Effect of Deep Placement of Controlled Release Nitrogen Fertilizer (Coated Urea) on Growth, Yield, and Nitrogen Fixation of Soybean Plants

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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: "^<15>N-labeled fertilizer," 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_2 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^2) treatments. The absorption efficiency of fertilizer N in the deep placement treatment was 49%, which was much higher than that in the top dressing treatment (27%). However, the contribution of fertilizer N to the total N absorption was found to be low at 16% in the deep placement, and 11% 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 N_2 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 N_2 fixation by top dressing. 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.
社団法人日本土壌肥料学会の論文

Effect of Deep Placement of Controlled Release Nitrogen Fertilizer (Coated Urea) on Growth, Yield, and Nitrogen Fixation of Soybean Plants

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