CRITICAL PERIOD OF WEED COMPETITION IN TRANSPLANT AUS RICE CV Bangladesh Agron. J. 2014, 17(1): 95-102 CRITICAL PERIOD OF WEED COMPETITION IN TRANSPLANT AUS RICE cv. BRRI dhan27 UNDER NON-SALINE AGRO-ECOSYSTEM M. T. Rahman, S. Ahmed, N. J. Lipi, M. H. Rashid and M. I. Hoque1 Department of Agronomy, Patuakhali Science and Technology University, Patuakhali, Bangladesh, 1Department of Environmental Science, Bangladesh Agricultural University, Mymensingh, Bangladesh Corresponding author: trahman302@gmail.com Key words: Critical period, weed competition, transplant Aus, BRRI dhan27 Abstract A study was conducted to determine the critical period of weed competition in transplant Aus rice for var. BRRI dhan27. Among the treatments, weed free condition, competition of weed for first 10, 20, 30, 40, 50, 60 and 70 days and weed free later on, unweeded condition, one weeding at 20 days after transplanting and one weeding at 40 days after transplanting, the unweeded control plots showed the poor performance result in case of maximum parameters where grain yield was reduced the highest percentage (38.54%). On the basis of cost benefit ratio it was observed that the critical period of crop weed competition extended up to 30 days after transplanting of aus var. BRRI dhan27. Introduction Rice is one of the most important staple foods for more than half of the world’s population (IRRI, 2006) and influences the livelihoods and economies of several billion people. In Asia, more than 80% of the people live on rice, and their primary food security is entirely dependent on the volume of rice produced in this part of the world (Kabir, 2006). It is estimated that 40% of more rice production will be required by 2030 to satisfy growing demand with no increases in cropping areas (Khush, 2005). Weeds are at present the major biotic constraint to increase rice production world wide (Zhang, 1996). About 33% of this loses are caused due to weeds alone (Mukherjee and Singh, 2005). The yield losses due to uncontrolled weed growth in lowland and upland rice ranged from 12 to 81% (Chopra and Chopra, 2003; Mukherjee and Singh, 2005). Normally the loss in rice yield ranges between 15-20% yet in severe cases the yield losses can be more than 50% depending upon the species and intensity of weeds (BRRI, 2006). To develop a comprehensive control program for the weed, it is important to know its critical period of competition in transplant rice. The critical period of weed competition depends on several factors like species of weed, life time duration of crops, climatic factors, crop species, environmental factors etc. Critical period of weed control is an integral part of integrated weed management (IWM) and can be considered the first step to design weed control strategy (Anonymous, 2003). In general critical period of crop weed competition is throughout in direct seeding situation and in transplanted it vary from 15 to 45 days (Singh and Bhan, 1988). The most critical period for competition between rice and weeds is when the rice is in the vegetative phase and the yield components of rice are being differentiated (Mukherjee and Singh, 2003). Though critical period of weed–crop competition is an important component of weed management technology package for any crop but for aus variety BRRI dhan27 it has not been investigated to find out the critical period of weed competition in transplant Aus rice cv. BRRI dhan27. Materials and Methods 96 Rahman et al. The study was conducted at the field Laboratory of the Department of Agronomy, Patuakhali Science and Technology University, Patuakhali during the period of April to August 2012. Geographically, the Patuakhali Science and Technology University is situated at 20°20″ N latitude and 90°20″ E longitude. It belongs to the Agro Ecological Zone (AEZ)-13 named Ganges Tidal Flood Plain. The experimental site was about 1.5 m above the sea level. The field of the experimental site was characterized by Non calcareous Grey Floodplain soil with silty clays. It was well drained and medium high. The