Appropriate P and K fertilizer recommendations for corn (Zea mays L.) and soybean [(Glycine max (L.) Merr.] in Ohio are essential, as water quality and nutrient management issues in the region have intensifi ed over the last several years. Th e objectives of this study were to: (i) evaluate corn and soybean grain yield response to P and K fertilization, (ii) examine soil test phosphorus (STP) and potassium (STK) and corn Leaf P and Leaf K trends, and (iii) compare the ability of soil and leaf tissue testing to refl ect corn and soybean response to fertilization. We evaluated three P and K fertilizer rates, no fertilizer (0×), an estimated nutrient removal rate (1×), and twice the estimated nutrient removal rate (2×), in corn-soybean rotations at three sites over 9 yr. Grain yield was generally non-responsive to P and K fertilization, with only 9 of 42 site-years yielding signifi cantly positive responses. Soil test P and K started in the maintenance range, but signifi cantly declined with the 1× rate at two of three sites for P and at all sites for K. Furthermore, the 2× rate of P and K failed to build STP and STK at any site, with signifi cant declines at one site. Th e results revealed an inability to maintain initial STP and STK levels with the 1× rate and call into question the suitability of current fertilizer P and K recommendations aimed at maintaining STP and STK. Th ese recommendations require updating to better refl ect fertilizer needs of modern corn and soybean.School of Environment and Natural Resources, Ohio State Univ. OARDC, Wooster, OH 44691.
To facilitate the incorporation and understanding of the Nitrogen Soil Test for Rice (N-STaR), field validation studies were implemented to evaluate the ability of N-STaR to predict the field-specific N rates required to maximize rice yield on silt loam soils in Arkansas. Before flooding, soil samples to a 45-cm depth were taken and analyzed by N-STaR, a direct steam distillation procedure. These field trials compared N rates from three calibration curves, developed to predict 90, 95, and 100% relative grain yield (RGY), with the standard recommendation for rice (Oryza sativa l.) grown on silt loam soils (168 kg N ha −1 ). Nitrogen fertilizer rates predicted from the three calibration curves ranged from 22 to 252 kg N ha −1 . Rice grain yields fertilized with N rates from the N-STaR 90% RGY curve were equal to or greater than the standard recommendation for nine of the 14 sites. Grain yields for rice receiving the N-STaR 95% RGY N rates were equal to or greater than the standard recommendation for 13 of the 14 sites. Similarly, rice yields obtained from the N-STaR 100% RGY curve were equal to or greater than the standard N rate at all of the study sites. Despite visual differences in rice height and color, there were little to no differences in rice yield. These results indicate the importance of field-scale demonstration trials of the N-STaR technology to educate producers, consultants, and extension personnel before full release of this soil-based N test for rice grown on silt loam soils.
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