Slow-Release Fertilizer Unlocks Bigger Maize Yields on China’s Salt-Damaged Farmland

On the salt-crusted farmland of Ningxia in northwest China, where soil pH climbs above 8.7 and evaporation relentlessly concentrates salts in the root zone, maize growers have long faced a frustrating paradox: the nitrogen fertilizer they pour onto their fields largely refuses to stay there. Conventional urea releases its nitrogen in a sudden early burst, much of which volatilizes as ammonia or leaches away before the crop can use it, leaving plants starved during the grain-filling weeks when nitrogen demand peaks. A two-year field experiment conducted in the Yellow River Irrigation District now offers a strikingly simple remedy. By replacing half of the standard urea dose with polymer-coated controlled-release fertilizer, researchers boosted grain yield by just over 18 percent while lifting nitrogen recovery efficiency by more than 68 percent and irrigation water productivity by 18 percent, all on moderately saline-alkali soil that would normally suppress productivity.

The study, published in the Journal of Agriculture and Food Research, was carried out in Pingluo County, Ningxia, a warm temperate arid zone receiving a mere 177 millimeters of rain per year. Roughly 30 percent of the cultivated land in this region is moderately saline-alkali, part of the roughly 99 million hectares of such soil across China, of which more than 40 percent lies in the arid and semi-arid northwest. With per capita arable land in China below 40 percent of the global average, and maize covering about 43 million hectares and supplying more than 40 percent of total grain production, the stakes of squeezing more grain from degraded soils could hardly be higher. The research team, led by Yueqi Li and Jili Liu, set out to test whether matching nitrogen release to crop demand could rewire the entire physiology of the plant, not merely feed it more efficiently.

The experimental design was elegantly straightforward. Six treatments were compared in a randomized block layout with three replicates each: a no-nitrogen control, a conventional urea-only treatment, and four treatments in which 25, 50, 75, or 100 percent of the nitrogen was supplied as polyurethane-coated urea with a 60-day release period. Every treatment received identical total nutrients, 300 kilograms of nitrogen, 180 kilograms of phosphorus pentoxide, and 90 kilograms of potassium oxide per hectare, so any difference in performance could be attributed purely to the timing and pattern of nitrogen delivery. The maize cultivar Xianyu 1225 was sown at a high density of 90,000 plants per hectare, and all plots received the same 2,700 cubic meters of irrigation water, applied in equal installments at the six-leaf, twelve-leaf, and grain-filling stages.

The 50 percent substitution treatment, labeled T50, emerged as the clear winner across nearly every metric the team measured. Compared with conventional urea alone, it raised the leaf chlorophyll index by 11.65 percent and the net photosynthetic rate by 18.43 percent, while lowering intercellular carbon dioxide concentration, a sign that carbon was being fixed more vigorously. More dramatically, the activities of four key nitrogen-metabolism enzymes surged: nitrate reductase by 64.95 percent, glutamate dehydrogenase by 36.63 percent, glutamine synthetase by 22.07 percent, and glutamate synthetase by 60.41 percent. These enzymes form the biochemical pipeline that converts soil nitrate into amino acids, and their heightened activity indicates that the slow-release nitrogen was not merely present in the soil but actively being assimilated into plant metabolism throughout the season.

The concept that unifies the paper’s findings is the source-flow-sink framework, a classical model of crop yield formation. The source comprises the leaves that capture sunlight and build sugars; the flow is the vascular transport system that moves stored assimilates from stems and leaves into the developing ears; and the sink is the grain itself, whose capacity and activity determine how much of that assimilate can actually be packed into harvestable kernels. Salt stress sabotages all three links simultaneously. High pH and osmotic pressure impair root uptake of water and nutrients, reactive oxygen species accelerate chloroplast breakdown and leaf senescence, and poor assimilate supply starves the grain-filling process, shrinking both grain number and grain weight. The controlled-release fertilizer, the researchers found, repaired each link in sequence.

