In Central Slovenia within a long term static experiment IOSDV we investigated the impact of mineral nitrogen (N) fertilisation (0, 65, 130, 195 kg/ha) on the N content and the N amount in winter wheat (larger roots, stems, spikes and leaves) in EC 81/82 and EC 90/91, employing three systems of management: farmyard manure ploughing in before forecrop maize, straw ploughing in and green manure, no organic fertilisation. At EC 81/82 the N content in larger roots was around twice as high as the N content in stems and around twice as low as the N content in spikes and leaves. There was 80% of the whole N amount in plant located in the spikes and leaves (33–168 kg/ha) in EC 81/82 and 90% in EC 90/91. Calculated N recovery from mineral fertiliser was 68–87%; it increased with the increasing N rates in the system with farmyard manure ploughing in and in the system with no organic fertilisation, but not in the system with straw ploughing in and green manure. Between EC 81/82 and EC 90/91 wheat gained from 4 to 34 kg N/ha, but there were more important translocations of N inside the plants, which were higher at higher mineral N rates. There was a significant impact of management system on the N uptake at the highest mineral N rate.

The mineral nitrogen (N) rate for wheat was determined in the IOSDV experiments at Jable and Raki can (Slovenia) in management systems with straw and farmyard manure considering 'The Third Approximation of the Yield Law', which enabled us to estimate the maximum yield, N rate for maximum yield and the N balance. At Raki can, mineral N rate for the maximum yield of wheat in the system with manure amounts to 40 -80 kg ha 71 N, fertilized in one to two side-dressings, when crops in the rotation 'maize-wheat-barley' get in the average 80 -90 kg ha 71 a 71 mineral N (Norg þ N-mineral: 150 -160 kg ha 71 a 71 N). In the system with straw wheat needs 84 kg ha 71 a 71 mineral N, fertilized in two side-dressings (rotation average 151 kg ha 71 a 71 N). At Jable wheat should be fertilized with 167 kg ha 71 a 71 mineral N in the system with manure to reach the maximum yield, and all the crops in the rotation should get in the average 210 kg ha 71 a 71 N (Norg þ N-mineral: 250 kg ha 71 a 71 N). To reach the maximum yield in the system with straw at Jable, mineral N rate is nearly the same as in the system with manure (168 kg ha 71 a 71 mineral N), fertilized in three side-dressings (rotation average 230 kg ha 71 a 71 N). N balance in the field crop rotation at the maximum yield of wheat is in accordance with the principles of 'good agricultural practice' at Raki can, while at Jable the amounts of mineral N should be lowered, because N amount for maximum wheat yield causes too high N balance. Maximum yields significantly differ regarding season and location, the impacts of season on the maximum yield differ regarding location. Using 'The Third Approximation of the Yield Law' was found to be a very appropriate way for the calculation of required mineral N rates for maximum yields and for N balance calculation at these N rates at both locations.