The study, led by researchers at the University of Florida and the USDA Agricultural Research Service, set out to determine how two contrasting light environments — full sun and 50% shade — combined with five cumulative fertilizer rates, ranging from no fertilizer to 240 grams per plant, would affect the morphophysiological performance of Plumeria rubra grown in containers. The team measured plant height, leaf number, chlorophyll content, canopy vigour, and a suite of nutrient dynamics in the container substrate, including nitrate, calcium, potassium, and sodium concentrations, as well as pH and soluble salts.

The results showed that both light and fertilizer had significant effects on plant growth and physiology, but that their interaction was particularly important for chlorophyll content and canopy vigour. Under full sun, plants receiving intermediate fertilizer rates produced the greatest leaf number and canopy vigour, while under shade, the same fertilizer rates produced the highest chlorophyll content. The team also found that nutrient dynamics in the container substrate were strongly influenced by light, with nitrate and calcium concentrations increasing under full sun and pH decreasing under the same conditions.

One of the most striking findings was the non-linear response of plant growth to fertilizer dose. Plants receiving intermediate fertilizer rates produced the greatest height and leaf number, while those receiving the highest rates showed no additional benefit and, in some cases, a slight decline. This pattern, the team suggests, reflects the classic non-linear response of ornamental species to nutrient supply, where additional fertilizer beyond an optimal dose provides no benefit and may even induce salt stress in the container substrate.

The researchers also found that the interaction between light and fertilizer had important implications for nutrient use efficiency. Under full sun, plants receiving intermediate fertilizer rates showed the greatest nutrient uptake, while under shade, the same rates produced the highest chlorophyll content but lower nutrient uptake. The team suggests that this pattern reflects the trade-off between photosynthetic capacity and nutrient acquisition, where plants under high light can acquire more nutrients but may also experience greater water loss and salt stress.

The study’s findings have important implications for nursery production of Plumeria rubra and other ornamental species grown in containers under subtropical conditions. The team suggests that growers can optimise production by matching fertilizer dose to light environment, using intermediate rates under full sun and the same rates under shade to produce the greatest growth and chlorophyll content. The findings also highlight the importance of monitoring nutrient dynamics in the container substrate, where nitrate and calcium concentrations can increase under high light and pH can decrease under the same conditions.

The researchers also note that their study has some limitations. The team measured only a single growing season and did not assess flowering, which is an important trait for ornamental species. The team also did not measure nutrient uptake by the plants themselves, relying instead on nutrient dynamics in the container substrate. Future studies, the team suggests, should assess flowering and nutrient uptake by the plants to provide a more complete picture of the interplay between light and fertilizer in nursery production.

Despite these limitations, the study offers some of the clearest evidence yet that the interplay between light intensity and fertilizer dose plays a decisive role in shaping the growth, physiology, and nutrient dynamics of Plumeria rubra grown in containers under subtropical conditions. The team suggests that growers can harness this interplay to optimise production, matching fertilizer dose to light environment and monitoring nutrient dynamics in the container substrate to produce the greatest growth and chlorophyll content. The findings also highlight the importance of non-linear responses to nutrient supply, where additional fertilizer beyond an optimal dose provides no benefit and may even induce salt stress.

The study, published in Frontiers in Horticulture, is part of a growing body of research on the interplay between environmental factors and nursery production of ornamental species. The team suggests that their findings can be applied to other ornamental species grown in containers under subtropical conditions, where the interplay between light and fertilizer can be harnessed to optimise production and reduce environmental impacts. The findings also highlight the importance of monitoring nutrient dynamics in the container substrate, where nitrate and calcium concentrations can increase under high light and pH can decrease under the same conditions.

