Ingrid Öborn

Element balances as a tool for sustainable nutrient management: a critical appraisal of their merits and limitations within an agronomic and environmental context

Element balances are widely used and are incorporated within national action programs to combat nutrient emissions from agriculture to the environment. They rely on data that are readily available at farm-gate and field level, and the information generated is easy to communicate to farmers and policy makers. This may have contributed to high expectations on element balances as a tool for optimising agricultural nutrient use efficiency and thereby reducing nutrient losses. Element balances are potentially useful as a screening tool across Europe provided the methods to calculate them are standardised, their limitations and usefulness defined and appropriate target values are established by which they can be compared. It is difficult to establish straightforward relationships between nutrient management, surplus, losses and environmental impact. Simple farm-gate and field balances need to be complemented by a better understanding of the processes regulating nutrient dynamics, and their spatial and temporal variability. Hence, agronomic and environmental reference or target values need to be established for different production systems, geographical areas and elements. Proper instruments and tools as well as training and educational programmes have to be developed for a successful implementation.

Migration of radiocaesium in Swedish soil profiles after the Chernobyl accident, 1987–1995

The study site comprises temporary and permanent grassland in areas in central and northern Sweden which were strongly affected by the Chernobyl fallout in 1986. The aim of the study was to investigate the vertical migration of radiocaesium from 1987 to 1995 in undisturbed soil profiles under field conditions, as related to soil type and texture. The sampled sites differ in soil types and textures, i.e. six cultivated or semi-natural mineral soils (Dystrochrept, Haploboroll, Udorthents, Cryorthent and Haplocryod) and two cultivated organic soils (Sulfihemists). The ground deposition of 137Cs ranged from 14 to 184 kBq m-2 (average 82). 137Cs-activities were measured in cm-sliced, 25-cm-deep soil cores and in soil horizons of the entire soil profiles down to 0.7–1.0 m depth. The soil cores were collected on two or three occasions between 1987 and 1995, and migration rates were calculated based on the median depths. Grass samples were taken from the same locations to measure the amount of 137Cs transferred from soil to grass. After eight years, most (50–92%) of the 137Cs fallout was still present in the upper 5 cm (median depth 2.3–5.1 cm), although considerable amounts had migrated to deeper soil layers. Downward migration was most pronounced in the organic soils and in the podzol where 137Cs was found to about 50 cm depth. Migration rates were in the range of 0.5–1.0 cm year-1 for the first year and thereafter 0.2–0.6 cm year-1. The transfer of 137Cs to grass was highest in two gravely sandy loam soils in the mountain region, intermediate in two organic soils, and lowest in soils from the river and coastal areas.

Field balances of some mineral nutrients and trace elements in organic and conventional dairy farming¿a case study at Öjebyn, Sweden

Abstract A field level input–output balance was calculated for macronutrients (phosphorus (P), potassium (K) and magnesium (Mg)) and trace elements (cadmium (Cd), copper (Cu) and zinc (Zn)) during one cropping season in adjacent conventional and organic dairy farming systems at the Ojebyn experimental farm in northern Sweden. Both systems had a 6-year crop rotation: forage crop (oats and peas) with undersown ley (year 1)—grass/clover ley (years 2–4)—barley (year 5)—potatoes/forage crop (year 6). All aboveground biomass was harvested except for the potato crop, where only the tubers were removed. Inputs via farmyard manure and urine were significant for all element balances except Mg where lime (dolomite) was the most important source. Inputs from atmospheric deposition and outputs via water run-off were important for the trace element balances. There were large differences in the element balances between individual crops, with a tendency for a positive balance for fields growing oats and peas, barley and potatoes and a negative balance for grass/clover ley. This could be attributed to management factors, especially the uneven manure and lime application that occurred between crops. Averaged field balances, calculated for the crops included in the crop rotation, indicated that P was approximately in balance for the organic system and slightly more positive in the conventional one. The K balance was negative in the organic system and positive in the conventional system. Positive balances in both farming systems were apparent for Mg, Cd and Zn. In contrast, the balances for Cu were both negative. The mass of materials involved, rather than differences in their composition, mainly accounted for differences in element flows between the two farming systems. Higher stocking rate, total volume of urine and lime application in the conventional system accounted for the main differences in element balances between systems.

