Effect of NPK and foliar application of Humic acid on growth and yield of broccoli

Introduction

Broccoli (Brassica oleracea var. italica) is an important cool season vegetable of family Brassicaceae (2n=18) believed to have originated in Italy. The edible part is the compact curd formed by a mass of unopened florets along with a portion of fleshy stem. It thrives well at day temperature of 18-26 °C and night temperature of 15-16 °C and prefers well drained sandy loam soil with pH 5.5 to 6.8 (Kohil et al., 2006) [10] . The world production of broccoli and cauliflower together was about 25 million tonnes from 1.4 million ha in 2022 (FAO, 2022) [7] , with China, India and USA as major producers. The crop is gaining popularity due to its rich nutritional profile, as it is a good source of vitamin C, vitamin K, folate, fibre and bioactive compounds like glucosinolates, sulforaphane and indoles having anti-cancer and antioxidant properties. The productivity and quality of broccoli largely depend on balanced nutrition. Nitrogen is required for vegetative growth and chlorophyll formation, phosphorus for root development and curd initiation, and potassium for maintaining water balance, enzyme activity and stress tolerance. Excess use of nitrogen alone may affect curd quality. Apart from major nutrients, humic acid as a bio stimulant and soil conditioner improves soil structure, water holding capacity, microbial activity and root growth, which helps in better nutrient availability and uptake by the plant. Considering the role of NPK and humic acid in growth and curd development, the present investigation was undertaken to study the effect of NPK and foliar application of humic acid on growth, yield and quality of broccoli.

treatments were tested in a Randomised Block Design with three replications: T 1 (75% RDF + 0.5% humic acid), T 2 (100% RDF + 0.5% humic acid), T 3 (125% RDF + 0.5% humic acid), T 4 (75% RDF + 1.5% humic acid), T 5 (100% RDF + 1.5% humic acid), T 6 (125% RDF + 1.5% humic acid), T 7 (75% RDF + 2.5% humic acid), T 8 (100% RDF + 2.5% humic acid), T 9 (125% RDF + 2.5% humic acid) and T 10 (100% RDF; 125:60:60 NPK kg ha -1) . Seedlings of broccoli were transplanted into the field on 5 th December 2024, spaced at 60 × 45 cm. Before transplanting, FYM was incorporated in the field @ 25 t ha⁻¹. Other than these treatments, the crop was managed as per the standard package of practices followed in the region. Growth was tracked through plant height and number of leaves plant -1 recorded at 30, 45 and 60 days after transplanting (DAT) and leaf area. For yield, the parameters recorded included days required to curd initiation, days required to 1 st harvest and curd yield ha -1 . Data were analysed statistically following Panse and Sukhatme (1989) [13] ; standard error of mean (S.E m±) and critical difference (CD) at the 5% level were computed for every character studied.

Results and Discussion

The application of RDF with humic acid significantly affected plant height at 30, 45 and 60 DAT. Among the treatments, 125% RDF + 1.5% humic acid (T 6 ) produced the tallest plants, recording 22.27, 53.33 and 71.47 cm, respectively, while the shortest plants were observed in 75% RDF + 0.5% humic acid (T 1 ) with 13.07, 32.13 and 43.67 cm. The greater plant height in T 6 could be attributed to the improved availability and uptake of nutrients under higher RDF, particularly nitrogen, which supports chlorophyll formation, protein synthesis and cell growth. The addition of humic acid may have further promoted root development and improved nutrient-use efficiency, thereby encouraging better vegetative growth. Comparable responses have been reported by Al-Jaf et al. (2018) [2] , who reported improved plant height in broccoli with humic acid application. (2019) [3] .

Stem diameter (cm): Among the treatments, stem diameter showed marked differences. T9 consisting of 125% RDF (156.25:75:75 NPK kg ha⁻¹) with 2.5% humic acid produced the boldest stems measuring 2.27 cm at 30 DAT, 3.17 cm at 45 DAT and 5.63 cm at 60 DAT, which remained statistically at par with T6 and T8 at 45 DAT (3.06 cm and 2.96 cm) and with T6 at 60 DAT (5.54 cm). The poorest stem growth of 1.26 cm, 2.54 cm and 4.49 cm at respective stages was recorded in T1 receiving 75% RDF with 0.5% humic acid. The better stem thickness in T9 could be attributed by sufficient nutrient availability from higher RDF level and the stimulatory effect of humic acid on root development, nutrient absorption and photosynthate accumulation. The results are in line with those reported by Selim and Mosa (2012) [15] .

