF₆) as the tracer gas, the limitations of this method prevented successful measurements being made on some of the stores and a modified method was used on the covered stores. The difference in concentration of the upwind and downwind samples and interfering sources were limiting factors. FYM emission measurements were successful only when the manure was stored indoors.Methane emissions were successfully measured over a 12 month period from the uncovered slurry stores. Emission rates from the uncovered slurry stores on the conventional farm and the organic farm ranged from 14.4 to 49.6 and from 12.4 to 42.3 g C m⁻³ d⁻¹, respectively, with the mean CH₄ emission rates of 35 and 26 g C m⁻³ d⁻¹. On both farms, nitrous oxide emissions were close to zero.Methane emissions measured from the indoor organic FYM in summer were 17.1 g C m⁻³ d⁻¹ and the nitrous oxide emission was 411 mg N m⁻³ d⁻¹.The covered slurry stores were in such close proximity to other GHG sources that the tracer ratio method was unsuitable and the air-injection method was adopted. The measured emissions from covered slurry stores of CH₄, CO₂ and NH₃ were, respectively, 14.9 g C m⁻³ d⁻¹, 12.9 g C m⁻³ d⁻¹ and 18.6 mg NH₃ m⁻² d⁻¹ of slurry in February and 12.0 g C m⁻³ d⁻¹, 9.5 g C m⁻³ d⁻¹ and 335 mg NH₃ m⁻² d⁻¹ slurry in March. No nitrous oxide production could be measured.     

Effectiveness of buffer strips in removing pollutants in runoff from a cultivated field in North-East Italy

Buffer strips are an efficient and economical way to reduce agricultural nonpoint source pollution. Local researches are necessary to gain information on buffer performance, with particular emphasis on narrow buffers. The effect of a 6 m buffer strip (BS) in reducing runoff, suspended solids and nutrients from a field growing maize, winter wheat and soybean was assessed in a field experiment conducted in North-East Italy during 1998–2001. The BS was composed of two rows of regularly alternating trees (Platanus hybrida Brot.) and shrubs (Viburnum opulus L.), with grass (Festuca arundinacea L.) in the inter-rows.The BS reduced total runoff by 78% compared to no-BS, in which cumulative runoff depth was 231 mm over 4 years. With no-BS runoff appeared to be influenced mostly by total rainfall, while with BS maximum rainfall intensity was more important. The filtering effect of the BS reduced total suspended solids (TSS), particularly after the second year, when the median yearly concentrations ranged from 0.28 to 0.99 mg L⁻¹ and were smaller than 0.14 mg L⁻¹, with no-BS and with BS respectively. The combination of lower concentrations and runoff volumes significantly reduced TSS losses from 6.9 to 0.4 t ha⁻¹ over the entire period.A tendency to increased concentrations of all forms of N (total, nitrate and ammonium) while passing through the BS was observed, but total N losses were reduced from 17.3 to 4.5 kg ha⁻¹ in terms of mass balance. On the contrary, P concentrations were unmodified (soluble P), or lowered (total P) by the BS, reducing total losses by about 80%. The effect on total P, composed mainly of sediment-bound forms, was related to particulate settling when passing through the BS.A numerical index (Eutrophic Load Index), integrating water quality and runoff volumes, was created to evaluate the eutrophication risk of runoff with or without the BS. It showed that the BS effect was mostly due to a reduction of runoff volumes rather than improving the overall water quality.     

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.     

Lodging in rice can be alleviated by atmospheric CO2 enrichment

The projected increase of atmospheric CO₂ concentration [CO₂] is expected to increase yield of agricultural C₃ crops, but little is known about effects of [CO₂] on lodging that can reduce yield. This study examined the interaction between [CO₂] and nitrogen (N) fertilization on the lodging of rice (Oryza sativa L.) using free-air CO₂ enrichment (FACE) systems installed in paddy fields at Shizukuishi, Iwate, Japan (39°38′N, 140°57′E). Rice plants were grown under two levels of [CO₂] (ambient = 365 μmol mol⁻¹; elevated [CO₂] = 548 μmol mol⁻¹) and three N fertilization regimes: a single initial basal application of controlled-release urea (8 g N m⁻², CRN), split fertilization with a standard amount of ammonium sulfate (9 g N m⁻², MN), and ample N (15 g N m⁻², HN). Lodging score (six ranks at 18° intervals, with larger scores indicating greater bending), yield, and yield components were measured at maturity. The lodging score was significantly higher under HN than under CRN and MN, but lodging was alleviated by elevated [CO₂] under HN. This alleviation was associated with the shortened and thickened lower internodes, but was not associated with a change in the plant's mass moment around the culm base. A positively significant correlation between lodging score and ripening percentage indicated that ripening percentage decreased by 4.5% per one-unit increase in lodging score. These findings will be useful to develop functional algorithm that can be incorporated into mechanistic crop models to predict rice production more accurately in a changing climate and with different cultural practices.     

