Pak. J. Weed Sci. Res. 10(3-4):119-128, 2004

Effect Of Seeding Rates And Herbicides On Weed Dynamics And Paddy Yield Of Direct Wet-Seeded Rice

Inayat Ullah Awan^[1], Khizar Hayat^[2], Gul Hassan^[3],

Mushtaq Kazmi^[4] and Nazir Hussain²

Abstract

Field experiments were conducted at Agricultural Research Institute, Dera Ismail Khan, Pakistan during 1999 and 2000 to develop a viable and economically feasible rice weed management technology for the rice growers of southern area of NWFP. Main objective of the study was to establish an appropriate weed management strategy for effective control of weed flora in direct wet-seeded rice. The experiments consisted of three seeding rates of 60, 90 and 120 kg ha^-1 in main plots and oxidizon (Ronstar 12L), oxidiargyl (Topstar), preticlachlor (Rifit) and acetachlor (Acelor) in the sub-plots were applied at post-emergence stage including weedy check. Herbicides pretilachlor and acetachlor with 120 kg ha^-1 seed rate proved effective control of grasses and sedges and increased the yield and yield attributes with increased net return over other herbicides and weedy check.

Key words: Rice Topstar Acelor Rifit Ronstar weed management.

Introduction

Rice is the main livelihood of rural population in many Asian, African and Latin American countries. In Pakistan, it is also the staple food for millions of people and is next to wheat. It plays a pivotal role in the economy of Pakistan by adding a handsome amount of foreign exchange into the national exchequer (Anonymous, 2001). Weeds are, no doubt, a major pest and constraint to reducing rice production. Weeds share light, nutrients and water with the crop and thus interfere with rice growth in many ways. Living or decaying weeds can secrete toxic root exudates or leaf leachates that depress the normal growth of rice plant. Weed infestation provides a habitat for growth of various pest organisms (insects, nematodes and pathogens), which adversely effect the production of rice and other crops. Similarly weeds demand high labor inputs for control (Labrada, 1998). Weed control has always been one of the major inputs in rice production. Various methods like cultural, mechanical, biological and chemicals are used for weed control. The chemical weed control method is becoming popular among the farmers because it is the most efficient means of reducing weeds competition with minimum labor cost (Baloch, 1994; Awan, 1988). Moreover, judicious use of herbicides is the only and logical alternative weed control method, especially in the wet-seeded rice (Moody and Cordova, 1985). Besides, weed control through chemicals, the cultural control method including the manipulation of planting density (seeding rate) is also one of the most effective ways of weed control. Close spacing is essential to minimize weed infestation and increase paddy yield (Nigam et al., 1988).

Materials and Methods

Experiments were laid out in a randomized complete block (RCB) design with split-plot arrangement having three replications during 1999 and 2000. The plot size was kept as 5´3 m² during both the years. Main-plots consisted of three seeding rates (60, 90 and 120 kg ha^-1) while four herbicides and the weedy check were kept in the sub-plots (Table-1).

Table-1. Detail of herbicidal treatments in sub-plots

The land was prepared to form a fine tilth by ploughing, harrowing and tillering once each. A total quantity of fertilizer @ 120-90-60 kg ha^-1 of N, P₂O₅ and K₂O were applied. Full dose of P₂O₅ and K₂O and half of N was applied at the time of planting, while the remaining half N was applied at the panicle initiation stage. Rice variety IR-6 seed was selected at a specific gravity of 1.13 in salt water, prepared by dissolving about ½ kg of salt in 100 liters of water.  The seed that sank in the salt water was selected for sowing and the light, floating, and unviable seed was discarded. After rinsing the salt water, the seed was kept immersed in water for 24 hours and then under moist gunny bags for 36 hours to a pigeon breast like shape i.e. having pre-germinate swollen seed stage. Pre-germinated seed was used.

1. Dry weed biomass (g m^-2).
2. Number of panicles m^-2.
3. Number of spikelets panicle^-1.
4. Sterility (%).
5. 1000-grain weight (g).
6. Paddy yield t ha^-1.

