Organic Arable Farming Research Articles

Collaborative partnerships between organic farmers in livestock-intensive areas of Denmark

Specialisation within organic agriculture in many western European countries has led to the decoupling of crop and animal systems, resulting in a shortfall in manure fertilisers on most farms and a surplus on others. One solution to solve a problem has been the establishment of collaborative partnerships between specialist organic farms for manure exchange. The aim of this study is to acquire factual knowledge about existing partnerships. A survey was undertaken of dairy farms in livestock-intensive areas of Denmark, identifying and comparing 95 partnerships between organic dairy farms and organic arable farms with 144 partnerships between conventional dairy farms and conventional arable farms. In order to understand the diversity of strategies among organic farmers, five types of partnerships were identified. The character and functioning of the organic partnerships are influenced by the high demand for organic-certified manure on organic arable farms, but many organic dairy-arable partners also have strong social connections irrespective of the distances involved. The five organic partnership types showed that the organic partners’ strategies were influenced by environmental regulations as well as social connections and location. Trust and reciprocal relationships through high-quality communication and well-functioning institutional arrangements seem to play pivotal roles for partnerships to be maintained. As organic farmers are continuously facing global market conditions and tightening regulations, the development of collaborative partnerships which could contribute to adaptability and flexibility is essential. These findings are not exclusive to organic farmers and may also apply to other intensive livestock regions in Europe.

Energy use and greenhouse gas emissions in organic and conventional farming systems in the Netherlands

Organic agriculture is often considered to contribute to reducing energy use and greenhouse gas (GHG) emissions, also on a per unit product basis. For energy, this is supported by a large number of studies, but the body of evidence for GHGs is smaller. Dutch agriculture is characterized by relatively intensive land use in both organic and conventional farming, which may affect their performance in terms of energy use and GHG emissions. This paper presents results of a model study on energy use and GHG emissions in Dutch organic and conventional farming systems. Energy use per unit milk in organic dairy is approximately 25% lower than in conventional dairy, while GHG emissions are 5-10% lower. Contrary to dairy farming, energy use and GHG emissions in organic crop production are higher than in conventional crop production. Energy use in organic arable farming is 10-30% and in organic vegetable farming 40-50% higher than in their respective conventional counterparts. GHG emissions in organic arable and vegetable farming are 0-15% and 35-40% higher, respectively. Our results correspond with other studies for dairy farming, but not for crop production. The most likely cause for higher energy use and GHG emissions in Dutch organic crop production is its high intensity level, which is expressed in crop rotations with a large share of high-value crops, relatively high fertiliser inputs and frequent field operations related to weeding.

Development of soil organic matter stocks under different farm types and tillage systems in the Organic Arable Farming Experiment Gladbacherhof

In 1998, the Organic Arable Farming Experiment Gladbacherhof (OAFEG) was started in order to explore the impact of different organic arable production systems (mixed farming, stockless farming with rotational ley, stockless cash crop farming) and of different tillage intensities (conventional plough as a full inversion tillage, two-layer plough, inversion tillage at reduced depth, non-inversion tillage) on sustainability parameters. In this article, we present results on the development of soil organic matter (SOM) levels. Starting with organic mixed farming with approximately 0.7 livestock units (LU) per ha cattle before set-up of the experiment, only the mixed farming system in the experiment was able to maintain SOM levels. The stockless system with ley maintained soil organic carbon (SOC), but lost soil total nitrogen (STN), and the stockless cash crop system had a significant SOM loss in the magnitude of 7.7 t SOM ha−1, or roughly 8.4% of the initial SOM mass. Reducing tillage intensity had no impact on SOM masses, but only on organic matter stratification in soils. We conclude that specialization of organic farms towards stockless arable crop production requires special attention on SOM reproduction to avoid detrimental effects. Further, reduced tillage intensity does not necessarily have a positive effect on SOM.

