Effect of potassium and zinc application on growth and yield attributes of mustard (Brassica juncea L.)

Introduction

One of the most significant oilseed crops in the Brassicaceae family, Indian mustard (Brassica juncea L.) is widely grown in India under a variety of agroclimatic conditions. It contributes significantly to the agricultural economy and plays an important part in the production of edible oil. Despite its significance, yield of mustard is comparatively low because of inadequate crop management techniques, nutritional shortages, and uneven fertilisation (Bastia et al., 2020) [4] . Final crop production is mostly determined by growth and yield characteristics including plant height, number of branches, leaf area, siliquae per plant, and seeds per siliqua. These characteristics are extremely sensitive to the availability of nutrients, especially zinc and potassium, which are necessary for a number of physiological and biochemical functions in plants.

Potassium is an important macro nutrient essential for protein synthesis, photosynthesis, enzyme activation, and helps in translocation of water and minerals. Additionally, it controls stomatal opening and closing, which enhances plants' ability to withstand stress and use water more efficiently. Sufficient potassium feeding improves the development of yield-contributing traits and fortifies plant structure (Subba Rao & Srinivasarao, 2010) [32] . An important micronutrient, zinc (Zn) is involved in protein metabolism, enzyme activation, and auxin production. It has a major impact on photosynthesis, growth regulation, and the production of chlorophyll. According to Singh et al. (2005) [30] , applying zinc has been shown to boost plant height, branch count, and yield characteristics such seeds per siliqua and siliquae per plant in mustard. Zinc also improves photosynthates' transfer to reproductive organs, which boosts agricultural productivity (Deo & Khandelwal, 2009) [12] . Crop growth and development are restricted in many Indian soils due to zinc deficiencies and inadequate potassium levels. Because high-yielding cultivars progressively deplete soil micronutrients, balanced fertilisation is crucial. Therefore, potassium and zinc if applied together judiciously can boost mustard's development parameters and production features. Keeping in view the importance of nutrient management, the present study was undertaken to evaluate the effect of potassium and zinc on growth and yield attributes of mustard (Brassica juncea L.).

Review of Literature

The development and yield characteristics of mustard are greatly impacted by the application of zinc and potassium. According to Pradhan et al. (2023) [25] , a combined treatment of 50 kg K/ha + 15 kg Zn/ha produced the highest plant height (193.45 cm), plant dry weight (35.25 g), siliquae per plant (302.20), and seeds per siliqua (17.60) under sandy loam soil conditions. Atkari et al. (2022) [3] found that potassium application at 45 kg/ha greatly increased plant height, branch count, dry matter accumulation and number of siliquae. Azotobacter + PSB plus 40 kg K/ha also enhanced siliqua per plant (134.53) and seeds per siliqua (31.67), according to Tripathi et al. (2022) [33] . According to Ajnar et al. (2021) [1] , the combined application of RDF, sulphur, vermicompost, and biofertilizers greatly increased test weight, siliqua per plant, and seeds per plant. Additionally, Jana et al. (2021) [16] found that RDF + foliar DAP @ 2% increased plant height, leaf area index, dry matter accumulation, and seed count. Additionally, Singh et al. (2005) [30] found that due to increased metabolic activity, zinc administration up to 6 kg/ha considerably boosted plant height, number of branches, and yield parameters. Similar to this, Deo and Khandelwal (2009) [12] found that applying zinc increased growth metrics because of its function in protein synthesis and enzyme activation. Furthermore, Choudhary et al. (2008) [11] noted that mustard growth indices and reproductive features are greatly enhanced by balanced fertilisation that includes micronutrients. Applying zinc greatly enhances mustard's growth and yield characteristics. According to Jannat et al. (2023) [17] , maximum plant height (140.57 cm), branches (5.84), pods per plant (87.57), and seeds per pod (31.53) were achieved with a combined basal and foliar application of Zn and B (100% basal + 25% Zn foliar). According to Jaswal et al. (2023) [18] , foliar spraying RDF + 1% urea + 0.5% ZnSO₄ + 0.5% FeSO₄ at 45 DAS greatly improved growth metrics and yield. Beulah et al. (2022) [6] found higher plant height (202.36 cm), branches (11.18), and dry weight (32.96 g) when Zn was applied @ 15 kg/ha under 40 cm spacing. Yanthan et al. (2021) [36] and Mhonthung et al. (2021) [23] reported that combined application of Zn and B significantly increased siliqua per plant (86.07), seeds per siliqua (40.27), and test weight (3.85 g). Similarly, Behara et al. (2021) [5] observed superior plant height (136.02 cm), dry weight (34.37 g), siliqua per plant (113), and seeds per siliqua (32.5) with Zn @10 kg/ha + S @30 kg/ha. Additionally, Zn @ 10 kg/ha combined with sulphur greatly increased the leaf area index and chlorophyll content, according to Verma et al. (2018) [34] . Sangwan et al. (2017) [29] found that foliar Zn (0.5% ZnSO₄) greatly increased growth and yield qualities under dryland circumstances. Kumar et al. (2018) [22] also noted better plant height, branches, siliqua per plant, and test weight with integrated use of RDF + FYM + Zn + S. Additionally, Sahito et al. (2014) [28] found that applying up to 8 kg/ha of zinc increased growth metrics. In general, mustard's vegetative development and production characteristics are improved by balanced nutrition management that incorporates potassium, zinc, and integrated sources.

