Crop growth rate and relative growth rate of high-density cotton in pigeonpea-based intercropping systems in Vertisols

Introduction

Pigeonpea (Cajanus cajan L.) is India's second most important pulse crop after chickpea. Pigeonpea is one of the most crucial rainy season (kharif) grain legume crop, grown predominantly under rainfed conditions in India. In India, Pigeonpea is growing in an area of 50.02 lakh ha with production of 4.34 million tonnes and productivity of 877 kg ha -1 . In the paired row Pigeonpea cotton intercropping system, the space between the two paired rows of Pigeonpea is effectively utilized for growing high-density cotton. Paired row planting system allows for better light interception by the crop and resource sharing for harvesting better yields (Rani et al., 2019) [9] . In addition to that, the paired row of Pigeonpea intercropping system enriches the soil by adding nitrogen, improving the soil physico-chemical and biological properties. Intercropping of Pigeonpea with other crops like cotton provides farmers with additional returns as a commercial crop. Pigeonpea improves soil quality, reduces climatic risks and chance of crop failure, enhances biodiversity, and ensures greater use of resources and land area (Maitra et al., 2001; Maitra and Ray, 2019) [5,6] . Pigeonpea is suitable for inter-cropping with different crops like cotton, sorghum, pearl millet, greengram, blackgram, maize, soybean and groundnut to increase production, resource use efficiency and maintain soil fertility. Paired row pigeonpea-based intercropping systems with high-density cotton represent a strategically designed cropping pattern that integrates the complementary growth habits of pigeonpea and cotton to maximize land productivity and resource use efficiency (Potdar et al., 1996) [8] In these systems, pigeonpea is sown in paired rows with adequate intra-pair spacing, often with the wider spaces between pairs utilized to accommodate high-density cotton rows. This arrangement allows for cultivating two crops simultaneously on the same land, leveraging the vertical structure and deep rooting ability of pigeonpea alongside the rapid canopy development and economic yield potential of high-density cotton. (Bhardwaj et al., 2023) [1] .

Materials and Methods

The experimental plot was clay loamy soil, slightly alkaline in reaction, medium organic carbon, low available nitrogen, high available phosphorus and medium available potassium, respectively. The experiment was laid out in a split-plot design with three replications and 18 treatments and conducted during kharif 2023-24 and 2024-25. The main plot treatments consisted of high density cotton spacings in paired row pigeonpea viz., M 1: Paired row of pigeonpea intercropped with high density planting of cotton at 60 cm x 15 cm (1,11,111 plants ha -1 ), M 2: Paired row of pigeonpea intercropped with high density planting of cotton at 75 cm x 20 cm (66,666 plants ha -1 ), M 3: Paired row of pigeonpea intercropped with normal planting of cotton at 100 cm x 15 cm (66, 666 plants ha -1 ) and sub plot treatments were consists of growth regulators and nitrogen management (S1: 100% RDN + Mepiquat chloride 50 ppm at square initiation, peak square formation and flowering stage, S2: 100% RDN + Mepiquat chloride 50 ppm at square formation and flowering stage, S3: 125% RDN + Mepiquat chloride 50 ppm at square formation and flowering stage, S4:100% RDN + Cycocel 60 ppm at square initiation, peak square formation and flowering stage, S5:100% RDN + Cycocel 60 ppm at square formation and flowering stage, S6: 125% RDN + Cycocel 60 ppm at square formation and flowering stage are replicated thrice. ADB-39 cotton variety and TDRG 59 pigeonpea variety were selected for the experiment and sown by dibbling at different spacings of high-density cotton. First paired row of pigeonpea was sown with spacing of 45 cm and the space between the two paired rows of pigeonpea was 3 metres and in between the two paired rows of pigeonpea, 60 cm x 15 cm (5 rows of high density cotton), 75 cm x 20 cm (4 rows of high density cotton), and 100 cm x 15 cm (3 rows of high-density cotton) of high density cotton were grown during both years of the experiment. Recommended dose of fertilizers (RDF) of pigeonpea is 20:50:00 NPK kg ha -1 . Pigeonpea RDF of 20 kg of N and 50 kg of P2O5 were applied as urea and single super phosphate respectively as basal dose to the all the plots of pigeonpea as per treatments. Weeds were controlled by spraying pre-emergence herbicide, pendimethalin @ 0.75 kg a.i. ha -1 second day of sowing followed by manual weeding at 40 and 70 DAS during both years of study (kharif, 2023-24 and 2024-25). The incidence of sucking pests was controlled by spraying Fipronil 5% SC @ 4 ml lit -1 . Later stages Imidacloprid @ 0.45 ml L -1 . To check the incidence of bollworms (Pectinophora gossipella), spraying was done with Chlorantraniliprole (10%) + Lambdacyhalothrin 5% ZC @ 0.5 ml lit -1 at boll development stage in 2023-24. Emamectin benzoate 5% SG @ 0.5 g L -1 was sprayed against bollworms at 105 DAS and 120 DAS in 2024-25.

