Soil Types In China Research Articles

Assessing the isotopic biases of soil water from cryogenic water extraction in different soil types in China

AbstractThe utilization of deuterium (δ2H) and oxygen (δ18O) isotope ratios in cryogenically extracted water from soil samples is a widely employed method in hydrological and ecological research. Nevertheless, an increasing body of research indicates that cryogenic water extraction (CWE) leads to δ2H depletion in soil water. To investigate the widespread existence of this phenomenon, samples from eight physicochemically distinct soils in China underwent rehydration with a reference water at five different water contents and were subsequently extracted using CWE. In comparison to the reference water, significant and inconsistent δ2H depletion was observed in all eight soil samples. The δ18O bias also exhibited variation, ranging from enrichment to depletion. Generally, Z score assessments indicated unacceptable results for all soils. Water content emerged as the most influential variable affecting both δ2H and δ18O biases, while soil properties had different impacts on these biases. Source water, as calculated by a linear regression model, revealed that the isotopic composition of extracted soil water differed from that of the reference water. The cryogenic extraction error in soil water could not solely attributed to fractionation processes during the extraction but resulted from the release of tightly bound soil water into the reference water. Using the influencing factors, correction models for δ2H and δ18O biases by CWE were developed. By these models, the δ2H and δ18O biases were mostly successful corrected. High soil water extraction efficiency (e.g., 99%) was recommended to minimize isotopic biases. These efforts necessitate further testing, particularly in ecohydrological studies involving isotope measurements of soil water through CWE.

Differences in Soil Microbial Communities across Soil Types in China’s Temperate Forests

Differences in Soil Microbial Communities across Soil Types in China’s Temperate Forests

Phosphorus uptake and rhizosphere properties of alfalfa in response to phosphorus fertilizer types in sandy soil and saline-alkali soil.

Phosphorus (P) fertilizer is critical to maintain a high yield and quality of alfalfa (Medicago sativa L.). There are several fertilizer types and soil types in China, and the application of a single type of P fertilizer may not be suitable for present-day alfalfa production. In order to select the optimal combination of alfalfa and soil type and fertilizer type for improving P utilization efficiency. We conducted a greenhouse pot experiment, calcium superphosphate (SSP), diammonium phosphate (DAP), ammonium polyphosphate (APP), potassium dihydrogen phosphate (KP), and no-fertilizer control treatments were applied to alfalfa in sandy and saline-alkali soils. The response of alfalfa root morphology and rhizosphere processes to different P fertilizers was investigated. The results showed that shoot biomass of alfalfa was slightly higher in sandy soil than in saline-alkali soil. Shoot biomass of alfalfa increased by 223%-354% in sandy soil under P treatments compared with the control, and total root length increased significantly by 74% and 53% in DAP and SSP treatments, respectively. In saline-alkali soil, alfalfa shoot biomass was significantly increased by 229% and 275% in KP and DAP treatments, and total root length was increased by 109% only in DAP treatment. Net P uptake of alfalfa in DAP treatment was the highest in both soils, which were 0.73 and 0.54 mg plant-1, respectively. Alfalfa shoot P concentration was significantly positively correlated with shoot and root biomass (P < 0.05, 0.01 or 0.001) whereas negatively correlated with acid phosphatase concentration (P < 0.05). Improvement of plant growth and P uptake induced by P fertilizer application was greater in sandy soil than in saline-alkali soil. DAP and KP was the most efficient P fertilizers in both sandy soil and saline-alkali soil.

Nitrogen functional profiles of microbiomes in diverse agricultural and forest soils and its driver at continental scale in China

Functional characteristics of microbiomes are good predictors of nitrogen (N) biogeochemistry, but soil microbial N-functional profiles under different land use practices and their dominant drivers at continental scale remain unclear. For this study, we selected soils having a broad range of edaphic factors across different land use practices and soil types in China and used metagenomic sequencing to investigate N-functional profiles of microbiomes. The N-pathway frequencies were highest in paddy soils, and the composition of N-cycling genes in paddy soils significantly diverged from upland and forest soils. Differential abundance analysis showed that genes associated with nitrogen dissimilatory pathways exhibited enrichment in paddy soils, whereas those linked to assimilatory pathways were enriched in forest soils. Aggregated boosted tree analysis revealed that the frequencies of N-pathways and relative abundances of N-cycling genes were mainly explained by soil moisture and pH. Partial Mantel and redundancy analysis consistently showed that N-functional composition correlated strongest with moisture and pH. Overall, our results demonstrated that soil moisture and pH were vital drivers of microbial N-functional profiles, providing novel evidence for soil moisture and pH’s role in driving whole nitrogen cycling. Considering the large fluctuations in moisture over time, soil pH, with minor seasonality, could be used as indicators to reflect microbial N-functional profiles at the continental scale.

