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Limited nutrient availability is one of the major challenges in organic farming. Little is known about nutrient budgets of organic farms, the underlying factors or effects on soil fertility. We therefore assessed farm gate nutrient budgets for nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg) and sulfur (S) of 20 organic farms in Germany and analyzed their soil nutri-ent status. In average, the budgets showed a surplus of N (19 kg ha−1), K (5 kg ha−1), S (12 kg ha−1), and Mg (7 kg ha−1), and a deficit of P (−3 kg ha−1). There was, however, high variability between farms (e.g. standard deviation up to ± 36 kg N ha−1), which was mainly explained by different degrees of reliance on biological N fixation (BNF) as N source. When farms obtained more than 60% of their N input through BNF, they had deficits of P (mean −8 kg P ha−1) and K (mean −18 kg K ha−1). Nutrient status of most soils was within the ad-vised corridor, but for P, K and Mg, 10–15% of fields were lower and 45–63% were higher than advised. Extractable soil nutrient contents did not correlate with the nutrient budgets, inputs or outputs. Only extractable soil P increased with increasing P inputs and outputs. Fur-thermore, a decrease in extractable soil P was detected with a prolonged history of organic farming, indicating a risk of soil P mining in organic farming systems. In conclusion, the study revealed nutrient imbalances in organic farming and pointed to P and K scarcity as a major challenge for organic farms with high reliance on BNF in the long term. [ABSTRACT FROM AUTHOR]

We test the hypothesis that agroforestry improves livelihoods and mitigates climate change in smallholder farming systems simultaneously. Data were collected using household surveys and standard biomass assessment approaches using locally relevant allometric equations. Summary statistics and regression analyses reveal linkages between on-farm carbon stocks and farm- and household characteristics. With an average of 4.07 ± 0.68 Mg C ha−1 and Shannon diversity index of 3.06, farm carbon stocks were significantly associated with farm size (r = 0.453, p < 0.05), tree density (r = − 0.58, p = 0.05) and the average size of trees on farm (r = − 0.42, p = 0.05), but not by Shannon diversity index (r = 0.36, p = 0.080), species richness (r = − 0.044, p = 0.833) or the number of land use categories (r = − 0.192, p = 0.356). Timber was considered the most important use of on-farm trees before firewood and construction material. The results suggest that gaining self-sufficiency in firewood is the most important benefit with on-farm carbon accumulation. The focus on exotic species for timber production presents a considerable trade-off between livelihood options and environmental goals. Heterogeneity in local environmental conditions over very short distances, less than 12 km, significantly determine livelihood strategies and on-farm carbon stocks. These results ostensibly contradict that carbon storage in smallholder farms is determined by diversity of tree species, suggest that livelihood strategy can equally drive carbon storage and demonstrate the diversity of livelihood and environmental benefits derived from trees on farms. [ABSTRACT FROM AUTHOR]

Agriculture is one of the major sources of nitrous oxide (NO), a potent greenhouse gas (GHG) whose atmospheric concentrations are estimated to increase with efforts to increase food production through increasing nitrogen (N) inputs. The objective of this study was to quantify NO emissions from maize ( Zea mays L.) and winter wheat ( Triticum aestivum L.) fields amended with inorganic, organic N and a combination of both sources (integrated management), in tropical (Zimbabwe) and temperate (China) climatic conditions. In Zimbabwe NO emissions were measured from maize plots, while in China emissions were measured from maize and winter wheat plots. In Zimbabwe the treatments were; (i) Control, (ii) 60 kg N ha ammonium nitrate (NHNO), (iii) 120 kg N ha NHNO, (iv) 60 kg ha cattle ( Bos primigenius) manure-N, plus 60 kg N ha NHNO, (v) 60 kg N ha cattle manure-N, and (vi) 120 kg N ha cattle manure-N. In China, treatments were; (i) Control, (ii) 300 kg N ha Urea, (iii) 92 kg N ha Urea plus 65 kg ha chicken ( Gallus domesticus) manure-N, (iv) 100 kg N ha Urea and (v) 100 kg N ha control release Urea. Our results showed that under both temperate and tropical conditions, integrated nutrient management resulted in lower NO emissions compared to inorganic fertilizers which had higher total and yield-scale NO emissions. We conclude that by combining organic and inorganic N sources, smallholder farmers in both China and Zimbabwe, and other countries with similar climatic conditions, can mitigate agricultural emissions without compromising productivity. [ABSTRACT FROM AUTHOR]

