Modelling heavy metal and phosphorus balances for farming systems

Accounting for agricultural activities such as P fertilization in regional models of heavy metal accumulation provides suitable sustainable management strategies to reduce nutrient surpluses and metal inputs in agricultural soils. Using the balance model PROTERRA-S, we assessed the phosphorus (P), cadmium (Cd) and zinc (Zn) flux balances in agricultural soils of a rural region in Switzerland for different farm types and crop types. The P requirements of crops on arable farms were mainly supplied by commercial fertilizers and sewage sludge, while on animal husbandry farms P fertilizer demands were met by animal manure alone. Metal accumulation in soil was very different between the balance units. Estimated net Cd fluxes ranged between 1.0 and 2.3 g ha^–1 yr^–1 for arable farm types, 0.6 and 2.0 g ha^–1 yr^–1 for dairy and mixed farm types, and 9.1 and 17.8 g ha^–1 yr^–1 for animal husbandry farm types. Largest net Zn fluxes of 17.9–39.8 kg ha^–1 yr^–1 were estimated for animal husbandry farms, whereas for arable farm types net Zn fluxes of 101–260 g ha^–1 yr^–1 and for dairy and mixed farm types of 349–3360 g ha^–1 yr^–1 were found. The results indicate that P management is a primary factor determining the variation of these net Cd and net Zn fluxes. The latter were highly sensitive to the Zn/P concentration ratio in animal manure, atmospheric deposition and crop concentrations. Variation of net Cd fluxes resulted mainly from uncertainty in crop concentrations, atmospheric deposition, leaching parameters and uncertainty in Cd/P concentration ratio of commercial fertilizers. In addition, element balances were sensitive to empirical assumptions on fertilization strategy of farmers, such as the partitioning of manure between balance units.     

Potential impact of agroforestry on soil nutrient balances at the farm scale in the East African Highlands

There is much current interest in the potential role of agroforestry in the mitigation of nutrient depletion in Sub-Saharan Africa. Using data from farm surveys and trials, a static model of N and P flows was constructed for a standard farm system, representative of typical subsistence farms in humid parts of the East African Highlands. The model was used to explore the possible impact of improved agroforestry systems on nutrient budgets, to identify priorities for research.Soil nutrient balances in the standard farm system were - 107 kg N and - 8 kg P ha^–1 yr^–1. Agroforestry systems did not significantly reduce the N deficits except when a high proportion of the total biomass was returned to the soil, rather than removed from the farm. Agroforestry increased N input through biological N fixation and deep N uptake, but this was offset by a larger nutrient removal from the farm in harvested products, which increased from 38 kg N in the standard system to 169 kg N ha^–1 yr^–1 in an intensive dairy-agroforestry system. Agroforestry did not increase P inputs, and harvested P increased from 6 kg P in the standard farm system to 29 kg P ha^–1 yr^–1 in the dairy-agroforestry system. Thus, moderate P inputs, of 20 kg P ha^–1 yr^–1 were required to maintain soil P stocks.N leaching from the field was the most significant nutrient loss from the farm system, with a range of 68 to 139 kg N ha^–1 yr^–1. The capture of subsoil N by deep-rooted trees in agroforestry systems substantially increased N-use efficiency, providing 60 kg N ha^–1 yr^–1 in the dairy-agroforestry system. The budgets were sensitive to N mineralization rates in subsoils, N losses from soils and manures, and effectiveness of deep-rooted plants in subsoil N capture, for which there is little data from the region. Therefore, high priority should be given to research in these areas.The current model can not account for important feedback mechanisms that would allow analysis of the long-term effects of nutrient budgets on nutrient availability and plant productivity. Dynamic models of farm nutrient budgets that include such interactions are needed to further assess the sustainability of farming systems.     

