Rice-wheat Rotation Research Articles

In situ effects of biochar field-aged for six years on net N mineralization in paddy soil

An understanding of nitrogen (N) mineralization is essential for tracing the supply of inorganic N for plant uptake. However, how microorganisms regulate N mineralization for carbon (C) sequestration under field-aged biochar amendment remains unclear. To address this, we investigated the soil net N mineralization rate (net Nmin), contents and hydrolytic enzyme activities of C and N, microbial biomass N, and native 15N values in bulk soil and aggregate size classes for six years after biochar application (20 and 40 t ha-−1) in a typical rice-wheat rotation. The results showed that aged biochar decreased net Nmin (normalized by total N content) by 10.5 %–69.9 %, and C and N hydrolytic enzyme activities per unit of microbial biomass C by 4.8–71.1 % and 24.0–77.8 %, respectively, compared with N fertilization in all soil aggregates except for ClayF size class (<2 μm). Microbial biomass N (MBN) increased by 21.5–130.9 % in soil aggregates, while the δ15N values decreased following biochar addition compared with those under N fertilization. The labile C:N ratios were higher in the bulk soil and MacroA size class (250−2000 μm) following biochar addition than under N fertilization, which would increase microbial N demand as evidenced by the lower enzymatic C:N ratios and higher MBN. Microorganisms obviously restrained net Nmin but did not increase N hydrolytic enzyme activity to meet their stoichiometric N demands. Structural equation modeling revealed that enzymatic C:N stoichiometry is a dominant indicator of net Nmin in bulk soil and the >53 μm size class, while the MBN is more important to net Nmin in the <53 μm size class. We conclude that the addition of aged biochar could meet microbial stoichiometric requirements and regulate extracellular enzyme production, resulting in the decline of net Nmin in soil aggregates, especially in MacroA size class.

Climate change and environmental impacts on and adaptation strategies for production in wheat-rice rotations in southern China

Process-based agricultural simulation models are effective tools which can be applied to assess the potential impact of climate change and agronomic practices on yield and nutrient cycling. This study investigates the effects of climate change and fertilization on yield, nitrogen (N) contribution efficiency (the percentage of remobilized N from the vegetative material in grains out of total N content in grains at harvest, (ANCE)), N loss to water and nitrous oxide (N2O) emissions in the wheat (Triticum aestivum L.) – rice (Oryza sativa L.) cropping system in southern China, using the SPACSYS (v6.0) model. The model was first evaluated using crop production and N accumulation data from three-year field experiments, and then applied to simulate production and N processes under three representative concentration pathway (RCP) scenarios for the wheat-rice cropping region, with projections for the years 2020 to 2100. Results indicated that N management as well as shifting sowing or transplantation dates could greatly mitigate the yield losses and N contribution efficiency (ANCE) reduction in the winter wheat-rice rotation system. Delaying sowing dates of wheat and transplanting rice earlier could reduce N leaching losses. Unexpectedly, climate change indirectly increased N2O emissions, showing significant variation depending on the interaction with high N fertilization for rice pre-anthesis, indicating that emissions can be limited by restricting fertilizer application. Changing growing season start dates, along with implementing appropriate N management practice is a potential way to increase resilience to climate change in the wheat-rice cropping system of China.

Additional Income Generation from Cultivation of Summer Mungbean in Rice-Wheat System of Haryana

Background: Mungbean [Vigna radiata (L.) Wilczek], also known as green gram is cultivated on area of 4.75 million ha in kharif and rabi/ spring seasons as monocrop or intercrop in India. It serves as a major source of dietary protein for the vast majority of vegetarian people in the country. Mungbean contributed 10.03 per cent of total pulses production (23.40 million tonnes) in the country with productivity level of 494 kg ha-1 in 2018-19. The pulses cultivation in Haryana is almost eliminated in kharif season owing to deviation of area towards cotton, cluster bean and pearlmillet because of low profitability. However, the new window opens for cultivation of mungbean in rice-wheat cropping system in summer season to generate additional farm income and to improve soil health. The area under summer mungbean in state was around 64 thousand ha with the production of 50 thousand tonnes and the average productivity of 780 kg/ha during 2017-18. Although rice-wheat system provides better farm returns, but it has imposed threat to soil health, availability and contamination of ground water, weed and biotic stress management. Methods: The data pertains to costs and returns from summer mungbean cultivation was gathered from 60 mungbean cultivators of Hisar, Kurukshetra and Panipat districts of Haryana having adequate irrigation water availability adopting personal interaction approach in 2018-19. Simple budgeting technique was employed to draw practical implications which ultimately help to take favourable policy decisions for enhancing acreage of summer mungbean. Result: The inquiry profound that mungbean cultivation in summer season particularly in rice-wheat was established as additional income generation farm enterprise. The net benefits accrued from short duration varieties of mungbean over variable cost was Rs. 31831 ha-1 with time span of 60-70 days by utilizing fallow land in summer season. The B-C ratio toiled considering expenses incurred on variable resources with value of 2.99 divulges economic viability of mungbean cultivation in the study area. It is imperative from results that cultivation of short duration cultivars of mungbean is viable option to enhance farm income, restoration of diminishing soil fertility owing to adoption of continuous rice-wheat rotation by inherent characteristics of converting atmospheric nitrogen. Distinctive efforts are essential to evolve mungbean cultivars suitable to prevailing cropping system in Haryana and assure market procurement. The exploration of mungbean cultivation will reduce dependency on import and improve net availability of pulses in India.

