Search

Increasing zinc (Zn) concentration in wheat grain is important to minimize human dietary Zn deficiency. This study aimed to investigate the effect of foliar Zn and soil nitrogen (N) applications on the accumulation and distribution of N and Zn in grain pearling fractions, N remobilization, and the relationships between nutrient concentration in the vegetative tissues and grain or its fractions in two cropping years in the North China Plain. The results showed a progressive decrease in N and Zn concentrations from the outer to the inner parts of grain, with most of the accumulation in the core endosperm. Foliar Zn application significantly increased N concentration in the pericarp, and soil N application increased N concentration in each grain fraction. Both treatments significantly increased core endosperm Zn concentration. Foliar Zn had no effect on grain N and Zn distribution. Soil N application made N concentrated in the aleurone, promoted Zn translocation to the core endosperm and also increased N remobilization and its efficiency from the shoot to the grain, but no improved contribution to grain was found. N concentration in grain and its fractions were positively correlated with N in vegetative organs at anthesis and maturity, while positive correlations were obtained between N concentration in the pericarp and progressive central area of the endosperm and Zn concentration in the core endosperm. Thus, foliar Zn and soil N applications effectively increased yield and N and Zn concentrations in the wheat grain, particularly in the endosperm, and could be promising strategies to address Zn deficiency.

TUdi - Transforming Unsustainable management of soils in key agricultural systems in EU and China. Developing an integrated platform of alternatives to reverse soil degradation. Referencia del proyecto: 101000224. Partner/Coordinador principal: José Alfonso Gómez Calero – Instituto de Agricultura Sostenible IAS- CSIC., Imprecise irrigation hinders the sustainable development of the fruit tree–crop intercropping system in the Loess Gully Area of China. Drip fertigation was applied for two years as part of an apple–soybean intercropping system to optimize local water and nutrient management patterns. The effects of different drip irrigation and fertilizer levels on photosynthetic characteristics, soil nutrients, and their interspecific competitions were studied. The treatments were four irrigation levels, namely 60% (W1), 70% (W2), 80% (W3), and 90% (W4) of field capacity (Fc), and three nitrogen fertilization levels, namely 59 (F1), 92 (F2), and 124 kg∙ha–1 (F3). The control (CK) was a rain-fed (neither irrigation nor fertilizer) crop. The net photosynthetic rate (Pn), transpiration rate (Tr), and soybean yield (GY) increased at first, but then decreased as irrigation and fertilizer application levels rose. The partial factor productivity (PFP) decreased as fertilization increased, but the soil available nitrogen content showed the opposite trend. The soil nutrients, and soybean Pn and Tr were positively correlated with distance from the apple tree row. The interspecific competition intensity for light and soil water decreased from 2018 to 2019, while root and soil nitrate nitrogen (NN) increased. The interspecific competition correlation between the aboveground and belowground parts was weak and varied between the two intercropping years. A principal component analysis showed that treatment W3F2 had the highest comprehensive score. Thus, a combination of irrigation at 80% Fc and 92 kg∙ha–1 nitrogen fertilizer application is optimal for the system. A multiple regression analysis indicated a water input range of 4624.49–4795.75 m3·ha−1·a−1 combined with 84.10–107.27 kg·ha−1·a−1 fertilizer application was suitable for optimal irrigation and fertilization management based on the integrated benefits to root length density, GY, Pn, and PFP during the first 4–5 years of the intercropping system., This work was financially supported by National Key Research and Development Program of China (2022YFE0115300) and National Natural Science Fund (32271960). We are grateful for the support from the Forest Ecosystem Studies, National Observation and Research Station, Jixian, Shanxi, China.

Quantifying net primary production (NPP) and its allocation is essential for understanding and modeling the carbon (C) cycling in forest ecosystems. We used biometry-based measurements to examine the NPP allocation for six temperate forest types with similar stand age and climate but diverse stand characteristics and site conditions in northeastern China. The forest types included four naturally-regenerated stands and two planted stands. Our objectives were to (1) compare the NPP and its allocation among the six forest types, and (2) explore the factors driving the inter-stand variability of the NPP allocation patterns. We found that the total NPP (TNPP) and NPP of short-lived biomass tissues (NPPSL) differed significantly among the forest types, varying from 709 to 927 gC m−2 yr−1 and from 364 to 594 gC m−2 yr−1, respectively. However, the NPP of long-lived tissues (NPPLL) did not differ significantly among the forest types, varying from 305 to 364 gC m−2 yr−1. These results suggested that the production of structural tissues be relatively stable under the same climate, and the inter-stand difference in TNPP be mainly attributed to the difference in NPPSL. Within the four natural stands, the foliage production was significantly and positively correlated with soil nitrogen (N) (R2 = 0.50) and phosphorus (P) stock (R2 = 0.37), whereas the fine root production was significantly and negatively correlated with soil C:P (R2 = 0.54) and N:P ratio (R2 = 0.47), implying that foliage and root production may be driven by different mechanisms. The convergence of NPPLL across forest types with different stand characteristics, site conditions and management practices but under the same climate has important implication in managing forest ecosystems for C sequestration, while the divergence of NPPSL implies that vegetation can adapt to the site conditions by changing resource-absorbing tissues production and its allocation.

This study was conducted during 2015–2016. Extensive field work was conducted to collect and record huge amount of data on important environmental variables. Data was collected using reliable digital equipment with high precision and accuracy where possible. Material and samples collected for chemical analysis were based upon standardized methods used by prestigious labs across the globe. The results showed that July (Temperature 33.67 °C) is the warmest while December(19.1 °C) is the coldest month of the year in the study area. Air humidity ranges from 52.44% to23.22% between Union councils (UCs). Steepness of the slope or slope angle was found between 55.5 and 24°. Soil pH was between 7.39 and 6.55. Soil Nitrogen contents were found to be in a range of 0.0543% and 0.0320%. as far as soil organic matter is concerned it was recorded in a range of 0.77% and 0.48%. electric conductivity was between2.56 dS/m and 2.393 dS/m. Interaction among different environmental variables results in the establishment of different environmental complexes each with specific microclimate.

Plastic film mulch and phosphorus (P) fertilization usually increase alfalfa (Medicago sativa L.) forage yield in semi-arid regions by improving soil moisture and P availability. However, this does not always occur. The present study explored the P level for highest forage yield under film mulch and the mechanism underlying yield decrease at high P levels. A six-year study was conducted with randomized blocks of split-plot design with and without plastic film mulch as main plots: M0, no film mulch with flat planting; and M1, film mulching with ridge-furrow field regimes. Four P rates were applied in sub-plots: P0, P1, P2 and P3 with 0, 9.73, 19.3 and 28.9 kg P ha–1, respectively. Film mulch greatly increased forage yield, resulting in 14% higher yield in M1P0 than in M0P3. Forage yield under mulching decreased for 19.3 and 28.9 kg P ha−1. The P rate for maximum yield was 16.1 kg P ha−1. Soil total nitrogen (N) and inorganic-N decreased at 19.3 and 28.9 kg P ha−1 with mulching compared with 9.73 kg P ha−1, and the latter was about 90% lower than that of alfalfa lands in semi-humid region. Soil microbial biomass carbon (C) and C/N ratio in microbial biomass in mulched P2 and P3 subplots were significantly lower than for P1. With mulching, soil organic C mineralization was significantly less for P3 than for P1 and P2. Shoot N/P ratio decreased with increasing P with mulching. Thus shoot N uptake for P2 and P3 mulched plots was associated with low soil N availability. It is concluded that the highest forage yield was obtained with mulching, P-saving and low risk of N loss on the semiarid Loess Plateau.