Nutrient loss pathways from grazed grasslands and the effects of decreasing inputs: experimental results for three soil types

Agriculture is a main contributor of diffuse emissions of N and P to the environment. For N the main loss pathways are NH₃-volatilization, leaching to ground and surface water and N₂(O) emissions. Currently, imposing restraints on farm inputs are used as policy tool to decrease N and P leaching to ground water and to surface water, and the same measure is suggested to combat emissions of N₂O. The response, however, to these measures largely depends on the soil type. In this study nutrient flows of three dairy farms in The Netherlands with comparable intensity on sand, peat and clay soils were monitored for at least 2 years. The first aim was to provide quantitative data on current nutrient loss pathways. The second aim was to explore the responses in partitioning of the nutrient loss pathways when farm inputs were altered. Mean denitrification rates ranged from 103 kg N ha⁻¹ year⁻¹ for the sandy soil to 170 kg N ha⁻¹ year⁻¹ for the peat soil and leaching to surface water was about 73 kg N ha⁻¹ year⁻¹ for the sandy soil, 15 kg N ha⁻¹ year⁻¹ for the clay soil and 38 kg N ha⁻¹ year⁻¹ for the peat soil. For P, leaching to surface water ranged from 2 kg P ha⁻¹ year⁻¹ for the sandy site to 5 kg P ha⁻¹ year⁻¹ for the peat site. The sandy soil was most responsive to changes in N surpluses on leaching to surface water, followed by the peat soil and least responsive was the clay soil. For P, a similar sequence was found. This article demonstrates that similar reductions of N and P inputs result in different responses in N and P loss pathways for different soil types. These differences should be taken into account when evaluating measures to improve environmental performance of (dairy) farms.     

Use of the partial nutrient budget as an indicator of nutrient depletion in the highlands of southwestern Uganda

Agricultural management has its roots in the manipulation of the system to optimise conditions for crop production. It is now widely recognised that this could result in land degradation with subsequent serious impact on crop productivity if the nutrient losses to the agricultural system are not replaced. A nutrient budget is an account of gains and losses of nutrients in an agricultural system, a tool that could be used to develop sound nutrient management and sustainable agriculture. This tool was applied to the annual crop farming system in the highlands of southwestern Uganda to demonstrate (i) within farm nutrient depletion and accumulating zones, and (ii) the extent of nutrient losses at farm and district levels through marketing pathways. Partial nutrient budgets were constructed at field and farm levels using farmer-recorded resource inputs and outputs over a period of one year, and at the district level using annual inventory data of agricultural imports and exports. The computed nutrient balances were highly variable at field and farm levels, but predominantly negative. Nitrogen (N) gains and losses averaged 30.6 and 72.3 kg ha^–1 yr^–1, respectively in the homestead fields; 10.8 and 33.4 kg ha^–1 yr^–1 in the outfields; 15.8 and 17.4 kg ha^–1 yr^–1 at the farm level; and only losses of 5.6 kg ha^–1 yr^–1 at the district level. Potassium (K) gains and losses followed a similar trend, although less in magnitude. The phosphorus (P) balance was positive but only in the homestead fields and at the farm level. Where agricultural produce were marketed, nutrient losses were reflected more at the higher scales (e.g. district level) and became tied up in pools from which recycling back to agriculture was barely feasible, and with quite alarming monetary implications. Such results can be used to influence policies at different scales on nutrient management.     

Nutrient Flows in Suckler Farm Systems Under Two Levels of Intensity

The potential release of nutrients from animal farms into soil, water and the atmosphere is a major concern in agronomy. Farm gate balances are widely utilised to validate the compatibility of a farming system to the surrounding environment, although they do not reveal the internal nutrient flow as influenced by production intensity and hence might mask local and spatial nutrient surpluses or deficiencies. In a three years experiment on Rengen Research Station (Eifel Mountains) of the University of Bonn (Germany) we examined the entire nutrient cycle of two suckler farm systems without (extensive, system “A”) and with (intensive, system “B”) nutrient input and with 20 suckler cows on 19 hectare each. Stall and grassland nutrient balance sheets give insight into sources of nutrient surpluses and losses in the farm compartments. The annual budgets of N in system “A” were nearly balanced (−18 to 15 kg N ha⁻¹ yr⁻¹) compared to system “B” which calculated 81–120 kg N ha⁻¹ yr⁻¹ surplus due to considerable N input with forage and higher dry matter contribution of white clover leading to higher annual N2 fixation. The maximum of total annual nutrient flow within the entire systems was 388, 42 and 317 kg ha⁻¹ yr⁻¹ with N, P, and K, respectively. Most of these nutrients circulated with forage and excreta on the pastures. This led to considerable losses mainly of nitrogen (44–50 kg N ha⁻¹ yr⁻¹) even in the extensive system. The intake, excretion and resulting losses of N were mainly determined by the allowance of N rich pasture forage and was mostly independent from nutrient input. Compared to the grazing season, stall balances were similar in both systems and all years and revealed very low surpluses with all nutrients. The authors deduce that internal nutrient flow analyses should be added to conventional balance sheets, including a ranking of nutrients related to chemical bond, solubility, volatility and predisposition to losses in the farm’s compartment and environment. An erratum to this article is available at .     

