Impact of sowing techniques and herbicide combinations on weed flora in wheat (Triticum aestivum)

Introduction

Wheat (Triticum aestivum L.) is rabi season crop which cover large area in world. In Punjab, the total area under wheat cultivation was 35.30 lakh hectares during 2020-21 with production of 171.8 lakh tonnes and average yield of 48.68 quintals per hectare. Traditional method of wheat establishment involves excessive tillage which is time & energy consuming (Tripathi et al. 2002) [8] . The sowing of wheat after harvest of transplanted rice is generally delayed due to intensive tillage operation for seed bed preparation under conventional system. This results in reduced crop duration, equivalent to an extent of 1.0-1.5% yield loss/hectare/day (Gathala et al. 2011) [4] . On the other hand, production of the wheat crop is directly impacted by several biotic and abiotic factors. Among these, the most limiting biological constraint is the infestation of weeds. The yield losses of wheat vary between 17-30% annually (Rao and Chauhan, 2015) [5] . Weed problem is one of the major barriers responsible for low productivity of wheat because weed competes with the crop for moisture, nutrients, space, light etc. Wheat is infested by both grass & broad leaf weeds. The prominent weeds noted in wheat field are Phalaris minor, Rumex dentatus, Rumex spinosus, Chenopodium album, Anagallis arvensis, Avena fatua, Convolvulus arvensis, Euphorbia helioscopia and Cannabis sativa. Phalaris minor is one of the very serious weed in wheat and sometimes almost 100% crop losses have been reported by Singh and Singh. No-till system in wheat under rice wheat system reduced the Phalaris minor (littleseed canarygrass) infestation (Chhokar et al. 2007, Singh 2007) [3,7] due to higher soil strength but favoured the infestation of broad-leaved weeds like Rumex dentatus (toothed dock), Malva parviflora (little mallow) and Medicago denticulate (burclover). That is why the use of herbicides could be the only way to check the weeds and improve the crop yields. Herbicide application increased grain yield as compared to un-weeded and hand weeding treatments (Amin et al. 2008) [1] . Combination of grassy and broad leaf herbicides was better than their separate application for weed control in wheat shift in weed species (Shahzad et al. 2016). Pre-mixed broad-spectrum herbicide is cost-effective against complex weed flora. In present study, the different methods of tillage and the efficiency of combination of pre and post-emergence herbicide used in sequence as tank-mix or as pre-mix against weeds on growth and yield of wheat was evaluated.

Materials and Methods

Field study was carried out during rabi seasons for year 2020-2021 at the Khalsa college, Amritsar (Location 31.63 o E and 74.87 o N, 234 metres above mean sea-level). It was a split plot experiment conducted replicated with thrice, having two factors. First factor comprised of three sowing methods, Conventional tillage (M1), Super seeder (M2) and Happy seeder (M3) whereas, second factor comprised of seven herbicides, viz., (W1) Pinoxaden+ Clodinafop-propargyl (70 g ha -1 ), (W2) Fenoxaprop+Metribuzin (110 g ha -1 ), (W3) Metsulfuronmethyl(4 g ha -1 ) +Carfentrazone-ethyl (25 g ha -1 ) +NIS, (W4) Pendimethalin (900 g ha -1 ) fb Pinoxaden+ Metsulfuron-methyl (60g ha -1 ), (W5) Isoproturon+2,4-D(500 g ha -1 ), (W6) Weed Free and (W7) Weedy Check. The wheat variety "Unnat PBW343" was grown and recommended doses of fertilizers were applied. Herbicides were sprayed by knapsack sprayer fitted with flat-fan and flood jet nozzle using a spray volume of 500 L/ha. Weedy check plots remained infested with native population of weeds till harvest. Observation on weed density and dry matter accumulation were recorded from 4 random quadrate of 30cm × 30cm in each plot at 30, 60 and 90 days after herbicide application. Total number of weeds falling within each quadrate were counted and cut at ground level for measuring weed dry weight data. The sample were first dried in sun and after then kept in oven at 65 °C. The dried samples were weighted and expressed in g/m 2 . Data on weeds were subjected to square-roots transformation to normalize their distribution. The Grain yield recorded in kg/plot was finally converted into grain yield kg/ha and then into q/ha. The statistical analysis of data was done using 5% level of significance.

