Abstract
ABSTRACT The physiological seed quality can be altered by nutritional management of the soybean crop, especially by the fertilization with nitrogen (N), which is a structural component of several organic compounds, including proteins, and has an important catalytic role in the activation of several enzymes. The aim of this research was to investigate the effects of sources and application rates of mineral N fertilizer associated with inoculation of Bradyrhizobium spp. on physiological quality of soybean seeds. The treatments were arranged in a completely randomized block design, in a 3 × 5 factorial arrangement [three N fertilizer sources (Bradyrhizobium spp. inoculation; Bradyrhizobium spp. inoculation + urea application; and, Bradyrhizobium spp. inoculation + ammonium sulfate application) and five N application rates (0, 50, 100, 150 and 200 kg N ha-1)], with four replicates. Nitrogen fertilizer was applied in topdressing at R2 stage when soybean plants were in full flowering. The quality parameters evaluated in soybean seeds were: 1,000-seed mass, seed protein content, germination, first germination count test, seedling emergence, emergence speed index, accelerated aging, electrical conductivity, vigor and viability of seeds by tetrazolium test. The application of 50 kg N ha-1 of mineral fertilizer (ammonium sulfate or urea) associated with the Bradyrhizobium spp. inoculation enhanced the physiological quality of soybean seeds, resulting in higher seed germination percentage and higher emergence and seedling emergence speed index. The application of ammonium sulfate or urea (50 kg N ha-1) at full flowering of soybean plants inoculated with Bradyrhizobium spp. can improve the physiological quality of soybean seeds.
Highlights
Soybean is the main oilseed crop in Brazil and the world, especially on account of wide socioeconomic importance for the world agricultural sector
Canonical correlation analysis was used to verify the contribution of each dependent variable measured in the physiological quality tests of soybean seeds as a function of N application sources (Figure 1) and N fertilizer rates (Figure 2)
When N was supplied only by the Bradyrhizobium spp. inoculation, the soybean plants had seed production with a higher viability percentage by the tetrazolium test (TT1-5) (Figure 1). These higher percentage of viable seeds from plants inoculated only with Bradyrhizobium spp. may indicate that all the soybean N supply was fully supplied by the biological N2 fixation process and by the small rate of N fertilizer applied at sowing (18 kg N ha–1 as monoammonium phosphate), which ensured the appropriate N nutrition of plants and formation of viable seeds
Summary
Soybean is the main oilseed crop in Brazil and the world, especially on account of wide socioeconomic importance for the world agricultural sector. The use of high-quality seeds is essential for the proper establishment of soybean agricultural fields (Zuffo et al, 2017). The proper plant establishment and development depends on balanced mineral nutrition management and this factor is essential for the commercial production of seeds with high vigor and high physiological quality (Carvalho; Nakagawa, 2012). Nitrogen stands out among the essential nutrients for plants, especially on account of its crucial role in the physiological and biochemical metabolism of plants and its participation as a structural component of chlorophylls, proteins, and organic compounds (Leghari et al, 2016). The N fertilization can raise the development and productivity of the soybean crop, counting enhance the size and the quality of seeds (Marcos-Filho, 2015). Endosperm and embryo formation and accumulation of reserve compounds is dependent an appropriate supply of nutrients (Carvalho; Nakagawa, 2012)
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