Modeling the soil nutrient balance of integrated agriculture-aquaculture systems in the Mekong Delta,Vietnam

This study quantifies soil nutrient balances of Integrated Agriculture-Aquaculture Systems in the Mekong Delta of Vietnam. Eleven farms were monitored to collect data on farm activities and nutrient inputs and outputs to compute these balances of the rice-based and high input fish system in O Mon district (R-HF); the rice-based and medium input fish system in Tam Binh district (R-MF); and the orchard-based and low input fish system in Cai Be district (O-LF). For the estimation, the Nutmon model has been adapted to the specific conditions in these integrated systems in Asia (Nutmon-Asia). New regression models of leaching and gaseous losses of nitrogen were applied to fields used for upland crops and paddy rice. Reference values were used for the assessment of nitrogen fixation in paddy soils, wet atmospheric deposition, and irrigation water. The results showed that farms in all three systems have nitrogen, phosphorus and potassium surpluses (84 kg N, 73 kg P, and 69 kg K ha⁻¹ year⁻¹). The O-LF system had the smallest nitrogen surplus while the smallest surplus of phosphorus and potassium was seen in the R-HF system. High surpluses of phosphorus and potassium were found in vegetable fields, whereas a negative potassium balance was found in the rice fields of all three systems. The positive farm nutrient balances indicate that it is likely that soil fertility will be maintained although there is a risk for environmental contamination.     

The contribution of dairy farming on peat soil to N and P loading of surface water

In agriculturally used peat land areas, surface water quality standards for nitrogen (N) and phosphorus (P) are frequently exceeded, but it is unclear to what extent agriculture is responsible for nutrient loading of the surface water. We quantified the contribution of different sources to the N and P loading of a ditch draining a grassland on peat soil (Terric Histosol) used for dairy farming in the Netherlands. Measurements were performed on N and P discharge at the end of the ditch, supply of N and P via inlet water, mineralization of soil organic matter, slush application, composition of the soil solution, and on N losses through denitrification in the ditch for 2 years (September 2000 to September 2002). Discharge rates at the end of the ditch were 32 kg N ha^–1y^–1 and 4.7 kg P ha^–1y^–1. For N, 43 to 50% of the discharge was accounted for by applications of fertilizers, manure and cattle droppings, 17 to 31% by mineralization of soil organic matter, 8 to 27% by nutrient-rich deeper peat layers, 8 to 9% by atmospheric deposition and 3 to 4% by inlet water. For P, these numbers were 10 to 48% for applications of fertilizers, manure and cattle droppings, 2 to 14% mineralization of soil organic matter, 33 to 82% nutrient-rich peat layers and 5 to 6% inlet water. The results of this paper demonstrate that nutrient loading of surface water in peat land areas involves several sources of nutrients, and therefore, reducing one source to reduce nutrient inputs to surface water is likely to result in modest effectiveness.     

Balanced pasture fertilization in the Basque Country: I. Phosphorus and potassium budgets on dairy farms

Dairy farming is the main agricultural activity of the Basque Country. A dairy farm is characterized as a system with soils and crops, forage, cattle and manure as main components, and in such a system, nutrient cycling is very important to maintain soil fertility and optimize forage production. To quantify nutrient transfers in the cycle, a simple system was developed and has been applied to seventeen farms to examine its ability to achieve a balanced P and K fertilization. These farms have provided data on inputs (fertilizer, feeds, concentrates), pasture and manure management, and outputs (milk production), and soil samples have been taken from farm pastures. Phosphorus and K in excreta and uneaten pasture is used with a relatively high efficiency as suggested by the relatively high efficiency of P and K utilization by the pasture that usually ranges from 70 to 90%. Concentrate feeding (3000 kg cow^–1 yr^–1) represents one of the main P and K inputs in Basque Country dairy farms, averaging 26 and 66 kg ha^–1, respectively. Besides, release of K in the soil through slow liberation from non-exchangeable sites was estimated as 30 kg ha^–1. Thus, a high efficiency in excreta recycling would diminish substantially P and K mineral fertilizer needs. Farm nutrient budgets appear to be a convenient tool for determining nutrient shortages and surpluses at farm level, and thus they are considered as a first step to support a better management of maintenance fertilization of permanent pastures.     

