Changes in the cycling of nitrogen, phosphorus, and potassium in a dairy farming system

The objective of this study was to quantify nitrogen (N), phosphorus (P), and potassium (K) use and cycling in a dairy farming system. The data were collected from the experimental farm at the National Institute of Livestock and Grassland Science in Tochigi Prefecture, Japan, using about 11 ha of forage crop fields and about 30 dairy cows. Forage crops grown in the field were ensiled and offered to the cows, and the subsequent compost from the animals’ excretion was applied to the field. The dairy farming system consisted of soil/crop, feed storage, animal, and compost components. Nutrient inputs and outputs and flows of the soil–plant–animal pathway for the whole farm and each component were measured for 5 years. Nutrient utilization was evaluated using nutrient balances, use efficiencies, and cycling indices. The 5 year average nutrient balances and nutrient use efficiencies of N, P, and K for the whole farm (kg ha^?1 year^?1) were 378, 97, and 199 and 0.25, 0.19, and 0.18, respectively. The characteristics of nutrient balances and use efficiencies for each component differed among N, P, and K. The average cycling indices of N, P, and K were 0.12, 0.11, and 0.37, respectively. Significant positive relationships between use efficiencies and cycling indices were observed in N and K. Year-to-year variations in flows were relatively large for compost application. The results suggested that improving N balance would be the most effective option for solving many of the environmental problems related to dairy farming.     

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.     

Effects of organic wastes digestion for biogas production on mineral nutrient availability of biogas effluents

Organic farming systems are characterized by the strong regulation of the import of nutrients into the farming system to replace nutrient losses via sold products. In the present study mineral nutrient flows and balances of P, K and magnesium (Mg) were analysed for a mixed organic cropping system with dairy husbandry and for a stockless organic farming system. Also the influence of biogas digestion of farmyard residues (stable wastes, crop residues, etc.) as well as the effect of the import of substrates for biogas digestion on plant mineral nutrient uptake and farmgate nutrient balances was analysed. The objectives of the current study were; (1) to study the effects of anaerobic digestion of cattle manure and crop residues on plant mineral nutrient uptake; and (2) to model nutrient flows and balances related to the input of different kind of substrates for biogas digestion at the farmgate. Results indicated that slurry digestion did not influence plant P and K uptake. Import of single allowed substrates for digestion would lead to large imbalances in nutrient inputs compared to withdrawals. Most of the suited substrates for biogas digestion were associated with large K surpluses and insufficient P returns in comparison to mineral nutrient outputs via sold animal and plant products.     

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 cycling in organic farms: stall balance of a suckler cow herd and beef bulls

In organic agriculture, the internal farm nutrient cycle must bequantified to ensure high system productivity accompanied by environmentallysound production processes. In contrast to common farm-gate and field balances,budgeting at the stall level is seldom undertaken. When budgeting mixed farmingsystems, a substantial lack of nutrients can be detected in the forageand straw input – stall – manure output nutrient flow chain.Therefore, stall balances focus on a central component of whole-farm nutrientbudgets for developing efficient nutrient management strategies. At theexperimental farm for organic agriculture at Wiesengut in Hennef, Germany, allsolid mass flows for a suckler herd and a herd of beef bulls were measured.Relative balance values obtained for dry matter and C (45 to 56%), N (16to 36%), P (–7 to 22.5%), K (0 to 13%) and ash(–4 to 7%) varied over a wide range. Balances are very sensitive tovariations in mass flow and nutrient content for components with high nutrientcontents and/or a large contribution to total mass flow (e.g. manure, silage).In developing strategies to minimise N losses, by reducing N surplus in theration, one must consider, that, in contrast to dairy farms, a suckler herd forbeef production integrated in an organic farm has to adapt to crop productiondemands.     

A comparative study of farm nutrient budgets and nutrient flows of certified organic and non-organic farms in China,Brazil and Egypt

Increased demand for certified organic products has led to an increase in the number of certified organic farms in developing countries. Knowledge of farmer nutrient management practices on certified organic farms in developing countries is limited. Thus, the aim of this study was to investigate the impact of the adoption of certified organic agriculture on farm nutrient flows and nutrient budgets, and evaluate to which degree organic farms comply with organic principles relating to nutrient management. The study is based on five case studies of different types of certified organic farming systems in Brazil, Egypt and China. Farm nutrient flows and nutrient budgets for nitrogen, phosphorous and potassium were created for each farm. Four of the five organic systems studied had nutrient surpluses on the farm budget. The surpluses were of varying magnitude. The main difference between organic and non-organic farm nutrient flows was the replacement of mineral fertilizers with organic inputs. However, the magnitude of nutrient flows were generally similar for organic and non-organic farms. Certified organic farms with positive nutrient budgets had a heavy reliance on external inputs. Continued high dependence on an external supply of nutrients, which typically originate from mineral sources, poses a significant challenge to organic farmers’ fulfilment of the principles of organic agriculture.     