Influence of reduced tillage on earthworm and microbial communities under organic arable farming

Although reduced tillage is an agricultural practice reported to decrease soil erosion and external inputs while enhancing soil fertility, it has still rarely been adopted by European organic farmers. The objective of this study was to assess the long-term interactive effects of tillage (conventional (CT) vs. reduced (RT)) and fertilization (slurry (S) vs. composted manure/slurry (MCS)) on earthworms and microbial communities in a clay soil under spelt in an organic 6-year crop rotation. Earthworm populations (species, density and biomass, cocoons) were investigated by handsorting the soil nine years after initial implementation of the treatments. Soil microbial carbon (Cmic) and nitrogen (Nmic) were measured by chloroform-fumigation extraction and a simplified phospholipid fatty acid (PLFA) analysis was used to separate for populations of bacteria, fungi and protozoa. Significantly increased total earthworm density in RT plots was mainly attributed to increased numbers of juveniles. Moreover, we found five times more cocoons with RT. Species richness was not affected by the treatments, but tillage treatments had differentially affected populations at the species-level. In addition, cluster analysis at the community level revealed two distinct groups of plots in relation to tillage treatments. In RT plots Cmic increased in the 0–10 cm and 10–20 cm soil layers, while PLFA concentrations indicative of Gram-negative bacteria, fungi and protozoa only increased in the topsoil. Lower bacteria-to-fungi ratios in the upper soil layer of RT plots indicated a shift to fungal-based decomposition of organic matter whereas a higher Cmic-to-Corg ratio pointed towards enhanced substrate availability. Slurry application decreased microbial biomass and enhanced density of juvenile anecic earthworms but overall fertilization effect was weak and no interactions with tillage were found. In conclusion, tillage is a major driver in altering communities of earthworms and microorganisms in arable soils. The use of reduced tillage provides an approach for eco-intensification by enhancing inherent soil biota functions under organic arable farming.

A guide for choosing the most appropriate method for multi-criteria assessment of agricultural systems according to decision-makers’ expectations

Modern agriculture must meet new challenges such as production of healthy food, adaptation to climate change, protection of natural resources, and conservation of landscape. These challenges require changes in current agricultural systems and therefore, environmentally-friendly agricultural systems must be designed and their sustainability assessed. Over the past several years, various methods have been developed for making such assessments (e.g. the Balancing and Ranking Method, MEACROS, MODAM, the modelling framework of Pacini et al., ROTAT+FarmImages, MASC, and ROTOR) but few studies put forward simple solutions for selecting one method over another. In this paper, we propose a simple guide to distinguish methods one from another. Categories of the guide include the type of systems to assess, the spatial and temporal scales at which systems are assessed, the dimensions of sustainability for which systems are assessed, the type of visualisation for comparing options, the target users, and the ability to generate alternative systems. The guide was developed and tested with a group of farm advisors involved in a three-year project called RotAB, which aimed to assess the sustainability of organic arable farming systems: the advisors looked for a method for sustainability assessment of cropping systems. We presented seven recent assessment methods as well as the guide to advisors. The guide’s key points allowed them to clearly express their requirements: the method they looked for had to evaluate cropping systems and helped advisors to propose new ones; it had to evaluate multiple sustainability criteria that are easily understandable by farmers; indicators had to be scientifically based, without the need for many input data; the method had to be easy to use and produced graphical output that can be discussed with farmers. Finally, the guide helped advisors to choose one of the seven methods (in that case they chose MASC). This guide can help decision-makers distinguish assessment tools from one another using simple categories and choose the one best adapted to their expectations.

Nitrate leaching from organic arable crop rotations is mostly determined by autumn field management

Two main challenges facing organic arable farming are the supply of nitrogen (N) to the crop and the control of perennial weeds. Nitrate leaching from different organic arable crop rotations was investigated over three consecutive four-year crop rotations in a field experiment at three locations in Denmark (12 years in total). The experimental treatments were: (i) crop rotation, (ii) catch crop and (iii) animal manure. Nitrate leaching was estimated from measured soil nitrate concentration in ceramic suction cells and modelled drainage. There were significant effects on annual N leaching of location (coarse sand > loamy sand > sandy loam) and catch crops (without > with). Including a grass-clover green manure on 25% of the area did not increase N leaching compared with crop rotations without green manure. Also the application of animal manure did not influence N leaching, probably because even in the manured treatments the application rate was lower than crop demand. The results identify management of crop and soil during autumn as the main determinant of N leaching. Nitrate leaching was lowest for a catch crop soil cover during autumn and winter (avg. 20 kg N ha −1), a soil cover of weeds/volunteers had on avg. 30 kg N ha −1, and the largest N leaching losses were found after stubble cultivation (avg. 55 kg N ha −1). The N leaching losses increased with increasing number of autumn soil cultivations.

