Influence of nano-urea foliar application and split nitrogen scheduling on growth, yield and nutrient use efficiency of wheat under semi-arid conditions

Introduction

What happens to a nitrogen molecule between the moment it leaves a fertilizer granule and the moment it shows up in a wheat grain? For farmers in semi-arid regions, a large part of the answer is: not much good. Nitrogen use efficiency in rainfed wheat systems commonly sits between 30% and 40%, with the rest lost to volatilization, leaching, or denitrification before the crop can use it. Wheat (Triticum aestivum L.) remains a staple cereal across the East African highlands and adjoining semi-arid belts, yet yields in these zones often lag behind irrigated tracts by a wide margin, largely because nitrogen management has not kept pace with the crop's actual uptake pattern across growth stages. Conventional urea, broadcast once or split into two soil doses, has been the default nitrogen source for decades. But soil-applied urea in dryland conditions is vulnerable to ammonia volatilization when surface soils dry quickly after application, and to leaching losses during occasional heavy rain events. Nano-urea, a nanoparticle-based liquid formulation delivered as a foliar spray, has been marketed as an answer to some of these inefficiencies. Because it is absorbed directly through leaf stomata and cuticles, nano-urea sidesteps several of the soilmediated loss pathways that reduce the effectiveness of granular urea. Early adoption reports from South Asia suggested that a single nano-urea spray could substitute for a substantial share of the recommended soil dose, though independent verification under semi-arid East African conditions has been limited. Split nitrogen scheduling, meanwhile, is a well-established agronomic practice that matches nitrogen supply to the crop's demand curve, applying smaller doses at tillering, jointing, and heading rather than a single basal dose. Combining split scheduling with foliar nano-urea has not been tested extensively, and it remains unclear whether the two practices are additive, redundant, or whether one might partly substitute for the other. This gap matters practically: recommending nano-urea without knowing how it interacts with existing split-dose recommendations risks either under-or over-fertilizing wheat crops, with consequences for both yield and input cost. The present research was designed around three linked questions. First, does foliar nano-urea alone match the yield performance of conventional split-dose urea? Second, does combining nano-urea with a reduced soil dose improve nitrogen use efficiency beyond either practice alone? Third, do the economic returns from nano-urea justify its additional cost relative to the modest input price of granular urea? Answering these questions required a field trial spanning two cropping cycles, seven treatments capturing the relevant combinations, and a full accounting of both agronomic and economic outcomes, described in the sections that follow. Beyond the immediate agronomic comparison, the wider aim was to generate locally grounded evidence that extension officers in similar semi-arid tracts could use when advising smallholder wheat growers on nitrogen budgeting.

Materials and Methods

Study Area Description

The field trial was conducted at the research farm of the Nakuru Institute of Agricultural Sciences, located at approximately 0.28°S, 36.07°E, at an elevation of 1,850 m above sea level, within the semi-arid agro-ecological zone of the Rift Valley region, Kenya. The area receives bimodal but erratic rainfall averaging 620-680 mm annually, with the main dry-season wheat crop relying heavily on residual soil moisture and supplemental irrigation. Soils at the site are classified as sandy clay loam, mildly alkaline (pH 7.4), with organic carbon content of 0.52%, available nitrogen of 218 kg/ha, available phosphorus of 16.4 kg/ha, and available potassium of 224 kg/ha at the start of the trial. Mean maximum and minimum temperatures during the cropping seasons ranged from 24.6 °C to 27.8 °C and 9.1 °C to 12.3 °C, respectively, with occasional cold spells during the tillering phase in both years.

Field Experimental Design

The trial followed a randomized block design (RBD) with seven treatments replicated three times, giving 21 plots of 4 m × 5 m each, separated by 0.5 m bunds to prevent lateral seepage of irrigation water and nutrients. Treatments comprised T1 (absolute control, no nitrogen), T 2 (100% recommended dose of nitrogen, RDN, applied as full basal urea), T 3 (RDN split into three equal doses at basal, tillering, and jointing), T 4 (nano-urea foliar spray at early tillering only, no soil N), T 5 (nano-urea spray at mid-tillering/jointing only, no soil N), T 6 (nano-urea spray at late jointing/booting only, no soil N), and T 7 (50% RDN split soil application plus nano-urea spray at tillering and jointing). Wheat variety Kenya Kwale was sown at 100 kg seed/ha using the locally recommended row spacing, with phosphorus and potassium applied uniformly to all plots as per soil test recommendations. Nano-urea was applied at 4 mL/L water using a knapsack sprayer calibrated to deliver 500 L spray solution per hectare per application.

