Foliar application of nutrients in Bt cotton: A means to enhance growth and yield

Introduction

Cotton (Gossypium hirsutum L.) is an indeterminate, perennial plant which is also known as 'King of fibers' due to its commercial and industrial importance. Cotton is also the source of edible oil and animal feed. Lint is the most important economical product, provides a source of quality fiber for textile industry. Cotton is a heavy feeder crop and removes large quantities of nutrients from the soil. Among the various factors of cotton production method of sowing and fertilizer application plays a significant role. Secondary (Ca, Mg, S) and micronutrients especially Zn, B are essential for higher productivity of cotton. Besides increasing nutrient use efficiency, Magnesium is essential for the production of the green pigment in chlorophyll, which is the driving force of photosynthesis and also essential for the metabolism of carbohydrates (sugars). Micronutrient deficiencies not only hamper crop productivity but also deteriorate produce quality. Boron plays an essential role in the growth and development of new cells in the growing meristem and also required for protein synthesis where nitrogen and carbohydrates are converted into protein. Furthermore, zinc is an element directly affecting the yield and quality of crop because of its role in activity of biological membrane stability, auxin synthesis and enzyme activation ability. Full potential of cotton can be exploited by applying fertilizer with appropriate method along with suitable sowing method. Soil application of Zn, B, Fe, Mn, and Cu on calcareous soils is less efficient, as these nutrients remain inaccessible to plant roots due to the higher soil pH (Rashid and Ryan 2004) [9] . However, an alternative approach under such circumstances is foliar application of nutrients (Rab and Haq, 2012) [6] as it eliminates the effects of soil pH on the availability of these nutrients (Ali, 2012) and it is more effective and less costly (Ali et al. 2007) [2] . External supplementation of nutrients needs to be therefore emphasized keeping in view their role in improving crop yield. Quantum of micronutrient deficiencies of Zn (49%), B (37%), Fe (12%), Mn (4%) and Cu (30%) reported in Indian soils demand urgent attention (Singh, 2009) [12] . Foliar application also improved the nutrient status of leaves compared to soil applied fertilizers alone.

This improvement in nutrient status resulted in an increase in the number of flowers, number of bolls, and ultimately seed-cotton yield. Keeping the point in view, the present investigation has been planned with the objective to study the effect of foliar application of nutrients on growth, yield and quality of Bt cotton.

Materials and Methods

A Field experiment was conducted during conducted at Cotton Research Area of Chaudhary Charan Singh Haryana Agricultural University, Hisar, during the year 2021. Hisar is situated in the sub-tropics at longitude 75º46'E, latitude 29º10'N and altitude of 215.2 m above mean sea level in Haryana state of India. The total rainfall received during the Kharif crop growing period was 770.6 mm. Weekly maximum and minimum temperature remained under a suitable range for different crop growth stages, mean weekly maximum and minimum temperature ranged between 28.9-41.4°C and 11.8-28.1°C, during Kharif 2021. The experiment was laid out in Randomized Block Design replicated thrice with eight treatments of foliar application of nutrients viz. T1: Control, T2:MgSO4 (0.5%), T3:ZnSO4 (0.5%), T4:FeSO4 (0.5%), T5: Borax (0.5%), T6:ZnSO4 (0.5%) +Urea (2%), T7: DAP (1%), T8: Urea (2%) applied at 60, 75, 90 DAS. Pre sowing irrigation was done with canal water 5-6 days before on 21 st April 2021 and sowing of cotton was done by dibbling method on 27 th April 2021. Gap filling was done five days after crop emergence. Two post sown irrigations were applied on 3 rd June and 19 th August 2021. Two hand pickings were performed on 8 th October and 3 rd November 2021.Weeds were removed by hand pulling from time to time in all the plots throughout the crop season. Full dose of P and half dose of N as per treatments were applied to the field before sowing and rest of N was top dressed after first irrigation. Five representative plants from each plot were selected randomly and tagged for recording the effect of different treatments on yield attributes. All yield attributes were recorded periodically on these randomly selected and tagged plants.

