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Soil texture, coupled with environmental factors, plays an important role in soil nutrient conservation. In order to evaluate the effect of soil texture on soil fertility of fluvo-aquic soil, a long-term experiment that included four fluvo-aquic soils with different textures (sand, sandy loam, sandy clay loam and loamy clay) was established in 1990. In 2017, soil samples were collected from the 0–20 cm depth to measure soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali-hydrolysable nitrogen (AN), available phosphorus (AP) and available potassium (AK) concentrations, water-stable aggregate distribution, and aggregate-associated carbon and nitrogen. After 27 years of the experiment, the sand content decreased and the silt and clay content increased in sand and sandy loam, while the sand content increased and the silt content decreased in loamy clay. The SOC, total and available N, P and K (except TK) increased more in coarse-textured soils than in finely textured soils, while the concentrations of SOC, TN, TP, AN and AK increased significantly with a decrease in the sand content. The SOC, TN, AN and AK concentrations in loamy clay were 2 to 3 times higher than those in the sand treatment. The mass percentage of each aggregate fraction, especially the content of macroaggregates, increased significantly with a decrease in the sand content. Soil aggregates play an important role in SOC and TN storage. 75–84% of SOC and 67–81% of TN were stored in macroaggregates and microaggregates. It was concluded that soil particle composition was affected by long-term cultivation. The finely textured soils had higher SOC, TN and TP storage capacity and provided more AN and AK. The formation and stability of aggregate structures were limited by the high content of sand particles, which led to a negative influence on the storage and supply of SOC and N in the fluvo-aquic soils.

A 15 N tracing study was conducted with soils from a long-term nitrogen (N) fertilization experiment to quantify the concurrent gross N transformation rates in soil and the underlying mechanisms for crop yield and N2O emission variability. The treatments were chemical fertilization (NPK, NP, PK, NK), organic fertilization (OF), half chemical/organic fertilization (HOF), and no fertilization (control, CK). The results showed that 30 years of repeated organic or chemical N applications significantly stimulated gross rates of N mineralization and autotrophic nitrification compared with CK. In addition, gross rates of N mineralization (except NP) and autotrophic nitrification (except CK, PK) in all treatments were significantly higher in 2019 (30 years) than in 2007 (18 years). However, the immobilization of mineral N decreased significantly (near to zero) after 30 years of repeated N applications compared to CK or the results of 18 years. The highest maize yields were observed in NPK, but they were not significantly different from HOF yields. The OM yields significantly increased with the duration of the experiment and reached values comparable to NPK yields after more than 12 years of repeated N applications. There was a logarithmic positive relationship between maize yields and gross N mineralization rates (p

Excessive application of nitrogen fertilizer has caused the reduction of nitrogen fertilizer utilization efficiency, resource waste and environmental problems in our country. There are disadvantages of long sampling and heavy workload using the traditional methods of acid absorption and box method for farmland ammonia volatilization measurement. In order to meet the application needs for on-line automatic measurement of ammonia volatilization in farmland, an in-situ automatic measurement device for ammonia volatilization was designed combined with laser spectroscopy technology. The main body of the measurement device is an integrated sampling box, with the advantages of long optical path measurement, heat resistance and corrosion resistance. The control circuit of the sampling box used ARM as the main controller for environmental data monitoring, automatic opening and closing of the cover and lens temperature controlling. The ammonia volatilization results were analyzed by the data acquisition and processing system after the laser passed through the sampling box to obtain ammonia spectroscopy signal. The device was used for observation at Fengqiu Ecological Station, CAS. The results showed that the ammonia volatilization rose rapidly after 90 minutes for nitrogen fertilizer applying, and it decreased gradually to a low value after 270 minutes. According to the experimental results, the continuous measurement time for cover closing can be set to 3 minutes, and the cover opening time can be set to 3 to 5 minutes. The working performance of the automatic measurement device was verified through these experiments, with the advantages of low power consumption, high measurement sensitivity, and no gas sampling. It realizes insitu automatic measurement for ammonia volatilization in farmland with the natural respiration condition of the soil.

