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Response of Onions to P Placement¹

Considerable variation in seedling size, vigor, and plant development occurs in onions (Allium cepa L.) where phosphate fertilizers are surface-applied and incorporated prior to planting. Our objective was to determine the influence of P rates and placement techniques on the growth and development of fall-seeded onions. During the fall of 1975 and 1977, two rates of P (21.8 and 43.6 kg/ha) were banded at planting at 0, 2.5, 5, 7.5, 10, and 15 cm directly below the seed and at 0, 2, 4, 6, and 8 cm laterally from the seed at a constant depth of 5 cm. The soil was a Aridic calciustoll, fine, mixed hyperthermic. Seedling growth and P uptake by onions were enhanced when P was applied in a band directly below the seed at a depth of 2.5 cm. Maximum yield was obtained when P was applied directly below the seed row at a depth of 2.5 to 7.5 cm. Yield was influenced more by P placement than rate of application. Maturity was effected by both depth and lateral placement of P. This experiment has shown that precise vertical and lateral placement of P must be achieved for optimum growth and development of onions.

Key Words: Onion nutrition • Allium cepa L.

² Associate professor, technician and associate professor, respectively, Texas A&M Univ. Agric. Res. and Ext. Cent, at Uvalde, TX 78801.

Received for publication January 8, 1979.