Effects of irrigation methods and salinity on CO2 emissions from farmland soil during growth and fallow periods

Multi-objective optimization of saline water irrigation in arid oasis regions: Integrating water-saving, salinity control, yield enhancement, and CO2 emission reduction for sustainable cotton production

Brackish water stands as a promising alternative to mitigate freshwater scarcity in arid regions. However, its application poses potential threats to agricultural sustainability. There is a need to establish a clear understanding of the economic and ecological benefits. We conducted a two-year (2021-2022) field experiment to investigate the effects of four different irrigation water salinity levels on soil electrical conductivity, cotton yield, water use efficiency, CO2 emissions, and carbon sequestration. The salinity levels were designated as CK (0.85 g L-1), S1 (3 g L-1), S2 (5 g L-1), and S3 (8 g L-1). Results indicated that using irrigation water with high salinity (≥5 g L-1) led to the accumulation of salt in the soil, and a decrease in plant biomass and seed cotton yield. Compared to CK, the S3 treatment decreased by 18.72 % and 20.10 % in the respective two years. Interestingly, using brackish water (3 L-1 and 5 g L-1) decreased the rate and cumulative CO2 emissions, and increased the carbon emission efficiency and carbon sequestration by 0.098-0.094 kg kg-1 and 871-1859 kg ha-1 in 2021, 0.098-0.094 kg kg-1 and 617-1995 kg ha-1 in 2022, respectively. To comprehensively evaluate the tradeoff between economic and ecological benefits, we employed the TOPSIS method, and S1 was identified as the optimal irrigation salinity. Through fitting analysis, the most suitable irrigation salinity levels for 2021 and 2022 were determined as 3.52 g L-1 and 3.31 g L-1, respectively. From the perspective of water conservation, salinity management, yield improvement, and reduction of CO2 emissions, it is feasible to utilize brackish water for irrigation purposes, as long as the salinity does not exceed 3.52 g L-1 (first year) and 3.31 g L-1 (second year).

Response of soil respiration and carbon budget to irrigation quantity/quality and biochar addition in a mulched maize field under drip irrigation

BACKGROUND

Biochar addition strongly alters net carbon (C) balance in agroecosystems. However, the effects of biochar addition on net C balance of maize field under various irrigation water quantities and qualities remains unclear. Thus, a field experiment combining two irrigation levels of full (W1) and deficit irrigation (W2 = 1/2 W1), two water salinity levels of fresh (S0, 0.71 g L-1 ) and brackish water (S1, 4 g L-1 ), and two biochar addition rates of 0 t ha-1 (B0) and 60 t ha-1 (B1) was conducted to investigate soil carbon dioxide (CO2 ) emissions, maize C sequestration and C budget.

RESULTS

Compared with W1, W2 reduced average cumulative CO2 emissions by 6.5% and 19.9% for 2020 and 2021, respectively. The average cumulative CO2 emissions under W1S1 treatments were 5.4% and 22.3% lower than W1S0 for 2020 and 2021, respectively, whereas W2S0 and W2S1 had similar cumulative CO2 emissions in both years. Biochar addition significantly increased cumulative CO2 emissions by 17.8-23.5% for all water and salt treatments in 2020, and reduced average cumulative CO2 emissions by 11.9% for W1 but enhanced it by 8.0% for W2 in 2021. Except for W2S1, biochar addition effectively increased total maize C sequestration by 6.9-14.8% for the other three treatments through ameliorating water and salt stress over the 2 years. Compared with W1S0, W1S1 did not affect net C sequestration, but W2 treatments significantly decreased it. Biochar addition increased net C sequestration by 39.47-43.65 t C ha-1 for four water and salt treatments for the 2 years.

CONCLUSION

These findings demonstrate that biochar addition is an effective strategy to increase both crop C sequestration and soil C storage under suitable water-saving irrigation methods in arid regions with limited freshwater resources. © 2023 Society of Chemical Industry.

Adapting crop production to climate change and air pollution at different scales

Air pollution and climate change are tightly interconnected and jointly affect field crop production and agroecosystem health. Although our understanding of the individual and combined impacts of air pollution and climate change factors is improving, the adaptation of crop production to concurrent air pollution and climate change remains challenging to resolve. Here we evaluate recent advances in the adaptation of crop production to climate change and air pollution at the plant, field and ecosystem scales. The main approaches at the plant level include the integration of genetic variation, molecular breeding and phenotyping. Field-level techniques include optimizing cultivation practices, promoting mixed cropping and diversification, and applying technologies such as antiozonants, nanotechnology and robot-assisted farming. Plant- and field-level techniques would be further facilitated by enhancing soil resilience, incorporating precision agriculture and modifying the hydrology and microclimate of agricultural landscapes at the ecosystem level. Strategies and opportunities for crop production under climate change and air pollution are discussed.