Quantitative assessments of soil microbial necromass improve our knowledge of soil carbon (C) sequestration, which is vital for addressing climate change and food security. Here, we revisit the quantitative contribution of microbial necromass to soil organic C (SOC) pool by using an optimized strategy that considers the stoichiometric differences of microbes and the full range of the microbial necromass proportion in soil nitrogen pool. We derive a more applicable estimate of the microbial necromass contribution to SOC pool, reporting a narrower range (24%–60%) compared with those in recent publications. We further find that the potential contribution of microbial necromass to SOC pool is controlled by the stoichiometry (C/N ratio) of microbes and soil. We suggest soil C sequestration strategy by increasing microbial necromass should well be exploited to improve soil N availability and use microbial species associated with high biomass C/N ratio to boost C accrual.

Soil nitrogen (N) availability is determined by microbial gross N mineralisation (GNM) and immobilisation, where net N mineralisation (NNM) represents their balance. Plants provide a substantial amount of their photosynthesized C belowground into the soil as rhizodeposition, which can stimulate microbial activity affecting GNM and NNM, but this activity also depends on soil N and phosphorus (P) availability. We examined how N (25 and 100 kg N ha−1 or 44 and 177 mg N pot−1) and P (10 and 40 kg P ha−1, or 18 and 71 mg P pot−1) fertilisation affected microbial N mineralisation in soil planted with two wheat genotypes (Suntop and 249) varying in root biomass and rhizodeposition. We used a continuous 13CO2 labelling method to track plant C rhizodeposition and a 15N pool dilution technique to investigate GNM. We further assessed NNM by comparing N pools in plant and soil at the start and end of the experiment. We observed increased GNM with increased P fertilisation, likely because of P-induced N limitation stimulating microbial mining for N, particularly at the low level of N fertilisation. N fertilisation did not affect GNM but the higher level of N fertilisation reduced NNM, likely because of increased microbial immobilisation of fertiliser N. Our results suggest that GNM was more sensitive to soil N and P availability than to rhizodeposition between wheat genotypes, although at high N fertilisation, rhizodeposition contributed to reduced NNM, likely because rhizodeposition enhanced microbial N immobilisation. We conclude that the relative availability of N and P in soil should be considered for managing GNM and NNM in soil.

The temperature-dependency of the photosynthetic response to CO2 was measured on apple (Malus domestica cv. Cox’s Orange) trees growing in orchard conditions with differing levels of nitrogen. Leaf nitrogen content varied from 1.7 to 2.2%. Nitrogen affected leaf attributes; larger areas but lower dry weights in high compared with low nitrogen trees. Across all leaf temperatures, higher rates of photosynthesis occurred in high nitrogen trees but rates differed mostly at 10 °C and progressively diminished to 35 °C. Rates of ribulose 1, 5-bisphosphate (RuBP) carboxylation, oxygenation and electron transport increased in a temperature-dependent pattern but nitrogen had no effect on rates at low (

Changes in dominant plant species can influence the net primary production (NPP) via changes in species traits, including nitrogen use efficiency (NUE) and belowground allocation enhancing N uptake, as well as soil N availability. We investigated changes in above- and belowground NPP, N uptake, and NUE in response to changes in soil N in natural forests and plantations, with and without changes in species compositions among the environmental gradient, respectively. In plantations, NPP increased with increasing availability of soil N in the presence of constant NUE and the proportion of belowground NPP to total NPP. However, in natural forests, aboveground, belowground, and total NPP were high for the available middle range soil N. Belowground NPP and the proportion of belowground NPP to total NPP in natural forests was positively related to aboveground NPP. Both belowground NPP and soil N mineralization rates explained stand N uptake rates. These results indicated that belowground allocation might facilitate aboveground NPP with enhancement of N uptake by root allocation. Stand NUE decreased with soil N availability in natural forests and was stable in plantations, and resulted in lower production in natural forests and higher production in plantations under high soil N availability. The community weighted mean (CWM) of N resorption efficiency was positively related to NUE. The CWM of juvenile root growth, as reported previously for planted juveniles, was positively related to belowground NPP allocation. In addition, the ranges of CWMs were broader in natural forests than in plantations. This suggested that the different changes in NPP in response to changes in soil N between natural forests and plantations was due to the changes in leaf and root species traits via changing in species composition among sites. In conclusion, the present study showed that the changes in species specific traits in root growth and leaf N strongly affected the relationship between soil N availability and stand carbon and N dynamics.

N is known to be the most limiting element for vegetation growth in temperate and boreal forests. The expected increases in global temperature are predicted to accelerate N mineralization, therefore incrementing N availability in the soil and affecting the soil C cycle as well. While there is an abundance of C data collected to fulfill the requirements for national GHG accounting, more limited information is available for soil N accumulation and storage in relation to forest categories and altitudinal gradients. The data collected by the second Italian National Forest Inventory, spanning a wide range of temperature and precipitation values (10° latitudinal range), represented a unique opportunity to calculate N content and C/N ratio of the different soil layers to a depth of 30 cm. Boosted Regression Tree (BRT) models were applied to investigate the main determinants of soil N distribution and C/N ratio. Forest category was shown to be the main explanatory factor of soil N variability in seven out of eight models, both for forest floor and mineral soil layers. Moreover latitude explained a larger share of variability than single climate variables. BRT models explained, on average, the 49% of the data variability, with the remaining fraction likely due to soil-related variables that were unaccounted for. Accurate estimations of N pools and their determinants in a climate change perspective are consequently required to predict the potential impact of their degradation on forest soil N pools.

Soil needs to be dried in order to determine water content, soil organic carbon content (SOC) and total nitrogen content (N). Water content is commonly measured using standard methods that involve drying temperatures of 105–110 °C. Recommended drying temperatures differ for the determination of SOC and N. However, at moderate drying temperatures, microbial activity might lead to organic matter mineralisation and nitrification, and thus to an underestimation of SOC and N. Furthermore, low drying temperatures might not dewater soils sufficiently to correctly determine water content or bulk density. Chemical processes such as thermal decomposition and volatilisation might occur at higher temperatures. This raises the question of whether the same sample can be used to determine water content, SOC and N. Further, the effect of drying, especially at different temperatures, on basal respiration of peat soils determined by incubation experiments is so far unknown. Effects of drying temperature might be especially severe for peat soils, which have high SOC and water contents. This study systematically evaluated the effect of different drying temperatures (20, 40, 60, 80 and 105 °C) on the determination of mass loss (proxy for water content), SOC and N over a wide range of 15 different peat soils comprising amorphous, Sphagnum and sedge peat substrate. The investigated peat soils had SOC contents ranging from approximately 16.8–52.5% with different degrees of decomposition. They were thus separated into two ‘peat groups’ (amorphous and weakly decomposed). In a subsequent investigation, an incubation experiment was carried out on a subset of five peat soils to investigate the pre-treatment effect of different drying temperatures on basal respiration. The results showed that amorphous samples should be dried at 105 °C to determine water content. The weakly decomposed peat soils in the study had reliable water contents for drying temperatures above 60 °C. For temperatures below 80 °C, the determined SOC and N were biased by residual water. This could be corrected for weakly decomposed samples, but for amorphous samples only for drying temperatures ≥60 °C. Thus, mineralisation of soil organic matter is likely to take place at lower drying temperatures which are not recommendable especially for amorphous peat prone to high mineralisation rates. This is supported by the results of the incubation experiment: The effect of peat type (amorphous topsoil vs. weakly decomposed subsoil) was greater than the effect of different drying temperatures, which nonetheless affected respiration rates. The differences between all five soils were consistent, irrespective of the drying temperature. Thus, incubation experiments might be possible using peat dried at moderate temperatures. © 2021 The Authors

Despite an abundance of research on the biomass response to nitrogen fertilizer in established switchgrass fields, there is a dearth of knowledge of the first year response in switchgrass, and nothing yet available for big bluestem. Based on differences in their C4 photosynthetic subtypes, big bluestem may show greater photosynthetic (PNUE) and above-ground whole plant nitrogen use efficiency (NUE) over switchgrass. Here we report the first year biomass response to nitrogen fertilizer for two cultivars of upland switchgrass and three cultivars of big bluestem. We first performed a greenhouse experiment with four nitrogen treatments ranging from 1.5 dmol m−3 to 16 mol m−3 aqueous nitrogen solutions. Here we measured PNUE mid-way through the experiment and harvested plants green to measure above-ground whole plant NUE. We also compared these cultivars at two field sites with contrasting soil nitrogen content. At low soil nitrogen, big bluestem “Prairie View” achieved both the highest NUE in the greenhouse and greatest biomass in the field. Switchgrass produced significantly more biomass than big bluestem at the high nitrogen field site, whereas biomass production was similar for both species at the low nitrogen field site. Although both species responded positively to increasing soil nitrogen, switchgrass did increasingly more so compared to big bluestem, with a 20% greater biomass stimulation in the greenhouse from low to high soil nitrogen. Net CO2 assimilation rates showed a similar response with biomass production to the nitrogen treatments, allowing switchgrass “Sunburst” to achieve a slightly greater PNUE compared to big bluestem “Prairie View”.