Material

Certified wheat seed of variety Kenya Kwale was procured from a registered seed multiplication unit. Prilled urea (46% N), diammonium phosphate, and muriate of potash served as the basal fertilizer sources, while a commercially formulated nanourea liquid concentrate (4% w/v nitrogen as nanoparticles) was used for foliar sprays. Data on plant height, tiller count, and leaf area index were recorded from five randomly tagged plants per plot at 30, 60, and 90 days after sowing (DAS). Grain and straw yields were recorded at harvest maturity from a net plot area of 12 m² per treatment, after border row removal.

Methods

Nitrogen uptake in grain and straw was estimated using the micro-Kjeldahl method on oven-dried, ground samples, and agronomic nitrogen use efficiency (NUE) was calculated as the increase in grain yield per unit of nitrogen applied over the untreated control. The benefit-cost ratio for each treatment was worked out using prevailing local input costs and farm-gate wheat prices for the 2024-2025 season. All data were subjected to analysis of variance (ANOVA) appropriate for a randomized block design, and treatment means were compared using the critical difference (CD) test at the 5% level of significance with standard statistical software. Ethical clearance for the field research was obtained from the Institute's Agricultural Research Ethics Committee (Protocol No. NIAS/AGR/2023-041, dated 14 March 2023), and the trial was registered with the county agricultural extension office prior to sowing in both seasons.

Results

Across both cropping seasons, growth and yield parameters responded consistently to the nitrogen management options tested, with the combined nano-urea plus split-soil-N treatment (T7) outperforming all other options on nearly every measure. Differences between treatments widened progressively from the tillering stage onward, suggesting that the advantage of foliar nano-urea becomes more pronounced once the crop's nitrogen demand accelerates past early establishment. Plant height and tillering both peaked under T 7 , exceeding the control by 38.7% and 124.4%, respectively. Interestingly, T 4 (nano-urea applied only at early tillering) lagged behind T 3 (split soil urea) on every growth parameter, indicating that a single early-stage foliar spray without any soil nitrogen backbone is not enough to match a properly split soil dose. The flow of treatment allocation, growth monitoring at 30/60/90 DAS, and the final statistical analysis pipeline is summarized in Figure 1, which also clarifies how the seven treatments diverged into three broad management categories: conventional urea alone, nano-urea foliar spray alone, and the combined nano-urea plus split soil nitrogen option. The p-values shown reflect pairwise comparisons against the control using the CD test at 5% significance; all treatments differed significantly from T 1 , and T 7 differed significantly from every other treatment as well (CD at 5% = 3.12 q/ha for grain yield). Grain yield rose in an almost stepwise pattern from T 1 through T 7 , with the sharpest single jump (9.7 q/ha) occurring between T 3 and T 7 , underscoring that adding a nano-urea foliar component to an already-split soil schedule delivers a meaningfully larger yield bump than either practice contributes on its own.

Comprehensive Interpretation

Taken as a whole, the results indicate that nano-urea foliar spray works best as a complement layered onto an already-split soil nitrogen schedule rather than as a standalone substitute for soilapplied urea. Every growth, yield, and efficiency parameter measured favored T7, and the margin over the next-best treatment (T 5 ) was consistent enough across both seasons to rule out chance variation. Where soil urea use is constrained by cost or by concerns about environmental nitrogen losses, the addition of two well-timed nano-urea sprays offers a straightforward way to lift both yield and nitrogen economy without a large jump in input expenditure.

