Wheat-corn Rotation Research Articles

Preliminary Effects of Crop Residue Management on Soil Quality and Crop Production under Different Soil Management Regimes in Corn-Wheat Rotation Systems

Strategic management of crop residues is essential to enhance soil quality for sustainable agriculture. However, little is known about the specific amounts of crop residues needed to improve soil quality characteristics which are key to develop economic plans. In this study, we investigated the effects of applying crop residue at five rates, including 100% (R100), 75% (R75), 50% (R50), 25% (R25), and 0% (R0), on wheat yield and soil properties. Field experiments were conducted for two cropping seasons in a wheat-corn rotation under conventional (CT) and no-till (NT) systems to observe the first results obtained during short-term periods (one-year application). During the study, the wheat and corn fields were irrigated. Application of plant residue resulted in increased soil organic carbon (SOC) and available nutrients and improved soil physical properties, i.e., aggregates mean weight diameter in wet (MWDw) and dry (MWDd) conditions, water-stable aggregates (WSA), dry-stable aggregates, (DSA), soil water infiltration (SWI), soil available water (SAW), and yield of wheat and corn. The effects were stronger at higher residue application rates. In the CT system, compared to R0, R100 resulted in the highest increase equal to 38, 29, 23, 34, 35, 41, and 11% for SOC, MWDw, MWDd, WSA, DSA, SAW, and wheat grain yield, respectively. This was equivalent to 28, 19.5, 19, 37, 44, 52, and 6% for the NT system, respectively. Generally, the NT system resulted in a stratification of the soil properties within 0–10 cm compared to 10–20 cm soil depth, but a uniform distribution for both depths under CT system. Overall, these results show that crop residue application can improve soil quality and yield in cereal production systems under semi-arid conditions during the first year of application. It will be key to monitor these changes in along-term field studies.

Nitrogen use efficiency and recovery in a wheat-corn rotation under tropical savannah conditions

Stable isotopes (e.g., 15N) can be used to develop best practices for fertilizer management in cereal crops under tropical conditions. The objectives of this study were to determine the N contribution from fertilizer and soil to wheat and corn grown in rotation and the residual N contribution from fertilizer applied to wheat and carried over to corn under Brazilian savannah conditions. This study was established in a no-till system on Rhodic Haplustox soil in a randomized complete block design with four replications. The N treatments applied to the wheat crops were 0, 20, 40, 60, 80 and 160 kg (urea-15N) ha−1. The residual effects of N on the succeeding corn crop were evaluated. During the corn phase, two additional treatments were included: a control (0 N) and a treatment with 160 kg N ha−1. Regression analysis showed that the highest estimated wheat yield (5415 kg ha−1) was observed with the application of 114 kg N ha−1. Significant effects from the residual N were observed in the corn shoot biomass and straw N uptake. On average, the recovery rate of the urea N fertilizer was 34% for wheat, and the residual urea N fertilizer use in corn (when applied to wheat) was less than 5% of the amount initially applied. The effect of the residual N was not enough to meet the N demands of the succeeding corn crop. The results of this study provide producers and the scientific community with good estimates of nitrogen use efficiency for wheat and corn.

Effects of fertilization and planting patterns on soil aggregate and carbon distribution in farmland of the Loess Plateau, Northwest China

