Explore the vast range of titles available.

Synthetic nitrogen (N) fertilizer has played a key role in enhancing food production and keeping half of the world's population adequately fed. However, decades of N fertilizer overuse in many parts of the world have contributed to soil, water, and air pollution; reducing excessive N losses and emissions is a central environmental challenge in the 21st century. China's participation is essential to global efforts in reducing N-related greenhouse gas (GHG) emissions because China is the largest producer and consumer of fertilizer N. To evaluate the impact of China's use of N fertilizer, we quantify the carbon footprint of China's N fertilizer production and consumption chain using life cycle analysis. For every ton of N fertilizer manufactured and used, 13.5 tons of CO₂-equivalent (eq) (tCO₂-eq) is emitted, compared with 9.7 t CO₂-eq in Europe. Emissions in China tripled from 1980 [131 terrogram (Tg) of CO₂-eq (Tg CO₂-eq)] to 2010 (452 Tg CO₂-eq). N fertilizer-related emissions constitute about 7% of GHG emissions from the entire Chinese economy and exceed soil carbon gain resulting from N fertilizer use by several-fold. We identified potential emission reductions by comparing prevailing technologies and management practices in China with more advanced options worldwide. Mitigation opportunities indude improving methane recovery during coal mining, enhancing energy efficiency in fertilizer manufacture, and minimizing N overuse in field-level crop production. We find that use of advanced technologies could cut N fertilizer-related emissions by 20-63%, amounting to 102-357 Tg CO₂-eq annually. Such reduction would decrease China's total GHG emissions by 2-6%, which is significant on a global scale.

Is nitrate harmful to humans? Are the current limits for nitrate concentration in drinking water justified by science? There is substantial disagreement among scientists over the interpretation of evidence on the issue. There are two main health issues: the linkage between nitrate and (i) infant methaemoglobinaemia, also known as blue baby syndrome, and (ii) cancers of the digestive tract. The evidence for nitrate as a cause of these serious diseases remains controversial. On one hand there is evidence that shows there is no clear association between nitrate in drinking water and the two main health issues with which it has been linked, and there is even evidence emerging of a possible benefit of nitrate in cardiovascular health. There is also evidence of nitrate intake giving protection against infections such as gastroenteritis. Some scientists suggest that there is sufficient evidence for increasing the permitted concentration of nitrate in drinking water without increasing risks to human health. However, subgroups within a population may be more susceptible than others to the adverse health effects of nitrate. Moreover, individuals with increased rates of endogenous formation of carcinogenic N-nitroso compounds are likely to be susceptible to the development of cancers in the digestive system. Given the lack of consensus, there is an urgent need for a comprehensive, independent study to determine whether the current nitrate limit for drinking water is scientifically justified or whether it could safely be raised.

To meet economic and environmental demands for about 10 billion people by the mid‐21st century, humanity will be challenged to double food production from the Earth's soil and diminish adverse effects of soil management on the wider environment. To meet these challenges, an array of scientific approaches is being used to increase understanding of long‐term soil trends and soil–environment interactions. One of these approaches, that of long‐term soil experiments (LTSEs), provides direct observations of soil change and functioning across time scales of decades, data critical for biological, biogeochemical, and environmental assessments of sustainability; for predictions of soil productivity and soil–environment interactions; and for developing models at a wide range of scales. Although LTSEs take years to mature, are vulnerable to loss, and have yet to be comprehensively inventoried or networked, LTSEs address a number of contemporary issues and yield data of special significance to soil management. The objective of this study was to evaluate how LTSEs address three questions that fundamentally challenge modern society: how soils can sustain a doubling of food production in the coming decades, how soils interact with the global C cycle, and how soil management can establish greater control over nutrient cycling. Results demonstrate how LTSEs produce significant data and perspectives for all three questions. Results also suggest the need for a review of the state of our long‐term soil‐research base and the establishment of an efficiently run network of LTSEs aimed at soil‐management sustainability and improving management control over C and nutrient cycling.

No-till agriculture is generally considered good for soils, and probably also beneficial in relation to climate change adaptation. However, this Perspective argues that the potential for climate change mitigation through soil carbon sequestration that is possible from a change to no-till agriculture has been widely overstated. The Emissions Gap Report 2013 from the United Nations Environment Programme restates the claim that changing to no-till practices in agriculture, as an alternative to conventional tillage, causes an accumulation of organic carbon in soil, thus mitigating climate change through carbon sequestration. But these claims ignore a large body of experimental evidence showing that the quantity of additional organic carbon in soil under no-till is relatively small: in large part apparent increases result from an altered depth distribution. The larger concentration near the surface in no-till is generally beneficial for soil properties that often, though not always, translate into improved crop growth. In many regions where no-till is practised it is common for soil to be cultivated conventionally every few years for a range of agronomic reasons, so any soil carbon benefit is then lost. We argue that no-till is beneficial for soil quality and adaptation of agriculture to climate change, but its role in mitigation is widely overstated.

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 chain.