Pore structure analysis via X-ray μCT: Enhancing soil macroaggregate models for water permeability and carbon sequestration

Soil macroaggregates are crucial for carbon sequestration, water retention, and soil fertility. Their ecological functions are influenced by their pore characteristics. Yet, the relationship between pore structure and the movement of water and carbon within macroaggregates is not fully understood. In this study, the porosity, connectivity, and morphology of macroaggregate pores in three typical soil types in China were characterized. Additionally, water permeability and carbon sequestration were modeled based on in-situ CT-scanning images. The results indicated that the macropores within the macroaggregates serve as the primary channels for water permeability, while pore morphology of mesopores significantly influences carbon sequestration. The water permeability increased with the presence of macropores and enhanced connectivity within the macroaggregates. Dissolved organic carbon (DOC) showed a pronounced correlation with oblate pores across all samples, and a more intricate structure offered more surface area space, trapping additional carbon particles. The established model not only elucidates how various pore structures influence the transport of carbon particles and carbon sequestration but also simulates the structural changes in macroaggregates throughout the process. This allows for an intuitive understanding of water and carbon distribution and migration. This research presents an innovative simulation of water and carbon distribution within macroaggregates using micron-scale CT data.

The role of inherited characteristics from parent materials in shaping bacterial communities in agricultural soils

Parent materials are crucial in soil formation and development, but their importance in shaping soil bacterial communities after thousands of years of soil formation remains unknown, especially in agricultural soils. To resolve the influence of underlying features inherited from parent materials on soil microbiome, the microbial community in 197 agricultural soils with long-term crop cultivation history and nonagricultural reference soils from four major types of soils in China, i.e., quaternary red clay soils, tertiary red sandstone soils, alluvial soils and black soils, were analyzed and compared. We found that different types of soils supported distinct bacterial communities. The characteristics inherited from parent materials explained more of the variation (31.47%) in bacterial community structure than the selected variables regulated by soil management (1.63%) and the climate condition (1.10%). Only 9.0% of total bacterial amplicon sequence variants (ASVs) which contributed, on average, 47% of the total bacterial abundances in a given agricultural soil, were shared by all soil types. These abundant common ASVs were closely related to agricultural practices, suggesting a strong enrichment effect of a small number of core taxa by long-term crop cultivation. In contrast, approximately 55.6% of ASVs with low relative abundance were specific to soil type. These specific groups were closely associated with the distinctive features of soil type, implying that they represent unique populations selected by the parent material features during pedogenesis. Collectively, soil type may have a strong selective pressure on the bacterial communities in matured agricultural soils, leading to a large pool of specific taxa with limited environmental occurrence. Whilst a small number of core taxa achieve high abundances by responding to long-term crop cultivation.

Characterisation of organic carbon distribution and turnover by stable carbon isotopes in major types of soils in China

Environmental context Soil carbon sequestration plays an important role in achieving the goal of carbon neutrality. We studied the characteristics of organic carbon distribution and sequestration by stable carbon isotopes in nine types of soils in China and found that macro-aggregates possessed more organic carbon with a low degree of decomposition, while the overall direction of organic carbon transfer between aggregates was from macro-aggregates through micro-aggregates to the grain-size fractions of chalky clay. These results provide a foundation for understanding soil carbon sequestration in China’s cultivated lands. Rationale Soil is the largest carbon reservoir of terrestrial ecosystems. Studying carbon turnover in cultivated soils is vital for China to achieve its carbon neutrality goal. Methodology In this research, we investigated the distribution characteristics of soil organic carbon and its turnover among aggregates in nine major soil types in China by 13C stable isotopes. Results Since the second national soil survey in China 1979, the surface soil organic carbon (SOC) content of cultivated lands in boggy soils, black soils and dark brown forest soils in northeastern China has decreased (129.06, 2.70 and 7.78 g kg−1, respectively) while increased in cinnamon soils, brown soils, red soils, latosols, paddy soils and chestnut soils (0.85–7.79 g kg−1). Overall, the SOC content was highest in 1–0.25 mm aggregates, lowest in 0.053–0.02 mm aggregates and higher in &lt;0.02 mm aggregates. The Δ13C value showed that the silt-clay size class fraction &gt; micro-aggregates &gt; macro-aggregates. Discussion The overall turnover direction of SOC among aggregates starts from macro-aggregates to micro-aggregates and ends with the silt-clay size class fraction. The result directly confirms both the ‘hierarchical development model’ and ‘embryonic development model’ of soil aggregate formation. The SOC flow direction and mobility potential between aggregates, as indicated by Δ13C values, suggest that cultivated soils are more susceptible to soil type than wasteland soils.