All the data were subjected to the analysis of variance to determine the significance of treatment means (Steel and Torrie, 1984). Duncan’s Multiple Range Test (DMRT) was used for comparing treatment mean (Duncan, 1955).

Results And Discussion

Dry weed biomass (g m^-2)

It is evident from the analysis of the data that herbicides, seeding rates and interaction of the herbicides with the seeding rates were significantly different during both the years for dry weed biomass (Table-2). Lowest dry weed biomass (77.57 g and 91.14 g) was recorded in the treatments applied with acetachlor herbicide during 1999 and 2000, respectively. It was statistically at par with preticlachlor (93.67 g) during 2000. The effective weed control of acetachlor may be due to its translocation from the leaves and shoots to the underground parts of the weeds and inhibiting the cell division. The highest dry weed biomass of 110.47 and 111.55 g was recorded in weedy check in both experiments. During 1999, oxadiangyl (89.70 g) and pretilachlor (88.24 g) were statistically equal for the said trait. The highest seed rate of 120 kg ha^-1 significantly affecting the weed biomass produced the minimum dry weight (81.99 g and 94.59 g) during 1999 and 2000, respectively. These results are in agreement with those of Moody (1977), Shad (1983) Sing et al. (1989), Mabbayad and Moody (1992) and Awan et al. (2000), regarding the effect of seeding rates and herbicides application on dry weed biomass.

Number of panicles m^-2

Results showed significant differences for seeding rates, herbicides and their interaction for number of panicles m^-2 during both the years. The seeding rate of 120 kg ha^-1 produced higher number of panicles m^-2 (432.9 and 593.4 ma^-2). However, it was statistically at par with seeding rate 90 kg ha^-1 during first year. Acetachlor gave more panicles m^-2 (458.1) than oxadiazon, but at par with pretilachlor (449.4 m^-2) during 1999 for the said trait. However, during 2000, the number of panicles produced by the acetachlor was significantly higher (580.4) than other herbicides. All the herbicides applications produced higher number of panicles than weedy check during both the years. Acetachlor herbicide when applied to 120 kg ha^-1 seeding rate produced highest number of panicles (473.3 and 678.0 m^-2), during 1999 and 2000, respectively (Table-3). This might have been due to high number of tillers in the plots where acetachlor was applied. The results are fully supported by the findings of Awan et al. (2000). They recorded significantly higher number of panicles with 120 kg ha^-1 seeding rates while acetachlor herbicide application produced more number of panicles per square meter being advocated by Qazzafi (2000). However, Awan et al. (2001) observed that pretilachlor herbicide caused more panicles production m^-2, whereas, Jones and Snyder (1987) reported higher panicle number with increased seeding rates.

Number of spikelets panicle^-1

Data regarding number of spikelets (Table-4) revealed that seeding rates, herbicides and their interaction influence the number of spikelets during both the years. The seeding rate of 120 kg ha^-1 gave the highest number of spikelets per panicles (132.7 and 144.9) during 1999 and 2000, respectively followed by 90 kg ha^-1 seeding rate. Minimum spikelets were noted with 60 kg ha^-1 during both the years. Herbicide acetachlor produced significantly more spikelets per panicle (135.2 and 144.3) during 1999 and 2000, respectively. Pretilachlor followed acetachlor for number of spikelets during both the trial years. Weedy check gave the minimum number of spikelets per panicle during both the years. The plants in weedy check were of very poor growth due to severe crop-weed competition. The growth of weeds in check plots went unchecked which reduced the availability of moisture and other plant nutrients to crop plants and eventually resulted in reduced size of panicles with lesser number of spikelets. Interaction between the seeding rates and herbicides also affected the number of spikelets and higher number of spikelets was recorded (140.0 and 158.0) during 1999 and 2000, respectively in the 120 kg ha^-1 seeding rate treated with acetachlor herbicide. Results were supported by Sohail et al. (1999), Awan et al. (2000) and Baloch et al. (2000), who observed maximum number of spikelets with 120 kg ha^-1 seeding rate, However, Awan et al. (2001) recorded larger number of spikelets per panicle with the application of acetachlor herbicide.