Life cycle assessment of energy self-sufficiency systems based on agricultural residues for organic arable farms

The agricultural industry today consumes large amounts of fossil fuels. This study used consequential life cycle assessment (LCA) to analyse two potential energy self-sufficient systems for organic arable farms, based on agricultural residues. The analysis focused on energy balance, resource use and greenhouse gas (GHG) emissions. A scenario based on straw was found to require straw harvest from 25% of the farm area; 45% of the total energy produced from the straw was required for energy carrier production and GHG emissions were reduced by 9% compared with a fossil fuel-based reference scenario. In a scenario based on anaerobic digestion of ley, the corresponding figures were 13%, 24% and 35%. The final result was sensitive to assumptions regarding, e.g., soil carbon content and handling of by-products.

Soil, crop and emission responses to seasonal-controlled traffic in organic vegetable farming on loam soil

Some organic arable and vegetable farms in the Netherlands use cm-precise guidance of machinery to restrict wheel traffic to fixed traffic lanes and to achieve non-trafficked cropping zones with optimized soil structure in between the lanes. Contrary to controlled traffic farming (CTF) the traffic lanes are not yet used for harvesting and primary tillage. Therefore, the system is called a seasonal-controlled traffic farming (SCTF) system. A field experiment was conducted on an organic vegetable farm to reveal soil, crop and emission responses of SCTF with traffic lanes at 3.15-m centres compared with conventional random traffic farming (RTF) using low ground pressures in spring from 2002 till 2005. The traffic systems were investigated in the crops green pea ( Pisum sativum L.), spinach ( Spinacea oleracea L.), onions ( Allium cepa L.) and carrots ( Daucus carota L.). Compared with RTF, the topsoil structure in the SCTF system improved for the crops sown on the flat but not for carrot grown on ridges. Crop yields increased significantly in green pea, spinach and planted onion sets but not in carrot and direct-sown onion. The available N-min at the end of the cropping period was not different between systems and, therefore, leaching losses in winter are expected to be the same. SCTF resulted in a significant reduction of N 2O emissions (by 20–50% compared to RTF). For CH 4, application of the SCTF system resulted in increased CH 4 uptake (by a factor 5–20) compared to the RTF system in three of the four measured fields. At the fourth field, lower (but not significant) CH 4 emissions (by a factor 4) were measured in the SCTF system compared to RTF. Effects of SCTF on timeliness and on the economic feasibility are discussed.

Winter cereal yields as affected by animal manure and green manure in organic arable farming

