Deposition and forest canopy interactions of airborne sulfur: Results from the integrated forest study

The Integrated Forest Study (IFS) was a long-term research project designed to determine the effects of atmospheric deposition on forest nutrient cycles. Concentrations and fluxes of airborne sulfur compounds were determined for several years at the 13 IFS research forests in North America and Europe using a standard set of protocols. Annual mean air concentrations of sulfur ranged from ∼1.5 to 8 μgSm⁻³ and were generally dominated by SO₂ (∼60% of total sulfur on the average). Atmospheric deposition of sulfate at these forests was highest at the high elevation (∼ 1000–2000 eq ha⁻¹yr⁻¹) and at the southeastern U.S. sites (∼800–1000 eq ha⁻¹yr⁻¹), and lowest in the Pacific northwest (∼300 eq ha⁻¹yr⁻¹). Cloud water contributed significantly to the sulfur flux at the mountain sites (45–50%), and dry deposition was comparable to wet at the drier southeastern sites (>40% of total). Deposited sulfur appeared to behave more or less conservatively in these canopies, showing little net uptake (ofSO₂) and minor foliar leaching (of soil-derived, internal SO₄²⁻) relative to the total atmospheric flux. The estimated fluxes in total deposition were generally within 15% of the measured fluxes in throughfall plus stemflow, indicating that useful estimates of total atmospheric deposition of sulfur can be derived from measurements of throughfall.     

Effects of manure and chemical fertilizers on insect pest populations on collards

Advocates of organic agriculture often assert that plants supplied exclusively with nutrient from biological materials are more resistant to insects than those grown using chemical fertilizer. This proposition was examined using collards grown in five treatments: two with fresh manure at two levels (12 and 220 ha⁻¹); one with ‘sheet composted’ manure at 220 ha⁻¹; a chemical fertilizer treatment (785 kg ha⁻¹ of 13:13:13 NPK); and a control treatment with no added nutrients. Population densities of two flea beetles and two lepidopteran pests were monitored weekly during a growing season. Plant size and foliar levels of reduced nitrogen (N), nitrate nitrogen (NO₃⁻-N), water and total glucosinolates were also measured four times during the season. During population peaks, flea beetle densities were significantly higher on plants receiving chemical fertilizers than on plants receiving similar amounts of macronutrients from manure. Flea beetle, imported cabbage worm and diamondback moth densities were significantly higher on untreated plants than on plants receiving any added nutrients. Flea beetle densities were also significantly higher on plants grown with ‘sheet composted’ manure than on those grown with fres manure. The nutrient treatments affected plant size, reduced N, NO₃⁻-N, water and glucosinolate content. These differences were not clearly associated with differences in insect population sizes but some patterns in the data are discussed. Although the potential exists for manipulating soil amendment regimes to affect pest insect populations in collards, an understanding of the mechanisms involved will require further investigation.     

The boll weevil in North America: Scientific conflicts over management of environmental resources

This paper is a historical and philosphical reconstruction of how U.S. entomologists attempted to mitigate the depradations of the boll weevil on cotton, the world's most important natural fiber. The boll weevil caused severe losses in the U.S. after 1892. Early control methods were based on altering the cultural practices of cotton growers. The discovery in 1917 that calcium arsenate was an effective insecticide for boll weevils eventually allowed some farmers to rely on chemical control. Development of synthetic, organic insecticides allowed many U.S. growers after 1945 to rely heavily on insecticides for boll weevils. By the 1960s, resistance of boll weevils to insecticides, induction of secondary pest outbreaks, and environmental health hazards threatened cotton production practices based on insecticides. U.S. entomologists devised two new strategies to rescue cotton production from its insecticide crisis: integrated pest management (IPM) and total population management (TPM). Eradication of key insect pests such as boll weevils was envisaged by TPM entomologists with adequate technology. E.F. Knipling, the USDA entomologist who designed TPM, gave 1968 as a target for possible boll weevil eradication. The pilot boll weevil eradication experiment (PBWEE) was conducted in 1971–1973. IPM entomologists argued the futility of attempting to eradicate the boll weevil from the U.S.A., but TPM adherents argued for a second test, which was held in Virginia, North Carolina and South Carolina (1978–1980). A new controversy erupted over how to interpret the fact that a few boll weevils were found at the end of the second test. IPM and TPM entomologists were once again pitted against one another on three major issues: defining eradication; explaining secondary pest behavior; and drawing conclusions about the wisdom of a national boll weevil eradication program. Currently, entomologists have reached a stalemate over boll weevil eradication in the U.S. Some entomologists are attempting to synthesize opposing views in the hope of reaching a professional consensus on appropriate boll weevil suppression methods. Significant distinctions separate IPM and TPM and will make it difficult to achieve an agreement. Budgetary problems in the U.S.A. argue for a management rather than eradication stance against boll weevils. The split in the U.S. entomological profession could have adverse effects on efforts to develop insect-control science outside of the U.S.     