Reducing the applications of mineral phosphorus (P) fertilizers and supplementing them by organic fertilizers is becoming a necessary practice in the North China Plain due to overuse of mineral P fertilizers and improper disposal of organic wastes. Knowledge is needed about how the long-term substitution of mineral fertilizers by organic fertilizers affects soil P forms in order to understand soil P transformation and crop P uptake. In this study, we used solution 31P nuclear magnetic resonance (NMR) spectroscopy to characterize P forms in fluvo-aquic soil after 26 years of different fertilization management strategies, organic compost (OM), half compost in combination with half mineral fertilizer NPK (1/2 OM), mineral fertilizer NPK (NPK), mineral fertilizer NK (NK), and an unfertilized control (CK). Results showed that the P extraction efficiency using NaOH-EDTA varied from 13.0 to 27.7% for the soils of the treatments. 31P NMR spectra indicated that the majority of P was in the form of orthophosphate for all the treatments, which constituted 64.3–83.5% of the total extracted P. The application of P fertilizers significantly increased the concentrations of orthophosphate, monoesters and diesters regardless of the P fertilization method, although the proportions of monoesters and diesters were higher in CK. The proportions and concentrations of orthophosphate significantly decreased when all mineral fertilizers were replaced by compost. There was no significant difference in the proportions and concentrations of total organic P, corrected monoesters and diesters in NaOH-EDTA extracts of soils among NPK, 1/2OM and OM treatments. Decreasing mineral P fertilizers and partly replacing them by organic fertilizer in fluvo-aquic soil might increase soil test (Olsen) P and crop P uptake through the degradation of applied organic P forms.

A field experiment was conducted to assess the accuracy of the backward Lagrangian stochastic (BLS) model combined with an open-path tunable diode laser (OPTDL) system for estimating ammonia emissions from rice field by comparing with the micrometeorological mass balance (MMB) method. During the experimental period, the average height of rice was 0.65 m, and the average height of laser path was 1.3 m. The results showed that there was no significant difference between the ammonia emission rates estimated by the two methods, indicating no significant effect of tall rice on the accuracy of the BLS model. The high temporal resolution data showed that ammonia emissions had a dramatic diurnal cycle: rise at daytime and fall at night. Although the OPTDL technique was not able to measure ammonia concentrations at low emission rates due to relatively high detection limit, the total ammonia loss estimated by the BLS model was not significant different from that of the MMB method. The results demonstrate the effectiveness of the BLS model with the OPTDL technique for estimating ammonia emissions from farmland covered with tall vegetation. Within the acceptable accuracy, the relatively low laser path height is recommended for farmland with tall vegetation due to relatively high detection limit of the OPTDL technique and low ammonia concentration of farmland.

The formation of aggregates plays a key role in shaping soil microenvironment, which in turn influences microbial community structure and organic carbon (C) dynamics in soil. The objective of this study was to identify the linkages between soil macroaggregation and microbial community as well as organic C accumulation using field samples following 9 years of conservation tillage. A wet-sieving method was used to fractionate soil aggregates and soil microbial abundance and community composition were determined using phospholipid fatty acid (PLFA) analysis. Compared to continuous tillage, reduced/no-tillage and straw returning significantly promoted soil macroaggregation and consequently increased organic C, C/N ratio and soil moisture but decreased the porosity and computed effective oxygen diffusion coefficients. The changes in these soil characteristics were closely related to the abundance and composition of microbial community. The abundance of microbial PLFAs in reduced/no-tillage soils was 30.0% higher in Gram-positive bacteria, 11.6% higher in Gram-negative bacteria, 71.7% higher in fungi and 45.4% lower in actinobacteria, whereas straw returning significantly increased all microbial PLFA abundances relative to straw removing. The ratios of bacteria/fungi (B/F) and monounsaturated/branched (M/B) PLFAs were significantly correlated with the volumetric soil water content, porosity, or computed effective oxygen diffusion coefficients. Soil macroaggregation and microbial community composition collectively explained 82.4% variation in organic C accumulation and their interaction made the largest contribution. Overall, soil macroaggregation under conservation tillage might cause a shift in microbial community to more fungi and anaerobes through primarily influencing soil moisture and aeration, which could effectively promote organic C accumulation in soil.

