Ed Barrett-Lennard

Context
Dry season irrigated rice has the potential to increase food production and cropping intensity in the salt-affected coastal areas of the Ganges Delta, but its success is often limited by seasonal salinity, scarcity of freshwater and elevated temperatures. We hypothesized that earlier transplanting would overcome these constraints and maximize productivity.

Objective
The objective of this study was to evaluate how transplanting times interact with salinity and temperature and affect rice yield and water productivity in a saline ecosystem.

Methods
Field experiments were conducted at Dacope, in the Khulna district of Bangladesh, during 2023–24 and 2024–25 seasons with a single salt-tolerant rice cultivar and six transplanting dates (15 and 30 December, 15 and 30 January, 14 and 28 February) in a randomized complete block design. Soil salinity (EC1:5), solute potential, crop growth parameters and water productivity were measured along with yield and its components at harvest.

Results
Seasonal rainfall, temperature, and salinity strongly influenced crop performance. Transplanting on 15 and 30 December was associated with higher leaf area, biomass, tillers m−2, grain panicle−1, thousand grain weight and grain yield (7.0–7.2 t ha−1 in 2023–24 and 7.4–7.6 t ha−1 in 2024–25). Irrigation water salinity was higher in 2023–24 (2.5–6.2 dS m−1) than in 2024–25 (1.9–4.0 dS m−1), largely due to lower rainfall in the first season. Delayed transplanting after 30 December decreased yield by 11–64 % in 2023–24 and 11–54 % in 2024–25. Higher yields on 15 and 30 December were associated with lower soil salinity, higher soil solute potential, and lower daily maximum temperature during the maximum vegetative and reproductive stages. In contrast, late planting after 30 December exposed crops to more days exceeding 33 0C during reproductive stage, along with higher salinity and lower solute potential during reproductive and ripening stages, which led to high levels of panicle sterility. Transplanting on 30 December also resulted in the highest irrigation water productivity (0.86–0.91 kg m−3) and total water (irrigation and rainfall) productivity (0.84–0.86 kg m−3), while crop water productivity based on evapotranspiration was the highest with 15 December transplanting (2.51–2.62 kg m−3).

Implications
Transplanting Boro rice by 30 December enables crops to escape high soil salinity and elevated temperature during reproductive growth, thereby improving both grain yield and water productivity in the salt-affected coastal areas of the Ganges Delta. Adopting this practice can help farmers intensify their cropping systems by integrating high yielding salt-tolerant dry season irrigated rice with monsoon-season rice production.

Context
Agricultural productivity in the coastal saline zones of the Ganges Delta in Bangladesh and West Bengal, India faces significant constraints due to high soil salinity, seasonal waterlogging, freshwater scarcity, and increasing climatic variability. These challenges collectively limit the sustainability and intensification of dry season (Rabi) cropping systems, thereby impeding regional food security and livelihoods.

Objective
This study aimed to assess the key biophysical constraints affecting Rabi season cropping systems and to evaluate the integration of key agronomic and water management technologies using a combination of field experimentation and cropping systems modelling, with the goal of supporting climate-resilient intensification in coastal saline environments.

Method
Two years of field experimentation were conducted across multiple locations, generating a comprehensive validation dataset comprising 139 crop instances, including transplanted Aman (T. Aman) rice, wheat, maize, sunflower, grass pea, and lentil. These datasets represented a diverse range of potentially integratable technologies and agroecological conditions. The Agricultural Production Systems Simulator (APSIM), employing the APSIM-SWIM3 module, was used to simulate crop production outcomes for a range of different integrated technologies. To achieve this, a novel modelling approach was developed to dynamically simulate surface soil salinity and moisture, and then its subsequent effects on crop production, using daily inputs of water table depth, salinity, irrigation, and climatic data.

