Effect of cultivation methods on weed seed distribution and seedling emergence

Weed Biology and Management

James

Grbavac

2006

Annual weed populations establish every year from persistent seed banks in the soil. This 3 year study investigated the relationship between the number of weed seeds in the soil seed bank and the resultant populations of major broadleaf and grass weeds in 30 maize fields. After planting the crop, 1 m 2 areas were protected from the pre-emergence herbicide application. Soil samples were collected soon after spraying to a depth of 100 mm and the weed seeds therein were enumerated. The emerged weed seedlings in the field sampling areas were counted over the following 8 weeks. Up to 67 broadleaf species and five grass weeds were identified, although not all were found at every site and some were specific to a region or soil type. For the most abundant weeds in the field plots, on average 2.1-8.2% of the seeds of the broadleaf species and 6.2-11.9% of the seeds of the grass weeds in the soil seed bank emerged in any one year, depending on the species. Overall, the results showed a strong linear relationship between the seed numbers in the soil and the seedling numbers in the field for all the grasses and for most broadleaf weeds. For some species, like Trifolium repens, only a weak relationship was observed. In the case of Chenopodium album, which had the largest seed bank, there was evidence of asymptotic behavior, with seedling emergence leveling off at high seed numbers. An estimate of the soil seed bank combined with knowledge of the germination and behavior of specific weed species would thus have good potential for predicting future weed infestations in maize fields.Keywords: broadleaf weeds, grass weeds, maize, soil seed bank, weed emergence, weed seed bank.The weed seed bank as a reservoir of weed seeds in the soil largely determines the potential density and species composition of weeds that subsequently interfere with crops during the growing season (Forcella 1993). In this respect, an estimate of the seedbank population in the soil, combined with knowledge of the germination and behavior of specific weed species, presents practical opportunities to develop integrated and environmentally sound weed management programs. Some bioeconomic weed management models now use seedbank estimates to predict weed population dynamics and competitiveness (Lybecker et al. 1991). Grundy (2003) has recently reviewed the current state of research using the methodologies presently available to predict weed emergence.The likely density and composition of weed plants arising after cultivation could, in most instances, be deter-

Section: Discussionsupporting

confidence: 88%

Section: Discussionmentioning

confidence: 99%

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Correlation between the soil seed bank and weed populations in maize fields

Weed Biology and Management

James

Grbavac

2006

“…The proportion of the active weed seedbank emerging as seedlings in the field reported here is in line with our earlier observations and overseas findings (Zhang et al 1998;Rahman et al 2000). However, just as important as being able to provide a realistic estimate of the density of emergence, is being able to predict the timing and spread of the flush of weed emergence over time or relative to environmental variables.…”

Section: Grasssupporting

confidence: 90%

Relationship between soil seedbank and field populations of grass weeds in maize

James²,

Mellsop³

et al. 2003

NZPP

Self Cite

The relationship between laboratory enumerations of the weed seedbank and field populations of major grass weeds was studied in several maize fields over a three year period. After planting the crop, 1 m 2 areas were protected from the pre-emergence herbicide application. Soil samples were collected soon after spraying from each area to a depth of 100 mm, and the seeds of the major grass weeds enumerated at a seed testing laboratory. Emerged weed seedlings were counted in each sampling area over the following 8 weeks. Grasses present at these sites included: summer grass (Digitaria sanguinalis), smooth witchgrass (Panicum dichotomiflorum), barnyard grass (Echinochloa crus-galli) and rough bristle grass (Setaria verticillata). On average 6-12% of the seed in the soil seedbank emerged in any one year depending on species. Significant linear relationships were established between seed numbers in the soil and the seedlings that emerged in the field.

“…The decline had the effect of halving the number of seed approximately every 5 cm increase in depth (Rahman et al 1999). A similar trend was recorded for many other weed species in a later study by Rahman et al (2000). As the trend was very similar for viable, non‐viable and empty seeds, it would appear that the distribution was not affected significantly by germination or predation (Table 2).…”

Section: Spatial Variability Of Weed Seedssupporting

confidence: 79%

Potential of weed seedbanks for managing weeds: a review of recent New Zealand research

Weed Biology and Management

James

Grbavac³

2001

Weed seedbanks are the primary source of weeds in cultivated soils. Some knowledge of the weed seedbank may therefore be appropriate for integrated weed management programs. It would also be very useful in planning herbicide programs and reducing the total herbicide use. However, a number of problems are inherent in the estimation of the seedbank size for arable weeds that usually have annual life cycles. In a long-term research project we have investigated the dynamics of weed seedbanks in corn fields for the past 8 years. Specific studies have included (i) developing cheap and efficient methods for estimating the weed seedbank; (ii) developing guidelines for efficient soil sampling (including the number and size of samples); (iii) influence of cultivation methods on weed seed distribution; (iv) mapping the spatial variability of the seedbank; (v) estimating the rate of seedbank decline for certain weed species; and (vi) assessing the potential of using the weed seed content in the soil to predict future weed problems. This paper reviews and summarizes the results of our research on the above aspects. The strong correlation between seedlings emerged in the greenhouse and seeds extracted in the laboratory for the most abundant weed species has demonstrated the potential for using the weed seed content of the soil to predict future weed infestations. The next step is to establish correlations with field emergence under commercial conditions using the sampling guidelines developed in our studies. Subsequently, we aim to offer the weed seedbank estimation as a commercial service to farmers for planning the most appropriate weed management options.