Sesbania aculeata a Cost Effective Alternative to Enhance the Soil Health and Productivity of Rice-Wheat System

Background: Cereal based cropping systems are predominantly followed in south Asia because of higher productivity and profitability and ensuring food security. Rice is grown once a year in rotation mainly with wheat. Continuous cultivation of rice results in the formation of a hard pan below the ploughing layer, which may act as a barrier to normal root growth of the subsequent wheat crop. Consequently, soil bulk density is increased and hydraulic conductivity is reduced thus leading to non-conducive soil physical characteristics for the subsequent wheat crop. To reduce these ill effects, FYM is used as organic source. But live stock population is not increasing in the ratio as it is required to meet the FYM demand. Organic source requirement cannot meet through use of FYM in rice-wheat system, which is vital for food security point of view. There is need of alternate cost effective source of FYM which could enhance the soil health as well as productivity of rice-wheat system. The present study aimed to see the efficacy of growing green manure crop (Sesbania aculeata) as an alternative of FYM in the rice-wheat rotation. Methods: In this experiment conducted during kharif and rabi seasons of 2014-15 and 2015-16 in on-going long term permanent manorial trial since 1984 at research farm (Bihar Agricultural University, Sabour, Bihar, India), twelve treatments were taken under RBD in four replications. Observations and analysis were carried out by following the standard procedures. Result: The present investigation showed that combination of inorganic fertilizer and Sesbania aculeata helped in increasing yield as well as improving soil health. Sesbania aculeata can be used as a viable and cost effective alternative through partial substitution of inorganic fertilizers to enhance the soil health and productivity of rice-wheat system.

Topsoil Bacterial Community Changes and Nutrient Dynamics Under Cereal Based Climate-Smart Agri-Food Systems.

Soil microorganisms play a critical role in soil biogeochemical processes, nutrient cycling, and resilience of agri-food systems and are immensely influenced by agronomic management practices. Understanding soil bacterial community and nutrient dynamics under contrasting management practices is of utmost importance for building climate-smart agri-food systems. Soil samples were collected at 0–15 cm soil depth from six management scenarios in long-term conservation agriculture (CA) and climate-smart agriculture (CSA) practices. These scenarios (Sc) involved; ScI-conventional tillage based rice-wheat rotation, ScII- partial CA based rice-wheat-mungbean, ScIII- partial CSA based rice-wheat-mungbean, ScIV is partial CSA based maize-wheat-mungbean, ScV and ScVI are CSA based scenarios, were similar to ScIII and ScIV respectively, layered with precision water & nutrient management. The sequencing of soil DNA results revealed that across the six scenarios, a total of forty bacterial phyla were observed, with Proteobacteria as dominant in all scenarios, followed by Acidobacteria and Actinobacteria. The relative abundance of Proteobacteria was 29% higher in rice-based CSA scenarios (ScIII and ScV) and 16% higher in maize-based CSA scenarios (ScIV and ScVI) compared to conventional-till practice (ScI). The relative abundance of Acidobacteria and Actinobacteria was respectively 29% and 91% higher in CT than CSA based rice and 27% and 110% higher than maize-based scenarios. Some taxa are present relatively in very low abundance or exclusively in some scenarios, but these might play important roles there. Three phyla are exclusively present in ScI and ScII i.e., Spirochaetes, Thermi, and Euryarchaeota. Shannon diversity index was 11% higher in CT compared to CSA scenarios. Maize based CSA scenarios recorded higher diversity indices than rice-based CSA scenarios. Similar to changes in soil bacterial community, the nutrient dynamics among the different scenarios also varied significantly. After nine years of continuous cropping, the soil organic carbon was improved by 111% and 31% in CSA and CA scenarios over the CT scenario. Similarly, the available nitrogen, phosphorus, and potassium were improved by, respectively, 38, 70, and 59% in CSA scenarios compared to the CT scenario. These results indicate that CSA based management has a positive influence on soil resilience in terms of relative abundances of bacterial groups, soil organic carbon & available plant nutrients and hence may play a critical role in the sustainability of the intensive cereal based agri-food systems.

