The effect of nitrogen fertilization and the use of biostimulators on the chemical composition of grains of two varieties of corn (Zea mays L.)

The aim of the research was to determine the impact of the use of biostimulators and different nitrogen doses on the yield quality of two varieties of corn grown for grain. The field experiment was carried out in 2015-2017 on an individual farm located in north-eastern Poland (52°30'N and 22°26'E). The following factors were examined in the experiment: group I-two corn varieties: PR38N86 (280 FAO); P8400 (240 FAO) group II-four doses of nitrogen fertilization: control treatment-without nitrogen application (0 kg·ha-1 N) nitrogen doses-80 kg·ha-1 N, 120 kg·ha-1 N, 160 kg·ha-1 N, group III-four types of biostimulators used: (1) control treatment-without the use of a biostimulator, (2) biostimulator containing sodium ortho-nitrophenol, sodium para-nitrophenol, 5-nitroguaiacol sodium, (3) biostimulator containing potassium para-nitrophenolate, potassium ortho-nitrophenolate, potassium 5-nitrovacollate, (4) biostimulator containing molybdenum, zinc. Different doses of nitrogen used in the experiment contributed to an increase in the total protein content in the grain of the tested corn varieties compared to the control treatment. The highest significant increase in protein content by an average of 18.96 g∙kg-1 was obtained after the application of 160 kg N∙ha-1, and after the application of 120 kg N∙ha-1 the value of this feature increased on average by 17.18 kg N∙ha-1. Nitrogen fertilization reduced the starch content and increased the fat content in the tested corn varieties. The lowest starch content was found after the application of 120 kg N∙ha-1 and 160 kg N∙ha-1, while the highest fat content was found in grain tested with 120 kg N∙ha-1. The highest protein content was demonstrated after the use of a biostimulator containing sodium ortho-nitrophenol, sodium para-nitrophenol, and sodium 5-nitroguaiacol. The biostimulators used increased the starch and fat content in the grain of the tested varieties, and the differences between them were statistically insignificant. After using a biostimulator containing sodium ortho-nitrophenol, sodium para-nitrophenol, sodium 5-nitroguaiacol, the protein content increased by an average of 6.0%. The biostimulators used increased the starch and fat content in the grain of the tested varieties, and the differences between them were statistically insignificant. The medium-early variety with FAO 240 was characterized by a higher content of total protein (on average by 7.95 g∙kg-1) and crude fat (on average by 1.5 g∙kg-1) compared to the medium-late variety. All tested varieties were distinguished by the highest concentration of total protein and crude fat in the second, optimal year of the study. The lowest protein content was found in the last year of the study with the highest annual rainfall and the lowest average air temperature, and crude fat content was found in a relatively dry growing season. The opposite tendency was obtained in the case of starch content in the grain of the tested varieties.