Abstract :
The present investigation entitled “Assessment of weed diversity and its impact on crop-weed interaction in upland rice-rapeseed cropping system under residue mulch” was undertaken during two consecutive seasons (kharif and rabi) of year 2016-17 and 2017-18 at the experimental upland Agronomy farm, ICAR-RC NEH region, Umiam to fulfill experimental field objectives (I and III) and chosen paddy fields survey in Ri-Bhoi district of Meghalaya (II). The soil was silty clay, acidic in soil reaction & normal in electrical conductivity, high in organic carbon & low in available nitrogen and sulphur, medium in available phosphorus & potassium. Two experiments were sown
on 29th June 2016, 15th Nov 2016, 24th June 2017 and 12th Nov 2018. Experiment I was laid out inrandomized block design with 3 replications comprising ten treatments viz., weeds until 14, 28, 42, 56 days after sowing (DAS) and harvest and weed free until 14, 28, 42, 56 DAS and harvest and Experiment II was laid out in split plot design with 3 replications comprising 10 residual weed competition rice plots {details mentioned in Experiment I} in main plots and 2mulching treatments {M0 – No mulch, M1- straw mulch} in sub-plots with test cultivars of IURON 514 and TS 67 in rice and rapeseed, respectively. In order to achieve the second objective of the present investigation, a study was conducted to assess the distribution and pattern of weed flora prevailing in the rice fields of Ri-Bhoi district of Meghalaya with the help of remote sensing and GIS tools. It includes a random field survey, diversity indices analysis, development of spatial and attribute database of rice fields using high resolution satellite imagery and thematic weed diversity maps.
The results in Experiment I revealed that the weed dynamics such as weed density, weed biomass, nutrient NPK removal by weeds was tended to decrease with increasing weeds free condition up to harvest. The lowest weed dynamics was observed in weed free until harvest. While, season long weedy treatment resulted in the highest weed dynamics. The growth attributes such as plant height, leaf area index and dry matter production, physiological parameters (CGR, RGR, NAR, chlorophyll (SPAD value)) and yield attributes viz., number of panicles plant-1, number of filled grains panicle-1, panicle weight and 1000 grain weight, grain and straw yield, harvest index, nutrient NPK content and uptake by rice crop were realized highest with season long weed free treatment followed by weedy for the first 14DAS, weed free until 56DAS and the lowest was observed in season long weedy treatment. Based on the 5% level of yield loss, the critical period for weed competition was between 9 – 56 DAS in 2016 and 14 to 57 DAS in 2017, whereas, the estimated critical period for upland rice at 10% RYL was between 17 to 43 and 24 to 44 DAS in 2016 and 2017, respectively. The dry matter content, filled grains and number of panicle were direct relationship with significant to increasing grain yield and Positive correlation was observed between plant height, number of tillers, leaf area index and grain weight. Significant but negative correlation was obtained between the relative yield loss, spikelet sterility, weed biomass, and nutrient removal of nitrogen, phosphors and potash from weed plants of respective treatment for grain yield.
In experiment II, among the weed species encountered in the survey under low land and upland rice, the species, Cyperus iria, Commelina diffusa and Echinochloa colona are commonly distributed in both type of cultivation. The weed flora on number wise doesn’t differ with each other counting around 21 (± 4). But by family wise the weeds are found vary in nature. Out of 21 wetland weeds recorded, the species belong to Cyperaceae and Poaceae had more than 5 species each whereas, in upland rice ecosystem, the weeds belong to 10 different families in which the family, Asteraceae with 10 species, followed by Poaceae was with four species. The wetland weeds which had higher relative abundance in descending order in both the years (2016 and 2017) were Rotala indica (27.11 and 22.21), Cyperus laevigatus (23.45 and 21.95), Monochoria vaginalis (15.12 and 18.16), Sagittaria sagittifolia (14.60 and 17.53) and Cyperus iria (14.19 and 16.02) and in upland rice ecosystem during the year 2016, weeds with higher relative abundance in descending order were Spermoce latifolia (20.27 and 16.87), Ageratum conyzoides (18.13 and 11.73), Ambrosia artemisiifolia (6.64 and 6.78) Conyza sumatrensis (6.02 and 7.80) and Bidens pilosa (5.35 and 7.61). Further, results from weed diversity indices revealed that wide range (medium to high) of weed density was observed in Umling and upper Umsning block in both the years of study. The diversity values ranged from 3 to 10 species per sq m in species richness, Margleaf index (0.48 to 2.28), the Shannon (H') diversity index (0.69 to 2.08), Simpson’s index (0.01 to 0.9), Pielou’s evenness (0.43 to 0.9) and Parker index (0.21 to 0.81). Weed species were more evenly distributed in lowland than the upland rice sites. Umling though had high to moderate levels of diversity, no new weed species were present compare to other blocks of the district.
In experiment III, The growth attributes such as plant height, number of primary branches and dry matter production, physiological parameters (CGR, RGR, NAR, chlorophyll (SPAD value), relative water content, leaf thickness, leaf temperature) and yield attributes viz., number of siliqua plant-1, number of seeds siliqua-1 and 1000 grain weight, seed and stover yield, harvest index, nutrient NPKS content and uptake by toria crop were failed to have significant variation with residual weed competition plots of rice however, maximum values were recorded with longer duration weed free treatments than weedy plots and further, straw mulched plots were recorded significantly higher values in all the parameters except in stomatal and root traits, which was found higher with no mulch treated plots of toria. Interaction effect of different treatments of residual weed competition of rice plots and mulch practices were found non-significant with all the parameters except dry matter, root studies and in S nutrient, which was found significant during the study.
The data on gross return and net return was observed highest with treatment’s kept weed free for longer duration in rice crop growth and vice versa. The significantly higher gross return of Rs. 57,432; net return of Rs. 27,238 and B: C ratio of 0.90 was found with season long weed free treatment which is followed by treatment T9, T1 and T8 respectively. The gross return Rs. 18,050; net return of Rs. 7196; B: C ratio of 0.66 of rapeseed was observed significantly higher under straw mulch than no mulch treatment, during both the years of investigation. Further, among the treatments, season long weed free treatment (T10) differed significantly and recorded higher rice equivalent yield (REY), system productivity, monetary net returns and production efficiency but land use efficiency was recorded higher with weed free until 56DAS during the study period.

Includes bibliographical references and index.