Deep Placement and Legumes Emerge as Top Ways to Boost Nitrogen Efficiency in Maize

Nitrogen is the engine of modern agriculture, and maize is one of its hungriest customers. Known as the queen of cereals, maize ranks third among the world’s staple crops after wheat and rice and supplies nearly 30 percent of caloric intake for more than 4.5 billion people. Yet the fertilizer that drives its yields is astonishingly wasteful: on average, only 25 to 50 percent of the nitrogen applied to fields actually ends up in the crop. The rest escapes into the air as ammonia and nitrous oxide, seeps into waterways as nitrate, and quietly degrades soil health. A sweeping new global meta-analysis, published in Discover Soil, has now quantified just how much of that waste farmers could eliminate with smarter agronomy, and the answer is substantial.

The research team, led by Saurabh Tripathi of Punjab Agricultural University together with colleagues at ICAR institutes in India, synthesized 97 peer-reviewed field studies published between 2000 and 2025, spanning 156 field experiments across diverse climates, soil types, and production systems. Rather than examining a single technology, the researchers compared four broad categories of intervention: fertilizer management, soil amendments, cropping systems, and decision-support systems. Within those groups, they evaluated nine specific practices, including biochar, deep fertilizer placement, legume intercropping, manure application, residue retention, slow-release fertilizers, split applications, and the Nutrient Expert decision-support tool. The analysis focused on three complementary measures of nitrogen use efficiency: agronomic nitrogen use efficiency, which captures yield gained per unit of nitrogen applied; apparent nitrogen recovery efficiency, which measures how much applied nitrogen the plant actually takes up; and partial factor productivity, the yield produced per kilogram of nitrogen input.

The statistical approach was rigorous. Effect sizes were calculated as natural log response ratios and pooled with a multi-level random-effects model that treated each site-year combination as an independent observation while accounting for non-independence among observations from the same study. Publication bias was assessed with funnel plots and Egger’s regression test, and heterogeneity was explored through meta-regression on moderators such as year, region, and soil texture. The headline result: agronomic interventions collectively improved agronomic nitrogen use efficiency by 14.7 percent, apparent recovery efficiency by 18 percent, and partial factor productivity by 4.8 percent compared with conventional farmer practice. Publication-bias tests confirmed the reliability of the overall effects, and moderators explained a large share of between-study variation, up to 71.8 percent for partial factor productivity.

Some interventions stood out dramatically. Deep placement of fertilizer, which puts nitrogen 15 to 35 centimeters below the surface rather than the conventional 5 to 8 centimeters, produced the largest gains in both agronomic efficiency and recovery, boosting agronomic nitrogen use efficiency by 71.7 percent and recovery efficiency by 40.1 percent. The mechanism is elegant: placing nitrogen closer to the active root zone synchronizes nutrient supply with crop demand, minimizes surface volatilization and runoff, and promotes more stable soil-plant nitrogen cycling. These findings align closely with earlier global syntheses, including an analysis of 99 studies showing that deep placement increased grain yields by 13 to 14 percent and nitrogen use efficiency by more than 30 percent while cutting nitrous oxide and ammonia losses, and a tracer-based dataset of 366 studies confirming that deeper or split placement consistently improves nitrogen recovery.

Cropping system diversification proved equally powerful. Legume intercropping, in which maize is grown alongside nitrogen-fixing legumes, raised agronomic efficiency by 57.8 percent and delivered the largest improvement in partial factor productivity. Legumes contribute roughly 125 kilograms of nitrogen per hectare per season through biological fixation, increase associated cereal yields by 30 to 35 percent, and stimulate microbial activity in the soil. Global analyses suggest that strategically expanding legume-based systems could reduce synthetic nitrogen requirements worldwide by 26 percent, a figure that gives the meta-analysis results real planetary significance. Cropping systems as a category showed the highest improvements across all three efficiency indices, with effect sizes of 0.43, 0.31, and 0.29 for agronomic efficiency, recovery efficiency, and partial factor productivity respectively.

