The magnesium and calcium mineral status of maize at physiological maturity as a tool for an evaluation of yield forming conditions

Grain yield of maize reflects the extent of nutrient imbalance during the growing period. The key objective of a post-harvest analysis of maize, based on chemical characteristics of each part of plants harvested at physiological maturity, is to determine mineral indices which can serve as indicators of grain yield. This assumption has been validated by a long-term field experiment with four levels of potassium and nitrogen supply (0, 100, 150, and 200 kg N ha-1). The potassium application systems were differentiated by the soil fertility level (Medium, High) and K fertilizer (K-, K+). The grain yield of maize was significantly affected by an interaction of the potassium fertilizing systems and years. The importance of this interaction for yield formation manifested itself most distinctly in 2005, when the weather was favourable for plant growth, and in 2004, a season with temporary drought, but not in 2006, when severe drought occurred during the period termed as the critical window. The study implicitly showed that stem leaves can be used as indicators of the management of magnesium by maize while the grain content of calcium indicates how the plant manages that element. The limited size of maize’s physiological sink, i.e. number of kernels per cob, significantly decreases the flow of magnesium from leaves to kernels. Therefore, an elevated concentration and/or content of magnesium in stem leaves can be considered as an indicator of some disturbance of the yielding performance. The calcium concentration in grain showed the highest year-to-year variability among the maize parts. Any increase of this grain characteristic resulted in a yield decline. The key reason was an imperfect structure of the cob due to the disturbed setting up of kernels.