RESPONSE OF Bt COTTON TO DIFFERENT DRIP IRRIGATION REGIMES AND FERTIGATION LEVELS
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Date
2016
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Professor Jayashankar Telangana State Agricultural University
Abstract
A field experiment entitled “Response of Bt cotton to different drip irrigation regimes and fertigation levels” was carried out on sandy clay soils at Water Technology Centre, College Farm, College of Agriculture, Rajendranagar, Hyderabad during kharif, 2013. The experiment was laid out in randomized block design and and replicated three times, having treatments based on surface drip irrigation and fertigation of recommended dose of fertilizers (RDF) viz., drip irrigation at 1.0 Epan and fertigation of RDF (T1) and 75% RDF (T2), drip irrigation at 0.8 Epan and fertigation of RDF (T3) and 75% RDF (T4), drip irrigation at 0.6Epan and fertigation of RDF (T5) and 75% RDF(T6) and drip irrigation at 1.0 Epan with fertilizer application as conventional method (T7), furrow irrigation (IW/CPE ratio of 0.8) with conventional method of fertilizer application (T8) and a rainfed crop with conventional method of fertilizer application (T9). The soil was sandy clay, medium in available nitrogen and potassium and high in available phosphorous with field capacity and permanent wilting point was 19.17% and 9.09% (w/w), respectively. The RDF was 150, 60 and 60 kg N, P2O5 and K2O ha-1, respectively and total P2O5 of RDF was applied as basal to all the treatments before sowing, N and K2O was applied in four splits at 20, 40, 60 and 80 days after sowing (DAS) in treatments of T7, T8 and T9 and for treatments T1 to T6, as fertigation in 16 equal splits through urea and sulphate of potash, from 10 to 115 DAS at weekly interval. The irrigation water was Class II (C4S1) without any residual alkalinity problem. Cotton (KCH-14k59-Jaadu) was sown adopting a spacing of 1.2 m between the rows and 0.45 m between the plants within a row to maintain a desired plant population of 18518 plants ha-1. Irrigations were scheduled based on the USWB Class A pan evaporation replenishment factor of 1.0, 0.8 and 0.6 for drip irrigation treatments through 12 mm lateral with 4 L h-1 drippers spaced at 50 cm apart and IW/PE ratio of 0.8 for furrow irrigation with mean irrigation water depth of 50 mm. Plant height of Bt cotton was influenced significantly by drip fertigation treatments. Higher plant height was recorded in 0.8 Epan + RDF (172 cm). Significantly higher leaf area index (LAI) and dry matter (kg ha-1) were recorded by drip fertigation of 0.8 Epan + RDF followed by drip fertigation of 1.0 Epan + RDF and significantly lower LAI and dry matter (g kg ha-1) were observed in rainfed + RDF applied as conventional method at all growth stages. Bolls plant-1 (111.4) was significantly higher with drip fertigation of 0.8 Epan + RDF, whereas rainfed + RDF under conventional soil application recorded significantly lower bolls plant-1 (70.1).
Significantly higher kapas yield (4197 kg ha-1) was observed in drip irrigation at 0.8 Epan + RDF , stalk yield (9549 kg ha-1) and total dry matter (13604 kg ha-1) were noticed by drip fertigation of 1.0 Epan + RDF and the lowest kapas yield was recorded in rainfed with RDF under conventional soil application (2658 kg ha-1). Similar trend was observed in plant nutrient uptake.
ETo estimated by modified pan evaporation methods was 555.5 mm and that of Penman Monteith method was 672.2 mm out of seasonal pan evaporation of 740.6 mm. ETc estimated was 583.9, 613.1, 629.9 mm under drip irrigation with 60%, 80% and 100% Epan respectively and was lower than furrow irrigation at 0.80 IW/CPE ratio (666.20 mm). The Kc values associated with drip
irrigation scheduled at 80% and 100% Epan were 0.50, 1.07, 1.22 &0.60, and 0.50, 1.08, 1.25 and 0.66 at 30, 90, 150 and 200 DAS, respectively with Penman-Monteith method and it was 0.59, 1.17, 1.48 & 0.87 and 0.59, 1.18, 1.51 & 0.97 at 30, 90, 150 and 200 DAS, respectively with modified pan method which were higher than Penman- Monteith methods and Kc values of both methods obtained in this study were higher than Kc reported in FAO-56.
The best fit response of cotton for irrigation water was obtained with quadratic water production function (r2= 0.923). The predicted maximum Bt cotton kapas yield (Ymax) of 4358.5 kg ha-1 was obtained with 621.51 mm of water and economic optimum yield (Yeco) of 4279.2 was obtained with 582.83 mm during kharif. Drip fertigation of 0.8 Epan + RDF recorded higher water productivity (6.89 kg mm-1) and was on par with drip fertigation of 0.6 Epan + RDF (6.82 kg mm1) and significantly lower water productivity (4.97 kg mm-1) was recorded by furrow irrigation with RDF under conventional soil applicaton.
Further, it was observed that growing of Bt cotton under drip fertigation was economically viable as net returns ( . 1, 17,900 ha-1) and B:C ratio (2.18 ) were significantly higher with drip irrigation at 0.8 Epan and fertigation of RDF followed by drip irrigation at 1.0 Epan and fertigation of RDF ( . 1,12, 100 ha-1 and 2.07, respectively) compared to furrow irrigation at 0.8 IW/CPE ratio ( . 89, 654 ha-1 and 1.69, respectively). Bt cotton under drip irrigation was economically viable.
Based on the results obtained in the present investigation, it can be concluded that Bt cotton can be grown under Rajendranagar conditions with drip irrigation at 0.8 or 1.0 Epan with fertigation of RDF for realising higher kapas yield (4197 and 4055 kg ha-1, respectievly) and was found remunerative (( . 1, 17,900 and 1,12, 100 ha-1 respectievly) with higher water productivity.
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D10,132