Nitrogen is the dominant factor affecting the rate of wheat growth and yielding. Water supply during the critical stages of yield component formation is a factor limiting the nitrogen use efficiency. A study dealing with this problem has been conducted, based on a long-term field experiment with four N levels (0, 60, 120, 180 kg N ha-1) against the background of four systems of potassium management, including: medium and high K soil fertility levels with and without K fertilizer (MK-, MK+, HK-, HK+). The objective of the study was to evaluate the wheat nitrogen nutritional status during the vegetative period of wheat growth according to nitrogen concentrations in leaves and stems. The research was run in 2003, with severe water deficit, and in 2004, under semi-dry weather conditions. The wheat grain yield responded to both experimental factors only in 2004. The nitrogen concentration in plant parts was dependent only on the N doses, which is indicative of the good adaptation of wheat to seasonal water supply fluctuations. The nitrogen concentration in leaves adhered to the quadratic regression model. This type of response indicates the N saturation status, which translates to a non-limiting effect of this factor on the plant growth. The pattern  of  N concentrations in stems was in accordance with the linear regression model. This type of response indicates the N-limited growth due to an insufficient nitrogen supply. The Critical Nitrogen Concentration (CNC) pattern proved significant adaptability of wheat to N fertilizer levels. The Nitrogen Nutrition Index, calculated from the CNC, can serve as an indicator of N dilution during the vegetative period of wheat growth.

19.2.2014