Irrigation and nitrogen (N) fertilization in excess of crop requirements are responsible for substantial nitrate accumulation in the soil profile and contamination of groundwater by nitrate leaching during intensive agricultural production. In this on-farm field trial, we compared 16 different water and N treatments on nitrate accumulation and its distribution in the soil profile (0-180cm), nitrate leaching potential, and groundwater nitrate concentration within a summer-maize (Zea mays L.) and winter-wheat (Triticum aestivum L.) rotation system in the Huang-Huai-Hai Plain over five cropping cycles (2006-2010). The results indicated that nitrate remaining in the soil profile after crop harvest and nitrate concentration of soil solutions at two depths (80cm and 180cm) declined with increasing irrigation amounts and increased greatly with increasing N application rates, especially for seasonal N application rates higher than 190kgNha-1. During the experimental period, continuous torrential rainfall was the main cause for nitrate leaching beyond the root zone (180cm), which could pose potential risks for contamination of groundwater. Nitrate concentration of groundwater varied from 0.2 to 2.9mgL-1, which was lower than the limit of 10mgL-1 as the maximum safe level for drinking water. In view of the balance between grain production and environmental consequences, seasonal N application rates of 190kgNha-1 and 150kgNha-1 were recommended for winter wheat and summer maize, respectively. Irrigation to the field capacity of 0-40cm and 0-60cm soil depth could be appropriate for maize and wheat, respectively. Therefore, taking grain yields, mineral N accumulation in the soil profile, nitrate leaching potential, and groundwater quality into account, coupled water and N management could provide an opportunity to promote grain production while reducing negative environmental impacts in this region.

This paper was primarily devoted to reveal the stock of soil organic carbon (C) as well as its lability and to compare their differences existing among tillage and residue practices, aiming to identify the effects on the accumulation process of organic C and its association with macroaggregation. Arable soils following 8-year contrasting managements were collected to determine aggregate size distribution, organic C content and its lability. A wet-sieving method was used to fractionate aggregate fractions including > 2000 μm large macroaggregates, 2000–250 μm small macroaggregates, 250–53 μm microaggregates, and

Humic substances are recalcitrant and might act as persistent binding agents to form macroaggregates. The focus of this study is in investigating the contribution of humic carbon (HC) to soil aggregation in response to various tillage and residue managements. Arable soils following 8-year contrasting managements were collected to determine aggregate size distribution and stability and HC fractions including humic acid (HA) and fulvic acid (FA). The contribution of HC to aggregation was divided into three special effects including positive effect (PE), negative effect (NE), and combined effect (CE), and these effects were measured using aggregate fractionation techniques. As well as to promote structural stability, HC bounds predominantly with the silt + clay fraction and secondarily with microaggregates to form larger aggregates. The PE increased with increasing aggregate size, whereas the NE followed the opposite pattern. A positive CE was observed for large and small macroaggregates, whereas the CE for microaggregates and the silt + clay fraction was negative. Compared to continuous tillage, reduced- and no-tillage decreased the PE for large and small macroaggregates by 1.58–30.98% at the 0–20 cm depth, and straw returning also slightly decreased the corresponding PE relative to straw removing. By contrast, a significantly higher NE for small macroaggregates at the 0–10 cm depth while 6.33–81.11% decreases in CE for large and small macroaggregates at the 0–10 cm depth as well as for large macroaggregates at the 10–20 cm depth, were observed under reduced- and no-tillage. The extraction of HC significantly reduced the aggregate stability and reduced- and no-tillage effectively limited its decrease magnitude. Small macroaggregates and microaggregates made larger contributions to soil HC accumulation than did other fractions. An averagely increased contribution from large or small macroaggregates was observed under both reduced-/no-tillage and straw returning at the 0–20 cm depth. A significant and positive relationship was found between the mass proportion of macroaggregates and the HC accumulation in 0–20 cm soil. Large macroaggregates had significantly higher HA/FA ratios than small macroaggregates, and reduced- and no-tillage significantly increased these ratios both in large and in small macroaggregates. The CE for large or small macroaggregates was also significantly negatively correlated with their HA/FA ratios. Overall, the HC accumulation in soil is likely to play a key role in macroaggregation, but conservation tillage might decrease the contribution magnitude of HC to large or small macroaggregation through increasing the corresponding HA/FA ratios.

The rate of ammonia emissions from a small circular plot of maize was estimated by three procedures: (i) by inverse dispersion (based on upwind and downwind laser concentration-detectors interpreted using a backward Lagrangian stochastic model); (ii) by the height-integrated horizontal flux measured by point flux-detectors arrayed along the axis of the plot (i.e., the integrated horizontal flux method, IHF); and (iii) by extrapolation from static flux chambers (SC). The results indicated that the estimates made by the open-path tunable diode laser (OPTDL) system combined with the backward Lagrangian stochastic (BLS) model were statistically equivalent to those made by the IHF method. The ammonia fluxes estimated by the OPTDL-BLS technique were only 2.3% higher than those from the IHF method. Although the OPTDL technique failed to monitor concentration differences at low ammonia fluxes due to its detection limit, the OPTDL-BLS technique estimated the total ammonia loss to be only 10.9% less than the IHF results. The SC method was found to underestimate ammonia emissions and cumulative ammonia loss significantly compared with both the OPTDL-BLS and IHF methods Although the ammonia emissions estimated by the OPTDL-BLS technique showed a similar emission pattern to those estimated by the IHF method, the former provided an opportunity to estimate the diurnal pattern of ammonia emissions and to understanding the primary driving factors. A clear diurnal cycle and a dominant net solar radiation dependence in ammonia emissions were found.