Nitrogen,phosphorus and potassium balances and cycles of Swiss agriculture from 1975 to 2008

Intensification of Swiss agriculture after 1950 led to an increase in productivity and a range of environmental and health problems provoked by growing inputs of nitrogen (N), phosphorus (P) and potassium (K) into the agricultural cycle. In 2008, farm-gate balances showed surpluses of 108 kg N ha⁻¹, 5.5 kg P ha⁻¹ and 28 kg K ha⁻¹ for Swiss agriculture. Nutrient surpluses rose between 1975 and 1980 and then decreased significantly until 2008, with percentage reductions being higher for P (80%) and K (54%) than for N (27%). The introduction of direct payments for ecological programmes such as integrated production in 1993 led to a more pronounced decrease in nutrient surpluses for several years, until most farmers had joined these programmes. Lower surpluses could primarily be attributed to reductions in mineral fertilizer use and N deposition. Biological N fixation and atmospheric deposition contributed most to the uncertainty in calculating nutrient balances. N cycle was characterized by substantial inputs into and outputs out of the agricultural sector, whereas P and K cycles were more closed. In future, nutrient balances at a regional level are required to identify areas with high surpluses. In Switzerland, a further reduction in surpluses could be achieved by better feeding strategies and an improved fertilizer management, mainly of animal manure.     

Nutrient flows in smallholder production systems in the humid forest zone of southern Cameroon

The flows and balances of N, P and K were studied in 20 farms in the Campo Ma’an area in Cameroon between March and August 2002 to assess the nutrient dynamics in smallholder farms. Data were collected through farmer interviews, field measurements and estimates from transfer functions. Nutrient input from mineral (IN1), animal feed (IN2a) and inorganic amendments (IN2b) was absent. Major outputs were through crop (OUT1a) and animal (OUT1b) products sold. Partial budgets for farmer managed flows were negative: −65 kg N, −5.5 kg P and −30.8 kg K ha⁻¹ year⁻¹. For inflows not managed by farmers, deep capture (IN6) was the major source: 16.6, 1.4 and 6.6 kg ha⁻¹ year⁻¹ of N, P and K, respectively. Atmospheric deposition (IN3) was estimated at 4.3 kg N, 1.0 kg P and 3.9 kg K ha⁻¹ year⁻¹, and biological nitrogen fixation (IN4) at 6.9 kg N ha⁻¹ year⁻¹. Major losses were leaching (OUT 3a): 26.4 kg N, and 0.88 kg K ha⁻¹ year⁻¹. Gaseous losses from the soil (OUT 4a) were estimated at 6.34 kg N, and human faeces (OUT 6) were estimated at 4 kg N, 0.64 kg P and 4.8 kg K ha⁻¹ year⁻¹. The highest losses were from burning (OUT 4c), i.e. 47.8 kg N, 1.8 kg P and 14.3 kg K ha⁻¹ year⁻¹. Partial budgets of environmentally controlled flows were negative only for N −4.8 kg N, +2.4 kg P and +9.6 kg K ha⁻¹ year⁻¹. The overall farm budgets were negative, with annual losses of 69 kg N, 3 kg P and 21 kg K ha⁻¹. Only cocoa had a positive nutrient balance: +9.3 kg N, +1.4 kg P and +7.6 kg K ha⁻¹ year⁻¹. Nutrients reaching the household waste (1.9 kg N, 2.8 kg P and 18.8 kg K ha⁻¹ year⁻¹), animal manure (4.9 kg N, 0.4 kg P and 1.6 kg K), and human faeces (4 kg N, 0.64 kg P and 4.8 kg K ha⁻¹ year⁻¹) were not recycled. Five alternative management scenarios were envisaged to improve the nutrient balances. Recycling animal manure, household waste and human faeces will bring the balance at −62.6 kg N, 0 kg P and +1 kg K ha⁻¹ year⁻¹. If, additionally, burning could be avoided, positive nutrient balances could be expected.     

