Population Distribution of Wild Radish (Raphanus Raphanistrum L.) Weed and Soil Depth of Seed Bank Across Different Land-Use Types in Horro District, Western Oromia, Ethiopia

Background: Wild radish (Raphanus raphanistrum L.) is an invasive weed in Ethiopia and hurting different land use types in the Horro district of the study area and fact, more research has not been done yet on the weed is highly infested and persisted for three decades. Therefore, this study was conducted to assess the weeds ora and seed bank status across different land use types in the Horro district of western Oromia, Ethiopia. Three locations and from each location ve different land use were purposively selected and a 1m 2 area of quadratic sampling techniques was used to record weed ora. From each quadrat, soil samples were taken having two soil depth levels (0-15cm and >15-30cm) to evaluate the soil seed bank of weeds. Results: The data of wild radish weed in different location and different land use types both eld survey and greenhouse experiments were found a statistically signicant difference (p<0.05) among the target action of land use types but there was found no signicant difference among soil depths. More all less, the highest wild radish population was recorded from grazing land land followed by wheat crop land and among the locations, Gitilo Dale has the highest weed density. Among the weed ora, again wild radish was highly dominated weed species than the other weed species in all land use types and locations. From soil seed bank status of soil depth, high weed population was recorded at 0-16cm of second season weed emergence from pot and Gitilo Dale was the highest infected location at this season, while barley crop land was the highest infected among land use types in rst season of weed emergence from pot. Among the weed species were recorded from soil depth, again wild radish was highly dominated in both seasons. The population of weed ora per quadrat was directly proportion with population recorded from soil depth that emerged from pot. Conclusions: This study this area has highly by wald (Raphanus raphanistrum)

was highly dominated weed species than the other weed species in all land use types and locations. From soil seed bank status of soil depth, high weed population was recorded at 0-16cm of second season weed emergence from pot and Gitilo Dale was the highest infected location at this season, while barley crop land was the highest infected among land use types in rst season of weed emergence from pot. Among the weed species were recorded from soil depth, again wild radish was highly dominated in both seasons. The population of weed ora per quadrat was directly proportion with population recorded from soil depth that emerged from pot.
Conclusions: This study has highly veri ed that this area has highly infected by wald radish (Raphanus raphanistrum) and there could be a source of weed seed. Generally, the concerned bodies should have to be given attention which should need immediate intervention strategies to mitigate the negative impacts of weed otherwise the area will be out of production soon. Therefore, an extensive integrated weed management strategies should be applied in all phases of cropping systems to sustain environment and reduce this weed in the future.

Background
Wild radish (Raphanus raphanistrum L.) is one of the most widespread and competitive weeds in the world and has successfully occupied a variety of locations and within a short time, its colonization has reached over the world [16,28]. For instance, its distribution has been reported in the cropping areas of Queensland, South Wales, South Austria, and Western Austria [26,7], and the species are also found in the Americas, Australia, Africa and Asia [5].
Wild radish grows over a wide range of ecological zone and this destructive colonizing performance might be a result of a new combination of parental traits or genetic variability of the population [24,14].
Wild radish has a strong taproot over one meter deep allowing it to survive periods of moisture stress and regrow following when slashing or grazing due to root reserves and up to 70% of the wild radish seed bank is dormant at the start of the winter cropping season and it can cause a yield loss of 10-90% in cereals and pulses [10,31].
It has been expected that this weed had been introduced to Ethiopia between 1930-1935 through Italy armed forces and is now causing a serious problem on crop and range land in the Horro district of western Oromia, Ethiopia, so far, there has been no concrete evidence on how wild radish introduced into Ethiopia. A report indicates that it became a serious weed of crop and range lands in West Shewa, particularly in Welmera and Chaliya, Southwest Shewa (Waliso), and in Horro Guduru Wollega Zone western Oromia region [2].
Horro district could be considered as the area where the weed has widely distributed and cause yield up to 28.9% grain yield loss [2], however, there has not been given evidence information regarding the current status of wild radish across different land use types and soil seed bank. This research has given a piece of basic information for strategic management practices of weed especially on integrated weed management program Therefore, this research was conducted with the objective; to assess the population and soil seed bank status of wild radish weeds across different land use types in Horro district, western Oromia, Ethiopia.

Study area
The study was conducted in Horro district, Oromia Regional State, and the Western part of Ethiopia. The location is found at 9 o 33 . 58'N Latitude and 37°5 . 19'E longitude and 314 km distance from Addis Ababa to the western direction of Ethiopia. The district has three agroecological categories; highland (49.9%), mid-high land (48.96%), and low land (1.24%) and the district receives an average annual rainfall of

Sampling procedures and experimental design
The study was conducted in 2018 growing season in three locations (Lakku Iggu, Doyo Bariso, and Gitilo Dale) of Horro district, Oromia state, western Ethiopia and from each location, ve land use types (wheat land, teff land, barley land, grazing land, and forest land) were purposely selected based on weed boundary, weed association, weed density, and distribution because reported that a wide variety of eld survey has to be con rmed that cause-effect dealings can be checked for generality [19]. For the oras survey, a 1m 2 area of quadrat was used randomly to assess the seedling population density of weed from each land use type [8]. Systematic sampling approach was used for soil sample having 0-15cm and 16-30cm soil depth to assess the status of the weed seed bank in greenhouse experiment and 20cm diameter pots was used to grow weed in a greenhouse [8,1]. The treatments were arranged in a randomized complete block design (RCBD) with three replications.