Concentrations and Pools of Heavy Metals in Urban Soils in Stockholm, Sweden

The concentrations of heavy metals (Cd, Cr, Cu, Hg, Ni, Pb andZn) and arsenic (As) were surveyed and the metal pools estimatedin soils in Stockholm Municipality. The sampling sites were distributed all over the entire municipality with a higher sampling density in the city centre. Soils were sampled to a maximum depth of 25 to 60 cm. Soil texture, total-C content, electrical conductivity and pH were analysed. Heavy metal concentrations were determined after wet digestion with boiling7 M HNO3.The results showed a wide range in heavy metal concentrations, as well as in other soil properties. The city centre soils constituted a rather homogeneous group whereas outside this areano geographical zones could be distinguished. These soils were grouped based on present land use, i.e. undisturbed soils, public parks, wasteland (mainly former industrial areas), and roadside soils. The city centre and wasteland soils generally hadenhanced heavy metal concentrations to at least 30 cm depth compared to park soils outside the city centre and rural (arable)soils in the region, which were used to estimate background levels. For example, the mean Hg concentration was 0.9 (max 3.3)mg kg-1 soil at 0–5 cm and 1.0 (max 2.9) at 30 cm depth in the city centre soils, while the background level was 0,04 mg kg-1. Corresponding values for Pb were 104 (max 444) and135 (max 339) mg kg-1, at 0–5 and 30 cm, respectively, while the background level was 17 mg kg-1.The average soil pools (0–30 cm depth) of Cu, Pb and Zn were 21,38 and 58 g m-2 respectively, which for Pb was 3–4 timeshigher and for Cu and Zn 1.5–2 times higher than the backgroundlevel. The total amount of accumulated metals (down to 30 cm)in the city centre soils (4.5*10 6 m2 public gardens and green areas) was estimated at 80, 1.1, 120 and 40 t for Cu, Hg, Pb and Zn, respectively. The study showed (1) thatfrom a metal contamination point of view, more homogeneous soilgroups were obtained based on present land use than on geographicdistance to the city centre, (2) the importance of establishing a background level in order to quantify the degree of contamination, and (3) soil samples has to be taken below the surface layer (and deeper than 30 cm) in order to quantify theaccumulated metal pools in urban soils.

Application of the PROFILE model to estimate potassium release from mineral weathering in Northern European agricultural soils

Negative potassium (K) balances have been reported from grass-dominated organic systems in several European countries, and in these systems delivery of K from soil primary minerals by weathering is probably crucial to sustained productivity. Mass balances and K budgets have been made at eight grass-dominated experimental agricultural systems, one each in Scotland and Sweden and six in Norway. Where no fertiliser K was applied, the deficits obtained were in the range 35–241 kg K ha−1 per year. An estimate of the weathering rate was determined by the biogeochemical PROFILE model that varied widely between locations (3–82 kg K ha−1 per year). This paper is a first attempt to apply the steady-state PROFILE model on agricultural soils by using data from experimental sites. The Monte Carlo simulation of the weathering rate calculation showed that differences in specific surface area and soil water content strongly influenced the predicted weathering rate, which was associated with a degree of uncertainty. All sites showed a negative annual K-balance, which means that the specific contribution that mineral weathering makes to the long-term replenishment of soil exchangeable-K is important but may not be sufficient to counteract large K removal associated with high crop yields. Despite the uncertainties in the weathering rate calculation, these preliminary results are still useful in several aspects because the simulations make it possible to compare different agroecosystems with different management regimes, climate, soil properties, etc. The simulations also indicate which environmental factors are likely to be the most influential on weathering rates. Soil physical properties, such as moisture content, bulk density and surface area, appeared to be amongst the most important input parameters controlling actual weathering rates within groups of soils having similar mineralogical and chemical compositions. There is now a need for improved laboratory experimental data that better describe the kinetics of mineral weathering in order to enhance the accuracy and precision of PROFILE.

Major nutrient balances in small-scale vegetable farming systems in peri-urban areas in China

Balances of major nutrients such as nitrogen (N), phosphorus (P), and potassium (K) in small-scale farming systems are of critical importance to nutrient management and sustainable agricultural development. Mass balances of N, P, and K and some of their influencing factors were studied for two years from July 2003 to July 2005 on small-scale vegetable-farming systems in two contrasting peri-urban areas (Nanjing and Wuxi) of the Yangtze river delta region of China. This balance approach considered organic fertilizer inputs (cow manure, pig manure, and human biosolids), inorganic fertilizer inputs (urea, composite fertilizer, and phosphates), irrigation water, and atmospheric deposition; and considered outputs by vegetables. Input via organic fertilizers was significant for all element balances in the Nanjing area. Inorganic and organic fertilizer, particularly inorganic fertilizer, contributed major nutrient inputs to the system in the Wuxi area. Compared with nutrient output by vegetables, there were significant surpluses of N and P on two vegetable farm systems. Furthermore, N surplus in the Nanjing area was higher than that in the Wuxi area with an inverse relationship to P surplus. In contrast, the general trend of K balances was negative on both sites; hence, the nutrient use efficiency was significantly lower for N and P than K. The nutrient imbalance may be attributed to the differences between fertilizer types and management modes driven by social economic status differences among farmer households. The large N and P net excess creates an environmental threat because of potential losses to ground or surface waters, whereas negative K balance creates soil fertility risks. The results highlight researchers’ and farmers’ need to develop rational fertilization technology to optimize nutrient management on vegetable farmlands to promote sustainable agricultural development in peri-urban areas.

