Soil health—useful terminology for communication or meaningless concept? Or both?

What is soil health? It is not essential to have a degree in soil science in order to have a valid opinion on this. In a very general sense, almost everybody has some impression of what is meant by a healthy soil, especially anyone who has done any gardening or even looked after a potted plant on a windowsill. They will probably say it should have a beautiful crumbly structure, should hold water but not become waterlogged, and be teeming with life; provided that life does not include insects or pathogens that damage the plants. In a somewhat analogous way, the word “wellbeing” is used concerning the way individual humans feel about themselves and we will all have our own ideas on what contributes to our personal wellbeing. It is likely to include being in good physical and mental health, being adequately fed and being housed. However, social scientists have taken the idea further, developing indicators of wellbeing and even using these to compare the state of wellbeing in different countries and assess the impact of policies on the way people feel. Some may consider that this is taking the “wellbeing” concept too far. With soil health, perhaps soil scientists make it too complicated. However, although anyone may have a general idea of what makes a healthy soil, if the term is to be used in anything other than general informal conversation, we do need to “dig a little deeper”, if readers will excuse the pun

Use of ammonium sulphate as a sulphur fertilizer: implications for ammonia volatilization

Ammonium sulphate is widely used as a sulphur (S) fertilizer, constituting about 50% of global S use. Within nitrogen (N) management it is well known that ammonium-based fertilizers are subject to ammonia (NH3) volatilization in soils with pH >7, but this has been overlooked in decision making on S fertilization. We reviewed 41 publications reporting measurements of NH3 loss from ammonium sulphate in 16 countries covering a wide range of soil types and climates. In field experiments loss was mostly 7.0 there was a wide range of losses (0-66%), with many in the 20-40% range and some indication of increased loss (ca. 5-15%) in soils with pH 6.5-7.0. We estimate that replacing ammonium sulphate with a different form of S for arable crops could decrease NH3 emissions from this source by 90%, even taking account of likely emissions from alternative fertilizers to replace the N, but chosen for low NH3 emission. In temperate climates emission from soils of pH >7.0 would decrease from 35.7 to 3.6 t NH3 per kt ammonium sulphate replaced. Other sources of S are readily available including single superphosphate, potassium sulphate, magnesium sulphate, calcium sulphate dihydrate (gypsum) and polyhalite (Polysulphate). In view of the large areas of high pH soils globally, this change of selection of S fertilizer would make a significant contribution to decreasing NH3 emissions worldwide, contributing to necessary cuts to meet agreed ceilings under the Gothenburg Convention

Challenging claimed benefits of soil carbon sequestration for mitigating climate change and increasing crop yields: heresy or sober realism?

There is overwhelming evidence that increasing the organic carbon (C) content of cropland soil improves its physical, chemical and biological properties, with benefits for the growth of crop roots and the functioning of soils in the wider environment (King et al., 2020; Kopittke et al., 2022; Lal 2020). This is entirely uncontroversial. It is currently relevant because there is evidence that soil organic carbon (SOC) in many cropland soils globally is declining (Sanderman et al., 2017) and is vulnerable to further loss from climate change (Lugato et al., 2021). It may, therefore, seem counterintuitive, and even heretical or downright unhelpful, for a paper to challenge two widely stated claims connected with SOC as is done in the paper entitled “Carbon for soils, not soils for carbon” by Moinet et al. (2023). The two claims challenged by the authors are: 1. Sequestration of C in agricultural soils can make a substantial contribution to climate change mitigation. 2. Increasing SOC will routinely lead to increased crop yields and contribute to global food security. The authors are particularly critical of these two assertions being combined to make the claim that SOC sequestration is a “win-win” strategy. They point out that climate change and food security have both been described as “wicked problems” of “daunting complexity” so blanket solutions that claim to solve both “should prompt some degree of scepticism.

Agriculture Green Development in China and the UK: common objectives and converging policy pathways

This paper has three aims. First, to examine how the negative environmental consequences of intensive agriculture have driven China and the UK to shift away from narrowly focused farm output policies and adopt more holistic green development pathways. Second, to explore the policy objectives they have in common. Third, to assess the numerous opportunities for joint research and knowledge sharing through the Sustainable Agriculture Innovation Network and other existing institutional mechanisms. The intensification of agricultural production in the UK started several decades earlier than in China as did the negative environmental consequences of the farm practices. However, their strategies and policies for sustainable intensification and green development have much in common. These are set out in two main documents: the Chinese State Council guidelines for green agriculture and the UK Department for Environment, Food and Rural Affairs 25 Year Environment Plan. There are substantial mutual advantages from greater collaboration on problem identification and monitoring; the development of appropriate technological and management responses and the formulation of sound policies. To achieve this potential, it is recommended that further thought be given to how best to bring together all of the key stakeholders along the whole food chai

