Combining biochar with irrigation management to alter the microbial community is a sustainable method for remediating soils contaminated by heavy metals. However, studies on how these treatments promote Cr(VI) reduction are limited, and the corresponding microbial mechanisms are unclear. Therefore, we conducted a pot experiment to explore the responses of soil microbial communities to combined biochar amendment and irrigation management strategies and their involvement in Cr transformation in paddy soils. Six treatments were established using varying concentrations of biochar (0, 1, and 2% [w/w]) combined with two irrigation management strategies (continuous flooding [CF] and dry–wet alternation [DWA]). The results showed that the combined biochar addition and irrigation management strategy significantly altered soil pH, redox potential, organic matter content, and Fe(II) and sulfide concentrations. In addition, the Cr(VI) concentration under CF irrigation management was conspicuously lower (48.2–54.4%) than that under DWA irrigation management. Biochar amendment also resulted in a substantial reduction (8.8–27.4%) in Cr(VI) concentration. Moreover, the changes in soil physicochemical properties remarkably affected the soil microbial community. The microbial diversity and abundance significantly increased with biochar amendment. Furthermore, the combined biochar amendment and CF strategy stimulated the growth of Geobacter- and Anaeromyxobacter-related Fe(III)-reducing bacteria, Gallionella-related Fe(II)-oxidizing bacteria, and Desulfovibro- and Clostridium-related sulfate-reducing bacteria, which simultaneously facilitated the generation of Fe(II) and sulfide, thereby enhancing Cr(VI) reduction. Consequently, our results suggest that the effectively increased abundance of Fe-reducing/oxidizing bacteria and sulfate-reducing bacteria via combined CF irrigation management and biochar addition may be a key factor in reducing Cr(VI) in paddy soil. The keystone genera responsible for Cr(VI) reduction were Geobacter, Anaeromyxobacter, Gallionella, Desulfovibro, and Clostridium. This study provides novel insights into the coupling mechanism of the Fe/S/Cr transformation mediated by Fe-reducing/oxidizing bacteria and sulfate-reducing bacteria.

High ammonia (NH₃) emissions from fertilized soil in China have led to various concerns regarding environmental safety and public health. In response to China's blue skies protection campaign, effective NH₃ reduction measures need to consider both mitigation efficiency and food security. In this context, we conducted a meta-analysis (including 2980 observations from 447 studies) to select effective measures based on absolute (AV) and yield-scaled (YSAV) NH₃ volatilization reduction potential, with the aim of establishing a comprehensive NH₃ mitigation framework covering various crop production sectors, and offering a range of potential solutions. The results showed that manipulating crop density, using an intermittent irrigation regime for paddy field rice, applying N as split applications or partially substituting inorganic fertilizer N with organic N sources could achieve reductions in AV and YSAV reduction of 10–20 %; adopting drip irrigation regimes, adding water surface barrier films to paddy fields, or using double inhibitor (urease and nitrification), slow-release or biofertilizers could achieve 20–40 % mitigation; plastic film mulching, applying fertilizer by irrigation or using controlled-release fertilizers could yield 40–60 % reduction; use of a urease inhibitor, fully substituting fertilizer N with organic N, or applying fertilizer by deep placement could decrease AV and YSAV by over 60 %. In addition, use of soil amendments, applying suitable inorganic N sources, or adopting crop rotation, intercropping or a rice-fish production model all had significant benefits to control AV. The adoption of any particular strategy should consider local accessibility and affordability, direct intervention by local/government authorities and demonstration to encourage the uptake of technologies and practices, particularly in NH₃ pollution hotspot areas. Together, this could ensure food security and environmental sustainability.