Sterility (%)

Sterility is the name given to unfertilized and unfilled spikelets. Data regarding sterility percentage (Table–5) showing that sterility was affected by herbicides during both the years and interaction of seeding rates with herbicides during 1999 only, while seed rates itself did not differ significantly during both the years. Acetachlor reduced sterility significantly (11.40%) as compared to weedy check during first year. However, all the herbicides were at par with one another and with the weedy check for the trait. During 2000, the sterility percentage was also significantly lower (22.04%) with the acetachlor than other herbicides. All the herbicides except oxadiargyl during 2000 gave significantly lower sterile spikelets than weedy check. The acetachlor herbicide treatment in 120 kg ha^-1 seeding rate produced lower sterility percentage (10.00% and 20.89%) during first and second year, respectively. Overall sterility percentage during 2000 was higher than that during the preceding year. This might have been due to difference in mean temperatures, humidity and weed flora during both years. The findings are in close agreement with Baloch et al. (2000), who reported higher sterility percentage with lower seeding rates in rice crop whereas, Awan et al. (2001) observed lower sterility percentage when acetachlor herbicide was applied. Qazzafi (2000) found no significant difference for the trait between the applications of different herbicides, including weedy check.

1000-grain weight (g)

Data regarding 1000-grain weight (Table–6), indicated that seedling rates, herbicides and their interaction during 1999 significantly influenced the 1000-grain weight during both years except seeding rates during 2000. The seeding rate of 120 kg ha^-1 gave significantly heavier grains (24.13 g) than 60 and 90 kg ha^-1. Acetachlor produced grains (25.42 g), which were statistically equal in weight to pretilachlor (25.40 g), but were significantly higher in weight produced by oxadiazon (22.48 g), oxadiargyl (23.82 g) and weedy check (16.29 g) during 1999. During 2000, all the herbicides were at par for the said trait, but were significantly higher than the weedy check. Interaction between the seeding rates and herbicides differed significantly from each other during both the years of experimentation. Higher 1000-grain weight was recorded in the 120 kg ha^-1 seeding rate with acetachlor (27.50 g) and oxadiargyl (27.10 g) during 1999. The heavier grains produced with the application of oxadiazon and oxadiargyl during the 2000 than when these herbicides were applied during 1999 might have been due to the higher percentage of sterility during the year than those during 1999 which may due to translocation of nutrients to the left over grains and might have caused the increase in the weight during 2000 as compared to that in 1999. Findings are in close agreement with results given by Awan et al. (2000) and Baloch et al. (2000), who observed heavier grain weight with 120 kg ha^-1 seeding rate. However, Qazzafi (2000) noted maximum 1000-gain weight when herbicide pretilachlor was applied.

Paddy yield (t ha^-1)

Analysis of the data regarding paddy yield indicated the significant effects of seeding rates, herbicide applications and their interaction during 1999 while during 2000 only herbicides significantly differed. Seeding rate of 120 kg ha^-1 produced significantly higher yield (7.74 ha^-1), which was followed by 90 kg ha^-1 (6.48 t ha^-1). Both the lower seeding rates did not differ significantly from each other during 1999. Herbicide acetachlor produced higher paddy yield (7.89 and 7.15 t ha^-1) during 1999 and 2000, respectively; but during the second year herbicides did not differ within themselves, while during first year acetachlor yield was at par with pretilachlor (7.50 t ha^-1). However, during both years, herbicides proved superiority to weedy check for paddy yield. Interaction between the seeding rate (120 kg ha^-1) and herbicide application of acetachlor during 1999 produced highest paddy yield (9.20 t ha^-1), which was at par with pretilachlor (8.50 t ha^-1) and oxadiargyl (8.33 t ha^-1) when applied to the same seeding rate during 1999. Acetachlor comparatively produced higher yield with 120 kg seeding rate during 2000, though the difference was not significant when compared within the same and the other seeding rates treated with herbicides (Table-7). Lower yields during the second year of the trial as compared to those obtained during 1999 might have been due to higher sterility percentage and comparatively more weed density. The results are in agreement with the findings of Parao, 1974; Gilal and Qureshi, 1976. All the workers reported increased paddy yield with narrow spacing. While, Baloch et al. and Awan et al. (2000) reported higher yields with 120 kg ha^-1 seeding rates. Awan et al.. (2001) observed more yield with the application of acetachlor herbicide in direct wet seeded rice.