Ammonia emission is one of the dominant pathways of nitrogen fertilizer loss from rice fields in China. It is difficult to measure ammonia emissions by high-frequency sampling with the chamber methods widely used in China, which is of great significance for investigating the environmental effects on the ammonia emissions. The chamber methods also can not accurately determine the ammonia emissions. In this study, the backward Lagrangian stochastic dispersion model, with ammonia concentrations continuously measured by the open-path tunable diode laser absorption spectroscopy technique, was used to determine ammonia emissions from a rice field after fertilizer application at excessive (270 kg N ha−1) and appropriate (210 kg N ha−1) rates in the Taihu Lake Region of China. High temporal resolution measurements of ammonia emissions revealed that high intraday fluctuations of ammonia emissions were significantly affected by the meteorological conditions. Multiple regression analysis showed a dominant solar radiation dependence of intraday ammonia emission cycles, especially during the rice panicle formation stage. The NH4+-N concentrations of the surface water of the rice field were found to be the decisive factor that influenced interday dynamics of ammonia emissions. Accurate quantifications of ammonia emissions indicated that the total ammonia losses under appropriate nitrogen application rate were 27.4 kg N ha−1 during the rice tillering stage and 11.2 kg N ha−1 during the panicle formation stage, which were 29.4% and 17.0% less than those under traditional excessive nitrogen application rate used by the local farmers, respectively. The ammonia loss proportions during the rice panicle formation stage were significantly lower than those of the tillering stage, which might be due to different nitrogen application rates and environmental effects during the two stages. This study indicated that the open-path tunable diode laser absorption spectroscopy technique could facilitate the investigation of high temporal resolution dynamic of ammonia emissions from farmland and the environmental influence on the ammonia emissions.

This paper was primarily devoted to reveal the composition of soil organic carbon (C) at a molecular level and to compare the differences existing among tillage practices after 8 years of contrasting managements, aiming to identify the effects of conservation tillage on the accumulation process of soil organic C and its association with macroaggregation. A sandy loam soil following 8-year conservation tillage was collected to identify the dynamics of organic components and their associations with macroaggregation. The content of particulate organic matter within macroaggregates was determined using aggregate fractionation techniques. Conservation tillage improved the accumulation efficiency of different C functional groups in large and small macroaggregates, and resulted in a higher soil organic C level. The content of C functional groups was significantly and positively correlated with the C amount of subfractions in macroaggregates. The accumulation of organic components, particularly the methoxyl/N-alkyl C in the 0–5 cm layer and the O-alkyl C in the 5–10 cm layer, in turn, accelerated soil macroaggregation. Overall, organic component accumulation and soil macroaggregation were interacted on each other. Our results suggested that the enrichment of methoxyl/N-alkyl C and O-alkyl C in the test soil following conservation tillage could effectively promote organic C accumulation and macroaggregation.

A 3-year field tillage and residue management experiment established in North China was used to analyse topsoil (0–15 cm) aggregation, and microbial functional diversity, enzyme activity and glomalin-related soil protein (GRSP) content within aggregates. Compared with conventional tillage (CT), no-tillage (NT) alone significantly (P 250 and

Atmospheric nitrogen (N) deposition, an important N source to agro-ecosystems, has increased intensively in China during recent decades. However, knowledge on temporal variations of total N deposition and their influencing factors is limited due to lack of systematic monitoring data. In this study, total N deposition, including dry and wet components, was monitored using the water surrogate surface method for a typical agro-ecosystem with a winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation system in the Huang-Huai-Hai Plain from May 2008 to April 2012. The results indicated that annual total N deposition ranged from 23.8 kg N ha−1 (2009–2010) to 40.3 kg N ha−1 (2008–2009) and averaged 31.8 kg N ha−1. Great inter-annual variations were observed during the sampling period, due to differences in annual rainfall and gaseous N losses from farmlands. Monthly total N deposition varied greatly, from less than 0.6 kg N ha−1 (January, 2010) to over 8.0 kg N ha−1 (August, 2008), with a mean value of 2.6 kg N ha−1. In contrast to wet deposition, dry portions generally contributed more to the total, except in the precipitation-intensive months, accounting for 65% in average. NH 4 + -N was the dominant species in N deposition and its contribution to total deposition varied from 6% (December, 2009) to 79% (July, 2008), averaging 53%. The role of organic N (O–N) in both dry and wet deposition was equal to or even greater than that of NO 3 − -N. Influencing factors such as precipitation and its seasonal distribution, reactive N sources, vegetation status, field management practices, and weather conditions were responsible for the temporal variations of atmospheric N deposition and its components. These results are helpful for reducing the knowledge gaps in the temporal variations of atmospheric N deposition and their influencing factors in different ecosystems, to improve the understandings on N budget in the typical agro-ecosystem, and to provide references and recommendations for field nutrient management in this region.