Agricultural soils are a leading source of atmospheric greenhouse gas (GHG) emissions and are major contributors to global climate change. Carbon dioxide (CO2) makes up 20% of the total GHG emitted from agricultural soil. Therefore, an evaluation of CO2 emissions from agricultural soil is necessary in order to make mitigation strategies for environmental efficiency and economic planning possible. However, quantification of CO2 emissions through experimental methods is constrained due to the large time and labour requirements for analysis. Therefore, a modelling approach is needed to achieve this objective. In this paper, the DeNitrification-DeComposition (DNDC), a process-based model, was modified to predict CO2 emissions for Canada from regional conditions. The modified DNDC model was applied at three experimental sites in the province of Saskatchewan. The results indicate that the simulations of the modified DNDC model are in good agreement with observations. The agricultural management of fertilization and irrigation were evaluated using scenario analysis. The simulated total annual CO2 flux changed on average by ±13% and ±1% following a ±50% variance of the total amount of N applied by fertilising and the total amount of water through irrigation applications, respectively. Therefore, careful management of irrigation and applications of fertiliser can help to reduce CO2 emissions from the agricultural sector.

The natural occurrence of arsenic (As) in groundwater & soils and its bioaccumulation in rice grains is a major health concern worldwide. To combat the problem, best combination of irrigation management and suitable rice variety altering As content in grains must be ensured. With this aim, a field trial was conducted with two rice varieties and water management including alternate wetting and drying (AWD) and continuous flooding (CF) irrigation regimes with As contaminated groundwater (AsW) and temporarily stored groundwater (TSG) and river water for only CF (as control). Results revealed that As content in different portions of paddy plant was significantly different (P < 0.001) with irrigation practices and rice varieties. AWD irrigation with TSG accumulated lower As in rice grains compared with CF-AsW for both varieties. Data showed that AWD-TSG practice led to 61.37% and 60.34% grain As reduction for BRRI dhan28 and BRRI dhan29, respectively, compared with CF-AsW. For Principle Component Analysis (PCA), first principle component (PC1) explained 91.7% of the variability and irrigation water As, soil total and available As, straw As, root As and husk As were the dominating parameters. With significant (P < 0.05) variation in yields between the genotypes, AWD increased grain yield by 29.25% in BRRI dhan29 Compared with CF. However, translocation factor (TF) and bioconcentration factor (BCF) for both varieties were less than one for all the treatments. The addition of this study to our knowledge base is that, AWD-TSG with BRRI dhan29 can be an As–safe practice without compromising yields.

Enhanced efficiency nitrogen fertilizers (EENFs), including nitrification inhibitors (NIs) and slow-release fertilizer (SRF), are considered promising approaches for mitigating nitrous oxide (N₂O) emissions while improving crop yield. This study investigated the combined application of EENFs with improved water and fertilizer management in an intensively irrigated spring maize rotation over five years in Northwestern China. High-frequency measurements of N₂O fluxes were made throughout each year (both during crop growth and the fallow season) in five treatments: no N fertilizer as a control (CK), conventional N fertilization and irrigation (Con), optimum N fertilization and irrigation (Opt, 33% reduction in N fertilizer and 25% reduction of irrigation water), optimum N fertilization and irrigation with nitrification inhibitor (Opt + NI), and optimum N fertilization and irrigation with slow-release fertilizer (Opt-SRF). Annual mean cumulative N₂O emissions reached 0.31 ± 0.07, 3.66 ± 0.19, 1.87 ± 0.16, 1.23 ± 0.13, and 1.61 ± 0.16 kg N₂O–N ha⁻¹ for CK, Con, Opt, Opt + NI, and Opt-SRF, respectively, with annual mean nitrogen use efficiency (NUE) of 36, 54, 61 and 59% for Con, Opt, Opt + NI, and Opt-SRF, respectively. The Opt, Opt + NI and Opt-SRF treatments significantly reduced cumulative N₂O emissions by 49%, 66%, and 56% (P < 0.05), respectively, and increased NUE by 51%, 70%, and 66% (P < 0.05), respectively, relative to Con. However, mean above-ground N uptake (288–309 kg N ha⁻¹) and mean grain yields (12.7–12.8 Mg ha⁻¹) did not differ significantly between the Con, Opt, Opt + NI, and Opt-SRF treatments during the five-year study. High N₂O emissions mainly occurred within a few days of fertilization with irrigation, which could have been produced by microbially-mediated nitrifier or nitrifier denitrification processes. The fallow seasons had significantly lower cumulative N₂O emissions, which were mainly attributed to the low temperature, low N inputs of crop residues, and low soil moisture conditions. Our study clearly indicated that the combined application of EENFs with optimum N fertilization and irrigation management can reduce environmental impacts while maintaining high crop yields in dryland regions such as Northwest China.