Based on a long-term experiment in the Changwu Agro-ecological Experimental Station in Xianyang, Shaanxi, China, we examined the effects of fertilization and planting patterns on soil aggregate quantity, aggregate stability and total carbon and organic carbon distribution in different aggregate fractions through dry and wet sieving methods, as well as the TOC combustion method. There were ten treatments, including uncultivated (R), wheat continuous cropping (CK/W), wheat-corn rotation (L), and nitrogen fertilizer (N), phosphorus fertilizer (P), nitrogen and phosphorus fertilizer (NP), organic fertilizer (M), nitrogen and organic fertilizer (NM), phosphorus and organic fertilizer (PM), nitrogen and phosphorus and organic fertilizer (NPM) for CK/W. The results showed that fertilizer application and planting patterns affected soil aggregate distribution and stability, the contents and contribution rates of total C and organic C. Force-stable aggregate was mainly constituted by >0.25 mm aggregate (>67%), which was reduced by fertilization. Continuous cropping decreased micro-aggregate while rotation facilitated it and the effect was larger than fertilization. Water-stable aggregate was mainly comprised of micro-aggregate (<0.25 mm), the contribution of which was larger than 61%. Both fertilizer application and planting pattern reduced water-stable micro-aggregate. Fertilizer application and planting pattern decreased the percentage of aggregate destruction rate (PAD) and increased macro-aggregate (>0.25 mm, R0.25) content. Organic fertilizer significantly improved total C and organic C concentrations in all the fractions of force-stable aggregates. Continuous cropping and rotation cropping increased total C concentration in all the aggregate fractions while rotation cropping significantly decreased organic C concentration. Single N and P fertilization decreased soil total C concentration, while mixed application of N and P fertilizers, and organic fertilizer significantly increased soil total C concentration. The effect of planting patterns on soil total C was lower than that of fertilization. Both continuous cropping and rotation cropping increased soil total C. Mixed application of N and P fertilizers, and organic fertilizer signifi-cantly increased soil organic C concentration while single N and P fertilization decreased it. The effect of planting patterns on soil organic C was lower than that of fertilization, while rotation cropping did not facilitate soil organic C. Micro-aggregate was the most notable size fraction to total carbon and organic C, with the contribution being 21.2%-33.6%. Fertilization and planting pattern increased the contribution rate of micro-aggregate in soil total C. NP and NPM significantly increased the contribution rate of micro-aggregate in soil total C and soil organic C. The effect of rotation cropping was most obvious in driving the contribution rate of micro-aggregate in soil total C and soil organic C.

Effects of Biochar Application on Soil Microbial Nutrient Limitations and Carbon Use Efficiency in Lou Soil

Soil microbial metabolism is vital for nutrient cycling and stability of an ecosystem. To elucidate the long-term effects of biochar application on nutrient limitations and carbon use efficiency (CUE) of soil microbial metabolisms, biochars pyrolyzed at 450℃ from trunks and branches of fruit trees under an oxygen-limited condition were mixed with the top Lou soils (0-20 cm) with application amounts of 0, 20, 40, 60, and 80 t·hm-2 in 2012. Corn-wheat rotation was carried out afterwards for seven years. The nutrient limitations of soil microbial metabolisms were analyzed quantitatively through ecoenzymatic stoichiometry in 2019. The results indicated that:① With an increase in the biochar application amount, soil moisture, organic carbon, total nitrogen, C:N, C:P, and N:P significantly increased, whereas there were no clear patterns for the active components of carbon, nitrogen, and phosphorus, microbial biomass carbon, nitrogen, phosphorus and total phosphorus. In contrast, the activities of five extracellular enzymes (β-1,4-glucosidase, cellobiohydrolase, leucine aminopeptidase, β-1,4-N-acetylglucosaminidase, and phosphatase) were significantly reduced. ② The soil microorganisms suffered from the phosphorus limitation under all treatments in this study. In the treatments of biochar application, the carbon and phosphorus limitations of microbial metabolisms increased significantly with increasing application amount, whereas the microbial CUE decreased significantly. When the application amount was 20 t·hm-2, the carbon limitation (0.625±0.022) and phosphorus limitation (62.153°±0.892°) were lowest, and the microorganism CUE (0.511±0.007) was highest. ③ Partial least-squares path modeling (PLS-PM) showed that soil carbon, nitrogen, phosphorus, and their stoichiometry had a very direct positive effect on phosphorus limitation (P<0.01), and there was a positive correlation between carbon limitation and phosphorus limitation (R2=0.242, P<0.001); in contrast, the carbon and phosphorus limitations had a very significant negative effect on CUE (P<0.001). It was revealed that the excessive application of biochar had caused a soil element stoichiometry imbalance, which deteriorated the phosphorus limitation of the soil microbial metabolism and further led to carbon limitation and reduction of CUE. When the biochar application amount was 20 t·hm-2, C and P limitations were lowest, and microbial CUE was highest. Therefore, 20 t·hm-2 was optimal for regulating soil microbial metabolism, maintaining ecological functions, and reducing carbon dioxide emission produced by microbial metabolism.

