Key Takeaways

• SAPs provided little benefit when water was plentiful. Under full irrigation, treated plots performed similarly to the untreated control because soil moisture was not limiting. 
• Benefits emerged as water became more limited. Under deficit irrigation, the best-performing treatments increased soybean yield by more than 20 bu/ac over the untreated control. 
• Rainfed conditions produced the greatest response. The top-performing polymer treatments more than doubled yield compared with the untreated control, though results varied by formulation and application rate. 
• Water-use efficiency improved under water-limited conditions. Crop water productivity roughly doubled under rainfed conditions, and irrigation efficiency more than doubled under deficit irrigation. 
• Application rate generally mattered more than formulation. Higher application rates produced the strongest responses, while differences among formulations became more apparent under severe drought stress. 
• These findings are preliminary. Results are based on a single site-year and were evaluated descriptively rather than statistically.

Considerations for Growers

• Focus SAPs where water is limiting. They appear best suited to dryland acres, deficit-irrigated ground and lighter soils with low water-holding capacity rather than fully irrigated fields. 
• The higher application rate generally performed best. Lower application rates showed limited benefit under deficit irrigation and produced mixed results under rainfed conditions. 
• Run the economics before investing. At a soybean price of $9 per bushel, products needed roughly 6–8 bu/ac of additional yield to break even for the powder and original granule formulations and about 11 bu/ac for the broader granules.

Background: Soil Water-Holding Polymers in Soybean

Water is the first thing that limits a soybean crop in Nebraska, whether you farm dryland or irrigate. So when a product promises to hold more water in the root zone and carry the crop through dry stretches, it’s worth a hard look. Superabsorbent polymers (SAPs) are soil-applied granules and powders that swell and hold many times their weight in water and have been marketed for exactly that job. 

The catch is that field data under real-world irrigation conditions has been limited. In 2025, we conducted a first-year trial on three SAP formulations in soybean at the Henry J. Stumpf International Wheat Center near Grant (40.84°N, 101.73°W) on a fine sandy loam.

2025 Field Study: Comparing Polymer Products

Soybean (variety P30A75E) was planted June 3, with product incorporated into the top 4 inches before planting. Seasonal rainfall totaled 588 mm (23 inches).

Polymer Products

We compared three formulations from EF Polymer: broader granules (BB), original granules (OG) and powder (PWR). Each was evaluated at a lower application rate of 17.7 lb/ac and a higher application rate of 120 lb/ac.

Irrigation Treatments

Every product and application rate was evaluated under three irrigation regimes, alongside an untreated control that received no polymer:

• Full irrigation (100% ET replacement): 246 mm applied, for 834 mm of total seasonal water.
• Deficit irrigation (50% ET): about 123 mm applied, for 711 mm total.
• Rainfed (Control): no irrigation, 588 mm from rainfall alone.

Field Measurements

We monitored volumetric water content (VWC) with a neutron probe in 12–inch increments to 36 inches, captured multispectral imagery at V7 (Aug. 8) and R2 (Sept. 3), counted pods, and hand-harvested the center rows. Because this is a single site-year, treatment effects were evaluated descriptively rather than tested statistically.

2025 Field Study: Results

Full Irrigation: A Saturation Effect

Under full irrigation, yields converged. The control produced 60.7 bu/ac, BB at the higher application rate reached 61.7, PWR at the higher application rate hit 60.1, and OG at the higher application rate actually trailed at 54.0. Crop water productivity (CWP) sat between 0.065 and 0.074 bu/ac/mm across the board, and irrigation efficiency (IE) held near 0.12–0.15 bu/ac/mm. 

When soil moisture was not limiting, a product designed to retain water had little opportunity to improve yield. As water became more limiting under deficit irrigation and rainfed conditions, however, the response increased.

Deficit and Rainfed: Where Yields Diverged

Under deficit irrigation (50% ET), the higher rate application treatments substantially outperformed the untreated control. At the higher application rate, OG yielded 64.0 bu/ac and BB produced 63.0 bu/ac — gains of more than 20 bu/ac over the untreated control (42.7 bu/ac). CWP increased 0.030 bu/ac/mm. Irrigation efficiency more than doubled for original granules and broader granules (Table 1). By comparison, the lower application rate provided little benefit under these conditions.

Rainfed conditions produced the widest differences among treatments. Two polymer-rate combinations more than doubled soybean yield compared with the untreated control: BB at the higher application rate yielded 55.1 bu/ac and OG at the lower application rate yielded 52.4 bu/ac, compared with 24.7 bu/ac for the control. 

