A PHYTOSOCIOLGICAL CASE STUDY OF SOME WEEDS ASSOCIATED WITH CROP SESAME (SESAMUM INDICUM L.) IN THE SEMI ARID REGION OF NORTH-WESTERN DESERT OF RAJASTHAN

A PHYTOSOCIOLGICAL CASE STUDY OF SOME WEEDS ASSOCIATED WITH CROP SESAME (SESAMUM INDICUM L.) IN THE SEMI ARID REGION OF NORTH-WESTERN DESERT OF RAJASTHAN. Dr. Pankaj Swami 1 , Dr. Shamindra Saxena 2 and Dr. Surendra Kumar Godara 3 . 1. Department of Botany Govt. Dungar College, Bikaner. 2. Department of Botany Govt. Dungar College, Bikaner. 3. Assistant Registrar, MGSU, Bikaner (Rajasthan). ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Weeds are excellent examples of successful struggle for existence. Weeds are adapted by their abundant seed production, dispersal, varied seed dormancies, high competitive potentiality and ability to spread rapidly. Weeds have unique potentialities for adaptation; they thrive in almost any environment and adjust themselves to the changed conditions. Survival is difficult in arid region, where conditions are most inhospitable and impose severe constraints on plant life. Once a certain weed species is introduced, its abundance or scarcity is determined largely by the degree of competition offered by the crop and the prevailing environment. In agro-ecosystem weeds are harmful because they interfere with agricultural operations, which increase labour, compete with crop for water, nutrients, space, soil, light etc., and finally reduce the crop yield. Not only this, weeds have enormous seed production, variety of seed dormancies, first to grow and multiply under stress conditions and power of vegetative multiplication. They show rapid spreading and a deep penetrating root system, resist drought, start flowering and fruiting much earlier than crop and finally produce seeds to continue their progeny .Weeds not only rob the crops of nutrients but also the moisture which is most important ingredient in rain fed cropping. In present study the crop weed association was composed of 22 species. High frequency percent was shown by Tribulusterrestris. Farestiahamiltonii, Tribulusalatus. The relative biomass of crop and weeds were somewhat in proportion to relative densities. The net production of crop was higher than that of weeds. The period between 30 to 60 days after sowing was most critical stage for crop weed competition.

…………………………………………………………………………………………………….... Introduction:-
Agriculture is the process of managing plant communities to obtain useful materials from the small set of species we call crops. Weeds comprise the "other" set of plant species found in agro-ecosystems. Although they are not intentionally sown, weed species are well adapted to environments dominated by humans and have been associated with crop production since the origins of agriculture. The ecological role of weeds can be seen in very different ways, depending on one's perspective. Most commonly, weeds are perceived as unwanted intruders into agro-999 ecosystems that compete for limited resources, reduce crop yields, and force the use of large amounts of human labor and technology to prevent even greater crop losses. In agro-ecosystem weeds are harmful because they interfere with agricultural operations, which increase labour, compete with crop for water, nutrients, space, soil, light etc., and finally reduce the crop yield. Not only this, weeds have enormous seed production, variety of seed dormancies, first to grow and multiply under stress conditions and power of vegetative multiplication. They show rapid spreading and a deep penetrating root system, resist drought, start flowering and fruiting much earlier than crop and finally produce seeds to continue their progeny. Weeds are plants growing where it is not desired or plants out of place (Kassasian, 1971) or any plant not sown in the field by farmer (Vaidya, et al., 1978) or uninvited plants in agro-ecosystem.

Materials and Method:-
Phytosociological studies were undertaken in general sowing at field of sesame in the year 2016 only by quadrate method (Tripathi and Misra, 1971) and the variety of sesame grown was RT 46. The size of quadrate had been 1m sq (Pandeya and Saha, 1966) as determined by species-area curve method (Braun-Blanquet, 1932;Misra, 1968).  The maximum numbers of weeds were present on 45 th and 60 th days after sowing and minimum on 15 th day after sowing. It seems that the competition at the time of germination was insignificant which could not affect the crop at its initial stage. A few weed Tribulusterrestris, Cenchrusbiflorus and Farsetiahamiltoni have been found on 15 th day after the sowing and remained in an agro-ecosystem for the entire period of crop growth.

Result and Discussion:-
Tribulusterrestris,Farsetiahamiltoni, Ipomeapestgridis, Crotolariaburhia and Elusinecompressa have been regularly dispersed and Trianthemaportulacastrum, Indigoferalinifolia and Cleome brachycarpa have been irregularly dispersed. The above ground biomass of the crop plants (sesame) increased with growth till harvest. The total above 1000 ground biomass of weeds also increased with growth, however, the value of the latter have been lower than those of crop plants at all the stages of growth. The above ground biomass has not been in proportion of frequency of weeds.
The relative biomass of crop (85.05 %) and weed (14.94 %) has been in proportion of relative densities at 15 th days after sowing at the site. But there after the relative above ground biomass has not been in proportion of relative density or relative frequency of either the crop or the weeds. PHYTOGRAM AT 15 DS (Fig no. 1) 1001 PHYTOGRAM AT 30 AND 45 DS (Fig no. 2)

Conclusion:-
The present study reveals that phytosociolgical study is of immense importance in context to arid zone farming and also helps to understand the phenomenon of improving the yield of particular crops. In present study the crop weed association was composed of 22 species. High frequency percent was shown by Tribulusterrestris. Farestiahamiltonii, Tribulusalatus. The relative biomass of crop and weeds were somewhat in proportion to relative densities. The net production of crop was higher than that of weeds. The period between 30 to 60 days after sowing was most critical stage for crop weed competition.