Leachate Concentrations of Ammonium, Nitrate, and Phosphorus as Affected by Nutrient Release From Four Different Types of Controlled-Release Fertilizers and Crop Development of Containerized Waxleaf Privet

Concentrations of ammonium, nitrate, and phosphorus in irrigation leachate were measured weekly over a 47-week period from a high-fertility, neutral-pH substrate into which four types of 12-month controlled-release fertilizers (Osmocote, Nutricote, Polyon, or Multicote) were incorporated. Containers of substrate were placed outdoors, with one-half of the 2.4-L containers planted with liners of waxleaf privet (Ligustrum japonicum 'Texanum'), while one-half of the containers remained unplanted. In substrate without plants, concentrations of ammonium were highest during the first 23 weeks of the study, and remained low thereafter. Nutrient uptake by developing root systems significantly reduced concentrations of ammonium in leachate from week 6 to week 20, including some notable reductions during the period of maximum nutrient release. Beyond week 20, reductions in ammonium concentration in leachates with the presence of growing plants often occurred, despite the already low concentrations noted in leachate from substrate without plants. Concentrations of nitrate in leachate from substrate without plants generally remained low during the first 4 weeks, followed by maximum levels and fluctuations through week 23, and then lower levels with fluctuations through the remainder of the study. Nutrient update by the growing plants resulted in more consistent reductions in leachate nitrate concentrations from week 27 to the end of the study. Concentrations of phosphorus in leachates from substrate containing Multicote and no plants were often higher than with substrate containing other fertilizers, with reductions in these same concentrations often noted with the presence of growing plants. Reduced phosphorus concentrations in leachates from substrate with plants tended to be seen more often from week 18 to the end of the study than in prior weeks.