Explore the vast range of titles available.

Background The dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (Po) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction. Scope We asked a group of experts to consider the global issues associated with Po in the terrestrial environment, methodological strengths and weaknesses, benefits to be gained from understanding the Po cycle, and to set priorities for Po research. Conclusions We identified seven key opportunities for Po research including: the need for integrated, quality controlled and functionally based methodologies; assessment of stoichiometry with other elements in organic matter; understanding the dynamics of Po in natural and managed systems; the role of microorganisms in controlling Po cycles; the implications of nanoparticles in the environment and the need for better modelling and communication of the research. Each priority is discussed and a statement of intent for the Po research community is made that highlights there are key contributions to be made toward understanding biogeochemical cycles, dynamics and function of natural ecosystems and the management of agricultural systems.

Effective nutrient management requires an accurate accounting of nutrients removed from soils in the harvested portion of a crop. Because the typical crop nutrient values that have historically been used may be different under current production practices, a study was conducted to measure nutrient uptake in grain harvested in 1998 and 1999 from 23 site‐years in the Mid‐Atlantic region of the USA. There were 10 hybrids included in the study, but each site grew only one hybrid each year. Corn (Zea mays L.) production practices followed local state extension recommendations. Minimum, maximum, and mean corn grain yields were 4.9, 16.7, and 10.3 Mg ha−1. Nutrient concentrations were determined on grain samples oven‐dried at 70°C for 24 h. Minimum, maximum, and median nutrient concentration values were as follows: 10.2, 15.0, and 12.9 g N kg−1; 2.2, 5.4, and 3.8 g P kg−1; 3.1, 6.2, and 4.8 g K kg−1; 0.13, 0.45, and 0.28 g Ca kg−1; 0.88, 2.18, and 1.45 g Mg kg−1; 0.9, 1.4, and 1.0 g S kg−1; 9.0, 89.5, and 33.6 mg Fe kg−1; 15.0, 34.5, and 26.8 mg Zn kg−1; 1.0, 9.8, and 5.3 mg Mn kg−1; 1.0, 5.8, and 3.0 mg Cu kg−1; and 2.3, 10.0, and 5.5 mg B kg−1. Median nutrient uptake values found in this study are similar to commonly used book values, but there was considerable variation among samples of corn grain. Concentrations of P and K in grain were positively associated with yield level, and concentrations of grain P were positively correlated with Mehlich‐3 soil test P. The variability in nutrient removal values seen in this study, even for the same hybrid, raises questions about the usefulness of average values for estimating crop nutrient removal across a range of cropping conditions. Research is needed to identify or develop a means to correct for the sources of variability.

Tremendous changes have occurred during the past century in the sources and methods for supplying nutrients for horticultural crops. Reliance on animal manure, cover crops, and animal tankage was insufficient to meet the crop nutrient demand for a rapidly expanding population. The Haber-Bosch process for ammonia synthesis (1910s) revolutionized the availability and affordability of nitrogen (N) fertilizer. Discovery of large-scale deposits of rock phosphate in South Carolina (1860s) and Florida (1880s) alleviated widespread nutrient deficiencies. Acidification of rock phosphate and bone material significantly improved phosphorus (P) availability for plants. Discovery of potassium (K)-bearing minerals in New Mexico (1920s) and later in Canada (1960s) now provide a long-term nutrient source. Modern fertilizer technology allows nutrients to be applied in the correct ratio and amount to meet crop needs. Advances in understanding plant nutrition, coupled with slow-release fertilizers, foliar fertilization, soluble nutrients, and the development of soil and tissue testing have all improved the yield and quality of horticultural crops. Future developments will likely focus on fertilization in an increasingly competitive global economy, while requiring sophisticated management to minimize environmental impacts.

Effective nutrient management requires an accurate accounting of nutrients removed from soils in the harvested portion of a crop. Because the typical crop nutrient values that have historically been used may be different under current production practices, a study was conducted to measure nutrient uptake in grain harvested in 1998 and 1999 from 23 site-years in the Mid-Atlantic region of the USA. There were 10 hybrids included in the study, but each site grew only one hybrid each year. Corn (Zea mays L.) production practices followed local state extension recommendations. Minimum, maximum, and mean corn grain yields were 4.9, 16.7, and 10.3 Mg ha−1 Nutrient concentrations were determined on grain samples oven-dried at 70°C for 24 h. Minimum, maximum, and median nutrient concentration values were as follows: 10.2, 15.0, and 12.9 g N kg−1; 2.2, 5.4, and 3.8 g P kg−1; 3.1, 6.2, and 4.8 g K kg−1; 0.13, 0.45, and 0.28 g Ca kg−1; 0.88, 2.18, and 1.45 g Mg kg−1; 0.9, 1.4, and 1.0 g S kg−1; 9.0, 89.5, and 33.6 mg Fe kg−1; 15.0, 34.5, and 26.8 mg Zn kg−1; 1.0, 9.8, and 5.3 mg Mn kg−1; 1.0, 5.8, and 3.0 mg Cu kg−1; and 2.3, 10.0, and 5.5 mg B kg−1 Median nutrient uptake values found in this study are similar to commonly used book values, but there was considerable variation among samples of corn grain. Concentrations of P and K in grain were positively associated with yield level, and concentrations of grain P were positively correlated with Mehlich-3 soil test P. The variability in nutrient removal values seen in this study, even for the same hybrid, raises questions about the usefulness of average values for estimating crop nutrient removal across a range of cropping conditions. Research is needed to identify or develop a means to correct for the sources of variability.

