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Loss on ignition (LOI) is one of the most widely used methods for measuring organic matter content in soils but does not have a universal standard protocol. A large number of factors may influence its accuracy, such as furnace type, sample mass, duration and temperature of ignition and clay content of samples. We conducted a series of experiments to quantify these effects, which enabled us to derive (i) guidelines for ignition conditions (sample mass, duration and temperature), (ii) temperature-specific soil organic matter (SOM) to soil organic carbon (SOC) conversion factors and (iii) clay content-dependent correction factors for structural water loss (SWL). Bulk samples of a sandy soil (4% clay) and a silt loam soil (25% clay) were used to evaluate the effects of ignition conditions. Samples with a range of clay contents (0-50%) were used to quantify conversion and correction factors. Two furnaces, one without and one with pre-heated air, did not show significant differences in terms of within-batch LOI variability. In both furnaces less combustion occurred close to the door, which necessitated tray turning at half-time as this reduced the standard deviation per batch significantly. Variation in mass loss declined exponentially with sample mass (range, 0.15-20g). The LOI increased with duration at lower temperatures (≤550°C) for the sandy soil. At greater temperatures (600 and 650°C), no effect of duration was found. For the silt loam soil, LOI values increased with duration for each temperature, which was attributed to SWL. The SOM to SOC conversion factor decreased strongly with temperature at an ignition duration of 3hours from 0.70 (350°C) to 0.57 (500°C) and stabilized around 0.55 between 550 and 650°C, indicating that at temperatures ≥550°C all SOM had been removed. The clay correction factor for SWL increased from 0.01 to 0.09 as the temperature of ignition increased from 350 to 650°C. To minimize within-batch LOI variation we recommend a standard ignition duration of 3hours, tray turning at half-time, a sample mass ≥20g and temperatures equal to or greater than 550°C. To avoid over-estimates of SOM through structural water loss, the presented SWL correction procedure should always be applied.

Small-scale bottom-up urban agriculture (UA) initiatives have a large potential to improve the quality of life in cities through their impact on ecological and social processes. However, it is unclear which criteria determine their successful establishment and continuity. We assessed these criteria for 29 projects in the Netherlands and Switzerland using a vulnerability analysis framework. We analyzed biophysical and socio-institutional criteria for project establishment by conducting interviews with project leaders. Projects were scored for their exposure to perturbations and their sensitivity and resilience after a perturbation, resulting in an overall vulnerability score per project. We found that the vulnerability of UA systems depends strongly on local circumstances. The main perturbations and causes of vulnerability originate from social-institutional and human conditions, such as the institutional sphere, assistance of local authorities, and the determination of project leaders. Different sources of resilience were found, such as social protest, and project leaders’ adaptation to local circumstances. Biophysical factors were of less influence as the adaptive capacity of projects provides resilience against such perturbations. As perturbations are case-specific, targeted policies would be desirable to support these promising initiatives.

Attempts to increase food crop yields by intensifying agricultural systems using high inputs of nonrenewable resources and chemicals frequently lead to de-gradation of natural resources, whereas most technological innovations are not accessible for smallholders that represent the majority of farmers world wide. Alternatively, cocultures consisting of assemblages of plant and animal species can support ecological processes of nutrient cycling and pest control, which may lead to increasing yields and declining susceptibility to extreme weather conditions with increasing complexity of the systems. Here we show that enhancing the complexity of a rice production system by adding combinations of compost, azolla, ducks, and fish resulted in strongly increased grain yields and revenues in a season with extremely adverse weather conditions on East Java, Indonesia. We found that azolla, duck, and fish increased plant nutrient content, tillering and leaf area expansion, and strongly reduced the density of six different pests. In the most complex system comprising all components the highest grain yield was obtained. The net revenues of this system from sales of rice grain, fish, and ducks, after correction for extra costs, were 114% higher than rice cultivation with only compost as fertilizer. These results provide more insight in the agro-ecological processes and demonstrate how complex agricultural systems can contribute to food security in a changing climate. If smallholders can be trained to manage these systems and are supported for initial investments by credits, their livelihoods can be improved while producing in an ecologically benign way.