Statistical Analysis

Data on different characters, viz., growth, yield attributes, yield, soil and plant analysis, and economics, were subjected to analysis of variance procedures as outlined for split-plot design (Gomez and Gomez, 1984). Statistically significance was tested by Fvalue at p=0.05 (5%) level of probability and critical difference was worked out wherever the effect was significant. Nonsignificant treatment differences were denoted as NS.

Results and Discussion

Crop growth rate (CGR) (g m -2 day -1 ) At 0-30 DAS and 30-60 DAS Among main plots, data indicated that high density cotton in paired row of pigeonpea was not significantly influenced the CGR recorded during 2023-24, 2024-25 and in the average over years results. Among sub-plots, growth regulators and nitrogen management exert non-significant influence on CGR recorded during 2023-24, 2024-25 and in the average over years results. Among main plot treatments, significantly highest CGR (2.79, 2.69 and 2.74) at 60-90 DAS, CGR (2.34, 2.21 and 2.27) at 90-120 DAS and CGR (1.9, 1.7 and 1.8) at 120 DAS-harvest was recorded with high density cotton spacing of 60 cm × 15 cm (M 1 ) during 2023-24, 2024-25 and in the average over years data results, respectively. The rest of the treatments, with high density cotton spacing of 75 cm × 20 cm (M 2 ) and 100 cm × 15 cm (M 3 ) performed on par with each other at 60-90 DAS and significantly the lowest CGR (2.10, 1.91 and 2.01) at 90-120 DAS and CGR (1.5, 1.4 and 1.5) at 120 DAS-harvest was obtained with high density cotton spacing of 100 cm × 15 cm (M 3 ) during both years and in the average over years data results, respectively. Among sub-plots, growth regulators and nitrogen management had significantly influenced the CGR of high-density cotton in paired row of pigeonpea. Application 125% RDN + mepiquat chloride 50 ppm at square formation and flowering stage (S 3 ) recorded significantly highest CGR (2.82, 2.70 and 2.76) at 60-90 DAS, CGR (2.34, 2.21 and 2.27) at 90-120 DAS and Crop growth rate (2.0, 1.8 and 1.9) at 120 DAS-harvest, however it was comparable with application of 100% RDN + mepiquat chloride 50 ppm at square formation and flowering stage (S 2 ) and with application of 125% RDN + cycocel 60 ppm at square formation and flowering stage (S 6 ) during 2023-24, 2024-25 and in the average over years data results respectively. In contrast, significantly the lowest CGR (2.30, 2.24 and 2.27) at 60-90 DAS, CGR (1.89, 1.81 and 1.85) at 90-120 DAS and Crop growth rate (1.3, 1.2 and 1.3) at 120 DAS -harvest was noted with 100% RDN + cycocel 60 ppm at square initiation, peak square formation and flowering stage (S 4 ) during both years and in the average over years results, respectively. Results revealed that among main plots, high density cotton spacing of 60 cm × 15 cm (M 1 ) recorded significantly more CGR. This might be due to more plants per unit area are utilizing available resources more efficiently it results in potentially increasing total biomass and yield up to an optimal density. The combined photosynthetic activity and resource capture by all the plants can exceed that of lower densities, leading to a higher CGR per unit area. Similar findings are reported by Hu et al. (2023) [2] and Sapkota et al. (2023) [11] . The CGR was increased with the increase in plant density as reported by Patel et al. (2021) [7] . Among the sub-plots, the highest CGR was recorded with application of 125% RDN + mepiquat chloride 50 ppm at square formation and flowering stage (S 3 ). This is due to the application of higher doses of nitrogen, its role in enhancing vegetative growth results in increasing dry matter production. Spraying of growth regulators (mepiquat chloride) can optimize plant architecture, reduce excessive vegetative growth, improve light penetration within the canopy, supporting efficient photosynthesis and higher CGR. Similar results were reported by Kumar et al. (2022) [4] and Wei et al. (2024) [12] .