The effect of nitrogen (N) supply through animal and green manures on grain yield of winter wheat and winter rye was investigated from 1997 to 2004 in an organic farming crop rotation experiment in Denmark on three different soil types varying from coarse sand to sandy loam. Two experimental factors were included in the experiment in a factorial design: (1) catch crop (with and without), and (2) manure (with and without). The four-course crop rotation was spring barley undersown with grass/clover – grass/clover – winter wheat or wheat rye – pulse crop. All cuttings of the grass–clover were left on the soil as mulch. Animal manure was applied as slurry to the cereal crops in the rotation in rates corresponding to 40% of the N demand of the cereal crops. Application of 50 kg NH 4–N ha −1 in manure increased average wheat grain yield by 0.4–0.9 Mg DM ha −1, whereas the use of catch crops did not significantly affect yield. The use of catch crops interacts with other management factors, including row spacing and weed control, and this may have contributed to the negligible effects of catch crops. There was considerable variation in the amount of N (100–600 kg N ha −1 year −1) accumulated in the mulched grass–clover cuttings prior to ploughing and sowing of the winter wheat. This was reflected in grain yield and grain N uptake. Manure application to the cereals in the rotation reduced N accumulation in grass–clover at two of the locations, and this was estimated to have reduced grain yields by 0.1–0.2 Mg DM ha −1 depending on site. Model estimations showed that the average yield reduction from weeds varied from 0.1 to 0.2 Mg DM ha −1. The weed infestation was larger in the manure treatments, and this was estimated to have reduced the yield benefit of manure application by up to 0.1 Mg DM ha −1. Adjusting for these model-estimated side-effects resulted in wheat grain yields gains from manure application of 0.7–1.1 Mg DM ha −1. The apparent recovery efficiency of N in grains (N use efficiency, NUE) from NH 4–N in applied manure varied from 23% to 44%. The NUE in the winter cereals of N accumulated in grass–clover cuttings varied from 14% to 39% with the lowest value on the coarse sandy soil, most likely due to high rates of N leaching at this location. Both NUE and grain yield benefit in the winter cereals declined with increasing amounts of N accumulated in the grass–clover cuttings. The model-estimated benefit of increasing N input in grass–clover from 100 to 500 kg N ha −1 varied from 0.8 to 2.0 Mg DM ha −1 between locations. This is a considerably smaller yield increase than obtained for manure application, and it suggests that the productivity in this system may be improved by removing the cuttings and applying the material to the cereals in the rotation, possibly after digestion in a biogas reactor. Cereal grain protein content was increased more by the N in the grass–clover than from manure application, probably due to different timing of N availability. Green-manure crops or manures with a relatively wide C:N ratio may therefore be critical for ensuring sufficiently high protein contents in high yielding winter wheat for bread making.

Relations between nitrogen leaching and food productivity in organic and conventional cropping systems in a long-term field study

An ideal agricultural system should both maximize food production and minimize undesirable effects on the environment. The long-term Apelsvoll cropping system experiment, located in southeast Norway, was used in this study, to compare yields, major N flows (in particular measured leaching/runoff losses) and the N loss-to-food production ratios (LFP-ratios) in six different cropping systems over a 4-year period. The experiment included three systems with cash-cropping (CA1: conventional arable farming; CA2: arable farming practice with environmentally sound management; OA: organic arable farming with 25% of the area as green manure, and three systems with both arable and fodder crops, representing mixed dairy production (CM: conventional farming practice with 50% grass–clover ley; OM1: organic farming with 50% grass–clover ley; OM2: organic farming with 75% grass–clover ley). The forage production was assumed to be used for milk and meat production, in amounts calculated on the basis of available feed and estimated requirements for dairy cattle. All farm produce (cereals, potatoes, milk and meat) was converted into metabolizable energy for human consumption. Organic cropping gave significantly lower yields than conventional cropping, for both arable and mixed dairy systems, most likely due to sub-optimal plant nutrition and the lack of plant protection in the organic systems. The average net energy production in CA1 and CA2 was 2.4–5.3 times greater than that in the other systems, which illustrates the energy costs of taking 25% of the area out of food production to produce green manure (OA) and the energy cost of including an extra trophic level in the nutrient chain (CM, OM1 and OM2). Only CA2 and CM appeared to have a balanced N budget, whereas the other systems all had N deficits, in particular CA1 and OA. The total N losses to drainage were largest from CA1, but not significantly larger than those from OA, which had the largest N runoff of the systems, most likely due to the green manure in its rotation. The conventional system with environmentally sound management (CA2) had the lowest LFP-ratios overall. Among the arable cropping systems, the organic system with 25% green manure (OA) had the highest LFP-ratios. The mixed dairy systems had generally higher LFP-ratios than the arable systems. Including leaching/runoff N losses in the LFP-ratio, CA1, CA2, OA, CM, OM1 and OM2 appeared to lose 0.6, 0.4, 1.1, 0.9, 1.2 and 1.1 kg N, respectively, per GJ of produced metabolizable energy for human consumption.