Factors determining soil water heterogeneity on the Chinese Loess Plateau as based on an empirical mode decomposition method

Soil water is a critical resource, and as such is the focus of considerable physical research. Characterization of the distribution and spatial variability of soil water content (SWC) offers important agronomic and environmental information. Estimation of non-stationary and non-linear SWC distribution at different scales is a research challenge. Based on this context, we performed a case study on the Chinese Loess Plateau, with objectives of investigating spatial variability of SWC and soil properties (i.e., soil particle composition, organic matter and bulk density), and determining multi-scale correlations between SWC and soil properties. A total of 86 in situ sampling sites were selected and 516 soil samples (0-60 cm depth with an interval of 10 cm) were collected in May and June of 2019 along the Yangling-Wugong-Qianxian transect, with a length of 25.5 km, in a typical wheat-corn rotation region of the Chinese Loess Plateau. Classical statistics and empirical mode decomposition (EMD) method were applied to evaluate characteristics of the overall and scale-specific spatial variation of SWC, and to explore scale-specific correlations between SWC and soil properties. Results showed that the spatial variability of SWC along the Yangling-Wugong-Qianxian transect was medium to weak, with a variability coefficient range of 0.06-0.18, and it was gradually decreased as scale increased. We categorized the overall SWC for each soil layer under an intrinsic mode function (IMF) number based on the scale of occurrence, and found that the component IMF1 exhibited the largest contribution rates of 36.45%-56.70%. Additionally, by using EMD method, we categorized the general variation of SWC under different numbers of IMFs according to occurrence scale, and the results showed that the calculated scales among SWC for each soil layer increased in correspondence with higher IMF numbers. Approximately 78.00% of the total variance of SWC was extracted in IMF1 and IMF2. Generally, soil texture was the dominant control on SWC, and the influence of the three types of soil properties (soil particle composition, organic matter and bulk density) was more prominent at larger scales along the sampling transect. The influential factors of soil water spatial distribution can be identified and ranked on the basis of the decomposed signal from the current approach, thereby providing critical information for other researchers and natural resource managers.

Effects of Different Amelioration Materials on Soil Fertility in Abandoned Homestead Reclaimed Soil

Abandoned homestead reclaimed soil has poor structural structure and lack of nutrients. In this study, organic fertilizer (F), curing agent (S) and fly ash (C) were used as amelioration materials to improve nutrient content of abandoned residential land reclamation soil. After 3 years of wheat-corn rotation, soil samples were collected to determine soil organic matter, total nitrogen, available phosphorus and available potassium contents. The results showed that soil organic matter content at the depth of 0-30 cm soil layer in the treatments of F increased significantly due to organic fertilizer input. The content of total nitrogen, available phosphorus and available potassium in the treated soil with improved materials increased significantly compared with the control. It indicated that the addition of amelioration materials and continuous tillage had significant effect on improving soil fertility in the abandoned homestead reclaimed soil.