The treatments significantly influenced leaf area in broccoli. Among all the treatments, 125% RDF + 2.5% humic acid (T 9 ) recorded significantly maximum leaf area (515.90 cm 2 ) which was statistically at par with 125% RDF + 1.5% humic acid (T 6 ) with leaf area of 511.20 cm 2 . The minimum leaf area (481.27 cm 2 ) was recorded in 75% RDF + 0.5% humic acid (T 1 ). The increase in leaf area under higher RDF and humic acid might be attributed to enhanced availability of nitrogen which is essential for cell division, cell expansion and overall vegetative growth, coupled with the beneficial effect of humic acid in improving nutrient uptake, photosynthetic efficiency and production of growth promoting substances. The present findings are in conformity with the results reported by Al-Jaf et al. (2018) [2] and Abdulrahman et al. (2025) [1] who reported enhanced leaf growth and leaf area in broccoli with humic acid and nutrient application.

Chlorophyll index:

The chlorophyll index of leaves varied significantly among treatments. The highest chlorophyll index of 70.59 was recorded in T 9 ; 125% RDF with 2.5% humic acid, which was comparable to T 6 (66.55) and T 3 (63.86), while the lowest reading of 52.88 was found in T 10 with only 100% RDF. This maximum chlorophyll index in T 9 might be because of more nitrogen available from the higher fertilizer dose, which is essential for chlorophyll synthesis, and humic acid further helped in better nutrient uptake and utilization. The low value in T 10 could be due to absence of humic acid. Similar results were reported by Vidigal et al. (2021) [16] and Ibrahim et al. (2024) [8] in broccoli. [2,11,15] in broccoli.

B. Yield and yield attributing parameters

Days to 1 st harvest:

The crop reached first harvest earliest under 125% RDF + 1.5% humic acid (T 6 ) in 66.07 days after transplanting, whereas 75% RDF + 0.5% humic acid (T 1 ) took the maximum of 75.23 days. It seems that with higher NPK, plants grew more vigorously and accumulated photosynthates faster, and the addition of humic acid at 1.5% helped in better root growth and nutrient uptake, so curds matured early. Interestingly, increasing humic acid to 2.5% did not give any further earliness, showing a concentration dependent response. Delayed harvest in low nutrient treatment was due to poor growth. These results are in conformity with Katiyar et al. (2012) [9] in broccoli.

Curd yield plant -1 (g): With respect to curd yield per plan, significant variation was observed due to different levels of NPK and humic acid. Treatment 125% RDF (156.25:75:75 NPK kg ha⁻¹) + 1.5% humic acid (T 6 ) produced the highest curd weight of 653.40 g plant⁻¹ and remained at par with 100% RDF + 1.5% humic acid (T 5 ) which gave 616.00 g. The lowest value of 457.08 g was obtained under 75% RDF + 0.5% humic acid (T 1 ). The increase in yield under 125% RDF + 1.5% humic acid might be because of higher nutrient supply coupled with humic acid on nutrient use efficiency, root development and photosynthesis which helped in better assimilate accumulation in the curd. At par yield of T5 and T6 indicates that beyond 100% RDF, yield did not improve markedly when 1.5% humic acid was applied. The poor performance under 75% RDF + 0.5% humic acid could be due to insufficient nutrition and restricted growth. These findings are in agreement with those of Selim and Mosa (2012) [15] , Al-Jaf et al. (2018) and Al-Taey et al. (2019) [2,3] in broccoli.

