Impact of weed management approaches on the performance of wheat (Triticum aestivum L.) and direct seeded basmati rice (Oryza sativa L.) in irrigated plains of Jammu sub-tropics

A scientific investigation entitled “Impact of weed management approaches on the performance of wheat ( Triticum aestivum L.) and direct seeded basmati rice (Oryza sativa L.) in irrigated plains of Jammu sub-tropics” was conducted at Research Farm , Main Campus Chatha of SKUAST- Jammu for two consecutive years from rabi season of 2013-14 to kharif season of 2015. The soil of the experimental field was sandy clay loam in texture, slightly alkaline in reaction, low in available nitrogen and organic carbon, while medium in phosphorous and potassium. Initially the experiment was laid out in randomised block design in rabi season for wheat crop and during kharif season the layout was converted into split-plot design for direct seeded basmati rice considering weed management approaches of wheat crop as main plot treatments and weed management approaches of direct seeded basmati rice as sub-plot treatments. The weed management treatments of wheat crop comprised of weedy check; mechanical weedings-2 at 30 and 60 DAS; isoproturon @ 1.0 kg/ha + 2,4- D @ 0.500 l/ha (PoE); clodinafop @ 0.060 kg/ha (PoE) and triasulfuron @ 0.015 kg/ha (PoE) whereas in basmati rice each treatment plot of wheat was split into four sub-plots and the weed management treatments of basmati rice consisted of weedy check; mechanical weedings-2 at 30 and 60 DAS; pendimethalin @ 1.0 kg/ha (PE); pendimethalin @ 1.0 kg/ha (PE) fb bispyrebac @ 0.30 kg/ha (PoE). A uniform recommended dose of N, P and K through inorganic sources of nutrients viz., Urea, DAP and MOP was applied to all the experimental plots of both wheat and rice crops along with other cultivation practices as per their respective recommended packages. The major weed flora observed in wheat field were Medicago denticulata, Anagalis arvensis, Cirsium arvense, Fumaria parviflora, Poa annua and Phalaris minor where as rice fields were mainly infested with Cyperus rotondus, Cyperus iria, Cynodon dactylon, Echinocloa colonum, Echinocloa crusgalli and Commolena benghalensis. Competition imposed by higher weed densities significantly reduced all crop growth parameters, yield attributes and final crop yields under weedy situations in both wheat and direct seeded basmati rice crops. All the weed management practices significantly improved almost all parameters of crop growth like plant height, leaf area index, dry matter accumulation, crop growth rate along with yield attributes such as number of ears or panicles/m2 , number of grains/ear or panicle and test weight leading to higher grain and straw yields in both crops under experimentation. In wheat, significant improvement in crop growth parameters, yield contributing factors and crop yields was recorded with the post emergence application of isoproturon @ 1.0 kg/ha + 2,4- D @ 0.500 l/ha which however, was statistically at par with two mechanical weedings given at 30 and 60 DAS. Reduction of weed densities, weed biomass and weed persistence resulting in higher weed control efficiencies, agronomic management, weed management and integrated weed management indices were credited to the superior control of weeds by these treatments. The main plots treatments of direct seeded basmati rice which were preceded by different weed management treatments applied to wheat did not differ significantly with respect to weeds and crop parameters under study, whereas in sub plot treatments, the best results were obtained with the application of pendimethalin @ 1.0 kg/ha (PE) fb bispyrebac @ 0.30 kg/ha (PoE) for almost all crop growth components, yield and yield attributes. The next best and statistically at par treatment turned out to be pendimethalin @ 1.0 kg/ha (PE). The weed suppressing ability of these superior treatments