Potassium Supplying Power of the Major Upland Inceptisols of Puerto Rico

Abstract

Capacity of the nine most extensive upland Inceptisols of Puerto Rico to supply potassium (K) was determined through intensive cropping in pots with Pangola grass during 4 consecutive years. In addition, field experiments were conducted on two of these soils, Mucara and Pandura, for comparison. Seven of the lnceptisols tested formed under a udic moisture regime. They supplied an average of 279/kg of K/ha to Pangola grass during the first year, and then dropped to 110, 114, and 93 kg/ha for the second, third and fourth years, respectively. The average of 106 kg/ha for the last 3 years probably represents the long term capacity of this group to supply K to plants. The amount of K released by Mucara and Pandura soils (both udic lnceptisols) in the field experiments agreed fairly well with values obtained in the pot experiments. Two of the lnceptisols tested formed under a ustic moisture regime released and average of 507 kg of K/ha during the first year, and then 254, 233, and 140 kg/ha the last 3 years. The average K release per year for the last 3 years was 209 kg/ha. However, the long range K supplying capacity of these soils is probably lower than this value. The exchangeable K values obtained at the beginning of the pot experiment were significantly correlated with the amount of K extracted by Pangola grass during the first year of cropping in pots, whereas the HN0₃-soluble K values were correlated with the average release of K during the last 3 cropping years.