Data collection
Weed ora was collected by direct counting of plant species in the habitats and quantitative analysis of weed population and relative weed density were competed according to the authors of the following formula [20,17].

Data analysis
Data were subjected to analysis of variance (ANOVA) with SAS computer software version 9.4 [29] and descriptive statistics were used to explain the average weed species population. Means of wild radish populations were compared with the least signi cance difference (LSD) at a 5% probability level.

Wild radish population
Mostly, this study was given as a clue about wild radish and other weed species and wild radish weed has the leading species in Horro district, western Oromia, Ethiopia. Correspondingly about ve weed species were recorded and well-identi ed from the area. The analysis of variance (ANOVA) indicated that the main effect of land use types and locations on wild radish was a highly signi cant difference (P< 0.001) among the treatments, however, the interaction of land use types and locations were found a nonsigni cant difference (P< 0.001) among the treatments (Table 1). From land use types, grazing land was more dominated by wild radish (276 (1.99) followed by wheat crop land 237 (1.96). From the locations, Gitilo Dale was more dominated by weed 253 (1.94) followed by Doyo Bariso location 149 (1.83), and Lakku Iggu was relatively less persisted by weed (Table 1). Table 1 The main effect of land use and locations for wild radish weed population Means followed by the same letter(s) within rows are not signi cantly different at P ≤ 0.05 level of signi cance, The gures in the parenthesis are the transformed values for wild radish count from the quadrant.

The population of weed species
This survey result shows as high population density and relative density were estimated on Raphanus raphanistrum in all land use types followed by Digiteria abyssinia. However, a little bit there was a difference in Barley crop land, and the second-highest weed population was estimated from Avena fatua and Plantago lanceolata weed species from Teff crop land (Table 2). A high population of Raphanus raphanistrum weed species was recorded in Gitilo Dale (253) location followed by Digiteria abysinica (117) whereas the lowest was recorded in Doyo Bariso (149) and Lakku (94) followed by Digiteria abysinica 111 and 60 respectively in both locations and from all locations, Galinsoga paniy ora species was recorded in the least population density (Table 3). Soil seed bank evaluation The analysis of variance (ANOVA) indicated that the main effect of land use types was found a signi cant difference (P< 0.001) on the rst and second season of wild radish emerged from pot. However, regarding weed species composition, there was found a non-signi cant difference (P< 0.001) on the rst and second season of weed ora emerged from the pot, and the main effect of soil depth also was found non-signi cant difference on all variables. The main effect of locations was found signi cant difference on the second season of wild radish emerged from the pot and species composition of weed ora of rst season variables, however, there was found non-signi cant difference on the rst season of wild radish emerged from the pot and species composition of weed ora of second season variables. In all interactions, it was found a non-signi cant difference in all variables (Table 4). A maximum number of wild radish population was recorded from Barley crop land of both rst and second season grown in a pot. However, for weed ora of weed species composition, grazing land, and forest land have led to both the rst and second season of weed emergence. The same phenomenon, maximum population of wild radish was emerged from 16-30cm soil depth than 0-15cm soil depth in both seasons, however, for weed species maximum number of weed ora was recorded from 0-15cm soil depth (Table 4). The rst season greenhouse works result indicated that about ve weed species were well identi ed including wild radish species which was emerged from pot. As a result, a maximum number of wild radish species was germinated from a pot which has been from barley land (11) and wheat land (10) followed by Avena fatua from teff land (7), while minimum weed species, Avena fatua, and Guizotia abysinica were recorded from forest land (Table 5). It was deviated in between 0.75-3.5 ranges. From the second season germination, the maximum number of individual species was recorded on Raphanus raphanistrum (9.00) in Barley land followed by wheat land and teff land (7.00), while the minimum number of species was recorded from all land use types (Table 5). The average number of Raphanus raphanistrum was compared with weed ora or weed species, wild radish was highly gured than the other weed species in location by soil depth. The number of weed ora from the soil seed bank has uctuated per soil depth or there was shown not many differences between the soil depth (Fig. 2).