The Adaptability of APSIM-Wheat Model in the Middle and Lower Reaches of the Yangtze River Plain of China: A Case Study of Winter Wheat in Hubei Province

The middle and lower reaches of the Yangtze River (MLYR) plain represent the second-largest wheat producing area in China; the winter wheat-rice system is one of the main planting systems in this region. The use of the agricultural production system simulator (APSIM)-wheat model to simulate wheat production potential and evaluate the impact of future climate change on wheat production in this region is of great importance. In this study, the adaptability of the APSIM-wheat model in the MLYR was evaluated based on observational data collected in field experiments and daily meteorological data from experimental stations in Wuhan, Jingmen, and Xiangyang in Hubei province. The results showed significant positive relationships between model-predicted wheat growth duration from sowing to anthesis and maturity and the observed values, with coefficients of determination (R2) in ranges of 0.90–0.97 and 0.93–0.96, respectively. The normalized root-mean-square error (NRMSE) of the simulated growth durations and measured values were lower than 1.6%, and the refined index of agreement (dr-values) was in the range of 0.74–0.87. The percent mean absolute relative error (PMARE) was cited here as a new index, with a value below 1.4%, indicating that the model’s rating was excellent. The model’s performance in terms of grain yield and above-ground biomass simulation was also acceptable, although it was not as good as the growth periods simulation. The R2 value was higher than 0.75 and 0.72 for the simulation of grain yield and biomass, respectively. The indices NRMSE and PMARE were lower than 19.8% and 19.9%, and the dr-value was higher than 0.71. According to our results, APSIM-wheat was an effective and accurate model for simulating the phenology and yield production processes of wheat in the MLYR, and the results also provided a theoretical basis and technical support for further research on the yield potential of wheat-rice rotation planting systems with clarification of the key factors limiting the yield gap in this region.

Effects of different water management strategies on the stability of cadmium and copper immobilization by biochar in rice-wheat rotation system

Chemical immobilization of heavy metals is a simple, low-cost, and environment-friendly technology for remediation of heavy metals contaminated soils. However, changes in environmental conditions, such as water management, acid deposition, temperature fluctuation, etc., might result in release of metal ions from the fixation sites, and the long-term stability of immobilization remediation is unclear. This study attempted to investigate the impact of water management strategies (wetting-drying cycle and dry cycle) on the stability of heavy metal immobilization by one-time application of biochar during 3 consecutive years of rice-wheat crop in Cu/Cd-contaminated soil. The transformation and accumulation of Cd and Cu in soil-crop system and the morphololgy and composition of biochar were analyzed. The results revealed that wetting-drying cycle and drying treatments reduced the contents of available Cd and Cu in soil by 15.9%–17.7% and 23.9%–31.5% and by 19.8%–62.7% and 16.1%–65.0%, as well as increased soil pH by 0.11–0.31 and 0.17–0.56, respectively. In the wetting-drying cycle treatment, biochar was more favorable for decrease in Cd and Cu accumulation in crop, when compared with that in dry treatment; however, the differences were insignificant in the subsequent years. Although the different water management strategies had no obvious effect on the soil total C, physicochemical analysis of the biochar collected after pot experiments indicated that the obvious structural decomposition of biochar in the drying treatment may have resulted in the release of heavy metals immobilized in biochar. These findings help in better understanding of the long-term immobilization mechanism of biochar in soil-plant system.

Long term ditch-buried straw return affects soil fungal community structure and carbon-degrading enzymatic activities in a rice-wheat rotation system

As a novel soil tillage practice to build fertility, ditch-buried straw return (DBSR) can affect soil carbon sequestration, nitrogen availability and hydrothermal processes in rice-wheat rotation systems. However, it is still not well-known how DBSR influences soil fungal community. A 6.5-year's field experiment was conducted to test the effects of DBSR on soil fungal community via comparing with rotary tillage straw return (RTSR) and no tillage with no straw (NTNS). Our results showed that soil fungal species composition under DBSR was significantly different from NTNS and RTSR. Also, DBSR showed distinctive impacts on soil fungal composition at the order level. DBSR significantly increased Shannon diversity index and evenness, decreased dominance, but did not affect species richness. Moreover, DBSR significantly increased the abundance of symbiotrophic fungi, but reduced the abundance of pathotrophic fungi. Especially, DBSR largely increased the abundance ratio of arbuscular mycorrhizal fungi to plant fungal pathogens. DBSR significantly reduced β-D-glucosidase activity but increased peroxidase activity while RTSR increased both cellobiohydrolase and peroxidase activity. Our results suggest that long term ditch-buried straw return can structure a unique soil fungal community from that of RTSR and NTNS, increase soil fungal diversity and promote the dominance of beneficial fungi over soil-borne plant fungal pathogens. These findings can provide solid evidence for future large-scale extension of ditch-buried straw return in practical agriculture.