Changes in pest management practice in almond orchards during the rainy season in California,USA

In California, regulatory agencies are concerned about organophosphate (OP) contamination of surface water. OPs originate in part from applications on dormant almond and stone fruit orchards that are washed off during winter rainstorms. Programs conducted by the University of California Statewide Integrated Pest Management Project, University of California Cooperative Extension, and the Biologically Integrated Orchard Systems (BIOS), a coalition of public and private groups, have promoted the replacement of OPs on almonds during the rainy season with alternative practices. Data from individual applicator records from the California Pesticide Use Reports demonstrated that during 1992–1997, almond growers in all nine major almond-producing counties significantly reduced use of OPs. The area of almond orchards treated with OPs during the dormant season was reduced by 40–55%, depending upon the region. Similarly, the percentage of growers who used OPs during the dormant season was reduced by 31–48%, and the mass of OPs applied to almond orchards during the dormant season was reduced by 22–57%. During the same period, there was a significant increase in the percentage of growers who used “reduced-risk” treatments: the microbial pesticide Bacillus thuringiensis at bloom-time, oil without an insecticide during the dormant season, and no treatment during the dormant or bloom season. In addition to the decrease in OPs during the dormant season, there was a significant decrease in the area treated with OPs during the growing season. However, there was also a significant increase in the use of pyrethroids during the dormant season, a practice that might result in some surface water and sediment contamination.     

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.     

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.     

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.     

Comparison of soil N availability and leaching potential,crop yields and weeds in organic,low-input and conventional farming systems in northern California

Increasing dependence on off-farm inputs including, fertilizers, pesticides and energy for food and fiber production in the United States and elsewhere is of questionable sustainability resulting in environmental degradation and human health risks. The organic (no synthetic fertilizer or pesticide use), and low-input (reduced amount of synthetic fertilizer and pesticide use), farming systems are considered to be an alternative to conventional farming systems, to enhance agricultural sustainability and environmental quality. Soil N availability and leaching potential, crop yields and weeds are important factors related to agricultural sustainability and environmental quality, yet information on long-term farming system effects on these factors, especially in the organic and low-input farming systems is limited. Four farming systems: organic, low-input, conventional (synthetic fertilizer and pesticides applied at recommended rates) 4-year rotation (conv-4) and a conventional 2-year rotation (conv-2) were evaluated for soil mineral N, potentially mineralizable N (PMN), crop yields and weed biomass in irrigated processing tomatoes (Lycopersicon esculentum L.) and corn (Zea mays L.) from 1994 to 1998 in California’s Sacramento Valley. Soil mineral N levels during the cropping season varied by crop, farming system, and the amount and source of N fertilization. The organic and low-input systems showed 112 and 36% greater PMN pools than the conventional systems, respectively. However, N mineralization rates of the conventional systems were 100% greater than in the organic and 28% greater than in the low-input system. Average tomato fruit yield for the 5-year period (1994–1998) was 71.0 Mg ha⁻¹ and average corn grain yield was 11.6 Mg ha⁻¹ and both were not significantly different among farming systems. The organic system had a greater aboveground weed biomass at harvest compared to other systems. The lower potential risk of N leaching from lower N mineralization rates in the organic and low-input farming systems appear to improve agricultural sustainability and environmental quality while maintaining similar crop yields.     

Effects of some eucalypts on yields of Vigna unguiculata L. Walp., Zea mays L. and Sorghum bicolor L.