resulted in reduction of weed population, weed dry matter, weed persistence and led to an enhancement in weed control efficiencies, crop resistance, agronomic management, weed management and integrated weed management indices and improvement in crop yields. Application of isoproturon @ 1.0 kg/ha + 2,4- D @ 0.500 l/ha (PoE) registered 75.61 % improvement in grain yield in wheat, similarly, in rice the use of pendimethalin @ 1.0 kg/ha (PE) fb bispyrebac @ 0.30 kg/ha (PoE) recorded 155.39 % increase grain yield over their respective weedy checks. As regards the nutrient uptake by the crops, significantly higher N, P and K uptake was recorded with the application of isoproturon @ 1.0 kg/ha + 2,4- D @ 0.500 l/ha (PoE) in wheat, however, it was statistically at par with mechanical weedings given at 30 and 60 DAS. In direct seeded basmati rice, the highest N, P and K uptake was recorded with the application of pendimethalin @ 1.0 kg/ha (PE) fb bispyrebac @ 0.30 kg/ha (PoE) and this, however, was statistically at par with pendimethalin @ 1.0 kg/ha applied alone as pre-emergence herbicide. The superior weed control treatments in both crops led to the enhanced growth resulting in higher nutrient removal by the crop from the soil. Higher nutrient uptake by weeds was found in treatments with low weed control efficiencies. In wheat, non- significant results were obtained for N, P and K removal by both weeds and crops at 30 DAS as all the weed management treatments in wheat were initiated 30 DAS. All herbicides in both wheat and direct seeded basmati rice had shown negative impact on soil microbial count taken 15 days after imposition of treatments. However, a marginal increase in the soil microbes was observed after 30 days of herbicide application. The differences in soil microbial count in mechanical weedings were not significant compared to weedy check though numerically lesser number of soil microbes were detected in these plots. Highest net returns to the tune of 50,954.45 and 60,805.45/ ha with B:C ratios of 2.26 and 2.66 were obtained with the application of isoproturon @ 1.0 kg/ha + 2,4- D @ 0.500 l/ha (PoE) in wheat during first and second years, respectively. In direct seeded basmati rice, highest net returns to the tune of 56,098.80 and 35,776.20/ ha with B:C ratios of 2.37 and 1.52 were attained with the weed management interventions through pendimethalin @ 1.0 kg/ha (PE) fb bispyrebac @ 0.30 kg/ha (PoE) in kharif 2014 and 2015, respectively. An analysis of sequential behavior of weed management practices applied in wheat - direct seeded basmati rice cropping system indicated that application of isoproturon @ 1.0 kg/ha + 2,4-D @ 0.500 l/ha (PoE) in wheat succeeded by pendimethalin @ 1.0 kg/ha (PE) fb bispyrebac @ 0.30 kg/ha (PoE) in direct seeded basmati rice resulted in lowest weed densities, weed dry weights vis-a-vis highest weed control efficiency and system productivity. This was closely followed by mechanical weedings-2 (30 & 60 DAS) in wheat succeeded by pendimethalin @ 1.0 kg/ha (PE) fb bispyrebac @ 0.30 kg/ha (PoE) or sole application of pendimethalin @ 1.0 kg/ha (PE) in DS basmati rice. Based on two years of experimentation, it is concluded that the best weed management strategy in irrigated plains of Jammu sub-tropics for individual crop of wheat and DS basmati rice is the post- emergence application of isoproturon @ 1.0 kg/ha + 2,4- D @ 0.500 l/ha or mechanical weedings twice at 30 and 60 DAS and pendimethalin @ 1.0 kg/ha (PE) fb bispyrebac @ 0.30 kg/ha (PoE) or pendimethalin @ 1.0 kg/ha (PE), respectively. However, the application of isoproturon @ 1.0 kg/ha + 2,4- D @ 0.500 l/ha (PoE) in wheat and pendimethalin @ 1.0 kg/ha (PE) fb bispyrebac @ 0.30 kg/ha (PoE) in direct seeded basmati rice in sequence is the most promising weed management approach in wheat – direct seeded basmati rice crop sequence in the irrigated plains of Jammu sub-tropics.