The field experiments were conducted at the Indian Agricultural Research Institute, New Delhi in summer-rainy seasons of 1980 and 1981 to study the effect of different sorghum-legume intercropping systems and weed control methods on growth, yield and nutrient uptake by different crops and on weeds. The intercropping of legumes increased growth, uptake of N, P and K and yield of sorghum compared with sole sorghum. However, maximum increase was obtained when it was grown in association with fodder cow pea. All intercrops smothered the weeds but maximum suppression was by fodder cow pea. The total uptake of nutrients (N, P and K) was also greater in intercropping systems. Pre-emergence application of fluchloralin at 0-5 kg/ha was most effective in all intercropping systems followed by nitrofen at 1-0 kg/ha. Hand weeding and fluchloralin application also led to higher nutrient uptake by sorghum and the whole system than the unweeded control. Application of fluchloralin and nitrofen controlled most of the weeds and reduced nutrient removal compared with the control but was less effective than hand weeding.
Leptochloa chinensis (L.) Nees. (Chinese sprangletop or Red sprangletop) is one of the most important invasive weeds in direct-seeded rice fields (Chin 2001). In Kerala, Chinese sprangletop was reported as a new weed specific to the alkaline soils of Chittoor taluk (Vidya et al. 2004). Though this weed is listed as an indicator plant for alkaline conditions, it is now seen spreading rapidly in acidic soils of Kerala also with typical example of weed shift. Continuous use of bispyribac-sodium, which is one of the most popular rice herbicides among farmers in Kerala, to control barnyard grass resulted in the dominance of Chinese sprangletop. In view of the growing menace of Leptochloa chinensis in the rice fields of Kerala, it is important to develop a new herbicide strategy by making use of the new molecule herbicides or the pre-and post-emergence herbicides already in use for effective control.A field experiment in wet seeded rice was conducted during second crop season of 2012 in a farmer's field of Thrissur district (75 0 58' latitude and 76 0 11' longitude and 1m below MSL), Kerala. The soil was clay loam with pH 5.2, organic C of 1.4%, available N of 890 kg/ha, available P of 24 kg/ha and available K of 281 kg/ha. The crop received 165.5 mm rainfall during 2012. The mean monthly minimum and maximum temperature were 33.9 o C and 23.2 o C. The experiment comprised 12 treatments. The herbicide oxyfluorfen 23.5 EC was sprayed as pre-emergence at 3 days after sowing (DAS), while butachlor 50 EC and pretilachlor 50 EC were applied at 6 DAS. Pyrazosulfuron-ethyl 10 WP was applied as early post-emergence at 8 DAS whereas cyhalofop butyl 10 EC, fenoxaprop-p-ethyl 6.9 EC, bispyribac-sodium 10 SC, metamifop 10 EC, azimsulfuron 50 DF and penoxsulam 24 SC were applied at 20 DAS. Hand-weeding twice at 20 and 40 DAS and weedy check were kept as controls. The treatments were applied in a randomized block design with three replications and a plot size of 20 m 2 . The rice variety used was 'Jyothi (PTB 39)'.The seed rate for sowing was 100 kg/ha. The crop was fertilized with 90, 35, 45 kg/ha of N, P2O5, and K2O respectively. One third dose of N and K and half of P were applied at I5 DAS, one third dose of N and K and half of P at 35 DAS and remaining one third N and K at 55 DAS (KAU, 2011). Observations on weed density and weed dry weight for total weeds and L.chinensis were recorded separately with the quadrate (0.25 x 0.25 m) placed randomly in each plot at 30 DAS, 60 DAS and at harvest. The data on weed count were subjected to square root transformation ( 0.5 x ) to normalize the distribution. Weed control efficiency (WCE) was computed separately for L. chinensis and total weeds by using weed dry weight, and weed index (WI) was computed using grain yield of weed free check and yield of treated plot. Yield attributing characters like panicles/m 2 , grains per panicle, fertility % and 1000 grain weight were recorded at harvest by placing the quadrate (0.25 x 0.25 m) in each plot. The cost of cultivation was worked out based...
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