Nutrient flows and balances in urban and peri-urban agroecosystems of Kano, Nigeria

Nutrient balances are useful indicators to assess the sustainability of farming systems. This study study investigates inflow and outflow of major nutrients in urban and periurban production systems in Kano, Nigeria. To this end, 16 households representing three different urban and peri-urban (UPA) farming systems were studied using the MONQI toolbox (formerly known as NUTMON) to calculate nutrient flows and economic performances. The farm nitrogen (N) balance was positive at 56.6, 67.4 and 56.4 kg farm^?1 year^?1 for commercial garden and crop-livestock (cGCL), commercial gardening and semi-commercial livestock (cGscL) and commercial livestock subsistence field cropping (cLsC) farm types, respectively. The same trend was observed for phosphorus (P) and potassium (K) in all farm types except an annual negative K balance of 16 kg farm^?1 in cGCL. Across the different activities within the farms, land uses had positive N (359, 387 and 563 kg N ha^?1 year^?1) and P (74, 219 and 411 kg P ha^?1 year^?1) balances for all farm types, but again a negative K balance in cGCL with an average loss of 533 kg K ha^?1 year^?1. Partial nutrient balances in livestock production indicated a positive balance for all nutrients across the farms types but were slightly negative for P in cLsC. Commercial livestock keeping (cLsC) was economically more profitable than the other farm types with an average annual gross margin (GM) and net cash flow (NCF) of $9,033 and $935. Cropping activities within cGCL and cGscL had GMs of $1,059 and $194 and NCFs of $757 and $206, respectively, but livestock activities in both farm types incurred financial losses. Potassium inputs were limited under vegetable and crop production of cGCL, threatening long-term K nutrient availability in this system. Overall, the results indicated large annual surpluses of N and P in urban and peri-urban vegetable and crop production systems which pose a potential threat when lost to the environment. Appropriate policies should aim at promoting sustainable production through efficient nutrient management in the Kano UPA sector.     

Identification of nutrients limiting cassava yield maintenance on a sedimentary soil in southern Benin,West Africa

Market opportunities will drive intensification of cassava production and fertilizer will play a role in this. A trial was initiated on 15 farmers fields (replications) in one village territory in Benin on a relatively fertile sedimentary soil site to identify nutrients limiting cassava yield using nutrient omission plots over three cropping years. There was no response to fertilizer in the first year when fresh root yields in the unamended control averaged 19.1 t ha^–1. In the second year, the control yield was 16 t ha^–1 and there were significant reductions from withholding P (3.5 t ha^–1) and K (2 t ha^–1) from a complete fertilizer regime. Nutrient balance after 1 and 2 years (cumulative) showed substantial P and K deficits in unamended plots. In the third year, the control yield was 12.9 t ha^–1 and effects of withholding K (5.3 t ha^–1), P (5.0 t ha^–1) and N (3.0 t ha^–1) were statistically significant. Soil K was a significant source of variation in yield in the third year. In the third year of annual nutrient additions soil P and K in the top 0.3 m were increased by 37 and 40%, respectively. Based on the cumulative nutrient balance calculation, the annual application needed to compensate nutrient depletion was 13 kg N, 10 kg P, and 60 kg K ha^–1. Partial budget analysis based on these amounts of fertilizer suggested that investment was clearly justified in the third year of continuous cropping at current low cassava prices.     

A phosphorus budget of a poultry farm and a dairy farm in the southeastern U.S., and the potential impacts of diet alterations

Current and potential environmental problems associated with P transport from lands receiving high application rates of animal waste are a major concern. Phosphorus management strategies are needed to reduce P loading on land. This study was conducted to compare on-farm P budgets for a modern broiler farm and a dairy farm under traditional diets and management practices. Phosphorus inputs, recycling and outputs were assessed for both farms. A typical broiler and a dairy farmer from North Carolina were interviewed and pertinent information for the study was obtained, in cooperation with extension agents, and other professionals associated with the farms. The annual on-farm P surplus for the broiler farm was 6,380 kg, while that for the dairy farm was 1,141 kg. This corresponds to an annual application of 65 kg P ha^–1 for the broiler farm and 20 kg P ha^–1 for the dairy farm in excess of removal. The potential for reducing P surpluses by the addition of phytase enzymes and/or the use of low phytic acid corn (Zea mays L.) feed in the broiler farm diet was also assessed. Estimates by animal nutritionists indicate that feed supplementation with phytase enzyme can reduce the broiler farm's P surplus by 33%. The use of low phytic acid corn can reduce the surplus by 49% and a combination of the two can reduce the surplus by 58%. In this study, the incorporation of soybean (Glycine max (L.) Merr.) and alfalfa (Medicago sativa) land into the waste utilization plan of the dairy farm decreases the annual P surplus from 20 to 9 kg P ha^–1. The use of new feed technology and expanding waste application to a larger land base can significantly alter the P budgets of broiler and dairy farms and reduce P surpluses, minimizing the risk of environmental problems.     

