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Changes in field management and climate will alter soil organic carbon (SOC) and nitrogen (SN) cycling in the coming decades. This study is to quantify the effects of various fertilisation strategies and climate change scenarios on crop yield, and soil C and N cycling by the end of this century. Data from a long-term experiment with a winter-wheat ( Triticum aestivium L.) and summer maize ( Zea mays L.) rotation in Northern China was used to calibrate and validate the SPACSYS model. Five fertiliser practices were used: control (CK); combined mineral nitrogen, phosphorus and potassium (NPK); NPK plus manure (NPKM); high application rate of NPK fertilisers plus manure (hNPKM) and NPK with straw incorporation (NPKS). Crop yields, and SOC and SN stocks by 2100 were predicted under four climate scenarios (Baseline, RCP2.6, RCP4.5 and RCP4.5). Results showed that the SPACSYS model can adequately simulate the dynamics of SOC and SN stocks and the yields of winter wheat and summer maize. An application of NPK plus manure or straw not only enhanced crop yield, but also substantially increased SOC and SN stocks. The predictions showed the positive effects of fertilisation and climate change on crop yields and SOC stocks compared with those under the baseline. However, SN stock under the RCP8.5 decreased by 3–14% by 2100 for various fertilisation strategies compared with that under the baseline. On the other hand, mineral fertiliser plus manure led to a higher soil respiration rate and nitrogen losses through leaching and surface runoff under all the climate scenarios. Therefore, application of mineral fertilisers plus manure could enhance crop productivity and sustain soil fertility but cause more carbon emitted to the atmosphere and nitrogen losses. More attention should be paid on optimising fertilisation in order to increase crop productivity while minimising environmental risks. [ABSTRACT FROM AUTHOR]

Abstract: Phosphate-solubilizing bacteria (PSBs) Pantoea cypripedii (PSB-3) and Pseudomonas plecoglossicida (PSB-5) isolated from organic field were studied for improvement of maize and wheat crop at multilocational sites with and without rock phosphate (RP) fertilization during two year of field study under different agroclimatic regions. Application of both the bacterial strains as bio-inoculants showed significant effect on maize and wheat grain yield and on soil fertility at all different agroclimatic regions. Grain yield, phosphorous (P) uptake, soil organic carbon, available P, enzyme activities and P-solubilizing bacterial population in all the experimental crop fields at different sites significantly increased due to inoculation. Improvement in crop yield and soil fertility at three different sites was more pronounced and significant when RP was supplemented along with seed inoculation compared to uninoculated control treatment. Present study results suggest that P. cypripedii (PSB-3) and P. plecoglossicida (PSB-5) along with RP fertilization play an important role in plant growth promotion and improvement of soil fertility in different agroclimatic regions. [Copyright &y& Elsevier]

Abstract: Soil management practices may change the soil properties. The magnitude of the change varies according to the soil property, the climate, and the type and time of implementation of a particular management system. The aim of this study was to evaluate the effects of no-tillage (NT) on the chemical and biological properties of an Entic Haploxeroll in Central Chile. Soil organic carbon (SOC), microbial biomass and associated indicators , q Mic , q Min , available N, P and K, pH, electrical conductivity (EC), and crop yield were determined in a field experiment having a wheat (Triticum turgidum L.)–maize (Zea mays L.) crop rotation. The change in soil chemical properties was further evaluated using a greenhouse bioassay in which ryegrass (Lolium perenne L.) was grown in soil samples extracted at 0–2, 2–5, and 5–15cm depth. After nine years SOC in the NT treatment was 29.7Mgha−1 compared to 24.8Mgha−1 of CT, resulting in 4.98Mgha−1 C gain. The NT therefore resulted in an average annual sequestration of 0.55MgCha−1 yr−1 in the upper 15cm soil. The soil organic C stored under NT was mainly accumulated in the top 2-cm of soil. The biological indicators showed a greater biological soil quality under NT than under CT. Soil organic C was positively associated with available N, P, and K, but negatively with soil pH. The ryegrass bioassay yielded higher biomass in NT than CT. An improvement in the soil chemical quality of the NT soil was considered to be the main reason for this result. The maize yield under NT had the tendency to improve in time as compared to CT. Wheat, however, had lower yield under NT. It was concluded that NT increased C sequestration and SOC improving the chemical and biological properties of this soil. [Copyright &y& Elsevier]

