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Abstract
No‐till planting of continuous‐crop small grains is being adopted to improve soil and water conservation. The increased N‐fertilizer requirements of this cropping system makes the need for maximizing fertilizer‐N efficiency and the accuracy of fertilizer recommendations more critical. Field experiments were conducted in the semi‐arid Northern Great Plains to relate soil N tests to (i) the efficiency of subsurface N‐fertilizer placement, and (ii) N‐fertilizer requirements for no‐till wheat and barley. Soils ranged from 7 to 118 kg/ha NO3‐N. Nitrogen placements were surface‐broadcast and subsurface‐banded 5 cm below and to the side of the seed in paired rows. Four N rates, which varied among locations, ranged from 0 to 135 kg/ha. Subsurface N placement produced higher grain yield than did surface N placement when soil NO3‐N was less than 56 kg/ha, while surface N‐placement produced the superior yield when soil NO3‐N was greater than 71 kg/ha. Grain yield at all sites responded to N applications. The best multiple regression estimates of Mg/ha yield (Yg) versus kg/ha soil NO3‐N (X1), kg/ha fertilizer‐N (X2), g/kg organic matter (X3), and soil NO3‐N x fertilizer‐N (X4), were the significant (P<0.001) linear equations Yg = 0.95 + 0.01X, + 0.02X2 + 0.02X3 ‐ 0.0001X4 (R2=0.50) for spring wheat; Yg = 1.00 + 0.02X, + 0.02X2 ‐0.0002X4 (R2=0.75) for winter wheat; and Yg = 2.17 + 0.02X2 ‐ 0.0002X4 (R2=0.67) for spring barley. Equations for total biological yield were also developed. Equations for straw yield were not statistically significant.
Notes
Contribution No. J‐2689 from the Montana Agric. Exp. Stn., Bozeman, MT. Funded in part by the Tennessee Valley Authority (Contract No. 39645A), the Potash and Phosphate Institute, and the Montana Wheat and Barley Committee.