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Abstract
Small grain producers often have difficulty interpreting Olsen P soil tests in Central and Northcentral Montana. This study was conducted to evaluate the Olsen P soil test and P response relationships for winter wheat grown on fallow. Treatments of 0, 5, 10, 15, 20, and 25 kg P/ha were applied at 19 locations from 1987 to 1989. Grain yield, protein content, and test weight were measured. Olsen P soil tests ranged from 11 to 35 mg/kg with a mean of 22 mg/kg while pH varied from 5.4 to 8.4 with a mean of 7.4. Grain yield response to applied P ranged from 0 to 1000 kg/ha. A P soil test critical level of 24 mg/kg for P response was determined using the Cate‐Nelson graphical method. Linear multiple regression analysis indicated that grain yield response was positively correlated with P rate and soil test x pH and negatively correlated with soil test, pH, and P rate x soil test with an R2 of 0.42 (P = 0.001). Grain protein and test weight were not influenced by P applications.
Notes
G. D. Jackson and G. D. Kushnak, Western Triangle Agric. Res. Or., Conrad, MT 59425; G. R. Carlson, Northern Agric. Res. Ctr., Havre, MT 59501; D. M. Wichman, Central Agric. Res. Ctr., Moccasin, MT 59462; J. S. Jacobsen, Plant and Soil Sci. Dept., Montana State University, Bozeman, MT 59717.
Contribution No. J‐2584 from the Montana Agric. Exp. Stn. and Ext. Ser., Bozeman, MT.