Subject of Research: Light–fertilizer interactions in Plumeria rubra nursery production

Article Title: Light–fertilizer interactions regulate morphophysiological performance and nutrient dynamics in Plumeria rubra under subtropical nursery conditions

Article References: Khoddamzadeh, A. A., Munoz-Salas, M. N., Cabrera, A., & Nageswara-Rao, M. (2026). Light–fertilizer interactions regulate morphophysiological performance and nutrient dynamics in Plumeria rubra under subtropical nursery conditions. Frontiers in Horticulture, 5, Article 1881853. https://doi.org/10.3389/fhort.2026.1881853

Image Credits: AI Generated

DOI: 10.3389/fhort.2026.1881853

Keywords: Plumeria rubra, light intensity, fertilizer dose, nursery production, ornamental species, nutrient dynamics, container substrate, subtropical conditions, chlorophyll content, canopy vigour, nitrate, calcium

The number matters because 1.4 parts per thousand is far below the salinity of seawater, which sits near 35 parts per thousand. It is also well within the range that brackish irrigation water can reach during the dry-season saline intrusion events that have increasingly battered the Vietnamese Mekong Delta, including the record intrusion disaster of 2020. In other words, the salinity levels that quietly destroy rice productivity are ones that farmers might taste as only faintly brackish. For a crop that supplies the majority of daily calories for billions of people, the margin between a good harvest and a failed one turns out to be vanishingly thin.

The experimental design was deliberately simple and rigorous. Rice plants of the Dai Thom 8 cultivar were grown under controlled greenhouse conditions and watered with solutions spanning a salinity gradient from zero to 4 parts per thousand. Rather than measuring only the end-of-season harvest, the team monitored the system continuously. They tracked soil electrical conductivity, a standard proxy for dissolved salt accumulation, and total soil nitrogen, a key nutrient indicator. On the plant side, they measured chlorophyll content in the leaves and gas-exchange parameters, which capture how effectively the foliage is taking up carbon dioxide and conducting photosynthesis. This combination allowed them to connect the dots across three linked domains: the chemistry of the soil, the physiology of the plant, and the productivity of the crop.

The soil data told the first part of the story. As irrigation water salinity increased, soil electrical conductivity climbed steadily, confirming that salts delivered in the water were accumulating in the root zone rather than being flushed away. At the same time, total soil nitrogen declined, a sign that the chemical fertility of the growing medium was deteriorating under saline conditions. This pairing is particularly worrying for farmers, because it means salinity does not merely stress plants directly; it also erodes the nutrient base on which any recovery would depend. Previous research has shown that salt-affected soils suffer reduced microbial activity and slower organic matter decomposition, which can starve crops of nitrogen even when fertilizer is applied, and the new results are consistent with that picture.

The plant physiology data filled in the second part of the story. Chlorophyll content fell as salinity rose, reflecting damage to the photosynthetic machinery itself. Gas-exchange measurements dropped in parallel, indicating that leaves were fixing less carbon per unit of time. Plant scientists interpret this combination as a classic salinity stress signature: excess sodium and chloride ions interfere with nutrient uptake, disrupt water balance, and generate reactive oxygen species that damage cellular components, while stomata partially close to limit salt intake, throttling carbon dioxide supply to the leaf. The result is a double hit, with less carbon captured and less efficient use of what is captured, and the Dai Thom 8 plants in this study displayed it clearly across the salinity gradient.

The yield response, however, was the study’s most striking finding, because it was emphatically nonlinear. Grain yield did not decline gently and proportionally as salt concentrations rose. Instead, the data showed a pronounced transition point at approximately 1.4 parts per thousand, where yield dropped by roughly 50 percent relative to unstressed controls. Below that threshold, the plants appeared to absorb the stress with comparatively modest losses; above it, the system tipped. This kind of nonlinear, threshold-driven behavior is exactly what makes salinity so dangerous in the field, because incremental worsening of water quality can appear tolerable season after season until a critical line is crossed and losses suddenly become catastrophic.

