Yield of maize depends on the nitrogen supply to the plant at critical stages of the formation of main yield components. In the rain-fed production system, the Yield of maize depends on nitrogen supply to the plant at critical stages of the formation of main yield components. In the rain-fed production system, the productivity of applied nitrogen is conditioned by water supply to growing crop. Potassium is considered to be a nutrient significantly affecting water use by crops. Therefore, an in-season nitrogen balance is needed to adjust N levels and predict yields. These assumptions were validated in a long-term static field experiment with four levels of potassium fertilizing. They were differentiated by two soil fertility levels (Medium, High) and applied fertilizer (K-, K+). The nutritional status of maize was evaluated at two stages: 5th leaf and the beginning of flowering, using three approaches: i) nutrient concentration, ii) nitrogen to other nutrient ratios, iii) DRIS (Diagnosis Recommended Integrated System) method. These studies showed that potassium management was the key contributor to the year-to-year grain yield variability. Thus, grain yield was the basis for verification of the tested indices. At the 5th leaf stage only phosphorus (concentration and N/P ratio) can be considered as a potential predictor of the final yield of grain. The ear leaf as a vegetative part proved to be useful for evaluation of nutritional indices in maize and for making predictions about yield. The optimal system of potassium managemet can be defined according to its impact on the N/K, N/Mg and N/Ca ratios and, consequently, on yields of maize. The N/K ratio reached the saturation status, as presented by the quadratic regression model. The other two ratios affected grain yield in accordance to the linear regression model. The applied DRIS procedure corroborated the importance of potassium management as a factor significantly affecting the nutritional balance in maize. This crop has a potential to produce high yield of grain on medium K fertile soil provided potassium fertilizer is supplied whenever needed.

19.2.2014