Results and conclusions
APSIM simulations closely matched observed field data, with performance metrics (RMSE, R2) falling within acceptable ranges of experimental uncertainty. Long-term (25-years) scenario analyses demonstrated that advancing sowing dates by 15–30 days could substantially increase yield potential by reducing salinity exposure during critical crop stages. However, early sowing increased the risk of waterlogging, especially in low-lying fields. In some cases, the incorporation of in-field drainage structures was shown to mitigate waterlogging risks effectively. In situations where this is not possible due to landscape constraints, model-based identification of optimal sowing periods provided a viable alternative to reduce risk of waterlogging. Additionally, the retention of crop residues was shown to reduce surface soil evaporation and salinity accumulation, increasing yield, particularly in late-sown Rabi crops.

Significance
Focusing on the integration of four key technologies— short-season improved Kharif rice varieties, early Rabi crop sowing, field drainage, and crop residue retention—this study delivers a validated, model-supported decision framework for enhancing Rabi cropping in coastal agroecosystems. The results offer a scalable foundation for site-specific agronomic planning, community-based water management, and policy formulation aimed at climate-resilient cropping system intensification in the vulnerable coastal saline regions of South Asia.

Background and aims
In Vietnam, Si accumulator crops like rice and maize crops are commonly rotated, but rice straw is often removed for animal feed. This study assessed whether rice straw mulch could improve soil available Si and maize growth.

Methods
A field experiment was conducted over three years in two fields with different soil Si levels. Four rice straw mulch levels (0, 3.5, 7, and 10.5 t ha⁻1) were applied during the maize growing season (Feb–Apr), and repeated for three years. In the 3rd year, soil samples were analyzed for available Si (phosphate buffer extraction) and Si fractions (CaCl2-Si, acetic acid-Si, H2O2-Si, oxalate-Si, and NaOH-Si). Maize yield and Si, N, P, K, and Na uptake were also evaluated.

Results
At the lower available Si field, rice straw mulch significantly increased the phosphate buffer-Si, CaCl2-Si and H2O2-Si in soil two weeks after sowing whereas the higher available Si field showed no differences among treatments. In contrast, the Si concentration in maize stems and leaves increased notably in the higher rice straw treatments at both sites. Furthermore, a negative correlation was found between Si and Na concentrations in the maize stems and leaves, suggesting that Si may play a role in mitigating Na uptake and reducing Na toxicity.

Conclusion
This study demonstrated that the application of 7 and 10.5 t ha⁻1crop⁻1 of rice straw to fields with low available Si may enhance the soil Si availability, and improve Si, N, P, K uptake and tolerance to salt stress.

Saline intrusion and freshwater scarcity is now common in the Mekong River Delta (MRD) Vietnam resulting in dry season rice crop failure. There is a need to identify suitable alternative crops that are fast maturing, water efficient and/or saline tolerant and optimise the practical irrigation of these crops. A glasshouse trial examined the suitability of quinoa (Chenopodium quinoa Kruso white), cowpea (Vigna unguiculata Red Caloona) and soybean (Glycine max Richmond) for growth in conditions representing of salinity and drought experienced in the MRD. Plants were irrigated with either fresh or saline (up to 4 g L−1) water. Chameleon soil moisture sensors were used to trigger irrigation events, either constantly (water potential 0 to single bond22 kPa) or intermittently (irrigating when the water potential was below single bond50 kPa). Water use, soil salinity, plant performance and stress parameters were measured. Saline treatments significantly affected the yield of all three species; however, quinoa grew in saline conditions for the longest duration. Cowpea and quinoa tolerated irrigation with 4 g L−1 during reproductive phases, whilst soybean experienced leaf chlorosis and premature senescence with saline irrigation. Cowpea was negatively affected by intermittent irrigation with higher proline concentrations in younger leaves. Chameleon sensors improved irrigation efficiency and could be used to aid farmers in developing irrigation schedules in agricultural producing regions affected by water shortages. High salinity during reproductive growth phases hindered the accuracy of the Chameleon sensors and thus their use would be most adventitious in vegetative stages to improve water use efficiency before salinity peaks.

Context
Salinity occurs in sodic soils in Australia, but its effect in Western Australia is poorly understood.

Aims
We determined the cause of salinity, the ions responsible, and their potential significance as constraints to crop growth on sodic soils at Merredin and Moorine Rock.