Decision-support systems emerged as a quiet revolution. The Nutrient Expert tool, which tailors nitrogen rates and timing to local yield potential, soil conditions, and climate, improved agronomic efficiency by 31.4 percent and recovery by 26 percent. Field validations across Asia and Africa have shown that such site-specific recommendations can increase yields by 4 to 11 percent while reducing nitrogen applications by 15 to 29 percent. Large-scale on-farm trials across more than 1,500 sites have documented consistent income gains and measurable reductions in global warming potential, confirming that these digital advisory tools are scalable, not merely promising in experimental plots.

Not every intervention worked, and the failures are as instructive as the successes. Manure application and residue retention showed statistically non-significant effects on recovery efficiency in the short term, likely because slow organic nitrogen mineralization delays their benefits beyond the experimental window. Biochar showed moderate positive effects on recovery but negligible effects on agronomic efficiency. Most strikingly, applying nitrogen above recommended rates actively backfired: it reduced agronomic efficiency by 17.7 percent, recovery efficiency by 25.7 percent, and partial factor productivity sharply, with an effect size of minus 0.45. Excess nitrogen is lost through volatilization, leaching, denitrification, and microbial immobilization, meaning farmers pay more to pollute more while gaining nothing in yield.

The analysis also revealed that soil texture profoundly modulates which strategy works where. Silty clay loam and loamy clay soils produced the highest agronomic efficiency, while clay soils favored nitrogen retention and recovery but showed lower partial factor productivity. Sandy soils, with high permeability and poor nutrient retention, suffered reduced efficiency across the board due to leaching losses and therefore stand to benefit most from deep placement and slow-release formulations. Silty loams, combining balanced aeration, moisture retention, and nutrient availability, responded most positively across all indices. This texture-dependence explains much of the residual heterogeneity in the global dataset and underscores why one-size-fits-all fertilizer advice fails: the same practice can be transformative on one field and ineffective on another.

The environmental stakes extend far beyond farm economics. Nitrous oxide released through denitrification and nitrification has a 100-year global warming potential roughly 310 times that of carbon dioxide, and an estimated 1.2 kilograms of nitrous oxide-nitrogen is emitted per 100 kilograms of nitrogen fertilizer applied. Ammonia volatilization and secondary formation of fine particulate matter degrade air quality, with cascading impacts on human health and biodiversity. In India, nitrogen use efficiency has actually declined from about 48 percent in the 1960s to 35 percent in 2018, illustrating how intensification without precision erodes efficiency over time. With maize productivity needing to rise an estimated 40 percent by 2050 to feed a growing population, closing the nitrogen efficiency gap is arguably one of the most consequential challenges in agriculture.

The authors frame their findings as a shift in philosophy: from maximizing nitrogen inputs to optimizing them. Conceptually, the efficiency gains followed a clear hierarchy, with placement and synchronization-based strategies outperforming biological integration, which in turn exceeded product-based innovations alone. Aligning nitrogen supply with crop demand in space and time, they conclude, matters more than simply adding technological complexity. The policy implications are concrete: incentivize deep-placement equipment, slow-release fertilizers, and digital advisory tools; blend organic and inorganic nutrient sources; and embed soil texture and climate information into fertilizer recommendations. Future research should prioritize long-term experiments tracking efficiency gains across soil-climate gradients, link them to greenhouse gas and leaching outcomes, and refine decision-support models with root-zone dynamics, microbial interactions, and real-time weather data. For a crop that feeds billions, the message of this synthesis is clear: the nitrogen problem is not a shortage of fertilizer but a mismatch of timing, placement, and context, and it is one that farmers, armed with the right tools, can fix.

Subject of Research: Effects of agronomic management practices on nitrogen use efficiency in global maize production

Article Title: Global meta-analysis shows that agronomic interventions enhance nitrogen use efficiency in maize

Article References: Tripathi, S., Bhagat, R., Paramesha, V., Walia, S. S., Ravisankar, N., Kaur, J., & Bhattacharjee, S. (2026). Global meta-analysis shows that agronomic interventions enhance nitrogen use efficiency in maize. Discover Soil, 3(1), Article 130. https://doi.org/10.1007/s44378-026-00285-y

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00285-y

Keywords: nitrogen use efficiency, maize, meta-analysis, deep fertilizer placement, legume intercropping, decision-support systems, slow-release fertilizers, soil texture, nitrous oxide emissions, sustainable agriculture, nutrient management, Discover Soil