1. KAUTIR (Kerala Agricultural University Theses Information and Retrieval)

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Has files: YesSubject: search.filters.subject.Crop weed competition in rice

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    Efficiency of thiobencarb in dry sown rice
    (Department of Agronomy, College of Horticulture, Vellanikkara, 1987) Jayasree, P K; Abraham, C T
    A field experiment was conducted at the Agricultural Research Station, Mannuthy of Kerala Agricultural University during the first crop season of 1986 to find out the best time and method of application of thiobencarb in dry sown rice. The treatments included combinations of six time and two method of applications and two controls (un weeded and hand weeded), laid out in RBD with three replications. The results showed that the count, dry matter production and nutrient removal of weeds were appreciably reduced by the weed control treatments, particularly by the spray applications at 6 and 9 days after sowing. Effective control of the weeds during the critical stages of the crop was obtained for the spray treatment. , while the new flushes of weeds after each hand weeding posed some competition in the hand weeded plot. The weed control efficiency was highest during the critical stages for the spray applications at 6 and 9 days after sowing, even higher than that of hand weeding. The herbicide did not produce any phytotoxicity symptoms on the crop. Tiller production was found to be adversely effected by weed competitions whereas the crop plants tended to grow taller with increased weed density. A significant negative correlation was found to exit between the crop and weed dry matter productions. The spray treatments at 6 and 9 days after sowing produced higher crop dry matter and resulted in maximum uptake of nutrients during the critical stages. The spray applications at 6 and 9 days after sowing gave significantly higher values of the yield attributes viz., the productive tillers per hill, length of panicle and number of grains per panicle, resulting in higher grain yields on per with the hand weeding. These treatments recorded higher straw yields also. The weed index values were lower for 6 and 9 days treatments after sowing. In terms of return per rupee invested, the spray application of herbicide at 6 days after sowing was the best.
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    Floristic diversity, autecology and competitive behaviour of weed flora in wetland rice ecosystem
    (Department of Agronomy, College of Agriculture, Vellayani, 2010) Sajith Babu, D; Sansamma George
    Floristic diversity, autecology and competitive behaviour of weed flora in the wetland rice ecosystem were studied by conducting a field survey and two field experiments. The field survey was conducted during the first and second crop seasons of 2003 in the rice fields of 30 panchayaths in Thiruvananthapuram district having more than 50 hectares of net sown area, covering all the four thaluks of the district. Weed flora was surveyed from both cultivated and fallow fields. The design adopted for conducting the floristic survey was Stratified Multistage Random Sampling and the methodology was Census Quadrate Method. The field experiments were conducted during the first crop seasons of 2003 and 2004 at College of Agriculture, Vellayani. The design adopted was Strip plot. The treatments included four levels of nutrient management and three levels of crop spacing and the number of replications was five. Part III of the investigation was an autecological study wherein the growth and development pattern of two of the major weed flora observed in the experimental area was studied by keeping an area of 1.2 X 4.2 m2 on the same side of all the plots in Part II. Perusal of the results of the field survey indicated that substantial diversity of weed flora existed in the wetland rice ecosystem in Thiruvananthapuram district of Kerala. In the cultivated rice fields, there were 46 weed specii during the first crop season and 49 species during the second crop season. In the rice fallows during the first crop season there were 43 specii while during the second crop season there were 54 specii. In the cultivated fields during both seasons, the most prominent species among the different classes of weeds (grasses, sedges and broad leaved weeds) were Isachne miliacea Roth ex Roem et Schult, Cyperus iria L. and Monochoria vaginalis (Burm.f.) Presl. Ex Kunth respectively. Isachne miliacea Roth ex Roem et Schult was the dominant grass weed in the fallows as well. However the dominant sedge weed in the fallows was Cyperus distans L.f. during the first crop season while it was Fimbristylis miliacea. during the second crop season. Monochoria vaginalis (Burm.f.) Presl. Ex Kunth and Ludwigia perennis topped the list of broad leaved weeds in the rice fallows during first and second crop seasons respectively. Results of the field experiment showed that weed growth in the rice field was influenced significantly by the sources and levels of nutrients as well as by crop spacing. During both the years at 20 and 40 DAT the weed density and dry weight were the lowest when the rice crop was treated with NPK @ 90:45:45 kg ha-1 applied with 25 per cent N as organic (N2) while at 60 DAT enhanced nutrient level (NPK @ 112.5:56:25:56.25 kg ha-1) applied with 25 per cent N as organic (N4) recorded the lowest value. During both the years, at all growth stages the weed density and dry weight were the lowest under the closer spacing of 15 X 15 cm (P1) The grain and straw yield were maximum under NPK @ 112.5:56:25:56.25 kg ha-1 applied with 25 per cent N as organic in combination with widest spacing (n4p3). Dead heart occurrence was minimum under the widest crop spacing The net income and Benefit : Cost ratio were the highest when rice crop was treated with 125 per cent of the recommended NPK with 25 per cent organic substitution in combination with widest spacing (n4p3) Autecological studies showed that the growth and development of Isachne miliacea Roth ex Roem et Schult. was significantly influenced by the management practices for the associated rice crop. The higher dose of NPK applied as chemical fertilizers only (N3) along with widest spacing (P3) stimulated all the vegetative parameters (shoot / root length and plant spread) of the weed. During both the years plants growing in rice fields treated with recommended dose of NPK with 25 per cent organic substitution (N2) and rice crop planted at wider spacing (P3) recorded delayed flowering but produced more seeds per panicle The root and shoot length of Cyperus iria L growing in rice fields treated with 100 per cent recommended NPK as chemical fertilizers (N1) with minimum spacing (P1) recorded the maximum value during the both years. Delayed flowering of the sedge was noticed under N2. The number of seeds produced per plant was significantly high under N4 and P3. The general trend was that addition of organic manures in rice delayed flowering but increased seed production in the associated sedge weed From the studies it may be concluded that by altering nutrient management and adjusting the plant population, the competitive ability and productivity of rice crop can be improved substantially. Though, closer spacing of 15 X 15 cm significantly reduced the density and dry weight of weeds, the wider spacing of 20 X 20 cm in conjunction with enhanced fertilizer dose of 112.5:56:25:56.25 kg NPK ha-1 applied with 25 per cent N as organic manures significantly enhanced the rice grain and straw yield. The treatment also resulted in significant enhancement in net income and B:C ratio in medium duration variety Aiswarya in first crop season.