Effects of Banded and Residual Fertilizer Phosphorus on Dryland Spring Wheat Yield in the Northern Plains

Although phosphate fertilizers are commonly applied either by surface broadcasting or banding with the seed to dryland spring wheat (Triticum aestivum L.), data are limited on the residual effects of previous fertilization on plant growth and grain yield. This is especially true in regions where there are drought periods during the growing season. Therefore, the residual effects of P fertilization on spring wheat grown on Parshall fine sandy loam (Pachic haploboroll) were determined in a field study at Mandan, North Dakota. Fertilizer rates of 0, 20, 40, 80, and 160 kg P/ha were broadcast in 1968 to establish several levels of residual P in the soil. In 1969 subplots were established on each of the broadcast P plots, to which P was banded with the seed at the rate of 15 kg/ha either (i) repeated to the same subplot each year for 6 years, (ii) on a new subplot (previously unfertilized) each year, or (iii) not at all. After 6 years of cropping, the residual effects of 160 kg P/ha broadcast in 1968 resulted in an average increase in grain yields of about 10% (200 kg ha⁻¹ year⁻¹. Banding of P with the seed resulted in an additional 10% increase in grain yields, with about half this increase due to current-year banding and about half due to residual effects of banding in previous years. Residual effects of banding and broadcast treatments were additive, with little interaction. Average plant P concentrations (1969–1974) were significantly increased by both the P initially applied and by the banded-P treatments at all growth stages. NaHCO₃-soluble P levels in the 0- to 15-cm soil depth decreased with time for all broadcast P treatments, but repeated banding of P on the same plot each year increased NaHCO₃-soluble P levels during the 6 years of study. An exception was the 160-kg P/ha broadcast-P treatments where NaHCO₃-soluble P level was still decreasing. The addition of banded P decreased percent fertilizer P recovery in grain, especially when P was repeatedly banded each year on the same site. Since yield increases resulted from banding P with the seed even when soil test levels were high, it was concluded that banding P may be beneficial for spring wheat in the cool springs of the northern Great Plains no matter what soil test level is present.