Arbuscular mycorrhizal fungi (AMF) play an important role in soil nitrogen cycling. However, the effect of AMF on soil N2O emission and its underlying mechanisms remain elusive. Here, we conducted a Bayesian meta-analysis to determine whether AMF has an N2O mitigation potential and what are the potential mechanisms. We found that AMF significantly decreased soil N2O emission (with an effect size of −0.90) and increased microbial biomass nitrogen and plant biomass compared to the non-AMF treatment. The effect size of soil water content and plant biomass nitrogen showed significantly positive and negative correlations with the effect size of soil N2O emission. We propose a conceptual framework with three potential mechanisms that AMF could affect soil N2O emission for further work.

Rice or Oryza sativa L. is the staple food of Indonesian society. Currently, the demand for rice in Indonesia is increasing, while the level of rice production is decreasing. Therefore, alternative technologies are needed to assist the community in increasing rice production. One of the important factors in the growth of rice is the quality of the soil that contains high levels of nitrogen for photosynthesis, protein formation, acid formation, and accelerating plant growth. This research was applied for soil nitrogen mapping with a smart prototype using the TCS3200 sensor combined with Naive Bayes algorithm and GIS (Geographical information systems). This system is carried through the Wemos D1 Mini microcontroller of TCS3200 sensor for reading data and sending the data to the web ceerduad.com . Geographical information systems (GIS) was developed to mapping area and to obtain training data for the Naive Bayes Algorithm which the researcher took 20 soil samples in Lendah sub-district. From the experiment results, a prototype of soil nitrogen content using the TCS3200 sensor can measure soil nitrogen levels with an accuracy of 87.5% and sending the sensor data to the web server. Implementation of GIS in this research was successfully mapping low, medium, and high levels of nitrogen.

Proteases play a crucial role in the soil nitrogen (N) cycle by converting protein to oligopeptides and amino acids. They are often viewed as a bottleneck in terrestrial N cycling; therefore, it is vital that we have robust methods for evaluating protease activity in soil to understand global patterns of protease activity. In response to this, several laboratory-based protease methods have been developed and subsequently modified. However, the validity of these different approaches remains largely unknown. In addition, the lack of standardised protocols makes it difficult to compare protease activity across studies. In this systematic synthesis, we critically evaluate the most common colorimetric and fluorimetric methods used to measure soil protease activity involving 680 independent studies and 1,491 individual assays. To investigate the key regulators of soil protease activity, we collected associated metadata on environmental (mean annual temperature and soil pH) and methodological (assay temperature and pH) factors. Protease activity measured with colorimetric substrates were centred around ca. 1000 nmol product g−1 h−1, whilst rates measured with fluorimetric substrates were lower at ca. 100 nmol product g−1 h−1. Fluorimetric and colorimetric substrates target different proteases which are likely to have different abundances, kinetic parameters, catalytic mechanism or ecological function suggesting why colorimetric substrates have a higher protease activity. We found soil protease activity varied widely around these peaks, likely due to a wide range of environmental or methodological factors that may influence/bias the result. We present the following recommendations for measuring soil protease activity: 1) report assay conditions and soil characteristics, particularly pH and temperature, 2) conduct the assay at either field or optimised pH and temperature conditions, and, 3) check that measurements lie between 0 and 5000 nmol product g−1 h−1. This will help reduce the variation in soil protease activity measurements due to methodological bias and improve reporting of abiotic and biotic associated data. Altogether this will lead to a better understanding of the ecological drivers of protease activity and refine parameterisation of global biogeochemical models.

Nitrogen (N) is one of the primary limiting elements in terrestrial ecosystems, and vegetation restoration has been regarded as an effective way to increase soil total nitrogen (STN) stocks. Despite compelling evidence indicating that mixed plantations can demonstrate higher vegetation productivity and carbon (C) sequestration capacity than monocultures, the effects of mixed plantations on STN stocks remain unclear. Therefore, we conducted a meta-analysis of 128 observations from 49 peer-reviewed articles across the Loess Plateau of China to evaluate the impact of different afforestation models (i.e., mixed plantations and monocultures) on the dynamics of STN stocks in mineral soil (0–30 cm). The results showed that, compared with monocultures, mixed plantations significantly increased STN stocks by 19.3%. For different mixed types, tree-shrub mixed plantations increased more STN stocks than tree-tree mixed plantations. However, the positive effect of mixed plantations on STN stocks was significant > 20 years after stand establishment. Moreover, for areas with steeper slope (>25°), lower elevation (

The long-term sustainability of rice-wheat system (RWS) requires robust interventions such as recycling of rice straw (RS) to improve soil health and minimal impact on environment. Therefore, the dynamic adjustments in fertilizer-N application with RS incorporation that impacts crop productivity, N availability, N use efficiency (NUE) and soil enzymatic activity are required. We investigated the long-term impacts of four rates of RS incorporation (0, 5.0, 7.5 and 10.0 Mg ha−1 year-1; RS0, RS5.0, RS7.5 and RS10.0) and four rates of fertilizer-N (0, 90, 120 and 150 kg N ha-1; N0, N90, N120 and N150) application in different combinations on N dynamics in soils, enzyme activity, crop yields and NUE. Results revealed that fertilizer-N application significantly (p

Changes in land use can result in soil erosion and the loss of soil organic carbon (SOC). However, the individual contribution of different land use types on SOC variability as well as the combined impacts of land use and soil erosion are still unclear. The aims of the present study were to: (1) evaluate soil erosion and SOC contents under different land use types, (2) identify the influences of soil depth and land use on SOC content, and (3) determine the contribution of land use and soil erosion on SOC variability. We assessed the SOC and total soil nitrogen (TSN) contents under three types of land use in the dry-hot valley in southern China. Caesium-137 (137Cs) and excess lead-210 (210Pbex) contents were also measured to determine soil-erosion rates. Land use was found to significantly affect soil erosion, and erosion rates were higher in orchard land (OL) relative to farmland (FL), which is in contrast with previous study results. SOC and TSN contents varied significantly between the three land use types, with highest values in forest land (FRL) and lowest values in OL. SOC was found to decrease with decreasing soil depth; the highest rate of reduction occurred in the reference site (RS), followed by FRL and FL. The interaction between soil erosion and land use significantly impacted SOC in the soil surface layer (0–12 cm); the direct impact of soil erosion accounted for 1.5% of the SOC variability, and the direct or indirect effects of land use accounted for the remainder of the variability. SOC content in deep soil was mainly affected by factors related to land uses (89.0%). This quantitative study furthers our understanding on the interactive mechanisms of land use and soil erosion on changes in soil organic carbon.

