Optimization of plant spacing and fertilizer levels for enhanced growth and yield of hybrid pigeonpea (Cajanus cajan L.)

Introduction

Pigeonpea (Cajanus cajan (L.) Millsp.) is a significant pulse crop extensively cultivated in the semi-arid tropics, notably in India. It plays a crucial role in human nutrition by providing protein, enhances soil fertility through biological nitrogen fixation, and improves soil organic matter content via leaf defoliation during maturity. Consequently, pulses are instrumental in advancing sustainable agricultural practices. (Nagalaxmi et al.). Pulses are popularly known as rich source of protein, they maintain soil fertility through biological nitrogen fixation and overall pulse production. On account of biological nitrogen fixation, addition of considerable amount of organic matter through root biomass and leaf fall, deep root-systems, mobilization of nutrients, protection of soil against erosion and improving microbial biomass, they keep soil productive and alive by bringing qualitative changes in physical, chemical and biological properties (Bansal et al., 2011) [1] . As a soil ameliorant, pigeonpea is known to provide several benefits to the soil in which it is cultivated (Murali et al., 2014) [7] . Despite its importance, average productivity of pigeonpea remains relatively low due to sub-optimal agronomic and nutrient management practices. Therefore, improved practices such as optimized plant geometry and balanced nutrient supply are essential to enhance crop performance and productivity sustainably. Plant spacing influences plant population dynamics, light interception, nutrient uptake, branch proliferation, and canopy structure, which directly affect yield attributes and final grain yield. Wider plant spacing can reduce intra-plant competition but may underutilize land area, whereas narrower spacing increases competition for water, nutrients and light, potentially reducing yield contribution per plant (Bathula Venkatesh et al., 2023) [2] . Studies on pigeonpea have shown that plant geometry significantly affects growth parameters, yield attributes, and productivity, demonstrating the necessity of identifying ideal row and plant spacing for specific agroecological conditions. Balanced fertilizer application is another crucial factor governing the growth and yield of pigeonpea. Fertilizer is a vital input in agriculture to boost the crop yields. (Madhu et al., 2024) [5] . Nitrogen (N), phosphorus (P) and potassium (K), collectively known as NPK, are essential macronutrients crucial for plant growth, supporting key physiological and biochemical processes such as photosynthesis, protein synthesis, and energy transfer. (Nagalaxmi Doddamani et al., 2024) [8] . Integrated nutrient management combining chemical fertilizers with bio-consortia or bio-fertilizers has been reported to improve nutrient availability, soil microbial activity and nutrient use efficiency, resulting in enhanced growth and yield. Biofertilizers such as phosphorus-solubilizing bacteria (PSB), Rhizobium and other microbial consortia play a significant role in mobilizing native soil nutrients, enhancing nodulation and supporting sustainable pulse production by reducing dependency on chemical fertilizers. Integrated nutrient management approaches combining bio-fertilizers with recommended fertilizer doses have been consistently shown to improve yield and maintain soil health in pigeonpea. Despite these documented effects, limited research has focused on the combined influence of plant spacing and integrated fertilizer management (including bio-consortia) in hybrid pigeonpea under field conditions. Therefore, the present field study was designed to standardize optimal plant spacing and fertilizer doses for maximizing growth and yield of hybrid pigeonpea under kharif conditions.

Materials and Methods

A field experiment was conducted at D-block, Regional Agriculture Research Station, Warangal, Telangana during kharif 2024-25. The experimental site is situated in the Central Telangana Agro-climatic zone. The soil of the experimental site was clay loam in texture with neutral pH level (7.2), an electrical conductivity (EC) of 0.60 dSm -1 , the organic carbon (%) was 0.31 and available nitrogen, phosphorus and potassium was 206, 29.5 and 297.4 kg/ha, respectively. The total rainfall received during the crop-growing period was 1082.6 mm.The experiment was laid out in a factorial randomized block design (FRBD), with two spacing's i.e. (S 1: 90 cm x 30 cm and S 2: 120 cm x 30 cm) and six fertilizer doses (F 1 -20: 40: 20: 20 Kg NPKS /ha; F 2 -25: 50:25: 20 kg NPKS /ha; F 3 -F 1 + Bio consortia @10 g/kg seed (NPKZn); F 4 -F 2 + Bio consortia @10g/kg seed(NPKZn); F 5 -15:30: 15: 20 kg NPKS /ha + Bio consortia @10g/kg seed (NPKZn); and F 6 -30:60:30:20 + Bio consortia @10 g/kg seed(NPKZn)replicated thrice.In all there were twelve treatment combinations. Plot size was maintained at 7.2 m × 4.2 m, and seeds of hybrid pigeonpea (IPH-15-3) were sown manually at specified plant spacings, sowing was carried out on 10 July 2024.Bio-consortia included microbial inoculants known to enhance nutrient mobilization (Rhizobium, phosphorussolubilizing bacteria, potassium-solubilizing bacteria and ZSB), improving nutrient availability beyond conventional fertilization. Fertilizers were applied basally and as per treatment specifications. Weeds were controlled properly with applying of pre-emergence and post-emergence herbicides. Appropriate plant protection measures were proactively implemented as required. Observations on key growth parameters (plant height, branches per plant), yield attributes (pods per plant, seeds per pods and seed weight), and final yield (seed and stalk yield) were recorded at the time of harvest. Soil and plant nutrient analysis, were carried out following standard laboratory protocols. The economics were worked out based on the prevailing market price. Statistical analysis of the data, collected using a factorial randomized block design, was performed via ANOVA.

