China's croplands have experienced drastic changes in management practices, such as fertilization, tillage, and residue treatments, since the 1980s. There is an ongoing debate about the impact of these changes on soil organic carbon (SOC) and its implications. Here we report results from an extensive study that provided direct evidence of cropland SOC sequestration in China. Based on the soil sampling locations recorded by the Second National Soil Survey of China in 1980, we collected 4,060 soil samples in 2011 from 58 counties that represent the typical cropping systems across China. Our results showed that across the country, the average SOC stock in the topsoil (0-20 cm) increased from 28.6 Mg C ha in 1980 to 32.9 Mg C ha in 2011, representing a net increase of 140 kg C ha year However, the SOC change differed among the major agricultural regions: SOC increased in all major agronomic regions except in Northeast China. The SOC sequestration was largely attributed to increased organic inputs driven by economics and policy: while higher root biomass resulting from enhanced crop productivity by chemical fertilizers predominated before 2000, higher residue inputs following the large-scale implementation of crop straw/stover return policy took over thereafter. The SOC change was negatively related to N inputs in East China, suggesting that the excessive N inputs, plus the shallowness of plow layers, may constrain the future C sequestration in Chinese croplands. Our results indicate that cropland SOC sequestration can be achieved through effectively manipulating economic and policy incentives to farmers.

We study the transport of vortices excited by an ac current in an Al film with an array of nanoengineered asymmetric antidots. The vortex response to the ac current is investigated by detailed measurements of the voltage output as a function of ac current amplitude, magnetic field and temperature. The measurements revealed pronounced voltage rectification effects which are mainly characterized by the two critical depinning forces of the asymmetric potential. The shape of the net dc voltage as a function of the excitation amplitude indicates that our vortex ratchet behaves in a way very different from standard overdamped models. Rather, as demonstrated by the observed output signal, the repinning force, necessary to stop vortex motion, is considerably smaller than the depinning force, resembling the behavior of the so-called inertia ratchets. Calculations based on an underdamped ratchet model provide a very good fit to the experimental data.PACS numbers: 05.40. 74.78.Na., 74.40.+k, From the point of view of classical thermodynamics, it is not possible to induce directed motion of particles by using equilibrium fluctuations only, otherwise it would constitute a perpetuum mobile of the second kind [1]. Nevertheless, non-equilibrium fluctuations, such as periodic excitations or a "colored" noise, are allowed to take advantage of the asymmetry of a periodic ratchet potential to promote motion of particles in a preferential direction [2]. New solid-state-based ratchet systems are currently being developed for controlling the motion of electrons [3] and fluxons, as well as for particle separation [4] and electrophoresis [5]. In particular, ratchet potentials in superconducting devices may be very useful to control the dissipative motion of fluxons, which causes undesired internal noise.Modern lithographic technics make it possible to fabricate periodic arrays of vortex pinning sites with size and shape that can be easily tuned, thus giving an interesting perspective for making different asymmetric pinning potentials. In this context, several ideas to control flux motion by applying an ac excitation have been proposed [6,7,8,9], but up to now only a few experiments have been realized [10,11]. One realization has been recently implemented on a Nb film with a square array of nanoscopic triangular magnetic dots [10]. The authors reported rectification of the ac driven vortices due to the asymmetric shape of the dots. Nevertheless, the detailed dynamics of vortices in such structures is not yet completely understood.In this Letter we investigate a composite square array of pinning sites, with its unit cell consisting of a small and a big square antidot separated by a narrow superconducting wall, as a vortex rectifier. As demonstrated by our dc and ac transport measurements at several fields and temperatures, this configuration is able to break the reflection symmetry of the total effective pinning potential and promote flux quanta rectification. Moreover, our data reveals a remarkable hysteresis in the currentinduced pinni...

Animal manure application as organic fertilizer does not only sustain agricultural productivity and increase soil organic carbon (SOC) stocks, but also affects soil nitrogen cycling and nitrous oxide (N O) emissions. However, given that the sign and magnitude of manure effects on soil N O emissions is uncertain, the net climatic impact of manure application in arable land is unknown. Here, we performed a global meta-analysis using field experimental data published in peer-reviewed journals prior to December 2015. In this meta-analysis, we quantified the responses of N O emissions to manure application relative to synthetic N fertilizer application from individual studies and analyzed manure characteristics, experimental duration, climate, and soil properties as explanatory factors. Manure application significantly increased N O emissions by an average 32.7% (95% confidence interval: 5.1-58.2%) compared to application of synthetic N fertilizer alone. The significant stimulation of N O emissions occurred following cattle and poultry manure applications, subsurface manure application, and raw manure application. Furthermore, the significant stimulatory effects on N O emissions were also observed for warm temperate climate, acid soils (pH < 6.5), and soil texture classes of sandy loam and clay loam. Average direct N O emission factors (EFs) of 1.87% and 0.24% were estimated for upland soils and rice paddy soils receiving manure application, respectively. Although manure application increased SOC stocks, our study suggested that the benefit of increasing SOC stocks as GHG sinks could be largely offset by stimulation of soil N O emissions and aggravated by CH emissions if, particularly for rice paddy soils, the stimulation of CH emissions by manure application was taken into account.