Nitrous oxide emission factors (N₂O-EF, percentage of N₂O–N emissions arising from applied fertilizer N) for cropland emission inventories can vary with agricultural management, soil properties and climate conditions. Establishing a regionally-specific EF usually requires the measurement of a whole year of N₂O emissions, whereas most studies measure N₂O emissions only during the crop growing season, neglecting emissions during non-growing periods. However, the difference in N₂O-EF (ΔEF) estimated using measurements over a whole year (EFwy) and those based on measurement only during the crop-growing season (EFgₛ) has received little attention. Here, we selected 21 studies including both the whole-year and growing-season N₂O emissions under control and fertilizer treatments, to obtain 123 ΔEFs from various agroecosystems globally. Using these data, we conducted a meta-analysis of the ΔEFs by bootstrapping resampling to assess the magnitude of differences in response to management-related and environmental factors. The results revealed that, as expected, the EFwy was significantly greater than the EFgₛ for most crop types. Vegetables showed the largest ΔEF (0.19%) among all crops (0.07%), followed by paddy rice (0.11%). A higher ΔEF was also identified in areas with rainfall ≥600 mm yr⁻¹, soil with organic carbon ≥1.3% and acidic soils. Moreover, fertilizer type, residue management, irrigation regime and duration of the non-growing season were other crucial factors controlling the magnitude of the ΔEFs. We also found that neglecting emissions from the non-growing season may underestimate the N₂O-EF by 30% for paddy fields, almost three times that for non-vegetable upland crops. This study highlights the importance of the inclusion of the non-growing season in the measurements of N₂O fluxes, the compilation of national inventories and the design of mitigation strategies.

Arsenic (As) is very common pollutant of the environment categorized as class-I human carcinogen. Rice crop is inherently efficient at accumulating As that is also triggered by conventional cropping methods (flooded conditions). A pot experiment was conducted with the objectives to (i) determine the accumulation of As in rice grains and shoots and As species in rice grains, (ii) determine the effect of As concentrations on physiological and agronomic characteristics of the rice crop, and (iii) assess the changes in fractions of As within the soil under different water regimes. Water regimes included flooding, intermittent, intermittent + aerobic, and aerobic irrigation. Grain As concentration from flood-irrigated rice was significantly (P ≤ 0.05) reduced in rice grown in 10 and 50 mg kg⁻¹ As-contaminated soil with less applied irrigation. Water management techniques have influenced As speciation in rice grains. As the irrigation techniques were shifted from flooding to intermittent, intermittent + aerobic, and aerobic irrigation, a significant decrease in concentration of inorganic species (11.98–76.81% at 10 mg kg⁻¹ and 66.04–93.61% at 50 mg kg⁻¹) was observed. Aerobic irrigation has effectively reduced the concentration of arsenic in rice grain as compared to other irrigation techniques in both the As-contaminated soils. This study indicated that irrigation management techniques other than flood irrigation have significantly affected the As (total and speciation) concentration within the rice grains and non-significantly affecting crop yield and this must be considered if regulations are based on inorganic As percentage of total As concentration.

