soil weed seed bank

Abundant empirical evidence of seed bank densities from five countries showed a consistent relationship between mean seed bank density and variance. Overall, the relationship was defined as log 10 s 2 = 0.45 + 1.41 log 10 m, which is an adaptation of Taylor’s Power Law. From this relationship, Dessaint et al. (1996) derived an equation that helps approximate sampling adequacy based upon differing levels of desired precision. That equation was.

Mead, A., Grundy, A.C. & Burston, S. 1998. Predicting the movement of seeds following cultivation. Aspects of Applied Biology 51: 91-98.

Mucher, T. 2000. Characterization of weed beet in Germany and Italy. J. of Sugar Beet Research 37: 9-38.

This technique (e.g. Teo-Sherrell and Mortensen, 2000) involves exhuming a soil core and replacing it with soil devoid of seeds except for those purposefully added. These studies seemingly are more natural in that the added seeds are exposed to similar microclimate, microbial, and microfaunal conditions as seed packets, but also the macrofauna that would be excluded by small-mesh nylon bags. The detraction of this method is that seeded cores must be retrieved precisely so as not to include the natural seed bank inadvertently, and then processed in a manner identical to standard soil cores for seed bank studies.

Seed banks are of ecological and evolutionary importance in the dynamics of weed populations and communities.

The second most important guidance we can supply is that there is no universal sampling protocol applicable to all studies of soil seed banks. Each investigator has specific objectives and unique limitations in terms of labour and equipment. Moreover, each agro-ecosystem to be studied also has characteristics that may demand distinctive experimental protocols. Unique protocols are most obvious for agricultural systems with specific weeds: e.g. rare – vs common, small – vs large-seeded, and widely dispersed – vs aggregated species. However, the physical environment also plays a large role in sampling efficiencies and protocols. For instance, wet clay soils are much more difficult to sample than moist loam soils. These differences must be taken into account when designing practical protocols for assessing weed seed banks.

Seeds of some species are not amenable to symmetrical bisection along the embryonic axis because of their small size or shape (e.g. Chenopodium album ). These types of seeds can be split in any fashion with a sharp razor so that the radicle or hypocotyl is exposed on at least one half of the seed. Because the appropriate half-seed is difficult to discern at this stage, incubate both halves of the seed in TZ. The seed is viable if either half exhibits red after 12 hours’ incubation.

Malone, C.R. 1967. A rapid method for enumeration of viable seeds in soil. Weeds 15: 381-382.

This approach was pioneered by Beal and others at the turn of the preceding century. The method has not been used recently. As the name implies, seeds are place in sand-filled bottles, the bottles are inverted, and then buried in soil. Bottles are retrieved at intervals, sometimes 20-year intervals, and examined for germination and viability. Because the bottles are inverted, the seeds are not exposed to the same level of hydration, drying, and rehydration as seeds in field soils. Longevity appears abnormally long for many species examined in these experiments.

Buhler, D.D. & Maxwell, B.D . 1993. Seed separation and enumeration from soil using K 2 SO 3 -centrifugation and image analysis. Weed Sci. 41: 298-302.

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.

Forcella, F. 1992. Prediction of weed seedling densities from buried seed reserves . Weed Res. 32: 29-38.

Once cores have been exhumed from the soil, there are two primary techniques for enumerating the number of seeds in these cores. The two methods give differing results, but the results of the two methods usually correlate with one another (Ball and Miller 1989, Barberi et al. 1998, Cardina and Sparrow, 1996; Forcella 1992).