Vigna unguiculata (beans), Zea mays (maize) and Sorghum bicolor (sorghum) were grown with and without fertiliser in a savanna grassland (control) and under the effects of decomposing parts of eucalyptus in an old eucalyptus plantation with a well-lit floor (treatment).Morphological characters of the beans, compared between the two sites, showed that leaf dry-matter production, expressed as specific leaf area (SLA), did not differ between plants in the two sites (fertilised and unfertilised). Although the organic-matter content and water-holding capacity of the plantation soil were significantly higher than those of the control plants. beans, grain yield ha⁻¹, shoot height, number of leaves and fruits were higher in the control plants. However, when beans were fertilised, shoot height did not differ between sites, but the other measured morphological characters and grain yield were significantly improved in both sites, although these characters still remained higher in the control. In maize and sorghum, grain yield ha⁻¹ did not vary significantly in the two sites (fertilised or unfertilised). These findings suggest that beans can be incompatible with eucalypts, while maize and sorghum may be compatible with eucalypts for agrosilvicultural practices, and that fertilisation can offset, to an extent, the depressive effects of eucalypts on crops.     

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.     

Quantification and valuation of ecosystem services in diverse production systems for informed decision-making

The empirical evidence of decline in ecosystem services (ES) over the last century has reinforced the call for ES quantification, monitoring and valuation. Usually, only provisioning ES are marketable and accounted for, whereas regulating, supporting and cultural ES are typically non-marketable and overlooked in connection with land-use or management decisions. The objective of this study was to quantify and value total ES (marketable and non-marketable) of diverse production systems and management intensities in Denmark to provide a basis for decisions based on economic values. The production systems were conventional wheat (Cwheat), a combined food and energy (CFE) production system and beech forest. Marketable (provisioning ES) and non-marketable ES (supporting, regulating and cultural) ES were quantified by dedicated on-site field measurements supplemented by literature data. The value of total ES was highest in CFE (US$ 3142 ha⁻¹ yr⁻¹) followed by Cwheat (US$ 2767 ha⁻¹ yr⁻¹) and beech forest (US$ 2328 ha⁻¹ yr⁻¹). As the production system shifted from Cwheat - CFE–beech, the marketable ES share decreased from 88% to 75% in CFE and 55% in beech whereas the non-marketable ES share increased to 12%, 25% and 45% of total ES in Cwheat, CFE and beech respectively, demonstrating production system and management effects on ES values. Total ES valuation, disintegrated into marketable and non-marketable share is a potential way forward to value ES and ‘tune’ our production systems for enhanced ES provision. Such monetary valuation can be used by policy makers and land managers as a tool to assess ES value and monitor the sustained flow of ES. The application of ES-based valuation for land management can enhance ES provision for maintaining the productive capacity of the land without depending on the external fossil-based fertilizer and chemical input.     

Carbon balance of an intensively grazed temperate pasture in two climatically contrasting years

Grazed grasslands occupy 26% of the earth's ice free land surface and are therefore an important component of the global C balance. In New Zealand, pastoral agriculture is the dominant land use and recent research has shown that soils under intensive dairy pastures have lost large amounts of carbon (∼1000 kg C ha⁻¹ y⁻¹) during the past few decades. The objective of this research was to determine the net ecosystem carbon balance (NECB) of an intensively grazed dairy pasture in New Zealand. Net ecosystem CO₂ exchange (NEE) was measured using an eddy covariance (EC) system from 1 January 2008 to 31 December 2009. Other C imports (feed) and exports (milk, methane, leaching, and harvested biomass) were calculated from farm production data and literature values. During 2008 there was a one in 100 year drought during summer/autumn, which was followed by a very wet winter. There were no prolonged periods of above or below average rainfall or soil moisture in 2009, but temperatures were consistently lower than 2008. The severe summer/autumn drought during 2008 caused a loss of CO₂ to the atmosphere, but annual NEE remained negative (a CO₂ sink, −1610 ± 500 kg C ha⁻¹), because CO₂ lost during the drought was regained during the winter and spring. The site was also a net CO₂ sink during 2009 despite the colder than usual conditions (−2290 ± 500 kg C ha⁻¹). Including C imports and exports in addition to CO₂ exchange revealed that the site was a C sink in both years, with a NECB of 590 ± 560 kg C ha⁻¹ in 2008, and 900 ± 560 kg C ha⁻¹ in 2009. The C sequestration found in this study is in agreement with most other Northern Hemisphere EC studies of grazed pastures on mineral soils, but is not consistent with the large C losses reported for soils under dairy pastures throughout New Zealand. In the current study (like many other EC studies) the influence of climatic conditions and management practices on the annual C balance was only semi-quantitatively assessed. An extended period of EC measurements combined with modelling is required to more accurately quantify the effect of different climatic conditions on the annual C balance, and the influence of different management practices needs to be quantified using specifically designed studies (such as paired EC towers), so that practices which minimise C losses and maximise C sequestration can be identified.     