Here, the dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (Po) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction. We asked a group of experts to consider the global issues associated with Po in the terrestrial environment, methodological strengths and weaknesses, benefits to be gained from understanding the Po cycle, and to set priorities for Po research. In conclusion, we identified seven key opportunities for Po research including: the need for integrated, quality controlled and functionally based methodologies; assessment of stoichiometry with other elements in organic matter; understanding the dynamics of Po in natural and managed systems; the role of microorganisms in controlling Po cycles; the implications of nanoparticles in the environment and the need for better modelling and communication of the research. Each priority is discussed and a statement of intent for the Po research community is made that highlights there are key contributions to be made toward understanding biogeochemical cycles, dynamics and function of natural ecosystems and the management of agricultural systems.

Nonetheless, for anyone interested in modeling plant nitrogen uptake, this should be the first source to go to for a solid overview of quantifying and understanding plant nitrogen uptake for systems modeling.

Astrophysical collisionless shocks are among the most powerful particle accelerators in the Universe. Generated by violent interactions of supersonic plasma flows with the interstellar medium, supernova remnant shocks are observed to amplify magnetic fields 1 and accelerate electrons and protons to highly relativistic speeds 2 – 4 . In the well-established model of diffusive shock acceleration 5 , relativistic particles are accelerated by repeated shock crossings. However, this requires a separate mechanism that pre-accelerates particles to enable shock crossing. This is known as the ‘injection problem’, which is particularly relevant for electrons, and remains one of the most important puzzles in shock acceleration 6 . In most astrophysical shocks, the details of the shock structure cannot be directly resolved, making it challenging to identify the injection mechanism. Here we report results from laser-driven plasma flow experiments, and related simulations, that probe the formation of turbulent collisionless shocks in conditions relevant to young supernova remnants. We show that electrons can be effectively accelerated in a first-order Fermi process by small-scale turbulence produced within the shock transition to relativistic non-thermal energies, helping overcome the injection problem. Our observations provide new insight into electron injection at shocks and open the way for controlled laboratory studies of the physics underlying cosmic accelerators. In laser–plasma experiments complemented by simulations, electron acceleration is observed in turbulent collisionless shocks. This work clarifies the pre-acceleration to relativistic energies required for the onset of diffusive shock acceleration.

Phosphorus fertilizer use has roughly quadrupled in the past century. Budgets constructed from historical data show that phosphorus rapidly accumulates in river basins during periods of high inputs and continues to mobilize after inputs decline. Global food production depends on phosphorus. Phosphorus is broadly applied as fertilizer, but excess phosphorus contributes to eutrophication of surface water bodies and coastal ecosystems 1 . Here we present an analysis of phosphorus fluxes in three large river basins, including published data on fertilizer, harvested crops, sewage, food waste and river fluxes 2 , 3 , 4 . Our analyses reveal that the magnitude of phosphorus accumulation has varied greatly over the past 30–70 years in mixed agricultural–urban landscapes of the Thames Basin, UK, the Yangtze Basin, China, and the rural Maumee Basin, USA. Fluxes of phosphorus in fertilizer, harvested crops, food waste and sewage dominate over the river fluxes. Since the late 1990s, net exports from the Thames and Maumee Basins have exceeded inputs, suggesting net mobilization of the phosphorus pool accumulated in earlier decades. In contrast, the Yangtze Basin has consistently accumulated phosphorus since 1980. Infrastructure modifications such as sewage treatment and dams may explain more recent declines in total phosphorus fluxes from the Thames and Yangtze Rivers 3 , 4 . We conclude that human-dominated river basins may undergo a prolonged but finite accumulation phase when phosphorus inputs exceed agricultural demand, and this accumulated phosphorus may continue to mobilize long after inputs decline.