In order to evaluate the beneficial effect of deep placement of coated urea fertilizer on soybean plant (Glycine max (L.) Merr. cv. Enrei) cultivation, a field experiment was conducted with three fertilizer N treatments: control, conventional basal dressing of 16 kg N ha-I as ammonium sulfate; basal deep placement of 100 kg N ha-1 as 100 d type coated urea; and top dressing of 100 kg N ha-1 as 70 d type coated urea just before the flowering stage. The seasonal variation in the N2 fixation activity by the nodules and N absorption rates by roots were estimated by the determination of the relative ureide-N abundance in the root bleeding xylem sap by calculating the increase in total N accumulation. The N recovery rate from fertilizers was measured by the 15N tracer method. The N recovery rate in the plants with deep placement of coated urea was about 62%, and much higher than that of the plants with top dressing of coated urea (33%) at the R7 stage. Top dressing treatment depressed the N2 fixation activity during the maturing stage and the N absorption rate was higher than that of the control plants. On the other hand, deep placement of coated urea did not depress the N2 fixation activity throughout the growth stages until maturity, though N from fertilizer was actively absorbed. Consequently, the plants with deep placement of coated urea accumulated more N both from N2 fixation and N absorption than the plants with control and top dressing treatments. Seed yield was higher in the deep placement (592 g m-2) compared with the control (480 g m-2) and the top dressing (531 g m-~) treatments. The basal deep placement of coated urea for soybean cultivation appears to be beneficial by supplementing soybean N without concomitant depression of N2 fixation, and by increasing the seed yield. High recovery rate of fertilizer N is also desirable from the economical and ecological view points.

The objective of these studies is to increase the productivity of soybean [ Glycine max (L.) Merr. cv. Enrei] with good quality by the application of controlled release nitrogen fertilizers. Soybean was grown in an upland field converted from a drained paddy field in Niigata. The fertilizer treatments were as follows: (a) control, conventional basal dressing of ammonium sulfate (16 kg N/ha); (b) deep placement, deep placement of coated urea, 100 day type (100 kg N/ha) with basal dressing of ammonium sulfate (16 kg N/ha); (c) top dressing, top dressing of coated urea, 70 day type (100 kg N/ha) just before the flowering stage with basal dressing of ammonium sulfate (16 kg N/ha).We employed the following methods and materials: "lSN-labeled fertilizers," to estimate the amount of N derived from fertilizers; "N-balance method" using the nodulating and non-nodulating isogenic line cv. T202 and T201, to estimate the amount of fixed N~ by root nodules; "relative ureide method" to determine the relative content of ureide-N in the root bleeding sap, in order to estimate the activity of the root nodules.The accumulation of dry matter and total N was the highest in the plants with the deep placement treatment, in which the promotion of leaf growth and retardation of senescence were observed during the maturation stage. The seed yield in this treatment which was 424 g/m 2, surpassed those in the control (373 g/m 2) and the top dressing (359 g/m s) treatments. The absorption efficiency of fertilizer N in the deep placement treatment was 49~o, which was much higher than that in the top dressing treatment (27~o). However, the contribution of fertilizer N to the total N absorption was found to be low at 16~o in the deep placement, and 11~o in the top dressing treatment at the R7 stage. In the deep placement treatment, a marked increase in N accumulation in shoots was observed especially from the R3 till R7 stages. The N-balance of the nodulating and non-nodulating cv. T202 and T201 at the R7 stage suggested that more than 80% of the accumulated N was derived from the fixed N2 by root nodules. On the other hand, in the top dressing treatment, the amount of N accumulated during the R3 to R7 stages was lower than that in the other treatments, possibly due to the depression of N2 fixation by top dressing.Abbreviations: DW: dry weight; cu-100: coated urea, I00 day type; cu-70: coated urea, 70 day type; Cont.: control; Deep pl.: deep placement of cu-100; Top dr.: top dressing of cu-70; LAI: leaf area index; DAS: days after sowing. Y. TAKAHASHI et al.The results suggested that the deep placement of coated urea as basal application improved soybean growth, and did not depress markedly the nitrogen fixation activity during the maturation stage, hence the increase of seed yield. Top dressing of coated urea inhibited the nodule activity after the R3 stage, and consequently the seed yield did not increase.

No abstract

No abstract