soil was mildly alkaline, non-saline, loam in texture and having soil PH ranges from 5.50 to 6.50. Organic matter content was low (1.1%) (SRDI, 2005). The experiment was laid out in a randomized complete block design with three replications and eleven treatments as: T1 = Weed free condition, T2 = Competition of weed for first 10 days and weed free later on, T3 = Competition of weed for first 20 days and weed free later on, T4 = Competition of weed for first 30 days and weed free later on, T5 = Competition of weed for first 40 days and weed free later on, T6 = Competition of weed for first 50 days and weed free later on, T7 = Competition of weed for first 60 days and weed free later on, T 8 = Competition of weed for first 70 days and weed free later on, T 9 = Unweeded condition, T10 = One weeding at 20 days after transplanting (DAT) and T11 = One weeding at 40 DAT. The area of a unit plot was 4 m × 2.5 m. The sprouted seeds were sown in the prepared seed beds on 5th April, 2012. The seedlings were transplanted in the main field @ 2 seedlings hill-1 with 20cm × 15 cm spacing on 30th April, 2012. Fertilizers were applied @ 168 g Urea, 60 g TSP, 30 g MoP, 17 g Gypsum and 5 g ZnSo 4 to the plots. The whole amount of fertilizers except N was applied before final land preparation. Urea was top dressed @ 56 g in three equal splits at 15, 30 and 45 days after transplanting. Proper crop protection measures were taken during the entire course of crop production. Weeds were collected at every 10 days interval according to the treatments mentioned. Number of weed plant of each species in the unit plot was counted with the help of a plant counter. The intensity of infestation of each species of weed was calculated as the number of weed stands per unit area divided by the number of hills per unit area. Three weed sample plot- 1 were collected at the time of weeding. The plant counter was placed at random in the unit plot and all the weeds within each 1 m2 were uprooted, dried first in the sun and thereafter, 24 hours in an electric oven maintaining a constant 1050 C. After drying weeds weight of each sample was measured and expressed in g m-2. Three weed sample plot-1 were collected at the time of harvesting. The crop of all plots was harvested on 3 July 2012. Crop and yield contributing were also recorded. Results and Discussion Seven species of weeds under four different families were found in the experimental field. Three species belonged to the family Cyperaceae, two from Gramineae and one from each of Onagraceae and Pontederiaceae (Table 1). Among those weed species, Cyperus difformis L., Jussiaea decurrens (Watt.) DC. Cynodon dactylon (L.) Pers. were predominated, and constituted about 84% of the total weed vegetation. Only Cyperus difformis L. constituted 63.82 percent of total weed infestation and it was followed by Jussiaea decurrens (Watt.) DC. (11.40 percent). In total 14.26 weeds competed against one hill of rice of which 10.16 belonged to the family Cyperaceae, 1.88 belonged to the Gramineae family and rest small portion was belonging to other two family. Thirteen types of weeds were found in direct seeded and transplanted aus rice as affected by method of planting and weeding regime by Sarker et al. (2002). Individually the highest intensity of weed infestation (9.09 hill-1) was recorded in Cyperus difformis L. Fimbristylis miliacea (L.) Vahl. showed the lowest intensity and numerically it was only 0.38 weeds hill-1. Jussiaea decurrens (Watt.) DC. and Cynodon dactylon (L.) Pers. was produced in an intensity of 1.63 and 1.22 weeds hill-1. In case of weed population per square meter space total 456 weeds were found m-2 and the highest and lowest number of weeds belonged to the family Cyperus difformis L. and Fimbristylis miliacea (L.) Vahl. respectively as percent of total weed vegetation and intensity of weed infestation at weeding. In a study Ahmed et al. (1986) found that the principal weeds were Monochlora vaginalis, Scirpus mucrontus and Cyperus iria in case of BR3 cultivation in Aus