A. P. Whitmore

A comparison of the performance of nine soil organic matter models using datasets from seven long-term experiments

Nine soil organic models were evaluated using twelve datasets from seven long-term experiments. Datasets represented three different land-uses (grassland, arable cropping and woodland) and a range of climatic conditions within the temperate region. Different treatments (inorganic fertilizer, organic manures and different rotations) at the same site allowed the effects of differing land management to be explored. Model simulations were evaluated against the measured data and the performance of the models was compared both qualitatively and quantitatively. Not all models were able to simulate all datasets; only four attempted all. No one model performed better than all others across all datasets. The performance of each model in simulating each dataset is discussed. A comparison of the overall performance of models across all datasets reveals that the model errors of one group of models (RothC, CANDY, DNDC, CENTURY, DAISY and NCSOIL) did not differ significantly from each other. Another group (SOMM, ITE and Verberne) did not differ significantly from each other but showed significantly larger model errors than did models in the first group. Possible reasons for differences in model performance are discussed in detail.

Optimizing nutrient management for farm systems

Increasing the inputs of nutrients has played a major role in increasing the supply of food to a continually growing world population. However, focusing attention on the most important nutrients, such as nitrogen (N), has in some cases led to nutrient imbalances, some excess applications especially of N, inefficient use and large losses to the environment with impacts on air and water quality, biodiversity and human health. In contrast, food exports from the developing to the developed world are depleting soils of nutrients in some countries. Better management of all essential nutrients is required that delivers sustainable agriculture and maintains the necessary increases in food production while minimizing waste, economic loss and environmental impacts. More extensive production systems typified by ‘organic farming’ may prove to be sustainable. However, for most of the developed world, and in the developing world where an ever-growing population demands more food, it will be essential to increase the efficiency of nutrient use in conventional systems. Nutrient management on farms is under the control of the land manger, the most effective of whom will already use various decision supports for calculating rates of application to achieve various production targets. Increasingly, land managers will need to conform to good practice to achieve production targets and to conform to environmental targets as well.

Long-term management changes topsoil and subsoil organic carbon and nitrogen dynamics in a temperate agricultural system

Summary Soil organic carbon (SOC) and nitrogen (N) contents are controlled partly by plant inputs that can be manipulated in agricultural systems. Although SOC and N pools occur mainly in the topsoil (upper 0.30 m), there are often substantial pools in the subsoil that are commonly assumed to be stable. We tested the hypothesis that contrasting long‐term management systems change the dynamics of SOC and N in the topsoil and subsoil (to 0.75 m) under temperate conditions. We used an established field experiment in the UK where control grassland was changed to arable (59 years before) and bare fallow (49 years before) systems. Losses of SOC and N were 65 and 61% under arable and 78 and 74% under fallow, respectively, in the upper 0.15 m when compared with the grass land soil, whereas at 0.3–0.6‐m depth losses under arable and fallow were 41 and 22% and 52 and 35%, respectively. The stable isotopes 13C and 15N showed the effects of different treatments. Concentrations of long‐chain n‐alkanes C27, C29 and C31 were greater in soil under grass than under arable and fallow. The dynamics of SOC and N changed in both topsoil and subsoil on a decadal time‐scale because of changes in the balance between inputs and turnover in perennial and annual systems. Isotopic and geochemical analyses suggested that fresh inputs and decomposition processes occur in the subsoil. There is a need to monitor and predict long‐term changes in soil properties in the whole soil profile if soil is to be managed sustainably. Highlights Land‐use change affects soil organic carbon and nitrogen, but usually the topsoil only is considered. Grassland cultivated to arable and fallow lost 13–78% SOC and N to 0.6 m depth within decades. Isotopic and biomarker analyses suggested changes in delivery and turnover of plant‐derived inputs. The full soil profile must be considered to assess soil quality and sustainability.

