Delayed Nitrogen Splits Boost Coastal Maize Yields in Saline Soils

A three-year field experiment on the salty floodplains of southern Bangladesh has delivered a strikingly simple message for farmers struggling to grow maize on marginal coastal land: hold back your nitrogen fertilizer. Researchers found that delaying the first dose of nitrogen until fifteen days after sowing, then applying it in three equal side-dressed installments, produced grain yields as high as 11.76 tonnes per hectare, roughly 20 percent more than conventional practices that place fertilizer in the soil at planting. The study, conducted across the Rabi seasons of 2022, 2023 and 2024 in Patuakhali district, offers one of the most detailed tests yet of how nitrogen timing and placement interact with soil salinity in the Ganges delta.

The challenge the researchers set out to address is both local and global. Coastal Bangladesh is dominated by soils that turn saline during the dry season, when seawater intrusion and capillary rise push electrical conductivity in the root zone to between three and four decisiemens per meter, a level classified as slightly saline but still enough to stress young crops. Traditionally, farmers in the region grow a single monsoon rice crop and leave their fields fallow for the rest of the year. Maize has emerged as a promising dry-season crop for these fallow lands, valued for food, feed and biofuel, yet fertilizer guidelines for the region remain rudimentary. Farmers commonly broadcast urea without regard to timing, placement or the crop’s actual demand, wasting money and losing nutrients to the environment.

Nitrogen is the engine of maize productivity, but it is also the most easily lost nutrient. Applied too early, urea sits in soil that the young crop barely taps during its first month of growth, when uptake is minimal. In warm, moist, salinity-affected soils, that idle nitrogen is vulnerable to ammonia volatilization, leaching and the ionic imbalances that salinity imposes on roots. The research team framed their experiment around the 4R nutrient stewardship framework, the right source, right rate, right time and right place, focusing on the two dimensions most neglected in coastal practice: timing and placement. Their question was whether synchronizing nitrogen supply with the crop’s rapid vegetative and reproductive growth phases could recover the yield potential that indiscriminate broadcasting squanders.

The trial was laid out as a randomized complete block design with seven treatments and three replications, all receiving the same total nitrogen rate of 225 kilograms per hectare, alongside uniform phosphorus and potassium. The treatments varied the schedule and method of delivery: some placed a third of the nitrogen at sowing by broadcasting, side banding or row placement before two later side dressings; others delayed or reshuffled the splits entirely. One treatment applied 20 percent of the nitrogen at fifteen days after sowing followed by 40 percent at each of the later dates, while others applied half the nitrogen at 35 days, or the entire dose in a single side dressing at 35 days. The test crop was the hybrid DON 111, a medium-duration variety with a yield potential of 12 to 13 tonnes per hectare under good management.

The winner was unambiguous. Applying nitrogen in three equal side-dressed splits at 15, 35 and 60 days after sowing produced the highest grain yield in every season: 10.87 tonnes per hectare in 2022, 11.76 in 2023 and 10.79 in 2024, all statistically significant at the one percent level. The pooled stover yield of 11.78 tonnes per hectare and root yield of 1.44 tonnes per hectare were also highest under this schedule. By contrast, the treatment that placed a third of the nitrogen directly in the seed furrow at planting recorded the lowest yields, a result the researchers attribute to urea’s close contact with seeds, which hampered germination and produced an uneven plant population. The conventional farmer practice of basal broadcasting followed by two side dressings fell well short of the delayed-split strategy.

The physiological story behind the yield gap is revealing. Side-dressed nitrogen delivered near the plant rows maintained an adequate supply through the later growth stages, extending the active life of green leaves and sustaining the accumulation of photosynthetic assimilates during grain filling. The delayed-split treatment produced the longest cobs, the most grains per cob, reaching 620 grains on pooled data, and the heaviest thousand-grain weight at 217 grams. Correlation analysis underscored how these components stack up: thousand-grain weight showed the strongest association with grain yield, with a correlation coefficient of 0.79, while root yield correlated at 0.77, suggesting that a well-fed root system underpins the whole yield architecture. Cob length and grain number per cob were likewise tightly linked to final yield.

Root development deserves particular attention in saline soils, where osmotic stress makes water and nutrient acquisition harder. The three-split side-dressing schedule produced the highest root yields in 2022 and 2023, and the pooled root yield advantage was highly significant. The researchers argue that delaying the first application until active root establishment improves the synchronization between nitrogen availability and crop uptake, which in turn enhances nitrogen use efficiency. Adequate nitrogen supports healthy root architecture, and a denser root system improves the plant’s capacity to buffer the salt-induced nutrient imbalances that characterize coastal soils in March and April, when conductivity peaks just as the crop approaches maturity.

The economics reinforce the agronomy. Compared with the farmer practice of basal broadcasting, the optimized schedule added 860 kilograms of grain per hectare on pooled yields, worth roughly 287 US dollars at local grain prices. The only extra cost was labor for the additional first side dressing at fifteen days, about 15 dollars per hectare for two extra workers. That leaves a net gain of more than 270 dollars per hectare from a change that requires no new inputs, no new varieties and no machinery, only a shift in when and where existing fertilizer is applied. For smallholders in one of the world’s most densely populated and climate-vulnerable deltas, that margin could determine whether dry-season maize is worth planting at all.

The findings also carry environmental weight. Nitrogen that is not captured by the crop does not simply vanish; it can escape as ammonia gas, leach into groundwater, or be transformed into nitrous oxide, a greenhouse gas nearly 300 times more potent than carbon dioxide. Previous work cited by the team shows that interactions between salinity and fertilizer type significantly shape ammonia and nitrous oxide fluxes, meaning that mismanaged nitrogen in coastal soils is doubly wasteful. By matching supply to demand, the delayed-split approach minimizes these losses while maintaining nutrient availability during the critical vegetative and reproductive phases. The authors note that their results align with the 4R stewardship principles and with earlier studies showing that split applications extend leaf greenness beyond anthesis in stay-green maize hybrids.

Caveats remain, as they always do. The trial was conducted on a single soil series, a silty clay loam of the Ramgoti series, at one site near the Bay of Bengal, and the 2023 season benefited from warmer vegetative-stage temperatures and some rainfall during grain filling. Salinity dynamics vary across the coastal zone, and recommendations will need validation across a wider range of soils and weather patterns. Still, the core insight travels well beyond Bangladesh: in seasonally saline environments, the cheapest yield gain available to farmers may lie not in more fertilizer but in better-timed fertilizer. As maize expands into the fallow lands of coastal deltas worldwide, the humble act of waiting two weeks before the first urea application could reshape the economics of farming at the salty edge of agriculture.

Subject of Research: Optimizing the timing and placement of split nitrogen fertilizer application to improve maize yield and nitrogen use efficiency in slightly saline coastal soils of Bangladesh.

Article Title: Optimizing split nitrogen application for enhanced maize yield in slightly saline coastal soils (ECe 3–4 dS m−1)

Article References: Haque, M. A., Bhuyan, M. I., Jharna, D. E., Jahiruddin, M., & Bell, R. W. (2026). Optimizing split nitrogen application for enhanced maize yield in slightly saline coastal soils (ECe 3–4 dS m−1). Discover Soil, 3(1), Article 123. https://doi.org/10.1007/s44378-026-00282-1

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00282-1

Keywords: maize, nitrogen fertilizer, split application, side dressing, soil salinity, coastal agriculture, Bangladesh, Ganges delta, nitrogen use efficiency, 4R nutrient stewardship, grain yield, fertilizer timing