EFFECTS OF NITROGEN APPLICATION ON BIOMASS ACCUMULATION, REMOBILIZATION, AND SOIL WATER CONTENTS IN A RAINFED WHEAT FIELD

Abstract

This study examined the effects of different levels of N fertilization on dry matter accumulation and remobilization, and soil water contents in a rainfed winter wheat field. The experiments were carried out during growth seasons in 2009 – 2012 in a hilly region in Shandong Province, China. The N rates applied were 0 (N0, the control), 90 (N1), 120 (N2), 150 (N3), 180 (N4), and 210 (N5) kg N ha 1 . Our results showed that N fertilization significantly increased dry matter accumulation and post-anthesis assimilates compared with controls. At anthesis, total above-ground biomass increased significantly with increasing N rate up to 150 kg ha 1 and then leveled off in the 2009 – 2010 and 2011 – 2012 growth seasons. However, the biomass in the 2010 – 2011 growth season did not vary with different N rates. At maturity, the accumulation of dry matter in vegetative organs significantly increased with increasing N rate up to 150 kg ha 1 and then leveled off in all growth seasons. Of all the treatments, N3 and N4 had relatively higher total above-ground biomass at maturity. In contrast, dry matter remobilization efficiency showed a declining trend under increasing N rate. The higher post-anthesis assimilates and the contribution of pre-anthesis assimilates to grains were obtained at N rates of 150 and 180 kg ha 1 in all growth seasons. Soil water contents in 0 – 120, 0 – 100, and 40 – 160 cm soil layers during each growth season decreased significantly with increasing N rate up to 150 kg ha 1 . The maximum grain yields were obtained under N rate of 150 kg ha 1 in all growth seasons, with the highest grain yield being 7160.8 kg ha 1 in the 2011 – 2012 growth season. Our results suggested that N fertilization at 150 kg N ha 1 was optimal for grain production via promoting above-ground biomass and soil water consumption in deep soil layers. These results should help provide guidance for N fertilization management for optimal and sustainable wheat production in the said region.