Fertilizers Affect Water and Substrate EC, pH, and Nutritional Concentrations for Nelumbo Production

Abstract

Sacred Lotus (Nelumbo nucifera Gaertn.) is an aquatic, herbaceous perennial considered to be one of the most valuable plants in the world. Each part of lotus is consumed throughout Asia for food or used for medicinal purposes. Effects of fertilizer type (conventional, organic, or no fertilizer), fertility rate, and water depth on water and substrate electrical conductivity (EC), pH, nitrate-nitrogen, and ammonium-nitrogen concentration were evaluated in greenhouse and outdoor studies to determine effect on potential lotus growth. All fertilizers influenced water and substrate EC, pH, and nutritional concentration. According to substrate analysis, EC rates were above recommended levels. Both organic treatments resulted in high sodium levels and the organic Nature Safe treatment resulted in higher levels of most macronutrients by termination of all studies. Results indicated increased water volumes led to reduced nutrient concentration and availability. All measured parameters decreased with increased water depths due to greater water volume and dilution factors and researchers determined a water depth of 15.2 cm (6 in) resulted in satisfactory EC levels for lotus production. There would be no additional benefit in maintaining shallower or greater depths. EC is a strong factor influencing lotus growth and with shallower depths, EC could rise close to toxic levels as was revealed in the organic Medina Growin’ Green treatment.

Toxic EC level of 1.0 mS•cm-1 was surpassed with increasing rates to 1.3 kg•m-3N among both conventional and organic treatments. Under greenhouse conditions with moderate temperatures, researchers determined 0.6 kg•m-3N was a potentially acceptable rate to target for the fertilizers tested for outdoor production. The rate resulted in toxic levels of soluble salts for some fertilizers and required removal and replacement of plants, substrate, and fertilizer; adjusting the rate to 0.4 kg•m-3N. A rate of 0.44 kg•m-3N resulted in acceptable EC levels for all fertilizers trialed and tested. More research needs to be conducted to determine the interactions, cause and effect of the many variables on specific fertilizer nutrient release to target a satisfactory level to maximize growth while minimizing any potential crop damage due to an increase in EC to toxic levels.