PRINCIPLE AND VERIFICATION OF THE GIESSEN MODEL FOR NITROGEN-FERTILIZER RATES TO WINTER CEREALS BASED ON EUF SOIL ANALYSIS

A model is presented for the determination of nitrogen fertilizer rate s for winter cereals. The model is based on soil nitrogen analysis by electro-ultrafiltration (EUF); it further more takes into account nitr ogen released from green manure and from residues of the preceding cro p according to the yield potential of the site. Soil samples were take n from the upper soil layer (0 cm to 30 cm) in late autumn. Nitrate an d ammonium analyzed is taken into account for the 1st nitrogen split a pplication, organic nitrogen, extracted by EUF for the following split applications. The model was verified under field conditions. In 1989 (9 sites) average grain yield of winter wheat obtained according to th e model recommendation amounted to 97 % of the economical maximum yiel d, 1990 (10 sites) 92 % of the economical maximum grain yield were obt ained. The figures of winter barley (9 sites 1989 and 10 sites 1990) w ere 93 % and 97 % of the economical maximum yield, respectively. In th ose particulare experiments the consideration of average values for EU F-N(org) yielded virtually the same N-fertilizer recommendations than the consideration of the site specific N(org) data. With 4 exceptions from 38 cases, nitrogen fertilizer rates recommended according to the model were lower than the rates requered for the economical maximum yi eld. Reasons why lower rates were recommended are discussed. Sixty sit es grown with winter wheat or winter barley and fertilized according t o the model were analyzed with the 0.01 M CaCl2-method for rest nitrat e + rest ammonium. Soil samples were taken from a soil depth of 0 cm t o 90 cm in late summer. In 85 % of the soils analyzed the rest nitrate + rest ammonium was lower than 45 kg N ha-1. This finding shows that the model is also of ecological relevance.