Relationships between field management, soil compaction, and crop productivity

ABSTRACT In southern Iran, intensive tillage operations and residue removal increased soil compaction, which reduces soil porosity, crop development, and yield. While conservation farming combined with crop residue retention showed encouraging results. A 2-year field experiment (2016–2017) was conducted to evaluate the effect of tillage methods (conventional tillage, CT; reduced tillage, RT; and no tillage, NT) on soil properties as well as crop yield of wheat and corn grown with or without crop residue removal, using a split-plot design with three replications near Shiraz, Iran. Results showed NT had higher soil bulk density (BD) at 0–10 cm soil depth (up to 1.32 Mg m−3), thereby lower cumulative water infiltration (less than 10 cm/150 min). The lowest soil organic carbon was obtained under CT with residue removal (less than 1%), while RT and NT either showed similar effects or RT was superior over NT. Reduced tillage produced higher yield of wheat and corn, which were 9190 and 14,996 kg ha−1, respectively. Our research has shown that replacing RT with CT and/or NT can greatly optimize crop yield, reduce soil compaction, and improve water infiltration under wheat-corn rotation, but it is based on the short-term results and evaluation of long-term experiment is highly recommended.

Soil microbial community shifts with long-term of different straw return in wheat-corn rotation system

Despite the integral role of the soil microbial community in straw decomposition, we still have a limited understanding of the complex response of microbial community to long-term of crop straw return in rotation system. Here we report on the structural and functional response of the soil bacterial and fungal community to more than 10 years of straw return in wheat-corn rotation system. Compared with single-season straw return, soil microbial phosphor lipid fatty acids (PLFAs) and catabolic activity were improved more greatly with double-season straw return. The relative abundance of bacteria and fungi decreased with double-season straw return, but increased with single-season straw return. The copiotrophic bacteria were more represented in the soils with corn straw return, while oligotrophic groups were more represented in soils with wheat straw return. Compared with wheat straw return, lower fungal community diversity and higher abundance of fungal pathogen (identified to be Leptosphaeria) were observed with corn straw return, especially at high return rates. Redundancy analysis showed that soil available potassium (P = 0.008) and ratio of C to N (P = 0.048) significantly affected the soil bacterial community, while soil electric conductivity (P = 0.04) was the significant factor impacting soil fungal community. It suggests that full corn straw return might have positive impact on soil mineral nutrient but negative impact on soil fungal community diversity and pathogenic risk, mainly due to the change in soil electric conductivity.

The Structure and Diversity of Nitrogen Functional Groups from Different Cropping Systems in Yellow River Delta.

The Yellow River Delta (YRD) region is an important production base in Shandong Province. It encompasses an array of diversified crop systems, including the corn–wheat rotation system (Wheat–Corn), soybean–corn rotation system (Soybean–Corn), fruits or vegetables system (Fruit), cotton system (Cotton) and rice system (Rice). In this study, the communities of ammonia oxidizer–, denitrifier– and nitrogen (N)–fixing bacteria in those cropping systems were investigated by Illumina Miseq sequencing. We found that Rice soil exhibited significantly higher diversity indices of investigated N–cycling microbial communities than other crop soils, possibly due to its high soil water content. Wheat–Corn soils had higher abundances of nitrification gene amoA and denitrification genes nirK and nirS, and exhibited higher soil potential nitrification rate (PNR), compared with Soybean–Corn, Cotton and Fruit soils. Consistently, redundancy analysis (RDA) showed that soil water content (SWC), electrical conductivity (EC), and total nitrogen (TN) were the most important influencing factors of the diversity and structure of the investigated N–cycling microbial.

Observation and estimation of mercury exchange fluxes from soil under different crop cultivars and planting densities in North China Plain

