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This article in AJ

  1. Vol. 72 No. 2, p. 271-275
    Received: Nov 9, 1978

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Foliar Fertilization of Soybeans: Absorption and Translocation of 15N-Labeled Urea1

  1. B. L. Vasilas,
  2. J. O. Legg and
  3. D. C. Wolf2



Foliar fertilization offers a possible means of increasing soybean (Glycine max (L.) Merr.] yields, but little is known of the utilization efficiency of foliarapplied nutrients. Field experiments were conducted in 1976 and 1917 to determine percentage recovery of foliar applied 15N-labeled urea by soybeans and translocation of 15N within the plant. Foliar treatments containing N, P, K, S or P, K, S were applied four times during growth stages R-5 to R-7. Urea, potassium polyphosphate and potassium sulfate were used to supply 84 + 9 + 28 + 5 kg/ha of N + P + K + S, respectively. The P, K, S treatment was similar except that urea was excluded

In 1976, the two foliar treatments tested on the cultivar ‘Williams’ did not result in a significant increase in seed yieId over the control value of 3,294 kg/ha. In 1977, using the cultivar ‘Kent,’ the N, P, K, S treatment resulted in a significant yield increase of 1,045 kg/ha over the control value of 3,203 kg/ha. Results from the P, K, S treatment, although consistently higher than control values, were not significantly different at the 5% level in either year. Of the total 15N aplied, 44 and 67% were recovered in the plants in 1976 and 1977, respectively. Approximately 94% of the recovered 15N ultimately was found in the seed. A maximum of 0.7 kg/ ha of the fertilizer N was translocated to the roots

In a separate experiment, (15NH4)2SO4 was sidedressed at the rate of 112 kg N/ha at weekly intervals to different experimental units during late R-4 to R-7 stages. The uptake of 15N decreased from 39 kg/ha with the first application to 19 kg/ha with the last application, but the rate of 15N uptake did not change appreciably with time. Total N in the plants was not influenced by the (14NH4)2SO4 applications. The data indicated that changes in the rate of nutrient absorption by roots during pod-fill were minimal and unlikely to be a major factor in determining the effectiveness of foliar fertilization.

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