The influence of compost and mineral fertilization on soil organic carbon (SOC) and physical properties varied greatly in previous studies because of differences in site conditions such as climate and soil. This study was conducted as a long-term (1989–2012) field experiment to evaluate the effects of mineral fertilization and compost application on SOC content and some physical properties of an intensively cultivated sandy loam soil in the North China Plain. The experiment consisted of seven treatments: organic compost (OM); half organic compost plus half mineral fertilizer NPK (1/2OM1/2NPK); mineral fertilizer NPK (NPK); mineral fertilizer NP (NP); mineral fertilizer PK (PK); mineral fertilizer NK (NK); and unfertilized control (CK), each with four replicates. Relative to CK, the SOC content was higher in all of the compost and mineral fertilizer treatments, but increments in SOC under the compost application treatments were higher than mineral fertilization application. Compost application (OM, 1/2OM1/2NPK) decreased soil bulk density and increased total porosity significantly in comparison with that in the CK plots. Soil bulk density and total porosity for the mineral fertilization treatments, except NP, did not significantly differ from CK. The lowest penetration resistance at 0–20 cm soil depth was observed in the NK plots, and the highest penetration resistance was found in the CK plots. Compost application increased the total amount of water-stable macro-aggregates (>0.25 mm); however, MWD was not significantly affected by compost application. The MWD in the NK treatment was lower than in CK by 0.2 mm, while its variation among NPK, OM, 1/2OM1/2NPK, NP, PK, and CK was not significant. The compost- and mineral fertilizer-treated soil had 34.6–91.7% higher volume of macropores than the CK soil. The OM and 1/2OM1/2NPK-treated soil had a significantly higher proportion of small pores (

The backward Lagrangian stochastic (BLS) model for estimating ammonia emissions from agricultural sources was assessed in an ammonia recovery experiment. The open-path tunable diode laser spectrometer was used to measure atmospheric ammonia concentrations. The results indicated that the ratio of estimated to actual emission ( Q BLS / Q ) decreased with increasing concentration measurement height, and the optimum measurement height increased as fetch ( F ) increased. The accuracy of Q BLS was insensitive to fetch with a range of 15–60 m. The optimum ratio of concentration measurement height to fetch decreased with increasing fetch. In this study, the optimum ratio of concentration measurement height to fetch was 0.083 and 0.045 for F = 15 m and F = 30 m, respectively. It is recommended that the laser sensor should be placed as close to the source as possible to reduce concentration measurement uncertainty for measurement of ammonia emission from farmland. The wheat canopy had a significant effect on Q BLS / Q when the concentration measurement height above the wheat canopy was no more than 0.38 m. The laser path should be placed at least 0.58 m above the wheat canopy to minimize the effect of wheat canopy on the accuracy of the BLS model.

Mechanisms of soil organic carbon (C) accumulation in response to no tillage (NT) are unclear. The extraradical hyphae of arbuscular mycorrhizal (AM) fungi are known to contribute to the formation and maintenance of soil aggregates through the exudation of glomalin. The objectives of this study were to evaluate the effects of different tillage management treatments on soil aggregates, AM fungal community, and glomalin contents and find out the main factors that influence aggregate C accumulation. A field experiment established in a sandy loam soil at Northern China has received 4-year continuous tillage treatments, including conventional tillage (CT), NT, and alternating tillage (AT, tillage in the wheat season and no tillage in the maize season). Undisturbed top soil samples (0–15 cm) from four individual plots per treatment were collected for the analysis of aggregates, which were separated according to the wet-sieving method. The organic C contents in different particle size aggregates were determined by the dichromate oxidization, and the glomalin-related soil protein (GRSP) was then extracted with citrate solution using bovine serum albumin (BSA) as a standard. The population size of AM fungi was determined by real-time PCR, and the community composition was analyzed using polymerase chain reaction plus denature gradient gel electrophoresis (PCR-DGGE), cloning, and sequencing techniques. Compared to CT, both NT and AT resulted in higher percentages of macroaggregates (>50 μm), and NT, rather than AT, significantly increased organic C contents in >250- and 50–2-μm aggregates, and also organic C contribution by macroaggregates. Both NT and AT significantly increased AM fungal population in 250–50-μm aggregates, but only NT increased it in >250-μm aggregates. NT, rather than AT, significantly increased easily extractable GRSP contents in 250–50- and