Fate and transfer of heavy metals following repeated biogas slurry application in a rice-wheat crop rotation

The application of biogas slurry, from anaerobic digestion of livestock excreta, to cropland has proven to be an effective mechanism for recycling nutrients within farms. However, the potential pollution of heavy metals from repeated biogas slurry fertilization has not received much attention. Here we present the results of a field experiment under rice-wheat rotation demonstrating the accumulation, speciation distribution and plant uptake of heavy metals (Cu, Zn, Pb and Cd) in soil following biogas slurry application. The treatments were: zero biogas slurry application (BS0), and biogas slurry application for three (BS3) and five (BS5) years, at a rate of 450 m3 ha−1 y−1. Our findings show that biogas slurry fertilization resulted in accumulation of Cu and Zn in the soil. The concentrations of soil Cu and Zn under BS5 were, respectively, 38 and 29% greater in the wheat season and 35 and 35% greater in the rice season relative to BS0 (p < 0.05). The bioavailability of soil Cu and Zn increased following biogas slurry application. Plant uptake of Cu and Zn to all parts of wheat and rice plants (excluding Cu in wheat straw) increased with the years of biogas slurry application (p < 0.05), and the concentration of Cd in wheat grain was significantly greater in BS5 relative to BS0 (p < 0.05). After five years of biogas slurry fertilization, concentrations of Cu, Zn, Pb and Cd in wheat grains were 3.28, 25.19, 0.11 and 0.053 mg kg−1 and 4.24, 33.78, 0.12 and 0.035 mg kg−1 for rice grains, respectively, all within the safety limits. Our results demonstrate that repeated biogas slurry fertilization for five years has a relatively low pollution risk of heavy metals. However, long-term field monitoring and co-application with metal-immobilizing materials are required to ensure the safety of its application to cropland.

Soil Organic Carbon and Soil Physical Characteristics as Affected by Land Uses under Semiarid Irrigated Conditions

ABSTRACT Rice-Wheat rotation is the dominant land use in the state of Punjab, resulting in over exploitation of ground water resources. Thus, it is necessary to evaluate other land uses that requires less water and are sustainable. The present investigation was planned with four land uses viz., fallow (FLU), rice-wheat (ALU), grasses (GLU) and pear (PLU) with respect to their effect on soil organic carbon and soil physical characteristics in surface and subsurface depth in district Ludhiana, Punjab. The soil organic carbon (SOC) content was higher by 10, 30.9 and 24.9% under rice-wheat, grasses, and pear than that under fallow. The grasses showed higher soil moisture characteristics curve (SMCC) and lower bulk density (Db) than that under rice-wheat. The larger mean weight diameter (MWD) were observed under pear, grasses and fallow than that under rice-wheat by 0.21, 0.51 and 0.41 mm, respectively. The saturated hydraulic conductivity (Ks) was higher in magnitude by 56.1, 55.4 and 28%, respectively under PLU, GLU and FLU over ALU. Of the evaluated land uses, pear and grasses proved to be more sustainable by retaining more moisture, maintaining better soil physical characteristics and SOC under semiarid irrigated conditions in the state on long term gradual response.

Boron and zinc fertilizer applications are essential in emerging vegetable‐based crop rotations in Nepal