Beyond adding up inputs and outputs: Process assessment and upscaling in modelling nutrient flows

Departing from the historical background of scientific interest in soil fertility and sustainable agricultural production in sub-Saharan Africa, a review is conducted of nutrient budget studies carried out in semi-arid West Africa at scales ranging from individual fields to the sub-continent. For both, nitrogen and phosphorus, the comparison discloses largely diverging balances calculated for similar agro-ecosystems. In a first step, the modes of calculation of the nutrient budgets are examined. It is demonstrated that the calculations used in the different studies differ by the variables and biophysical processes taken into account, and by the choice of spatial scales as well as related time scales. One important discrepancy between approaches is whether and to which extent nutrient flows are internalized when upscaling. The extent to which the impact of individual and communal management, especially of pastoral and forestry resources, on nutrient flows is accounted for is a second cause of divergence. Moreover, it was observed that nutrient budgets tend to be increasingly negative as the spatial scale of the study increases from farm to sub-continent. This unexpected trend is traced back to the lack of internalization of nutrient flows when upscaling. The complexity of the scale patterns of nutrient flows and that of the interactions and the tradeoffs in the effects of management calls for the use of models to calculate nutrient budgets. Therefore, in a second step, examples of a static model, a multiple-goal linear programming model and a decision rules model were reviewed, all of which include the calculation of nutrient flows and balances and which were applied to West-African farming systems. The models are analyzed for their way of dealing with the critical issues of spatial and temporal scales and the impact of resource management on nutrient flows, taking into account that they have different objectives and were designed for different spatio-temporal scales. To conclude, suggestions were made for strengthening the use of models as tools enabling ex-ante testing of alternative agricultural technologies and policies that could improve soil nutrient balances in semi-arid sub-Saharan Africa.     

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.     

Beyond adding up inputs and outputs: Process assessment and upscaling in modelling nutrient flows

Departing from the historical background of scientific interest in soil fertility and sustainable agricultural production in sub-Saharan Africa, a review is conducted of nutrient budget studies carried out in semi-arid West Africa at scales ranging from individual fields to the sub-continent. For both, nitrogen and phosphorus, the comparison discloses largely diverging balances calculated for similar agro-ecosystems. In a first step, the modes of calculation of the nutrient budgets are examined. It is demonstrated that the calculations used in the different studies differ by the variables and biophysical processes taken into account, and by the choice of spatial scales as well as related time scales. One important discrepancy between approaches is whether and to which extent nutrient flows are internalized when upscaling. The extent to which the impact of individual and communal management, especially of pastoral and forestry resources, on nutrient flows is accounted for is a second cause of divergence. Moreover, it was observed that nutrient budgets tend to be increasingly negative as the spatial scale of the study increases from farm to sub-continent. This unexpected trend is traced back to the lack of internalization of nutrient flows when upscaling. The complexity of the scale patterns of nutrient flows and that of the interactions and the tradeoffs in the effects of management calls for the use of models to calculate nutrient budgets. Therefore, in a second step, examples of a static model, a multiple-goal linear programming model and a decision rules model were reviewed, all of which include the calculation of nutrient flows and balances and which were applied to West-African farming systems. The models are analyzed for their way of dealing with the critical issues of spatial and temporal scales and the impact of resource management on nutrient flows, taking into account that they have different objectives and were designed for different spatio-temporal scales. To conclude, suggestions were made for strengthening the use of models as tools enabling ex-ante testing of alternative agricultural technologies and policies that could improve soil nutrient balances in semi-arid sub-Saharan Africa.     

Research on soil fertility decline in tropical environments: integration of spatial scales

Soil nutrient depletion is increasingly regarded as a major constraint to sustainable food production in tropical environments. Research in the recent past focused on different scales, but few attempts were made to link them. In this paper, two cases are elaborated in Central America (CA) and Sub-Saharan Africa (SSA), in which the integration of different scales has been studied. Soil nutrient depletion has been calculated for fields, and has then been aggregated to farms, regions, and subcontinents. Key problems on aggregation of field nutrient balances to farms include nutrient flows between fields. Aggregation of farms to regions requires a generalization of individual farms into a farm typology. Aggregation of regions into subcontinents implies that the farm typology concept can mostly not be maintained, resulting in a generalized calculation based on national soil, climate and land use data bases. The field-farm step proved complicated for SSA due to the occurrence of a wide variety of nutrient flows between fields, whereas in CA these flows were much less pronounced; the farm-region step turned out to be manageable for both CA and SSA as farm typology adequately covered observed variation; the region-subcontinent step proved difficult for CA due to the considerable variation in management and input levels in farming systems, whereas this was less the case in SSA. The study shows that integration of spatial scales is constrained by both data availability (the tropical parameter crisis) and by scale-specific variability.     

