. Efficient use of nitrogen on crop land in the Northeast. Plants; Soils. Bulletin 792 C HORIZON 320 360. Figure 17. Six-year average of nitrate-N contents in soil solu- tions from plots that received no N. Open circles are po- tatoes, closed circles are buckwheat. ( Rourke, Maine) Figure 16. Cumulative N uptake derived from fertilizer N (FN), soil N (SN) ond grass clippings of the current year (CNl) end of the previous two years (CN2-CN3). Arrows indicate dotes of fertilizer application. (Data of Starr and DeRoo, Connecticut) 56 kg/ha was not needed. As can be seen in Table 9, N
. Efficient use of nitrogen on crop land in the Northeast. Plants; Soils. Bulletin 792 C HORIZON 320 360. Figure 17. Six-year average of nitrate-N contents in soil solu- tions from plots that received no N. Open circles are po- tatoes, closed circles are buckwheat. ( Rourke, Maine) Figure 16. Cumulative N uptake derived from fertilizer N (FN), soil N (SN) ond grass clippings of the current year (CNl) end of the previous two years (CN2-CN3). Arrows indicate dotes of fertilizer application. (Data of Starr and DeRoo, Connecticut) 56 kg/ha was not needed. As can be seen in Table 9, N removal in tubers was not significantly different when the 168 kg/ha and 224 kg/ha rates were com- pared. The excess N at the highest rate remained in the soil to leach, denitrify, or be incorporated into the soil organic matter. Table 8. Yield of Katahdin potatoes obtained with three levels of N at Presque Isle, Maine. Rate of N 1973 1974 1975 1976 1977 1978 kg/ho q/ha 0 116 a* 205 a 150 a 184 a 125 a 174 a 168 179 b 394 b 239 b 341 b 277 b 318b 224 185 b 396 b 289b 314b 279 b 299 b • Numbers followed by the same letter within columns are not significantly different at Boyes .05 level. Data of Rourke, University of Maine, Orono. Nitrate-N levels in soil solution from B or C hori- zons of the plots fertilized with various rates of N over a 6-year period are presented graphically for buckwheat and potatoes in Figures 17 through 19. The data in Figure 17 show that NO3-N levels were higher in the B horizon when the area was planted to potatoes that received no N than when buckwheat was rotated on the same plots. In both of the rota- tions, peak values of NO3-N in the B horizon were reached by late August. Less than 10 ppm NO3-N existed in the soil solution from the B horizon of plots seeded to buckwheat by late August. Nitrate-N concentrations in soil solutions from the B horizon did not drop to less than 10 ppm on the potato plots until late October. Peak levels of NO3-N
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