Relative Growth Rate (RGR) (g g -1 day -1 ) Among main plot treatments, significantly highest RGR (0.018, 0.015 and 0.017) at 90-120 DAS and highest RGR (0.010, 0.010 and 0.010) at 120 DAS to harvest was observed with high-density cotton spacing of 100 cm × 15 cm (M 3 ) in paired row of pigeonpea as compared to the rest of the treatments. In contrast, the lowest RGR was recorded with high density cotton spacing of 60 cm x 15 cm (M 1 ) during both years and in the average over years results, respectively. Among the sub-plots, application of 125% RDN + mepiquat chloride 50 ppm at square formation and flowering stage (S 3 ) recorded the highest RGR (0.0198, 0.0147 and 0.0170 g g -1 day - 1 ) at 90-120 DAS and highest Relative growth rate (0.01, 0.009 and 0.011) at 129 DAS to harvest, however it was on par with application of 100% RDN + mepiquat chloride 50 ppm at square formation and flowering stage (S 2 ) and with application of 125% RDN + cycocel 60 ppm at square formation and flowering stage (S 6 ) during both the years and in the average over years data results, respectively. Results revealed that RGR was not significantly influenced by high density cotton spacing in paired row of pigeonpea. However, among main plots high density cotton spacing of 100 cm × 15 cm (M 3 ) recorded the higher RGR. This might be due to wider spacing allowed for each plant so as to have greater access to light, water and nutrients, thereby enhancing photosynthesis and faster growth per plant. Similar findings were reported by Ibrahim et al. (2022) [3] . Among the sub-plots, highest RGR was recorded with application of 125% RDN + mepiquat chloride 50 ppm at square formation and flowering stage (S 3 ). The increase in RGR after application of growth regulators could be attributed to increased photosynthetic efficiency as a result of increased leaf thickness, higher chlorophyll content and efficient translocation of photosynthates. These results were in agreement with the findings of Sabale et al. (2017) [10] . Higher N availability increases leaf area, dry matter accumulation, directly boosting RGR and it declined at later stages of crop growth, which might be due to partitioning of extra photosynthates towards the developing sink during reproductive development. Similar findings were reported by Kumar et al. (2022) [4] .

Conclusion

It is concluded that high-density cotton spacing of 60 x 15 cm (M 1 ) in paired row pigeonpea recorded the highest crop growth rate while 100 x 15 cm recorded the highest relative growth rate. Among the subplots, application of 125% RDN + Mepiquat chloride 50 ppm at square formation and flowering stage (S 3 ) recorded the highest crop growth rate and relative growth rate as compared to the rest of the treatments during both 2023-24, 2024-25 and in mean data. The lowest was observed with the application of 100% RDN + Cycocel 60 ppm at square initiation, peak square formation and flowering stage (S 4 ). It is concluded that high density cotton in paired row pigeonpea was performing well with the application of growth regulators and the recommended dose of nitrogen during both years of the experiment.

References

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