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.     

The significance of available nutrient fluxes in N and P budgets for maize cropping on a Rhodic Kandiustox: a study with compost,NP fertilizer and stubble removal

Nutrient budgets may be useful tools for nutrient management of crops especially if they estimate the nutrient fluxes available from a variety of sources including organic and inorganic fertilizer, crop residues and soil organic matter. The aim of the present study was to develop a budget of available nutrients by determining the contribution of mineralized nutrient fluxes and fertilizer input relative to nutrient losses and removal in harvested products in the overall N and P balances. N and P inputs and outputs and available N and P fluxes in the soil were estimated for 3 consecutive maize crops where inputs and outputs were altered by NP fertilizer, compost and stubble removal on a Rhodic Kandiustox. A sensitivity analysis of calculated and measured nutrient budget items was conducted to identify the main factors affecting the accuracy of the nutrient balance calculations. Mineral fertilizer rate was the major factor for maize nutrient budgets as shown by its contribution to N and P balances. Without mineral fertilizer application, soil organic matter (SOM) mineralization was the most important within-season nutrient input. In the case of N, shoot uptake was the main output followed by denitrification. Phosphorus adsorption by the soil was the major P output from the available pools followed by shoot uptake. SOM mineralization maintained the pools of available N and P if stubble of the previous crop was returned. Mineral fertilizer application, which produced surplus balances of N and P, would however, be needed to attain high yield, even with stubble return. The available N and P from compost were not significant inputs in the nutrient balances until year 3. Total N and resin extractable P in soil after five crops supported the calculated nutrient balances indicating the importance of available nutrient fluxes in calculating N and P balances.     

Modeling farm nutrient flows in the North China Plain to reduce nutrient losses

Years of poor nutrient management practices in the agriculture industry in the North China Plain have led to large losses of nutrients to the environment, causing severe ecological consequences. Analyzing farm nutrient flows is urgently needed in order to reduce nutrient losses. A farm-level nutrient flow model was developed in this study based on the NUFER (NUtrient flows in Food chains, Environment and Resources use) model, and was used to analyze nitrogen (N) and phosphorus (P) flows, use efficiencies, and losses for nine representative farm types in the North China Plain. Data from 401 farms were evaluated for the years 2012–2015. The analysis showed that mixed farms were more efficient in nutrient utilization than crop-based or landless livestock farms. The efficiencies of N and P used in crop production were highest for mixed dairy farms, reaching 67% for N and 68% for P. Consistently, mixed dairy farms had the lowest N and P surpluses and losses in crop production. Mixed swine farms were 5 and 9% higher in N and P efficiency in livestock production than landless swine farms, respectively. Losses of N and P from the animal manure management chain were 20–42% lower for mixed swine and 69–78% lower for mixed poultry farms than for landless farms of the same animal type. This is at least partially due to more frequent manure removal. Integrated crop-livestock production using livestock wastes as crop fertilizer was shown to be the most sustainable model in nutrient use for the agriculture industry in the North China Plain.     

Nitrogen,phosphorus, and potassium budgets in Indian agriculture

Nutrient budgeting is a useful tool in determining present and future productivity of agricultural land as well as undesirable effects of nutrient mining and environmental pollution. Budgets of N, P, and K were calculated for India for 2000–2001 taking into consideration the inputs through inorganic fertilizer, animal manure, compost, green manure, leguminous fixation, non-leguminous fixation, crop residues, rain and irrigation water and outputs through crop uptake and losses through leaching, volatilization and denitrification. Inorganic fertilizer was the dominant source contributing 64% of N and 78% of P inputs in Indian agriculture, whereas K input through inorganic fertilizer was 26%. Removals of N, P, and K by major agricultural crops in the country were 7.7, 1.3 and 7.5 Mt, respectively. There were positive balances of N (1.4 Mt) and P (1.0 Mt) and a negative balance of K (3.3 Mt). It was projected that N, P, and K requirement by Indian agriculture would be 9.78, 1.57 and 9.52 Mt, respectively, to meet the food demand of 1.3 billion people by 2020. The study identified the ‘hotspots’ of excess nutrient loads as well as of nutrient mining regions in India to improve our ability to predict environmental degradation due to imbalanced fertilizer use. However, there are some uncertainties in India’s nutrient budget and more research is required to reduce these uncertainties.     

