Alfalfa yield components and soil potassium depletion as affected by potassium fertilization.

Abstract

Potassium fertilization recommendations for alfalfa (Medicago sativaL.) vary depending on the area of production, soil levels, and crop management. The objectives of this study were to determine the impact of K fertilization on irrigated alfalfa yield, yield components, and soil exchangeable K (Ke) values in a Mediterranean climate. A field experiment was conducted during a period of 4 yr (2002–2006) in Spain, on a soil with moderate levels of Ke(161 mg K kg –1). The treatments applied were five annual rates of K (0, 100, 200, 300, and 400 kg K ha–1). Total 4-yr dry matter (DM) yields averaged 74.9 Mg ha–1 without differences between K fertilizer rates, although the unfertilized control produced the lowest DM yields. The 4-yr crop uptake of K reached 1738 kg ha–1 with the application of 400 kg K ha–1yr–1 , and 756 kg K ha–1for the 0 K fertilization. The removal was greater than the K applied. The results suggest that large amounts of K should not be applied to alfalfa because the crop uses excess K without increasing yield. Soil Ke concentrations decreased every year for all K rates except for the highest treatmentof 400 kg K ha–1yr–1. Lack of K fertilization did not affect stand density but the shoot weight was the yield component most closely related to K fertilization.