Phosphorus and Compost on Potatoes

The potato industry in southern Alberta has expanded from about 22,000 acres in 1997 to around 43,000 acres in 2001. Soil testing laboratories and agronomists in Alberta are uncertain as to what phosphorus (P) recommendations should be used for potatoes. Petiole testing for P has only recently been used in the area. Standards for what are adequate levels of P in petioles are not adequately defined. The objectives of this project were to examine the effect of high rates of P fertilizer on yield and quality of potatoes, determine critical soil and tissue levels at which a response to P can be expected, and to compare compost with mineral P fertilizer as a means of supplying P to potatoes.

At Brooks from 1996 to 1999, soil P and tissue P on potatoes were measured. Tissue P frequently was adequate (according to U.S. standards) in early July, but sometimes became deficient later in the season. In some cases, strips of higher rates of P were applied, with no response in yield of tubers. In 2000, three field scale experiments were conducted, two were on soils with 20 to 30 parts per million (ppm) P and the third on a soil with 57 ppm P (modified Kelowna). Two additional field trials were completed in 2001. Five rates of P and three rates of compost were applied. Tuber yield was maximized at the lowest P rate (45 lb P₂O₅/A) in both years. Petiole P levels increased with applications of fertilizer or compost. Assessment of the 2001 crop data is expected to help clarify how potato P should be assessed in irrigated fields of southern Alberta. AB-21F