A spatially explicit methodology to quantify soil nutrient balances and their uncertainties at the national level

A soil nutrient balance is a commonly used indicator to assess changes in soil fertility. In this paper, an earlier developed methodology by Stoorvogel and Smaling to assess the soil nutrient balance is given a major overhaul, based on growing insights and advances in data availability and modelling. The soil nutrient balance is treated as the net balance of five inflows (mineral fertilizer, organic inputs, atmospheric deposition, nitrogen fixation and sedimentation) and five outflows (crop products, crop residues, leaching, gaseous losses and erosion). This study aims to improve the existing methodology by making it spatially explicit, improving various transfer functions, and by modelling explicitly the uncertainties in the estimations. Spatially explicit modelling has become possible through a novel methodology to create a simulated land use map on the basis of the principles of traditional qualitative land evaluation. New literature data on the various inputs and outputs allowed improvement of the estimations of deposition, sedimentation, leaching, and erosion. Moreover, the uncertainty of the calculated soil nutrient balances was assessed. To illustrate the improved methodology, we applied it to Burkina Faso and revealed that nutrient depletion is occurring throughout the country at rates of , and . The resulting spatial soil nutrient balances at the national level can constitute the basis for targeting soil fertility policies at lower levels.     

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.     

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.     

Smallholders’ Soil Fertility Management in the Central Highlands of Ethiopia: Implications for Nutrient Stocks, Balances and Sustainability of Agroecosystems

Low agricultural productivity caused by soil degradation is a serious problem in the Ethiopian Highlands. Here, we report how differences in soil fertility management between farming systems, based either on enset (Ensete ventricosum) or on teff (Eragrostis tef) as the major crops, affect the extent of nutrient stocks, balances and ecosystem sustainability. We collected information on farmers’ resources and nutrient management practices from stratified randomly selected households in two watersheds in the Central Highlands of Ethiopia. In addition, we collected soil samples from each land use and calculated nutrient stocks, partial and full nutrient balances (N, P and K) for one cropping season. Our results show that farmers in the two farming systems manage their soils differently and that nutrient inputs were positively related to farmers’ wealth status. The watershed with the enset-based system had higher soil N and K stocks than the watershed with the teff-based system, while P stocks were not different. Management related N?and K fluxes were more negative in the teff-based system (?28 kg N ha^?1 yr^?1 and ?34 kg K ha^?1 yr^?1) than in the enset-based system (?6 kg N ha^?1 yr^?1 and ?14 kg K ha^?1 yr^?1) while P fluxes were almost neutral or slightly positive. Within the enset-based system, a strong redistribution of N, P and K took place from the meadows and cereals (negative balance) to enset (positive balances). Although in the teff-based system, N, P and K were redistributed from meadows, small cereals and pulses to maize, the latter still showed a negative nutrient balance. In contrast to nutrient balances at land use level, nutrient balances at the watershed scale masked contrasting areas within the system where nutrient oversupply and deficiencies occurred.     

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.     

Crop residue,manure and fertilizer in dryland maize under reduced tillage in northern China: II nutrient balances and soil fertility

A long-term experiment was carried out in the dryland of northern China to assess the effects of applications of maize stover, cattle manure and NP (1:0.44) fertilizer on partial nitrogen (N), phosphorus (P) and potassium (K) balances, extractable soil N (SEN), P and K, and soil organic matter (SOM) in a spring maize cropping system, under reduced tillage conditions. The experiment was set-up according to an incomplete, optimal design, with three factors at five levels and 12 treatments, including a control with two replications. Statistical analyses using multiple regression models showed that the partial N, P and K balances were strongly influenced by annual variations in the amounts of soil water at seeding (SWS) and growing season rainfall (GSR). Most treatments had positive P but negative N and K balances. Cumulative P and K balances were reflected in extractable soil P (P-Olsen) and K (exchangeable K), but the weak relationships indicated that the sorption of P and buffering of K were strong. Cumulative balances of effective organic carbon (C) were weakly related to soil organic C (SOC) content after 12 years. Negative C balances were related to decreases in SOC, but positive C balances were not translated into increases in SOC. The analysis of nutrient balances and soil fertility indices revealed that nutrient inputs in most treatments were far from balanced. It is concluded that the concepts of ‘ideal soil fertility level’ and ‘response nutrient management’ provide practical guidelines for improving nutrient management under the variable rainfall conditions of dry land areas in northern China.