season. In another study in case of direct seeded upland rice cultivation Cyperus rotundus and Echinochloa crusgalli 97 Critical Period of Weed Competition in Transplant Aus Rice was the principal weed (Mamun et al., 1986). Mercado (1979) found that competition of Echinochloa crusgalli was found to be the highest at a density of 20 plants m-2 within the critical period of crop-weed competition. This difference might be due to climatic change, varietal change and other cultural management. Table 1. Infested weed species and their population in transplant Aus rice cv. BRRI dhan27 Name of weeds Family Weed populatio n m-2 % of total weed Intensity of weed (hill-1) Local Name English Name Scientific Name Sobuj nakful Green flatsedge Cyperus difformis L. Cyperaceae 291 63.82 9.09 Pani morich Winged water primorse Jussiaea decurrens (Watt.) DC. Onagraceae 52 11.40 1.63 Durba Bermuda grass Cynodon dactylon (L.) Pers. Gramineae 39 8.55 1.22 Chechra Bog bulrush Scirpus mucronatus L. Cyperaceae 22 4.82 0.69 Chela Sheand grass Parapholis incurve L. Gramineae 21 4.61 0.66 Soto panikochu Pickerel weed Monochria vaginalis (Burm. F.) presl. Potedariac- eae 19 4.17 0.59 Joina Globe fringerush Fimbristylis miliacea (L.) Vahl. Cyperaceae 12 2.63 0.38 The weed population increased gradually from the competition of weed for first 10 to 60 days and weed free later on. The highest (598.00) weed population was found in T7 (competition of weed for first 60 days and weed free later on) and the lowest one (77.00) was found in T 2 ( for first 10 days and weed free later on). During harvesting time no weed was found in the experimental plot as the plots were kept weed free after every weeding treatment (Table 2). The highest (498.30) number of weeds were found in the plots which were kept unweeded (T9) and the lowest (288.70) was found in T 11 (One weeding at 40 DAT). All the treatments had significant effect on weeds dry weight m-2 at weeding. Treatment T7 produced the highest (254.20 g) weeds dry weight at weeding whereas T2 produced the lowest (6.54 g). The treatments T9 and T10 gave the highest (204.20 g) and the lowest (144.30 g) dry weight of weeds. Similar result was found by Sarker et al. (2002). On average 33.8% weed dry weight was reduced due to competition from Aus rice (Karim, 2000). Table 2. Effect of duration of weed competition on the population and dry matter production of weeds in cultivation of transplant Aus rice cv. BRRI dhan27 Treatments Weeds population (m-2) Weeds dry weight (m-2) At weeding At harvest At weeding At harvest T1 0.00j 0.00d 0.00 i 0.00d T2 77.00 i 0.00d 6.54h 0.00d T3 152.00h 0.00d 7.69h 0.00d T4 218.00g 0.00d 51.84f 0.00d T5 361.00d 0.00d 147.30e 0.00d 98 Rahman et al. T6 415.00b 0.00d 168.60b 0.00 d T7 598.00a 0.00d 254.20a 0.00d T8 398.00c 0.00d 162.90c 0.00d T9 0.00 j 498.30a 0.00 i 204.20a T10 287.00f 311.70b 48.31g 144.30c T11 332.00e 288.70c 158.40d 165.20b LSD (0.05) 0.69 1.55 3.19 2.94 Different treatments had significant effect on the plant height of transplant Aus rice cv. BRRI dhan27. Numerically the plots which were kept weed free for whole the cultivation period (T 1) gave the highest (138.8 cm) plant height and it was followed (136.1 cm) by 10 days for weed competition. On the other hand, the plots which were allowed for competition of weed for first 60 and 70 days; and the plots which were weeded only once at 40 days after transplanting (DAT) gave the lower plant height than others (fig. 1). Perera et al. (1992) and Sultana (2000) also found similar reduction on rice plant height due to competition of E. crusgalli. Fig. 1. Effect of duration of weed competition on plant height of transplant Aus rice cv. BRRI dhan27 (LSD (0.05) = 4.67) All the plots except those were kept unweeded (T9) for the entire cultivation period showed statistically at par in terms of panicle length. Treatments T1 to T4 produced higher panicle length than others where the longest (24.14 cm) panicle was produced where kept weed free throughout the cropping period (T1). The plots in which first weeding