Response of sugar beets to phosphorus and potassium fertilization, taking into account electro-ultrafiltration soil reserves

Trials were conducted from 1979 to 1988 on Gleyic Phaoezem, Haplic Chernozem, Cromic Cambisol and Gleyic Luvisol soils to determine necessary maintenance fertilization or the relationship between the electro-ultrafiltration soil reserves of phosphorus and potassium and the performance characteristics of sugar beets as well as the required PK application. The nutrient uptake of the beet plants was 263 kg N, 93 kg P205, 369 kg K20, 80 kg Na, 70 kg Ca, 63 kg Mg, 144 kg Cl, 76 kg SO4, 0.153 kg Mn, 0.133 kg Cu, 0.461 kg Zn, and 0.435 kg B per hectare. The phosphorus content of the beet plants in the period of maximum yields in October ranged between 0.12% and 0.15% in the leaves and crowns, and around 0.12% in the roots. The potassium content in leaves and crowns ranged between 2.25% and 3.83%. First EUF fraction contents of around 2.0 mg P/100 g soil did not change in the course of the eight-year trial even with zero fertilization (second EUF fraction: 1.24 mg P/100 g soil). First EUF fraction contents between 1.6 and 1.3 mg P/100 g soil experienced some decrease which was to be countered by a maintenance application of about 54 kg P205/(ha o a). In cases where the first EUF fraction contents were less than 0.9 mg P/100 g soil, the soil reserves were sharply reduced by the uptake. In such cases, a maintenance or replacement application of up to 174 kg P205/(ha oa) was indicated. Yields increased significantly with potassium applications of 240 kg K20 per (ha o a) where 8.7 mg K/100 g soil were present in the first EUF fraction and 4.4 mg K/100 g soil in the second EUF fraction. With 10.6-16.2 mg K/100 g soil in the first EUF fraction and 8.8-12.0 mg K/100 g soil in the second EUF fraction, an annual maintenance application of up to 120 kg K20/ha sufficed.