At the extreme end of the gradient, the consequences were essentially total. When irrigation water reached 4 parts per thousand, grain yield was nearly completely lost, meaning the plants survived to harvest but produced almost nothing of value. That severity is consistent with rice’s reputation as one of the more salt-sensitive cereal crops, particularly during reproductive stages when pollen viability and grain filling are acutely vulnerable. Earlier field studies in semi-arid irrigated rice systems have documented similar sensitivities to floodwater salinity, and breeders have long sought varieties that maintain yield under moderate salt stress. The fact that a widely grown, locally favored cultivar like Dai Thom 8 shows such a sharp cliff underscores how much work remains before salt-tolerant varieties can be relied upon to buffer delta agriculture.

Perhaps the most scientifically valuable contribution of the study is its demonstration that soil and plant indicators move together in a coordinated way across the salinity gradient. Grain yield was strongly associated with soil electrical conductivity, total nitrogen, and chlorophyll content, meaning that a handful of measurable variables jointly tracked the health of the whole soil-plant system. The authors argue that this integration carries a practical message: assessments of rice response to salinity should not rely on soil chemistry or plant physiology alone, but should combine both. A farmer or extension officer measuring only soil conductivity might miss early physiological warning signs, while one measuring only leaf chlorophyll might misattribute stress to nutrient deficiency rather than salt. Read together, the indicators offer a more reliable early-warning system.

The regional context amplifies the urgency. The Mekong Delta, where the research was conducted, is home to some of the most productive rice land on the planet and supplies a large share of Vietnam’s rice exports, yet it is simultaneously squeezed by sea-level rise, upstream damming that reduces dry-season river flow, and land subsidence. Saline intrusion events have reshaped the delta’s agricultural landscape in recent decades, and projections suggest the problem will intensify. Globally, salt-affected soils already degrade enormous areas of cropland, and the economics of salt-induced land degradation run into billions of dollars annually. Studies like this one, which pin down precise thresholds for specific cultivars under controlled conditions, give modelers and policymakers the quantitative anchors they need to translate climate and hydrology projections into realistic yield forecasts.

For farmers on the ground, the practical implications are immediate. Irrigation water that tests at or above roughly 1.4 parts per thousand should be treated as a serious risk to rice production, and monitoring soil electrical conductivity alongside plant indicators such as leaf chlorophyll could help identify stress before the yield cliff is reached. Management options, from alternating fresh and saline water applications to leaching salts with scarce freshwater supplies, all depend on knowing where the danger line lies. The Can Tho University team, working without external funding and supported by the university’s JICA-funded Advanced Environmental Techniques Laboratory, has provided one of the clearest such lines yet for a major Vietnamese cultivar. As brackish water pushes further into the world’s rice bowls, knowing exactly where the cliff edge sits may prove as valuable as any new seed variety.

Subject of Research: Effects of irrigation water salinity on soil chemistry, rice physiology, and grain yield thresholds

Article Title: Relationships among soil chemical properties, plant physiological responses, and rice (Oryza sativa L.) performance under irrigation salinity

Article References: Loc, N. X., Thanh, N. T. T., Tuyen, P. T. T., & Phuong, D. T. M. (2026). Relationships among soil chemical properties, plant physiological responses, and rice (Oryza sativa L.) performance under irrigation salinity. Plant and Soil. https://doi.org/10.1007/s11104-026-09037-x

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09037-x

Keywords: rice, salinity stress, soil electrical conductivity, chlorophyll content, grain yield, Oryza sativa, Mekong Delta, soil nitrogen, photosynthesis, irrigation water quality, salt tolerance, food security

The study, conducted at the College of Agriculture and Natural Resources of Darab at Shiraz University, focused on triticale, a hardy hybrid of wheat and rye often grown for grain and forage on marginal land. In a factorial pot experiment arranged in a completely randomized design, the researchers crossed three silicon levels — zero, 200, and 400 milligrams per kilogram of soil — with four biochar treatments: no biochar, sheep manure biochar, rice husk biochar, and municipal waste biochar. Every pot then received the same lead dose, and the plants were left to reveal which combination could best shield them.