High-precision zinc isotopic characterization of twenty soil reference materials from China determined by MC-ICP-MS.

Zinc isotopic ratios serve as powerful tools for tracing biochemical cycling of metals at Earth's surface, including the distribution, transportation, and enrichment of zinc (Zn) in soil. To conduct such studies and enable inter-laboratory comparisons, high-precision Zn isotopic measurements require the use of soil reference materials (RMs). However, there have been limited reports on the high-precision Zn isotope ratios of soil RMs thus far. In this study, we have developed a two-step Zn chemical separation protocol utilizing Bio-Rad AG MP-1M resin columns. This method has demonstrated excellent reproducibility for measuring the external δ66Zn values (relative to JMC-Lyon) of standard soil reference materials over an extended time period, with a better than 0.06‰ (2SD) precision. Remarkably, this study is the first to report the Zn isotopic compositions of 20 soil reference materials from various soil types in China. With the exception of one sample obtained from a mining area, the Zn isotopic compositions of all the analyzed soil reference materials exhibit remarkable similarity, with an average δ66Zn value of 0.31 ± 0.12‰, which aligns closely with the values observed in igneous rocks. The exceptional sample, with a higher δ66Zn value of 0.61 ± 0.02‰, indicates potential contamination during mining activities.

Characteristics of Soil Erodibility in the Yinna Mountainous Area, Eastern Guangdong Province, China

Soil erodibility research is of theoretical and practical significance to the prediction and prevention of regional soil erosion. At present, the study on soil erodibility in the lateritic red soil area of eastern Guangdong province is relatively lacking. Taking the forest land soil of the Yinna mountainous area as the research object, the physical and chemical properties (organic matter mass fraction, texture, moisture, bulk density, pH, aggregate content) of soil samples at different altitudes were measured with field survey sampling and indoor analysis. Soil erodibility K values were simulated with different models (the EPIC model, the Torri model, and the Shirazi model) and the regional applicability of the K simulation models was discussed. The influence of soil properties on soil erodibility was analyzed. The results showed that: (1) K values in the Yinna mountainous area are between 0.0250 and 0.0331 t·hm2·h/MJ·mm·hm2, and the K value in the subsoil layer (20-40 cm) is higher than that of the topsoil layer (0-20 cm). These values decreased significantly with the increase of altitude. The soil in the study area belongs to low-medium to medium erodible soil types. (2) The three models have certain applicability in the Yinna mountainous area, but the simulation results still lack validation. (3) Soil particle size composition is the most important factor affecting the K value in the study area. As far as the topsoil is concerned, K values increase with the increase of clay and silt content and decrease with the increase of sand content and aggregate stability. Soil erodibility has no significant correlation with pH and bulk density and has no clear relationship with the content of soil organic carbon and soil moisture. The research results can provide basic data for regional soil and water conservation and the construction of K value databases of different soil types in China.