Methods
Soil was collected from 76 profiles to depths of 1.0–1.4 m (388 samples). Samples were analysed for EC1:5, pH, texture, and exchangeable and soluble ions.

Results
Exchangeable cations were best calculated as the difference between total cations (determined from BaCl2/NH4Cl extracts) and soluble ions (determined from water-soluble extracts). Profiles showed increasing sodicity, alkalinity and salinity with depth. The major soluble cation responsible for salinity was Na+; the major soluble anions were Cl−, HCO3−, SO42−, and CO32−. High salinity in subsoils (depth > 0.2 m) was strongly correlated with dispersive charge (adj. R2 = 0.73). Osmotic potentials were calculated for two levels of gravimetric soil water, the water content of the soils at sampling, or assuming 30% (dry mass basis) soil water. At Moorine Rock, soils mostly had osmotic potentials less than −1.5 MPa. Increasing soil water content to 30% made osmotic potentials less negative. At Merredin, there was strong stratification of osmotic potentials; surface soils mostly had osmotic potentials between 0 and −0.5 MPa, but subsoils mostly had osmotic potentials between −1.0 and −1.5 MPa.

Conclusions
Crop growth in these landscapes is likely to be constrained by salinity, particularly in dry years.

A well-designed drainage system can alleviate soil salinity and waterlogging, leading to increased crop yield if the drainage does not cause a water shortage late in the growing season. We conducted three field experiments with sunflower across two dry seasons (Experiment I in 2019–20, and II and III in 2020–21) in a tropical landscape to examine the effectiveness of shallow drains and mulch in overcoming these constraints. In Experiment I, four surface drains of 0.1 or 0.2 m depth spaced 1.2 or 1.8 m apart were tested along with an undrained treatment. In Experiment II, the same four drainage treatments and an undrained treatment in the main plots were split into mulch (-M and +M) sub-plots. Experiment III had four main treatments, undrained, surface drains (SD; 0.1 m deep, 1.8 m apart), subsoil drains (SSD; 0.5 m deep, 4.5 m apart) and SSD+SD each split for mulch (-M and +M) sub-plots. At vegetative emergence and at the 8-leaf stage, all plots were inundated (3–5 cm depth; ECw: 1.5–2.5 dS m–1) for 24 h before opening the drains. Drainage treatments without mulch reduced SEW30 (waterlogging index, sum of excess water within 30 cm soil depth) and soil EC1:5 at 0–15 cm, while increasing sunflower yield by 15–100 % compared to the undrained no-mulch treatment. Relative to the undrained no-mulch treatment, drains with straw mulch conserved soil water, reduced EC1:5 at 0–15 cm and increased yield in Experiments II and III by 40–47 and 76–143 %, respectively. There were no yield differences among the combinations of shallow drains. Although combined drains (SSD+SD) added 25–30 % extra yield relative to surface drains, these have higher installation costs. Shallow surface drains at 1.2–1.8 m spacing coupled with mulch are effective options for smallholder farmers to reduce salinity, waterlogging and drought stresses, and increase yield on saline, clay soils.
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Context
Water is widely assumed to be the factor most limiting the growth of annual crops in rainfed environments, but this is rarely tested at sub-continental scale.

Aims
Our study aimed to determine the key environmental and management variables influencing the yield of wheat and barley in the grain-production regions of southern Australia, using data from National Variety Trials.

Methods
We used generalised additive models to determine the importance of climatic and management variables on wheat and barley grain yield. We determined the effects of the best one, two or three variables and their interactions.

Key results
The aridity index, defined as the ratio of cumulative rainfall to potential evapotranspiration, was the single strongest determinant of grain yield for both crops. Model performance was further improved by separating the aridity index into pre-seasonal and seasonal components. Interestingly, other variables that might be expected to influence yield, such as nitrogen fertilisation and extreme temperatures, had relatively minor effects. A comparison between data collected over two 6-year periods showed that there had been yield gains and increased water-use efficiency with time, especially in wetter environments.

Conclusions
Our findings illustrate the importance of water availability for grain production in this region and suggest opportunities for benchmarking and yield prediction through use of readily available climate data.

