Response of short-rotation Melia dubia Cav. agroforestry plantation to mineral fertilization in a semiarid Alfisol

Introduction

The National Forest Policy (2014) emphasizes production of woody raw materials on farmers' fields, which has led to organized agroforestry for the production of wood-based raw materials. It also paved the way for increased participation of industries in using the agroforestry products at appropriate prices without disturbing the forest ecosystem. In India, the industrially important exotic tree species such as Eucalyptus, Casuarina, Leucaena, and Populus require specific climatic conditions and grow well in certain agro-climatic areas. On the other hand, Melia dubia is one of the indigenous fast-growing alternate pulpwood species that are adaptive to wide agroclimatic conditions (Thakur et al., 2017) [1] and the inclusion of Melia dubia in agroforestry has been found to be superior to many exotic tree plantations in terms of economic returns and ecosystem services like enhancing soil fertility and atmospheric carbon sequestration (Jayakumar et al., 2025) [2] . Furthermore, M. dubia is being advocated as an amenable tree species for agro-forestry without any deleterious effects on under-storied agricultural crops (Kumar et al., 2017 and Parmer et al., 2018) [3,4] . The industrial and ecological importance of M. dubia has encouraged farmers to take large-scale plantations with various intercrops. Under commercial exploitation, knowledge of nutrient management needs to be clarified to the small and marginal farmers, who have been practicing traditional methods. The available information on the growth response of M. dubia to mineral fertilization is not sufficient for making suitable decisions on the use of fertilizers and the time of applications. The application of mineral fertilizers, particularly the nitrogen (N), phosphorus (P), and potassium (K) has been seen as a means to enhance the productivity of short-rotation renewable forest plantations (Pukkala, 2017) [5] . The deficiency of any of these nutrients will negatively affect the growth and development of the plantations (Khalofah et al., 2022) [6] . N is essential for chlorophyll synthesis and vegetative growth and therefore should remain available during vegetative growth. P stimulates cell division and promotes root development and its deficiency delays growth increments. K plays a vital role in plant protection by maintaining cell turgidity throughout the lifecycle. However, excess or deficient nutrition will negatively impact the growth and targeted yield of the plantations (Alem, 2024) [7] . Furthermore, mineral fertilizers have not been widely used in agroforestry mainly due to a lack of knowledge about the quantities of fertilizer needed for different species and specific soil types. Information on optimum dosages of inorganic nutrients for better growth of Melia dubia is lacking or very limited under Indian conditions. Generation of such information will be helpful in standardizing the most favorable dosage of nutrients for Melia dubia plantations to obtain maximum wood productivity. Even though this study was principally aimed at optimizing the mineral fertilizer dose for a commercial agroforestry M. dubia plantation grown under semiarid conditions, we studied the annual growth increment and the effect of different doses of mineral fertilization on the GBH, height, stand volume, and carbon sequestration through a residual standardized regression model. This study will provide insight into mineral fertilizer application to short-rotation M. dubia plantations.

Materials and Methods

Field experiment

A field experiment for optimizing mineral nutrition for the shortrotation M. dubia clone GK-10 was conducted at plantation research block of TNPL, situated under semiarid conditions. The sandy loam alfisol soil was neutral in pH with non-saline nature, having 182 kg ha -1 of N, 16 kg ha -1 of P and 396 kg ha -1 of K, respectively. The experiment was laid out in a randomized block design in three replications with the mineral fertilizer treatments as depicted in Table 1: Planting was established at a spacing of 3.0 m × 1.5 m with a population of 2,222 plants ha -1 . Each treatment plot had a gross plot area and a net plot area of 144 m 2 and 54 m 2 , respectively. After the necessary land preparations, the M. dubia clone GK-10 plants were planted in all the plots during the first week of January 2018. The entire fertilizer doses were applied through drip irrigation according to the treatments using commercial grade water soluble fertilizers in 24 equal monthly splits.