No tillage (NT) is a common conservation tillage practice used to enhance soil C sequestration. However, to date, the understanding regarding the impact of NT on soil nitrogen (N) transformations remains limited. Here, we used 15N tracing to investigate the effects of 14 years of NT on the gross N transformation rates in black soil in China. We also evaluated the risk of N loss from soil in NT systems compared to that treated with conventional tillage (CT). The gross N mineralization rates in the top 5 cm of NT-treated soil was more than three times higher than the rates in the 5–15 cm layer (P

The addition of organic amendments with a low Carbon:Nitrogen (C:N) ratio to restore degraded soils may increase the emission of greenhouse gases and affect the storage of these elements in the topsoil. Our objectives were to evaluate the effect of the addition to the surface of organic amendments to a non-tilled and non-cultivated soil, compared with the addition of cover crop residues, with respect to: (i) N2O emissions and their relationships with soil variables, (ii) C and N content in the topsoil. We conducted an experiment during two consecutive years in Paraná, Argentina (−31° 50.9′ S; −60°32.3′ W). Treatments included the addition of organic amendments (composted poultry litter and poultry manure) and cover crops residues [wheat (Triticum aestivum L.) and white sweet clover (Melilotus albus Medik.)]. Soil variables that are most commonly reported as critical for N2O emissions, i.e. soil nitrates (N-NO3) and water filled pore space (WFPS), showed more differences among treatments in Year 1 than in Year 2, which was associated with a higher frequency and amount of rainfall. N2O flux ranged between 0.12–50 μg N m−2d−1 (Year 1) and 0.62-13.7 μg N m−2d−1 (Year 2). N2O flux was significantly associated with WFPS in both Years (P

The Yellow River valley is one of the three largest cotton production areas in China. An experiment was performed in cotton fields of Anyang, China from 2013 to 2014 to investigate the effects of nitrogen (N) application rate and the ratio between basal and topdressing N fertilizer on N balance in a soil-plant system, N use efficiency, and cotton yield. Five N application rates as treatments were applied with the same split application ratio. Half of the N (50% basal fertilizer) was applied at pre-planting and the other half (50% topdressing fertilizer) at the initial flowering stage. These treatments were: zero N (N0, control), 90 kg N ha −1 (N90 (5/5)), 180 kg N ha −1 (N180 (5/5)), 270 kg N ha −1 (N270 (5/5), a reduced N rate), and 360 kg N ha −1 (N360 (5/5), a conventional N rate). Additional 2 split application ratios as treatments were applied with the same N rate of 270 kg N ha −1 . The split application ratios between basal N and topdressing N were 30%:70% (N270 (3/7)) and 70%:30% (N270 (7/3)). Results demonstrated that soil NH 4 -N content in the 0–60 cm layer and NO 3 -N content in the 0–20 cm layer increased with increased N rate at the squaring and boll-opening stages and then decreased to lower levels at the initial flowering and harvest stages. Soil NO 3 -N content in the 20–60 cm layer after the initial flowering stage increased with the increase of topdressing N rate. Soil apparent N surplus varied at different growth stages, while the soil apparent N surplus over the entire growth period exhibited a positive relationship at N rates over 180 kg ha −1 . Seed cotton yield of N270 (3/7) was the highest of all treatments. Plant N uptake, N agronomic efficiency, and apparent N recovery efficiency of N270 (3/7) were significantly higher than those of N270 (5/5) and N270 (7/3) in both growing seasons. These suggest both economic and ecological benefits in cotton production in the Yellow River valley could be created, by appropriately reducing total N application rate and increasing the ratio of topdressing to basal N fertilizer at the initial flowering stage.

Fertilizer inputs affect plant uptake of native soil nitrogen (N), yet the underlying mechanisms remain elusive. To increase mechanistic insight into this phenomenon, we evaluated the effect of fertilizer addition on mineralization (in the absence of plants) and plant uptake of native soil N. We synthesized 43 isotope tracer (15N) studies and estimated the effects of fertilizer addition using meta-analysis. We found that organic fertilizer tended to reduce native soil N mineralization (−99 kg ha−1 year−1; p = 0.09) while inorganic fertilizer tended to increase N priming (58 kg ha−1 year−1; p = 0.17). In contrast, both organic and inorganic fertilizers significantly increased plant uptake of native soil N (179 and 107 kg ha−1 year−1). Organic fertilizer had greater effect on plant uptake than on mineralization of native soil N (p

The importance of di-nitrogen (N2) production via aerobic pathways has been verified in a significant number of pure microbial strains. However, to date there are no reports confirming this in situ. In this study, we extracted micro-biota from three typical upland soils with variable properties and incubated them under aerobic and anaerobic conditions, with nitrate, to investigate whether N2 production occurred via aerobic pathways and the relative importance of it when compared with the N2 production via anaerobic pathways. Our results showed that N2 can be produced in soil extracts under aerobic conditions, and that the N2 produced via aerobic pathways equated to 29–51% of that produced via anaerobic pathways. Thus N2 production via aerobic pathways may play a significant role in soil nitrogen (N) cycling. Our results demonstrate that an O2 deficit may not to be a requirement for converting reactive N back into inert N2, and consequently this process may be more widespread in upland soils than currently thought.

Plant phenolic compounds (phenylpropanoids) act as defense chemicals against herbivores and can mediate ecosystem processes. Tropospheric ozone (O3) pollution alters concentrations of plant phenolics; however, little is known about how these phytochemicals respond to different levels of O3 exposure. Here, we investigated the effects of five different O3 exposure levels on foliar concentrations of phenylpropanoids (53 compounds in total) and antioxidative capacity in hybrid Populus (Populus euramericana cv. ‘74/76’) saplings grown in the presence of high or low soil nitrogen (N) load. Increasing O3 exposure initially increased and then decreased total concentrations of phenolic compounds, revealing a biphasic exposure-response profile (hormetic zone: 1.1–36.3 ppm h AOT40). This biphasic response pattern was driven by changes in a subset of phenylpropanoids with high antioxidative capacity (e.g. condensed tannins) but not in phenolics with low antioxidative capacity (e.g. salicinoids). The O3 exposure-response relationships of some phenylpropanoids (e.g. flavonoids and chlorogenic acids) varied in response to soil N, with hormesis occurring in high N soil but not in low N soil. Collectively, our findings indicated that plant phenolic compounds exhibit nonlinear responses to increasing O3 exposure, and that the responses vary in relation to phenolic compound class, antioxidative capacity, and soil nitrogen conditions. Our findings further suggest that the impact of O3 on ecological processes mediated by phenolics will be concentration-dependent, highlighting the complexity of the ecological effects of ground-level O3 pollution.

Microbes simultaneously drive multiple functions (multifunctionality) that support human well-being. However, the structure and function of microbial communities and their impact on soil multifunctionality following grassland afforestation remains unknown, thus hindering our ability to formulate conservation policies. We compared soil bacterial and fungal communities, soil abiotic properties, and soil nitrogen (N) function and multifunctionality in the afforested sites that were previously grassland, on a subtropical plateau in China. We also explored the degree to which the niche complementarity effect and the selection effect of microbes are linked to soil N function and multifunctionality. We found that afforestation of grassland significantly decreased pH, available N concentration and density, and soil multifunctionality. However, afforestation significantly increased C (carbon) limitation and shifted soil microbes from being limited by N to, instead, being co-limited by N and P (phosphorus). The significant decrease in available N was primarily driven by soil microbes. In shaping soil N availability, the effect of bacterial diversities was stronger than that of fungal diversities, and the effect of fungal functional diversities was stronger than that of bacterial functional diversities. The effect of functional diversities was greater than that of all the significant changes in the functions and, also, the significant changes in the N-related functions. These results further emphasized that functional niche complementarity dominated soil N availability. In addition, bacterial taxonomic diversities showed positive effects of niche complementarity on soil multifunctionality; ultimately, the losses in bacterial taxonomic diversities derived from the increases in C limitation and the shifts in NP limitation combined to impaired soil multifunctionality. Our results suggested that the optimization of soil microbial functional diversities might increase soil N availability, and that minimizing losses of soil microbial taxonomic diversities by optimizing soil abiotic environments might improve soil multifunctionality.