Food Security Through Better Soil Carbon Management

Soils store and filter water, prevent flooding, support the production of fuel and fibre, provide habitat, help to create landscape and are a major carbon (C) store. They are, thus, an essential component of supporting, provisioning, regulating and cultural ecosystem services and determinants and constituents of well-being, providing security, the basic material for a good life, health and good social relations. However, calculations based on inherent land quality classes show that fertile soil (that is, soil free of constraints for agricultural production) irregularly covers no more than 12 % of the terrestrial land surface. More generally, soil fertility/quality is determined by the interactions between land management interventions by humans and the inherent physical, chemical and biological properties of a soil. Land and soil management based on the understanding of these interactions is one part of delivering food security. Even small changes in C content can have disproportionately large impacts on key soil properties. Practices to encourage maintenance of soil organic carbon (SOC) are important for ensuring sustainability of most if not all soil functions. This chapter considers the relationship between SOC and soil fertility and structure, ways of increasing SOC, some disadvantages of increasing SOC and two proposed ways of increasing SOC, fertility and sequestering C: the soil application of biochar and the cultivation of deeper rooting crops.

Commentary: Developing sustainable farming systems by valuing ecosystem services

‘Sustainability’ is a much used and abused word. A long-standing definition is that implicit in the Brundtland Commission’s (1987) statement: ‘Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs’. Future generations are predicted to comprise 9 billion people by 2050. In the context of food security, as well as pure numbers, current economic development in countries such as India and China is driving the consumption of more meat (and therefore the use of cereals for livestock feed) as well as a general increased demand for more and better-quality food. In contrast, over the last 20 years, developed countries such as the UK have seen an abundance of cheap food and an emphasis on the environment and biodiversity, with agriculture being perceived as a polluter. The economic crisis, the use of grain for biofuel and the increasing demand for food in India and China resulted in a short-term food shortage and steeply rising prices in late 2008 and again in late 2010, causing general as well as scientific concern (Parker 2011); such pressures on food and prices are certain to return. Other threats to sustainability come from an over-reliance on pesticides, leading to increasing risks of resistance, and on non-renewable minerals such as phosphate, and from projections that predicted climate change will constrain production through drought, heat, floods and pests and diseases. In response to these pressures, the Royal Society (2009) has clearly and authoritatively stated a need for ‘Sustainable Intensification’. Its view is that little, if any, new agricultural land is available, so it is better to maintain the natural landscapes that exist and intensify production in areas currently under agriculture; James Lovelock (2009) reluctantly thinks that it is inevitable. The ‘Foresight Report’ (Foresight 2011, Box 7.1, p. 31) defines sustainability as ‘. . .the use of resources at rates that do not exceed the capacity of the earth to replace them’. It notes that ‘Sustainability also entails resilience, such that the food system. . .is robust to transitory shocks and stresses’. Thus it seems that an intensified, sustainable farming system must meet multiple aims, not compromise any single aim by the attainment of another, and any perturbation as a result of environmental or management change must result in either improvement or a rapid return to the initial state, not system failure. Quite a challenge for farmers! The Millennium Ecosystem Assessment (MEA 2005) defines a number of ecosystem services that can be used to understand the state of ecosystems, and these are valuable in understanding sustainability. One of the biggest challenges to sustainability in agriculture is optimizing the supporting and regulating ecosystem services (such as soil quality, nutrient cycling, pest and disease

Evidence for functional state transitions in intensively-managed soil ecosystems

Soils are fundamental to terrestrial ecosystem functioning and food security, thus their resilience to disturbances is critical. Furthermore, they provide effective models of complex natural systems to explore resilience concepts over experimentally-tractable short timescales. We studied soils derived from experimental plots with different land-use histories of long-term grass, arable and fallow to determine whether regimes of extreme drying and re-wetting would tip the systems into alternative stable states, contingent on their historical management. Prior to disturbance, grass and arable soils produced similar respiration responses when processing an introduced complex carbon substrate. A distinct respiration response from fallow soil here indicated a different prior functional state. Initial dry:wet disturbances reduced the respiration in all soils, suggesting that the microbial community was perturbed such that its function was impaired. After 12 drying and rewetting cycles, despite the extreme disturbance regime, soil from the grass plots, and those that had recently been grass, adapted and returned to their prior functional state. Arable soils were less resilient and shifted towards a functional state more similar to that of the fallow soil. Hence repeated stresses can apparently induce persistent shifts in functional states in soils, which are influenced by management history.