Biometric observations

The biometric observations were made in 12-, 24-, and 36month-old plantations. The total height of the trees (m) was measured using a Haga altimeter. All the trees were marked at 1.37 m from ground level, and GBH (cm) was measured using tailor's tape. The volume of standing trees (m3) was estimated using the formula of Chaturvedi and Khanna (1982) [8]: V = πr 2 h × Form Factor (0.58), where V is the volume of the tree; r is the radius at breast height and h is the height of the tree. The measurement of total biomass, including the above ground (AGB) and below ground (BGB) was done using destructive sampling method in triplicate. The representative trees were felled at ground level and the fresh weights of the above ground tree components (stem, twigs and leaves) and below ground tree components (coarse and fine roots) were measured immediately. The dry matter production (DMP) of AGB and BGB was calculated after drying them to a constant weight and converted into fixed carbon by multiplying the DMP by 0.50 (Brown and Lugo, 1982) [9] and expanded to t ha -1 , which is considered the carbon sequestration potential of M. dubia plantation. From the biometric recordings, annual growth increments in growth parameters, viz., GBH, tree height, stand volume, total biomass and C sequestration were calculated for the 2 nd year and 3 rd year and the mean annual increments were presented.

Statistical analysis

Data were subjected to univariate analysis of variance (ANOVA) to find the effect of different doses of mineral fertilization on mean annual increments in growth parameters. A post hoc test of Duncan's multiple range test (DMRT) was employed to find the significant difference in wood yield and carbon sequestration. With the observed growth data, a residual standardized regression analysis was performed to predict the significant effect of fertilizer application on the dependent growth variables and carbon sequestration of M. dubia plantations. All statistical analyses were conducted using SPSS ver. 30 (SPSS Inc., Chicago, USA).

Results and Discussion

In general, it was observed that the fertilized trees were found to be significantly superior in mean annual growth increments compared to the trees in control plots, confirming the important role of mineral fertilizers in short-rotation agroforestry plantations. The highest wood yield was obtained with the fertilizer application at the rate of 200:150:200 kg ha -1 of NPK throughout the growth period (Fig 1). This was followed by the application of 150:75:150 kg of NPK ha -1 . The minimal dose of fertilizer application (100:50:100 kg NPK ha -1 ) had no significant effect in this regard, as the yield was statistically comparable with the control treatment. However, the treatments F4 and F3, which received a higher dose of fertilizers, were found to be statistically on par and superior in sequestering atmospheric carbon at 36 months after planting (MAP). During the first year, the response of M. dubia plantation to different doses of inorganic fertilizer was minimal in increasing the growth rate and carbon sequestration, which was likely because of underdeveloped root system and limited exploitation of the rhizospheric zone (Fig 1). However, from the second year onwards, a clear trend was noted among the fertilizer doses. Studies revealed that mineral fertilization increases the GBH of early wood by thickening the cell wall. However, the magnitude of this effect is mainly dependent on the frequency and cumulative quantity of fertilizer application (Shmulsky and Jones 2019) [10] . In the present study, a cumulative application of 200:100:200 kg NPK ha -1 at a monthly frequency for two years recorded significantly higher GBH (F = 9.974; p =. 001; Table 2). The application of 150:75:150 kg NPK ha -1 followed this treatment in increasing the tree GBH. The lowest fertilizer rate of application (100:50:100 kg NPK ha -1 ; F2) showed no statistical advantage over control treatment in increasing the GBH. Although the p-value of this parameter was higher than 0.05, indicating that it did not reach statistical significance, the regression analysis showed a generalized significant effect of fertilizer application on the GBH increments in M. dubia plantation (F = 6.433; p =. 015; Fig. 2a). Therefore, it is worth considering even a small quantity of fertilizer application over no fertilization for increasing the GBH in M. dubia plantations. The doses of fertilizer application showed no significant difference in increasing the height of M. dubia trees (F =. 840; p =. 498; Table 2), which was confirmed in regression analysis (F = 1.561; p =. 218; Fig. 2b). In many of the earlier studies, the height potential of M. dubia traits was reported to be between 10 m and 12 m only (Goswami et al., 2020; Sharma et al., 2021; Jayakumar et al., 2025) [11,12,2] . Since the height parameter in M. dubia is more of a genetic character, rather than an environmental influence, the exogenous fertilizer application had a minor effect in increasing the height of the trees. The statistical analyses, viz., ANOVA as well as residual standardized regression showed a significant effect of mineral fertilization on increasing the volume of M. dubia plantation (p =. 012 in ANOVA-Table 2 and p =. 014 in regression analysis-Fig. 2c), indicating that stand volume in M. dubia plantations can be increased through mineral fertilizers from the first year onwards, even though the height of the trees remains unalterable. This can be explained by the fact that the increment in stand volume was mainly attributed to the increment in GBH of individual trees (Prasad et al., 2011) [13] . Further, the lower quantity and greater frequency of fertilizer application through the drip irrigation system provided effective utilization of mineral nutrition by individual trees and resulted in an increase in the volume of the plantation (Neupane et al., 2024) [14] . The positive effect of mineral fertilization extended to total biomass increment and C sequestration as well. Though the ANOVA in Table 2 showed a significance of F = 4.012 and p =. 034, the residual standardized regression in Fig. 2d recorded a relatively less significant F value of 4.774 at p = 0.34 for biomass production. While applying mineral nutrition to shortterm agroforestry plantations, the duration of the fertilizer effect should also be considered for effective plantation management.

