Impact of long-term phosphorus and potassium fertilization on growth, persistence, and physiology of alfalfa (Medicago sativa)
Abstract
Phosphorus (P) and potassium (K) are essential for alfalfa growth, however, the long-term effects of application of these nutrients remain unclear. The objectives of this study were: (1) to characterize physiological attributes of alfalfa stands that differ in agronomic performance; (2) to determine the effectiveness of using herbage P and K concentrations as a diagnostic of alfalfa performance; (3) to investigate the effect of stand age and P and K fertilization on forage quality; and (4) to study the effect of P and K fertility on heat-stress tolerance of alfalfa. For Objectives 1 to 3, a 7-year field study was conducted using a factorial combination of four P treatments and five K treatments. Herbage and soil samples were collected and yield and yield components determined. For Objective 4 a controlled environment study was conducted using four contrasting P and K fertility treatments and two cultivars grown in high, intermediate, or cool temperature regimes. Yield components, herbage P and K concentrations, and taproot carbon (C) and nitrogen (N) reserves were analyzed before, during, and after exposure to the temperature regimes. The long-term field study revealed that balanced fertility is important for maximizing yield and persistence of alfalfa. Cluster analysis showed that high fertilizer application did not always result in highest yield, indicating that factors other than P and K fertilizer application affected plant performance. Herbage P and K concentrations and the ratio between these parameters could categorize plots as having acceptable or unacceptable yield. Stand age increased forage quality, especially at low fertilizer rates and was associated with reduced yield. However, higher yield compensated for lower forage quality in well-fertilized stands by increasing the total amount of nutrients produced per hectare. The controlled environment study showed that High temperature and low P and K fertility decreased biomass production. Reduced biomass also was associated with low taproot amino-N concentrations.
Degree
Ph.D.
Advisors
Brouder, Purdue University.
Subject Area
Agronomy
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