Curd yield ha -1 (q): Among all treatments, 125% RDF + 1.5% humic acid recorded significantly maximum (242.00 q ha -1 ) curd yield, which was found to be statistically at par with 100% RDF + 1.5% humic acid (228.14 q ha⁻¹), whereas minimum (169.28 q ha -1 ) curd yield recorded in 75% RDF + 0.5% humic acid (T 1 ). The significantly higher yield under 125% RDF + 1.5% humic acid (T 6 ) may be attributed to adequate nutrient availability, enhanced vegetative growth, photosynthetic activity and better assimilate translocation towards curd development, while humic acid further promoted root growth and nutrient uptake improving nutrient utilization, whereas the lower yield under 75% RDF + 0.5% humic acid (T 1) indicates limited nutrient availability and restricted growth under reduced RDF; these findings are in close agreement with Selim and Mosa (2012) [15] who reported increased total marketable yield of broccoli with humic substances along with NPK, Al-Jaf et al. (2018) [2] who observed improved total yield with humic acid. C. Available NPK in soil (kg ha -1 ) Available nitrogen (kg ha -1 ): Available nitrogen varied significantly across treatments. The maximum available nitrogen of 135.2 kg ha⁻¹ was recorded in T 9 (125% RDF + 2.5% humic acid), while the lowest of 131.7 kg ha⁻¹ was in T 1 (75% RDF + 0.5% humic acid). In general, 125% RDF treatments retained more nitrogen than 75% and 100% RDF. This might be because T 9 supplied more nitrogen and humic acid helped to hold nutrients and boost microbial activity, keeping nitrogen available. Lower nitrogen in T 1 was likely due to low fertilizer and humic acid dose. Similar trends were reported by Ibrahim et al. (2024) [8] and Ampong et al.

The available phosphorus content in soil changed significantly with treatments.

Maximum available phosphorus of 17.86 kg ha⁻¹ was recorded in T 9 ; 125% RDF with 2.5% humic acid, which was at par with T 6 and T 3 , while lowest of 14.86 kg ha⁻¹ was in T 1 ; 75% RDF with 0.5% humic acid. In general, treatments receiving higher RDF showed more phosphorus in soil. This may be because more phosphorus was added through 125% RDF and humic acid helped to reduce its fixation in soil and keep it in available form. Low available phosphorus in T 1 could be simply due to less fertilizer and low humic acid. Similar results were also reported by Wang et al. (1995) and Du et al. (2013) [6,17] .

Available Potassium (kg ha -1 ): Available potassium differed significantly among treatments, with the maximum available potassium in soil, 360.0 kg ha⁻¹ recorded in T 9 (125% RDF + 2.5% humic acid) and the lowest of 353.0 kg ha⁻¹ in T 1 (75% RDF + 0.5% humic acid), and overall 125% RDF maintained more potassium than 75% and 100% RDF, possibly due to higher potassium input and humic acid improving retention and availability, while low values in T 1 were due to lower fertilizer and humic acid; similar results were reported by Selim and Mosa (2012) [15] and Ayyar (2018) [5] .

D. Plant uptake

Nitrogen uptake: Nitrogen uptake varied significantly among the treatments, with maximum uptake of 129.09 kg ha⁻¹ in T 6 (125% RDF + 1.5% humic acid) which was at par with T 9 (125.81 kg ha⁻¹) and minimum uptake of 81.17 kg ha⁻¹ in T 10 (100% RDF alone); better uptake with 125% RDF + humic acid could be due to higher nitrogen availability and improved root growth and absorption by humic acid, while low uptake in T 10 was due to absence of humic acid, similar to Selim and Mosa (2012) and Selladurai and Purakayastha (2016) [14,15] .

Phosphorus uptake: Phosphorus uptake differed significantly, with maximum of 38.57 kg ha⁻¹ in T 6 (125% RDF + 1.5% humic acid) at par with T 9 (36.30 kg ha⁻¹) and minimum of 21.13 kg ha⁻¹ in T 1 (75% RDF + 0.5% humic acid); higher uptake in T 6 may be due to more phosphorus supply and humic acid improving root growth and availability, while [8,12] .

Potassium uptake: Potassium uptake varied significantly among the treatments, with maximum uptake of 117.6 kg ha⁻¹ in T 6 (125% RDF + 1.5% humic acid) which was at par with T 9 (108.6 kg ha⁻¹) and minimum of 95.58 kg ha⁻¹ in T 10 (100% RDF alone); better uptake in T 6 could be due to higher potassium availability and humic acid improving root growth and nutrient retention, while 1.5% to 2.5% humic acid did not give extra benefit, in line with Selim and Mosa (2012), Mohapatra et al. (2014) [12,15] .

Future Scope

The optimum dose, concentration, time of application and number of foliar sprays of humic acid along with varying levels of NPK in broccoli still needs to be standardized, and their effect should be studied in detail. There is also scope to test these combinations on different cultivars, in different seasons and under varied agro-climatic conditions to confirm the results on a broader scale. Future studies should also focus on the impact on soil properties, nutrient uptake, shelf life and post-harvest quality of broccoli as well as its economic viability under actual field conditions, which would require multi-season and multi-location trials beyond the present single-season investigation.

