EFFECT OF NITROGEN AND NITROGEN PLACEMENT ON NO-TILL SMALL GRAINS - PLANT-YIELD RELATIONSHIPS

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 (Y(g)) 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 Y(g) = 0.95 + 0.01X1 + 0.02X2 + 0.02X3 - 0.0001X4 (R2 = 0.50) for spring wheat; Y(g) = 1.00 + 0.02X1 + 0.02X2 - 0.0002X4 (R2 = 0.75) for winter wheat; and Y(g) = 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.