AbstractBackground: Since recently, the traditional rice–wheat rotation systems in Nepal are subject to drastic changes. Progressing urbanisation and shifting consumer preferences drive a replacement of wheat by high‐value vegetables during the cold dry season, particularly in the peri‐urban fringes, while emerging water shortages prevent permanent soil flooding during the monsoon season, leading to partial substitution of lowland rice by less water‐consuming upland crops. Associated changes in soil aeration status affect soil nutrient availability while particularly vegetables enhance the demand for the critically limiting micronutrients boron (B) and zinc (Zn).Aim: In both rice‐ (anaerobic) and maize‐based (aerobic) systems we assessed the differential response of traditional winter wheat in comparison to cauliflower and tomato to applied B and Zn fertilizers.Methods: Experiments were conducted (1) in a pot trial with two contrasting soil types (Acrisol vs. Fluvisol) and (2) in field validation trials at two contrasting sites (representing lowland vs. mid‐hills) in Nepal.Results: The on‐going shift from flooded rice to aerobic maize during the wet season negatively affected dry matter accumulation and grain yield of the dry season wheat, but not of cauliflower and tomato. While Zn application tended to increase wheat yields under field conditions, B application induced no significant effect, irrespective of the soil or production site. However, low to moderate applications of B (2.0–4.4 kg ha−1) and Zn (3.3–4.4 kg ha−1) nearly doubled biomass accumulation and nutrient uptake of vegetables and increased the economic yields of cauliflower and tomato between 8 and &gt; 100%. These responses were generally more pronounced in the Fluvisol than the Acrisol. While overall yields of wheat and temperate vegetables were higher in the cool mid‐hills the relative yield responses to applied B were more pronounced in the lowland than the mid‐hill sites. On average, the partial factor productivities of applied fertilizer were low to moderate in wheat, with 1 and 8 € increase in net revenue per € of investment in B and Zn, respectively. In the vegetables, this partial factor productivity increased to about 4 € €−1 investment with Zn, and reached about 43 € €−1 investment in B, irrespective of the production site.Conclusions: While the application of Zn fertilizers can moderately improve the performance of traditional rice–wheat rotations, B and to a lesser extent Zn application become essential and highly profitable when shifting towards vegetable cropping. The demand for B and Zn fertilizers is foreseen to dramatically increase with progressing urbanisation and the associated shifts in production systems of Nepal.

Diagnosis of zinc and boron availability in emerging vegetable‐based crop rotations in Nepal

AbstractBackground: Nepal's traditional rice–wheat rotation systems are subject to continuing changes. Changing consumer demand currently drives a replacement of wheat by high‐value vegetables during the dry season, while emerging water shortages lead to a substitution of rice by maize in the wet season. Hence, associated changes in soil aeration status and shifting conditions of soil nutrient supply to match crop nutrient demand are expected to increase the requirements for the principle limiting micro‐nutrients such as boron (B) and zinc (Zn).Aim: Our aim was to investigate the changes in B and Zn availability as well as crop yields and nutrient uptake after system shifts from rice to maize and from wheat to vegetables.Method: We analyzed the B and Zn availability in rice‐ and maize‐based systems as well as crop yields and the nutrient uptake by wheat, cauliflower, and tomato during the dry season in Nepal. Plants were grown at two field sites (midhills vs. lowland) and under greenhouse conditions using soils from the field sites.Results: A change from irrigated rice to maize reduced soil C and N contents with resulting decreases in dry season crop yields. Low soil Zn after rice cultivation led to shortage in Zn uptake by vegetables in both greenhouse and field experiments. The shift from wheat to vegetables increased the demand for B and to a lesser extent for Zn, and consequently vegetables showed visual symptoms of B deficiency. Boron concentrations in dry biomass were below the critical limits with &lt; 10 mg B kg−1 in wheat, &lt; 21 mg B kg−1 in cauliflower, and &lt; 23 mg B kg−1 in tomato.Conclusions: Soils in larger parts of Nepal are low in available B and that the ongoing system shifts increase in the demand for B and Zn in the currently emerging and more diversified production systems.

Effects of long-term straw retention on soil microorganisms under a rice–wheat cropping system

The objective of this study was to investigate how straw-incorporating practices affect bacterial communities and carbon source utilization capacity under a rice-wheat rotational farming practice in central China. To clarify the effect of long-term straw incorporation in microbial abundance and carbon metabolism, a long-term field experiment was initiated in May 2005 (rice-planting season). Soil bacterial communities were revealed by high-throughput sequencing technology. After ten cycles of annual rice-wheat rotation (2005-2015), 2M (straw incorporation) and 2M + NPK (high straw incorporation + chemical fertilizer) treatments had significantly more bacterial phyla compared with CK (non-fertilization) and NPK (chemical fertilizer) treatments. Taxonomic analysis revealed that 2M and NPK + 2M treatments had a significantly greater abundance of microbial communities, especially the Gemmatimonadetes, Acidobacteria, Firmicutes, and Actinobacteria. In the NPK versus 2M, 2M treatment had a significantly greater abundance of Rozellomycota (P < 0.05). In the NPK + 2M versus NPK, NPK + 2M treatment also had significantly greater abundance of Ascomycota (P < 0.05). Principal component analysis (PCA) analysis showed that 2M treatment was separate from other treatments. Using biolog-ECO method, the metabolic diversity and functional characteristics of microbial communities were used to indicate the ability of microorganisms to utilize carbon source. The carbon utilization ability of soil microorganisms in 2M + NPK treatment was significantly higher than that of CK treatment (P < 0.05). The utilization ability of carboxylic acids, polymers, and other mixtures of carbon sources in 2M treatment was higher than those of other treatments. These findings suggest that long-term straw incorporation affects the abundance and carbon utilization ability of soil microorganisms within 0-20cm soil depths, among which, Gemmatimonadetes, Firmicutes, and Actinobacteria may play crucial roles in bacterial communities and carbon source utilization capacity.