Understanding the soil nitrogen cycle

A quantitative knowledge of nitrogen cycle processes is required to design strategies for decreasing leakage of N from agriculture to the wider environment. However, it is remarkably difficult to make reliable measurements of many of the key processes under realistic field conditions. In impermeable soils hydrologically separated plots provide an invaluable method of measuring leaching and runoff. Estimates of nitrate leaching using porous ceramic cups agree well with lysimeter measurements on sandy soil but are suspect on more structured soils. Estimates of N2O flux from soil are subject to great spatial heterogeneity; developing long path-length measuring techniques may overcome this problem. N-15 labelling is valuable for assessing fertilizer N loss, forms of N left in soil and the fate of N from crop residues. The combination of experimental and modelling approaches can provide insights that are otherwise unattainable, including a basis for more precise advice on N fertilization. Mineralization of soil organic matter and crop or animal residues provides much of the nitrate leached during winter under the climatic conditions of north-west Europe, because mineralization is poorly synchronized with crop N uptake. Maintenance of crop cover during winter can greatly decrease leaching but the long-term effects on the N cycle of winter cover crops or incorporating cereal straw are not yet clear

Effect of four plant species on soil 15N-access and herbage yield in temporary agricultural grasslands

Positive plant diversity-productivity relationships have been reported for experimental semi-natural grasslands (Cardinale et al. 2006; Hector et al. 1999; Tilman et al. 1996) as well as temporary agricultural grasslands (Frankow-Lindberg et al. 2009; Kirwan et al. 2007; Nyfeler et al. 2009; Picasso et al. 2008). Generally, these relationships are explained, on the one hand, by niche differentiation and facilitation (Hector et al. 2002; Tilman et al. 2002) and, on the other hand, by greater probability of including a highly productive plant species in high diversity plots (Huston 1997). Both explanations accept that diversity is significant because species differ in characteristics, such as root architecture, nutrient acquisition and water use efficiency, to name a few, resulting in composition and diversity being important for improved productivity and resource use (Naeem et al. 1994; Tilman et al. 2002). Plant diversity is generally low in temporary agricultural grasslands grown for ruminant fodder production. Grass in pure stands is common, but requires high nitrogen (N) inputs. In terms of N input, two-species grass-legume mixtures are more sustainable than grass in pure stands and consequently dominate low N input grasslands (Crews and Peoples 2004; Nyfeler et al. 2009; Nyfeler et al. 2011). In temperate grasslands, N is often the limiting factor for productivity (Whitehead 1995). Plant available soil N is generally concentrated in the upper soil layers, but may leach to deeper layers, especially in grasslands that include legumes (Scherer-Lorenzen et al. 2003) and under conditions with surplus precipitation (Thorup-Kristensen 2006). To improve soil N use efficiency in temporary grasslands, we propose the addition of deep-rooting plant species to a mixture of perennial ryegrass and white clover, which are the most widespread forage plant species in temporary grasslands in a temperate climate (Moore 2003). Perennial ryegrass and white clover possess relatively shallow root systems (Kutschera and Lichtenegger 1982; Kutschera and Lichtenegger 1992) with effective rooting depths of <0.7 m on a silt loamy site (Pollock and Mead 2008). Grassland species, such as lucerne and chicory, grow their tap-roots into deep soil layers and exploit soil nutrients and water in soil layers that the commonly grown shallow-rooting grassland species cannot reach (Braun et al. 2010; Skinner 2008). Chicory grown as a catch crop after barley reduced the inorganic soil N down to 2.5 m depth during the growing season, while perennial ryegrass affected the inorganic soil N only down to 1 m depth (Thorup-Kristensen 2006). Further, on a Wakanui silt loam in New Zealand chicory extracted water down to 1.9 m and lucerne down to 2.3 m soil depth, which resulted in greater herbage yields compared with a perennial ryegrass-white clover mixture, especially for dryland plots (Brown et al. 2005). There is little information on both the ability of deep- and shallow-rooting grassland species to access soil N from different vertical soil layers and the relation of soil N-access and herbage yield in temporary agricultural grasslands. Therefore, the objective of the present work was to test the hypotheses 1) that a mixture comprising both shallow- and deep-rooting plant species has greater herbage yields than a shallow-rooting binary mixture and pure stands, 2) that deep-rooting plant species (chicory and lucerne) are superior in accessing soil N from 1.2 m soil depth compared with shallow-rooting plant species, 3) that shallow-rooting plant species (perennial ryegrass and white clover) are superior in accessing soil N from 0.4 m soil depth compared with deep-rooting plant species, 4) that a mixture of deep- and shallow-rooting plant species has greater access to soil N from three soil layers compared with a shallow-rooting two-species mixture and that 5) the leguminous grassland plants, lucerne and white clover, have a strong impact on grassland N acquisition, because of their ability to derive N from the soil and the atmosphere

Why do we make changes to the long-term experiments at Rothamsted?

The long-term field experiments at Rothamsted in south-east England (UK) are an important resource that has been used extensively to study the effects of land management, atmospheric pollution and climate change on soil fertility and the sustainability of crop yields. However, for these and other long-term experiments around the world to remain useful, changes are sometimes needed. These changes may be required to ensure that the experiment is not compromised by e.g. acidification or weeds, but often they are needed to ensure that the experiment remains relevant to current agricultural practice, e.g. the introduction of new cultivars and the judicious use of pesticides. However, changes should not be made just for the sake of change or to investigate aspects of management that could be better resolved in a short-term experiment. Rather, modifications should only be made after carefully considered discussion, involving scientists from different disciplines. It must be remembered however that there are limitations to what can be achieved in one experiment. In this paper we give examples of why certain changes were made to the Rothamsted experiments and what the results of those changes have been. We also highlight the value of archiving crop and soil samples for future studies