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Calibration of Nitrogen and Phosphorus Soil Tests with Yield of Proso Millet

Univ. Nacional Agraria-La Molina, Aptdo 456, Lima, Peru

G. A. Peterson^* and D. G. Westfall

Dep. of Agronomy, Colorado State Univ., Fort Collins, CO 80523

*Corresponding author.

ABSTRACT

Current fertilizer recommendations for proso millet (Panicum miliaceum L.) are based on soil test calibrations developed for related crops such as corn (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench]. Therefore, their accuracy may be questionable. A study was initiated to correlate and calibrate the AB-DTPA, Olsen P, Bray P-1, and Mehlich P-1 soil tests for P and the soil profile NO₃-N test with proso millet yields. Most of the soils studied were Argiustolls. Fourteen dryland field experiments were conducted from 1985 through 1987 in eastern Colorado. The experiments were N and P factorials with N levels of 0, 22, 45 and 67 kg ha^–1 and P levels of 0, 8, and 17 kg ha^–1. Profile soil samples were taken and analyzed for P by each of the soil P tests and for extractable NO₃-N. Grain yield was measured at maturity. Critical levels were established for each soil P and N test. Critical levels (point below which response to fertilizer is expected) were 6, 12, 20, and 35 mg kg^–1 of P (0-15-cm sample depth) for the AB-DTPA, Olsen P, Bray P-1, and Mehlich P-1 tests respectively. For N the critical level was 58 kg ha^–1 in the 0- to 90-cm soil profile. Soil test categories for each P test were established. The amount of P needed to correct deficiency and obtain maximum yield was 16, 12, 7 and 0 kg ha^–1 for VL, L, M, and H categories, respectively. The amounts of N were 45, 25, 15 and 0 kg ha^–1 for the respective categories.

Received for publication March 14, 1989.