MSc

The study entitled “Integrated weed management in sorghum (Sorghum bicolor (L.) Moench)” was undertaken at the College of Agriculture, Vellayani during 2022-2024. The objectives were to formulate an integrated weed management (IWM) strategy for sorghum and to assess the effect of IWM on growth, yield and economics of sorghum.
The field experiment was conducted from November 2023 to February 2024 at the Farming Systems Research Station (FSRS), Sadanandapuram. The experiment was laid out in a randomised block design with ten treatments, replicated thrice. The treatments comprised T1: broadcasting cowpea seeds @ 15 kg ha -1, T2: broadcasting cowpea seeds @ 30 kg ha -1, T3:T1 + brown manuring with 2,4-D @1 kg ha-1at 20 days after sowing (DAS), T4:T2 + brown manuring with 2,4-D @1 kg ha-1at 20 DAS, T5: pre-emergence (PE) pretilachlor @ 0.75 kg ha-1fb one hand weeding (HW) at 25 DAS, T6: post directed application (PDA) of fenoxaprop-p-ethyl @ 0.06 kg ha-1 at 20 DAS, T7: post emergence (PoE) 2,4-D @ 1 kg ha-1 at 20 DAS, T8:HW at 20 DAS, T9: weed free control and T10: weedy check. In T1 and T2, cowpea seeds were broadcast on the same day of sowing and maintained as live mulch until 20 DAS, after which the cowpea plants and weeds were uprooted and retained as mulch. The sorghum variety CO-32 was raised and managed as per the recommendations of the KAU Package of Practices.
The study revealed that weed management practices had a significant effect on the growth parameters of sorghum. The treatment T2 resulted in significantly taller plants (155.17cm and 219.67cm at 45 DAS and at harvest respectively), leaf area per plant (681.68 cm2 and 4693.01cm2 at 30 and 45 DAS respectively), leaf area index (LAI) (1.01 and 6.95 at 30 and 45 DAS respectively) and dry matter production (DMP) (25.87 g per plant and 71.49 g per plant at 45 DAS and at harvest respectively) and was comparable to T4, T5 and T6.
The results indicated that the yield attributes of sorghum were significantly influenced by the weed management practices. T2 resulted in a higher number of grains per panicle (2991.3) and grain weight per panicle (64.30 g) which was comparable with T6, T5 and T4. Grain yield (2679 kg ha-1) and stover yield (9896 kg ha-1) of sorghum were higher in T2 and were comparable with T6 (grain yield of 2567 kg ha-1and stover yield of
9561 kg ha-1) and T4 (grain yield of 2462 kg ha-1 and stover yield of 9387 kg ha-1). The weed index was found to be the lowest in T2 (-2.97 %) and was comparable with T6 (1.36 %), T5 (2.78 %) and T4 (5.38%).
In the experimental field, grasses were the most dominant weed flora. The total weed count was notably influenced by weed management practices. Among the treatments, T5 and T9 consistently resulted in the lowest absolute frequency of grasses, sedges, and BLW at all stages. IWM integrating pretilachlor application and cowpea mulching effectively reduced the relative frequency of grasses, sedges, and BLW in sorghum. Notably, T2 (00.30 g m-2and 10.22 %), T5 (00.06 g m-2 and 10.22 %) and T6 (0.00 g m-2 and 0.00 %) exhibited comparable lower dry weight and importance value (IV) of grasses at 30 DAS. T9 demonstrated the highest weed control efficiency (WCE) (100.00%) at all stages. At 30 and 45 DAS, it was comparable to T5 (99.93 % and 94.84 % respectively) and T2 (99.65% and 98.73% respectively).
Integrated weed management practices influenced the dehydrogenase enzyme activity in the soil at 15, 30 and 45 DAS. Among the treatments, T5 exhibited the highest enzyme activity at 15 DAS (83.33 μg TPF g⁻¹ soil d⁻¹). T2 resulted in higher total carbohydrate (72.50 %), crude protein (13.69 %) and crude fiber content (5.86 %) and was comparable with T4 and T5 on a dry weight basis. Higher organic carbon content was recorded in T2 which was significantly higher than the weed-free control. T2 resulted in higher available soil N (187.35 kg ha⁻¹), T5 registered higher available P (61.19 kg ha⁻¹) and T9 had the higher available K (185.35 kg ha⁻¹). The economic analysis indicated that T6 resulted in higher net return (₹33,395 ha⁻¹) and benefit-cost ratio (BCR) (1.50), followed by treatments involving brown manuring and live mulch.
The study has identified broadcasting cowpea seeds at 30 kg ha⁻¹ followed by uprooting and retaining as mulch at 20 DAS as the most effective weed management strategy in terms of yield, weed control efficiency and gross return in sorghum. However, post-directed application of fenoxaprop-p-ethyl at 0.06 kg ha⁻¹ at 20 DAS turned out to be the most economical in terms of net return and BCR. Broadcasting cowpea seeds at 30 kg ha⁻¹ followed by brown manuring with 2,4-D at 1 kg ha⁻¹ at 20 DAS could be identified as the most effective IWM method for achieving higher grain and stover yields in sorghum.