Bioenergy developments could lead to large-scale removal of cereal straw from fields, with consequences for soil organic carbon (SOC) and related properties. In 25 experiments of 6 to 56 yr duration there was a trend for SOC and total soil N content to increase where straw was incorporated annually. However the increases were only significant in six experiments and were <10% in the majority of cases. Increases in microbial biomass C or N were always proportionately greater than for SOC or N. In simulations of annual straw incorporation using the RothC model, 90% of the microbial biomass C increase in 100 yr was reached within 20 yr as biomass C moves toward a new equilibrium value more rapidly than total SOC. Simulations also showed that if straw was removed in 50% of years, SOC and biomass C increases were about 50% of those with annual straw incorporation. There is considerable evidence that small changes in total SOC have disproportionately large impacts on soil physical properties such as aggregate stability, water infiltration rate, and plow draft and that microbial activity is crucial in the formation of stable aggregates. We conclude that, although changes in SOC resulting from addition or removal of straw are small, it would be unwise to remove straw every year as this is likely to lead to deterioration in soil physical properties. Local assessments are required to determine the frequency of straw removal that is acceptable for soil functioning; this will influence the capacity of bioenergy installations.

Organic farming gives no climate change benefit through soil carbon sequestration

Within the context of sustainable development, soil degradation driven by land use change is considered a serious global problem, but the conversion from growing cereals to vegetables is a change that has received limited attention, especially in subtropical regions. Here, we studied the effects of the conversion from paddy rice to an oilseed rape rotation to vegetable production in southwestern China on soil organic carbon (SOC), total nitrogen (TN), the C/N ratio, pH, phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) based on face-to-face farmer surveys and soil analysis. In the vegetable cropping system, fertilizer application often exceeds the crop demand or levels recommended by the local extension service several times over. Thus, the crop use efficiency of N, P, K, Ca, and Mg was only 26 %, 8 %, 56 %, 23 %, and 28 %, respectively. In the vegetable cropping system studied, SOC, C stock, TN, and N stock were decreased significantly due to low organic inputs from crop residues and high tillage frequency. Furthermore, the soil C/N ratio decreased slightly; available P (AP) in the topsoil increased by 1.92 mg kg−1 for every 100 kg ha−1 of P surplus, and the critical levels of AP and CaCl2-soluble P in P leaching were 104 and 0.80 mg P kg−1. Besides, compared to the current paddy–rape rotation system, a clear trend of soil acidification was observed in the vegetable fields. However, increasing the contents of soil Ca and Mg significantly alleviated topsoil acidification, with the effect increasing over time. Given our findings, the potential benefits of conservation agricultural practices, integrated soil–crop system management strategies, and agricultural technology services for recovering the degraded soil and improving the vegetable productivity are discussed here.

The possibility that the carbon sink in agricultural soils can be enhanced has taken on great political significance since the Kyoto Protocol was finalised in December 1997. The Kyoto Protocol allows carbon emissions to be offset by demonstrable removal of carbon from the atmosphere. Thus, forestry activities (Article 3.3) and changes in the use of agricultural soils (Article 3.4) that are shown to reduce atmospheric CO2levels may be included in the Kyoto emission reduction targets. The European Union is committed to a reduction in CO2 emissions to 92% of baseline (1990) levels during the first commitment period (2008–2012). We have shown recently that there are a number of agricultural land-management changes that show some potential to increase the carbon sink in agricultural soils and others that allow alternative forms of carbon mitigation (i.e. through fossil fuel substitution), but the options differ greatly in their potential for carbon mitigation. The changes examined were, (a) switching all animal manure use to arable land, (b) applying all sewage sludge to arable land, (c) incorporating all surplus cereal straw, (d) conversion to no-till agriculture, (e) use of surplus arable land to de-intensify 1/3 of current intensive crop production (through use of 1/3 grass/arable rotations), (f) use of surplus arable land to allow natural woodland regeneration, and (g) use of surplus arable land for bioenergy crop production. In this paper, we attempt for the first time to assess other (non-CO2) effects of these land-management changes on (a) the emission of the other important agricultural greenhouse gases, methane and nitrous oxide, and (b) other aspects of the ecology of the agroecosystems. We find that the relative importance of trace gas fluxes varies enormously among the scenarios. In some such as the sewage sludge, woodland regeneration and bioenergy production scenarios, the inclusion of trace gases makes only a small (<10%) difference to the CO2-C mitigation potential. In other cases, for example the no-till, animal manure and agricultural de-intensification scenarios, trace gases have a large impact, sometimes halving or more than doubling the CO2-C mitigation potential. The scenarios showing the greatest increase when including trace gases are those in which manure management changes significantly. In the one scenario (no-till) where the carbon mitigation potential was reduced greatly, a small increase in methane oxidation was outweighed by a sharp increase in N2O emissions. When these land-management options are combined to examine the whole agricultural land area of Europe, most of the changes in mitigation potential are small, but depending upon assumptions for the animal manure scenario, the total mitigation potential either increases by about 20% or decreases by about 10%, shifting the mitigation potential of the scenario from just above the EU's 8% Kyoto emission reduction target (98.9 Tg C y−1) to just below it. Our results suggest that (a) trace gas fluxes may change the mitigation potential of a land management option significantly and should always be considered alongside CO2-C mitigation potentials and (b) agricultural management options show considerable potential for carbon mitigation even after accounting for trace gas fluxes.