Nitrogen budgets and environmental capacity in farm systems in a large-scale karst region, southern China

Field surplus nitrogen (N) and farm disposal N are major sources of water pollution in farming systems. These sources are estimated from N budgets in field and whole farms, which are associated with the production and consumption of food. This study was conducted to evaluate these two pollution sources in the steep mountainous karst region of Quibainong, Guangxi Province, southern China. The region is, characterized as an area of upland farms, due to the shallow soils and rapid water drainage through cracks in the limestone. Although field surplus N in 1960 was only 4.1 kg N ha^–1, current field surplus N ranged from 10.1 to 463 kg N ha^–1, with values above 50 kg N ha^–1 in farms along roads and less than 40 kg N ha^–1 in the farms away from roads. The results obtained in near-road farms were similar to those in a previous study of N budgets in China. There was a significant positive correlation between the field surplus N and N application rate, including when the previous data were incorporated. The proportion of manure to total N application decreased with increase of N application. Chemical fertilizer was applied in greater quantity in economically rich farms. Therefore, the increase of field surplus N in Quibainong may be caused by economic improvement. Although livestock and human excreta were stocked in manure barns, unused excreta N increased with the increase of N excreted. The unused excreta N also increased with the decrease of feed self-sufficiency, but was not related to N application rate. These facts indicate that livestock husbandry in Quibainong is related to economic status of farms, but independently of crop production.The N application rate of more than 160 kg N ha^–1 increased field surplus N to an extent greater than crop uptake N, and a N application rate of more than 185 kg N ha^–1 increased the potential nitrate-N concentration to more than 10 mg L^–1. Therefore, 160–185 kg N ha^–1 is suggested to be the environmental capacity to sustain optimal N cycling in Quibainong. The average value of excreta N produced on near-road farms in Quibainong was 171 kg N ha^–1. If excreta N was used evenly for crop cultivation without chemical fertilizer in whole fields, the optimal N cycling would be maintained.The survey conducted here using a questionnaire was effective in evaluating all kind of N flows in the farming systems.     

Nutrient input-output budget of shifting agriculture in Eastern Amazonia

A case study on the nutrient input-output budget of slash and burn agriculture was carried out in Northeast-Pará, Brazil, where such a land-use system has been practised for about 100 years. A common cropping period lasts for two years and the fields lie fallow for 4 to 8 years. We quantified rates of deposition, fertilization, and losses due to the burn, harvest and leaching. Six fields of different phases in the rotational cycle were under study during a 19 month period. During the fallow period, the input of Na, K, Mg, N, P and S via deposition exceeded the estimated losses with the seepage water. The Ca budget was almost balanced. The balance of fields in the transition from the fallow to the cropping phase was negative for Na, K, Ca, Mg, N, and S. The P balance was positive when NPK fertilizer was applied, and negative without fertilizer application. The nutrient balance for K, Mg, Ca, N, and P was also negative on the field in transition from the cropping to the fallow period. The nutrient budget for an entire land-use cycle of 9 years was estimated by the false time series approach. In the case of an NPK fertilization during the cropping period there were net losses of 75 kg K ha^–1, 125 kg Ca ha^–1, 16 kg Mg ha^–1, 285 kg N ha^–1 and 13 kg S ha^–1. Na (86 kg ha^–1) and P (11 kg ha^–1) were accumulated. The harvest was the most important flux for the K (61%) and P (62%) output. The element transfer into the atmosphere during the burn caused the main losses of N (60%), S (65%), Ca (58%) and Mg (41%). The most important path of Na loss was leaching (92%). The net K losses were severe as they represented 45% of the K store found extractable in the soil down to 1m depth and in the above ground biomass. The presented results may be useful in planning a sustainable and environmentally protective method of land-use within a shifting cultivation system. It is strongly recommended that slash burning be abandoned in order to keep the nutrients in the ecosystem.     