Analysis of soil fertility and optimal nitrogen application of brown earth (luvisols) in China

AbstractThe excessive application of nitrogen (N) has caused a series of environmental problems. Brown earth (BE) is one of the main soil types in China, and the specific soil‐forming conditions make it high risk of nutrient leaching. Determining the soil fertility of BE and optimal N application rates for main crops’ production is important to reduce nitrogen leaching. Based on China's second national soil survey, the basic fertility level of BE was defined, and the effects of four N management methods [one‐time base fertilizer (BF), topdressing (TF), combined organic fertilizer (OF) and controlled‐release fertilizer (CF)] on maize and wheat yield and N efficiency were analysed. The study found that except for lower phosphorus content (level 4), the soil fertility of BE was at a moderate level (level 3). Compared with no N application, these four N management methods significantly increased the maize and wheat yield and showed the trend of OF &gt; CF &gt; TF &gt; BF; TF, CF and OF significantly increased the N efficiency comparison with BF. The optimal N application rates for wheat and maize were 129–174 kg ha−1 and 170–235 kg ha−1, respectively, when considering the win–win of yield and N efficiency. N fertilizer reduction in BE needs to be further strengthened, and the specific N application rates to achieve profit maximization should be adjusted depending on environmental factors.

Community Composition and Co-Occurrence Patterns of Diazotrophs along a Soil Profile in Paddy Fields of Three Soil Types in China.

Diazotrophs play a key role in biological nitrogen (N2) fixation. However, we know little about the distribution of the diazotrophic community along the soil profile in paddy fields. Here, we used Illumina MiSeq sequencing, targeting the nitrogenase reductase (nifH) gene, to investigate changes with depth (0-100cm) in the diazotrophic community in paddy soils of three regions (Changshu, Hailun, and Yingtan) in China. The results indicated that most diazotrophs belonged to the phylum Proteobacteria, accounting for 78.05% of the total number of sequences. The diazotrophic diversity was generally highest in the 10-20cm layer, and then significantly decreased with soil depth. Principal coordinate analysis and PERMANOVA indicated that the diazotrophic community structure was significantly affected by region and soil depth. There were obvious differences in the composition of the diazotrophic community between the topsoil (0-40cm) and the subsoil (40-100cm). Anaeromyxobacter, Sideroxydans, Methylomonas, Nostoc, Methanocella, and Methanosaeta were enriched in the topsoil, while Geobacter, Azoarcus, Bradyrhizobium, and Dechloromonas were concentrated in the subsoil. Furthermore, co-occurrence network analysis showed that the diazotrophic network in the topsoil was more complex than that in the subsoil. Distance-based redundancy analysis indicated that soil total C and N content and pH were the main factors influencing the vertical variation in the diazotrophic community. These results highlighted that depth has a great impact on the diazotrophic diversity, community composition, and co-occurrence patterns in paddy soil.

Fertilization changes soil microbiome functioning, especially phagotrophic protists

The soil microbiome determines crop production and drives nutrient cycling, functions that are altered by fertilization. Yet, we have only begun to understand the effects of fertilization on taxonomic changes on soil microorganisms, while impacts on functional groups across the microbiome and therefore potential soil functioning have never been assessed. Here, using a range of methods including high-throughput sequencing, we identified 77 functional parameters of the main microbiome groups including bacteria, fungi, and protists in three common agricultural soil types in China (black, fluvo-aquic, and red soil), which were fertilized in the same way over two years. We show that fertilization most strongly and generally throughout soil types reduced the relative abundance of the main microbial predators, phagotrophic protists, by 31%. Ten functional groups within the microbiome showed soil type-specific responses to fertilization. For example, ammonia-oxidizing bacteria, and predatory/exoparasitic bacteria were reduced by fertilization in the acidic black and the red soils, while, no other microbial functional group than phagotrophic protists was suppressed by fertilization in the alkaline fluvo-aquic soil. The significant reductions in microbial functional groups especially in acidic soils could be explained by nitrogen enrichment, increased soil acidification and potential biotic links between the functional groups within the microbiome. Together, we show that the fertilization-induced abiotic changes alter microbial functions that depend on the soil and environmental conditions. Particularly the most profound changes on the group of microbial predators might subsequently affect other soil functions performed by bacteria and fungi.

