COMPARACIÓN DE DOS FUENTES FOSFATADAS EN SUELOS VOLCÁNICOS CULTIVADOS CON CAFÉ DEL SOCONUSCO, CHIAPAS, MÉXICO COMPARISON OF TWO PHOSPHATE FERTILIZERS IN VOLCANIC SOILS CULTIVATED WITH COFFEE, OF SOCONUSCO, CHIAPAS, MÉXICO

Volcanic soils of several coffee-producing regions of Soconusco, Chiapas, México, classified as Andisols, have peculiar physical and chemical characteristics and a udic moisture regime. The objective of this study was to evaluate the function of phosphorus and phosphorus-related problems in the cultivation of coffee (Coffea arabica). Physical and chemical properties of the volcanic ash soils under a representative coffee plantation were determined. Two sources of phosphate fertilizers (triple superphosphate, ST; rock phosphate, RF) were compared. Phosphorus content in soil and plant was assessed, as well as its effect in four seasons of the year over five years. Besides, the residual effect of the phosphate sources and the effect of organic fertilizer on phosphorus contents of soil and plant was compared. The commercial formula (18-12- 06) and two controls (18-00-12 and 00-00-00) were used. The study was conducted in the Municipality of Unión Juárez, Chiapas, México. An analysis of variance was performed with the data, and means were compared with the Tukey test. A high level of P fixation in the soil was found. The highest concentrations of P in the soil and coffee plant were obtained with 18-20-12 RF and 18- 20-12 ST. The highest concentrations of P were observed in June and September. There was better P residuality in the soil with RF than with ST, while with organic fertilizer there was no satisfactory response.