SEED BANK OF SUMMER WEEDS IN WHEAT FIELDS OF DIFFERENT RAINFALL ZONESOF PUNJAB, PAKISTAN

The soil seed reserves of different summer weeds were studied in the f ields of different rainfall zones of Punjab, Pakistan. Composite soil samples collected from fields comprising of very low (150-300 mm), low (300-500 mm), medium, (500-1000 mm) and high (1000-1500 mm) annual ra infall areas were kept in trays of uniform size in the green house at National Agricultural Research Centre, Islamabad. An environmental con dition was provided for germination of weed seeds. Seedlings emerging over a period of three years were identified, recorded and removed at intervals. The seed reserves of different zones differed from each oth er in terms of weed seed composition, seed number by species and total number of seeds in the soil. The species diversity and number of seed s in the soil remained lowest in very low rainfall area. With the incr ease in annual rainfall, both the parameters also increased with highe st values in the high annual rainfall area.