Effect of K fertilization on yield and leaf nutrient concentrations of potatoes grown on a sandy soil

A large percentage of winter and spring potatoes (Solanum tuberosum, L.) grown in the USA is produced in northeast Florida (NEF) on sandy soils with low cation exchange capacity. Maintaining adequate K nutrition is a major concern. A study was conducted on an Elzey fine sand (sandy, siliceous, hyperthermic Typic Humaquept) in NEF to relate yield and leaf K to soil and fertilizer K levels. In 1981, Mehlich-I soil K in the 0–15 cm depth averaged 73 mg/kg. Yields of 35 t/ha were obtained without any K fertilization and no response to K sidedressed at rates up to 70 kg/ha was obtained. In the following three years, soil K prior to fertilization was < 40 mg/kg. In 1982 and 1983, significant differences in yield were obtained as a result of K fertilization at planting at rates up to 186 kg/ha. In 1984, no yield differences were obtained with K fertilizer rates ranging from 94 to 280 kg/ha. Differences in maximum tuber yields from year to year were related to the number of growing-degree days accumulated between planting and harvest. Yield-leaf K relationships for leaf samples taken late in the season showed that the critical leaf K concentration for 35 t/ha yields was no more than about 20 g/kg; that for yields approaching 40 t/ha was no more than about 45 g/kg. The results of this study indicated that current K fertilizer recommendations are higher than necessary for the yields being obtained by most NEF potato growers.