Discussion
Weed problems are becoming increasingly di cult to mitigate that currently, Ethiopia has faced, especially there has been at higher risk of exotic weed like wild radish as result of an increase in the travel trade and poor quarantine agency as well as by nature wild radish emergence is more aggressive and proli c before crop emergence and this may be partly responsible for its large effects on crop growth and yield loss [10,34]. Some authors have reported that the anthropogenic development of weed distribution and dispersal are also in uenced by annual activities in the current cropping system and spatial variability in current agronomic practices within the eld. Thus, the real-time approaches for the di culty to having actual data of the study areas especially in disturbed land or cropping land use and has been reported that pending action and mapping for future attempt to take control measurements [14,3].
This survey would have to be preferable to use weed density and relative weed density measurements in Weed species including wild radish (Raphanus raphanistrum) with wide geographical distributions might look a strong selection to adapt to new environments and the colonization ability and persistency could be strongly in uenced by the population's ability to evolutionarily adapt to new abiotic and biotic environments [4,14,28], otherwise, species may be preadapted to new environmental conditions by chance [30,23]. The altitude, soil type, temperature, and soil texture class are the factors, and this geographically differentiated weed that would have affected the distribution of weeds in the study area and quantitative oristic inventories provide a necessary context for planning and interpreting long-term ecological research [15]. The populations from the nearby location would show greater similarity than more widely separated locations, for instance, most of the time alike population of individual species has shown in Lakku Iggu location which is different from either Doyo Bariso and Gitilo Dale, which is supported by the reports has emphasis, environmentally similar sites would show greater similarity than from dissimilar sites [4].
In the Horro district especially the study area, wild radish was introduced for a long list of about more than 30 years because it is obvious, the seed dormancy assists the survival of plants in several ways; including ensuring the persistence of species in risky environments, enabling germination to agree with the season most favorable for plant growth and interacting with other life cycle traits in helping the plant to maintain itself [33], and it is the most persisted weed species in this area in various land use types because it is one of the most problematic and competitive [25,2,9] reports. Plant attributes particularly important to weeds include adaptations for effective seed dispersal, seed dormancy, long-lived seed bank, rapid growth, and phenotypic plasticity [4]. The seed bank remains high even under the worst conditions for seed production and seeds can remain viable in the soil for 15 to 20 years [26,18]. There would no disturbances, because there would be fewer human activities that affected the emergence of wild radish in forest land and a little bit in grazing land, so that in one area more seeds produced from a single plant that one can have an opportunity for more seed production and more seed bank.
The primarily important aspect of this study would have that wild radish has an effective and long-lasting dormancy mechanism and it is similar to the successful exotic annual legumes, most of which have dormancy mechanisms lasting several years [4]. It is likely to achieve that Raphanus raphanistrum is a highly spreading weed causing a devastating effect on cereal crop production in the study area as compared to other weed species. The nding result supports that the cultivation leads to shallow burial of wild radish seed in moist soil enhancing germination [7]. And Cultivation enhances seedling emergence and reduces the seed bank [22]. The result shows that in barley and wheat crops land this weed has more distributed but in forest and grazing lands it has shown as the lowest distribution because those lands were not cultivated or undisturbed lands and this uncultivated land has deeper burial depth and decreases weed seed emergence. This result supports the nding of the average depth of emergence in all soil conditions up to 16 cm soil depth [36,12,3].
When camper to the result of the evaluation of the rst season and second season seed bank in the soil at different soil depth it relatively the same at the depth of soil sample in 0-15cm and 16-30cm because the depth not more much far from each and the soil sample is taken to analysis is the same. The difference in weed distribution might be due to the soil type and this could be affected the seed dormancy of weeds. This nding would have supported with [27] report that seed numbers in soil declined with time but the loss was much slower at 100 mm depth than with shallower burial [35]. A cultural weed control strategy probably, increasing crop density can suppress wild radish and reduce its population especially it would be preferable for the weed seed-bank management programs and could be an important constituent of an integrated weed management program [10].
Several information has given that recently increasing consideration to external drivers of weed distribution, including the relationship between weeds and environmental properties, as well as anthropogenic drivers of weed distributions [32]. Usually, biological and ecological procedures have designed the source of Spatio-temporal weed models with certain stress on processes such as dispersal and competition, which become predominantly appropriate when considering spatial distributions of the study area. Ecological based information is still needed for the operation of weed management and some practices may be di cult or impossible to implement in certain topographies, but knowledge and some level of certainty must be added and decision-making processes should be required for weed control and prevent crop yield losses [19,21,11]. Therefore, a wide range of weed management options that target all phases of the cropping systems and environmental manipulation is needed to sustain to reduce this weed in the future.

Conclusion
Our study demonstrates, this area has highly veri ed by wild radish (Raphanus raphanistrum) and there could be a source of weed seed. Subsequently, there are the marginalized area where the researchers were not given attention and farmers are strongly competing with weed by individual. Even though, Ethiopian ministry of agriculture and regional administration have tried to supply some agriculture input, still they no concretive evidence about the distribution of the wild radish weed except the local administration and farmers, that is true also they have no capacity to overcome the effects of this weed.
In fact, one trips of survey would not be concluded and could not be given concrete information unless it requires wide investigation for several times over a wide range of locations. Some information has given that recently increasing consideration to outward drivers of weed distribution. Generally, the concerned bodies should have to be given attention which should need immediate intervention strategies to mitigate the negative impacts of weed otherwise the area will be out of production soon. Therefore, an extensive integrated weed management strategies should be applied in all phases of cropping systems to sustain environment and reduce this weed in the future.   Figure 1