The emission of mercury (Hg) from cropland soil greatly affects the global Hg cycle. Combinations of different crop cultivars and planting densities will result in different light transmittance under canopies, which directly affects the solar and heat radiation flux received by the soil surface below crops. In turn, this might lead to differences in the soil–air total gaseous mercury (TGM) exchange under different cropping patterns. However, soil–air TGM exchange fluxes in croplands under differing canopies have been poorly investigated. Here, a one-year observation of TGM exchange flux was conducted for cropland soils covering five different crop cultivars and three planting densities in North China Plain using the dynamic flux chamber method. The results showed that light transmittance under the canopies was the key control on soil–air TGM exchange fluxes. High light transmittance can enhance soil TGM emission rates and increase the magnitude of diurnal variations in soil–air TGM exchange fluxes. Furthermore, we found that there were piecewise–function relationships (Peak function–constant equation) between light transmittance under the different canopies and the numbers of days after crop sowing. The soil–air TGM exchange fluxes showed a parabolic response to changes in light transmittance under the different canopies. A second-order model was established for the response relationship between soil–air TGM exchange flux and soil Hg concentration, total solar radiation above the canopy, and numbers of days after sowing. The estimated annual average soil–air TGM exchange flux was 5.46 ± 21.69 ng m−2 h−1 at corn–wheat rotation cropland with 30 cm row spacing using this second-order model. Our results might a data reference and a promising foundation for future model development of soil–air TGM exchange in croplands under different crop cultivars and planting densities.

Inorganic Phosphorus Distribution in Soil Aggregates Under Different Cropping Patterns in Northwest China

Accurate information on soil inorganic phosphorus (Pi) is crucial for the sustainable development of agriculture in arid regions. An experiment was conducted to investigate the effect of cropping patterns on Pi concentrations in soil aggregates from the 0–10 cm depth in northwest China. The three cropping patterns were as follows: continuous cotton (CC), corn-wheat rotation (CW), and tree-cotton intercropping (TC). The results showed that more than 89% of the soil mass was in the macroaggregates (> 0.25 mm) in all cropping patterns, indicating a good soil structure in the study area. Total Pi and available P concentrations were significantly higher in the TC > CW. Additionally, the O-P concentrations were enriched in the CC treatment. But, the Ca8-P, Al-P and Fe-P concentrations were significantly greater in CW and TC than in CC. These results suggested that continuous cotton production leads to plant available Pi (Ca8-P, Al-P, and Fe-P) convert into unavailable Pi forms (Ca10-P and O-P). The TC system had the greatest contribution to total P in > 0.25 mm aggregates (p < 0.05), suggesting TC had a greater capacity to supply soil P. TC may be an appropriate farming practice for maximum availability of P in arid farmland ecosystems.

Soil treatment and crop rotation for in situ remediation of heavy metal-contaminated agricultural soil in gold mining areas

In many areas of China, agricultural land is subject to heavy metal contamination from mining activity. This study investigates an in situ remediation program suitable for the recovery of heavy metal-contaminated agricultural soil around mining areas. A 1-year field experiment was conducted in a gold mining area of Tongguan, Shaanxi Province, China, to evaluate the effectiveness of engineering remediation measures, including adding a layer of noncontaminated soil, or soil homogenization to 40 cm and 80 cm depths, and three crop rotation systems, including rye-corn rotation, wheat-corn rotation, and potato-adzuki bean rotation on ameliorating heavy metal pollutants from contaminated agricultural soil around mining areas. The results showed that soil treatment and crop rotation significantly decreased soil heavy metal concentrations, with 80 cm homogenization and wheat-corn rotation being most effective. After 1 year of in situ remediation using this combination, the concentrations of Hg, Cd, and Pb in topsoil (0–20 cm) were 71.7%, 82.4%, and 21.8% lower, respectively, than before remediation. The single and Nemero indexes of the edible parts of wheat and corn were both <1, indicating they were safe for consumption. The results provide a solution for the in situ remediation of heavy metal-contaminated agricultural soil in mining areas.

Development of a predictive tool for rapid assessment of soil total nitrogen in wheat-corn double cropping system with hyperspectral data

ABSTRACTPrecision farming based on soil total nitrogen status is crucial to informed fertilization strategies while enhancing environmental quality of agricultural ecosystems. Hyperspectral technology was applied for rapid assessment of soil total nitrogen content in a long-term fertilization experiment of wheat-corn rotation system. The first-order derivative of squared spectra and Soil Adjusted Spectral Index transformation provided the highest correlation with soil total nitrogen contents. Inversion modeling results involving multiple linear regression, back propagation neural network (BPNN), and partial least square regression indicated that BPNN provided the best performance with coefficient of determination (R2) reaching 0.8 and 0.9, respectively, for wheat and corn seasons. Model performance with wheat and corn season combined was poor due to seasonal difference in hyperspectral patterns and different decomposition of straws returned to the field. This study provided a quantitative tool for rapid and accurate diagnosis of soil total nitrogen content for precision agriculture.