Impact factor analysis, prediction, and mapping of soil corrosion of carbon steel across China based on MIV-BP artificial neural network and GIS

Q235 carbon steel is one of the most widely used carbon steels, and soil corrosion and failures of it caused accidents, casualties, and great financial losses. Corrosion of Q235 carbon steel differed in spatial because of spatial variation in soil environmental factors. However, the national scale spatial pattern of soil corrosion of Q235 carbon steel across China has not been explored. The values of 12 impact factors, corrosion rate, and pitting corrosion rate at 25 sites covered all soil types in China were collected. Mean impact value (MIV) algorithm and back propagation artificial neural network (BP ANN) were combined and applied in the impact factor analysis. Prediction models for corrosion rate and pitting corrosion were developed based on BP ANN. The proposed prediction models and information about soil properties with high resolution (1 km × 1 km) were used in the prediction of corrosion rate. Based on geographical information system (GIS), the national scale spatial pattern of soil corrosion of Q235 carbon steel across China were analyzed. The water content and pH were of the largest influence (|MIV| > 0.522) on both corrosion rate and pitting corrosion rate. For prediction models of corrosion rate and pitting corrosion rate, the predicted values were close to the measured values. Corrosion rates were of higher spatial differences, ranged from 0.632 to 5.181 g/(dm2·a). Pitting corrosion rates in the northeast were higher than other areas, which might be caused by higher values of total salt content, organic matter, and total voidage. Average corrosion rate in soil type 1 (1.161 mm/a) was nearly two times of that in soil type 2 (0.610 mm/a) and over three times of that in other types, indicating that corrosion rate varied largely among different soil types. The importance of 12 impact factors of corrosion of Q235 carbon steel were evaluated, and the national scale corrosion rate and pitting corrosion rate in China were predicted and mapped for the first time. Both pitting corrosion rates and corrosion rates were of strong spatial variation.

Distribution characteristics of fungal communities with depth in paddy fields of three soil types in China.

Little is known about the distribution of fungal communities with soil depth on relatively large scales. In this study, typical paddy soils in three regions (Hailun, Changshu, and Yingtan) from north to south China were selected to investigate the vertical distribution (0-100 cm) of the fungal community by Illumina MiSeq sequencing, and to identify the main factors influencing the fungal community distribution. The results indicated that the structure of the soil fungal community changed significantly with region and soil depth. Soil fungal taxa such as Zygomycota, Glomeromycota, Saccharomycete, Kazachstania, Mortierella, Massariosphaeria, Hypholoma, and Zopfiella were enriched at depths of 0-20 cm, whereas Dothideomycetes, Microbotryomycetes, Tremellomycetes, Sporobolomyces, Cryptococcus, Rhodotorula, Fusarium, and Pyrenochaetopsis had high relative abundances at 80-100 cm. Variance partitioning analysis indicated that the geographic distance contributed more to the fungal community variation than environmental variables on a large scale. In addition, soil total carbon and nitrogen contents were the main environmental factors driving the vertical distribution of the fungal community in paddy soils.

Long-term phosphorus deficiency decreased bacterial-fungal network complexity and efficiency across three soil types in China as revealed by network analysis

Soil bacteria and fungi are essential constituents of arable ecosystems. Long-term phosphorus (P) deficiency has been proven to significantly affect microbial community diversity and composition. However, how P deficiency impacts the interplay between bacteria and fungi remains unclear. The objective was to explore the bacterial-fungal co-occurrence patterns in soil as influenced by long-term P deficiency, using network analysis. Bacterial and fungal community datasets were obtained from soils which have consistently and continuously been fertilized with P (+P) or without P (−P) for >20 years in three long-term field experiments in China. Our results showed that the −P network was less complex and less efficient as indicated by fewer edges, lower average degree and higher average path length. Chronic P deficiency simultaneously decreased positive and negative bacterial-fungal edges, implying that both synergistic and antagonistic interactions were enhanced by P application. The keystone species differed between +P and −P network, and those from the +P network showed significant correlations with less soil properties, indicating the −P network was more sensitive to environmental disturbances. Four major modules were observed in both +P and −P networks, and they related with different soil properties, suggesting distinct habitat heterogeneity or niche partitioning. All the modules had similar ecological roles, while the module composition was altered by long-term P deficiency, indicating a possible ecological redundancy. Most of the fungi from the −P treatment were distributed in a special module negatively correlated with available P, indicating that fungi may prefer niches with low P concentration. Taken together, our results illustrated the crucial roles of P availability in microbial community assembly and investigated the responses of co-occurrence patterns to long-term P deficiency by regulating the topological properties, keystone species and module composition of the bacterial-fungal network.

