Context Coastal saline regions of the Ganges Delta often contain excess soil water after the monsoon season, delaying Rabi crop establishment. Subsequent unseasonal heavy rainfall further exacerbates waterlogging, reducing crop productivity. Although surface drainage can alleviate waterlogging, the optimum surface drainage depth for sunflower remains unclear. Objective This study aimed to identify the optimal surface drainage depth for sunflower cultivation and assess long–term (LT, 1975–2024) yield variability under different seasonal rainfall conditions. Methods Field trials in Dacope, Khulna, tested three surface drainage depths (no drain, 15 cm, and 30 cm, the depth of the open channel) from 2022 to 2024. Data on crop, soil water and soil salinity were used to calibrate the APSIM crop simulation model for local conditions. Model performance was evaluated using R2, Root Mean Square Error (RMSE), normalised RMSE, and Student’s t–test. Subsequent scenario analyses then compared LT yields across three dry season rainfall ranges: low (0–100 mm), medium (100–300 mm), and high (300–637 mm) based on 50 years of records. Results Model calibration and parameter adjustment helped address previously observed shortcomings of the APSIM-Sunflower module and enhanced its simulation accuracy for the variables of interest. High R2 values (0.79–0.98) and acceptable RMSE values between observed and simulated data (7.4 & 6.4 day, 106 & 153 kg/ha, 543 & 549 kg/ha, 0.026 & 0.036 cm3/cm3, and 46 & 119 mg/kg) were achieved for both calibration and validation across phenology, yield, biomass, soil water, and chloride content (CL), respectively. From LT yield prediction, a 30 cm drainage depth was optimal for all seasonal rainfall categories, resulting in yields 1.1–1.8 times higher than those with 15 cm or no drainage. The LT yields showed a significant (p < 0.001) positive correlation with seasonal rainfall and solute potential, and a significant (p < 0.001) negative correlation with CL. All results were within the range of experimental error, confirming the model's reliability. Conclusion The APSIM model demonstrated strong performance in simulating daily phenology, yield, biomass, soil water, salinity, and LT yield for surface drainage depths in coastal soils, and 30 cm was shown to be the best depth. Implications With further improvement by adding a surface drainage module, APSIM could serve as a valuable decision–support tool for researchers and policymakers for managing LT risks in dry season cropping and increasing smallholders’ farm income through cropping systems intensification in the saline coastal zone of the Ganges Delta and similar environments.
Background Soil organic carbon (SOC), a widely used indicator of soil organic matter status, is known to improve average crop yield, but its role in contributing to yield stability under environmental stress remains poorly understood, particularly in paddy ecosystems. Purpose This study aimed to quantify the effects of long-term organic matter application on SOC accumulation, rice productivity, and yield stability across diverse environmental conditions in Japan. Methods We used a dataset from 14 nationwide long-term experiments (LTEs) under continuous rice monoculture spanning 11–54 years. Of these, 11 sites were on Lowland soils and 3 on Andosols. We compared three treatments: inorganic fertilizer only (NPK), NPK with rice straw (RS), and NPK with compost (COM). To evaluate potential associations between SOC concentration and yield stability, we analyzed SOC accumulation rates, mean grain yield, long-term yield variability, and relative yield during objectively defined “low-yield years” (years in which NPK yields fell by >1 SD below the long-term mean). Results While NPK plots in Lowland soils frequently exhibited SOC depletion, continuous COM application significantly increased SOC in most sites across both soil types, with SOC accumulation rates ranging from 0.083 to 0.531 g C kg−1 yr−1 in Lowland soils and from 0.166 to 0.514 g C kg−1 yr−1 in Andosols. Organic amendments generally enhanced mean grain yields, although the magnitude of the response varied among sites. Based on mean treatment-to-NPK yield ratios, yields were on average 3.6% higher in RS and 6.3% higher in COM plots in Lowland soils, with corresponding yield advantages of 7.2% and 9.4% in Andosols. No significant relationship was observed between SOC concentration and long-term yield variability. In contrast, SOC concentration was positively associated with relative yield during low-yield years in Lowland soils (R² = 0.15, p < 0.05). Although the relationship explained only a limited proportion of the observed variation, its positive direction was generally maintained across alternative analytical approaches, suggesting that higher SOC concentrations were associated with a modest reduction in yield decline under unfavorable conditions. Site-specific comparisons further showed that the relative yield advantage of organic amendment treatments tended to be greater during low-yield years than during normal years, particularly in Lowland soils. No statistically significant relationship was observed in Andosols, possibly reflecting their inherently high SOC concentrations and other unique physicochemical properties associated with volcanic ash soils. Conclusions This study provides empirical evidence of a positive association between SOC concentration and yield stability in Lowland paddy soils, although the magnitude of the relationship was modest. Continuous organic matter inputs represent an important pathway for building and maintaining SOC and, alongside other factors, may contribute to the maintenance of rice productivity under unfavorable conditions, particularly in Lowland soils.