Yield gaps of ∼50 % of water limited yield potential occur in wheat globally. Nitrogen (N) deficiency frequently contributes to the gap, but it is difficult to predict an appropriate rate of N to apply because of uncertainty about the forthcoming season and hence water limited potential yield and crop N requirements. We investigated closing the water limited yield gap attributable to N supply by maintaining a “bank” of soil mineral N that is nonlimiting for wheat yields in most seasons. The yield, loss of NO3−-N in leaching and denitrification, and gross margins of wheat crops were simulated at four Australian locations with contrasting soil types and potential yields, in response to N inputs calculated by reference to N banks ranging from 50 to 400 kg N ha-1, the Yield Prophet® decision support tool and the national average N rate. The N bank providing best yields at each location was close in amount to the long-term average rate calculated with Yield Prophet®. Compared to the national average rate of N fertiliser application (45 kg N ha-1), the highest-yielding N bank treatment on average increased the amount of N applied by 3–234 kg N ha-1, the fraction of water limited potential yield by 0.0 to 0.61, and gross margins by AUD 0–1,026 ha-1. Combined losses of N to the environment in NO3−leaching and through denitrification in these strategies also increased but by a disproportionately small amount compared to the increase in the amount applied (-3 to 8.5 kg N ha-1). These losses were relatively insensitive to the amount of N applied at three of the four locations; at the fourth location large episodic losses could occur from sandy soil despite low rainfall when the N bank exceeded water limited potential yield. The N bank approach to determining fertiliser rate has potential to sustainably reduce the yield gap where the target amount is matched to average site-specific yield potential.

In soil, ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) are regarded as key factors mediating nitrous oxide (N2O) production and emission. However, there are scarce reports about the effect of film mulching on ammonia oxidizers, and the biological nitrification process of N2O emission is unclear. This study was based on potato field experiments under different mulching films, including polyethylene mulching film (PM), transparent degradable mulching film (TDM), black degradable mulching film (BDM), and bare land (CK). AOB and AOA abundances were estimated using real-time PCR, and their diversity and community structure were measured using high-throughput sequencing. Result revealed that the total N2O emission from CK was 12.32%–41.03% higher than that from film mulching soil. Under film mulching, according to total N2O emission from soil and N2O concentration in soil treatments were ordered as PM > BDM > TDM, and N2O production was closely correlated with copy numbers of the amoA gene. BDM significantly increased the number of amoA-AOB gene copies (P

Previous studies on the source apportionment of soil total nitrogen (TN) and total phosphorus (TP) mainly focused on specific spatial point sites and the closely related information such as soil-type map was seldom used. Moreover, traditional geostatistical models are usually sensitive to outliers. To address these problems, this study first proposed robust residual kriging (RRK) with soil-type data as auxiliary information to increase the spatial prediction accuracies for TN and TP in topsoil (0–20 cm) in Jintan County, China. Then, the spatial distribution patterns of the background concentrations of soil TN and TP were quantitatively assessed based on profile samples (80–100 cm) and the soil-type map. Last, the spatial distribution patterns of exogenous net inputs of TN and TP in topsoil and the corresponding contribution ratios were further calculated. Model comparisons showed that the relative improvement (RI) accuracies of RRK and residual kriging (RK) over the traditionally-used ordinary kriging (OK) were 23.91% and 15.22% for soil TN and 24.14% and 20.69% for soil TP, respectively. The results of the source apportionment indicated that (i) the exogenous net inputs of TN and TP had similar spatial distribution patterns, with the low inputs mainly in the west and high inputs mainly in the northeast and east of the county; (ii) high contribution ratio of exogenous net input of TN (≥67%) in topsoil was mainly located in the north, southeast, and middle of the study area, and the area with the contribution ratio over 70% is 294.16 km2, covering 30.16% of the area of the county; (iii) high contribution ratio of exogenous net input of TP (≥53%) in topsoil was mainly located in the north, northeast, and southeast of the county, and the area with contribution ratio over 70% is 24.35 km2, covering 2.50% of the area of the county. These results provided more accurate spatial decision support for effectively regulating TN and TP in topsoil.

Degradation by wind erosion is detrimental to both soil and land quality in arid regions. This study was conducted to investigate the effectiveness of some organic amendment - poultry manure (PM), farmyard manure (FYM) and rice husk (RH) and were applied on the sandy soil surface at 1 and 3 cm thickness and control (no treatment; C) to make clear the sand particles stabilization. Total soil nitrogen, organic carbon (OC), and pH in the PM and FYM treatments exceeded those in the RH treatment. Soil hardness in the PM compost was 6.7, 1.4, and 2.7 times the mean determined in the control, FYM and RH, respectively, whereas CaCO3 in the PM treatment was 56 and 69% higher than the levels in FYM and RH, respectively. Soil hardness varied in the order of PM 3 cm > PM 1 cm > FYM 1 cm > FYM 3 cm > RH 1 cm > RH 3 cm > C. The erodible fraction (0.85–1.0 mm) decreased linearly with increase in soil hardness (R2 > 0.9), OC, CaCO3. Farmyard manure and PM composts decreased the erodible fractions by up to 5 and 15%, respectively. Surface application of PM compost is an effectively stabilized the sand particles during this study.

Little is known about the effect of phosphorus (P) on plant biomass production or soil nitrogen (N) in alpine meadows. We conducted a four-year P addition experiment to assess the responses of plant biomass, plant N and P concentration, soil N availability, and microbial activities to a multi-level P enrichment (0, 2.5, 5, 10, 15 g P m(-2) year(-1)) in an alpine meadow on the Qinghai-Tibetan Plateau, China. The P treatments increased plant P and soil available P, but had no effect on plant biomass or plant N, soil available N, NH4+-N, NO3- -N, and soil microbial activity during three consecutive sampling years. These results suggest that P is not a limiting nutrient for plant growth and not a key factor on regulating N cycling in this alpine meadow. Further research is needed to identify the role of P in driving vegetation biomass production and soil N dynamics and clarify whether vegetation and soil characteristics on alpine meadows are sensitive to P enrichment. (C) 2016 Elsevier B.V. All rights reserved.

Soil alkali-hydrolyzable nitrogen, which is sensitive to N fertilization rate, is one of the indicators of soil nitrogen supplying capacity. Two field experiments were conducted in Dongtai (120°19″ E, 32°52″ N), Jiangsu, China in 2009 and Dafeng (120°28″ E, 33°12″ N), Jiangsu province, China in 2010. Six nitrogen rates (0, 150, 300, 375, 450, and 600 kg ha− 1) were used to study the effect of N fertilization rate on soil alkali-hydrolyzable nitrogen content (SAHNC), subtending leaf nitrogen concentration (SLNC), yield, and fiber quality. In both Dongtai and Dafeng experiment station, the highest yield (1709 kg ha− 1), best quality (fiber length 30.6 mm, fiber strength 31.6 cN tex− 1, micronaire 4.82), and highest N agronomic efficiency (2.03 kg kg− 1) were achieved at the nitrogen fertilization rate of 375 kg ha− 1. The dynamics of SAHNC and SLNC could be simulated with a cubic and an exponential function, respectively. The changes in SAHNC were consistent with the changes in SLNC. Optimal average rate (0.276 mg day− 1) and duration (51.8 days) of SAHNC rapid decline were similar to the values obtained at the nitrogen rate of 375 kg ha− 1 at which cotton showed highest fiber yield, quality, and N agronomic efficiency. Thus, the levels and strategies of nitrogen fertilization can affect SAHNC dynamics. The N fertilization rate that optimizes soil alkali-hydrolyzable nitrogen content would optimize the subtending leaf nitrogen concentration and thereby increase the yield and quality of the cotton fiber.