Stoichiometric Characteristics of Purple Sloping Cropland Under Long-term Fertilization and Cultivation

Clarification of the effects of long-term fertilization and cultivation on soil organic carbon (C), nitrogen (N), phosphorus (P), and potassium (K) contents and their stoichiometric ratios can contribute to existing research on the C and nutrient biogeochemical cycles and their interacting mechanisms. Such information is also of great significance to fertilization management and for the control of non-point pollution. Fifteen plots (8 m long, 4 m wide) were set up on a representative purple hillslope (15°). Five treatments (three replications) were used on the plots:i) no fertilizer with downslope cultivation (CK), ii) combined application of manure and fertilizer with downslope cultivation (T1), iii) chemical fertilizers with downslope cultivation (T2), iv) chemical fertilizer with increasing fertilization with downslope cultivation (T3), and v) chemical fertilizer with contour cultivation (T4). The C, N, P and K contents and their ratios in the five treatments corresponding to 0-10 cm and 10-20 cm soil depths were compared. The results showed that C, N and P contents for the different treatments were differed significant and could be ranked:T1 > T3 > T4 > T2 > CK (P<0.05). K content was not significantly different among the four fertilizations (P>0.05) but was significantly higher than the CK treatment (P<0.05), and could be ranked:T4 > T3 > T2 > T1 > CK. The C:N ratios in the five treatments were significantly different (P<0.05) at a soil depth of 10-20 cm (T4 > T3 > T1 > CK > T2). The C:P ratios in the five treatments were significantly different (P<0.05) at a soil depth of 0-10 cm (T1 > T3 > CK > T4 > T2). The C:K, N:P, N:K, and P:K ratios for the five treatments at both of the soil depths showed significant differences (P<0.05), and the C:K, N:K, and P:K were ranked as T1 > T3 > T4 > T2 > CK, whereas the N:P ratio was ranked as T1 > CK > T4 > T3 > T2. The C, N, P, and K contents and their stoichiometric ratios decreased with increasing soil depth. Soil C, N and P in the study site showed moderate variations based on their coefficient of variation (CV):37.50%, 38.91%, and 25.35%, respectively. Soil K on the other hand showed a weak variation (CV 5.03%). Soil C:N and C:P also showed a weak variation with a CV of 7.52% and 14.38%, respectively. Soil C:K, N:P, N:K, and P:K showed moderate variations, with a CV of 35.62%, 17.01%, 37.24% and 44.78%, respectively. There were significant positive interrelations among soil C, N, P, and K contents and their stoichiometric ratios (P<0.05). The average N:P ratio was 2.09, which was much lower than the average value for various soil types in China. Our results indicate that soil N is the key limiting nutrient in purple hillslope land, and that the combination of organic and inorganic fertilizers can effectively alleviate the N deficiency in the study area.

Phosphorus retention and loss in three types of soils with implications for geographical pattern of eutrophication in China

AbstractPhosphorus (P) loss from soil to water bodies is an important process associated with eutrophication of lakes and reservoirs. Phosphorus concentration in China's waterbodies changes geographically, increasing substantially with latitude. It is assumed that the geographical pattern results from change in soil retention and loss features of P. To test this assumption, we designed a soil column leaching experiment to measure the P retention capacity of three common types of soils in China: red, black and loess. Results showed that red soil possessed a much higher P retention capacity than black and loess soils. Red soil retained P primarily through binding by aluminium and iron, with half of the total retained P contributed by iron binding. Phosphorus loss in all three soils was influenced by pH of the used acid solution and the leaching rate. Specifically, acidification tends to promote soil P loss, whereas leaching rate decreases P loss.

Assessing the viability of soil successive straw biochar amendment based on a five-year column trial with six different soils: Views from crop production, carbon sequestration and net ecosystem economic benefits