Mitigation of greenhouse gas emissions by anaerobic digestion of cattle slurry

Biogas treatment of animal manures is an upcoming technology because it is a way of producing renewable energy (biogas). However, little is known about effects of this management strategy on greenhouse gas (GHG) emissions during fermentation, storage, and field application of the substrates compared to untreated slurries. In this study, we compared cattle slurry and cattle slurry with potato starch as additive during the process of fermentation, during storage and after field application. The addition of potato starch strongly enhanced CH₄ production from 4230 l CH₄ m⁻³ to 8625 l CH₄ m⁻³ in the fermenter at a hydraulic retention time (HRT) of 29 days. Extending the HRT to 56 days had only a small effect on the CH₄ production. Methane emissions from stored slurry depended on storage temperature and were highest from unfermented slurry followed by the slurry/starch mixture. Gas emissions from untreated and fermented slurry during storage were further analyzed in a pilot-scale experiment with different levels of covering such as straw cover, a wooden lid and no cover. Emissions of greenhouse gases (CH₄, N₂O, NH₃) were in the range of 14.3–17.1 kg CO₂ eq. m⁻³ during winter (100 day storage period) and 40.5–90.5 kg CO₂ eq. m⁻³ during summer (140 day storage period). A straw cover reduced NH₃ losses, but not overall GHG emissions, whereas a solid cover reduced CH₄ and NH₃ emissions. After field application, there were no significant differences between slurry types in GHG emissions (4.15–8.12 kg CO₂ eq. m⁻³ a⁻¹). GHG emissions from slurry stores were more important than emissions after field application. Co-digestion of slurry with additives such as starch has a large potential to substitute fossil energy by biogas. On a biogas plant, slurry stores should be covered gas-tight in order to eliminate GHG emissions and collect CH₄ for electricity production.     

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.     

Linkages between land management activities and water quality in an intensively farmed catchment in southern New Zealand

Linkages between land management activities and stream water quality are reported for a 2480 ha catchment used for dairy farming, sheep–beef farming and forestry in Southland, New Zealand. Our approach was to reconcile measured loads of nutrients exported from the catchment with those estimated based on characterisation of farming practices within the catchment. The latter was based upon detailed surveys of farm practices and soil quality. Monthly stream monitoring showed that median nutrient (N and P), sediment and faecal bacteria concentrations exceeded guidelines recommended for surface waters. Measured specific yields for suspended sediment (SS), total N (TN) and phosphorus (P) discharged from the catchment were 58, 8.2 and 0.43 kg ha⁻¹ year⁻¹, respectively, for the 2001–2005 monitoring period. In comparison, model estimates of N and P losses in drainage and overland flow from farms in the catchment were 10.1 and 0.59 kg ha⁻¹ year⁻¹, respectively. Field measurements, farm management surveys and farm systems modeling have identified some land management practices that appear to be key sources of many of these pollutants. These sources include subsurface drainage systems (including the preferential flow of irrigated effluent through these soils), overland flow from the heavy soils used for dairy farming in the catchment and the practice of intensively wintering cows on forage crops. Modeling suggests that a significant improvement in catchment water quality could be achieved through the implementation of targeted best management practices (BMPs) on dairy farms in the catchment. These include (i) covered feedpad wintering systems for controlling N losses, (ii) nitrification inhibitor use on milking platforms, (iii) deferred irrigation and low rate application of farm dairy effluent and (iv) limiting soil Olsen P to economically optimum levels. The adoption of these BMPs will, in part, depend on their economic viability. This paper therefore presents a double-bottom-line analysis (i.e. environmental and economic) of some of these BMPs and discusses their potential to cost-effectively deliver improved water quality in the Bog Burn catchment.