Results and Discussion

Phenological Studies

In attaining different phenological stages of Bt cotton, various foliar spray of nutrients have marked effects (Table 1). Number of days to 50% square formation of cotton ranged from 55.49 to 57.71 and various foliar sprays of nutrients fails to significantly influenced days to 50% flowering. But days taken to 50% flowering and days to 50% boll formation of Bt cotton were significantly influenced due to various foliar spray of nutrients. Days to 50% flowering were significantly less in treatment T8 in which Urea (2%) as foliar spray at 60, 75 and 90 DAS was applied which was at par with treatment T3, T5, T6 and T7. Days taken to 50 percent flowering of cotton were late by 3.5 days in control treatment over T8. Among various foliar spray of nutrient treatment T5being at par with treatment T3, T6, T7 and T8 recorded lowest number of days to 50% boll formation which was significantly lower than treatment T1, T2 and T4. This might be due to the fact that Boron and Magnesium are the essential elements required for the growth and development of crop plant having specific role in cell division and cell metabolism. Venugopalan and Tarhalkar (1998) [14] also observed that shortduration rainfed cotton may suffer from N deficiency during peak flowering, which could be remedied by a foliar spray of 2 percent Urea 75 days after sowing. [11] while studying the effect of foliar application of nutrients (N, Mg, Fe, Zn, Mn and B) on Bt cotton also observed non-significant effects of foliar application of nutrients on monopods per plant. Among various foliar spray of nutrients number of sympods /plant was highest in treatment T5 which was at par with T6 and T7 but significantly higher than other treatments. Increasing the amount of micronutrients in leaves may have improved the synthesis of synthetic metabolites that help to produce more fruiting branches. Similar trend was found for sympodial branches (22.2) by Eleyan et al. (2014) [3] . Similar result has been reported by Ramulu et al. (2020) who reported higher sympodial branches of cotton with foliar applications of ZnSO4 @ 0.2 percent at 30 days, ZnSO4 + Borax @ 0.2 percent each at 45 days, Borax @ 0.2 percent + MgSO4 @ 1 percent at 60 days, and MgSO4 @ 1 percent at 75 days after sowing along with soil application of recommended dose of fertilizers. Tallest plant at 105 and 135 DAS were recorded in treatment T6 followed by T5. Tallest plant at harvest was recorded with T6 followed by T7 (Table 3). This may be due to significant elongation of the intermodal distance in each main stem which caused the plant to grow taller. This result agrees with those obtained by Eleyan et al. (2014) [3] , More et al. (2018) [5] and Raj and Chandrasekar (2019) [7] .

Yield attributes and yield

The perusal of data in Table 4 revealed that application of ZnSO4 (0.5%) +Urea ((T6) being at par with T2, T3, T5 and T8 produced significantly more number of bolls per plant (45) than T1, T4 and T7.The number of bolls per plant recorded in treatment T1, T4 and T7 were at par with each other. Foliar spray of ZnSO4 (0.5%) +Urea (2%) recorded 12.50 and 18.42% higher number of bolls per plant then control and foliar spray of DAP (1%).

Higher number of bolls per plant of Bt cotton due to additional nutrition through foliar feeding might be due to fact that foliar spray of nutrients provides a method of delivering fundamental nutrients at key growth stages when the plants is at peak nutrient requirements and could not be made available through soil application. Micronutrients have a favourable relationship with the quantity of cotton bolls produced per plant, according to Eleyan et al. (2014) [3] and Iqbal et al. (2022) [4] . Among various foliar spray of nutrients boll weight (g) of Bt cotton was highest in treatment T2 which differ significantly over other treatments except T5, T6, T7 and T8. Our findings coincide with results of Singh et al. (2015) [11] who reported increase in boll weight by foliar application of MgSO4 + Zn SO4. The perusal of data in Table 4 revealed that highest seed cotton yield was recorded in treatment T6 which was significantly superior to T4 and T1 (Control) but at par with rest all treatments (T2, T3, T4, T5, T7 and T8). Treatment T6 (ZnSO4 (0.5%) +Urea (2%) as foliar spray) recorded 25.91% higher seed cotton yield than control treatment which might be due better yield attributes in these treatments. Higher yield of cotton might be due to the fact that Zinc has important functions in carbohydrate and protein metabolism which directly affecting the yield and quality of crop because of its role in activity of biological membrane stability, auxin synthesis and enzyme activation ability. This increase in seed cotton yield might be due to increase in yield contributing parameters such as number of bolls and boll weight (Table 4.5). These results confirm the findings of Yaseen et al. (2013) [15] ; Ali et al. (2007) [2] ; Eleyan et al. (2014) [3] ; Shivamurthy and Biradar (2014) [10] and Iqbal et al. (2022) [4] who found a significant increase in yield of cotton by foliar use of micronutrients in cotton. Highest seed index (8.98 g) was recorded in treatment T7 (DAP (1%) as foliar spray) which was 13.09% higher than control treatment. These results are in conformity with the finding of Swetha et al. (2020) [13] and Iqbal et al. (2022) [4] .