INFLUENCE OF POTASSIUM FERTILIZATION ON LEAF TO STEM RATIO, NODULATION, HERBAGE YIELD, LEAF DROP, AND COMMON LEAF SPOT DISEASE OF ALFALFA

Abstract

An on-farm field experiment was conducted to investigate the effects of potassium (K) application on nodulation, leaf to stem ratio, herbage yield, leaf drop, and disease severity of common leaf spot disease (caused by fungus Pseudopeziza medicaginis) in dryland alfalfa (cv. Genesis) (Medicago sativa L). The soil of the experiment site was dark greyish clay with a pH of 7.3 (1 : 5 Calcium chloride). Topsoil (0–15 cm) had 1.03 meq 100 g−1 K and subsoil (15–30 cm) had 0.88 meq 100 g−1 K (Ammonium Acetate extracted K). The experiment was conducted in a randomized complete block design with 6 rates of K supply (0, 20, 40, 60, 80, and 100 kg K ha−1). The source of K was potassium chloride. Potassium application has a significant beneficial impact on nodulation, herbage yield, and leaf to stem ratio of alfalfa plants. There were also significant reductions in leaf drop and common leaf spot disease severity of alfalfa with K application. The adequate K rates for reducing the common leaf spot disease severity and leaf drop were observed to be 75 kg K ha−1 and 71 kg K ha−1 respectively, while the adequate K rate for nodulation and herbage yield was comparatively lower (61 kg K ha−1). These results suggest that common leaf spot disease severity, nodulation, and leaf drop have an association with K nutrition of alfalfa. These associations may have widespread implications in managing the growth, herbage yield, and potential nitrogen contributions of alfalfa rotations in low K soils.