By contrast, PWR at the higher application rate yielded 23.2 bu/ac and BB at the lower application rate yielded 25.7 bu/ac, both similar to the control, while OG at the higher application rate yielded 33.6 bu/ac — a modest increase. 

These mixed results illustrate the variability typical of a first-year study. The rainfed gains are promising but not yet consistent across formulations and application rates.

^{— indicates irrigation efficiency was not calculated because no irrigation was applied.}

Soil Water and Canopy Response

The soil-water measurements largely mirrored the yield results. As a mid-season average, treated plots carried higher volumetric water content in the upper profile. 

BB at the higher application rate held 21% at the surface (0–12 inches) compared with 18% in the control — a 17% relative increase. At the mid-root zone (12–24 inches), it maintained 17% compared with 15% in the control. PWR at the higher application rate held its advantage deepest, reaching 14.5% at 24–36 inches — an 11% relative increase over the control. 

The lower application rate of OG barely changed volumetric water content, confirming a rate-dependent retention response. Under deficit irrigation, treated plots maintained roughly 13–15% volumetric water content where the control dropped to about 11%.

Canopy reflectance showed the same pattern. At V7 (Aug. 8), the control ran Normalized Difference Vegetation Index (NDVI) — a satellite-based indicator of plant health — of 0.75–0.85 against 0.82–0.86 in irrigated plots, and the higher application rate held 0.81–0.89. By the R2 growth stage (Sept. 3), NDVI values had become more similar across treatments as the canopy matured. Under rainfed conditions, plots that maintained NDVI above 0.90 also preserved yield. Early in the season, rate drove canopy stability more than formulation did; product differences only emerged late, under the most severe deficit.

Pods Versus Seed Fill

Pod counts increased with polymer, but they pointed to a different mechanism of yield improvement. Treated plots averaged 38–45 pods per plant against 31.8 in the control, and counts fell with water — about 50 pods per plant under full irrigation, 43 at 50% ET and 33 rainfed. 

Notably, the lower application rate carried slightly higher pod counts than the higher application rate (for example, 50.7 versus 42.2 pods per plant under full irrigation), yet the higher application rate preserved more yield under stress. That points to the yield benefit coming through improved seed fill and seed mass rather than added pod set.

Does It Pencil Out?

We ran a preliminary partial-budget analysis at $9/bu. Break-even yield gains — the extra bushels needed just to cover product cost — ranged from 6.2 to 11.1 bu/ac depending on formulation: 

• 6.2–7.8 bu/ac for the powder ($56–70/ac)
• 7.1–8.9 bu/ac for the granular forms ($64–80/ac)
• 11.1 bu/ac for the broader granules ($100/ac)

Under full irrigation, the treatments did not recover their cost. The best-performing treatment, BB at the higher application rate, increased yield by just 1.0 bu/ac — about $9 per acre in additional revenue — resulting in an estimated net loss of $91 per acre after the $100 product cost. 

Under deficit irrigation, the outlook improved. BB at the higher application rate increased yield by 20.3 bu/ac, generating about $183 per acre in additional revenue and an estimated net return of $83 per acre. 

Rainfed conditions produced the strongest returns, with BB at the higher application rate netting about $143 per acre and PWR at the lower application rate returning an estimated $62–$76 per acre.

Where This Leaves Us

For 2025, the SAPs behaved as drought-buffering inputs, not yield builders. They contributed little under non-limiting water and returned the most under deficit and rainfed conditions, where crop water productivity roughly doubled and irrigation efficiency more than doubled relative to the control. That profile suggest SAPs may be best suited to dryland acres, deficit-irrigated ground and lighter soils with low water-holding capacity, with the strongest performance generally occurring at the higher application rate.

Two important limitations should be kept in mind. It is a single site-year evaluated descriptively, and the plot-to-plot swings under drought were large enough that several results — the weak rainfed performance of PWR and OG at the higher application rate, for instance — don’t yet have a clean explanation. There is also the added cost and labor of incorporating the polymers, which full-irrigation fields are unlikely to recover. 

Acknowledgment and Disclosure

This study was conducted in collaboration with EF Polymer Pvt. Ltd., which supplied the polymer products evaluated and provided in-kind support. Data collection, analysis and interpretation were conducted independently by the University of Nebraska-Lincoln, and the company had no role in the decision to publish or in the conclusions drawn. Mention of trade names is for informational purposes and does not imply endorsement by UNL. Thanks to the UNL staff at the Stumpf International Wheat Center for field support.

The full report is accessible on UNL Digital Commons.