Effect of Deep Placement of N Fertilizers and Different Inoculation Methods of Bradyrhizobia on Growth, N₂ Fixation Activity and N Absorption Rate of Field‐grown Soybean Plants

Abstract

The effects of deep placement (supplied at 20 cm depth from soil surface below plants) of 100 kg N ha−1 of N fertilizers, urea, coated urea or calcium cyanamide (lime nitrogen) on the growth, nitrogen fixation activity, nitrogen absorption rate and seed yield of soybean (Glycine max L. Merr.) plants were examined by comparing them with control plots without deep placement of N fertilizer in sandy dune field. In addition, three different inoculation methods of bradyrhizobia were used for each N treatment: (1) transplantation of 10‐day‐old seedling in a paper pot with vermiculite inoculated with Bradyrhizobium japonicum USDA110, (2) direct transplantation of inoculated 10‐day‐old seedlings, and (3) transplantation of 10‐day‐old seedlings in a non‐inoculated paper pot. The deep placement of N fertilizers, especially calcium cyanamide and coated urea, markedly increased the growth and total N accumulation in shoot, roots and nodules, which resulted in an increase in seed yield. Daily N2 fixation activity and N absorption rate were estimated by relative abundance of ureide‐N analysed from the concentration of N constituents (ureide‐N, amide‐N and nitrate‐N) in root bleeding xylem sap and increase in total N accumulation in whole plants at R1, R3, R5 and R7 stages. The total amount of N2 fixation was about 50 % higher in the plants with calcium cyanamide and coated urea deep placements compared with control plants. Deep placement of slow release fertilizers kept nodule dry weight higher in the maturing stage of seed, possibly through abundant supply of photoassimilate to the nodules by supporting leaf area and activity until late reproductive stages. The results indicate that deep placement of calcium cyanamide or coated urea enhances N2 fixation activity, which ultimately increases the seed yield. The promotive effect was observed with the seedlings transplanted in paper pot with inoculum of bradyrhizobia within any treatments, although nodulation by indigenous rhizobia was observed in the plants transplanted with non‐inoculated paper pot.

Role of Nitrogen on Growth and Seed Yield of Soybean and a New Fertilization Technique to Promote Nitrogen Fixation and Seed Yield

“…Seed yield of soybean cultivated with deep placement of N fertilizers and different inoculation methods in three fields of Niigata in 2001. Data from Tewari et al [47][48][49].…”

“…The effects of different depths of placement of lime nitrogen at 10, 15, and 20 cm were compared in a rotated paddy field at the Niigata Agricultural Research Institute in 2003 [49]. In addition to conventional basal application of mixed chemical fertilizer (ammonium sulfate 16 k kgN ha ).…”

“…However, as the price of coated urea is relatively expensive about five times higher than urea, the cost of it may be a burden for farmers. Tewari et al compared the effect of deep placement of lime nitrogen (LN) with coated urea [41,42,[47][48][49][50][51]. Lime nitrogen has been produced by artificial nitrogen fixation, which was done by Frank and Caro in 1901 prior to the establishment of Harber and Bosch process to convert atmospheric N 2 to ammonia in 1906.…”

15N Analysis of the Promotive Effect of Deep Placement of Slow-Release N Fertilizers on Growth and Seed Yield of Soybean

“…Deep placement of LN which was performed in our previous experiments (Tewari et al 2002(Tewari et al ,2003(Tewari et al ,2004b, led to the same as or a higher level of plant growth and seed yield compared with the use of CU-100. In the field experiment conducted in a sandy dune field in Niigata in 200 1, the seed yield was significantly higher in the LN (3.32 t ha-') and CU (3.05 t ha-') treatments (Tewari et al 2004b).…”

Effect of placement of urea and coated urea fertilizers on yield and quality of soybean (Glycine max(L.) Merr.) seeds

“…Also since the nitrogen concentration in the surface layers did not change by this treatment, the nodulation and N2 fixation in the surface layers were not depressed, but rather promoted through the enhancement of plant growth and photosynthetic activity. The effect of deep placement of urea, coated urea, and calcium cyanamide was compared in a paddy field converted to an upland field (Tewari et al 2002), a newly reclaimed soybean field (Tewari et al 2003), and a sandy dune field (Tewari et al 2004). In all these experiments, deep placement of coated urea and calcium cyanamide led to the increase of seed yield compared to the control and deep placement of urea.…”