|Keywords (Extracted from title, table of contents and abstract of thesis)
weed flora, rainfed wheat, asphodelus lenuifolius, convolvulus arvensis, trigonella monanlha, tribulus lerreslris, euphorbia dracunculoides, trigonella monantha, convolvulus arvensis, anagallis arvensis, fumaria indica, carthamus oxyacantha, fumaria indica medicago polymorpha, anagallis arvensis, vicia sativa, ranunculus muricatus, veronica didyma, lamium amplexicaule, stellaria media, medicago polymorpha, ranunculus muricatus, weed emergence pattern, vegetation analysis
For the purpose of this study the rainfed area of Punjab was divided into four zones. The weed flora, their emergence pattern, reproductive potential, soil seed reserves, nutrient losses and moisture losses by weeds and their correlations with different soil characteristics were studied in these zones during the year 1986-87, 1987-88 and 1989-90.
Zone I comprised of Mianwali and Bhakkar with 150-300 mm annual rainfall; zone 11 was around Talagang and Fatehjang with 300-500 mm; zone III was around Islamabad and Rawalpindi with 500-1000 mm and zone IV being around Murree with 1000 - 1500 mm annual rainfall.
The first five dominating weeds in these zones were as the following: Zone I: Asphodelus lenuifolius, Convolvulus arvensis, Trigonella monanlha, Tribulus lerreslris and Euphorbia dracunculoides; Zone 11: Trigonella monantha, Convolvulus arvensis, Anagallis arvensis, Fumaria indica and Carthamus oxyacantha;Zone III: Fumaria indica Medicago polymorpha, Anagallis arvensis, Vicia sativa and Ranunculus muricatus and Zone IV: Veronica didyma, Lamium amplexicaule, Stellaria media, Medicago polymorpha and Ranunculus muricatus.
Zone III was found richest in terms of weed species as well as their density. Zone IV was the second rich zone whereas zone I remained at the bottom. Similarly, the weed biomass, the moisture content and the nutrient uptake showed the same pattern in these rainfall zones.
The weed emergence pattern in these zones differed from each other. Within a zone also it varied with the time and duration of rainfall. Besides many other weeds emerging earlier in zone I, Convolvulus arvensis and Asphodelus tenuifolius were the important ones due to their high density whereas in zone 11 besides these two weeds Fumaria indica also emerged earlier with considerable density. In zone Ill, the important weeds emerging earlier with comparatively high density were Fumaria indica, Medicago polymorpha, Melilotus indicus and Ranunculus muricatus whereas in zone IV it was Lamium amplexicaule, Medicago polymorpha and Veronica didyma which were amongst the important early emerging weeds because of their high density.
Like biomass, moisture content and nutrient uptake, different weeds varied in their reproductive behaviour in different rainfall zones. On the whole zone I had the lowest number of seeds produced by weeds whereas it increased with the increase in annual rainfall. Similarly, the soil seed reserves of weeds also increased with the increase in the annual rainfall Le., lowest in zone I and highest in zone IV.
Different ecological factors like soil moisture, water holding capacity, soil texture, organic matter, pH, electrical conductivity and the nutrient status of soil were found to affect the establishment of different weeds. However, their effect changed under different zones suggesting their role in a much complex interaction with each other as well as various other environmental factors.
Different sets of numerous variables were tried to forecast the weed problem but none of them was found perfectly valid. It was primarily because of the uncertainty of rainfall which makes the situation quite unpredictive. However, on the basis of the averages regarding the three year data of weed density,a weed management programme has been suggested which includes tillage operation for zone I and 11. Broadleaf herbicides like Bromoxynil and 2,4-D can also be used in zone 11. For zone III and IV alongwith these herbicides, broadspectrum herbicides such as Chlortoluron + MCP A or any other isoproturan, may also be used in case Avenafatua is present in high densities. In zone IV manual picking is suggested for Galium aparine along with integrated weed management for other weeds.