Conclusion

On the whole, among all the treatments, 125% RDF + 1.5% humic acid (T 6 ) was found to be the most effective. It recorded higher plant height, more leaves per plant, earlier curd initiation and earliest harvesting along with maximum curd yield per plant, yield per hectare and uptake of NPK by plant. For parameters like leaf area, stem diameter and available NPK in soil, 125% RDF + 2.5% humic acid (T 9 ) showed better results and gave maximum values.

Acknowledgement

AcknowledgementI would like to thank Dr. A. M. Sonkamble, Professor and Head, Department of Vegetable Science, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, for his guidance and support throughout this work, and the Department of Vegetable Science, Dr. PDKV, Akola, for the facilities that made this investigation possible.

References

1. Abdulrahman NM, Qadir NJ, Maruf HA, Sharif SF. Interactive effects of foliar applied nano NPK and humic acid on growth and yield of broccoli (Brassica oleracea var. italica). University of Thi-Qar Journal of Agricultural Research. 2015;14(2):282-292.
2. Al-Jaf HI, Raheem SM, Tofiq GK. Growth and yield of broccoli (Brassica oleracea L. var. Corato) as affected by humic acid application. Journal of Plant Production. 2018;9(9):739-741.
3. Al-Taey DK, Al-Shareefi MJH, Mijwel AK, Al Tawaha ARM. The beneficial effects of bio-fertilizers combinations and humic acid on growth, yield parameters and nitrogen content of broccoli grown under drip irrigation system. Bulgarian Journal of Agricultural Science. 2019;25(5):959-966.
4. Ampong K, Thilakaranthna MS, Gorim LY. Understanding the role of humic acids on crop performance and soil health. Frontiers in Agronomy. 2022;4:848621.
5. Ayyar S. Effect of mulching and humic acid on the nutrient availability and nutrient uptake of tomato under fertigation. Environment and Ecology. 2018;36(2A):583-592.
6. Du ZY, Wang QH, Liu FC, Ma HL, Ma BY, Malhi SS. Movement of phosphorus in a calcareous soil as affected by humic acid. Pedosphere. 2013;23(2):229235.
7. Food and Agriculture Organization. Agricultural Statistical Database for 2022. Rome: FAO; 2022.
8. Ibrahim EA, Ebrahim NES, Mohamed GZ. Mitigation of water stress in broccoli by soil application of humic acid. Scientific Reports. 2024;14:2765.
9. Katiyar D, Tripathi SM, Dwivedi AK, Pandey V. Effect of nitrogen and phosphorus on crop growth, head yield and quality of broccoli (Brassica oleracea L. var. italica). International Journal of Agricultural Sciences. 2011;1(2):172-174.
10. Kohil R, Singh R, Kumar S. Effect of different nutrient management practices on growth and yield of broccoli (Brassica oleracea var. italica). Journal of Applied Horticulture. 2006;8(2):115-118.
11. Kumar R, Kandpal K. Influence of foliar fertilization of boron on broccoli (Brassica oleracea var. italica) in boron deficient soil of Doon Valley, India. Progressive Horticulture. 2017;49(1):65-68.
12. Mohapatra SK, Mahapatra P, Munsi PS. Effect of organic manures, bioinoculants and inorganic fertilizers on yield, nutrient uptake and nutrient recovery by broccoli. Indian Journal of Horticulture. 2014;71(4):584-587.
13. Panse VG, Sukhatme PV. Statistical methods for agricultural workers. New Delhi: Indian Council of Agricultural Research; 1985.
14. Selladurai R, Purakayastha TJ. Effect of humic acid multinutrient fertilizers on yield and nutrient use efficiency of potato. Journal of Plant Nutrition. 2016;39(7):949-956.
15. Selim EM, Mosa AA. Fertigation of humic substances improves yield and quality of broccoli and nutrient retention in a sandy soil. Journal of Plant Nutrition and Soil Science. 2012;175(2):273-281.
16. Vidigal SM, Puiatti M, Lopes IPC, Sediyama MAN. Nitrogen content, SPAD index and production of single head broccoli. Horticultura Brasileira. 2021;39(1):5257.
17. Wang XJ, Wang ZQ, Li SG. The effect of humic acids on the availability of phosphorus fertilizers in alkaline soils. Soil Use and Management. 1995;11(2):99-102.