Objectives of investigations were to determine optimal nitrogen rates for the highest soybean seed yield, compare reaction of nodulating and nonodulating soybean varieties to nitrogen fertilization and estimate the amounts of symbiotically fixed nitrogen depending on nitrogen rates. Estimation of the amounts of symbiotically fixed nitrogen was done using the nitrogen contents in soil before and after the vegetation and nitrogen contents in whole plants of nodulating and nonodulating varieties. Nitrogen fertilization (0, 153, 306 and 459 mg N/pot) had significant influence on straw dry matter yield. The highest soybean seed yields in 1991 were obtained at 306 and 459 mg N/pot, but in 1992 nitrogen fertilization had no influence on soybean seed yield. In 1991 nitrogen fertilization increased the nitrogen content in straw with pods' walls. Nodulating variety Zagrepčanka had in 1991 higher nitrogen content in straw with pods' walls but in 1992 differences between varieties were not significant. Nitrogen fertilization had no influence on nitrogen content in soybean seeds, and nodulating variety had higher nitrogen content in seeds in both years. In 1991 the higher amounts of symbiotically fixed nitrogen (573 mg N/plant) was obtained at 306 mg N/pot but difference between 153, 306 and 459 mg N/pot were not statistically significant. In 1992 nitrogen fertilization had no influence on symbiotic fixation but amount of symbiotically fixed nitrogen decline at higher nitrogen rates.

soybean; nitrogen fertilization; symbiotic fixation

Published by University of Zagreb, Faculty of Agriculture, Zagreb, CROATIA
Sponsored by Ministry Science and Education of the Republic of Croatia