Cropland productivity has been significantly impacted by soil acidification resulted from nitrogen (N) fertilization, especially as a result of excess ammoniacal N input. With decades' intensive agricultural cultivation and heavy chemical N input in the Huang-Huai-Hai Plain, the impact extent of induced proton input on soil pH in the long term was not yet clear. In this study, acidification rates of different soil layers in the soil profile (0–120 cm) were calculated by pH buffer capacity (pHBC) and net input of protons due to chemical N incorporation. Topsoil (0–20 cm) pH changes of a long-term fertilization field (from 1989) were determined to validate the predicted values. The results showed that the acid and alkali buffer capacities varied significantly in the soil profile, averaged 692 and 39.8 mmolc kg−1 pH−1, respectively. A significant (P

Gaseous nitrogen (N) losses are mainly responsible for low N use efficiency of applied fertilizers and their derivative environmental hazards, while N application rates and soil water regime are important factors regulating these N processes. In this study, gaseous N losses via ammonia volatilization (AV) and denitrification, determined by sponge trapping-KCl extraction and acetylene inhibition-soil core incubation, respectively, were investigated under different coupled water-N management practices with a winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation system in the Huang-Huai-Hai Plain. Ammonia volatilization after urea application, particularly after topdressing during maize growing seasons, was the dominant gaseous N loss, amounting up to 53.2 kg N ha−1 (38.6 % of the applied N). Ammonia volatilization generally decreased by increasing irrigation rate applied immediately after fertilization. Denitrification N losses were lower than ammonia-N losses, accounting for 1.3 to 18.7 kg N ha−1 year−1, with more than 90 % occurring during the maize growing seasons. Total gaseous N losses showed a significant (P

The backward Lagrangian stochastic (BLS) model and open-path tunable diode laser (OPTDL) analyzer were used to monitor ammonia (NH3) emissions from urea applied to winter wheat in the North China Plain. The high-temporal resolution measurements of ammonia concentrations provided an opportunity for estimating the diel patterns of ammonia emissions, as well as valuable information about the factors that influence NH3 emissions. The results showed both large diel variability and daily variability in NH3 volatilization, with NH3 emissions highest during the daytime. The diel pattern of ammonia volatilization depended mainly on the diel variation of wind speed and soil temperature, while the overall pattern of NH3 loss was strongly affected by soil moisture content, soil NH4 +-N concentration, wind speed and soil temperature. At the end of the measurement period, the cumulative NH3 loss was 12.21–16.43 kg N ha−1, calculated based on different time scale average Q BLS. Due to sensitivity of the OPTDL analyzer, the estimated total ammonia loss was still doubtful in this study.

Soil phosphorus (P) composition and phosphatase activities in aggregates are essential for agricultural productivity and remain poorly understood. A field experiment was conducted from 2007 to study the effect of tillage systems (conventional tillage, T and no tillage, NT) and crop residue management (0, 50% and 100% crop residue incorporation/coverage) on P composition determined by 31 P nuclear magnetic resonance (NMR) and phosphatase activities in soil aggregates (>2 mm, 0.25–2 mm and 0.053–0.25 mm). The results showed that crop residue input influenced the concentrations of soil phosphate monoesters and diesters, alkaline phosphomonoesterase (AlP), acid phosphomonoesterase (AcP), phosphodiesterase (PD) activities, and soil aggregate stability significantly, and the addition of crop residue was significantly more effective than tillage. The NT had significantly higher soil phosphatase activities than tillage treatment but not more soil P content. The 0.25–2 mm aggregates showed higher total P, organic P, concentrations of monoesters and diesters, and AlP activity. The structure equation model showed that soil aggregate stability could increase concentrations of monoesters and diesters indirectly by its direct effects on soil phosphatases. Our results suggest that NT and crop residue input could increase the P store and sustainable supply in soil aggregates and that the 0.25–2 mm size aggregates may play an important role in soil organic P maintenance and transformation.

