Pulse fertiliser response in WA: it’s about species and soil, not rules of thumb
Three years of Grain Research and Development Corporation (GRDC) – funded trials across the WA wheatbelt are showing that phosphorus and potassium responses in grain legumes are highly variable, and that legume break crops still deliver consistent rotation benefits to following crops.
Growers have long flagged uncertainty around fertilising grain legumes, with many defaulting to ‘rule of thumb’ rates or simple nutrient replacement. With pulse interest rebuilding on the back of volatile nitrogen prices and improved varieties, Living Farm is working to put numbers behind those decisions through the GRDC project Fertiliser recommendations for grain legumes in Western region with limited production area (LIV2402-003RTX).
Now in its third year, the project has run small plot field trials, grower managed legacy trials and glasshouse pot studies across six legume species – lupins, field peas, chickpeas, faba beans, lentils and vetch, at numerous locations across the WA wheatbelt.
Rotation benefits hold up
Across five 2025 grower sown legacy trials, residual phosphorus and potassium (or sulphur) applied to the 2024 legume crop produced little to no significant carryover effect on yield or grain quality of the following wheat or canola crop. Wheat following lupins, vetch, field peas, faba beans or chickpeas yielded 11–16% more than continuous wheat, depending on site and species. At Kojonup, wheat after legumes had higher protein on average (13.9–14.0%) than wheat on wheat (12.7%). At Mingenew, wheat after lupins out yielded wheat after vetch by around 14%. Carryover gains were less pronounced at York, where canola yields and oil content following legumes were only modestly different from canola on wheat stubble.
Phosphorus: response is species and soil specific
Phosphorus (P) trials at York, Kojonup, Eneabba, Esperance, Boxwood Hill, Ardath and Varley in 2025 applied 0, 12, 18, 24 or 36 kg P/ha. P consistently increased early season growth and yield against the nil control, but grain quality wasn’t affected and the size of the response varied considerably.
Lentils, lupins, field peas and wheat were the most responsive. Lupins at Varley jumped from 1.78 t/ha at nil P to 3.24 t/ha at 12 kg P/ha, an 82% lift, with little gained beyond that rate. At York, lupin yields kept rising to 4.68 t/ha at 36 kg P/ha. Faba beans showed yield gains despite flat NDVI responses; chickpeas and vetch were the least responsive overall. In several cases, yields plateaued or even dipped at 36 kg P/ha, suggesting diminishing returns past 12–24 kg P/ha.
Importantly, Colwell P values alone didn’t determine responsiveness. York and Ardath had similar topsoil Colwell P (39 vs 38 mg/kg), but York responded strongly due to high PBI and very low DGT-P, while Ardath barely shifted. These results indicate that growers should read Colwell P, PBI and DGT-P together, alongside soil type, pH and seasonal conditions.
Potassium: faba beans and vetch the most responsive species
A UWA glasshouse pot study was run with six K rates (0–75 mg K/kg). Faba beans and vetch were the most responsive, with faba bean shoot dry weight climbing from 18.6 g/pot at nil K to 25.5 g/pot at 15 mg K/kg, with K also lifting flower and pod counts. Chickpeas and lentils showed little to no response. Across responsive species, biggest biomass gains occurred between 0 and 15 mg K/kg, with diminishing returns above that.
What it means for growers
The headline message is that recommended rates must be tailored, and what works for one species or soil type may not work for another. Pulses still earn their place in the rotation, but P decisions need to be made with soil tests in mind, and K demand differs sharply between species. A fertiliser calculator for growers combining crop, target yield, Colwell P, PBI and DGT-P is currently in development. In 2026, additional legacy trials and grower scale trials will test whether these patterns hold under commercial conditions.
Ends.
Media Contact
Gemma Cao – Research Agronomist and GLP Principle Investigator
Living Farm
gemma@livingfarm.com.au
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