Subtropical seed-bank of a Bay of Plenty dairy farm

Abstract

An examination of the grass seed-bank on a Bay of Plenty dairy farm in October 1994 found seed numbers of all grass species were greatest in the top O-50 mm of the soil profile and declined steeply at two lower sampling depths (5 l-150 mm, 15 l- 250 mm). C, grass species comprised 58% of the total viable seed in the upper sampling layer and greater than 80% in the other two horizons. Panicum dichotomiflorum was the dominant C, grass, especially at the lowest sampling depth where it comprised over 90% of the C, seeds and 78% of the total seeds found. Previous management was also an important influence on both the total seed loading and its distribution within the soil profile. Paddocks cultivated within the last 4 years had more total viable seeds at all depths and more Panicum dichotomiflorum seed at the deeper sampling depths than paddocks not cultivated within the last 4 years. The almost total absence of perennial ryegrass (Loliumperenne) seed indicates that it has a very short residual life in the seedbank. Therefore, if ryegrass plants are not maintained by vegetative propagation ryegrassbased pastures are susceptible to invasion from species that have a long residence time in the seedbank. These results also show that seed-bank surveys provide a method for assessing the potential changes in botanical composition of pastures and the geographical distribution of species such as subtropical grasses that is independent of the growing conditions at the time of sampling. Keywords: C, grasses, Panicum dichotomiflorum, seed-bank, subtropical grasses