Abstract: The rhizosphere and the detritusphere are hot spots of microbial activity, but little is known about the interface between rhizosphere and detritusphere. We used a three-compartment pot design to study microbial community structure and enzyme activity in this interface. All three compartments were filled with soil from a long-term field trial. The two outer compartments were planted with maize (root compartment) or amended with mature wheat shoot residues from a free air CO2 enrichment experiment (residue compartment) and were separated by a 50 μm mesh from the inner compartment. Soil, residues and maize differed in 13C signature (δ13C soil −26.5‰, maize roots −14.1‰ and wheat residues −44.1‰) which allowed tracking of root- and residue-derived C into microbial phospholipid fatty acids (PLFA). The abundance of bacterial and fungal PLFAs showed clear gradients with highest abundance in the first 1–2 mm of the root and residue compartment, and generally higher values in the vicinity of the residue compartment. The δ13C of the PLFAs indicated that soil microorganisms incorporated more carbon from the residues than from the rhizodeposits and that the microbial use of wheat residue carbon was restricted to 1 mm from the residue compartment. Carbon incorporation into soil microorganisms in the interface was accompanied by strong microbial N immobilisation evident from the depletion of inorganic N in the rhizosphere and detritusphere. Extracellular enzyme activities involved in the degradation of organic C, N and P compounds (β-glucosidase, xylosidase, acid phosphatase and leucin peptidase) did not show distinct gradients in rhizosphere or detritusphere. Our microscale study showed that rhizosphere and detritusphere differentially influenced microbial C cycling and that the zone of influence depended on the parameter assessed. These results are highly relevant for defining the size of different microbial hot spots and understanding microbial ecology in soils. [Copyright &y& Elsevier]

Abstract: On sites where C4-plants have replaced C3-plants, changes in soil δ13C allow the turnover of C3- and C4-derived C to be separated. Studies of decadal scale turnover of soil C following conversion to C4-plants generally lack δ13C values for previous C4-residue inputs and assume that estimates of C4-derived soil C to be based on a fixed δ13C value. Further assumptions are that changes in the initial (time-zero) soil δ13C values are insignificant following conversion to C4-plants. We tested these assumptions by measuring: 1) the δ13C of annual samples of silage maize biomass (C4-plant) and winter wheat grains (C3-plant) grown during 1988 to 2006, and 2) the δ13C of soil kept under bare fallow during 1956 to 1983. The δ13C of plants was related to climate variables, and the impact of maize δ13C was based on estimates of maize-derived soil C using different approaches to establish the δ13C in maize inputs. The δ13C of both maize and wheat decreased with time, but the rate of change and annual variations were considerably larger for wheat than for maize. Maize as well as wheat δ13C was best related to year (probably reflecting a decrease in atmospheric δ13C) and the water balance during the active growth period. Using the smallest (−12.44‰) and the largest (−11.26‰) δ13C measured during 1988 and 2006, estimates of maize-derived C in soil after 18 years ranged from 13.2% to 14.2% of the soil total C. Despite a loss of 31% of the soil C pool under bare fallow, the increase in soil δ13C was significant only at P < 0.10. We conclude that annual variations in maize δ13C values and changes in the δ13C of the soil C fraction derived from the pre-conversion C3-vegetation have only little impact on estimates of maize-derived soil C that cover a few decades. For estimates covering several decades to centuries, the subtle but consistent changes in plant and soil δ13C need to be accounted for. The variability in δ13C in wheat grains suggest that the use of any fixed δ13C value for C3-residues in estimates of C turnover in soils on which C4-plants have been replaced by C3-plants can be associated with considerable uncertainty. [Copyright &y& Elsevier]

Abstract: The issue of soil C sequestration is of special interest in Mediterranean areas, where, due to climatic conditions and agricultural practices, SOC (soil organic carbon) content is low, and is likely to be affected by climate change. Besides, losses of SOC have a relevant role in decreasing agricultural soil quality and could have a negative effect in productivity. Therefore, it is crucial to estimate whether modifying traditional soil management would have beneficial effects under future climate conditions. We used the EPIC model to simulate the interactive effect of climate change, CO2 enrichment, soil management (conventional tillage—CT vs. no tillage—NT) and two crop rotations, durum wheat–sunflower and durum wheat–maize, on crops yields and SOC in central Italy. The model was calibrated using soil and crop yield data collected from a long-term field experiment run in central Italy with CT and NT treatments. Maize and sunflower grain yields were significantly reduced by NT, primarily because of poor establishment, while durum wheat was almost not affected by tillage treatments. Projected durum wheat (Dw) and maize (Ma) grain yields were negatively affected by climate change (up to −25% and −10% respectively) while sunflower (Sf) yield increased. Tillage effects appear to be the most important factor in sequestering/releasing C. No-tillage practices sequestered in all profile (0–100cm depth) from 0.03 to 0.2tha−1 y−1 in 30 years, depending on climate scenario and plant C input, while conventional tillage (CT) led to massive C loss rates (up to −0.9tha−1 y−1). Beyond all uncertainties in the use of models, the results demonstrated that soil tillage and, to a certain extent, crop rotation, can play a relevant role in reducing (NT) or reinforcing (CT) the impact of climate change on SOC. No-tillage farming, if sufficient C input is ensured by the cropping system, could effectively contribute to increase soil C sequestration in Mediterranean rainfed environments. [Copyright &y& Elsevier]