A metabolism stall study examined the fate of dicyandiamide (DCD) administered to dairy cows by either oral drenching or via a supplementary feed source (pasture silage) as a practical method to achieve targeted DCD excretion in individual urinations to reduce nitrogen (N) losses from grazed pasture systems. The study consisted of two experiments; firstly, lactating dairy cows were orally administered an aqueous solution of DCD at two rates (3 or 30 g cow −1 day −1 ) to examine the output in urine, faeces and milk, and secondly, non-lactating dairy cows were fed pasture silage amended with fine-crystalline DCD powder (30 g DCD cow −1 day −1 ) to investigate concentrations of DCD in excreta (urine and faeces) and the subsequent inhibition of nitrification of urinary-N in soil. Administration of DCD to lactating dairy cows in solution resulted in DCD being predominantly recovered in urine at 61% relative to 19% in faeces and 1.2% in milk (SEM 2.3, 1.0 and 0.08, respectively). Increased DCD administration rate led to higher ( P

Clay minerals can fix high amounts of ammonium in non-exchangeable form, which can be of management importance when some ammonium applied with fertilisers is sequestered and not available to the crop. Non-exchangeable ammonium can be released slowly and increase soil N availability. The percentage of ammonium fixed depends, among other factors, on the ammonium dose applied. We applied increasing amounts of ammonium to three soils and then measured (after 48 h) the soil equilibrium concentration of non-exchangeable, exchangeable, and soluble ammonium. At a 70 mg NH 4 –N kg − 1 dose, non-exchangeable ammonium measured 60, 24, and 17% on the three soils, while at 2800 mg NH 4 –N kg − 1 the fixation percentage decreased non-linearly to 12, 4, and 5%. Ammonium equilibrium concentrations in non-exchangeable, exchangeable, and soluble fractions as a function of ammonium applied were simulated with two innovative analytically-solved models using two Langmuir equations, one for each pair of pools. Both models predicted well the three ammonium fractions in all soils, with average relative root mean squared errors ranging from 2 to 5%. Sensitivity analysis demonstrated the importance of all four model parameters; however, to extend the model to other soils requires measurement of two parameters — cation exchange capacity and maximum fixation of ammonium in non-exchangeable form. The other two parameters are equilibrium constants that vary little among soils, according to our preliminary results. Therefore, to simplify model use, averaged optimised constant values on multiple soils might suffice. Additional experiments on more soils are needed to verify this hypothesis.

With ongoing global climate change and human activities, increasing desertification plays a predominant role in increasing soil nutrient losses. Soil nitrogen (N) is the essential limiting nutrient supporting plant growth and evaluating soil nutrient content, especially in desert ecosystems. N microbial processes will ultimately restore and maintain the balance in the soil N cycle, but the damage caused by desertification to soil N functional microorganisms associated with N supply, transformation, and loss is poorly understood. We examined changes in soil N and N functional gene (NFG) abundances within vertical profiles (i.e., soil depths of 0–100 cm) throughout the desertification process. We found that the abundance of N functional genes (NFGs) (except the N-fixation gene) decreased during the desertification process, almost all NFGs were attenuated along the vertical profiles, and available phosphorus (AP), soil water content (SWC) and pH were the best explanatory variables. The sums of (AOA + AOB) (associated with available N transformation) and (nirK + nirS + qnorB + nosZ) (associated with N loss) significantly decreased as desertification progressed, leading to decreased N transformation and loss potential. The (nifH + chiA) associated with available N supply increased along the desertification process gradient, suggesting enhanced potential for the acquisition available N. The increased ratio of (nifH + chiA + AOA + AOB)/(nirK + nirS + qnorB + nosZ) (associated with available N storage) collaboratively contributed to enhanced available N storage potential throughout the desertification process. Our results lay the foundation for better understanding the distinct responses of NFGs to desertification and the process through which they ultimately regulate available N storage in the degraded soils of desert ecosystems.

Soil nitrogen (N) availability, which is crucial to plant growth, largely relies on the turnover of soil organic N into inorganic N through mineralization. However, the patterns and drivers of global soil N turnover rates (NTR) have not been carefully examined so far. We compiled a dataset that consists of 1175 observations from 159 published articles across various terrestrial ecosystems in the world. Our analysis of this dataset showed that changes in soil NTR successfully predicted global NH4+–N content, a key indicator of soil N availability. Our analysis also revealed a clear latitudinal pattern of soil NTR, which was high in low latitude but low in high latitude. Soil NTR was greater in croplands than grasslands and wetlands. The dominant driving variables were mean annual temperature which accounted for 23% of the total variation in soil NTR. Soil clay content explained 15% of the total variation and it strongly inhibited soil NTR. However, the key driver in soil NTR differed with ecosystem type, i.e. soil microbial biomass in croplands, clay content in forests and grasslands, and soil C:N ratio in wetlands. This study highlights the importance of climatic factors and soil properties on soil NTR, which should be integrated into biogeochemical models to better predict the changes of soil N availability at the global scale.

Highlights • Genotype by Environment Interaction (GEI) makes it difficult for breeders and growers to select stable, high yielding varieties across different environments thereby reducing the effectiveness of the selection process. • Determining the magnitude of GEI and the stability of varieties can be challenging, as such, crop models can be employed to complement this process. • Dynamic models that can simulate the response of growth and development of crops to varying abiotic environmental factors have the potential to explain yield differences due to temporal and spatial variability. • Crop Simulation Models were used to complement multi environment trials (METs) with a view to enhancing selection of high yielding varieties across multiple locations. • The model simulations matched actual observations and produced similar ranking, indicating that properly calibrated and evaluated CERES-Maize model can complement METs., When properly calibrated and evaluated, dynamic crop simulation models can provide insights into the different components of genotype by environment interactions (GEIs). Modelled outputs could be used to complement data from multi-environment trials. Field experiments were conducted in the rainy and dry seasons of 2015 and 2016 across four locations in maize growing regions of Northern Nigeria using 16 maize varieties planted under near-optimal conditions of moisture and soil nitrogen. The CERES-Maize model was calibrated using data from three locations and two seasons (rainy and dry) and evaluated using data from one location and two seasons all in 2015. Observed data from the four locations and two seasons in 2016 was used to create eight different environments. Two profile pits were dug in each location and were used separately in the simulations for each environment to provide replicated data for stability analysis in a combined ANOVA. The effects of the environment, genotype and GEI were highly significant (p = 0.001) for both observed and simulated grain yields. The environment explained 67 % and 64 % of the variations in observed and simulated grain yields respectively. The variance component of GEI (13 % for observed and 15 % for simulated) were lower but still considerable when compared to that of genotypes (19 % for observed and 21 % for simulated). From the stability analysis of the observed and simulated grain yields using six different stability models, three models (ASV, Ecovalence, and Sigma) ranked Ife Hybrid as the most stable variety. The slope of the regression (bi) model ranked Sammaz 11 as the most stable variety, while the Shukla model ranked Sammaz 28 as the most stable variety. Long-term seasonal analysis with the CERES-Maize model revealed that early and intermediate maturing varieties produce high yields in both wet and dry savannas, early and extra-early varieties produce high yields only in the dry savannas, while late maturing varieties produce high yields only in the wet savannas. When properly calibrated and evaluated, the CERES-Maize model can be used to generate data for GEI and stability studies of maize genotype in the absence of observed field data.

The presence of small burrowing herbivores often cause extensive disturbance to the grassland soil nutrient stocks. This study investigated the effect of small burrowing herbivore presence, the plateau pika (Ochotona curzoniae), and variation in disturbance intensity on soil nitrogen stocks at five alpine meadow sites. Disturbed plots occupied by plateau pikas consist of burrows and their associated bare soil patches in a matrix of continuous alpine meadow. The percentage of the bare soil area in a disturbed plot was used as a proxy for disturbance intensity of plateau pikas. This study showed that the soil total nitrogen stock was lower of bare soil than vegetated soil within disturbed plots, while ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), inorganic nitrogen and ammonium nitrogen/nitrate nitrogen ratio (ANR) were higher in bare soil than vegetated soil within the disturbed plots. This study further showed that the NH4+-N, inorganic nitrogen and ANR of disturbed plots were higher than those of undisturbed plots, whereas soil total nitrogen and the NO3−-N stock was not different between disturbed plots and undisturbed plots. This study also showed that the soil total nitrogen, NH4+-N and inorganic nitrogen stocks of disturbed plots were higher at intermediate disturbance intensities of plateau pikas, whereas the NO3−-N stock and ANR were not related to disturbance intensities. These results suggest that the NH4+-N and inorganic nitrogen stocks were higher in the presence of plateau pikas, and intermediate disturbance intensity of plateau pikas was beneficial for soil quality due to higher soil total nitrogen, NH4+-N and inorganic nitrogen stocks. The findings of this study present a possible approach for estimating how the presence of a small burrowing herbivore influences grassland soil nitrogen stock.