Results and Discussion

Weeds caused substantial yield losses to wheat. The crop-weed competition for nutrients, space, moisture, light etc. The narrow leaf weeds causes very heavy losses to the wheat crop. In the pertaining data, table 1, showed that the weed count was maximum in conventional tillage (7.86) under main plots followed by super seeder (7.71) and minimum in happy seeder (7.25) throughout the crop season. At 60,90, 120DAS and at harvest the minimum weed count was observed in happy seeder, this might be due to the sowing method and minimum soil disturbance due to which the narrow leaf weeds cannot come to upper surface of soil and thereby lowering the narrow weed leaf flora in happy seeder sown wheat. The weed count of super seeder (65.49) sown wheat recorded 4.04% reduction in weed density when compared with conventional tillage (68.25), however when conventional tillage was compared with happy seeder (58.02) there was 17.63% reduction in weed density of narrow-leaf weeds. In sub-plots, throughout the crop season weed count was recorded highest in W7 (weedy check) and minimum in W4 treatment followed by W1, W2, W3 andW5 treatment. Among chemical weed control treatments, the maximum weed count was observed in W5 followed by W3, W2 and W1, at 60, 90,120 DAS and at harvest. The percentage decrease in weed count of W1, W2, W3, W4, W5 and W6 when compared with W7 was 93.46%, 93.07%, 87.83%, 97.59%, 76.74% and 100%.

The dry matter accumulation by weed shows that throughout the cropping season much nutrition is acquired by weeds. The losses caused by these weeds leads to the poor crop yield.In happy seeder sown wheat, narrow-leaf weeds accumulated the least dry matter throughout the cropping season and conventional tillage received comparatively highest weed dry weight. The weed dry matter of super seeder (8.34) wheat recorded 7.74% reduction in weed density when compared with conventional tillage (9.04), however when conventional tillage was compared with happy seeder (7.64) there was 15.48% reduction in weed dry matter of narrow-leaf weeds. W4 treatment had the lowest weed dry weight of narrow-leaf weeds, followed by W1, W2, W3, W5 and treatment throughout the crop season. The percentage decrease in weed dry weight of W1, W2, W3, W4, W5 and W6 when compared with W7 was 87.44%, 82.35%, 76.57%, 99.30%, 29.42% and 100%. It was observed that the interaction was not significant.

Dry matter accumulation of broad leaf weeds (q ha -1 ) Super-seeder sown wheat had the lowest dry matter buildup of broad-leaf weeds, and highest in happy seeder sown wheat. But the differences were not reached to significant level. The weed dry matter of conventional tillage (5.65) recorded 7.37% reduction in weed density when compared with happy seeder (6.10), however when conventional tillage was compared with super seeder (5.19) there was 14.51% reduction in weed density of broad-leaf weeds. W4 had the lowest weed dry matter accumulation and W7 had the highest dry matter accumulation of broad-leaf weeds across the various weed management strategies. W1 andW2, were shown to be significantly differ from W3 and W5. Further difference between W3 and W5 was significant. The descending order of weed dry matter was 15.83, 15.18, 4.18, 2.19, 2.08 and 0.09 in W7, W5, W3, W2, W1 and W4 respectively. The percentage decrease in dry matter of W1, W2, W3, W4, W5 and W6 when compared with W7 was 86.86%, 86.16%, 73.59%, 99.43%, 4.10% and 100%. Straw yield (q ha -1 ) Straw yield is a significant measure of biological yield for determining its productivity index and determining the photosynthetic mass's ultimate efficacy. Wheat straw has a significant impact on the efficacy of several treatments examined in a study. The results showed that among the various methods of sowing wheat, super seeder sown wheat produced the highest straw yield, which was much higher than conventional tillage seeded wheat, but happy seeder sown wheat produced the lowest grain yield. Because there were more tillers per metre row length and more grains per ear in super seeder sown wheat, the straw production was 14.76 percent higher than in happy seeder (62.44) seeded wheat. The percentage increase in straw yield in super seeder (71.66) when compared with conventional tillage (68.26) was 4.98% and with happy seeder was 14.76%. Among the different weed control practices, W6 (weed free) treatment had the highest straw yield and it was significantly at par with W4 (pendimethalin fb pinoxaden + metsulfuronmethyl), W1(pinoxaden + clodinafop) and W2 (fenoxaprop + metribuzin), which were significantly higher than W3, W5 and W7treatments. The treatment W3 and W2 were also significantly at par with each other. The W7 treatment, on the other hand, produced the lowest straw yield. The number of tillers per metre row length and the number of grains per ear were both reduced in the control as compared to weed-free treatment, resulting in 48.03 percent loss in straw yield. The percentage increase in straw yield of W1, W2, W3, W4, W5 and W6when compared with W7 was 42.04%, 41.42%, 35.16%, 46.76%, 13.72% and 48.03%.

Harvest index

The harvest index is a crucial metric that displays how photosynthates are divided up economically. The higher the harvest index, the more efficient the plant is at producing economic yield. The highest harvest index was observed in happy seeder sown wheat, while the lowest harvest index was reported in super seeder sown wheat. The highest harvest index was observed in the W3 (metsulfuron + carfentrazone + NIS) treatment, while the lowest harvest index was reported in the W7 (weedy check) treatment, which could be attributable to more weed flora in weedy check treatment.

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