Phosphorus Fertilization and Sugar Yields of Fall Planted Sugarbeets 1

Fall planted sugarbeets ( Beta vulgaris L.) are commonly subjected to low winter soil temperatures which contribute to low available soil P. Two field experiments were conducted near Phoenix, Ariz. to determine the effects of P fertilizer and feedlot manure on residual available P and sugarbeet production. Sugarbeets grown on a Laveen clay loam (Coarseloamy, mixed, hyperthermic Typic Calciorthid) soil that had not received P fertilizer for 10 years were compared with those grown on the same soil that had received annual applications of P fertilizer prior to that crop. The effect of residual P was studied at four levels of N (0 to 300 kg N ha ‐1 ). Another experiment on the same soil type evaluated residual P from manure applied at rates of 22,45, and 67 Mg ha ‐1 two seasons prior to that crop. Maintaining a high level of residual P by applying P fertilizer to other crops in the rotation was an effective method of avoiding P deficiency in sugarbeets. Both sucrose concentration and sugar yield were influenced by high residual soil P. Soluble P measurements in petioles collected when soils were cold were generally related to sucrose concentration. Winter month soil temperatures as low as 6 C were observed in the Phoenix area. Sugarbeets responded equally to P fertilized soil relatively high in residual soil P compared with soil having residual P from feedlot manure with P fertilizer applied 2 Years earlier.