Converting straw to biochar (BC) followed by successive application to soil has been increasingly suggested as a multi-win approach for soil fertility improvement, carbon (C) sequestration and efficient disposal of straw residues in intensive cropping agroecosystems. However, different soil types response differently in terms of crop growth and non-CO2 greenhouse gas (GHG) emissions after BC application. Furthermore, few studies have comprehensively evaluated the net global warming potential (GWP) and net ecosystem economic benefits (NEEB) after long-term BC incorporation across representative soil types in China. A five-year outdoor column experiment was conducted using three rice-wheat rotated paddy soils and three millet-wheat rotated upland soils developed from different parent materials. Rice straw BC application rates of 0, 2.25 and 11.3 Mg ha−1 were used in each crop season with identical doses of NPK fertilizers. Compared with the no BC controls, BC significantly boosted crop growth, enhanced C sequestration, and decreased cumulative N2O and CH4 emissions in all six soils over five rotation cycles. The response of the upland soils to BC was better in terms of crop growth and N2O mitigation, whereas the soil organic carbon (SOC) increment and CH4 mitigation were less effective compared with the paddy soils. Net GWP decreased 0.6–19 fold after BC application; however, given the low trade price of CO2 (0.21 × 103 CNY Mg−1), only a small contribution was made in terms of C costs to the NEEB. The BC-induced NEEB was mainly dependent on grain yield gains and BC costs. These findings highlight that widespread adoption of successive straw BC application to farmland requires an increase in crop yield and substantial lowering of the BC cost regardless of the soil type. From the standpoints of agronomics, environment and economics, acid upland soil shows most potential in terms of BC application.

Benefits and limitations to straw- and plastic-film mulch on maize yield and water use efficiency: A meta-analysis across hydrothermal gradients

Abstract Ridge-furrow mulching can reduce soil evaporation and conserve rainfall, thereby increasing crop yield and water use efficiency (WUE) in dryland cropping systems. In this study, we collected 837 observations from 50 published papers and used meta-analysis to investigate whether ridge-furrow and mulching practices are equally effective on maize yield, WUE and evapotranspiration (ET) across a range of precipitation and temperature gradients and soil types in China. Five practices were included: (i) straw mulch on flat plots (SMF), (ii) straw mulch on ridge-furrow plots (SMR), (iii) plastic mulch on flat plots (PMF), (iv) plastic mulch on ridge-furrow plots (PMR), and (v) flat plots without mulch, which was used as a control (CK). The meta-analysis showed that both straw mulch and plastic mulch significantly increased maize yields and WUE (except for SMR), and that plastic mulch was more effective than straw mulch in increasing yields, particularly in cold and dry environments. PMR has the highest yields and is more effective in clay loam than in silt loam soils. Straw mulch, but particularly plastic mulch, increased the soil moisture compared to the CK, while plastic mulch increased soil temperature, mainly in spring. However, the positive effect of plastic mulch on maize yield diminished with increasing mean growing-season temperature and precipitation, reaching zero (similar to the CK of no mulch and flat plots) when the growing-season precipitation was greater than 770 mm and the mean growing-season air temperature exceeded 24 °C. The small benefit of straw mulch (on average about 12%) was similar across the precipitation and temperature gradients, including when the benefits of plastic mulch reached zero. While our analysis has shown the benefits of ridge-furrow plastic mulch on yield and water-use efficiency, it has also highlighted the limitations of the benefits. The results provide a guide to the regions where plastic-film mulch and ridge-furrow planting are likely to improve maize yields and regions where the benefits are likely to be limited.

The shadow price of nitrogen

PurposeThe most recent and prestigious scientific research shows that nitrogen leaching caused by over-used nitrogen fertilizer rapidly acidifies all soil types in China, revolutionizing the basic understanding of the mechanism of soil acidification. The purpose of this paper is to study the impact of nitrogen on soil acidity over the long run, which is the shadow price of nitrogen.Design/methodology/approachIn a discrete dynamic programming model, this paper compares the nitrogen application and soil pH between optimal nitrogen control that takes the shadow price of nitrogen into consideration and myopic nitrogen control that ignores that shadow price. Using a five-year panel experimental data on a rapeseed-rice rotation, this paper simulates and numerically solves the dynamic model.FindingsBoth theoretically and empirically, this paper shows that the over-use of nitrogen and the decline in soil pH are explained by ignorance of the shadow price of nitrogen. Compared with optimal nitrogen control, myopic nitrogen control applies more nitrogen in total, resulting in lower soil pH. In addition, over-use in the first season contributes to soil acidification and the carry-over effects mitigate that problem.Originality/valueThis paper enriches the literature by extending the study of the environmental impact of nitrogen leaching to its impact on the long-term loss in agricultural production, providing a new theoretical framework in which to study soil acidification rather than conventionally treating soil acidification as a secondary consequence of acid rain, and showing the possibility of using nitrogen control to mitigate soil acidification when lime applications are not feasible due to socio-economic constraints.