English

English

Carbon and nitrogen forms in soil organic matter influenced by incorporated wheat and corn residues

ABSTRACTWe have investigated molecular-scale changes in soil organic matter (SOM) as incorporated wheat and corn residues decompose and whether those changes are correlated with soil nitrogen forms. The ‘initial litter quality hypothesis’ that compositional variations in plant residues may persist during decomposition of these residues as they are transformed to SOM was tested. We studied soils in 6-year field experiments of a double-cropped corn–wheat rotation system designed with the following treatments: no crop residue and no chemical fertilizer, chemical fertilizer alone, wheat straw + chemical fertilizer, corn stover + chemical fertilizer, and corn plus wheat residue + chemical fertilizer. Organic carbon and nitrogen forms were assessed, and SOM chemical structures were examined by Fourier transform infrared and solid-state nuclear magnetic resonance spectroscopy. We found that concentrations of organic-N in corn residues plus fertilizer treatment were significantly larger than those in wheat straw plus fertilizer treatment. In addition, concentrations of amide groups and NCH in SOM with corn residue treatment were larger than those in SOM with wheat residue treatment. Incorporation of both corn and wheat residues led to an increase in carbohydrate-derived components of SOM. Compared with the check treatment, aromaticity, alkyl C/O-alkyl C, and hydrophobicity/hydrophilicity indices of the SOM were lower with addition of residue. Aromaticity was greater in corn residue treatment than in wheat residue treatment. This study provides support for the hypothesis that the variation in chemical composition of SOM reflected the incorporation of distinct chemical structures in wheat and corn straw residues.

Effects of tillage and broiler litter on crop productions in an eroded soil

This study was initiated in 2005 at the Plant Material Center, NRCS, in Coffeeville MS, on an eroded Loring silt loam soil with 1⿿3% slope to determine the effects of broiler litter with tillage and cropping systems on improving soil quality and crop production. A randomized complete block design with three replications and split-plot arrangement of treatments was used. The main plots were tillage and no-till and the sub-plots were an unfertilized control, broiler litter at low (9Mgha⿿1) and high (18Mgha⿿1) rates. The cropping system was corn-wheat rotation. Broiler litter was applied as N source to corn (Zea mays) grown under no-tillage (NT) and conventional tillage (CT) in 2005 and 2007. Winter wheat (Triticum spp) was planted after harvesting corn and harvested for grain in June 2006 and 2008 in the same plots that previously received litter. Corn grain yield, grain N and P uptake were significantly increased with increasing broiler litter applications. Averaged across years, corn grain yield and N uptake were greater with conventional tillage (4014 and 63kgha⿿1) than no-till corn (2608 and 42kgha⿿1), respectively. Residual effect of broiler litter at the high rate significantly increased wheat grain yield and grain N uptake (1778 and 26kgha⿿1) as compared to the control (901 and 14kgha⿿1), respectively. Biennial application of broiler litter to an eroded soil enhanced corn- wheat productions, and improved soil quality by increasing soil C, water stable aggregate and infiltration and reducing soil penetration resistance.