Exploring the spatially varying relationships between cadmium accumulations and the main influential factors in the rice-wheat rotation system in a large-scale area

Cadmium (Cd) accumulations in crops and the effects of the related soil factors on them are critical to developing precise soil management measures for food safety. Traditionally-used non-spatial multiple linear regression (MLR) cannot adequately model the spatially varying effects of the related soil properties on Cd accumulations in crop (or soil). Moreover, the traditionally-used methods for exploring the spatial accumulation characteristics (e.g., ordinary kriging) and the effects of other factors on Cd accumulations (e.g., MLR) are sensitive to outliers. In this study, robust geostatistics, enrichment index, and bioavailability index were first used to explore the spatial accumulation characteristics of Cd in wheat grain (wheat-Cd), Cd in rice grain (rice-Cd), and soil DTPA-extractable Cd (DTPA-Cd) in Jintan County, a typical rice-wheat rotation area in China. Then, robust geographically weighted regression (RGWR), established in geographic space rather than variable space, was used to explore the spatially varying relationships between Cd accumulations and the corresponding main influential factors determined by stepwise regression. Last, the modelling accuracy of RGWR was compared with those of basic GWR and MLR. Results showed that (i) outliers affected the spatial predictions of soil total Cd, soil DTPA-Cd, wheat-Cd, and rice-Cd and robust variograms should be used; (ii) the enrichment index of wheat grain was significantly higher than that of rice grain in almost the whole study area; (iii) the areas with the high bioavailability index of soil Cd mainly located in the southeast, southwest, and centre of the study area; (iv) RGWR acquired higher modelling accuracy than GWR and MLR; (v) the spatially varying relationships between Cd accumulations and the corresponding influential factors were revealed by RGWR, which cannot be determined by MLR. The methods suggested in this study provided more precise spatial decision support for soil management measures to guarantee main agricultural product safety in large-scale areas.

The impacts of ditch-buried straw layers on the interface soil physicochemical and microbial properties in a rice-wheat rotation system

Ditch-buried straw return (DB-SR) is a novel soil tillage and fertility-building practice, which may allow for the formation of a straw layer structure in rice–wheat rotation systems. However, it is presently unknown how the straw layer affects soil physicochemical and microbial processes in the interface between straw layer and bulk soils. Thus, we conducted a field experiment from 2008 to 2014 to determine whether there were changes in soil structure, temperature, available nitrogen, and microbial properties in the soil layer close to the straw layers (± 5 cm). Three treatments were included: control with no-till and straw removal (CK), ditch-buried straw return to a depth of 20 cm (DB-SR-20), and ditch-buried straw return to a depth of 40 cm (DB-SR-40). Our results showed that soil macroaggregate formation was increased with the duration of straw return in the soils 5 cm below the straw layers under DB-SR-20 and above the straw layers under DB-SR-40. The straw layers could significantly increase soil temperature below the straw layers, but a larger increase was observed for DB-SR-40 than DB-SR-20. We also found that DB-SR-20 largely increased the NH4+ concentration in both the soil layers above and below the straw layers, but DB-SR-40 only increased NO3− in the soils above the straw layers. In addition, the catabolic profile of soil microbial communities was largely affected by the straw layers, but the effects decreased with the duration of the treatment. These findings suggest that the straw layer largely alters the spatio-temporal processes of physicochemical and microbial properties in the interface soils after long-term implementation of ditch-buried straw return. Some of the positive alterations may cascade to facilitate crop growth and enhance the productivity of rice-wheat rotation systems.

Long-term effects of straw return and straw-derived biochar amendment on bacterial communities in soil aggregates

Improving soil structure, fertility, and production is of major concern for establishing sustainable agroecosystems. Further research is needed to evaluate whether different methods of straw returning determine the variations of soil aggregation and the microbial community in aggregates in the long term. In this study, we comparatively investigated the effects of long-term fertilization regimes performed over six years, namely, non-fertilization (CK), chemical fertilization (CF), continuous straw return (CS), and continuous straw-derived biochar amendment (CB), on soil aggregation and bacterial communities in rice-wheat rotation systems. The results showed that straw/biochar application increased soil nutrient content and soil aggregate size distribution and stability at both 0–20 cm and 20–40 cm soil depths, compared with those of CF and CK; CB performed better than CS. CB increased bacterial community diversity and richness in 0–20 cm soil, and evenness in 0–40 cm soil (p < 0.05); CS had no significant effect on these aspects. Variations in the relative abundance of Actinobacteria, Chloroflexi, Bacteroidetes, Nitrospirae, Gemmatimonadetes, and Latescibacteria in specific aggregates confirmed the different effects of straw/biochar on bacterial community structure. The partial least squares discrimination analysis and permutation multivariate analysis of variance revealed that fertilization, aggregate size fractions, and soil depth affected the bacterial community, although their effects differed. This study suggests that CB may reduce chemical fertilizer usage and improve the sustainability of rice-wheat cropping systems over the long term, with a better overall outcome than CS.