The N-cycle as determined by intensive agriculture – examples from central Europe and China

Using a scientific assessment concept of sustainability in crop-production based on the entropy production minimization principle of thermodynamics, formation and non-use of soluble and volatile (by-)products of the nutrient cycles within the system are interpreted as indicators or measures of the low efficiency/sustainability of recent forms of intensive agriculture. The simultaneous high energy input in modern crop production systems further shows the difference between these and quasi-stationary natural systems with maximum bioproduction having minimum energy dissipation and entropy production. Using balance sheets and dynamic approaches, the practical implications regarding the nitrogen cycle in central Europe (FR Germany) and China are exemplified and discussed. The average N balance of arable systems in Germany shows surplus N amounts of 110–130 kg N ha^-1 yr^-1. A high N immobilization in accordance with deepened top soil layers has governed N balances in Germany since about 1960. In China Nbalance surpluses in intensive agricultural (double-cropping) systems on the southern edge of the Loess Plateau now reach 125–230 kg N ha^-1 yr^-1. In field experiments, mineral N contents in the profiles (0–1.2 m depth) were 72–342 and 78–108 kg ha^-1 at harvest of summer maize and winter wheat, respectively. In the Taihu region in eastern China, surpluses in the N balance (rice-wheat double cropping) amount to 217–335 kg N ha^-1 yr^-1. N_min contents in the 0–0.9 m profiles of between 50 and 100 kg N ha^-1 were frequently found after winter wheat harvest. In two separate investigations of ground and well water samples in China, nitrate contents exceeded the critical WHO value for drinking water in 38–50% of the locations investigated.     

Soil nutrient content and nutrient balances in newly-built solar greenhouses in northern China

Soil nutrient content and nutrient balances in newly-built solar greenhouses in the southern part of China??s Loess Plateau were investigated over two consecutive years. Farmers applied manure and inorganic fertilizers at average annual rates of 1,907?kg?N ha^?1, 1,601?kg?P₂O₅?ha^?1 and 1,742?kg?K₂O?ha^?1. Manure accounted for 65?% of the total N input, 57?% of the total P input and 55?% of the total K input. The average annual nutrient surpluses were 1,374?kg?N?ha^?1, 1,468?kg?P₂O₅?ha^?1 and 881?kg?K₂O?ha^?1. Soil organic matter, total N, available P, available K and electrical conductivity (EC) increased significantly across time in the topsoil (0?C20?cm depth), but not in the subsoil (20?C100?cm depth). The nitrate?CN concentrations (mg?N?kg^?1) of the 0?C100?cm depth increased by 163?C336?% over 2?years. The average accumulation of nitrate?CN (kg?N?ha^?1) of the 0?C100?cm depth increased by 241?% and leveled out at 511?kg?N?ha^?1; and it was 1,015?kg?N?ha^?1 in the 0?C200?cm depth. In conclusion, over-fertilization led to large nutrient surpluses in the soil of newly-built greenhouses.     

Distribution of acid extractable P and exchangeable K in a grassland soil as affected by long-term surface application of N, P and K fertilizers

Information on the fate and distribution of surface-applied fertilizer P and K in soil is needed in order to assess their availability to plants and potential for water contamination. Distribution of extractable P (in 0.03 M NH₄F + 0.03 M H₂SO₄ solution) and exchangeable K (in neutral 1.0 M ammonium acetate solution) in the soil as a result of selected combinations of 30 years (1968–1997) of N fertilization (84–336 kg N ha^–1), 10 years of P fertilization (0–132 kg P ha^–1), and 14 years of K fertilization (0 and 46 kg K ha^–1) was studied in a field experiment on a thin Black Chernozem loam under smooth bromegrass (Bromus inermis Leyss.) at Crossfield, Alberta, Canada. Soil samples were taken at regular intervals in October 1997 from 0–5, 5–10, 10–15, 15–30, 30–60, 60–90 and 90–120 cm layers. Soil pH decreased with N rate and this declined with soil depth. Increase in extractable P concentration in the soil reflected 10 years of P fertilization relative to no P fertilization, even though it had been terminated 20 years prior to soil sampling. The magnitude and depth of increase in extractable P paralleled N and P rates. The extractable P concentration in the 0–5 cm soil layer increased by 2.2, 20.7, 30.4 and 34.5 mg P kg^–1 soil at 84, 168, 280 and 336 kg N ha^–1, respectively. The increase in extractable P concentration in the 0–15 cm soil depth was 1.5 and 12.8 mg P kg^–1 soil with application of 16 and 33 kg P ha^–1 (N rate of 84 N ha^–1 for both treatments), respectively; and it was 81.6 and 155.2 mg P kg^–1 soil with application of 66 and 132 kg P ha^–1 (N rate of 336 N ha^–1 for both treatments), respectively. The increase in extractable P at high N rates was attributed to N-induced soil acidification. Most of the increase in extractable P occurred in the top 10-cm soil layer and almost none was noticed below 30 cm depth. Surface-applied K was able to prevent depletion of exchangeable K from the 0–90 cm soil, which occurred with increased bromegrass production from N fertilization in the absence of K application. As only a small increase of exchangeable K was observed in the 10–30 cm soil, 46 kg K ha^–1 year^–1 was considered necessary to achieve a balance between fertilization and bromegrass uptake for K. The potential for P contamination of surface water may be increased with the high N and P rates, as most of the increase in extractable P occurred near the soil surface.     

