NITROGEN UPTAKE OF MESQUITE SEEDLINGS AT CONVENTIONAL AND EXPONENTIAL FERTILIZATION SCHEDULES

Exponential nutrient additions have been shown to induce steady-state nutrition in plants and enhance seedling growth and nutrient status, which suggests improved nutrient efficiencies during the growing season. The objective of this study was to compare periodic growth, plant nutrient status, and N uptake of desert mesquite (Prosopis chilensis Mol.) seedlings that received 200 mg N seedling-1 as complete fertilizer delivered either conventionally (as single dose or constant top dressing) or exponentially (as pure or modified exponentially increasing additions) during a 12-wk rotation. Steady-state nutrition (characterized by a stable tissue nutrient concentration) was induced for the cultural period in the modified-exponential fertility regime. The nutrients were supplied exponentially except for higher initial amounts that compensated for the incomplete accessibility of growing medium to the small root systems. These seedlings showed consistently higher N accumulation that matched dry-matter production, reflecting higher fertilizer-N uptake efficiency throughout the growing season. During the same growing season, pure exponential nutrient-addition rates appeared to achieve steady-state conditions 4 wk later because of incomplete interception of applied nutrients by small root systems during establishment. Conventional fertility regimes caused nutrient dilution in plants with time. Nutrient uptake did not match growth in these seedlings, resulting in nutrient stress at varying stages of seedling development.