The flotation method often is used after the soil sample has been washed free of clay, silt, and fine sands, but whole unprocessed samples can be used as well. Here, the goal is to affect the buoyancy of seeds and soil particles differentially. A number of differing salts can be used for this purpose. Potassium carbonate has proven to be useful in this endeavour, in that it permits separation of the seeds from the soil particles. Short exposure to it is not toxic for seeds of some species (Buhler and Maxwell, 1993), but it may have a detrimental effect on others (Luschei et al. 1998). Some organic debris typically floats with the seeds. If large tubes are used to hold the samples and potassium carbonate solution, these can be centrifuged to affect separation of seeds from soil particles (Buhler and Maxwell, (1993)). This method is most useful if a single species is of interest, and detergent and salt concentrations that are effective, but not toxic, can be determined. All direct seed extraction methods provide estimates of total seed bank densities, including densities of dead seeds (see below). Thus, this technique is especially valuable for studies involved with population dynamics of weeds. The technique may not be always appropriate for the correlation of seed banks with seedling populations, as the technique may confuse dead, dormant, and non-dormant seeds with one another. Additional and routine tests are available to determine viability in the isolated seeds (see below), but as yet there is no routine method to distinguish dormant from non-dormant seeds (but see Fennimore et al. 1999).

Cardina, J., Sparrow, D.H. & McCoy, E.L. 1996. Spatial relationship between seedbank and seedling populations of common lambsquarters ( Chenopodium album ) and annual grasses. Weed Sci. 44: 298-308.

The most common species (highest value of m ) in Table 1 was T. arvense , which had the lowest CV and one of the highest k values, meaning that it was not as aggregated as most other species. The least common species was F. convolvulus , which might have been expected to be the most aggregated, but in this instance it was the least aggregated plant (highest k value). A. myosuroides was the most aggregated species ( k was lowest), and its CV was highest and m almost the lowest among the species. These results suggest that the most difficult species to detect in this particular field would be A. myosuroides . Nevertheless, with the proper sample number and size, even the density of A. myosuroides could be established with some certainty.

The sample can be pre-soaked for a short time to saturate and loosen clay aggregates. Soaking the soil sample in a solution of sodium hexametaphosphate will improve dispersal of clay aggregates. The next step is to remove clay, silt, and fine sand particles from the sample. This commonly is done by shaking the sample while it is held by the screen, or by passing a jet of water over the sample. Once the fine particles have passed through the screen, the remainder of the sample includes seeds, organic debris, sand particles, and in clay-rich soils, clay aggregates that did not fully disperse. These latter clay aggregates often can be eliminated by applying gentle pressure with fingertips until the aggregates crush and pass through the screen. The seeds and organic debris that remain on the screen are separated from the sand particles by differential flotation (see below). If sand particles are not abundant, the sample can washed onto mesh (e.g. cheese cloth) and air-dried, whereupon the seeds are separated from the organic debris by hand. Air-driven seed cleaners also can be used to separate organic debris from seeds in dried samples.

Where possible, split air-dried seeds symmetrically with a single-edged razor to bisect and expose the embryo. Thus, the cut surface of each half of the seed should show at least parts of the radicle and hypocotyl (e.g. Abutilon theophrasti Medik.) or the radicle and coleoptile (e.g. Setaria faberi Herrm.). Choose the half-seed that appears most intact, place on blotter paper saturated with 0.2 percent TZ, and incubate at 25 C. After 12 hours’ incubation, viable seeds exhibit red growing points, whereas dead seeds retain their original colour. The period of incubation usually is too short for substantial growth of micro-organisms.

To use the stale seed bed most effectively, start several weeks before planting. An initial cultivation kills any emerged weeds that have overwintered. It also brings weed seeds to the surface where exposure to light and oxygen stimulate germination. Depending on the weather and types of seeds present in the soil, weeds may sprout up overnight or over a few weeks. When weeds have germinated and are still small and young, they are easy to kill with a second light cultivation. This process is then repeated as needed and as time allows. As few as three cycles of light/ shallow tillage can reduce the number of subsequent weeds noticeably. For fields and gardens with very heavy weed infestations more cycles of repeated tillage over a few years will be needed. Using a stale seed bed may push back your planting date; but in the absence of weed competition, the crop will have more access to water and sunlight and be able to make up for lost time.

Keys to Success.

Ah spring! The war against weeds begins anew. The first major skirmish of the growing season should happen before planting. The stale seed bed technique is an often over-looked practice that can be used before planting. It works by first encouraging weeds to sprout and then killing them when they are young and most vulnerable. For organic growers, a stale seed bed can replace the effects of a pre-emergence herbicide. And when used properly, it can contribute to both short-term and long-term weed management.