Evaluation of current fertilizer practice and soil fertility in vegetable production in the Beijing region

A survey on current fertilizer practices and their effects on soil fertility and soil salinity was conducted from 1996 to 2000 in Beijing Province, a major vegetable production area in the North China Plain. Inputs of the major nutrients (NPK) and fertilizer application methods and sources for different vegetable species and field conditions were evaluated. Excessive N and P fertilizer application, often up to about 5 times the crop requirement in the case of N, was very common, especially for high-value crops. Potassium supply may have been inadequate for some crops such as leafy vegetables. Urea, diammonium orthophosphate ((NH₄)₂HPO₄) and chicken manure were the major nutrient sources for vegetable production in the region. Over 50% of N, 60% of P and nearly 90% of K applied originated from organic manure. Total N application rate for open-field Chinese cabbage from organic manure and inorganic fertilizers ranged from 300 to 900 kg N ha^–1 on 78% of the farms surveyed. More than 35% of the surveyed greenhouse-grown tomato crops received > 1000 kg N ha^–1 from organic and inorganic sources. A negative K balance (applied K minus K removed by the crop) was found in two-thirds of the surveyed fields of open-field Chinese cabbage and half of the surveyed fields of greenhouse-grown tomato. Plant-available N, P and K increased with increasing length of the period the greenhouse soils had been used for vegetable production. Similarly, soil salinity increased more in greenhouse soils than in open-field soils. The results indicate that balanced NPK fertilizer use and maintenance of soil quality are important for the development of sustainable vegetable production systems in this region.     

Assessment of phosphorus leaching losses from a free draining grassland soil

Intact soil monoliths (70 cm deep, 50 cm diameter), collected from a free draining Lismore silt loam soil (Udic Haplustept) under grassland, were used to evaluate phosphorus (P) leaching for two years. The objective of the study was to investigate the effect of the application of mineral P fertiliser (at 45 or 90 kg P ha^–1 y^–1) and/or farm dairy effluent (FDE) (30 to 60 kg P ha^–1 y^–1) on P losses by leaching. Annual mean total P (TP) concentrations and losses were higher from the treatments that received both FDE and P fertiliser (203–429 g L^–1; 1.4–2.5 kg ha^–1) compared with P fertiliser alone (77–151 g L^–1; 0.6–1.3 kg ha^–1). The form of applied P influenced the pattern of P forms leached. For example, significantly higher P losses in different P forms were observed for the combined mineral P fertiliser and FDE treatment (P45/FDE200) than fertiliser alone (P90/N200/U). This is due to the inclusion of liquid FDE in the former treatment although the total P inputs were similar for both treatments. This illustrates the potential of these soils to adsorb soluble inorganic P applied from mineral P fertiliser, while FDE contained unreactive P forms that were mobile in the soil profile. There was a distinct pattern of P forms leached in the following order: particulate unreactive P (PUP: 40–70%)>dissolved unreactive P (DUP: 14–53%)>particulate reactive P (PRP: 5–12%)>dissolved reactive P (DRP: 1–11%). Results also suggest that changing the irrigation method from flood to spray may be the most effective means to reduce P loss in these stony, free-draining soils.