Potassium (K⁺) in Soil Profiles and Foliar Content as Related to K⁺ at Two Depths over Time in Coconut Plantations of Guerrero, Mexico

Potassium (K) is a key nutrient in maintaining high levels of turgor and adequate water levels to regulate sugar during cell division. It is the most required during reproductive stage in coconut. Despite its importance, very little is known about its dynamic in soils. This study aimed to assess the content of K in soil deep profiles complemented with individual samples (IS) at 0 - 30 and 30 - 60 cm depth, taken during different years (year 1 and 4) in coconut plantations of Guerrero, Mexico. A Random Systematic Two-Dimensional Method (RSTDM) was used to select IS. A Completely Random Design was for soil profiles while a Multifactorial Random Block Design was for IS. Foliar analysis was taken to remark the relationship between soil and plant in year 4. In Costa Chica region the Altos de Ventura (AV) location was selected (Profile 1); in Costa Grande, two profiles were described, one in Aguas Blancas (AB) (Profile 2) and another in Las Tunas (LT) (Profile 3). No statistics differences were found between profiles. The average available K in the profiles of AV, AB, and LT were: 0.34, 0.40, 0.51 Cmol∙Kg⁻¹, respectively; AV with the lowest and LT with the highest one. On the other hand, high statistic differences between factors (years, localities and depths) in the IS were found, but without interaction between factors. There was a decrease of K over time with, practically, a loss of 37% in all locations. Being 0.40 vs. 0.25 in AV, 0.37 vs. 0.23 in AB and 0.54 vs. 0.34 in LT until reaching the minimum of the Critical Level (0.25 - 0.86 Cmol∙Kg⁻¹) mainly in AV and AB. The leaves showed more K in LT with 0.99% while the other locations had 0.83% (AV) and 0.82% (AB), all below the critical level of 1.6% reported for Green Dwarf coconuts.