PhD

Competition from weeds and consequent yield reduction is a major problem in rice cultivation, which warrants proper weed management strategies. The present study was undertaken to develop and refine stale seed bed techniques and subsequent cultural practices for semi-dry and wet-seeded rice and to find out the optimum plant spacing, which can give maximum weed control efficiency coupled with better grain yield. Survey and documentation of prevailing weed control practices followed by rice farmers was another objective of the study.

Surveys conducted in Palakkad, Kole, Kuttanad and Pokkali regions revealed the popularity of physical and chemical methods of weed control among farmers. Among various herbicides available for use in rice, Fernoxone (2,4-D) is the major chemical used by the majority of farmers of Palakkad, Kole and Kuttanad regions.

The experiment on stale seed bed techniques for semi-dry rice was conducted during first crop seasons of 2006 and 2007 at Agricultural Research Station, Mannuthy and stale seed bed for wet-seeded rice was conducted in Alappad kole, Thrissur district during second crop seasons of 2005-06 and 2006-07. Seed bed preparation significantly influenced the germination and establishment of weeds both under semi-dry and wet-seeded conditions. Population and dry weight of weeds were the lowest in stale seed bed for 14 days. Stale seed bed technique adopted for forcing the germination of weed seeds showed differential response by different groups of weeds. Grass weeds gave the highest germination percentage immediately after seed bed preparation followed by broad leaf weeds. However, seed bed preparation was not effective on sedges.

Stale seed bed technique provided a partially weed free environment during the early crop growth stages and allowed the crop to yield better than normal seed bed. The yield difference between normal seed bed and stale seed bed decreased with reduction in the stale seed bed period mainly because of the short time available to achieve the optimum environment essential for the germination of buried seeds. Among the sub plot treatments, pre emergence spraying of herbicides and concurrent growing of green manure crops gave significant reduction in the population and dry weight of weeds and thus better grain yield. Stale seed bed for 14 days gave the highest benefit ratio both under semi-dry and wet-seeded situation during both years of the experiment.

Experiment to assess the influence of plant stand on crop-weed competition was conducted in farmer’s field at Alappad Kole, Thrissur district during the second crop season of 2005-06 and 2006-07. Canopy modification by altering plant spacing significantly helped the crop to maintain a dominant position over weeds as indicated by the decreased weed problems in closer plant spacing. Higher grain yields of 8858 kg ha-1 and 7825 kg ha-1 during first and second years of study were observed in closer spacing of 10 cm X 10 cm spacing under the recommended package of practices of Kerala Agricultural University followed by 20 cm x 10 cm. Among the weeded plots, the lowest grain yield was in SRI plots with cono weeding.

Plants at wider spacing (30 cm X 30 cm) produced more number of tillers per hill. However, on unit area basis a reverse trend was observed. Increase in plant density under closer spacing significantly reduced the dry matter production of weeds. The weed problem was very high in SRI management, even after four cono weedings.

The reduction in grain yield in unweeded plots under closer plant spacing was negligible when compared to weeded plots. This indicates the possibility of maintaining the field without much economic loss from weeds by transplanting 20-day old seedlings, with two seedlings per hill at a closer spacing of 10 cm X 10 cm. This is both economical and ecofriendly as the need for hand weeding or herbicides is eliminated. The present experiment indicates that SRI system does not hold much promise in regions where farmers follow recommended package of practices.