Black wattle ( Acacia mearnsii, De Wild.) is a fast growing tree species introduced into South Africa in the nineteenth century for commercial purposes. While being an important source of timber and firewood for local communities, black wattle is an aggressive invasive species and has pervasive adverse environmental impacts in South Africa. Little is known about the effects of black wattle encroachment on soil carbon, therefore the aim of this study was to investigate the impact of black wattle encroachment of natural grassland on soil carbon stocks and dynamics. Focussing on two sites in the Eastern Cape, South Africa, the study analysed carbon stocks in soil and litter on a chronosequence of black wattle stands of varying ages (up to >50 years) and compared these with adjacent native grassland. The study found that woody encroachment of grassland at one site had an insignificant effect on soil and litter carbon stocks. The second site showed a clear decline in combined soil and litter carbon stocks following wattle encroachment. The lowest stock was in the oldest wattle stand, meaning that carbon stocks are still declining after 50 years of encroachment. The results from the two sites demonstrate the importance of considering changes in soil carbon when evaluating ecosystem effects of invasive species. [ABSTRACT FROM AUTHOR]

Soil fertility management in organic systems, regulated by the organic standards, should seek to build healthy, fertile soils and reduce reliance on external inputs. The use of nutrients from conventional sources, such as animal manures from conventional farms, is currently permitted, with restrictions, in the organic regulations. However, the reliance of organic agriculture on the conventional system is considered problematic. In light of this, the organic sector in Denmark has recently decided to gradually phase out, and ultimately ban, the use of conventional manures and straws in organic agriculture in Denmark. Core focal areas for phasing out conventional nutrients are as follows: (1) amendments to crop selection and rotations, (2) alternative nutrient sources (organic wastes) and (3) increased cooperation between organic livestock and arable farmers. Using Denmark as a case, this article discusses the background and implications of the strategy to phase out conventional manure and straw, and explores possible solutions to the challenge of ensuring a sustainable nutrient supply to organic systems. Alternative strategies to ensure nutrient supply will require a tapestry of small solutions. One element of this tapestry is to review the volume and type of nutrient sources available in alternative, non-farm organic waste streams and consider their suitability for use in organic systems. [ABSTRACT FROM AUTHOR]

Certified organic agriculture stipulates a range of principles and standards, which govern farmer practices. The recent global expansion of organic agriculture has raised new challenges for organic agriculture, particularly whether management practices in organic farms are subject to the forces of conventionalisation. We studied changes in agroecological practices in certified organic farms in China, Brazil and Egypt. The study takes departure in the conventionalisation hypothesis and the analysis is framed using organic and agroecological principles. The study focuses on agroecological design principles, inherent to organic agriculture, of diversity in crop production, pest, disease and weed management, and soil fertility management. The research design was as a multiple case study of five cases in China, Brazil and Egypt. We show that the adoption of organic agriculture has induced fundamental changes in organic farmer management practices, although agroecological practices of organic farmers do not fulfil organic principles. The forces of conventionalisation exert a strong influence on changes in organic farmer practices. Organic 'niche' market crops with a high-value influence organic farmers' management decisions, particularly regarding the prioritisation of diversity in the cropping systems for agroecological purposes. The farming systems have therefore not undergone major changes of their cropping patterns. Furthermore, there was a general heavy reliance upon input substitution for pest and soil fertility management. This study thus presents new data and a novel analysis of the implications at the farm scale of the global expansion of organic agriculture, and the influence of conventionalisation on farmers practices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]