The standout result came from sheep manure biochar applied together with 200 milligrams of silicon per kilogram of soil. Compared with untreated control plants, that combination increased leaf weight by a striking 108.3 percent and leaf area by 29.7 percent. Those are not cosmetic gains. Leaf area is the engine of photosynthesis, and a plant that can hold nearly twice the leaf biomass under heavy metal stress has, in effect, rebuilt its solar panels while the poison is still in the ground.

What makes the finding particularly interesting is that the researchers traced the improvement down to the plant’s internal plumbing. Microscopic examination of the leaves showed that the winning treatment enlarged the midrib — the central vascular bundle of the leaf — along with the metaxylem and protoxylem, the water-conducting tissues inside it. Wider xylem vessels mean better hydraulic conductivity, so water and dissolved nutrients can move more freely from root to leaf even when lead is interfering with root function. In effect, the biochar-and-silicon pairing did not just protect the leaf chemically; it physically re-engineered it for better transport under stress.

The biochemical story was just as dramatic. Plants receiving sheep manure biochar with the moderate silicon dose showed a 101.3 percent increase in total chlorophyll content, effectively doubling the pigment machinery that captures light. Carotenoid levels also rose, which matters because carotenoids act as accessory pigments and as quenchers of reactive oxygen species, the destructive molecules that heavy metals generate inside cells. Membrane stability — a key indicator of cellular integrity under stress — improved significantly in the same treatment, suggesting that the combination was keeping lead’s corrosive chemistry at bay at the level of the cell’s outer defenses.

Enzyme activity provided further evidence of a coordinated protective response. Catalase and peroxidase, two of the plant’s frontline antioxidant enzymes, both increased under the optimal treatment. These enzymes dismantle hydrogen peroxide and other reactive oxygen species before they can shred membranes, proteins, and DNA. Elevated catalase and peroxidase activity in the sheep manure biochar plus silicon-200 plants indicates that the treatment did not merely mask stress symptoms but actively strengthened the plant’s oxidative stress mitigation machinery — a hallmark of genuine stress alleviation rather than simple dilution of the toxin.

Dosage, however, proved to be the decisive variable. When the silicon supply was doubled to 400 milligrams per kilogram, the positive effects collapsed. Stomatal area — the size of the microscopic pores that regulate gas exchange and water loss — shrank noticeably at the high dose, a sign that the plants were closing down their exchange surfaces. At that elevated silicon level, rice husk biochar performed particularly poorly, reducing stomatal area by 25.6 percent compared with sheep manure biochar. The authors interpret this as an antagonistic effect: silicon, beneficial in moderation, becomes counterproductive in excess, underscoring that field applications will demand precise dosage optimization rather than generous blanket application.

The downstream consequences for yield were substantial. Plants grown with sheep manure biochar and 200 milligrams of silicon per kilogram grew 19.8 percent taller than controls and accumulated 69.5 percent more total dry matter. Reproductive performance followed suit: the number of grains per spike rose by 65.8 percent, and grain yield climbed by 68.0 percent relative to untreated plants growing in the same lead-laden soil. For a crop like triticale, which is often grown precisely because it tolerates poor conditions, a two-thirds yield recovery under heavy metal stress is a meaningful agronomic margin.

Why did sheep manure biochar outperform its rice husk and municipal waste counterparts? The answer likely lies in feedstock chemistry. Biochars differ enormously in pH, cation exchange capacity, nutrient content, and aromatic carbon structure depending on what they were made from and how they were pyrolyzed. Manure-derived biochars tend to be rich in minerals and alkaline, which can immobilize lead by precipitating it as phosphates and carbonates while simultaneously supplying nutrients. Combined with silicon’s well-documented role in strengthening cell walls, reducing metal translocation, and bolstering antioxidant defenses, the two amendments appear to act synergistically — the biochar locking lead away in the soil while silicon fortifies the plant against whatever it cannot avoid absorbing.