Soil nitrogen (N) leaching is recognized to have negative effects on the environment. There is a lack of studies on different simultaneously occurring drivers of environmental change, including changing rainfall and N deposition, on soil N leaching. In this study, a two factorial field experiment was conducted in a Korean pine forest with the following four treatments: 30% of throughfall reduction (TR), 50 kg N ha−1 yr−1 of N addition (N+), throughfall reduction plus N addition (TRN+) and natural forest (CK). The zero-tension pan lysimeter method was used to assess the response of soil N leaching loss to manipulated N addition and throughfall reduction. The results showed that the soil N leaching loss in natural forest was 5.0 ± 0.4 kg N ha−1yr−1, of which dissolved organic nitrogen (DON) accounted for 48%. Compared to natural forest, six years of N addition (NH4NO3, 50 kg N ha−1 year−1) significantly (P

Changes in rainfall patterns can affect the soil nitrogen (N) cycles. Most studies have focused on the effect of the amount of rainfall, but the effect of the frequency of rainfall has rarely been considered. In this study, we conducted a field experiment in the Zoige alpine wetland that examined two levels of the amount of rainfall, i.e. 100% or 70% of the natural amounts of rainfall. In addition, we examined three frequencies of rainfall events. First was the natural interval, while the second and third were increases of 50% and 100% of the inter-rainfall dry periods based on the natural interval of the rainfall events, respectively. We found that the amount and frequency of rainfall had significant interactive effects on N mineralization, and thus influenced the concentration of mineral N in the Zoige alpine wetland. The reduction of the rainfall amount significantly increased N mineralization rate, NO3−-N concentration and mineral N stock in the high frequency treatment, and N mineralization rate, decreased them in the low frequency treatment. The variation of the soil NH4+-N, NO3−-N, and mineral N stock increased with the reduction in the rainfall frequency and the increase in the soil depth. Thus prolonged drought (low frequency of rainfall) and reduced rainfall due to future climatic change may decrease the mineral N concentration and N mineralization rate in Zoige alpine wetland, which may probably have a profound impact on the alpine wetland ecosystem.

Reserves in cotyledons and nutrients in soil are essential for the early development of seedlings of oaks. However, much less is known to what extent the reserves in seeds and/or soil nutrients contribute to seedling development and growth at early stages, especially at multi-species level. We carried out an indoor experiment in which the soil was enriched in 15N to quantify N uptake and its distribution in the seedlings of five red and white oak species. Dry masses of seedlings did not vary significantly with N fertilization rates, reflecting the low morphological and physiological plasticity of oak seedlings to soil fertility. However, dry masses of roots of white oak species were much higher than those of red oak species. Soil-derived N incorporated into the seedlings of the five oak species increased with seedling growth and enhanced 15N fertilization rates. Soil-derived N in the seedlings of white oak species was much higher than those of red oak species. Acorn-derived N in seedlings decreased with N fertilization rates, implying that acorn N mobilization can be accelerated under low soil nutrient level. We found higher soil N/acorn N ratio in the seedlings of white oak species than those of red oak species, indicating the rapid uptake of soil N in the seedlings of white oak species. Acorn N rather than soil N played a crucial role in supporting oak seedling development and growth at the early stage. Our results provide insight into the role of acorn N and soil fertility to 1-year oak seedlings and have great implication for forest fertilization and management.

Biogeochemical models are useful tools for integrating the effects of agricultural management on GHG emissions; however, their development is often hampered by the incomplete temporal and spatial representation of measurements. Adding to the problem is that a full complement of ancillary measurements necessary to understand and validate the soil processes responsible for GHG emissions is often not available. This study presents a rare case where continuous N 2 O emissions, measured over seven years using a flux gradient technique, along with a robust set of ancillary measurements were used to assess the ability of the DNDC model for estimating N 2 O emissions under varying crop-management regimes. The analysis revealed that the model estimated soil water content more precisely in the normal and wet years (ARE 3.4%) than during the dry years (ARE 11.5%). This was attributed to the model’s inability to characterize episodic preferential flow through clay cracks. Soil mineral N across differing management regimes (ARE 2%) proved to be well estimated by DNDC. The model captured the relative differences in N 2 O emissions between the annual (measured: 35.5 kg N 2 O-N ha −1 , modeled: 30.1 kg N 2 O-N ha −1 ) and annual-perennial (measured: 26.6 kg N 2 O-N ha −1 , modeled: 21.2 kg N 2 O-N ha −1 ) cropping systems over the 7 year period but overestimated emissions from alfalfa production and underestimated emissions after spring applied anhydrous ammonia. Model predictions compared well with the measured total N 2 O emissions (ARE −11%) while Tier II comparison to measurements (ARE −75%) helped to illustrate the strengths of a mechanistic approach in characterizing the site specific drivers responsible for N 2 O emissions. Overall this study demonstrated the benefits of having near continuous GHG flux measurements coupled with detailed ancillary measurements towards identifying soil process interactions responsible for regulating GHG emissions.

The method to estimate the Gross Nitrogen Budget proposed by Eurostat and the OECD was developed under the assumption of no changes in soil nitrogen stock, due to the lack of available data. We estimated the national and regional nitrogen budgets of agriculture in Turkey, calculated according to the recommended methodology at the level of administrative regions. Results suggest that changes in soil nitrogen stocks are likely for some regions. In such cases, the method warns that its estimated indicators (gross nutrient surplus and nitrogen use efficiency (NUE)) are not valid. We propose two different approaches to improve the Eurostat/OECD method, based on assumptions of minimum and maximum NUE, and on regressing the N-input and N-output relationship for regions without obvious soil nitrogen stock changes. Our results show that both approaches give reasonable results for all regions, including those for which the Eurostat/OECD method failed. The results also suggest that soil nitrogen accumulates in some regions and depletes in others. Results give a range of 6–93 kg N ha −1 yr −1 (mean 35 kg N ha −1 yr −1 ) for the Gross Nitrogen Surplus, and a range of 49–82% (mean 62%) for the NUE.

The usefulness of the C/N ratio as an indicator of the decomposability of organic matter in forest soil was assessed. The assessment was based on the relationship between the C/N ratio and the contents of soil organic carbon (SOC), soil nitrogen (total N), dissolved total organic carbon (DTOC) and dissolved inorganic nitrogen (DIN). SOC, total N, DTOC and DIN were determined in soils sampled in coniferous and coniferous–deciduous forest sites from genetic horizons of 48 soil profiles. The variability of the above soil parameters was determined and the correlation between these parameters and the C/N values were calculated. It was found that the C/N ratio in soil was shaped by the difference in the mobility of both elements, whereas the decrease in the C content in subsequent horizons was mostly higher than the decrease in the N content, which means that the C/N value decreased with the depth of a soil profile. When the loss of SOC and total N contents occurs at a similar rate, the C/N ratio is maintained at a more or less stable level despite the advancing SOM mineralization. When the rate of the carbon release from SOM differs from that of nitrogen or when there is an N input from external sources, the C/N ratio does not adequately describe the process of SOM mineralization as well. The correlation coefficients between the C/N ratio and other parameters indicate that the relationships between them are not significant or that there is no correlation at all. It was found that the percentage of DTOC in SOC seemed to be a better indicator of SOM mineralization than the C/N ratio.