On the flow side, the results were particularly emphatic. Dry matter translocation, the movement of carbohydrates stored in stems and leaves into the grain after flowering, rose by 76.06 percent under T50 compared with urea alone, and the contribution of these pre-anthesis reserves to final grain yield climbed by nearly 18 percent. Grain filling, modeled with a logistic growth curve that fit the data with coefficients of determination above 0.98, was faster and heavier: the maximum filling rate increased by 32.48 percent, the average filling rate by 49.01 percent, and the peak filling date arrived nine days earlier. Ear weight, kernels per ear, and hundred-grain weight all rose by roughly 10 to 19 percent, confirming that the sink had genuinely expanded rather than simply being fed longer.

Why did 50 percent substitution outperform both lower and higher ratios? The authors argue that the answer lies in matching the nitrogen supply curve to the crop’s demand curve. Conventional urea floods the soil with available nitrogen early, promoting lush vegetative growth that later collapses into premature senescence when the supply runs out just as the grain-filling demand peaks. Pure controlled-release fertilizer, by contrast, releases nitrogen too slowly at the start, failing to support the rapid canopy expansion between the six-leaf and twelve-leaf stages and limiting the photosynthetic machinery that must be built early. The 50 percent blend, with conventional urea topdressed at two early stages and coated urea releasing steadily through mid-season, delivers what the authors describe as an early-stage support, mid-stage stability, late-stage sustainability pattern, sustaining leaf function precisely when salt stress would otherwise cut photosynthesis short.

The team backed these physiological interpretations with a battery of statistical tools. Mantel tests confirmed significant correlations between the substitution ratio and source traits such as leaf area index, leaf area duration, and chlorophyll content. Random forest modeling ranked dry matter translocation rate, stomatal conductance, and glutamate synthetase activity as the top contributors to grain yield, while grain weight per ear and mean filling rate dominated predictions of nitrogen use efficiency and irrigation water productivity. A partial least squares structural equation model then tied the whole story together: the substitution ratio acted positively on source, flow, and sink characteristics, with the strongest path coefficient, 0.71, linking it to sink traits, and sink characteristics in turn showed the strongest association with grain yield at 0.76. The model also revealed a negative association between the substitution ratio and the source-sink ratio, indicating a better balance between leaf supply and grain demand.

The efficiency gains carry real economic and environmental weight. Agronomic efficiency of nitrogen, the yield gained per kilogram of fertilizer applied, jumped by 72.79 percent under the optimal treatment, while nitrogen recovery efficiency rose by 68.39 percent and apparent recovery by 40.40 percent. Because irrigation volumes were identical across treatments, the 18.06 percent gain in irrigation water productivity reflects purely the yield increase, meaning every cubic meter of scarce irrigation water in this arid basin produced more grain. The authors caution, however, that their conclusions rest on two years of data from a single site, one maize cultivar, and a warm temperate continental climate, and that nitrogen loss pathways such as ammonia volatilization and nitrate leaching were inferred indirectly from plant uptake rather than measured directly in the soil.

Even with those caveats, the implications are considerable for a country wrestling with food security on degraded land. Controlled-release fertilizers remain more expensive than commodity urea, but a 50 percent substitution strategy halves the added cost while capturing most of the agronomic benefit, and the yield and efficiency gains documented here suggest the premium could pay for itself in saline-alkali regions. As China pushes to bring its vast salt-affected reserves into productive agriculture, the study offers a physiologically grounded template: rather than simply applying more fertilizer, farmers may get far more from every kilogram by controlling when the nitrogen arrives. The humble polymer coating, it turns out, does not just slow a chemical reaction. It re-orchestrates the entire source-flow-sink economy of the maize plant, turning hostile soil into a stage for one of the more quietly impressive yield breakthroughs of recent agronomy.

Subject of Research: Controlled-release fertilizer substitution effects on maize source-sink physiology, yield, and water-nitrogen use efficiency in saline-alkali soil

Article Title: Controlled-release fertilizer substitution boosts maize yield and water-nitrogen use efficiency via optimizing source-sink characteristics in saline-alkali soil

Article References: Controlled-release fertilizer substitution boosts maize yield and water-nitrogen use efficiency via optimizing source-sink characteristics in saline-alkali soil. (n.d.). https://doi.org/10.1016/j.jafr.2026.103312

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103312

Keywords: maize, controlled-release fertilizer, saline-alkali soil, nitrogen use efficiency, source-sink relationship, grain filling, dry matter translocation, irrigation water productivity, Ningxia, urea, photosynthesis, soil salinity