Manuring and fertilization effects on phosphorus accumulation in soils and potential environmental implications

Phosphorus application as manure to agricultural soils in intensive livestock farming and arable cropping systems often exceeds P offtake by crops. This surplus could lead to P accumulation in soils, making them long-term diffuse sources of P loss to water. We investigated the impact of a range of manuring and fertilization practices in intensive farming systems on the accumulation of P in soils, soil test phosphorus (STP), distribution of organic and inorganic P, P-sorption capacity and degree of soil saturation with P (DSSP). The results from the 10 long-term sites investigated showed increases in both total soil P content and STP values (Olsen-P and Mehlich-3 P), as a result of P surpluses. The net total P accumulation in the soils across the sites ranged from 16 to 232 kg P ha⁻¹ year⁻¹. The effects of long-term P surpluses were a significant reduction in P-retention capacity and increase in DSSP. The sites investigated would attain 25% DSSP in 10–150 years, depending upon the size of P surplus and sorption capacity. A combination of large P surplus and low P-sorption capacity could saturate soils to 25% DSSP within 10–30 years. The values of Olsen (85 mg P kg⁻¹) and Mehlich-3 (305 mg P kg⁻¹) extractable-P predicted for the 25% DSSP are likely to result in environmentally significant P losses.     

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.     

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.     

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.     

Impact of variable nitrogen fertilisation on arthropods in cotton in Georgia, USA

Reducing fertiliser applications can reduce production costs for cotton (Gossypium hirsutum L.) growers, as well as nitrogen (N) leaching into the soil and contamination of surface and ground water. But altered N fertilisation may also affect pests and their natural enemies. In this study, plots with four different levels of fertiliser input (0, 45, 90 and 135 kg ha⁻¹ N) were used to investigate the influence of N on cotton pest and beneficial arthropod populations, and on cotton yield in Tifton, GA, USA. We predicted that (1) N fertilisation will correlate positively with cotton plant growth; (2) increased N fertilisation will increase pest populations because plants with more N will be more nutritious for and attractive to herbivores; (3) populations of beneficial arthropods and predation of pests will decline with increased N fertilisation because of reduced plant signaling; (4) increased N fertilisation will increase pest mortality due to parasitoids because of increased host quality. Cotton plant growth was enhanced by N fertilisation but yield was unaffected. N fertilisation significantly affected some pest arthropods but inconsistently. Mirids were most abundant in the high N treatment in 1 year of the study and cotton aphids were most abundant in the highest N treatment in the other year of the study. Arthropod predators were generally more abundant in the high N treatment but only spiders and Geocoris spp. were significantly affected by N treatment, with highest numbers present in the highest N treatment but the significant differences were each only in a single year. The greatest mortality of sentinel pest eggs (Spodoptera exigua) due to predation occurred under low N conditions. N fertilisation had no significant effects on parasitism of feral or sentinel caterpillars.     

Integrated mite control in apples in Queensland, Australia

An interdisciplinary team introduced Integrated Mite Control (IMC) to the Queensland apple industry in Australia from 1989 to 1992. Project funding supported the employment of a consultant to monitor mite levels and provide management advice to growers who paid for the service. Interviews at the beginning and end of the project showed widespread adoption of IMC over this period. Overall use of chemicals was not reduced, but the use pattern changed towards wider use of chemicals that are less toxic to predatory mites. The future of IMC in the Queensland apple industry is in doubt because the seasonal nature of apple production does not allow the paid consultancy service to be self-sustaining. Indications are that the integrated approach to pest management may not be generally accepted as a strategic management process while the availability of effective chemicals allows the continuation of a spray routine for mite control. The lack of availability of effective and proven methods of pest control was seen by growers as the major constraint to adoption of IMC.     

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.     

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.