Establishment of Sod‐seeded Alfalfa at Various Levels of Soil Moisture and Grass Competition1

Abstract

AbstractAlfalfa (Medicago sativa L.) establishment in competition with grass sods is not always successful, especially under conditions of soil moisture deficiency. Our objective was to evaluate the effect of soil moisture concentration and grass competition on alfalfa establishment and yield when it was interseeded into perennial grass sods.In a greenhouse experiment, alfalfa was seeded into Kentucky bluegrass (Poa pratensis L.) or smooth bromegrass (Bromus inermis Leyss.) sods which had been sprayed with 0, 0.6, and 2.2 kg/ha glyphosate [N‐(phosphonomethyl)glycine]. Three soil moisture regimes were established by watering to field capacity when soil moisture tensions reached 0.1, 1, and 12 bars. Grass‐shading treatments were also applied.At two field locations alfalfa was seeded into an unimproved Kentucky bluegrass, smooth bromegrass, and quackgrass (Agropyron repens L.) pasture and into a smooth bromegrass pasture. The soil at both locations was a Waukegan silt loam (Typic Hapludoll). Three levels of grass suppression were obtained by spraying with 0, 0.8, and 3.3 kg glyphosate/ha. Soil moisture regimes consisted of watering to field capacity when soil moisture tension reached 1 and 15 bars.Under shaded conditions in the greenhouse and with low grass suppression (no glyphosate) in the field, moisture did not significantly affect alfalfa establishment or dry matter yield. However, when shading was eliminated or grass suppression increased, low soil moisture tensions resulted in increased legume yields.In the greenhouse, alfalfa dry matter yields and root weights were generally greater when it was seeded into Kentucky bluegrass compared to smooth bromegrass. Smooth bromegrass was more tolerant of glyphosate application than Kentucky bluegrass. When seeded into smooth bromegrass, alfalfa yields from low and medium moisture level treatments were not significantly different, but when seeded into Kentucky bluegrass yields from high and medium moisture levels were significantly greater than for the low moisture treatment.Our results show that both adequate soil moisture and reduced grass competition for light are important for successful alfalfa sod‐seeding.