Occurrence of Rhexocercosporidium carotae on cold stored carrot roots in the Netherlands

Winter carrot for the fresh market is an important cash crop for many organic arable farms in the Netherlands. In recent years carrot roots from cold stores have been affected by superficial dark brown to black spots. To gain insight into the pathogens causing the blemish and the effect of agronomic practices on their occurrence, surveys were carried out among crops harvested in 2001 and 2002. In addition carrots harvested in 2003 were screened for root spotting pathogens. Rhexocercosporidium carotae (syn. Acrothecium carotae and Pseudocercosporidium carotae) was the dominant pathogen in blackish spots on carrots harvested in 2001. On carrots harvested in 2002 and 2003 Alternaria radicina was detected more frequently. Multiple regression analysis indicated that a higher occurrence of the blemish may be linked with harvest conditions and presence of umbelliferous plants. The effect of the temperature on conidial germination, mycelial growth and pathogenicity of R. carotae was studied. The estimated optimum and maximum temperature for growth of R. carotae was 19 and 29°C, respectively. Inoculation experiments demonstrated that wounds are good invasion routes. Infection occurred at 3, 10 and 20°C, but not at 30°C. Penetration into wounds was greatest at 20°C.

Conversion to organic arable farming in The Netherlands: A dynamic linear programming analysis

Several studies show that organic farming is more profitable than conventional farming. However, in reality not many farmers convert to organic farming. Policy makers and farmers do not have clear insight into factors which hamper or stimulate the conversion to organic farming. The objective of this paper is to develop a dynamic linear programming model to analyse the effects of different limiting factors on the conversion process of farms over time. The model is developed for a typical arable farm in The Netherlands central clay region, and is based on two static liner programming models (conventional and organic). The objective of the model is to maximise the net present value over a 10-year planning horizon. The results of the analysis of a basic scenario show that conversion to organic farming is more profitable than staying conventional. In order to arrive at the actual profitable phase of organic farming, the farmer has to pass through the economically difficult 2-year conversion period. Sensitivity analysis shows that if depreciation is 25% higher than conventional fixed costs due to machinery made superfluous by conversion, conversion is less profitable than staying conventional. Also the availability of hired labour, which can be constrained in peak periods, has a strong effect on the cropping plan and the amount of area converted. Further analysis shows that a slight drop (2%) in organic prices lowers the labour income of the farmer and makes conversion less profitable than conventional farming. For farmers, a minimum labour income can be required to ‘survive’. The analysis shows that constraint on minimum labour income makes stepwise conversion the best way for farmers to overcome economic difficulties during conversion.

Comparison of Conventional and Organic Arable Farming Systems in the Netherlands by Means of Bio-Economic Modelling

ABSTRACT Growing environmental concern in society combined with policy stimuli has encouraged farmers to switch from conventional to organic production technologies. However, so far not many have made this switch. This raises the question, what could lie behind the decisions of farmers concerning conversion. A first step in studying this decision is to compare farming results in an organic situation with conventional farm results from technical, economic and environmental points of view. In this paper a linear programming model of a conventional arable farm and an organic arable farm are presented. The models include environmental externalities such as losses of nutrients and pesticide use, the levels of which can be influenced by using different production structures (cropping plans). With the conventional model two different crop rotations (3-year and 4-year), and with the organic model one rotation (6-year) are analysed and the results of these three situations are compared. The example farm modelled is typical for the central clay region in The Netherlands. The results show that organic farming leads to less intensive land use, better environmental results and better economic results. Expenditure on hired labour is much higher in organic farming which also leads to higher variable costs. Prices for organic products are higher than for similar conventional products, but lower yields and the less intensive cropping plan mitigates the effects on total revenues.

ROTOR, a tool for generating and evaluating crop rotations for organic farming systems