Sustainable development of food production: a case study on scenarios for pig production.

Abstract To study future, sustainable production systems, a step-wise method was used to create three future scenarios for pig production based on different sustainability goals. The first scenario focused on animal welfare and the natural behavior of the animals. The second targeted low impacts on the environment and the efficient use of natural resources. The third scenario aimed at product quality and safety. Each scenario fulfilled different aspects of sustainability, but there were goal conflicts because no scenario fulfilled all sustainability goals. The scenarios were then parameterized. The environmental impact was calculated using the life-cycle assessment (LCA) methodology, and the economic cost was calculated from the same data set. The cost per kilo of pork was highest for the animal welfare scenario and similar for the other two scenarios. The environmental scenario had the lowest environmental impact, and the product-quality scenario the highest. The results are discussed based on different future priorities.

Properties and classification of some acid sulfate soils in Sweden

Abstract Morphology, physical features and chemical composition of the horizons of seven acid sulfate soils in Sweden were investigated. The resulting data are presented first and the profiles are then classified in the USDA “Soil Taxonomy” and identified in the legend for the FAO-Unesco “Soil Map of the World.” The suitabilities of the classification and the identification are discussed. Two profiles near the coast of the Gulf of Bothnia were classified as an Aeric Humic Cryaquept and a Humic Cryaquept in present Soil Taxonomy. A new subgroup of Sulfic Cryaquepts is proposed as a better alternative. These two profiles were identified as a Thionic Fluvisol and a Humic Gleysol, respectively, in the FAO legend. Features of the first profile would be represented better if it were identified as a Thionic Gleysol. Three profiles from central Sweden were classified as a Humic Haplaquept, a Histic Humaquept and a Fluvaquentic Humaquept in present Soil Taxonomy. Addition of a subgroup of Fluvaquentic Haplaquepts is proposed to better represent the features of the first profile. The first of the three profiles was identified as a Dystric Gleysol and the other two as Humic Gleysols in the FAO legend. This identification is not wholly satisfactory. Two profiles from southeastern Sweden were classified as a Sulfic Fluvaquent and a Typic Sulfaquent in present Soil Taxonomy. Both profiles would fit better in the proposed suborder of Limnists, in which they would be Sulfilimnists. Both profiles were identified as Thionic Fluvisols in the FAO legend although neither was formed in recent sediments.

A Systems Approach to Assess Farm-scale Nutrient and Trace Element Dynamics: A Case Study at the Öjebyn Dairy Farm

Abstract A systems analysis approach was used to assess farm-scale nutrient and trace element sustainability by combining full-scale field experiments with specific studies of nutrient release from mineral weathering and trace-element cycling. At the Öjebyn dairy farm in northern Sweden, a farm-scale case study including phosphorus (P), potassium (K), and zinc (Zn) was run to compare organic and conventional agricultural management practices. By combining different element-balance approaches (at farm-gate, barn, and field scales) and further adapting these to the FARMFLOW model, we were able to combine mass flows and pools within the subsystems and establish links between subsystems in order to make farm-scale predictions. It was found that internal element flows on the farm are large and that there are farm internal sources (Zn) and loss terms (K). The approaches developed and tested at the Öjebyn farm are promising and considered generally adaptable to any farm.

Source identification and spatial variability of nitrogen, phosphorus, and selected heavy metals in surface water and sediment in the riverine systems of a peri-urban interface

This study was conducted, using an elaborate sampling activity of surface water and sediment within an industrially developed peri-urban interface with a riverine system in Wuxi, Taihu Lake area, China, to address the following objectives: (i) to identify possible sources of selected nutrients such as N and P, and heavy metals such as Cu, Zn, Pb, Cr, and Cd in surface water and sediments, and (ii) to determine the spatial variability of these elements around the source areas. The results showed that concentrations of N and P in the surface water and Cu, Zn, Cr, and Pb in most of sediments had exceeded trigger levels established by the nation, while all metal concentrations in surface water were still below the levels. The source identification of these pollutants in water and sediments in terms of their spatial distribution pattern and principal component analysis showed that: (i) Pb, N and organic carbon (OC) were closely related to the influence of urban runoff and domestic wastewater; (ii) Cu and Cr were related to the influence of industries; and (iii) P and Zn were related to the effect of both urban and industries. The results of this study showed that urbanization is the main contributor for N and P in the peri-urban interface instead of agricultural sources. The concentrations of N, P, Cu, Zn, Pb, and Cr in the sediment along the main river decreased with the distance away from the source area. The concentrations of these elements decreased to the background levels at about 4.5–5.5 km downstream of the source of origin.