Soil Test P Level and Tillage Effect on Corn Yield.

Nebraska P (Phosphorus) fertilization recommendations in corn (Zea mays L.) are based on the deficiency correction approach, where a critical soil test P level is maintained. With current varieties, high yield situations and different tillage, this method may not be the highest yielding. Research was conducted to compare the effect of five P management treatments and 2 tillage systems on yield of continuous corn at 3 locations from 2011 through 2016 under rain fed conditions at Concord, NE and irrigation at Mead, NE and North Platte, NE. P fertilization recommendation treatments of: 1.) No P applied; 2) P applied according to UNL recommendations; 3) P applied to replace P removed; 4) Bray-1 P raised and maintained at 25 mg kg^-1; and 5) Bray-1 P raised and maintained at 35 mg kg^-1 were implemented under no-till and annual disk tillage. Grain yield was 9.3% greater with P applied compared to with no P. There was no tillage effect on grain yield at Mead and North Platte while at Concord yield on average was 7.4% greater in annual disc than in no-till systems. P applied to replace P removed and Bray-1 P raised and maintained at 35 mg kg^-1 resulted in grain yields of 10.64 and 10.66 Mg ha^-1 respectively, which was significantly greater than P applied according to UNL recommendations (10.29 Mg ha^-1), while P raised and maintained at 25 mg kg^-1 resulted in an intermediate grain yield of 10.45 Mg ha^-1 . Recommendations other than UNL recommendations could result in greater grain yields, however, crop and P fertilizer cost should also be considered.