Effect of Spray/Planting Intervals and Various Grass Sods on No‐Till Establishment of Alfalfa1

Abstract

AbstractConsistently successful legume establishment using sod‐seeding techniques has been difficult to achieve. There is increasing evidence that substances released from herbicide‐treated grass swards have an inhibitory effect on legume germination and seedling growth. Field, greenhouse, and laboratory studies were undertaken to evaluate the effect of spray/planting intervals of 1, 7, 14, and 28 days on the establishment of alfalfa [Medicago sativa] when seeded into sods of orchardgrass [Dactylis glomerata L.] timothy [Phleum pratense L.], and Kentucky bluegrass [Poa pratensis L.], and to examine a possible phytoxic effect of glyphosate [N(phosphonomethyl) glycine] on germination and sod seedling growth of alfalfa. Identical field tests were conducted in the spring of 1981 and 1982 on an Enfield silt loam (coarse‐silty over sandy or sandy skeletal, mixed, mesic Typic Dystrochrept). With few exceptions, the number of alfalfa seedlings, seedling development and alfalfa yields increased as the interval increased between spraying of the sod and seeding. Rate of alfalfa seedling development was reduced in all sods, with timothy being the most inhibitory. Two harvests of alfalfa following seeding confirmed that yields were reduced by killed sod, particularly in orchardgrass and timothy, at early intervals after spraying. There were significant positive correlations between seedling numbers and first harvest yields and between seedling development and first harvest yields of alfalfa. Alfalfa germination was inhibited, seedling development was delayed and total dry weight was reduced when glyphosate‐sprayed grass shoot tissue was soil incorporated in growth chamber seeding tests. However, unsprayed fresh grass tissue was more inhibitory than sprayed grass tissue. Alfalfa germination and hypocotyl and radicle length were reduced by aqueous extracts from glyphosate‐sprayed grass shoot tissue but less so than with extracts from unsprayed herbage. No evidence for a phytotoxic effect of glyphosate could be detected, and it appeared that the inhibition of alfalfa germination and seedling growth was due to allelochemics released from fresh herbage and during the early stages of decomposition.