Soil and microbial biomass stoichiometry regulate soil organic carbon and nitrogen mineralization in rice-wheat rotation subjected to long-term fertilization

Soil microbial biomass (SMB), as the source and sink of soil nutrients, and its stoichiometry play a key role in soil organic carbon (SOC) and nitrogen (N) mineralization. The objective of this study was to investigate the responses of SOC and N mineralization to changes in microbial biomass and SOC, N, and phosphorus (P) stoichiometry resulted from long-term fertilization regimes. Soil was sampled from a rice-wheat rotation system subjected to 37 years of nine fertilization treatments with different nutrient input amounts: control (CK), N alone, N combined with mineral phosphorus (NP), NP plus potassium (NPK), manure alone (M), and M combined with N (MN), NP (MNP), NPK (MNPK), and a higher rate of M with NPK (hMNPK). The sampled soil was incubated for the determination of SOC and N mineralization, C, N, and P stoichiometry of soil and SMB, and associated soil enzymes related to C and N cycling. Relative to the CK and treatments with mineral fertilizers, treatments with manure (M, MN, MNP, MNPK, and hMNPK) significantly increased SOC and N mineralization by 48–78% and 54–97%, respectively. Microbial metabolic quotient (qCO2) decreased by 32–55% in treatments with manure compared to the N and NP treatments, but showed no effect on the qCO2 when compared to the NPK treatment. The leucine amino peptidase (LAP) enzyme showed significant positive correlation with SOC and N mineralization, and negatively related to the qCO2. Significantly negative correlations were also observed between SOC and N mineralization and soil C:P and N:P ratio, as well as microbial biomass SMBC:SMBP and SMBN:SMBP stoichiometry, respectively. However, the availability of N and P had limited effects on the qCO2 after reaching a certain value (0.69–0.72 mg CO2-C g−1 MBC h−1). Lower soil elemental (C:P and N:P) and microbial biomass stoichiometry (SMBC:SMBP and SMBN:SMBP) and increase of LAP resulted from combined application of manure and mineral fertilizers, accelerated SOC, and N mineralization. Mineral nutrient input with manure amendments could be an optimal strategy to meet the microbial stoichiometric demands and enhance nutrient availability for crops in agricultural ecosystems.

Effects of controlled-release fertilizer on rice grain yield, nitrogen use efficiency, and greenhouse gas emissions in a paddy field with straw incorporation

The incorporation of crop straw to cropland is increasingly being recommended due to its ability to improve soil fertility. Controlled-release fertilizer could enhance nitrogen (N) use efficiency and crop grain yield in a rice–wheat rotation cropping system. The effects of controlled-release fertilizer with wheat straw incorporation on rice grain yield and greenhouse gas (GHG) emissions is poorly understood. Four treatments, i.e., chemical fertilizer (CF), chemical fertilizer with straw incorporation (CF + WS), controlled-release urea with straw incorporation (CRU + WS), and no fertilizer (C), were applied to investigate the effects of CRU + WS on rice grain yield, N use efficiency and GHG emissions in multiple rice growing seasons. Relative to CF, rice grain yield from CF + WS decreased by 0.4–2.3% in 2012 and 2013 seasons but increased by 2.3–4.0% in 2014 and 2015 seasons, and significantly enhanced by 9.3% in 2016 season (p < 0.05). No significant difference in N use efficiency was observed between CF and CF + WS in any season, although the trend in that followed the similar pattern as rice grain yield when compared CF + WS with CF. CRU + WS significantly increased rice grain yield by 6.8–18.2% (p < 0.05) and enhanced N use efficiency by 42.0–150.5% (p < 0.05) compared to CF + WS. CH4 emissions from CF + WS and CRU + WS were comparable with each other, which were greatly higher by 156.8–358.6% and by 163.7–364.9% than that from CF, respectively. CF + WS had the potential to reduce N2O emission relative to CF in most rice growing seasons, whereas CRU + WS greatly stimulated N2O emission by 153.0–399.3% and 41.5–319.4% compared to CF and CF + WS, respectively. The GHG emission intensity (GHGI), calculated from greenhouse gases (CH4 and N2O) emissions and rice grain yield from CRU + WS were comparable with that from CF + WS in all rice growing seasons, and they enhanced the GHGI by 165.6–197.7% and by 128.0–253.1% relative to CF, respectively. In conclusion, in the paddy fields with wheat straw incorporation, the application of CRU, rather than conventional CF, could remarkably enhance rice grain yield, improve N use efficiency, but have little effect on GHGI due to its stimulation in N2O emission. More efforts are required to mitigate N2O emission when CRU is used in the future.

