ABSTRACT. To calculate economically and technically optimal fertiliser rates, we frequently use the Mitscherlich-Baule function as a response of the crop to increasing fertiliser rates. Fertilisation has different thresholds of efficiency depending on a number of factors: in agricultural practice, there are situations in which, for economic or technical considerations, we cannot reach optimal fertiliser rates and fertilisation is sometimes even deficitary. Worldwide and in Romania, they are carrying on research in the field of optimising plant nutrition correlated with specific technical and economic factors. Relatively recently, there have also been researches aiming at establishing economically minimal fertiliser rates. Within the research we have carried out, we have taken into account the impact of the factor nitrogen on yield and on some technical and economic optimal elements in winter wheat. This approach is motivated by the fact that they frequently fertilise based on a single nutritious element – nitrogen – as a result of financial constraints. Previous research has allowed us to design a mathematical model for the establishment of the share of microelements of fertilisation of different crops. Unilateral nitrogen fertilisation is justified scientifically and efficient up to a certain level of consumption of nutritious elements as a specific plant nutrition requirement. Using as a mathematical instrument the monofactorial function (2 nd degree parabolic function) we have assessed the interdependence between fertiliser rates and yield, the correlation coefficient, maximum fertiliser rate technically and economically, maximum production, and optimal production. We have also assessed a few economic elements generated by the use of fertilisers, cost increase, income increase, benefit increase, as well as maximum benefit. With the fertiliser price of 0.8 Euro/kg of active substance nitrogen (present price), nitrogen fertilisation is profitable up to fertiliser rates of 65-70 kg/ha, a fertiliser rate at which the benefit is annulated by the cost increase. This level of fertilisation can be met frequently on many an agricultural exploitation. With the technical and economic conditions in which we have processed experimental data, optimal yield is 4,010.65 kg/ha that corresponds to a fertiliser rate of 151.24 kg of active substance nitrogen, while the maximum fertiliser rate is of 186.09 kg/ha of active substance nitrogen.

nitrogen fertiliser, economic aspects, optimal fertiliser rates, economic optimum, provisional model

Presentation: oral