Weed seedbank estimation, spatial distribution, decline and potential for predicting future weed populations
A. RahmanA, T.K. JamesA, G. BourdôtB and N. GrbavacC
A AgResearch, Ruakura Research Centre, Hamilton, New Zealand.
B AgResearch, Canterbury Agricultural and Science Centre, Lincoln, New Zealand.
C MAFQual, Official Seed Testing Station, Palmerston North, New Zealand.
Seedbank species composition and density were determined in soils collected from five arable sites in 1994 and from a further six sites in 1995. The methods used were (i) seed extraction by washing and dry sieving, and (ii) seedling enumeration under different growing conditions. Both methods gave similar estimates for grass weeds but the seed extraction method generally gave higher values for broadleaf weed species. There was significant variation between samples within each of the sites, both in terms of the number of species and the number of seeds or seedlings recorded. No obvious differences due to variations in soil type were noted in the weed density or weed seed numbers between the six sites.
Soil samples collected from the headlands of maize fields produced seedlings of more weed species, although the number of seeds or seedlings were not significantly different between samples collected from inner and outer areas of the fields. The initial rate of seedbank decline varied between sites from different parts of the country. However, the seedbank of most grass and broadleaf weeds present declined in the absence of seed input over the four year period to between 1 and 2% of the original number, although this still represented a very large seedbank. The high ratio of seedlings emerged to seeds extracted in all samples demonstrates the potential for using the weed seed content of the soil to predict future weed problems in the field.
Plant Protection Quarterly (1998) 13 (3) 117-122.