The broader implications reach well beyond a single pot experiment. Heavy metal contamination of agricultural soils threatens food security worldwide, and cheap, locally producible amendments like biochar and silicon fertilizers offer a remediation path that farmers in affected regions could actually afford. The study’s central lesson is one of precision: the synergy between biochar and silicon is real and powerful, but it sits on a knife’s edge of dosage, with the optimal silicon rate doubling chlorophyll and boosting yield by more than two-thirds while an excessive rate constricted stomata and eroded the gains. As the researchers conclude, reclaiming lead-contaminated soils with this pairing is feasible — but only if application rates are tuned with care rather than guesswork.

Subject of Research: Synergistic effects of biochar and silicon fertilization on triticale physiology and yield under lead-contaminated soil

Article Title: Combination of biochar and silicon influenced the leaf structure, phytochemical properties and yield of triticale under lead-contaminated soil

Article References: Bijanzadeh, E., Boostani, H. R., & Najafi-Ghiri, M. (2026). Combination of biochar and silicon influenced the leaf structure, phytochemical properties and yield of triticale under lead-contaminated soil. Discover Sustainability. https://doi.org/10.1007/s43621-026-04899-8

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04899-8

Keywords: biochar, silicon fertilization, lead toxicity, triticale, heavy metal contamination, chlorophyll content, antioxidant enzymes, metaxylem, soil remediation, grain yield, stomata, oxidative stress

The research team, led by Kisman Bhattarai and Nithya Rajan of Texas A&M’s Department of Soil and Crop Sciences, conducted field experiments at the university’s research farm near College Station in 2021 and 2022. The site sits on Weswood silty clay loam in a humid subtropical climate, and the region’s rivers ultimately drain into the Gulf of Mexico, where nutrient-driven hypoxia has become a serious ecological concern. Maize in central Texas is grown primarily as a rainfed crop, making the interaction between fertilizer timing and rainfall a matter of both economic and environmental consequence.

The experimental design was thorough. The researchers tested eight different split nitrogen applications in 2021, ranging from applying all nitrogen at planting (a 100:0 split) to dividing it evenly between planting and the R1 silking stage (a 50:50 split). The full fertilizer rate was 240 kilograms of nitrogen per hectare, based on the highest recommended rate for corn in the region. In 2022, they added two reduced-rate treatments—50 percent and 25 percent of the full rate—to see whether cutting nitrogen inputs could maintain yields under stress. All treatments were replicated four times in a randomized complete block design, and the team measured everything from plant height and leaf area index to chlorophyll content, biomass, grain yield, plant nitrogen uptake, and residual soil nitrate at multiple depths down to 60 centimeters.

The two growing seasons could not have been more different, and that contrast turned out to be the study’s greatest asset. In 2021, growing-season precipitation totaled 572 millimeters, above the 20-year average of 508 millimeters, and timely rains coincided with the reproductive stages. In 2022, by stark contrast, only 100 millimeters of rain fell during the growing season—just 20 percent of the long-term average—accompanied by air temperatures one to three degrees Celsius higher than the previous year. The 2022 season was classified as drought-prone, and the results reflected it: average grain yield in fertilized plots collapsed from 11.67 megagrams per hectare in 2021 to 4.09 megagrams per hectare in 2022, a 63 percent decline.

Under the favorable conditions of 2021, the timing of nitrogen application had surprisingly little effect on final outcomes. Split applications did not change aboveground biomass or grain yield, although delaying 50 percent of the nitrogen until the R1 stage temporarily reduced leaf area index and chlorophyll content. Crucially, the plants recovered. Once the second fertilizer dose was applied, all split treatments showed rapid nitrogen uptake during early reproductive growth, and by the R5 stage there were no significant differences in plant nitrogen uptake among the split treatments. This recovery demonstrates that maize can compensate for early-season nitrogen deficits when water is available, absorbing substantial nitrogen during grain filling when demand peaks.

