Monday, November 13, 2006 - 1:00 PM

Impact of Long-Term P and K Fertilization on Alfalfa Forage Quality.

Sofia Lissbrant1, Samuel Stratton2, Suzanne Cunningham1, and Jeffrey Volenec1. (1) Dept. of Agronomy, Purdue University, 915 West State St., West Lafayette, IN 47907-2054, (2) FFR Cooperative, 4846 East 450 North, 4846 East 450 North, Lafayette, IN 47905, United States of America

Phosphorous (P) and potassium (K) increase alfalfa (Medicago sativa L.) yield and persistence but little information is available regarding how forage quality is affected by P and K fertilization. The objectives of this study were to investigate how forage quality is influenced by P and K fertilization and stand age.   
A factorial combination of four P treatments (0, 25, 50, and 75 kg P per ha per year) and five K treatments (0, 100, 200, 300, and 400 kg K per ha per year) were replicated four times. Beginning in 1998, herbage samples were collected in May, June, July and September. Samples were dried, ground and analyzed for crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) using near-infrared reflectance spectroscopy. Tissues also were analyzed for P and K concentrations using ICP. Fertility and stand age both influenced forage quality. Crude protein did not change between years, but increased in Harvest 3 and 4, while NDF, ADF and lignin were lower in these harvests. Concentrations of NDF, ADF, and lignin decreased with stand age. Averaged over years and harvests, the highest CP values were found in the low fertility treatments, however, CP concentrations increased with P fertilizer application within K treatments. The NDF and ADF values were lowest in the low fertility treatments and increased with P and K fertilization. Addition of P fertilizer increased NDF and ADF concentrations within K treatments. Acquiring information regarding the influence of P and K fertilization on forage quality will contribute to a better understanding of the impact of fertilization on alfalfa performance and utilization.