What the research measured
Starter raised early corn growth far more often than grain yield. Across 100 Wisconsin on-farm sites, most testing excessively high in P and K, starter raised yield by about 4 bu/ac statewide each year, individual responses ranged from −10 to +42 bu/ac, and 40% of sites showed a positive economic response. In Iowa, in-furrow starter raised no-till yield in 7 of 11 fields and lowered it in one; in 13 on-farm trials P-K fertilization raised yield at 5 sites; and in 16 further trials, starter added on top of broadcast P-K did not raise yield at any site.
Four Iowa State and University of Wisconsin field programs in farmers’ fields (11, 13, 16 and 100 sites), published 1999–2005 in Agronomy Journal, Journal of Production Agriculture and a regional conference, plus a 2022 Iowa State extension summary covering 31 Iowa trials.5 independent sources.What it is. A small dose of liquid or dry N-P-K fertilizer placed by the planter, either in the seed furrow or in a band about 2 inches beside and 2 inches below the seed, so seedling roots meet concentrated nutrients in cold spring soil. The trials here used in-furrow 3-18-18 at 10 to 14 lb P2O5 and K2O/ac in Iowa and a 2×2 band averaging 15+26+32 lb N+P2O5+K2O/ac in Wisconsin.
Study conditions and limitations
- Soil-test P is the main switch: Iowa no-till yield gains were large (200–671 kg/ha, about 3–11 bu/ac) where Bray-1 P was below 16 mg/kg and small (80–194 kg/ha, about 1–3 bu/ac) with in-furrow starter on high-P soils; Iowa State says yield responses to starter P are seldom observed when the recommended pre-plant P rate is broadcast.
- Early growth is not yield: early growth response averaged 32% against a 2.4% yield response in the no-till study (r = 0.44), and early growth rose in 9 of 11 sampled sites in the 13-trial study while yield rose at 5.
- In-furrow rates are capped by salt: Iowa State’s rule of thumb is less than 10 to 12 lb of N plus K2O per acre in the furrow, and urea, ammonium sulfate and ammonium or potassium thiosulfate are not recommended in-furrow in the north-central region.
- Wisconsin responses were more frequent with soil K below 140 ppm and with later planting dates and longer-maturity hybrids (planting date plus RM above 235), not with early planting as often assumed.
- Starter in addition to a 2-year broadcast P-K rate did not raise yield at any of 16 Iowa sites, and in-furrow starter alone yielded less than broadcast P-K at 5 sites, 4 of them testing low in P (15 mg/kg or less).
- In high-testing soils, Iowa State attributes the infrequent yield responses to N-P-K starter mostly to the N, under no-till, corn after corn, or when the main N rate is not applied pre-plant in spring.
Read the sources · 5
- Site-Specific Factors Affecting Corn Response to Starter Fertilizer ↗
At 100 Wisconsin on-farm sites over three years, most with excessively high soil-test P and K, a 2×2 starter averaging 15+26+32 lb N+P2O5+K2O/ac raised yield by about 4 bu/ac statewide each year; site responses ranged from −10 to +42 bu/ac and 40% of sites had a positive economic response, more often where soil K was below 140 ppm and with later planting plus longer-RM hybrids.
- Yield and Early Growth Responses to Starter Fertilizer in No-Till Corn Assessed with Precision Agriculture Technologies ↗
Eleven no-till Iowa strip trials: liquid N-P-K starter increased yield in seven fields and reduced it in one (−231 kg/ha). Gains were 200–671 kg/ha where Bray-1 P was below 16 mg/kg and 80–194 kg/ha with in-furrow starter on high-P areas; early growth rose 32% against a 2.4% yield response.
- In-Furrow Starter and Broadcast Phosphorus and Potassium Fertilization for Corn ↗
Thirteen Iowa on-farm trials over three years compared in-furrow 3-18-18 at 10 to 14 lb P2O5 and K2O/ac with broadcast P-K (100–110 lb P2O5, 120 lb K2O). Fertilization raised yield at five sites, with starter matching broadcast at four of them; early growth rose at 9 of 11 sampled sites.
- Corn Grain Yield, Early Growth, and Early Nutrient Uptake as Affected by Broadcast and In-Furrow Starter Fertilization ↗
Sixteen Iowa trials with soil-test P from 5 to 77 mg/kg: fertilization raised yield at nine sites (0.80 to 2.11 Mg/ha), starter alone yielded less than broadcast P-K at five sites (0.30 to 1.48 Mg/ha less, four of them low in P), and starter added to broadcast did not raise yield at any site.
- Starter Fertilizer for Corn: A Potentially Useful Practice with a Cold Spring and High Fertilizer Prices ↗
Summarizes 31 Iowa trials: early growth responses to starter P-K (5 to 25 lb P2O5 and K2O/ac) were far larger than yield responses, which are seldom seen when the recommended pre-plant P rate is broadcast. The in-furrow rule of thumb is less than 10 to 12 lb of N plus K2O per acre.
Before you buy, ask
- What did my soil test show, and did the cited studies respond at similar levels?
- What rate, source, and timing were tested, and what did the untreated check receive?
- How does the price per pound of nutrient compare with the sources I already use?
Record
- Sources checked
- October 12, 2026. Every figure shown is printed on the linked page; unit conversions are noted on the chart.
- Company response
- None yet. Makers and suppliers of this product can send corrections, additional trials, or a statement; it is published here, labelled, and never edits the research summary. Send a correction →