The drought year told a different and arguably more important story. Under severe water stress, reducing the nitrogen rate to 50 percent of the full application—120 kilograms per hectare instead of 240—did not reduce biomass or grain yield compared to full rates. Even more striking, the reduced rate improved nitrogen uptake efficiency and agronomic efficiency while slashing residual soil nitrate. The 50 percent treatment left 83 percent less residual nitrogen in the soil than the full-rate treatments, and the 25 percent treatment left 58 percent less. In 2022, between 40 and 60 percent of applied nitrogen remained as residual soil nitrate after harvest in the full-rate plots, with the highest treatment accumulating nearly 160 kilograms of residual nitrogen per hectare—fertilizer that had been paid for but never used, sitting in the soil as a future source of water contamination.

The physiological measurements revealed why drought changed the calculus. When soil moisture is scarce, plants cannot take up nitrogen regardless of how much is available, so extra fertilizer simply accumulates. Chlorophyll readings, taken with a handheld SPAD meter, declined from the V6 stage onward in all plots in 2022, even as plant nitrogen uptake continued to rise slowly. In 2021, by contrast, plant nitrogen uptake explained 86 percent of the variability in chlorophyll content at the silking stage, but in 2022 that relationship broke down entirely when both growth stages were combined. The study also found that cutting nitrogen to 25 percent of the full rate significantly reduced plant height, leaf area, chlorophyll content, and grain yield—establishing that there is a floor below which nitrogen reduction becomes genuinely yield-limiting, even under stress.

The efficiency metrics told a nuanced story. In the drought year, nitrogen uptake efficiency and agronomic efficiency were highest in the reduced-rate treatments, meaning each kilogram of fertilizer produced more grain and was recovered more completely by the crop. However, nitrogen utilization efficiency—grain yield per unit of nitrogen in the plant—declined at the 25 percent rate, showing that the crop could not convert such scarce nitrogen into grain effectively. Delaying 50 percent of nitrogen until R1 produced the highest nitrogen utilization efficiency in 2022, hinting that well-timed late applications help the crop convert absorbed nitrogen into yield even under stress.

The practical implications are significant for dryland maize systems facing increasingly erratic weather. The findings suggest a strategy of applying 50 percent of nitrogen at planting and holding the remainder in reserve, then deciding based on seasonal conditions whether to apply it. In a wet year, the second application supports rapid uptake during the nitrogen-hungry reproductive stages. In a drought year, farmers can skip or reduce the second application, saving money on fertilizer and fuel while avoiding the accumulation of unused nitrate that could leach into groundwater or run off into the Gulf of Mexico. With nitrogen fertilizer prices having risen sharply in recent years, the economic argument aligns neatly with the environmental one.

The authors caution that the differences in seasonal precipitation limited their ability to test nitrogen strategies under ideal conditions in both years, and they recommend further validation in non-drought seasons. Still, the core message is clear and actionable: adaptive nitrogen management—splitting applications, monitoring the weather, and adjusting rates in real time—can maintain productivity, enhance nitrogen use efficiency, and reduce environmental risk in dryland maize production. In an era when agriculture must feed a growing population while shrinking its footprint on water and climate, getting the timing and amount of nitrogen right may be one of the most powerful levers available.

Subject of Research: Effects of split and reduced nitrogen fertilizer application on maize growth, yield, and nitrogen use efficiency under variable rainfall conditions

Article Title: Split nitrogen application to soil improves maize agronomic performance and nitrogen use efficiency

Article References: Bhattarai, K., Salehin, S. M. U., Rajan, N., & Schnell, R. W. (2026). Split nitrogen application to soil improves maize agronomic performance and nitrogen use efficiency. Discover Soil, 3(1), Article 144. https://doi.org/10.1007/s44378-026-00295-w

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00295-w

Keywords: maize, nitrogen fertilizer, split application, nitrogen use efficiency, drought, dryland agriculture, residual soil nitrate, grain yield, chlorophyll content, leaf area index, agronomic efficiency, sustainable farming