Phosphorus (P) and potassium (K) impact on alfalfa yield dynamics and nutrient utilization
Abstract
The objectives of this study were to determine the long-term impact of P and K nutrition on yield and yield components, and taproot physiology and biochemistry of alfalfa. Treatments were the factorial combinations of four P rates (0, 25, 50, and 75 kg P ha−1) and five K rates (0, 100, 200, 300, and 400 kg K ha−1) arranged in a randomized complete block design with four replications. Forage harvests occurred four times annually, and yield, mass shoot−1, and shoots areas −1 were determined. Roots were dug and plant populations determined in early December and following the first forage harvest (late May) in each year as well as following each forage harvest in 2002 and 2003 to ascertain when alfalfa populations were declining. Taproots also were sampled after defoliation in June 2002 and 2003 (Days 0, 1, 3, 6, 10, 14, 21, and 30), September 2002 and 2003 (Days 0, 7, 14, 21, 28, 42, 56, 70, and 84), and weekly following the ending of winter dormancy in 2003 and 2004 through the first forage harvest in May 17. Additions of P and K increased alfalfa yield. Yield was most positively associated with yield per shoot not shoots per area or plants per area. Plant populations were consistently decreased with addition of P, but were maintained at higher levels with K fertilizer application. Decreases in alfalfa population occurred primarily during the summer and not over-winter. Addition of K fertilizer increased organic taproot reserves (starch, sugar, protein, and amino-N) during the summer, fall acclimation, and spring regrowth sampling periods with the exception of taproot sugar concentrations, which generally decreased P and K fertilization. Additions of P did not consistently influence any of the taproot C and N pools across sample times. Taproot VSP protein abundance was dramatically reduced after defoliation in alfalfa fertilized with P, but not K, while taproot VSP levels in alfalfa proved both P and K were relatively constant after shoot removal. Knowledge of the mechanisms that enhance alfalfa performance and how these mechanisms are influenced by P and K fertilization will lead to a better understanding of why these nutrients are vital to increase yield and persistence in alfalfa.
Degree
Ph.D.
Advisors
Volenec, Purdue University.
Subject Area
Agronomy
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.