Introduction
Millet grows in unfavorable conditions such as extreme heat and low rainfall and needs a shorter growing season and has high water use efficiency compared to small grains. Pre-sowing by changing the type of plant and different cultivation operations cause the composition of the weed seed bank to change. Nitrogen, as one of the most consumed plant elements, is one of the most limiting nutrient elements in agricultural production, the correct application of nitrogen in agriculture increases yield, reduce production costs and environmental pollution. This research was conducted to study the effects of chickpea pre-sowing and nitrogen fertilizer on weed species diversity in millet.

Materials and Methods
The experiment was conducted on split factorial based on randomized complete block design with three replications in the research field at University of Jiroft during 2018-2019. The treatments included two levels of with or no chickpeas pre-sowing, three levels of nitrogen fertilizer 200, 300, 400 kg. ha^-1 from the source of urea and three types of millet, Pearl (Pennisetum glaucum), Foxtail (Setaria italica) and common millet (Panicum miliaceum). The size of each experimental plot was 3 × 2 m^-2. The seeds were sown manually with an intera and inter row 50 and 5 cm respectively. Drip irrigation system was used and no chemical pesticides or weed control were used during different stages of plant growth. In order to measure the dynamics of the weed population, sampling was done 20, 40 and 60 days after planting. Plots of 100×100 cm^-2 were used for sampling weeds, then the weeds were sorted and counted according to species. Weed biomass weight was measured and stability coefficient evaluation, Shannon index), Simpson and dominance were calculated by Post software. Data analysis was done using SAS 9.4 software, comparison of mean was evaluated Duncan's test.

Results and Discussion
Sampling during the three growth stages of millet plants showed 10 weed species in different treatments was observed such as Cyperus rotendus, Poa nemoralis and Echinochloa galli. Different studies have shown that the stability of plant species is influenced by various factors. In the treatment of using different amounts of nitrogen, the stability coefficients of the species varied, so that in most cases, the highest stability coefficient of the weed species was obtained by increasing the amount of fertilizer. Also, most of the weed species observed in the weed range were random and temporary, and only Cyperus rotendus species was stable. The amount of Shannon's diversity index was higher in all three stages of sampling, in the treatment of chickpea pre-sowing and the third level of nitrogen fertilizer. The highest index of Margalef was assigned to the treatment of the third level of nitrogen fertilizer (1.08) in the first sampling stage located at the beginning of the growth of millet plant and the treatment of chickpea pre-sowing (2.11). The trend of Simpson's index changes was variable in all samplings. Fertilization and application of nutrients increase the competitiveness of weeds and affect their establishment, emergence, density and development. In the present study, weed density and biomass increased with increasing nitrogen fertilizer levels. In the first stage of weed sampling, there was no statistically significant difference in the dry weight of weeds in all three millet fields. With the increase of days after planting time and the increase of plant growth rate in the second stage of sampling, the dry weight of common millet weeds decreased by 14% and 21% respectively compared to pearl millet and foxtail pearl millet. In the third stage, the dry weight of common millet weeds decreased by 13.5% and 20.8% compared to pearl millet and foxtail, respectively.

Conclusions
The results of the present study showed that pre-sowing chickpea treatments, different levels of nitrogen fertilizer and millet species are effective on the population and biodiversity indicators of weeds. According to the results of this research, in order to prevent the invasion of weeds and competition with the target plant, it is suggested to use suitable pre-sowing and the use of nutrients based on the needs of the plant.