Spacing and weed management in transplanted basmati rice

. Abstract: A field investigation was carried out at the Instructional farm, College of Agriculture, Vellayani during 2000-2001 to assess the effect of spacing and weed management practices on the performance of basmati rice. The treatments comprised of three spacings (15x15, 20x10 and 15x10 cm) and five weed control treatments (weed free check, unweeded control, hand weeding twice at 20 and 40 DAT, anilofos+2,4-DEE (readymix) 0.40+0.53 kg ha -1 at 6 DAT supplemented with hand weeding at 20 DAT and anilofos+2,4-DEE (readymix) 0.40+0.53 kg ha -1 at 6 DAT supplemented with 2,4-D sodium salt 1 kg ha -1 at 20 DAT). Grasses were the predominant weed species observed in the experimental field. Unchecked weed competition reduced grain yield to the tune of 46%. Herbicides were most effective in controlling the weeds. The results revealed that with 20x1 Ocm spacing (50 hills m -2 ), pre-emergence application of anilofos+2,4-DEE (readymix) 0.40+0.53 kg ha -1 supplemented with 2,4-D sodium salt 1 kg ha -1 could result in maximum grain yield and minimum weed competition.


Introduction
There had been a steady but progressive increase in exports of basmati rice all through the post-liberalisation period.From just 2,32,412 tonnes in 1990-91, India's basmati exports went up almost four-folds to touch 8,47,458 tonnes in 2000-2001.Plant spacing is an important factor that can be used to exploit the potential of the high yielding improved rice varieties (Paraye et al. 1996).Among the problems encountered in cultivation of scented rice, control of weeds is of utmost importance.Scented rice varieties are inherently poor competitors of weeds due to their initial slow growth (Chander and Pandey, 2001).The most critical period of weed competition is between 20 and 45 days after transplanting rice for a medium duration rice variety like Pusa Basmai-1 with a duration of 130 days.Traditional hand weeding is time consuming, labourious and expensive.So, herbicides are required for weed control in situations where labour is scarce and expensive.Herbicide combinations will broaden the spectrum of herbicidal action for controlling different weeds.Hence, the present investigation was conducted to evaluate the different weed control practices in transplanted scented rice.

Materials and Methods
The field experiment was carried out during winter 2001 at the Instructional Farm, College of Agriculture, Vellayani on sandy clay loam soils.The experiment with 15 treatment combinations replicated three times, was laid out in a randomised block design.The treatments comprised of three spacings (15x15, 20x10 and 15x10 cm) and five weed control treatments (weed free check, unweeded control, hand weeding twice at 20 and 40 DAT, anilofos+2,4-DEE 0.40+0.53kg ha -1 at 6 DAT supplemented with hand weeding at 20 DAT and anilofos+2,4-DEE 0.40+0.53kg ha" 1 at 6 DAT supplemented with 2,4-D sodium salt 1 kg ha -1 at 20 DAT).Values in parenthesis indicate original values, fb-followed by, NS -not significant HW -hand weeding, DAT -days after transplanting.
Required dose of herbicides as per treatments were mixed with water, 500 lha -1 and sprayed uniformly using knapsack sprayer with flat fan type nozzle.FYM @ 5 tonnes ha -1 was applied uniformly to the field at the time of field preparation and incorporated.A fertilizer dose of 90:45:45 kg N, P 2 O 5 and K 2 O ha -1 was applied.Half N and K 2 O and full P 2 O 5 were applied as basal.The remaining half N and K 2 O were applied in two equal splits at active tillering and flowering stages, respectively.Twenty four day old seedlings of rice variety 'Pusa Basmati 1' (130 days duration) were transplanted using 3 seedlings/hill, during third week of October.
Weed flora infesting experimental site were identified and enlisted category wise.Weed count was recorded at different stages of crop growth in a randomly selected area of 100 cm x 100 cm quadrant and were classified into 3 groups viz.grasses, sedges and broadleaved weeds.The dry weight of weeds, nutrient uptake by crop and weeds, yield and yield attributing characters were recorded and statistically analysed.Data on weed density showed high variation and was subjected to square root transformation (√x+0.5)(Little and Hills, 1977).Data on weed control efficiency was not subjected to transformation, as the variation is not large.Gross and net returns (Rs ha -1 ) and profitability (B : C ratio) were also calculated.

Weed flora
The predominant weed species observed in the field were Echinochloa colona, Echinochloa, crus-galli and

Weed Density
At all the stages, the maximum number of weeds was observed under weedy check (Table 1).Pre-emergence application of anilofos+2,4-D EE supplemented with 2,4-D sodium drastically reduced the weed density which was superior to anilofos+2,4-D EE supplemented with hand weeding.Rao (1995) reported similar results.Treatments involving pre-emergence herbicides followed by post-emergence herbicides proved to be better than treatments involving one hand weeding in addition to pre-emergence herbicides.Grassy weeds were predominant (63.81% at 40 DAT and 68.81% at 60 DAT) followed by sedges (18.24% at 40 DAT and 15.80% at 60 DAT) and broad leaf weeds (17.94% at 40 DAT and 15.39% at 60 DAT).Treatments involving herbicides supplemented with hand weeding showed a predominance of grasses (51.60%) followed by broad leaf weeds (26.45%) and sedges (21.95%).