In contrast to agricultural crops, agroforestry plantations exhibit a long duration response to mineral fertilizers. Even though N is associated with short-term response, the effect persists for a mid-term rotation of 8-10 years (Akello et al., 2024) [15] . Some research points out an even higher response period of 15 years after the last application of N (Smolander et al., 2022) [16] . The response of P application to tree plantations was found to be longer than that of N and K, due to its effective retention in agroforestry systems, with the potential to improve tree growth even in subsequent rotations of 20 years (Everett and Palm-Leis, 2009; Akello et al., 2024) [17,15] . The application of K nutrient to tree crops could be a reserve for the present as well as subsequent short and mid-term rotations, as the applied K is fixed in the soil system and released gradually with the progress of rhizo-acidification (Crous et al., 2009) [18] . With the addition of mineral NPK fertilizers, the availability of these nutrients is further enhanced in the soil, as about 70-80% of the nutrients are recycled in agroforestry plantations (Patil et al., 2017) [19] . From ANOVA, it is apparent that mineral fertilizer application increased the mean annual growth increments (Table 2). However, the results of the regression analysis (Fig. 2) suggest that the biomass production and subsequent C sequestration in short-rotation M. dubia plantations are governed by other factors as well, in addition to mineral nutrition. For instance, Deng et al.

(2024) [20] noted that the fertilizer response of perennial trees is influenced by factors such as the genetic nature of the species, soil fertility level, and prevailing climatic conditions.

Conclusion

This study found that a mineral fertilizer application of 200:100:200 kg NPK ha -1 to M. dubia plantations at a monthly interval of 24 months was found to be better in relation to commercial wood production at 36 month of age, with a potential of further improving the yield in subsequent years. It is, however, the regression analysis that clearly indicated that the fertilizer application for total biomass production in the M. dubia plantation has a non-significant effect, likely due to the short responsive growth period of 3 years. Therefore, this fertilizer recommendation cannot be generalized without considering the similarities in soil (alfisol) and climatic (semiarid) conditions, and the purpose for which M. dubia plantations are raised: for wood production or total biomass production. From the results of this study, it is possible to conclude that a mineral fertilizer dose of 200:100:200 kg NPK ha -1 can be applied to short-rotation M. dubia plantations for higher wood productivity. In addition, extending the rotational period will result in a higher fertilizer response, with increased wood and biomass productivity and farm income. Future studies should focus on the residual effects of applied mineral fertilizers in subsequent rotations.