were done after 40, 50, 60 and 70 days after transplanting and unweeded throughout the cropping period gave lower number of total tillers than others (Table 3). Table 3. Effect of duration of weed competition on the yield contributing characters of transplant Aus rice cv. BRRI dhan27 Treatments Panicle length (cm) Total tillers hill-1 (No.) Filled grains panicle-1 (No.) Unfilled grains panicle-1 (No.) 1000-grain weight (g) T1 24.14a 11.09a 108.0a 16.72a 31.55a T2 23.90ab 10.75a 104.7ab 14.46b 31.55a T3 23.77abc 10.82a 101.4bc 10.56d 31.58a T4 23.10bcd 9.557b 98.13c 14.60b 31.22ab T5 22.84cde 8.837c 98.54c 9.493e 31.54a T6 22.61def 8.820c 92.11d 16.49a 31.00abc 99 Critical Period of Weed Competition in Transplant Aus Rice T7 22.24def 8.297cd 84.40e 10.46d 30.77bcd T8 21.65f 8.543cd 78.31f 12.25c 30.46cd T9 19.14g 8.003d 74.42g 14.26b 30.15d T10 22.04ef 9.647b 84.84e 7.710f 30.73bcd T11 21.90ef 9.650b 86.75e 14.60b 30.53cd LSD (0.05) 1.01 0.65 3.56 0.64 0.66 The plots which were kept weed free throughout the whole cultivation period, and the plots in which first weeding were done at 10, 20, and 30 DAT i.e. T1 to T4 gave statistically higher number (9.865–10.37) of effective tillers (Fig. 2). Fig. 2. Effect of critical period of rice weeds competition on effective tillers hill- 1 of transplant Aus rice cv. BRRI dhan27 (LSD (0.05) = 0.80) The highest (108.00) number of filled grains panicle-1 was recorded from the plots which were kept weed free for the total cropping duration. Plots which were weeded for the first time at 20 DAT and kept weed free for later on (T3) showed the highest 1000- grain weight (31.58 g). The plots which were weeded only once at 20 and 40 DAT (T 10 and T11) showed similar effect (3.29 and 3. 28 t ha -1) in terms of grain yield of BRRI dhan27. Percent grain yield reduction was increased with the increasing of weed competition period and it reached to the highest as 34.54% in unweeded control plots. In case of one weeding, weeding at 20 and 40 days after transplanting reduced the grain yield of about 17% of that of the weeded control plots. Weed free plots and the plots in which the competition of weed were allowed for first 10, 20, 30 days and kept weed free for later on gave higher yield than others. Grain yield of T. Aus rice cv. BRRI dhan27 was significantly affected by the treatments of weeding. The plots which were kept weed free from transplanting to harvesting gave the highest (3.97 t ha-1) grain yield and it was followed (3.94 t ha-1) by T2 .The unwedded plots gave the lowest (2.44 t ha -1) yield and it was followed by treatments (Table 4). When weed infestation is increased, the rice plants deprive from nutrient and other environmental components. As a result, the long time weed infested plot showed lower performance than short time weed infestation. Table 4. Effect of duration of weed competition on the yield of transplant Aus rice cv. BRRI dhan27 Treatments Grain yield Straw yield t ha-1 % reduction t ha-1 % reduction T1 3.97 a - 3.22 ab - T2 3.94 a 0.76 3.36 a -4.25 100 Rahman et al. T3 3.90 a 1.76 3.22 ab 0.00 T4 3.89 ab 2.02 3.09 ab 4.04 T5 3.76 b 5.29 2.86 bc 11.18 T6 3.50 c 11.84 2.65 cd 17.70 T7 3.05 e 23.17 2.53 cd 21.43 T8 2.49 f 37.28 2.34 d 27.33 T9 2.44 f 38.54 2.42 d 24.84 T10 3.29 d 17.13 2.65 cd 17.70 T11 3.28 d 17.38 2.57 cd 20.19 LSD (0.05) 0.13 - 0.42 - Weed population and their dry weight was increasing with the increasing of weed competition duration and weed removal delayed up to 60 days after transplanting and decreased thereafter. It might be due to death of some older weeds and thinning of newly germinated weeds. Unweeded control plots showed the poor result in case of maximum parameter where the grain yield reduced in the highest percentage (38.54%). In case of grain and straw yield the plots which were allowed for 10 days weed competition (T2) showed the highest performance. Treatment T2 gave better plant height (136.1), panicle length (23.90) and effective tillers hill-1 (10.13). 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