Implications
Our study reinforces the importance of factors such as water-use efficiency and drought tolerance as goals for cultivar development and agronomic research in wheat and barley. It also highlights the potential of National Variety Trial data as a resource for understanding grain production systems and climate resilience. Further work could explore the value of additional variables and improved weather data.

CONTEXT

Inland saline intrusion is occurring during the dry season in the Mekong River Delta (MRD), Vietnam. Rising sea levels, tidal fluctuations, drought, and changes to upstream flow contribute to extensive salinisation of rice producing areas of the MRD, leading to substantial rice crop losses.

OBJECTIVE

The identification, evaluation and implementation of alternative crop and soil management solutions are required to complement on-going rice production in the region.

METHODS

A review of scientific and grey literature was conducted regarding the nature and extent of salinisation in the MRD and the adoption and management of alternative crops to rice.

RESULTS

Familiar crops in Vietnam (e.g., maize, soybean), as well as novel crops to the MRD (e.g., quinoa, cowpea) were explored as potential options to replace dry season rice. Management options including surface soil mulches and plastic coverings help maintain soil moisture and reduce salinity damage to plants, and the use of drainage and seed preparation techniques can improve plant establishment and yield. Factors contributing to the success of alternative crops include salt tolerance, timing and efficiency of water use, ability to grow in the dry growing season, tolerance to pests and diseases, labour intensiveness and the crops' marketability.

SIGNIFICANCE

The identification of suitable alternative crops to replace dry season rice in saline affected areas of the MRD, combined with management practices like mulching and soil moisture monitoring, could provide farmers with income opportunities to offset rice losses. Documenting the factors contributing to successful crop diversification can assist with decision-making and support initiatives among farmers, agribusiness, and government agencies.
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Purpose
Crop sensitivity to root zone salinity can vary over time, which can lead to severe damage when high sensitivity coincides with high soil salinity. The variation in salinity sensitivity of sunflower during its growth cycle is unknown.

Methods
Two pot experiments were conducted in sand culture with a complete nutrient solution. Solutions were flushed through pots in excess to maintain specified salt concentrations in the soil solution. In Experiment 1, salt-sensitive stages were determined by applying solutions with an electrical conductivity of < 0.7, 2, 4 or 8 dS m− 1 through the vegetative, flowering or grain filling stages. In Experiment 2, the most sensitive stage to root-zone salinity was determined by exposing plants to 10-day periods of salinity (< 0.7, 8, 16 and 24 dS m− 1) overlapping by 4 days starting from 13-leaf to grain filling.

Results
In both experiments, decreases in seed yield were associated with exposure of plants to elevated EC during the period before opening of disk flower to ~ 95% anthesis, while grain filling was the least sensitive. The decline in yield was correlated with a decrease in mature seed number. Increasing salinity from 4 to 8 dS m− 1 during flowering increased the area without seeds at the centre of the disk. In experiment 2, measurements of leaf ion concentrations and photosynthesis suggested that Na+ toxicity decreased yield due to decreases in availability of photosynthate to flowers.

Conclusion
To maximise sunflower yield in saline soils, it is important to minimise salinity stress from before flower opening to anthesis.

Food production on present and future saline soils deserves the world’s attention particularly because food security is a pressing issue, millions of hectares of degraded soils are available worldwide, freshwater is becoming increasingly scarce, and the global sea-level rise threatens food production in fertile coastal lowlands. Future of Sustainable Agriculture in Saline Environments aims to showcase the global potential of saline agriculture. The book covers the essential topics, such as policy and awareness, soil management, future crops, and genetic developments, all supplemented by case studies that show how this knowledge has been applied. It offers an overview of current research themes and practical cases focused on enhancing food production on saline lands.

FEATURES
• Describes the critical role of the revitalization of salt-degraded lands in achieving sustainability in agriculture on a global scale
• Discusses practical solutions toward using drylands and delta areas threatened by salinity for sustainable food production
• Presents strategies for adaptation to climate change and sea-level rise through food production under saline conditions
• Addresses the diverse aspects of crop salt tolerance and microbiological associations
• Highlights the complex problem of salinity and waterlogging and safer management of poor-quality water, supplemented by case studies