Materials and Methods

A field experiment was carried out during the Rabi season of 2022-2023 at the Department of Agriculture's experimental farm at Jigyasa University (formerly Himgiri Zee University), Dehradun, Uttarakhand. The location of the site was 650 meters above mean sea level, at latitude of 30°19' N and longitude 78°04' E. The soil had a sandy loam texture, a pH of 7.49, and 0.40% organic carbon. Soil Sampling was done prior to sowing from four distinct locations at a depth of 0 to 15 cm. The samples were combined to create a composite sample, which was then examined for physico-chemical characteristics. Temperatures throughout the crop season varied from 4.0°C to 14.0°C (min.) and from 19.8°C to 34.4°C (max.). The experiment was set up using a Randomised Block Design (RBD) with three replications and sixteen treatments. Observations were recorded from five tagged plants per plot at different growth stages (20,

Results and Discussion

At every growth stage, potassium and zinc had a substantial impact on plant height (Table 1). The T 13 treatment (50 kg K/ha + 15 kg Zn/ha) recorded the highest plant height (14.95 cm) at 20 DAS, (55.93 cm) at 40 DAS, (84.59 cm) at 60 DAS, (134.16 cm) at 80 DAS, (179.45 cm) at 100 DAS, and (193.45 cm) at harvest, while the lowest (162.89 cm) at harvest was recorded under T 1 6 (100% RDF). Potassium plays a vital role in enzyme activation, osmotic regulation, and stomatal functioning, thereby enhancing cell expansion and water relations, while zinc is essential for auxin synthesis, protein metabolism, and membrane integrity. This coordinated action promotes cell division and elongation, resulting in increased plant height, as also reported by Ismail Cakmak (2019) [10] and Hafeez et al. (2020) [13] . Plant dry weight was greatly impacted by treatments and rose steadily with crop age (Table 1). The dry weight under T 13 (50 kg K/ha + 15 kg Zn/ha) ranged from 0.85 g (20 DAS) to 35.25 g (at harvest), whereas the dry weight under T 1 6 (100% RDF) was the lowest (31.87 g at harvest). Potassium facilitates the translocation of photosynthates from source to sink, whereas zinc enhances chlorophyll synthesis and carbonic anhydrase activity, thereby improving carbon fixation. The lower dry weight under RDF alone (T 1 6) highlights the importance of micronutrient supplementation for optimal biomass production. Similar findings were reported by Raza et al. (2020) [26] and Imran et al. (2021) [14] , who emphasized the role of balanced fertilization in enhancing crop growth. CGR rose during the early to mid-growth phases before falling. Under T 13 (50 kg K/ha + 15 kg Zn/ha), the highest CGR was measured at intervals of 7.19, 10.82, 19.70, and 10.53 g/m²/day. T 1 6 (100% RDF) had the lowest CGR (Table 2). The highest CGR under T 13 suggests efficient conversion of intercepted radiation into biomass due to optimal nutrient supply. As crop age increased, the relative growth rate exhibited a decreasing tendency. T 13 had the highest RGR (0.0425, 0.0179, 0.0137, and 0.0055 g/g/day at successive intervals), whereas T 1 6 (100% RDF) had the lowest values. This suggests that a diet rich in potassium