A viable method—open-path tunable diode laser absorption spectroscopy (OPTDL) in conjunction with a backward Lagrangian stochastic (bLS) dispersion model—has been used for micrometeorological monitoring of ammonia fluxes. In this technique, the gas concentration measured with the OPTDL sensor is used to infer the surface emission rate with the aid of dispersion model calculations. On the basis of numerous assessment experiments and field trials, several beneficial strategies for using the OPTDL technique properly to monitor atmospheric NH3 concentrations in the field have been summarized. Theoretically, the location of the concentration measurement can be anywhere in the emission plume, but in practice, the concentration measurement position must be carefully selected to avoid making measurements which are on the periphery of the downwind plume or are affected by obstructions. To obtain accurate estimates, periods with low friction velocity or extreme atmospheric stability, where Monin–Obukhov similarity theory-based relationships are invalid, or unrepresentative estimates due to unsuitable wind direction, should be excluded. A validation experiment showed that there was no significant difference between the ammonia emission rates obtained by the micrometeorological mass balance method and those obtained by the bLS model combined with the OPTDL technique. This study also indicated the potential of the bLS and OPTDL technique for investigation of diurnal emission patterns and environmental influences.

A backward Lagrangian stochastic (BLS) model for estimating ammonia emission in the field, utilizing data from ammonia concentration measurements by the open-path tunable diode laser method, was assessed by comparing it with the benchmark provided by simultaneous monitoring by the micrometeorological mass balance (MMB) technique. The results indicated that after rejecting data with u* ≤ 0.15 m s−1 or |L| < 10 m, the ammonia emissions derived by the BLS model were very similar to those by MMB (regression gradient = 0.966, R2 = 0.959). The BLS model was also compared with the static chamber (SC) method of monitoring changes in gas concentration (enrichment/depletion) over time; it was found that these methods yielded significantly different results for both diurnal ammonia fluctuations and total ammonia loss. The results also showed that the mean time had little effect on the accuracy of the BLS method, but a short averaging time was preferable when investigating diurnal change of ammonia emissions.

The impacts of tillage system (conventional tillage and no-tillage) and residue management (0, 50, and 100%) on soil properties and soil microbial community structure were determined in the Fengqiu State Key Agro-Ecological Experimental Station, North China. The microbial community structure was investigated by phospholipid fatty acid (PLFA) profiles. The results showed that tillage had significant effects on soil properties and soil microbial commu nities. In no-tillage (NT), microbial biomass carbon (MBC), total N, microbial biomass carbon/soil organic carbon (MBC/SOC), total microbes, and arbuscular mycorrhiza fungi increased, while actinomycetes, G + /G – bacteria ratio and monounsaturated fatty acids/saturated fatty acids (MUFA/STFA) decreased, compared with those in conventional tillage (CT). Residue had a significant positive effect on C/N ratio and MUFA/STFA. Canonical correspon dence analysis indicated that tillage explained 76.1%, and residue management explained 0.6% of the variations in soil microbial communities, respectively. Soil microbial communities were significantly correlated with MBC, total N, C/N ratio and MBC/SOC. Among the six treatments, NT with 100% residue application obviously improved soil microbiological properties, and could be a proper management practice in the Huang-Huai-Hai Plain of China.

Linear mixing models and δ D– δ 18 O plots with stable hydrogen and oxygen isotopes have been widely used to identify water sources consumed by various plants; however, each of these methods is incapable of quantifying the contribution of different water sources used if more than three sources exist simultaneously. In this study, we developed a coupled model to solve this problem and applied it to determine the contribution of various water sources to maize during different growth stages. A field experiment was conducted from June 5 to September 12, 2007. The results revealed that primary water sources for maize varied with growth stages, and that generally more water from deeper depths was used as the plants grew. Additionally, calculation of the coupled model was in accordance with the linear mixing model, which indicated that the coupled model could enable the successful identification of various water sources that contribute the total water used by plants.

The effects of tillage and residue input amounts on soil phosphatase (alkaline phosphomonoesterase ALP, acid phosphomonoesterase ACP, phosphodiesterase PD, and inorganic pyrophosphatase IPP) activities and soil phosphorus (P) forms (total P, organic P, and available P) were evaluated using soils collected from a three-year experiment. The results showed that no-till increased soil total and organic P, but not available P as compared to conventional tillage treatments. Total P was increased as inputs of crop residue increased for no-till treatment. There were higher ALP and IPP activities in no-till treatments, while higher PD activity was found in tillage treat ments and tillage had no significant effect on ACP activity. Overall phosphatase activities increased with an in crease of crop residue amounts. Soil total P was correlated negatively with PD activity and positively with other phosphatase activities. Organic P had a positive correlation with ACP activity, but a negative correlation with PD activity. Available P had no significant correlation with phosphatase activities. Our data suggests that no-till and residue input could increase soil P contents and enhance the activities of phosphatase.

