Field pea response to phosphorus applied with seed

G. J. Endres, B. G. Schatz, and S. F. Zwinger Current NDSU recommendations for seed-placed phosphorus (P) for field pea is a maximum of 40 pounds/acre of 11-52-0 or 10-50-0(MAP). A trial was established at the Carrington Center in 1997 to determine if recommendations on P application with pea seed should potentially be revised.

The trial was established on a loam soil with a low P level (7 ppm). Treatments included: 1) untreated check, 2) 20 lb/ac MAP with seed, 3) 40 lb/ac MAP with seed, 4) 20 lb/ac DAP (18-46-0) with seed, 5) 40 lb/ac DAP with seed, 6) 24 fl oz/ac ASA Plus(7.5% N, 0.01% Cl, and 8.5% Zn) + 40 lb/ac MAP preplant incorporated (PPI), 7) 'Provide' (seed inoculant that releases bound P at the root zone) with seed, and 8) 40 lb/ac MAP PPI. Treatments 2 and 4 received 20 lb/ac MAP PPI to supplement seed-placed P. All P rates are actual P. Inoculated 'Profi' was planted on May 23 at 300,000 pure live seeds/ac.

All seed-placed P treatments reduced crop stand 12 to 37% (see table). Remaining plants appeared to compensate as seed yield was similar among treatments. However, there was a trend of reduced yield with the high rates of MAP or DAP. A yield improvement did not occur with any P application compared to the untreated check. Plant density was highest and yield tended to be highest with Provide-treated seed. The trial will continue in the future.

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