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Legumes form part of an ecological-based solution to intensification in areas with limited access to external inputs. Despite a number of decades of intervention, uptake of legumes has been slow within smallholder farming systems in sub-Saharan Africa. We explore the drivers behind the adoption of legumes by developing an indicator of household legume cultivation (HLC) from a bespoke survey of small-scale farm households in Kenya and the Democratic Republic of the Congo. A beta regression framework identifies the range of intensities across sites and farms, indicating a limited influence of agro-ecological zones and formal institutions on uptake. Age, income and gender have positive but very marginal effects. Intensive legume cultivations were less driven by commercial growth objectives or access to market oppourtunities indicating lack of legume markets to incentivize production. There was little interest in expanding farm area, which reflects the lack of assets available to these farmers and leads to the use of legumes for providing home nutrition, or supporting farm fertility and livestock feed. Further development of this HLC metric would be enabled by consistent data gathering across regions, or at least equally detailed studies of legume uptake. [ABSTRACT FROM AUTHOR]

Understanding crop performance and productivity in relation to intercropped tree species, tree management and prevailing environmental conditions may assist farmers in managing agroforestry systems appropriately. Our study evaluated the management and spatial effect of six dominant tree species (Eucalyptus spp., Sesbania sesban, Grevillea robusta, Calliandra calothyrsus, Markhamia lutea and Croton macrostachyus) on water availability and crop performance in smallholders' maize fields in Rift valley, Kenya. Maize performance under C. macrostachyus and M. lutea was also evaluated at on-station experiment in the same area. The smallholder farmers in the study area remain important maize producers in Kenya with an average maize yield of 6.5 tons ha−1 recorded. Maize yield under the dominant tree species in studied smallholder farms showed significant differences (P < 0.001) with leguminous species (C. calothyrsus and S. sesban) recording the highest amount of grain weight. Farmers selectively prune tree they perceive as competitive but still want to maintain them in the farms such as Eucalyptus spp. and G. robusta but miss to equally prune M. lutea and C. macrostachyus which would greatly improve performance of associated crops. In addition to presence of great tree management diversity, the study clearly showed that tree in smallholder farms either have competitive, complementary or balanced-off interaction with crops. Lastly, despite the adequate rainfall throughout the cropping season, dominant tree species in smallholder farms were shown to significantly (P < 0.0001) influence the spatial distribution of soil water. [ABSTRACT FROM AUTHOR]

Climate variability is contributing to water-scarcity problems in Kenya and to extreme flooding and drought in Vietnam. This paper compares diversity-based climate adaptation approaches in current land use in the Cam Xuyen district, Ha Tinh province, Central Vietnam and in the Kapingazi river watershed in Embu district, Eastern province, Kenya, in order to understand local responses to climate variability and examine the potential for policy support of diversity management by local people. Literature reviews and trend analysis of local time series of rainfall and temperature were combined with stakeholder interviews and workshops to identify technology and policy options for dealing with current and future climate variability. At all study sites, diversity in land use at farm level and along agriculture–forestry landscape gradients was a key strategy. Policy options to support such an approach could include legalization of agroforestry in Vietnam and a combination of regulations and incentive-based approaches to reconcile household decision-making with longer term and collective actions to benefit landscape diversity in Kenya. Lessons learnt in both study areas about payments for environmental services can be used in policy discussions. [ABSTRACT FROM AUTHOR]

Annual potassium (K) balances have been calculated over a 40-year period for five field experiments located on varying parent materials (from loamy sand to clay) in south and central Sweden. Each experiment consisted of a number of K fertilizer regimes and was divided into two crop rotations, mixed arable/livestock (I) and arable only (II). Annual calculations were based on data for K inputs through manure and fertilizer, and outputs in crop removal. Plots receiving no K fertilizer showed negative K balances which ranged from 30 to 65 kg ha−1 year−1 in rotation I, compared with 10–26 kg ha−1 year−1 for rotation II. On sandy loam and clay soils, the K yield of nil K plots (rotation I) increased significantly with time during the experimental period indicating increasing release of K from soil minerals, uptake from deeper soil horizons and/or depletion of exchangeable soil K (Kex). Significant depletion of Kex in the topsoil was only found in the loamy sand indicating a K supply from internal sources in the sandy loam and clay soils. On silty clay and clay soils, a grass/clover ley K concentration of ∼2% (dry weight) was maintained during the 40-year study period on the nil K plots, but on the sandy loam, loam and loamy sand, herbage concentrations were generally less than 2% K. [ABSTRACT FROM AUTHOR]