and zinc improves growth efficiency, particularly in the early phases of growth. Potassium enhances ATP production and enzyme activity, while zinc improves nitrogen metabolism and protein synthesis, leading to higher growth rates (Ali et al., 2022) [2] . Likewise, Relative Growth Rate (RGR) decreased with crop age due to increased structural biomass; however, higher RGR values in early stages under T 13 indicate better metabolic efficiency and nutrient utilization, as supported by Singh et al. (2021) [31] . Zinc and potassium had a substantial impact on the number of siliquae per plant (Table 2 and Fig. 1). The highest number of siliqua (302.20) was found under T 13 (50 kg K/ha + 15 kg Zn/ha), whereas the lowest number (266.53) was found under 100% RDF (T 1 6). Higher nutrition levels were found to significantly enhance the number of seeds per siliqua. T 13 had the greatest value (17.60), while T 1 6 had the lowest (13.87). The higher values under T 13 can be attributed to improved reproductive development, enhanced pollen viability, and efficient assimilate translocation to reproductive organs. Zinc plays a critical role in flowering and fertilization processes, while potassium ensures effective carbohydrate transport, resulting in improved sink development. These findings are in agreement with Bhati et al. (2014) [7] , Kour et al. (2017) [20] , and Khan et al. (2022) [19] . Better reproductive development and increased metabolic activity under balanced potassium and zinc nutrition are the causes of this improvement. It was discovered that the test weight was not significant. However, the highest value (3.73 g) was recorded under T 13 , and the lowest (3.23 g) under T 1 6. Although test weight was statistically non-significant, higher values under T 13 suggest improved seed filling due to better nutrient availability. Potassium is particularly important in starch synthesis and grain development, while zinc supports enzymatic activities involved in seed maturation (Yadav et al., 2020) [35] . Overall, the study highlights that balanced application of potassium and zinc enhances growth efficiency, biomass accumulation, and reproductive performance, ultimately leading to improved crop productivity compared to RDF alone. 1.20 0.001 T1: 30 kg K/ha + 5 kg Zn/ha; T2: 30 kg K/ha + 10 kg Zn/ha; T3: 30 kg K/ha + 15 kg Zn/ha; T4: 30 kg K/ha + 20 kg Zn/ha; T5: 30 kg K/ha + 25 kg Zn/ha; T6: 40 kg K/ha + 5 kg Zn/ha; T7: 40 kg K/ha + 10 kg Zn/ha; T8: 40 kg K/ha + 15 kg Zn/ha; T9: 40 kg K/ha + 20 kg Zn/ha; T10: 40 kg K/ha + 25 kg Zn/ha; T11: 50 kg K/ha + 5 kg Zn/ha; T12: 50 kg K/ha + 10 kg Zn/ha; T13: 50 kg K/ha + 15 kg Zn/ha; T14: 50 kg K/ha + 20 kg Zn/ha; T15: 50 kg K/ha + 25 kg Zn/ha; T16: 100% RDF

Conclusion

The study comes to the conclusion that applying 50 kg K/ha + 15 kg Zn/ha together greatly improved mustard yield attributes and growth metrics. Better nutrition absorption, increased physiological activity, and effective assimilate translocation were the causes of this improvement. Therefore, this therapy can be suggested to improve crop output and growth characteristics.

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