Context and objective Under high-density planting, partially substituting organic fertilizer for chemical fertilizer may regulate source–sink relationships, thereby providing a promising strategy for achieving high maize yield. However, the mechanisms through which organic fertilizer substitution interacts with planting density to regulate source–sink relationships in drip-irrigated maize in arid regions remain unclear. This study aimed to determine how organic fertilizer substitution affects canopy structure, leaf physiological performance, source–sink balance, and yield formation in drip-irrigated maize under different planting densities. Methods A three-year field experiment was conducted during the maize-growing seasons from 2023 to 2025. Two planting densities, 70,000 (D1) and 100,000 plants ha⁻¹ (D2), were evaluated in all three years, with a third density of 130,000 plants ha⁻¹ (D3) added in 2025. Four fertilization treatments were applied at each density: no fertilizer (F0), chemical fertilizer alone (F1), and substitution of 17% (F2) or 34% (F3) of total N input with organic fertilizer. Results Increasing planting density increased the leaf area index (LAI) but reduced source capacity on a per-plant basis. The F2 treatment further improved canopy structure by increasing the proportion of leaf area distributed in the middle and upper canopy layers. At the D2 density, F2 increased the maximum leaf area index by 2.39%–15.29% relative to F1 across the three experimental years. Averaged across planting densities, F2 increased SPAD value and net photosynthetic rate by 23.95%–48.96% and 24.75%–86.17%, respectively, compared with F0, and enhanced sink capacity and grain-filling rate. D2F2 showed relatively favorable source–sink matching, particularly in 2023 and 2025, while increasing grain yield per unit area by 7.46%–23.83% relative to D1F1. Partial least squares structural equation modeling showed that the fertilization regime exerted a positive total effect on grain yield, primarily by improving canopy structure and leaf physiological performance and, consequently, optimizing source–sink balance. Conclusions Combining a planting density of 100,000 plants ha⁻¹ with 17% organic fertilizer substitution improved source–sink coordination and supported high maize yield under the tested environments. Implications This study elucidates the physiological mechanisms through which moderate increases in planting density and partial organic fertilizer substitution regulate maize yield by coordinating canopy development, leaf physiological performance, and source–sink relationships. These findings provide a new perspective on the physiological basis of maize yield improvement.
Background Meeting the increasing food demand under changing land use, constrained water resources, and rising climatic variability requires resource-conserving management of the rice–wheat (R-W) system in the Indian mid-Himalayas. Zero tillage (ZT) and improved irrigation scheduling may maintain crop productivity, while reduce cultivation cost and improve water-use efficiency. Objectives This study evaluated the long-term response crop and system productivity, water-use indices, economic performances, and yield sustainability to contrasting tillage practices and irrigation regimes. Methods A 19-year field experiment (2001–02–2019–20) to compared zero tillage (ZT) and conventional tillage (CT) under four irrigation regimes: These comprised pre-sowing irrigation only (IR1); pre-sowing plus active tillering in rice/crown-root initiation in wheat (IR2); IR2 plus panicle initiation in rice/flowering in wheat (IR3); and IR3 plus irrigation at grain filling (IR4). Results Rice yield declined significantly over time across tillage practices and irrigation regimes, indicating that long-term reduction in system productivity was largely associated with declining rice yield. Mean wheat yield under ZT showed a modest upward trend (+18.7 kg ha−1year−1), whereas the corresponding trend under CT was negative. Irrigation significantly influenced the mean yields of both crops and overall system, with IR4 producing the highest productivity. However, increasing irrigation frequency reduced wheat and system water-use efficiency (WUE), demonstrating a trade-off between yield maximization and efficient use of irrigation water. ZT wheat WUE from 10.2 to 10.6 kg ha−1 mm−1 and increased system net returns by 68.8% while reducing cultivation cost by 14.9% relative to CT. Conclusion and Implications Irrigation regime exerted a stronger influence on long-term R-W system productivity than tillage. IR4 was most suitable for maximum productivity, profitability, and yield sustainability where irrigation water was adequate. Under limited water availability, IR3 offered a more balanced option because it maintained relatively high productivity and water-use performance with a stable sustainability trend. Although ZT did not significantly increase mean system yield, it maintained productivity comparable to CT while lowering cultivation costs and improving economic and water-use performance. These findings support the selection of tillage and irrigation practices according to water availability and production objectives in the Indian mid-Himalaya.
