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soil weed seed bank

Received | September 29, 2017 ; Accepted | October 27, 2017 ; Published | November 21, 2017

1 Department of Agronomy, Pir Mehr Ali Shah, Arid Agriculture University, Rawalpindi, Pakistan; 2 Ecotoxicology Research Institute, National Agricultural Research Centre Islamabad, Pakistan; 3 Crop Sciences Institute, National Agricultural Research Centre, Islamabad, Pakistan; 4 Research Farm Crops, Agriculture Department, AJ and K, Baldmas District Kotli, Pakistan.

Citation | Hussain, M., S. Ali, M.N. Tahir, G.A. Shah, I. Ahmad, M.A. Sarwar and S. Latif. 2017. A comparative study of soil weed seed bank determination in pothwar region by using different methodologies . Pakistan Journal of Agricultural Research , 30(4): 310-315.

Weed seeds may enter in the seed bank through many sources from plant seed production, together with primary and secondary dispersal such as farm equipment, contaminated crop seeds, animals, wind and manure ( Buhler et al., 1997 ). Among these sources, the largest source of weed seeds in the seed bank is plants producing seed within the field. Weed seeds also drive the spread of weed patches in fields, both for annual ( Steinmann and Klingebiel, 2004 ) and perennial weed species ( Blumenthal and Jordan, 2001 ), and are the only source of population increase for annual weed species. Decline in weed seed bank may occur by various factors such as germination, seed predation ( Van Mourik et al., 2005 ), seed decay and death ( Gallandt, 2006 ) and deep seed burial to layers from where emergence onto the soil surface is impossible ( Honda, 2008 ). These seed banks range from near 0 to as much as 1 million seeds m -2 ( Radosevich et al., 1997 ).

Benoit, D.L., Derksen, D.A. & Panneton, B. 1992. Innovative approaches to seedbank studies. Weed Sci. 40: 660-669.

Fennimore, S.A., Nyquist, W.E., Shaner, G.E., Doerge, R.W. & Fole, M.E. 1999 . A genetic model and molecular markers for wild oat (Avena fatua L.) seed dormancy. Theoretical and Applied Genetics 99: 711-719.

Table 2. The number of soil cores (5 cm diameter) necessary to determine seed bank densities under four levels of desired precision assuming various seed densities.

Benoit, D.L., Kenkel, N.C. & Cavers, P.B. 1989. Factors influencing the precision of soil seed bank estimates. Can. J. of Botany 67: 2833-2840.

The diameter of the core usually depends upon available equipment. Most hand-held soil sampling equipment was developed for soil scientists, and much of it is about 2-3 cm in diameter. Although, theoretically, any soil core diameter is suitable for sampling weed seed banks, certain sizes are far more practical than others.

Gross, K.L. & Renner, K.A. 1989. A new method for estimating seed numbers in soil. Weed Sci. 37: 836-839.

However, also other factors are involved in the choice of diameters of soil-coring devices. The most significant of these is soil texture and soil water content. Wet soils with high percentages of expanding clays are notoriously difficult to remove from sample tubes, especially from small-diameter tubes. Cores with diameters of up to 10 cm should be considered for such soils. Application of non-toxic oils (vegetable oils) to the coring implement helps greatly in preventing clay from sticking to the device. Orifices that are a few millimetres narrower than the diameter of the sampling tube also may aid in preventing the soil from adhering too tightly to the inside of the sample tube. However, these types of coring tools are more likely to compress soils with low bulk densities while the coring tool is being driven into the soil. This compaction of the core confounds reliability of core depths. In contrast, very dry soil can resist penetration by coring implements. In these cases, narrow cores may be more practical than the recommended 5 cm diameter cores. Researchers must be practical and balance multiple factors when choosing sampling equipment.

How much soil to sample?

The weeds present four weeks after crop sowing usually represent the most important proportion of the total weed population, at least from the standpoint of in-crop weed control. The density represented by this proportion, however, may not correlate necessarily with seed bank density. In this case, researchers are advised to attempt a correlation between seed bank densities and weed densities at times a + b, a + b + c, b + c, and so forth. Only after these types of assessments have been made can researchers conclude that relationships exist or do not exist between seed bank densities and aboveground vegetation.