References

1. Thakur NS, Kumar D, Gunaga RP, Singh S. Allelopathic propensity of the aqueous leaf extract and leaf litter of Melia dubia cav. on pulse crops. J Exp Biol Agric Sci. 2017;5(5):644-55. doi:10.18006/2017.5(5).644.655.
2. Jayakumar K, Prasath V, Sudhakar P, Chezhian P, Stalin T, Rajesh R. Stand density influences pulpwood yield, soil fertility and carbon sequestration in semiarid Melia dubia Cav. plantation. Am J Agric For. 2025;13(1):28-37. doi:10.11648/j.ajaf.20251301.14.
3. Parmar AG, Thakur NS, Gunaga RP. Melia dubia Cav. leaf litter allelochemicals have ephemeral allelopathic proclivity. Agrofor Syst. 2018;93:1-14. doi:10.1007/s10457-018-02435.
4. Pukkala T. Optimal nitrogen fertilization of boreal conifer forest. Forest Ecosyst. 2017;4(3). doi:10.1186/s40663-0170090-2.
5. Khalofah A, Ghramh HA, Al-Qthanin RN, L'taief B. The impact of NPK fertilizer on growth and nutrient accumulation in juniper (Juniperus procera) trees grown on fire-damaged and intact soils. PLoS ONE. 2022;17(1):e0262685. doi:10.1371/journal.pone.0262685.
6. Alem S. Response of the growth and survival of tree species planted in a degraded land with a supplement of diammonium phosphate (DAP) fertilizer. Land Degrad Dev. 2024;35:2543-9. doi:10.1002/ldr.5079.
7. Chaturvedi AN, Khanna IS. Forest mensuration. International Book distributers; 1984.
8. Brown S, Lugo AE. The storage and production of organic matter in tropical forests and their role in the global carbon cycle. Biotropica. 1982;14:161-87.
9. Shmulsky R, Jones PD. Silvicultural practices and wood quality. In: Forest products and wood science. 7th ed. Wiley; 2019. p. 257-92. doi:10.1002/9781119426400.ch11.
10. Goswami M, Bhagta S, Sharma D. Melia dubia and its importance: a review. Int J Econ Plants. 2020;7:29-33. doi:10.23910/2/2020.0351.
11. Sharma S, Negi A, Behera J, Narya R. Suitability of medium density particle board from Acacia catechu and Melia dubia. J Trop Forest Sci. 2021;33:247-60. doi:10.26525/jtfs2021.33.3.247.
12. Prasad JVNS, Korwar GR, Rao KV, Mandal U. Optimum stand density of Leucaena leucocephala for wood production in Andra Pradesh, Southern India. Biomass Bioenergy. 2011;35(1):227-35. doi:10.1016/j.biombioe.2010.08.012.
13. Neupane K, Witcher A, Baysal-Gurel F. An Evaluation of the Effect of Fertilizer Rate on Tree Growth and the Detection of Nutrient Stress in Different Irrigation Systems. Horticulturae. 2024;10:767. doi:10.3390/horticulturae10070767.
14. Akello S, du Toit B, Balboni BM, Wessels CB. A review of the effect of fertilization on the wood properties of pinus trees. Eur J Forest Res. 2024;143:1291-305. doi:10.1007/s10342-024-01709-6.
15. Smolander A, Henttonen HM, Nojd P, Soronen P, Makinen H. Long-term response of soil and stem wood properties to repeated nitrogen fertilization in a N-limited Scots pine stand. Eur J Forest Res. 2022;141(3):421-31. doi:10.1007/s10342-022-01448-6.
16. Everett C, Palm-Leis H. Availability of residual phosphorus fertilizer for loblolly pine. Forest Ecol Manag. 2009;258(10):2207-13. doi:10.1016/j.foreco.2008.11.029.
17. Crous JW, Morris AR, Scholes MC. Effect of phosphorus and potassium fertiliser on tree growth and dry timber production of Pinus patula on gabbro-derived soils in Swaziland. South Forests. 2009;71(3):235-43. doi:10.2989/SF.2009.71.3.8.920.
18. Patil HY, Karatangi G, Kirankumar, Mutanal SM. rowth and productivity of Melia dubia under different plant density. Int J Forest Crop Improv. 2017;8(1):30-3. doi:10.15740/HAS/IJFCI/8.1/30-33.
19. Deng Y, Ni G, Liu Y. Influence of fertilizer rates, planting density and light transmittance on yield and quality of P. cyrtonema. Int J Agric Sustain. 2024;22(1):2409490. doi:10.1080/14735903.2024.2409490.