Interactive effects of irrigation system and level on grain yield, crop water use, and greenhouse gas emissions of summer maize in North China Plain

Irrigation management is one of most critical factors influencing soil N₂O and CO₂ emissions in dryland agriculture. To explore the effects of irrigation systems and levels on the mitigation of N₂O and CO₂ emissions from maize fields and to determine the balance among greenhouse gases (GHG) emission, water-saving and grain yield, a two-year field experiment was conducted in the North China Plain (NCP) during the growing seasons of 2018 and 2019. Two irrigation systems (i.e., flood irrigation, FI, and drip irrigation, DI) were adopted with four irrigation levels in each system, including 65 mm/event (sufficient irrigation, CK), 50 mm/event (decreased by 23 %), 35 mm/event (by 46 %) and 20 mm/event (by 69 %), respectively. The results showed that both irrigation systems and levels had significant effects on soil N₂O and CO₂ emissions (P < 0.05). Nitrous oxide (N₂O) and CO₂ emissions peaked following irrigation or irrigation + fertilization events during sowing to early filling stage (R1), with the peak values increasing with irrigation levels. Meanwhile, peak values from FI were higher than those from DI at 50 mm and 65 mm irrigation levels. The average cumulative N₂O and CO₂ emissions of DI treatments were 14.9 % and 6.23 % lower than those of FI treatments (P < 0.05), respectively. Soil moisture was identified as one of the most crucial factors influencing N₂O and CO₂ fluxes. Deficit irrigation efficiently deceased cumulative N₂O and CO₂ emissions, but moderate to severe deficit irrigation brought significant reduction in grain yield. Drip irrigation with a slight deficit irrigation level (decreased by 23 %) obtained the best economic and environmental benefits, which achieved the dual goal of lower GHG emissions but higher WUE without sacrificing grain yield.

Water chemistry and stable isotope characteristics of subsidence lakes in coal mining areas, Eastern China

Many subsidence lakes have formed in eastern China as a result of underground coal mining. These coal mining-related subsidence lakes vary in their formation time and connectivity with rivers. These factors may influence the water chemistry and hydrogen and oxygen stable isotope characteristics of the lake water. This study collected and tested subsidence lake water, atmospheric precipitation, river water, and shallow groundwater in the study area. The results showed that the water chemical types of the subsidence lake water and river water are Cl-Na and HCO₃·Cl-Na and that the water chemical types of the shallow groundwater are mainly HCO₃·Cl-Na and HCO₃·Cl-Ca. There are no significant differences in the water chemical characteristics of subsidence lakes with different subsidence ages and types. The major ions in each water body mainly come from evaporite dissolution and silicate weathering, and ion exchange occurs. Reverse ion exchange occurs in some shallow groundwater samples. The stable isotopes of hydrogen and oxygen in the subsidence lake water, river water, and shallow groundwater are distributed along a straight line with a slope less than that of the LMWL, indicating that these water bodies have a common source, namely, precipitation. With increases in the formation time of the subsidence lakes, the heavy isotopes in the lake water gradually become depleted, and the d value gradually increases, mainly driven by precipitation dilution, weakening evaporation, river recharge, and groundwater recharge. The isotopic values of different types of lakes with the same subsidence time differ little. The research results may provide scientific guidance for the rational development and utilization of water resources in coal mining subsidence areas, enrich the study of the hydrological cycle in the area, and are of great significance for the protection of the local water balance and water environment.

Hydrochemistry characteristics of groundwater with the influence of spatial variability and water flow in Hetao Irrigation District, China

Groundwater is an important resource of water in arid and semi-arid agricultural regions. Thus, identification of hydrogeochemical characters and the influence of geospatial variability and flow pooling are of significance on groundwater resources management and making irrigation decisions in salinized areas. The study specifically focused on the Hetao Irrigation District located in the semi-arid region of northern China. A total of 85 groundwater samples (42 from the upstream Shenwu Irrigation Area (SWIA), 43 from the downstream Wulate Irrigation Area (WLTIA)) were collected, and 15 water quality indexes were analyzed. Methods including mathematical statistics, Piper diagram, Gibbs model, forward succession model, and ionic rations were used to analyze the hydrochemical characteristics and evolution mechanisms, RSBC, PS, SAR, WQI were selected to evaluate water quality and irrigation suitability from the perspective of salt and alkali damage. Results showed that the groundwater of the study area is weakly alkaline, SWIA is mainly fresh water (47.62%), WLTIA is mainly brackish water (65.12%), and the hydrochemistry of the groundwater consists of Cl-Na type and Cl·SO-Ca·Mg. The solute content of downstream (WLTIA) is higher than that of upstream (SWIA), Na⁺ and Cl^- have obvious advantages in WLTIA, and they are the main contribution indicators of groundwater TDS in the study area. The groundwater is subjected to the ongoing influence of rock weathering, ions exchange, and evaporate crystallization Na⁺ mainly originates from the dissolution of evaporate salt rock and silicate rock, and Ca²⁺ from the dissolution of gypsum and carbonate. The order of contribution of different rocks is evaporation rock > silicate rock > carbonate rock. Based on the classifications of sodium absorption ratio (SAR), residual sodium bicarbonate (RSBC), and potential salinity (PS), most of the groundwater samples are unsuitable for irrigating, and the groundwater quality of the SWIA is better than that of the WLTIA.