As with conventional farming, the improvement of organic farming systems requires agronomic planning tools to enhance economic performance. Crop rotation planning plays a crucial role in organic arable farming systems due to the renunciation of mineral nitrogen fertilisers and pesticides. Our objective was to develop a tool for generating and evaluating site-specific and agronomically sustainable crop rotations for organic farming systems in central Europe. The resulting static rule-based model, called ROTOR, consists of two basic steps: (A) A set of annual crop production activities (CPAs) is assembled semi-automatically from single site and crop-specific field operations using a relational data base. The database includes all relevant crops recorded separately with inputs and outputs, machinery and timing. Starting from stubble tillage and ending with the last harvest measure, the CPAs describe the current best cropping practices. Different CPAs are included for each crop according to (i) the type of crop preceding and (ii) the field operations following: whether ploughing or non-inverting tillage, undersowing crops, using catch crops, manuring, straw harvesting, or mechanical weed control. The former allows for the modelling of all possible positions of a crop within a crop rotation and the consequential effects of preceding crops. The CPAs are evaluated using rule-based assessment modules for yield, economic performance, N balance, nitrate leaching, and weed infestation risks. These modules have been developed using data from field experiments, farm trials and surveys, expert knowledge and a soil–crop simulation model. (B) Within the crop generation module, all possible sequences of CPAs are linked to 3–8-year preliminary crop rotations. Agronomically sustainable crop rotations are selected according to exclusion criteria (i.e., thresholds for N balance, weed infestation risks, phytosanitary and chronological restrictions) and ranked, e.g. by economic performance. The model was tested by comparing (i) estimated with observed yields and (ii) generated with existing rotations. These comparisons, based on data obtained from two farm surveys from North Eastern Germany, indicate the validity and usability of the model approach. ROTOR was found to support the complex crop rotation planning in organic farming systems requiring rotations with overlapping undersown main and cover crops. ROTOR is able to reduce the risk of planning failures by offering a quantitative method of optimisation of weed and site-specific N management.

The value of catch crops and organic manures for spring barley in organic arable farming

The effect of nitrogen (N) supply and weeds on grain yield of spring barley was investigated from 1997 to 2004 in an organic farming crop rotation experiment in Denmark on three different soil types varying from coarse sand to sandy loam. Two experimental factors were included in the experiment in a factorial design: (1) catch crop (with and without), and (2) manure (with and without). The crop rotation included grass-clover as a green manure crop. Animal manure was applied as slurry in rates corresponding to 40% of the N demand of the cereal crops. Application of 50 kg NH 4-N ha −1 in manure (slurry) increased average barley grain DM yield by 1.0–1.3 Mg DM ha −1, whereas the use of catch crops (primarily perennial ryegrass) increased grain DM yield by 0.2–0.4 Mg DM ha −1 with the smallest effect on the loamy sand and sandy loam soils and the greatest effect on the coarse sandy soil. Model estimations showed that the average yield reduction from weeds varied from 0.2 to 0.4 Mg DM ha −1 depending on weed species and density. The yield effects of N supply were more predictable and less variable than the effects of weed infestation. The infestation level of leaf diseases was low and not a significant source of yield variation. The apparent recovery efficiency of N in grains (N use efficiency, NUE) from NH 4-N in applied manure varied from 29 to 38%. The NUE of above-ground N in catch crops sampled in November prior to the spring barley varied from 16 to 52% with the largest value on the coarse sandy soil and the smallest value on the sandy loam soil. A comparison of grain yield levels obtained at the different locations with changes in soil organic matter indicated a NUE of 21–26% for soil N mineralisation, which is smaller than that for the mineral N applied in manure. However, this estimate is uncertain and further studies are needed to quantify differences in NUE from various sources of N. The proportion of perennial weeds in total biomass increased during the experiment, particularly in treatments without manure application. The results show that manure application is a key factor in maintaining good crop yields in arable organic farming on sandy soils, and in securing crops that are sufficiently competitive against perennial weeds.

Estimated N leaching losses for organic and conventional farming in Denmark

The impact of organic, compared with conventional, farming practices on N leaching loss was studied for Danish mixed dairy and arable farms using an N balance approach based on representative data. On mixed dairy farms, a simple N balance method was used to estimate N surplus and N leaching loss. On arable farms, the simple N balance method was unreliable due to changes in the soil N pool. Consequently, the Farm ASSEssment Tool (FASSET) simulation model was used to estimate N surplus, N leaching loss and the changes in the soil N pool.The study found a lower N leaching loss from organic than conventional mixed dairy farms, primarily due to lower N inputs. On organic arable farms, the soil N pool increased over time but the N leaching loss was comparable with conventional arable farms. The soil N pool was increased primarily by organic farming practices and incorporation of straw. The highest increase in the soil N pool was seen on soils with a low initial level of organic matter. The N leaching loss was dependent on soil type, the use of catch crops and the level of soil organic matter, whereas incorporation of straw had a minor effect. N leaching was highest on sandy soils with a high level of soil organic matter and no catch crops. The present results stress the importance of using representative data from organic and conventional farming practices in comparative studies of N leaching loss. Lack of representative data has been a major weakness of previous comparisons on N leaching losses on organic and conventional farms.

