The elaboration and introduction of an environment-friendly N fertilisation system requires studies on the soil N regime, and on NO3-N accumulation and leaching under field conditions. The N balance of the soil and the depth distribution of NO3-N in the 200-300 cm soil layer was studied at four N supply levels (0, 80, 160 and 240 kgha-1) in selected treatments in the 4th, 8th, 11th, 14th and 18th, years of a long-term mineral fertilisation experiment set up in 1989 on a chernozem meadow soil in Szarvas with 4Nx4Px4K = 64 treatment combinations. The soil was calcareous in the deeper layers, with an 85-100 cm humous layer had pH(KCl) 5.0-5.2, humus content 3.0-3.2 %, upper level of plasticity according to Arany (KA) 50, clay content 32 %. The following conclusions could be drawn from the experimental results: The chernozem meadow soil, which had a humus content of 3.0-3.2 %, possessed good N-supplying capacity, the total N quantity taken up by the plants over the course of 18 years amounted to 2273 kgha-1, equivalent to a mean annual N supply rate of 126 kgha-1. The annual N uptake ranged from 40-275 kgha-1 in the unfertilised plots, depending on the water supplies, the consequent crop yields and the N requirements of the crop. The soil N balance was negative at the 80 kgha-1 N fertiliser rate, but at this N supply rate the mean N uptake rate was 170 kgha-1year-1 and at higher N rates (160, 240 kgha-1) this only increased by 15-20 kgha-1 on average, with no significant increase in yield. N leaching was observed at the annual 80 kgha-1 N fertiliser rate and even in the unfertilised plots if deficiencies in the water supplies led to low yields and prevented the crops from absorbing all the available nitrogen. At 160 kgha-1 N the accumulated N balance was only slightly negative. In 7 of the 18 years plant N uptake was below 160 kgha-1. Under the given experimental conditions, considering the natural N-supplying capacity of the soil, the 160 kgha-1 N fertiliser rate proved to be excessive, surpassing the N requirements of the potential crop yield in most years and resulting in NO3-N leaching. The cumulative N balance for plots given 240 kgha-1 N fertiliser and in 11 of the 18 years the plant N uptake was less than kgha-1. There was no increase in yield at this N supply level, and yield depresion was recorded in some years, with considerable levels of NO3-N leaching. The substantial rise and fall of the groundwater as the result of excessively wet and dry years caused the leaching of substantial quantities of NO3-N.

N fertilisation; N turnover; NO3-N leaching; long-term trial

Presentation: oral