Soil nitrogen sequestration in a long-term fertilizer experiment in central China

Aim of study: To evaluate the effects of a long-term manuring and fertilization experiment on the soil total N concentration and its storage and sequestration rates in the rice-wheat cropping system.Area of study: A rice-wheat rotation area in central China.Material and methods: A 35-yr long-term fertilizer experiment was conducted with 9 treatments: unfertilized (Control), N, P, and K fertilizers, manure (M) and M combined with N, P, and K fertilizers treatments. Soil total N input amount, total N concentration, total N storage amount and N sequestration rate in soil were calculated.Main results: The soil total N input amount, N concentration, N storage amount and N sequestration rate were significantly influenced by M and chemical fertilizers. In total, 0.017-0.021 g N/kg soil accumulated in the organic M plots, whereas only 0.005-0.007 g in chemical fertilizer alone plots. The highest soil total N storage amount was 6.09 t/hain the M alone plot, and the lowest value was 4.46 tN/ha in the N fertilizer alone plot. The highest N sequestration rate in soil was 0.061 t N/ha/yr in the high amount M plus NPK fertilizers plot, and the lowest value was 0.002 tN/ha/yr in the N fertilizer alone plot. A significant nonlinear regression relationship existed between the total N sequestration rate in soil and annual total N input amount. Moreover, the average soil total N concentration was significantly positively correlated with the average grain yield of crop and soil organic C concentration. The soil total N sequestration rate in M alone or M combined with inorganic fertilizer treatments were increased compared with inorganic fertilizer alone treatments.Research highlights: Considering crop yields and total N sequestration rate in soil, the use of manure combined with inorganic fertilizer should be recommended in the rice-wheat cropping system.

Effects of Changing Fertilization since the 1980s on Nitrogen Runoff and Leaching in Rice–Wheat Rotation Systems, Taihu Lake Basin

The nitrogen (N) loss associated with intensive agricultural activities is a significant cause of eutrophication and algal blooms in freshwater ecosystems. Taihu Lake has experienced serious surface water quality deterioration and eutrophication problems since the 1980s. The objective of this study is to examine the effect of fertilization changes since the 1980s on the N loss with runoff and leaching in the rice–wheat cropping rotation system. According to the results published in the literature since the 1980s, we set up four fertilization scenarios—N1980s: a fertilization rate of 350 kg N·ha−1·year−1 with 30% in manure fertilization to simulate fertilization in the 1980s; NA1990s: a fertilization rate of 500 kg N·ha−1·year−1 with 10% in manure fertilization to simulate fertilization in the early 1990s; NL1990s: fertilization rate of 600 kg N·ha−1·year−1 with 10% in manure fertilization to simulate fertilization in the late 1990s; and N2000s: fertilization rate of 550 kg N·ha−1·year−1 with all chemicals to simulate fertilization in the 2000s. Then, we calibrated and validated the DNDC (denitrification–decomposition) model through field experiments in two rice–wheat rotation seasons from November 2011 to October 2013 and simulated the N loss with runoff and leaching since the 1980s. The results show that N losses with leaching in the four periods (N 1980s, NA1990s, NL1990s, and N2000s) were 5.2 ± 2.1, 9.4 ± 3.2, 14.4 ± 4.6 and 13.5 ± 4.6 kg N·ha−1·year−1, respectively. N losses with surface runoff were 7.9 ± 3.9, 18.3 ± 7.2, 25.4 ± 10.2, and 26.5 ± 10.6 kg N·ha−1·year−1, respectively. The total N loss through runoff and leaching showed an increasing trend from 1980 to the late 1990s, when it reached its peak. The increase in N export to water due to fertilizer application occurs mainly during the rainy season from March to August, and especially from June to August, when rainfall events and intensive rice fertilization activities are frequent. After the 1990s, when the fertilizer rate was above 500 kg N·ha−1·year−1, the crop yields no longer increased significantly, which indicates that the optimized fertilization rate to balance crop yields and N loss to water is lower than 500 kg N·ha−1·year−1. The increase in fertilizer use has been unnecessary since the early 1990s, and at least about 30% of the N loss could have been prevented without reducing crop yields.