Tank systems are essential for the agricultural growth and the livelihood of rural populations in India. Comprehending the multiple benefits from these traditional systems, tank rehabilitation has been one of the policy significances at the state level. The study was undertaken with the objective of assessing the impact of tank rehabilitation on cropped area, cropping pattern change, cost returns and income of farmers in a selected study village of south Tamil Nadu. The study was conducted on the basis of primary data obtained from 102 sample farmers belonging to “Pelasur” village of Thiruvannamalai district in south Tamil Nadu using a stratified sampling method. There was a significant difference in the cropped area, cropping intensity and irrigation intensity among the farmers before and after tank rehabilitation. It is found that there is an increase of 41.02 ha cultivated area and an increase in the net amount of Rs. 7,99,945. Many farmers shifted from paddy to sugarcane (cash crops) cultivation due to the availability of excess surface water in the tank and improved water table in their wells. Cropping intensity has been increased to 26% in the post-rehabilitation period. Thus, investment in tank rehabilitation shows a positive implication on marginal farmers and landless labours. Using SPSS, a paired-sample t-test is applied for analysing data collected from respondents.

A shortage in available water resources for rice production makes the evaluation of rice yield and greenhouse gas emission in response to drought caused by water scarcity vital. Here, we examined three forms of irrigation management (normal amount [NA], 70 % of NA [NA 70 %], and 30 % of NA [NA30%]) and two rice varieties (Oryza sativa L. cv. Hanyou 8 and Oryza sativa L. cv. Huayou 14) to determine their effects on CH₄ emission and rice yield in two rice growing seasons. Hanyou 8 is a variety of water-saving and drought-resistance rice (WDR), while Huayou 14 is a common rice variety with no known adaptation to drought conditions. NA 70 % reduced CH₄ emission by 30.3–53.3 %, and NA 30 % further depressed CH₄ emission by 51.0–76.7 % relative to NA in both seasons. However, NA 70 % and NA 30 % significantly decreased rice yield by 6.3 % (P < 0.05) and 10.1 % (P < 0.01), respectively, for Huayou 14 when compared with NA in the relatively dry season. Conversely, no differences in rice yield among different irrigation managements were observed for Hanyou 8 in both seasons, suggesting that Hanyou 8 is more drought-resistant than Huayou 14 in terms of rice yield. The results suggest that, to meet the water scarcity, the use of rice varieties with water-saving and drought-resistant traits may minimize rice yield loss and mitigate CH₄ emission in the rice-cultivated regions of the world.

This study evaluated the effects of abattoir wastewater irrigation on plant growth and development. The soils used in this study were collected from Primo Smallgoods Abattoir (Port Wakefield, South Australia) at different sites such as currently irrigated (CI), currently not irrigated (CNI) and soil outside the irrigation area as control (CTRL). A completely randomised block design was employed for the plant growth experiment, where four crops (Pennisetum purpureum, Medicago sativa, Sinapis alba and Helianthus annuus) were grown separately on three different soils (CI, CNI and CTRL) in plastic pots. Two types of water (tap water and wastewater) and two loadings were applied throughout the planting period based on the field capacity (FC 100 and 150 %). The overall dry matter yield was compared between the soils and treatments. Under wastewater irrigation, among the four species grown in the CI soil, P. purpureum (171 g) and H. annuus (151 g) showed high biomass yields, followed by S. alba (115 g) and M. sativa (31 g). The plants grown under tap water showed about 70 % lower yields compared to the abattoir wastewater irrigation (AWW). Similar trends in the biomass yields were observed for CNI and CTRL soils under the two water treatments, with the biomass yields in the following order CI > CNI > CTRL soils. The results confirm the beneficial effects of AWW at the greenhouse level. However, a proper cropping pattern and wastewater irrigation management plan is essential to utilise the nutrients available in the wastewater-irrigated land treatment sites. The increase in fertility is evident from the effects of wastewater on biomass growth and also the abundance of nutrients accumulated in plants. A mass balance calculation on the applied, residual and the plant-accumulated nutrients over a few cropping periods will help us in understanding the nutrient cycling processes involved in the abattoir-irrigated land treatment sites, which will serve as an effective tool for the environmental management.