The experiment, conducted across three growing seasons from 2021 to 2024, was designed as a split-plot field trial with nine treatment combinations. Three drip irrigation levels were tested: D1 at 65 percent of field capacity, D2 at 75 percent, and D3 at 85 percent, where field capacity represents the amount of water a soil retains after gravitational drainage. Each irrigation level was crossed with three nitrogen application rates: N1 at 150 kilograms per hectare, N2 at 210 kilograms per hectare, and N3 at 270 kilograms per hectare. Field capacity is a critical anchor in irrigation science, because targeting a percentage of it determines how closely soil moisture is held near the ideal range where roots can extract water with minimal effort while excess drainage and deep percolation of nitrate are minimized.

The headline result is that the middle combination, D2N2, outperformed the other eight treatments on the metrics farmers care about most. Grain yield rose by 1.88 to 17.9 percent relative to the alternatives, and water use efficiency climbed by 7.65 to 14.5 percent. That dual gain is significant because yield and efficiency often pull in opposite directions: pushing more water and fertilizer onto a crop can inflate yields while quietly eroding the return on every additional unit of input. The D2N2 treatment appears to thread the needle, keeping the crop near its yield potential without wasting the resources used to get there.

There was, however, a trade-off the researchers were careful to document. The D2N2 combination reduced nitrogen partial factor productivity, a measure of how many kilograms of grain are produced per kilogram of nitrogen applied. Because D2N2 applies a moderate nitrogen rate while achieving high yields, the ratio shifts in ways that depend on how the metric is calculated relative to other treatments. This kind of tension is precisely why the team framed the work as a multi-objective optimization problem rather than a search for a single best number. In real farming systems, no single metric captures sustainability; the goal is a combination of inputs that performs acceptably across yield, efficiency, and the slower-moving variables that determine whether the soil remains productive for decades.

Stability emerged as another dimension of the story. Across the three seasons, the D2N2, D3N2, and D3N3 treatments promoted higher yield stability and sustainability than the drier or more nitrogen-starved combinations. Yield stability matters enormously in a region where interannual variability in rainfall and temperature can swing harvests dramatically. A treatment that produces a spectacular yield in one favorable year but collapses in a dry one is less valuable than one that delivers consistently strong results. The fact that the moderately wetter irrigation regimes with moderate to high nitrogen supported stability suggests that maintaining adequate soil moisture buffers the crop against the stresses that otherwise amplify year-to-year variation.

Perhaps the most novel contribution of the study is its treatment of soil quality as a first-class objective rather than an afterthought. The researchers constructed a soil quality index, or SQI, that integrates physical, chemical, and biological indicators of soil health. Under D2N2, soil physical quality improved by 3.23 to 18.7 percent and soil biological quality improved by 4.53 to 36.6 percent compared with the other eight treatments. Comprehensively, the SQI under D2N2 was enhanced by 3.98 to 28.9 percent. The mechanisms behind these gains are interconnected: better soil physical structure improves water retention and aeration, which in turn supports nutrient availability and the microbial communities that cycle nitrogen and carbon through the root zone. Drip fertigation, by avoiding the waterlogging and crusting associated with surface flooding, appears to create a soil environment in which those beneficial feedbacks can accumulate over multiple seasons.

To move from individual treatment comparisons to a generalizable prescription, the team applied response surface methodology, a statistical technique that models how a response variable changes across a continuous space of input settings rather than only at the discrete points actually tested. Fitting response surfaces to the yield, efficiency, and soil quality data allowed the researchers to interpolate between treatments and identify the ranges where all objectives were simultaneously satisfied. The result was strikingly specific: an irrigation level of 77 to 85 percent of field capacity, coupled with a nitrogen application rate of 181 to 194 kilograms per hectare. That nitrogen window sits below the highest rate tested, reinforcing a recurring theme in modern agronomy: more fertilizer is not better fertilizer, and the marginal kilogram of nitrogen beyond a crop’s capacity to use it tends to leach away, acidify soil, or escape as greenhouse gas rather than become grain.

The implications for the North China Plain are considerable. The region produces a large share of China’s wheat but has paid for that productivity with some of the fastest-declining aquifers in the world, and with nitrate contamination that traces directly back to over-application of synthetic nitrogen. Drip fertigation has been promoted as a remedy, but adoption has been hampered by uncertainty about how to operate the systems: too little water stresses the crop, too much negates the savings, and the interaction with nitrogen rate is nonlinear. By quantifying those interactions across three full seasons and folding soil health into the optimization, the study gives extension services and growers a defensible target rather than a rule of thumb. The finding that the optimal irrigation range extends up to 85 percent of field capacity is particularly useful, because it suggests farmers can err slightly toward wetter soils without sacrificing efficiency, provided nitrogen is held in the moderate range.

The work also fills a methodological gap that the authors explicitly identify. Previous studies of drip-fertigated winter wheat in the region typically optimized for yield and water or nitrogen use efficiency alone, leaving soil quality out of the objective function. Incorporating the SQI changes the answer. A combination that maximizes short-term yield might degrade soil structure or suppress microbial activity in ways that only become apparent years later, so including soil indicators in the optimization shifts the recommended operating point toward regimes that sustain the resource base. This is a quiet but consequential reframing: it treats soil not as an inert growing medium but as a living system whose condition is part of the farm’s output.

Caveats remain, as they do in any field study. The results come from a specific soil, climate, and management context in the North China Plain, and the optimal ranges may shift elsewhere or under different cultivars and residue practices. The three-season span, while substantial for a field trial, is still short relative to the timescales over which soil quality evolves, so longer-term monitoring will be needed to confirm that the SQI gains persist. The study was supported by China’s National Key R&D Program, the S&T Program of Hebei, and the State Key Laboratory of North China Crop Improvement and Regulation, and it is published open access, making the detailed data available to researchers worldwide. For a region where every cubic meter of water and every kilogram of nitrogen is contested, the message is clear and actionable: irrigate near the upper-middle of the soil moisture range, feed the crop moderately rather than generously, and the payoff arrives not just in this season’s grain but in the ground beneath it.

Subject of Research: Multi-objective optimization of subsurface drip fertigation for winter wheat in the North China Plain

Article Title: Multi-objective optimization of subsurface drip fertigation for winter wheat in the North China Plain: balancing grain yield, resource use efficiency, and soil quality

Article References: Wang, B., Wang, P., Zhang, Y., Yang, J., Li, L., He, F., & Wang, G. (2026). Multi-objective optimization of subsurface drip fertigation for winter wheat in the North China Plain: balancing grain yield, resource use efficiency, and soil quality. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10067-x

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10067-x

Keywords: drip fertigation, winter wheat, North China Plain, soil quality index, water use efficiency, nitrogen management, multi-objective optimization, response surface methodology, sustainable agriculture, irrigation scheduling, soil microbial activity, grain yield