Revegetation is a very important way to improve soil quality and fertility in the hilly–gully region of the Loess Plateau, where serious soil nutrient loss and degradation due to water loss and soil erosion were experienced. The creation of an artificial forest is an important measure to restore the local vegetation. Caragana korshinskii (CK) is an ideal tree species in the recovery of vegetation in the Loess hilly regions because it has a strong compatibility and reproduction ability and the ability to artificially regenerate vegetatively. The slope aspects of the Loess Plateau influenced its community and asexual reproduction characteristics. Determining the relationship between the soil physicochemical properties and the soil microbial characteristics under different slope aspects can provide useful information for vegetation restoration in the Loess Plateau. This study aimed to investigate the effects of different slope aspects on soil nitrogen, soil microbial activity and community structures in a Loess hilly–gully region. According to the levels of sun exposure, four sample sites (about 35-year-old CK plantation) were selected from four different slope aspects, including sunny, shady, half-shady and hilltop slopes in the Zhifanggou watershed of Ansai (Shaanxi Province). The soil samples were collected at three different depths (0–10 cm, 10–30 cm and 30–60 cm) at each site and analyzed to determine the nitrogen (N) content, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), basal respiration (BR) and level of microbial phospholipid fatty acids (PLFAs). The slope aspect affected (p

Objective: The goal of this study was to test for the effects of land use and soil type on soil organic carbon (SOC) and total soil nitrogen (N) stocks in an arid region with a long history of cultivation and animal husbandry. Arid to semi-arid landscapes cover a large proportion of the Earth's surface and are sensitive to agricultural intensification and projected changes in climate, yet data on landscape controls on SOC and N remain scarce. Methods: We used a state factor approach to study the effects of soil type and land use on surface SOC and total soil N (0-25cm) across 35 sites in a 200km2 area in the Konya Basin, an important agricultural region of Turkey. Using Landsat-based land cover maps, we identified three representative land uses - annual-crop agriculture, orchards and grazing lands - stratified across Aridisols formed on three different parent materials: alluvial clay-loam, lacustrine clay and terrace sandy loam soils. Results: SOC and N stocks depended strongly on soil type with strong interactions between soil type and land use. On alluvial soils, grazing land SOC and N stocks were 37% and 23% greater, respectively, than those of agricultural sites and 63% and 50% greater than at orchard sites. In contrast, agricultural sites on lacustrine soils contained 41% more SOC and 42% more soil N. There were no land use effects on terrace soils. The vertical distribution in SOC and N within the top 25. cm, representing the plow layer in the agricultural sites, differed by soil type and land use. Conclusions: Soil type best explained landscape-scale variability of SOC and N stocks. Interactions between soil type and land use indicate that the long-term effects of land use on SOC and N were mediated by soil type. Differences in SOC and N stocks across soil types even within the same soil order highlight the importance of identifying pedogenic differences in soil properties, such as texture and mineralogy, which can influence the response of SOC and N to land use. Practice implications: Our study contributes baseline data on SOC and N for a semi-arid region, which can be used to aid development of landscape-scale models of SOC and N dynamics and inform land management. Our data reveal that assessments of regional land use effects on SOC and N in arid to semi-arid environments should account for landscape to regional variability in soils developing on different geomorphic surfaces and parent materials. © 2014 Elsevier B.V. 0549407 National Science Foundation We thank Dr. Suha Berberoglu for his assistance with logistics in the field and Mahmut Yavuz at the City of Eregli Agricultural Engineer's Office for orientation and introductions to the landscape and people of Eregli and the eastern Konya Basin. We thank the many village muftars (headmen) and farmers who generously gave us access to their fields and village lands. We thank Emily Atkinson, Dr. Joe Mason and members of the Marin-Spiotta lab for their assistance with processing samples. Two reviewers provided helpful comments that improved the manuscript. Finally, we thank Dr. Titus De Meester and Dr. Bert Janssen for original copies of their research publications from the Konya Basin and fruitful discussions that informed the analysis and interpretation of our data. This work was funded by the NSF -IGERT program (CHANGE-IGERT, UW-Madison, NSF Award # 0549407 ) and a CHANGE-IGERT Fellowship to Marc Mayes.

Free air CO 2 enrichment (FACE) and nitrogen (N) have marked effects on rice root growth, and numerical simulation can explain these effects. To further define the effects of FACE on root growth of rice, an experiment was performed, using the hybrid indica cultivar Xianyou 63. The effects of increasing atmospheric CO 2 concentration [CO 2 ], 200 μmol mol − 1 higher than ambient, on the growth of rice adventitious roots were evaluated, with two levels of N: low (LN, 125 kg ha − 1 ) and normal (NN, 250 kg ha − 1 ). The results showed a significant increase in both adventitious root number (ARN) and adventitious root length (ARL) under FACE treatment. The application of nitrogen also increased ARN and ARL, but these increases were smaller than that under FACE treatment. On the basis of the FACE experiment, numerical models for rice adventitious root number and length were constructed with time as the driving factor. The models illustrated the dynamic development of rice adventitious root number and length after transplanting, regulated either by atmospheric [CO 2 ] or by N application. The simulation result was supported by statistical tests comparing experimental data from different years, and the model yields realistic predictions of root growth. These results suggest that the models have strong predictive potential under conditions of atmospheric [CO 2 ] rises in the future.

Measurable soil organic carbon (SOC) fractions are recommended to be used in soil organic matter (SOM) models to replace the conceptual pools in order to reduce uncertainty related to model initialization. However, changes in SOM pools require derivation of the decomposition rate for the new pools and also impact on simulation of nutrient cycling in soil. Here, we used the Agricultural Production Systems sIMulator (APSIM) to explore the impact of adopting measurable SOM pools on simulated SOC and nitrogen dynamics under three agro-ecosystems at Brigalow, Tarlee and Wagga Wagga in Australia. The decomposition rates for the measurable pools were derived based on the data in the top 30 cm soil at Brigalow. With those decomposition rates, the model could predict the variation in observed total SOC, and also captured the dynamics of the measured SOC fractions at the three sites. However, the re-parameterized model overestimated soil nitrogen. Extending the model simulations to centurial scales led to the distinct difference in simulated soil carbon and nitrogen dynamics, due to the difference in pool sizes, decomposition rates and C:N ratios between the two approaches. Sensitivity analysis based on measurable pool approach indicated that simulated soil carbon dynamics was most sensitive to the partitioning of carbon in the sub-pools of new plant material, decomposition rates of particulate and humic organic matter. The simulated soil nitrogen dynamics was most sensitive to the C:N ratio of humic organic matter. In order to accurately simulate the long-term carbon and nitrogen dynamics, more detailed information on the composition of the measurable SOM pools, particularly their C:N ratios and the underlying mechanisms controlling their decomposition and transformation among different pools across different environments are needed.

Ammonium (NH4(+)) toxicity is a significant ecological and agricultural issue, and an important phenomenon in cell biology. As a result of increasing soil nitrogen input and atmospheric deposition, plants have to deal with unprecedented NH4(+) stress from sources below and above ground. In this review, we describe recent advances in elucidating the signaling pathways and identifying the main physiological targets and genetic loci involved in the effects of NH4(+) stress in the roots and shoots of Arabidopsis thaliana. We outline new experimental approaches that are being used to study NH4(+) toxicity in Arabidopsis and propose an integrated view of behavior and signaling in response to NH4(+) stress in the Arabidopsis system.

We report on the seasonal responses of soil nitrogen (N) pools to soil warming in a cool temperate forest where mild freeze–thaw cycles occur during winter. Artificial soil warming of 2–5 °C was implemented to prevent freezing, making it possible to evaluate the effects of soil freezing on soil characteristics. At control sites, the dissolved organic N and NH4–N pools were largest in winter. Soil warming decreased these solute pools to 17–25% of control levels during winter, but not in other seasons. These results confirm that soil freezing is the driving force of N dynamics during winter, and is easily lost by a few degrees of warming at this study site. The substantial reduction of solute N pools may reduce N availability in the cool temperate forest.