Atmospheric nitrogen (N) deposition has been widely considered as an important N input into agroecosystems, but its measurement involves considerable uncertainties with various methods. In this study, a field sampler with distilled water as a surrogate surface was developed and trialed for the collection of dry and wet N deposition. The direct measuring results were compared with the value calculated by the N mass balance method (crop N uptake from plots receiving no N fertilizers of the long-term fertilization experiment in the monitoring station). The results indicated that exposure durations of 3–5 days and water volumes of 2000–2800 ml were tested to be suitable to collect dry N deposition, while water volumes of less than 1000 ml and sampling conducted immediately after rain event were found to be appropriate for wet N collection under the present experimental conditions. The monitoring work was conducted from June 2008 to May 2009, and annual N deposition totaled up to 40.32 kg N ha −1 , of which dry deposition accounted for 62.45%. NH 4 –N was the dominant species in N deposition and contributed 62.68% and 66.00% to wet and dry deposition, respectively. Organic N (O-N) was found to make greater contributions than NO 3 –N in both dry and wet depositions. Total N deposition was parallel to the results estimated by the method of mass N balance from the long-term experiment, as 45.6 kg N ha −1 . These results provide helpful knowledge to elucidate the N deposition scenario of a typical agroecosystem and can be of great importance for the calculation of fertilizer recommendations in the Huang-Huai-Hai Plain.

Soil acid and alkali buffer capacity, as a major indicator for evaluating its vulnerability and resistibility to acidification and alkalization, is an important factor affecting the sustainable agriculture, through knowledge on which soil acidification process can be predicted and modified. In this study, titration curve method was adopted to investigate the pH buffer capacity (pHBC) of fluvor-aquic soil, and separate titration curves were established by adding incremental amounts of either standardized hydrochloric acid (HCl) (0.12 mol L−1) or sodium hydroxide (NaOH) (0.10 mol L−1) to soil suspended in deionized water (soil:solution = 1:5). Soil pH was measured after 7 d resuspension and isothermal equilibrium (T = 25°C). Linear regressions were fitted to the linear portion of each titration curve and the slopes of these lines were derived as the soil pHBC. The results showed that significant correlations between the amounts of adding acid or alkali and each pH change were presented, and titration curve method was feasible for measurement of pHBC on typical fluvor-aquic soil in Huang-Huai-Hai Plain, and the coefficients of determination were higher than the similar researches on acid soil (R2 = 0.96). The slope-derived pHBC of acid and alkali were 158.71 and 25.02 mmol kg−1, respectively. According to the classification of soil buffer systems, the soil tested belongs to the calcium carbonate buffer system, carbonates contribute the most to pHBC, and the contribution of soil organic matter relatively less than it.

Goal, Scope and Background Andisols are widespread in Japan and have some special properties such as high anion exchange capacity, low bulk density, and high organic matter content, which might influence the accumulation or chemical fractionation of heavy metals. However, few such data exist in Japanese andisols. The primary objective of this study was to investigate the distribution and chemical fractions of Cu, Zn, Ni, and Cr in the soil profiles and subsequently to assess their potential environmental hazard.

High nitrogen fertilizer input is the main manner to maintain the high-yield crops in farmland in China. The average application quantity of nitrogen fertilizer in China is significantly higher than some developed countries in the world. However, the nitrogen fertilizer utilization efficiency is very low. Thus, high sensitivity sensing and on-line monitoring ammonia concentration were needed to quickly acquire the soil nutrient information and to get the nitrogen fertilizer utilization efficiency. A high sensitivity ammonia concentration sensor used in farmland has been developed based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology, high frequency modulation technique and long optical path technique. TDLAS is a method to obtain the spectroscopy of gas molecule single absorption line in the characteristic absorption spectrum region as the characteristic of the distributed feed back (DFB) laser with narrow line width and tunability. A sensor array formed with three ammonia concentration sensors by distributed sensing technique was used for ammonia volatilization experiment in a wide range of farmland. It was verified that the performance consistency of the three ammonia sensors was good and the sensor array realized the regional ammonia concentration monitoring. Continuous measurement results showed that the ammonia concentration influenced by the volatile source location, wind direction, weather and other factors, and it was positively correlated with the ammonia volatilization rate. The ammonia sensor array is suitable for continuously ammonia volatilization monitoring in a wide range of farmland environment with its high sensitivity, rapid response time without gas sampling.