Yield response of corn to nitrogen (N) and phosphorous (P) and soybean response to P has been documented to vary within and between fields. USDA and university scientists, Drs. D. Lambert, J. Lowenberg-DeBoer and G. Malzer, reported findings from a five-year study evaluating yield variability and the profitability of variable-rate application (VR) of N and P.1
The field research site near Windom, Minn., was cropped with corn in 1997, 1999 and 2001. Soybeans were the test crop in 1998 and 2000. Replicated treatments included 0, 60, 100, 140 and 180 pounds per acre (lbs/a) N and 0, 50 and 100 lbs/a P2O5. The researchers found that spatial variation of crop response was significant and that response by both crops to P was temporally stable in some parts of the field but not in others. Response to N was not temporally stable. Based upon yield results from this five-year study, the average return over those five years from variable rate N and P management strategy was $13 per acre higher than rates returned under a uniform application strategy. VR strategy for N over multiple growing seasons was more difficult than special management of P. Future research is expected to help agronomists better understand the temporal and spatial mechanisms regulating crop nutrient removal and nutrient carryover dynamics.
1Agron. J. 98:43-54 (2006)