Long-term changes in soil fertility in organic arable farming systems in England, with particular reference to phosphorus and potassium

Organic farming has undergone significant expansion in Europe over the last decade and it is often seen as a sustainable alternative to intensive agricultural systems. If it is to be truly sustainable, it must maintain levels of soil fertility sufficient for economic crop production in the long-term, whilst also protecting the environment. This paper presents results comparing soils managed organically for at least 15 years, with soils under conventional management, on four arable farms in England. There were no significant differences in total soil organic matter, total nitrogen or C:N ratio between the conventionally and organically managed soils. However, concentrations of extractable potassium and phosphorus were significantly lower in soils managed organically. The largest difference between the conventional and organic fields in potassium concentration was on the oldest organic farm. These results support the argument that organic mixed arable systems are mining reserves of potassium and phosphorus, built up during conventional management, and that changes to organic management practices to increase inputs of potassium and phosphorus are required, if long-term declines in soil fertility, and thus, yields are to be avoided.

Effects of organic versus conventional arable farming on soil structure and organic matter dynamics in a marine loam in the Netherlands

Abstract. We compared the effects of conventional and organic arable farming on soil organic matter (SOM) content, soil structure, aggregate stability and C and N mineralization, which are considered important factors in defining sustainable land management. Within one soil series, three different farming systems were selected, including a conventional and an organic arable system and permanent pasture without tillage. The old pasture represents optimal conditions in terms of soil structure and organic matter inputs and is characterized by high earthworm activity. More than 70 years of different management has caused significant differences in soil properties. SOM content, mineralization, earthworm activity and water‐stable aggregation decreased as a result of tillage and arable cropping when compared with pasture, but were significantly greater under organic farming than under conventional farming. Total SOM contents between 0 and 20 cm depth amounted to 15, 24 and 46 g kg−1 for the conventional arable, organic arable and permanent pasture fields, respectively. Although less sensitive to slaking than the conventionally managed field, the soil under organic farming was susceptible to compaction when high pressures were exerted on the soil under wet conditions. The beneficial effects of organic farming are generally associated with soil biochemical properties, but soil physical aspects should also be considered. Depending on soil type and climate, organic farmers need to be careful not to destroy the soil structure, so that they can enjoy maximum advantage from their organic farming systems.

A concept of food-web structure in organic arable farming systems

A proposal for a descriptive or topological farm food web is derived from field observations and from references in literature. Important themes in the food-web theory are tentatively applied to this preliminary model, explaining differences between local farm food-web structures and how they are related to farm and/or ecological infrastructure (EI) management. Predictions are made for four different farm food-web structures for extremes of farm and environmental gradients corresponding to the length of organic duration and amount/quality of EI. The implications with regard to farming practices and nature conservation are that both organic duration and the amount/quality of ecological infrastructure may contribute to ecosystem services and nature conservation. However, an optimisation of the farm food web with regard to ecosystem services, may possibly run counter to nature conservation goals.

Introduction of earthworms into an organic arable farming system

Earthworms were inoculated into an experimental field on a reclaimed polder soil in 1988, using a sod transplantation method. The donor field was a clover grass ley in an organic farm with a comparable sandy clay loam soil. The receptor field received different manurial treatments (farmyard manure, deep pit chicken manure or no manure) in replicate plots, and earthworms were introduced into one half of each plot. Five introduced species became established in manured plots, with dispersal rates of about 2 m per year in the first 4 years, increasing to about 11 m per year in the following 4 years and reaching a maximum population density of 776 earthworms per m 2 to a depth of 30 cm. Differences between effects of manurial treatments were not significant, whereas crop and cultivation direction significantly influenced earthworm distribution. The species composition did not differ with manure treatment, but the Shannon–Weaver diversity index was highest in the chicken manure-treated plots and lowest in the unmanured plots