Effect of Different Densities of Isachne globosa (Thunb.) O.Ktze on Growth and Yield of Rice (Oryza sativa L.)

Abstract

Weeds are the major biotic stress in rice production while act as a universal pest in agriculture. Weed management is the key factor towards achieving high productivity in rice cultivation. It has been reported in Sri Lanka that 30-40% of rice yields are generally lost due to weed competition in Sri Lanka (Abeysekera, 2001). Degree of loss due to weeds could be varied, depending on type of weed species, weed density, duration of crop weed interference, rice cultivar and cultural practices. Weeds grow quickly in direct seeded wetland rice cultivation compared with the weeds growth in wetland transplanted rice cultivation and other crops. Isachne globosa is one of the major noxious weed associated with the yield reduction of rice, across all agro ecological zones of the country. Even more present of I. globosa on rice field may not be economic to control and contemplate on herbicide spraying also depends on the density of weeds. No scientific study has conducted to find out the competitiveness of I. globosa and its effect on growth and yield of rice. Hence, the objective of this study was to find the effect of different densities of I. globosa on growth and yield of rice.

Methodology

A field experiment was conducted in an open ground at the Weed Science Division of Rice Research and Development Institute, Batalagoda which is in the Low country Intermediate Zone of Sri Lanka, during Dry season (Yala) from May to September 2013. The pots were filled with puddle soil which was directly taken from the field, with a pH of 5.95, cation exchange capacity 115μS/cm, soil organic matter 1.80%, available N 18meq/100g, lsen’s P 1 ppm, and available K 0.11meq/100g. In this experiment, 30cm*30cm pots were used in Complete Randomized design (CRD) with three replicates. The treatments were consisted with seven and control. Three months old rice variety Bg 300 was used in the study and sprouted seeds were sown in the 7.5cm*7.5cm and I. globosa stem cuttings were planted surrounding the rice seedlings maintaining equal distance. The un-introduced weeds were uprooted time to time to maintain the desired weed density. All the other plant protection and agronomic practices were adopted according to the recommendations of the Department of Agriculture. Plant growth parameters were collected in two weeks interval and 56 days old weeds were uprooted to measure the dry weight. The number of panicles per square meter, number of grains per panicle, filled grain percentage, thousand grain weight and grain yield per square meter were recorded after harvest. The data were statistically analyzed using the statistical package Minitab15.