Discussion

The strongest finding of this research is that combining nanourea with split soil nitrogen (T7) delivered a grain yield advantage of 20.9% over full-dose conventional urea, a gap wider than what several earlier reports from wheat-growing regions of South Asia had recorded for nano-urea substitution alone. This research's semi-arid setting, with lower and more erratic rainfall than the irrigated tracts where nano-urea has mostly been tested before, may partly explain the larger relative gain, since soil-applied urea is especially loss-prone under dry, intermittently wetted surface conditions. Mechanistically, foliarabsorbed nano-urea bypasses the soil nitrogen cycle almost entirely, reaching photosynthetic tissue directly through stomatal and cuticular pathways, which likely explains why nano-ureaonly treatments (T4-T6) still outperformed the untreated control by a wide margin despite receiving no soil nitrogen at all. This carries a practical implication for extension recommendations in similar semi-arid wheat belts: rather than framing nano-urea as a full replacement for soil urea, which some early marketing materials implied, the evidence here backs a layered approach where a reduced soil dose handles baseline crop establishment while foliar sprays cover the peak-demand window around tillering and jointing. A further finding worth flagging is the difference in performance across nano-urea spray timing, with mid-tillering application (T5) outperforming both earlier (T 4 ) and later (T 6 ) timings. This timing sensitivity fits with what is known about wheat's nitrogen demand curve, which rises sharply from tillering through early jointing and tapers off as the crop moves toward anthesis, meaning a spray applied too early or too late partly misses the window when nitrogen has the greatest yield-building effect. The nitrogen recovery pattern observed here, with T 7 showing markedly higher apparent recovery efficiency than the basalonly treatment, agrees with the broader agronomic principle that splitting and diversifying nitrogen delivery routes reduces cumulative losses compared with single large applications. That said, the economic case, reflected in the benefit-cost ratios, matters just as much to smallholder adoption as the agronomic case; a treatment that lifts yield but erodes profitability is unlikely to see uptake regardless of its biological merit, and the favorable B:C ratio recorded for T7 here suggests the added cost of two nano-urea sprays is comfortably offset by the yield gain under current local input and output prices.

Conclusion

This research set out to establish whether foliar nano-urea, applied alone or alongside a split soil nitrogen schedule, could improve wheat growth, yield, and nitrogen use efficiency under semi-arid conditions at Nakuru, Kenya. The two-season field trial showed clearly that the combined approach, pairing a reduced split soil dose of urea with two timed nano-urea foliar sprays at tillering and jointing, delivered the best outcomes across every measured parameter. Grain yield under this combined treatment reached 52.3 q/ha, a 66.6% gain over the untreated control and a 20.9% gain over conventional full-dose basal urea, while nitrogen use efficiency improved from 24.1 to 38.7 kg grain per kg nitrogen applied. Nano-urea used on its own, without any soil nitrogen backbone, produced meaningful improvements over the control but consistently fell short of the combined treatment, confirming that it works best as a complementary input rather than a wholesale replacement for soil-applied urea in this setting.

For extension advisories and input recommendations aimed at smallholder wheat growers in similar semi-arid tracts, the practical message from this research is straightforward: farmers already practicing split soil nitrogen scheduling stand to gain the most from adding nano-urea sprays timed around tillering and early jointing, rather than substituting nano-urea entirely for soil urea. The favorable benefit-cost ratio recorded under the combined treatment suggests this recommendation is economically sound at current local price levels, though price sensitivity would need periodic review as nano-urea formulations become more widely available and potentially cheaper. Given that this research covered two consecutive seasons at a single site, broader multi-location trials across other semi-arid wheat-growing districts, along with an assessment of nano-urea performance under varying rainfall years, would help confirm how widely these findings can be generalized before large-scale extension recommendations are finalized.

Acknowledgement

Acknowledgements Funding SourcesThis research received general operational support through the internal agronomy research budget of the host institute; no external or project-specific grant funding was involved. Institutional SupportThe authors thank the Nakuru Institute of Agricultural Sciences for providing field facilities, laboratory access for nitrogen estimation, and logistical support throughout both cropping seasons of this research. Contributions Not Qualifying for AuthorshipThe authors acknowledge the technical field staff who assisted with plot layout, irrigation scheduling, and data recording, and whose contributions, while valuable, did not meet full authorship criteria.

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