Weed control can be handled with short-term or long-term approaches. Short-term management focuses on controlling weeds during the first part of crop growth when weeds are more likely to affect crop yields. Long-term weed management, however, works all season-long to deplete weed seeds from the seedbank (the reservoir of viable weed seeds in the soil). Whichever approach you take, using a stale seed bed is a great cultural weed control technique.

Stale Seedbed is most effective when it’s part of a zero weed threshold system.

The common short-term approach to managing weeds(which weed scientists usually call the “critical period approach”) is to control weeds aggressively during the first 4-6 weeks after the crop is planted. This 4-6-week period is the critical period during which crops stands are established and yield is secured. Afterwards weeds are of less threat to production; therefore, many farmers scale back control efforts. However, weeds that grow before and after the critical period are still a problem. If allowed to flower and set seed, they will be planting a future crop of weed problems. A long-term approach to weed management, called zero weed seed threshold, requires constant diligence and removal of all weeds before they produce seeds–even after harvest. Research indicates that 3-4 years of using this approach will result in a field with relatively few weeds, provided weed seeds are not introduced from without the field (in seed, irrigation water, on equipment, etc.).

There are a number of methods that have been used to determine the density and composition of soil weed seed bank. These methods are categorized into two main techniques that are used to find out the number of seeds from the soil samples, i.e. (1) weed seed extraction method and (2) weed seedling emergence method. In direct seed extraction method, weed seeds are extracted by washing and floatation methods while in the second technique, weed seedling emergence, the soil sample is placed in the greenhouse or controlled environment, watered on regular basis in order to emerge the weed seedling and these emerged seedlings are then identified and counted ( Luschei, 2003 ).

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

*Correspondence | Ijaz Ahmad, Ecotoxicology Research Institute, National Agricultural Research Centre Islamabad, Pakistan; Email: [email protected]

Keywords | Comparative study, Weed seed bank, Sieving method, Seedling emergence method.

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.

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.

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 ).

Abstract | Soil weed seed bank is a natural source for weed infestation. Determination of soil weed seed bank has primary importance to get complete picture of weed seed reservoir in the soil profile. An experiment was conducted at University Research Farm, Chakwal Road, Rawalpindi to compare the techniques for determination of soil weed seed bank during winter 2012-2013 under rainfed conditions of Pothowar. Soil samples for the weed seed bank analysis were taken from the experimental field before wheat sowing from 0-10 cm, 11-20 cm and 21-30 cm soil depth. Two soil weed seed bank determination techniques were compared viz., sieving method and seedling emergence method. The data were collected on the seed density m -2 , seed frequency, diversity of weed species and relative importance value. The input and output data was also collected to find out the socioeconomic feasibility of the techniques. The comparative analysis of seed bank extraction methods revealed higher weed seeds density, weed frequency with more diversity of weed species under sieving method in comparison to seedling emergence method. Therefore, sieving method was considered superior over seedling emergence method. The feasibility analysis of seed bank extraction methods indicated that sieving was cost-effective, less time consuming, more user friendly with higher accuracy over seedling emergence method.

S oil acts as storage house for different macro and microorganisms including insects, micro-organism, fungi, algae, spores, nematodes and seeds of different weeds. Weed plants after maturation shed their seeds and these weed seeds ultimately accumulated in the soil profile which form weed seed bank in the soil. Soil weed seed bank comprises of all viable, dormant and non-dormant seeds present in the soil profile ( Forcella et al., 2003 ). Knowledge of soil weed seed bank is important for population dynamics studied, establishment of appropriate weed management programs ( Ambrosio et al., 2004 ) and forecasting of weed infestations ( Ball and Miller, 1989 ; Creech et al., 2008 ).

The objective of current study was the determination of soil weed seed bank of Pothowar region and to compare different methods to find out the most accurate, efficient, handy and economical technique for the determination of soil weed seed bank.