Table–2.   Dry weed biomass (g m^-2) 45 DAS as affected by different seeding rates and herbicides application in direct wet-seeded rice during 1999 and 2000

CV = 2.46%                                                      CV = 3.712%

LSD _0.05 = 1.920 (S. Rates)                                  LSD _0.05 = 2.148 (S. Rates)

LSD _0.05 = 2.219 (Herbicides)                               LSD _0.05 = 3.105 (Herbicides)

LSD _0.05 = 3.843 (Interaction)                               LSD _0.05 = 5.378 (Interaction)

Means followed by the same letter (s) in the respective category are non significant P £ 0.05.

Table-3.     Number of panicles (m^-2) as affected by different seeding rates and herbicides application in direct wet-seeded rice during 1999 and 2000

CV = 6.00%                                                        CV = 1.55%                 

LSD _0.05 = 21.62 (S. Rates)                                  LSD _0.05 = 4.871 (S. Rates)

LSD _0.05 = 23.87 (Herbicides)                               LSD _0.05 = 7.994 (Herbicides)

LSD _0.05 = 41.34 (Interaction)                               LSD _0.05 = 13.85 (Interaction)

Means followed by the same letter (s) in the respective category are non significant

P £ 0.05.

Table-4.  Number of spikelets per panicle as affected by different seeding rates and herbicides application in direct wet-seeded rice during 1999 and 2000

CV = 1.56%                                                      CV = 2.43%

LSD _0.05 = 1.762 (S. Rates)                                  LSD _0.05 = 3.174 (S. Rates)

LSD _0.05 = 1.969 (Herbicides)                               LSD _0.05 = 3.201 (Herbicides)

LSD _0.05 = 3.410 (Interaction)                               LSD _0.05 = 5.544 (Interaction)

Means followed by the same letter (s) in the respective category are non significant P £ 0.05.

Table–5.     Sterility percentage as affected by different seeding rates and herbicides application in direct wet-seeded rice during 1999 and 2000

CV = 8.99%                                                      CV = 11.37%

LSD _0.05 = 1.447 (Herbicides)                               LSD _0.05 = 2.887 (Herbicides)

LSD _0.05 = 1.863 (Interaction)      

Means followed by the same letter (s) in the respective category are non significant P £ 0.05.

Table-6.     1000-grain weight as affected by different seeding rates and herbicides application in direct wet-seeded rice during 1999 and 2000

CV = 6.61%                                                      CV = 3.49%

LSD _0.05 = 2.068 (S. Rates)                                  LSD _0.05 = 1.98 (Herbicides)

LSD _0.05 = 1.458 (Herbicides)                               LSD _0.05 = 1.472 (Interaction)

LSD _0.05 = 2.526 (Interaction)                              

Means followed by the same letter (s) in the respective category are non significant P £ 0.05.

Table-7.     Paddy yield (t ha^-1) as affected by different seeding rates and herbicides application in direct wet-seeded rice during 1999 and 2000

CV = 10.97%                                         CV = 11.25%

LSD _0.05 = 0.612 (S. Rates)                      LSD _0.05 =  0.6776 (Herbicides)

LSD _0.05 = 0.5748 (Herbicides)                 LSD _0.05 = 0.9955 (Interaction)                 

Means followed by the same letter (s) in the respective category are non significant P £ 0.05.

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