EFFECT OF NITROGEN ON THE ACCUMULATION AND REUTILIZATION OF DRY MASS IN GRAIN SORGHUM

Abstract

Accumulation and reutilization of dry mass until anthesis and during a grain filling
period of sorghum in response to nitrogen fertilization in rates 0, 60, 120, 180, 240
and 300 kg N.ha-1 was studied in a field experiment. Grain sorghum hybrid EC
Alize was grown under not- irrigated conditions in the experimental field of
Agricultural University of Plovdiv, Bulgaria. The experimental design was a
randomized, complete block design with four replications with a size of
experimental plots of 20 m2 after wheat as predecessor. Standard farming practices
for the region of Southern Bulgaria were applied. It was established that nitrogen
fertilization significantly increased the amount of accumulated dry mass at anthesis
and total above ground dry mass at maturity compared to N0. Not significant effect
of higher rates (180, 240 and 300 kg N.ha-1) on the dry mass accumulation of
sorghum was found. Average post anthesis net dry mass accumulation was 3291
kg.ha-1 and its amount increased in parallel with the nitrogen rate up to N180. The
highest dry mass translocation, translocation efficiency, and contribution of preanthesis
assimilations of the grain was established at nitrogen rate N120 with values
2073 kg.ha-1, 25.0 % and 41,8 %, respectively. Growth of sorghum at higher
nitrogen rates N180, N240, N300 significantly decreased efficiency of dry mass
translocation and contribution of pre-anthesis assimilations of the grain. Nitrogen
fertilization had very strong negative correlation with dry mass translocation
efficiency (-0.860*) and contribution of pre-anthesis assimilations of the grain (-
0.863*). Very strong positive correlation (0.988**) was found between dry mass
translocation efficiency and contribution of pre-anthesis assimilations of the grain.