Biochar based nano carriers for enhanced herbicide bio-efficacy

Abstract

The study entitled “Biochar based nano-carriers for enhanced herbicide bio efficacy” was undertaken at College of Agriculture, Vellayani, during 2021-2023. The objectives of the study were formulation and characterization of rice husk-biochar nano-carrier based 2, 4-D; assessing the bio-efficacy of the formulation on broad leaf weed and sedge and testing its efficacy for weed management in upland rice. Rice husk nano carrier (RHNC) and rice husk-biochar nano-carrier (RHBNC) were synthesized in the laboratory and loaded with the herbicide 2, 4-D sodium salt following a standard protocol. The characterization studies like X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and Scanning electron microscopy revealed an average size of 503.8 nm for the RHBNC. The bio-efficacy of RHNC and RHBNC based 2, 4-D formulations were assessed on Limnocharis flava (L.) Buchenau (broad leaf weed) and Cyperus rotundus (sedge) as a pot study at College of Agriculture, Vellayani during June 2023. The experiment comprised 10 treatments replicated thrice in a completely randomized design. The treatments were T1- RHNC based 2, 4-D in the weight ratio (1:0.10) at 0.8 kg a.i. ha-1, T2- RHNC based 2, 4-D in the weight ratio (1:0.25) at 0.8 kg a.i. ha-1, T3- RHNC based 2, 4-D in the weight ratio (1:0.10) at 0.6 kg a.i. ha-1, T4- RHNC based 2, 4-D in the weight ratio (1:0.25) at 0.6 kg a.i. ha-1, T5- RHBNC based 2, 4-D in the weight ratio (1:0.10) at 0.8 kg a.i. ha-1, T6- RHBNC based 2, 4-D in the weight ratio (1:0.25) at 0.8 kg a.i. ha-1, T7- RHBNC based 2, 4-D in the weight ratio (1:0.10) at 0.6 kg a.i. ha-1, T8- RHBNC based 2, 4-D in the weight ratio (1:0.25) at 0.6 kg a.i. ha-1, T9- conventional 2, 4-D at 0.8 kg a.i. ha-1, T10- Control (weedy check). The growth parameters of the weeds L. flava and C. rotundus were adversely affected by RHNC and RHBNC-based 2, 4-D formulations. In L. flava, significantly higher per cent reduction in population (62.06) was recorded in RHBNC based 2, 4-D in the weight ratio (1:0.25) applied at 0.8 kg a.i ha-1 (T6) which was on par with T1 (57.46), T9 (57.46) and T8 (53.93). In C. rotundus, T6 recorded significantly higher per cent reduction in population (66.66), shoot and tuber dry weight and was on par with T9. This treatment resulted in highest weed control efficiency of 95.33 per cent and 98.74 per cent in L. flava and C.rotundus respectively. The chlorophyll content of L. 128 flava (0.25 mg g-1 fresh weight) and C. rotundus (0.44 mg g-1 fresh weight) was significantly lower in T6. In L. flava, regeneration was observed in T2, T3, T4 and T5 at 28 days after treatment. However, in C. rotundus was no regeneration was observed in any of the treatments. The efficacy of RHNC and RHBNC based 2, 4-D formulations for weed management was tested under field condition in upland rice at the Instructional Farm, College of Agriculture, Vellayani from August 2023 to November 2023. The experiment was laid out in randomised complete block design with nine treatments, replicated thrice. The treatments were T1- RHBNC based 2, 4-D in the weight ratio (1:0.25) at 0.6 kg a.i. ha-1, T2- RHNC based 2, 4-D in the weight ratio (1:0.10) at 0.8 kg a.i. ha-1, T3- RHBNC based 2, 4-D in the weight ratio (1:0.10) at 0.6 kg a.i. ha-1, T4- RHNC based 2, 4-D in the weight ratio (1:0.10) at 0.6 kg a.i. ha-1, T5- RHBNC based 2, 4-D in the weight ratio (1:0.25) at 0.8 kg a.i. ha-1, T6- RHBNC based 2, 4-D in the weight ratio (1:0.10) at 0.8 kg a.i. ha-1, T7- Conventional 2, 4-D at 0.8 kg a.i. ha 1 , T8- hand weeding (HW) twice at 15 and 30 days after sowing (DAS), T9- weedy check. The variety KAU Manuratna was dibbled at a spacing of 20 cm x10 cm in upland and managed as per KAU POP. Broad leaf weeds and sedges dominated the weed flora composition. At 40 DAS, dry weight of sedges and broad leaf weeds was the lowest in T8 which was followed by T5 and at 60 DAS it was statistically on par with T5. The treatment, T8 recorded higher weed control efficiency (84.95%, 72%) and weed control index (56.33%, 49.28%) at 40 and 60 DAS respectively and was on par with T5. Rice husk nano-carrier and rice husk-biochar nano-carrier based 2, 4-D formulations significantly influenced the growth attributes of rice including plant height, leaf area index, number of tillers m-2 and total dry matter production at all growth stages. Among the formulations, T5 recorded significantly taller plants (72.03 cm, 74.08 cm) and leaf area index (3.80, 4.29) at 40 DAS and 60 DAS respectively and was comparable with T8. The treatment, T5 exhibited higher yield attributes like number of productive tillers per m-2 (389.33) and filled grains per panicle (100.96) which was on par with T8. Grain yield was significantly higher in T8 (3103 kg ha-1) and was comparable with T5 (2840 kg ha-1). Higher harvest index was recorded in T5 129 (0.441) which was on par with T8 (0.440) and T2 (0.440). Weed index which signifies yield loss due to weeds was the lowest in T5 (17.96). Nutrient uptake by crop (N, P and K) was higher in T8 and was comparable with T5. Also, the treatment, T8 exhibited lower nutrient removal by weeds and was on par with T5. Dehydrogenase enzyme activity at 40 DAS and 60 DAS was higher in treatments T5, T2 and T6. Microbial population showed enhanced growth in all herbicide treated plots when compared with T8 and T9 (weedy check). The study identified RHBNC based 2, 4-D in the weight ratio (1:0.25) applied at 0.8 kg a.i. ha-1 as the most effective formulation for the management of L. flava and C. rotundus in terms of weed control efficiency and lower regeneration count. The formulation was found to enhance the bio-efficacy of 2,4-D for weed management in upland rice improving yield and weed control efficiency than conventional 2, 4-D herbicide.