. Changes in agricultural subsidies in Europe and the ready availability of fertilizers have allowed a spatial decoupling of livestock and crop production. This has increased the flow of nutrients that occurs between farms compared to within individual farms. In terms of nutrient cycling, mixed farms provide the opportunity to re-integrate aspects of agricultural production. The degree of integration between crop and livestock production is denned by the reliance on the use of home-produced feed compared to imported feed, and is independent of intensity. Management of inputs and/or internal flows offers the scope to improve nutrient use efficiency (NUE) on mixed farms. Greatest uncertainties in calculating NUE are associated with variation in yield and composition of home-produced feed, and consequent manure composition. Three key areas are addressed to highlight the interchange of nutrients (and risks for losses) between crop and livestock production; (i) the role of livestock diet in manipulating the amount and availability of manure nutrients; (ii) the impact of manure management on nutrient losses; and (iii) nutrient management through the integration of crops and livestock in rotations. While not all the associated issues are unique to mixed farming, these three areas all influence NUE. [ABSTRACT FROM AUTHOR]

. Fertilizer and manure application rate and timing are often based on the optimal nitrogen rate and not on potassium (K) requirements. This can lead to excess or shortage of K depending on the crop and rotation. In grass-dominated agricultural production, including many organic farming systems, K has become a critical element, especially in areas dominated by coarse-textured or organic soils. In this paper we review K management in relation to long-term sustainability of both the soil resource and the production of crops of high yield and quality. One question for the future is whether we can adopt management options that favour efficient use of K and secure a sustainable future for global K reserves. For example, is it possible to enhance the release rate of K from soil mineral sources so that we require less fertilizer K from K-bearing salt deposits? A reduction in external K inputs requires improved on-farm recycling of K in order to reduce losses. We also need a better understanding of soil processes and soil-plant interactions and decision-support tools to predict the potential K release from mineral weathering. Certain areas dominated by young, clay-rich soils can potentially supply enough K, whereas other areas with coarse sandy or organic soils have a very low weathering potential and would thus need external inputs of K. [ABSTRACT FROM AUTHOR]

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. [Copyright &y& Elsevier]

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 O¨jebyn 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. [Copyright &y& Elsevier]

Abstract: Cadmium (Cd) is a toxic heavy metal which to a relatively large extent is ingested via wheat-based products. Conflicting results have been reported on how the application of nitrogen (N) fertilizers to winter wheat (Triticum aestivum L.) affects the Cd concentration in grain. The objectives of this study were to investigate how and to what degree application of N fertilizer affected the Cd concentration in winter wheat grain under field conditions and how consistent such effects were between sites and cultivars. Two wheat cultivars fertilized with four rates of nitrate of lime (100, 145, 190 and 235kgNha−1) were investigated in field trials, where the fertilizer was applied on two occasions as is common for bread wheat. In addition, data on Cd and N concentrations in grain of wheat, oats and barley from a Swedish soil monitoring programme were evaluated. In the field trials the grain Cd concentration increased with increasing N rate, irrespective of the Cd concentration in soil and grain. Each 10kg increase in N application gave an increased Cd concentration in grain of approximately 0.001–0.003mgkg−1. The relative increase in Cd concentration as a function of N rate varied between 6 and 14% across sites and cultivars when the N rate was increased from 145 to 175kg N. The grain Cd concentration was also positively correlated to the grain N concentration. The data from the Swedish soil monitoring programme showed a significant positive correlation between the N and Cd concentrations in grain of winter wheat, oats and barley. A possible explanation for the increase in grain Cd concentration could be ion exchange reactions in the soil solution, where an increased concentration of the fertilizer cation Ca2+ may have caused an increased concentration of Cd2+ in soil solution and eventually in wheat grain. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Understanding the structure, densities and utilization of tree populations in agricultural landscapes is useful in determining the species influencing agroecosystem function. Our study evaluated agroforestry adoption and practices within smallholder farms in a former large-scale maize growing area of Trans Nzoia County, Rift Valley Province, Kenya. This was followed by investigation of factors influencing heterogeneity in the adoption and practices. The factors include: household resource endowment, land tenure and time under current management. Five settlement schemes which were formerly large estates dominated by maize mono-cropping were selected for the current study. Tree inventories of the farms were obtained through transect walks across each settlement. A total of 123 farms were assessed representing households of different resource endowment levels, tenure and number of years under current management. Different analyses were carried out including farm size and tree number, tree density, tree diversity and utilization of the dominant tree species. In total, we identified 44 tree/shrub species, 24 of which were indigenous and the rest exotic. However, the exotic tree species dominated strongly in abundance with Eucalyptus spp. being the most frequent taxon and constituting 34.6% of all trees. Species richness was found to be low compared to other agricultural landscapes in the region. Resource constrained households were found to prefer fruit tree species and maintained high tree diversity on their farms. Households with secure tenure had higher tree diversity than those without who had higherspecies richness and opted for fast growing fodder and fertilizer/firewood trees. Younger farms had fewer trees but higher species richness than older farms. The study, therefore, explains heterogeneity in agroforestry adoption in terms of variation in household resource endowment, land tenure and time under current management levels. [ABSTRACT FROM AUTHOR]