1. Researchers using the adaptive management paradigm consider learning about the behaviour of social-ecological systems as an inherent element of endeavours to improve the provision of ecosystem services. Learning-by-experience about social-ecological systems is a slow process attributable to system complexity. We review recent developments in systems modelling which support learning by creating a salient diversity of management alternatives and by translating science-based results into stakeholder perspectives. 2. Design-oriented learning cycles aimed at developing ecosystem services could be improved using systematic model-based diversification and selection of natural resource management alternatives. 3. Recent advances in spatially explicit computer-based ecological modelling and in visualization of results can effectively support repeated learning cycles. 4. Prioritization and weighing of conservation objectives and ecosystem services should be postponed until after the exploration of the synergies and trade-offs among objectives. 5. Investigating whether this evolutionary design approach can increase adoption of management adjustments and help to avoid lock-in onto unsustainable development trajectories should be part of efforts to understand the way we learn

Changes in fermentability of cell walls and cell contents of Italian ryegrass leaves at two stages of maturity were measured to explain the generally observed decline in herbage quality with ageing. A herbage fractionation method was developed to separate cell contents and cell walls. Cell walls were either untreated or protease-treated. Fermentation characteristics of all cell wall and cell contents fractions, as well as whole and recombined leaves, were measured using cumulative gas and volatile fatty acid (VFA) production. The gas production profiles of all substrates contained two significant phases. After fractionation, addition of the profiles from separated cell contents and untreated cell walls resulted in the same profile as for the recombined leaf. The strongest reduction in gas and VFA production due to leaf ageing was observed for cell contents. The increased ratio between branched and straight chain VFAs suggested that there had been an increase in the protein fermentation. Treatment of cell walls may have removed some easily fermentable cell wall components, as seen in the small differences in gas and VFA production between whole and recombined leaves. It has been concluded that the phases of gas production, separable in kinetic fermentability studies of complex animal feeds, need to be interpreted with caution. The large reduction in fermentability of cell contents with plant maturity, compared with the cell walls, indicated the importance of determining the role of cell contents in herbage quality studies, as the cell contents clearly do not remain uniform.

For modelling of grass digestibility throughout the growing season, the impact of cutting on individual leaves needs to be quantified. Therefore, a glasshouse experiment was carried out with Italian ryegrass (Lolium multiflorum Lam) grown from seed. Half of the plants were grown undisturbed until leaf stage 8, while the other half were cut at leaf stage 4, after which they were allowed to grow until leaf stage 9. The composition and digestibility characteristics of leaves 6, 7 and 8 on the main shoot of plants from both treatments were quantified. In the uncut plants, leaf blade length and mass and specific cell wall (CW) and organic matter (OM) mass (mg cm−2) was higher for consecutive leaves. During leaf ageing specific CW mass remained unchanged, while specific OM mass and CW digestibility declined, resulting in a decline of OM digestibility. CW digestibility of leaves decreased to c 78%, a value also found in an earlier experiment. The newly formed leaves after cutting had a reduced leaf size and specific leaf mass (SLM, mg DM cm−2). Leaf 6, that was damaged by cutting, showed a lower initial CW content and a rapid decline of specific CW and OM mass and of digestibility during ageing. Its low specific mass and digestibility of CW could have been related to cessation of CW synthesis during its growth after cutting, as was evidenced by the lower CW thickness of sclerenchyma cells. The later-formed leaves, 7 and 8, had digestibility characteristics similar to those of the uncut plants. Since leaf 6 hardly contributed to the total plant dry matter mass, the cut and the uncut plants differed only slightly in digestibility of the total leaf fraction. It can be concluded that cutting sets back leaf size and growth rate but has little effect on digestibility characteristics during ageing. © 1999 Society of Chemical Industry