Seasonal variations in metallic mercury (Hg&amp;lt;sup&amp;gt;0&amp;lt;/sup&amp;gt;) vapor exchange over biannual wheat–corn rotation cropland in the North China Plain

Abstract. Air–surface gas exchange of Hg0 was measured in five approximately bi-weekly campaigns (in total 87 days) over a wheat–corn rotation cropland located on the North China Plain (NCP) using the relaxed eddy accumulation (REA) technique. The campaigns were separated over the duration of a full-year period (2012–2013) aiming to capture the flux pattern over essential growing stages of the planting system with a low homogeneous topsoil Hg content ( ∼ 45 ng g−1). Contrasting pollution regimes influenced air masses at the site and corresponding Hg0 concentration means (3.3 in late summer to 6.2 ng m−3 in winter) were unanimously above the typical hemispheric background of 1.5–1.7 ng m−3 during the campaigns. Extreme values in bi-directional net Hg0 exchange were primarily observed during episodes of peaking Hg0 concentrations. In tandem with under-canopy chamber measurements, the above-canopy REA measurements provided evidence for a balance between Hg0 ground emissions and uptake of Hg0 by the developed canopies. During the wheat growing season covering ∼ 2 / 3 of the year at the site, net field-scale Hg0 emission prevailed for periods of active plant growth until canopy senescence (mean flux: 20.0 ng m−3), showing the dominance of Hg0 soil efflux during warmer seasons. In the final vegetative stage of corn and wheat, ground and above-canopy Hg0 flux displayed inversed daytime courses with a near mid-day maximum (emission) and minimum (deposition), respectively. In contrast to wheat, Hg0 uptake of the corn canopy at this stage offset ground Hg0 emissions with additional removal of Hg0 from the atmosphere. Differential uptake of Hg0 between wheat (C3 species) and corn (C4 species) foliage is discernible from estimated Hg0 flux (per leaf area) and Hg content in mature cereal leaves, being a factor of &gt; 3 higher for wheat (at ∼ 120 ng g−1 dry weight). Furthermore, this study shows that intermittent flood irrigation of the air-dry field induced a short pulse of Hg0 emission due to displacement of Hg0 present in the surface soil horizon. A more lingering effect of flood irrigation is however suppressed Hg0 soil emissions, which for wet soil ( ∼ 30 % vol) beneath the corn canopy was on average a factor of ∼ 3 lower than that for drier soil (&lt; 10 % vol) within wheat stands. Extrapolation of the campaign Hg0 flux data (mean: 7.1 ng m−2 h−1) to the whole year suggests the wheat–corn rotation cropland to be a net source of atmospheric Hg0. The observed magnitude of annual wet deposition flux ( ∼ 8.8 µg Hg m−2) accounted for a minor fraction of soil Hg0 evasion flux prevailing over the majority of the year. Therefore, we suggest that dry deposition of other forms of airborne Hg constitutes the dominant pathway of Hg input to this local ecosystem and that these deposited forms would be gradually transformed and re-emitted as Hg0 rather than being sequestered here. In addition, after crop harvesting, the practice of burning agricultural residue with considerable Hg content rather than straw return management yields seasonally substantial atmospheric Hg0 emissions from croplands in the NCP region.

Effects of soil tillage system on yield and weeding level in wheat crop

This paper presents the yield and evolution of weeding level in wheat crop, as part of a three-year soybean-winter wheat-corn rotation, with the implementation of minimum soil tillage variants with: rotary harrow, paraplow and chisel plough. The experiment has been conducted on a Phaeozem argic soil type in Transylvania Plain, with conventional and four minimum tillage systems of soil cultivation. The level of weeding was influenced by the soil tillage system in the phase of springing up to the harvest of the wheat crop. At crop spring­ing, the total number of weeds was 31.8 weeds/m2 in the variant with plough + rotary har­row and between 31.6-34.7 weeds/m2 in minimum tillage variants. A greater number of perennial dicotyledonous weeds can be recorded in the minimum tillage variant (between 1.2-1.6 weeds/m2), when compared with plough + rotary harrow variant (0.9 weeds/m2). At the crop harvest stage, the number of weeds was 8.2-50.6% higher in the variants with minimum tillage system, when compared to the conventional tillage system. A decrease in the percent of annual dicotyledonous weeds is evident, from 85.9% in the variant with plough, to 71.5-78.9% in the variants with minimum tillage systems, with an increase in perennial dicotyledonous (from 7.9% to 8.4-13.8%) and monocotyledonous weeds (from 6.2 to 11.6-20%). The changes in the floristic content of weeding level indicates the need for changing the strategies of weed control in winter wheat crop in the variants with mini­mum soil tillage systems. Increasing the percent of perennial dicotyledonous weeds by 59% (from 7.9% to 13.8%) makes the wheat cultivation in crop rotation with leguminous nec­essary, completed with the use of specific herbicide methods, in previous crop and wheat crop. The presence of monocotyledonous weeds of about 11.6% to 20.0% completes the necessity for the application of different strategies of control and correlation, for the weed­ing level as well as the type of weed, including their annual or perennial character. Yields obtained by applying minimum tillage were 97.8-98.2%, when paraplow and chisel are compared to plough and were significantly lower in the rotary harrow variant, while weed­ing level was the highest.

