Effect of basal side-dressing of various types of coated urea fertilizer on shoot growth, yield components and seed composition of soybean (Glycine max (L.) Merr.)

Application of nitrogen (N) fertilizer at different times affected the shoot characters, yield components and seed composition of the soybean cultivar "Enrei" and its non-nodulating line "En1282". Soybean plants were cultivated using various types of coated urea fertilizers for controlled released of N. The control treatment consisted of basal side-dressing of readily available mixed fertilizer, which contained 1.6 g N m⁻², 6.0 g P₂O₅ m⁻² and 8.0 g K₂O m⁻². Various types of coated urea fertilizers were applied with basal side-dressing of 6 g N m⁻² in addition to the mixed fertilizer. The types of coated urea fertilizers were as follows: linear release types CU70, CU100 and CU140, and sigmoid release types CUS80, CUS100 and CUS120. A major part of the N from CU70 and CU100 was released before the middle-stage of growth (beginning of pod stage), whereas CUS80 and CUS100 released N at approximately the middle-stage and CUS120 released N after the mid-stage. CU140 fertilizer is a uniform release type throughout the growth period. At the middle stage of growth, the chlorophyll content (leaf color) of En1282 was high with CU100 treatment, while the CUS100 treatment led to high chlorophyll content during the filling period. Leaf chlorophyll content of Enrei tended to increase with the CUS120 treatment during the filling period. The N₂ fixation activity of nodulating Enrei, which was estimated using the relative ureide method, significantly decreased in the CU70, CU100 and CU140 treatments compared with the control at the flowering stage. At the beginning of the pod stage, treatment with CUS120 tended to lead to a higher N₂ fixation activity than the control, whereas the CUS80 and CUS100 treatments depressed the N₂ fixation activity during the seed filling period. The amount of N that accumulated in the shoots in all the coated urea treatments increased significantly compared with the control treatment in En1282 at the beginning of the maturity stage, whereas in Enrei it increased significantly only in CUS120 compared with the control. The yield was significantly higher in all the coated urea treatments compared with the control (49 g m⁻²), particularly in the CUS80 treatment (184 g m⁻²) in which N supply from the flowering period to the beginning of the pod stage resulted in the highest yield in En1282. In addition, in Enrei the seed yield increased significantly in each coated urea treatment and the largest increase was induced by CUS120 (498 g m⁻²) compared with the control (363 g m⁻²). In non-nodulating En1282, the amount of N released from flowering to the beginning of the pod stages showed a significant correlation with the total number of nodes, seed yield and seed weight. In nodulating Enrei, there was a significant relationship between N release from the beginning of the pod to the beginning of the maturity stages and the length of the main stem, seed yield and seed protein content. There was no significant difference in the free amino acid and total free sugar contents of seeds among the various fertilization treatments. Although the rate of the β-subunit of the β- conglycinin of storage protein increased significantly with the release of N from coated urea during the second half of the growth period in the seeds of En1282, there was no relationship with fertilization in the seeds of Enrei.