Mombaça Grass Responds to Partial Replacement of K+ by Na+ with Supplemental Ca2+ Addition in Low Fertility Soil

Partial replacement of potassium by sodium may be an alternative to reduce the cost of pasture fertilization and reduce the dependence on imported potassium sources. The objective of this study was to evaluate different sources and doses of calcium as enhancers of sodium effect on the partial replacement of potassium by sodium. Here, Mombaça grass (Megathyrsus maximus) was grown on low fertility soil. The experiment was conducted in a factorial (3 × 5) based on a completely randomized design with 4 replications as follow: three sources of Ca2+ (dolomitic limestone, agricultural gypsum and calcium chloride), five doses of Ca2+ (0, 10, 20, 30 and 40 mg dm-3) and two additional treatments (fertilization with 100% of K+ without application of Ca2+ and one control without any fertilization). Potassium was partially replaced (25%) by Na+ prior to Ca2+ additions. Plant height, growth rate, dry weight, Na+, K+, K+/Na+ and shoot proline contents were evaluated as well as Na+ levels and the electrical conductivity of the soil. The results show that the addition of Ca2+ provided better plant development when K+ was partially replaced by Na+ and that the supply of Ca2+ reduced the absorption of sodium by plants. The partial replacement of K+ by Na+ did not increase soil salinity or caused stress to the plants.