Field-applied biochar-based MgO and sepiolite composites possess CO2 capture potential and alter organic C mineralization and C-cycling bacterial structure in fertilized soils

Agricultural soils contribute a significant amount of anthropogenic CO₂ emission, a greenhouse gas of global environmental concern. Hence, discovering sustainable materials that can capture CO₂ in cultivated soils is paramount. Since the effect of biochar on C mineralization/retention in fertilized soils is unclear, we produced biochar-based MgO and sepiolite-nanocomposites with CO₂ capture potential. The field-scale impacts of the modified-biochars were evaluated on net C exchange rate (NCER) periodically for 3 months in fertilized plots. The effects of the modified-biochar on organic-C mineralization, the activities, and dynamics of C-cycling-related 16S rRNA which are unknown, were investigated. Results revealed an initial rapid and higher cumulative CO₂ emission from the sole fertilizer treatment (F). Unlike the biochar treatment (BF), the successful incorporation of MgO/Mg(OH)₂ nanoparticles into the matrix and surface of biochar, and the potential formation of MgCO₃ with soil CO₂, mitigated CO₂ emission, especially in the MgO-modified biochar (MgOBF), compared to the sepiolite-biochar treatment (SBF). Compared to F and BF, the higher C retention as MgCO₃ in the modified biochar treatments led to an increase in cellulase activity, stimulation of key C-cycling-related bacteria, and the expression of genes associated with starch, sucrose, amino sugar, nucleotide sugar, ascorbate, aldarate, cellulose, and chitin degradation, thus, increasing organic C mineralization. Among the modified-biochar treatments, higher C mineralization was recorded in SBF, resulting in increased cumulative CO₂ emission, despite its initial capture for up to 42 days. However, MgOBF was effective in capturing soil-derived CO₂, despite the increased C mineralization compared to biochar. The changes in soil moisture and temperature significantly regulated NCER. Also, the modified biochars positively influenced the distribution of C-cycling-related bacteria by improving soil pH and available nutrients. Among the modified biochars, the observed higher mitigation effect of MgOBF on NCER indicated that it could be preferably applied in agricultural soils.

Mitigating global warming potential while coordinating economic benefits by optimizing irrigation managements in maize production

China is the second largest irrigated country in the world. Increasing irrigation intensity costs more water and energy, and produces more greenhouse gas (GHG). In the present study, the responses of maize economic and environmental benefits to different irrigation managements were analyzed in a 2-year field study. A purposely designed tube-study was conducted to explore mechanism underlying effects of irrigation managements in detail. Three treatments, rainfed (RF), flood irrigation (FI), and drip irrigation (DI) were included in the field. Five treatments, no irrigation, flood irrigation, irrigation in 0-30, 30-60, and 0-90 cm depth were conducted in the tube study. Compared to RF, grain yields of FI and DI significantly increased by 22.1 % and 35.7 %, respectively, the net ecosystem economic budget significantly increased by 34.2 % and 35.6 %, and carbon footprint decreased by 7.0 % and 12.7 % in the field study. The irrigation treatments in the tube study increased the global warming potential by 12.0-32.8 % and grain yield by 44.5-203.9 %, and reduced GHG intensity by 24.3-57.4 %, compared with no irrigation treatment. Water content at the top soil layer had the greatest impact on GHG emissions. In conclusion, the differences in grain yield and GHG emissions among irrigation managements are mainly due to the soil water content in space and time. Drip irrigation decreases GHG intensity by producing more grain yield due to the optimized soil water distribution in the root zone. Irrigation management with appropriate amount and frequency can increase economic benefit and reduce environmental cost in maize production.

Understanding the Role of Shallow Groundwater in Improving Field Water Productivity in Arid Areas

Soil water and salt transport in soil profiles and capillary rise from shallow groundwater are significant seasonal responses that help determine irrigation schedules and agricultural development in arid areas. In this study the Agricultural Water Productivity Model for Shallow Groundwater (AWPM-SG) was modified by adding a soil salinity simulation to precisely describe the soil water and salt cycle, calculating capillary fluxes from shallow groundwater using readily available data, and simulating the effect of soil salinity on crop growth. The model combines an analytical solution of upward flux from groundwater using the Environmental Policy Integrated Climate (EPIC) crop growth model. The modified AWPM-SG was calibrated and validated with a maize field experiment run in 2016 in which predicted soil moisture, soil salinity, groundwater depth, and leaf area index were in agreement with the observations. To investigate the response of the model, various scenarios with varying groundwater depth and groundwater salinity were run. The inhibition of groundwater salinity on crop yield was slightly less than that on crop water use, while the water consumption of maize with a groundwater depth of 1 m is 3% less than that of 2 m, and the yield of maize with groundwater depth of 1 m is only 1% less than that of 2 m, under the groundwater salinity of 2.0 g/L. At the same groundwater depth, the higher the salinity, the greater the corn water productivity, and the smaller the corn irrigation water productivity. Consequently, using modified AWPM-SG in irrigation scheduling will be beneficial to save more water in areas with shallow groundwater.