Results and Discussion

Growth parameters and Yield attributes Plant spacing did not significantly influence plant height, number of branches and seed index of hybrid pigeonpea (Table 1). However, wider spacing of 120 cm × 30 cm recorded numerically higher number of pods per plant (112) and seeds per 10 pods (49.9) compared to closer spacing (90 × 30 cm). Wider spacing reduces inter-plant competition and improves light interception, nutrient availability, and photosynthetic efficiency, resulting in better reproductive growth (Venkatesh et al., 2025; Ganajaxi Math et al., (2023) [2,14,3] . Among fertilizer treatments, integrated application of inorganic fertilizers along with bioconsortia (NPKZn) significantly improved yield attributes. Treatments F 4 (25:50:25:20 kg NPKS ha⁻¹ + bio-consortia) and F 3 (20:40:20:20 kg NPKS ha⁻¹ + bio-consortia) recorded significantly higher pods/plant (119 & 120) and seeds/pod (58 & 52.7 respectively) compared to fertilizer-alone treatments. The beneficial effects of biofertilizers are attributed to enhanced biological nitrogen fixation, phosphorus solubilization, zinc mobilization and improved root growth, which collectively enhance nutrient uptake and assimilate partitioning. The significant interaction between spacing and fertilizer levels for yield attributes indicates that optimum nutrient supply expresses its full potential under favorable plant geo-metry, which is in agreement with findings reported in pigeonpea and other pulse crops.

Grain yield and Economics

Wider plant spacing (120 cm × 30 cm) recorded higher seed yield (1178 kg/ha), gross monetary returns, net monetary returns (50769 Rs./ha), and benefit-cost ratio (2.33) compared to closer spacing, although differences were statistically non-significant (Table 2). Improved yield under wider spacing may be attributed to better canopy architecture, higher photosynthate accumulation, and efficient translocation towards flowers and developing pods (Mula, M.G. et al., 2011) [6] . Among fertilizer treatments, F 4 (25:50:25:20 kg NPKS ha⁻¹ + bio-consortia) produced the highest seed yield (1276 kg ha⁻¹) and net monetary returns, followed closely by F 3 , which recorded the highest B:C ratio (2.48). Integrated nutrient management ensures balanced and continuous nutrient availability throughout the crop growth period, leading to higher productivity and economic returns (Sd Sabeeha Sultana et al., 2018) [12] . Phosphorus plays an important role in the higher yield, by stimulation of root development, metabolic processes and energy transformation in the plants, which in turn, resulted in higher translocation of photosynthates towards the sink development. Ultimately the seed yield plant -1 was improved which resulted in higher seed yield. The similar results were reported by Goud et al., (2012) [4] . The significant interaction effect on seed yield and economic parameters suggests that appropriate fertilizer management combined with suitable spacing is crucial for realizing higher productivity and profitability in hybrid pigeonpea, corroborating earlier reports by (Venkatesh et al., 2023, Venkatesh et al., 2025) [2,14] . The hybrid pigeonpea exhibited a highly favorable environment for effective utilization of available nutrients with maximum root development. [3] in pigeonpea (Table 3). Among fertilizer treatments, F [11] . Interaction effects were significant only for final soil potassium content, while nutrient uptake remained non-significant, suggesting that fertilizer dose had a stronger influence on nutrient dynamics than plant spacing alone. These findings align with earlier studies emphasizing the role of integrated nutrient management in sustaining soil health and crop productivity (Sharma et al.).

Conclusion

Considering the findings from a year of experimentation, it can be concluded that the wider spacing of 120 x 30 cm (27,777 plants/ha) proved to be the most advantageous plant geometry with highest benefit-cost ratio (2.33) application of inorganic fertilizers (F 3 ) 25:50:25:20 kg NPKS/ha or (F 4 ) 20: 40: 20: 20 Kg NPKS /ha along with NPKZn Bio-consortia @10 g/kg seed as seed treatment recorded significantly higher grain yield, net returns of pigeonpea and it may be proved productive, profitable and economically viable to the farmers.

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