Weed dry matter
Minimum weed biomass of 37.58 g m 2 was noted with 15x10 cm which was followed in an increasing order by 20x10 cm (40.71gm with hand weeding (14.97 gm -2 at 40 DAT and 38.10 g m -2 at 60 DAT) and caused significant decrease in the dry matter of weeds.This might be due to better and prolonged weed control due to sequential application of herbicides.The maximum dry matter of weeds was found in weedy check (111.55 g m -2 at 40 DAT and 162.84 gm -2 at 60 DAT).Rao (1995) also reported lower weed dry weight in rice with pre-emergence application of aniofos+2,4-D EE supplemented with 2,4-D sodium, which supports the present investigation.

Weed control efficiency (WCE)
Weed control treatments recorded higher weed control efficiency at all stages of crop growth except unweeded control (Table 1).Anilofos+2,4-D EE supplemented with 2,4-D sodium recorded highest WCE of 88.96 and 89.18 per cent at 40 and 60 DAT respectively which was superior to anilofos+2,4-D EE supplemented with hand weeding (86.50% at 40 DAT and 76.57% at 60 DAT).This might be due to effective control of weeds up to the critical stage of crop weed competition.This was followed by hand weeding twice (57.68% at 40 DAT and 65.51% at 60 DAT).This is in conformity with the results obtained by Rao and Singh (1997).

Weed index
The lower dry weight and lesser weed density resulted in lower weed index with treatment combination of 20x10 cm spacing and anilifos+2,4-D EE supplemented with 2,4-D sodium.This might be due to weed free condition achieved during most of the crop growth period.Weed index of unweeded control indicated that there was a yield loss of 46.30 per cent due to heavy infestation of weeds.

Nutrient uptake by crop and weeds
Weed free check recorded maximum uptake of nutrients by crop (174.20 kg N, 91.16 kg P 2 O 5 and 168.43 kg K 2 O ha -1 ).Chaudhary et al. (1995) reported similar results.Apart from weed free check, maximum uptake of nutrients by crop (157.03kg N, 79.37 kg P 2 O 5 and 147.61 kg K 2 O ha -1 ) was recorded in anilofos+2,4-D EE supplemented with 2,4-D sodium and was followed by anilofos+2,4-D EE supplemented with hand weeding (146.34 kg N, 74.15 kg P 2 O 5 and 135.00 kg K 2 O ha -1 ) and hand weeding twice (140.25 kg N, 70.57kg P 2 O 5 and 129.13 kg K 2 O ha -1 ) (Table 2).This might be due to weed free environment during most of the crop growth period which resulted in lesser competition of weeds and there by increased availability of nutrients (NPK) to the crop.Maximum nutrient uptake of weeds was observed in weedy check (41.14 kg N, 10.95 kg P 2 O 5 and 24.78 kg K 2 O ha -1 ) which might be due to heavy weed infestation that made the plants weak and unhealthy and thereby reduced the growth and development of crop resulting in higher nutrient uptake by weeds.
Apart from failing to utilize the available nutrients, weeds prevented rice plants from utilizing these nutrients because both crop and weeds together could use only 136.00, 58.17 and 106.23 kg ha -1 N, P 2 O 5 and K 2 O in unweeded check thus clearly showing that some amount of nutrients remained unabsorbed in soil due to weed competition.Similar results regarding nutrient uptake was reported by Rajan (2000) in rice.

Yield and yield attributes
Higher grain yield of 3991 kg ha -1 was recorded in 20x10 cm spacing, which was significantly superior to all other spacings.Lourduraj (1999) had reported that for medium duration rice cultivars, 20x10 cm is optimum plant spacing for achieving maximum yield.
Highest yield of 3928 kg ha -1 was recorded with anilofos+2,4-D EE supplemented with 2,4-D sodium and was superior to anilofos+2,4-D EE supplemented with hand weeding (3645 kg ha -1 ) and hand weeding twice (3378 kg ha -1 ) (Table 3).This might be due to the better expression of yield attributes viz.more number of effective tillers hill -1 (9.4) and maximum filled grains per panicle (119.95).Lowest yield (2305 kg ha -1 ) obtained from weedy check might be due to heavy weed infestation which has reduced effective tillers hill -1 and filled grains per panicle.Positive correlation between effective tillers hill -1 and filled grains panicle -1 vs grain yield (r = 0.94 and 0.96, respectively) and negative correlations between weed biomass and grain yield (r = -0.82)further confirmed the result.

Economics
Of the various spacings and weed management practices, 20x10 cm spacing and anilofos+2,4-D EE supplemented with hand weeding was most economical for rice (Table 3).All weed management practices proved their superiority over the controls (weed free and unweeded) by registering a benefit : cost ratio of more than 1.00.Combination of anilofos + 2,4-DEE supplemented with 2,4-D sodium resulted in the highest net income (Rs 58,209 ha -1 ) and benefit: cost ratio (2.07).
Thus, adoption of 20x10 cm plant spacing and resorting to pre-emergence application of anilofos+2,4-DEE supplemented with 2,4-D sodium could achieve higher productivity in basmati rice.

Table 1 .
Weed density (No m -2 ), weed control efficiency (%) and weed index (%) as influenced by different spacing and weed control practices

Table 2 .
Nutrient uptake by crop and weeds as influenced by different spacing and weed control practices Treatments

Table 3 .
Yield attributes, yield and economics as influenced by different spacing and weed control practices fb > followed by, HW-hand weeding, DAT-days after transplanting.