Calibration of DNDC model for nitrate leaching from an intensively cultivated region of Northern China

Nitrogen (N) loss through nitrate leaching in arable cropping systems in China has been recognized as one of the most common agricultural sources of groundwater contamination. The Denitrification–Decomposition or DNDC model, equipped with detailed soil hydrological and biogeochemical processes, was adopted in the study to quantify nitrate leaching for an intensively cultivated region in northern China. Several key parameters embedded in DNDC were calibrated against leaching data measured at a typical field with winter wheat–corn rotation within the target domain region. Five more sites representing the predominant cropping systems in the study region were selected for validating the modified model. In comparison with the original version of DNDC, the revised version yielded better results in simulated soil water and N leaching losses. To upscale the model simulation to regional level, we linked the validated DNDC to a regional database containing meteorological data, soil properties, vegetation types, and management practices for the target domain. Results from the regional simulation indicated that the total potential nitrate leaching load from the simulated 16.31millionha croplands (sown area) ranged from 1.5 to 2.15TgN per year, with an average of 1.8TgN, which was equivalent to 26.1% of the total amount of N fertilizer applied in the region in 2009. The modeled results showed clear spatial patterns of nitrate leaching rates across the region due to the spatially differentiated fertilizer application rates as well as the soil water regimes. Alternative water management practices were suggested to effectively reduce nitrate leaching losses from the agricultural region in northern China.

Development of a generic auto-calibration package for regional ecological modeling and application in the Central Plains of the United States

Process-oriented ecological models are frequently used for predicting potential impacts of global changes such as climate and land-cover changes, which can be useful for policy making. It is critical but challenging to automatically derive optimal parameter values at different scales, especially at regional scale, and validate the model performance. In this study, we developed an automatic calibration (auto-calibration) function for a well-established biogeochemical model—the General Ensemble Biogeochemical Modeling System (GEMS)-Erosion Deposition Carbon Model (EDCM)—using data assimilation technique: the Shuffled Complex Evolution algorithm and a model-inversion R package—Flexible Modeling Environment (FME). The new functionality can support multi-parameter and multi-objective auto-calibration of EDCM at the both pixel and regional levels. We also developed a post-processing procedure for GEMS to provide options to save the pixel-based or aggregated county-land cover specific parameter values for subsequent simulations. In our case study, we successfully applied the updated model (EDCM-Auto) for a single crop pixel with a corn–wheat rotation and a large ecological region (Level II)—Central USA Plains. The evaluation results indicate that EDCM-Auto is applicable at multiple scales and is capable to handle land cover changes (e.g., crop rotations). The model also performs well in capturing the spatial pattern of grain yield production for crops and net primary production (NPP) for other ecosystems across the region, which is a good example for implementing calibration and validation of ecological models with readily available survey data (grain yield) and remote sensing data (NPP) at regional and national levels. The developed platform for auto-calibration can be readily expanded to incorporate other model inversion algorithms and potential R packages, and also be applied to other ecological models.