| Abstract |
India's agriculture sector, accounting for 18.2 percent of the GDP and employing nearly half of the workforce, relies significantly on imported fertilizers. This dependency is a fiscal burden on the economy and contributes to soil degradation and pollution. Rice, the staple food in Kerala and most parts of India, is experiencing a production deficit, satisfying only one-fifth of the state’s annual requirement, primarily due to the declining area under rice cultivation. Enhancing the productivity of existing agricultural lands is vital to address this deficit. To mitigate this dependency and enhance soil fertility, the practice of tree-based green leaf manuring offers a sustainable solution. Traditionally, green leaf manuring was once a popular practice among Kerala paddy farmers. But changes in cropping systems, reduced tree availability, land constraints, and labour shortages hindered this practice. Boundary plantations with green leaf manuring potential offer an ecologically sound and locally feasible approach to rejuvenate this eco-friendly practice and enhance soil fertility, reduce external input dependency, and ensure sustainable paddy cultivation. Tree plantations along agricultural field boundaries not only utilize underexploited space but also provide regular biomass inputs, recycle nutrients, improve soil structure, and offer ecosystem services. In this backdrop, two separate field experiments were conducted at the State Seed Farm, Mannuthy, Thrissur, Kerala, during 2022-2024. First experiment focused on assessing growth performance, green biomass production, soil fertility enhancement and carbon sequestration potential of high density block plantation with twelve green manure tree species (Acrocarpusfraxinifolius, Pongamiapinnata, Cassia siamea, Macarangapeltata, Thespesiapopulnea, Garugapinnata, Brideliaretusa, Gmelinaarborea, Terminalia arjuna, Neolamarckiacadamba, Hibiscus tiliaceus and Gliricidiasepium) planted at a spacing of 1.5 m × 1m, in a Randomized Block Design (RBD) with three replications, along the boundaries of wetland paddy fields. The second experiment, designed in an RBD with two replications, assessed the nutrient content of different green leaf manure (GLM) derived from the boundary plantations and the influence of green leaf manuring on paddy growth, yield attributes, nutrient uptake, economy and soil fertility. The findings of the first experiment on boundary plantation revealed significant interspecific variation in tree growth, biomass production, and soil fertility enhancement. N. cadamba exhibited the most robust growth performance, with maximum height (6.73 m), collar diameter (11.64 cm), DBH (8.00 cm), and branches (20.67), alongside with higher annual green biomass yield (50.08 Mg ha⁻¹). H. tiliaceus, G. sepium, G. arborea, B. retusa, T. arjuna and C. siamea also demonstrated vigorous growth and substantial biomass production. In contrast, G. pinnata showed zero survivability while P. pinnata and A. fraxinifolius exhibited poor survivability, with stunted growth and low biomass production, making them less suitable for wetland paddy boundary conditions. The order of biomass production of different tree species by the second year are as follows: N. Cadamba (50.08) H. tiliaceus (35.50) > G. sepium (31.47) > B. retusa (23.77) > C. siamea (21) > T. arjuna (20.92) > T. populnea (13.56) > M. peltata (13.44) > G. arborea (13.31) > A. fraxinifolius (2.61) > P. pinnata (1.54). The effect of high-density boundary plantation of different tree species on soil physico-chemical-biological parameters showed significant improvement compared to the treeless boundary. Among all species, Hibiscus tiliaceus, Cassia siamea, and Thespesiapopulnea emerged as the top-performing species in enhancing soil fertility under boundary plantation systems, while Acrocarpusfraxinifolius was identified as the least effective. In terms of total system carbon sequestration, G. arborea recorded the highest carbon stock (106.74 Mg ha⁻¹) and sequestration potential (391.36 Mg CO₂ eq ha⁻¹) followed by T. populnea and B. retusa. All the tree-based treatments showed significantly greater carbon sequestration potential than the treeless boundary (155.82 Mg CO₂ eq ha⁻¹), confirming the superior carbon dynamics of tree-based integrated systems. In the second experiment, application of different tree-based GLM significantly enhanced paddy yield and N uptake compared to the control (FYM + RDF). The plots treated with G. sepium GLM recorded the highest grain yield (5.32 Mg ha-1) and nutrient uptake (111.90, 8.16 and 71.02 kg ha-1 N, P and K, respectively), followed by C. siamea, B. retusa, H. tiliaceus and M. peltata. Conversely, Pongamiapinnata and Garugapinnata recorded the lowest yield, nutrient uptake, and economic returns due to the lower nutrient content in biomass. Therefore, the farmers have to apply green biomass of these species in higher quantities to get a higher yield performance. The order of grain yield of paddy under different GLM treatments (Mg ha-1) are as follows: G. Sepium (5.32) > C. siamea (4.96) > B. retusa (4.54) > H. tiliaceus (4.29) > M. peltata (3.81) > N. cadamba and T. arjuna (3.60) > A. fraxinifolius (3.57) > G. arborea (3.55) > FYM (3.37) > T. populnea (3.20) > G. pinnata (3.13) > P. pinnata (2.36). The application of GLM notably improved the fertility status of the paddy soils by increasing the macro and micronutrient levels, enhancing microbial populations and dehydrogenase activity compared to the initial soil fertility status. Species like Cassia siamea, Macarangapeltata, Gliricidiasepium, and Hibiscus tiliaceus outperformed the FYM + RDF in terms of nutrient enrichment, microbial health and enzymatic activity, indicating their superior green manuring potential. These results underscore the capacity of tree-based green manuring to not only sustain crop productivity but also to restore soil fertility in rice systems, thereby enhancing long-term soil productivity and resilience. In conclusion, the study demonstrates that integrating fast-growing, biomass-rich tree species like N. cadamba, G. sepium, B. retusa, M. peltata, T. arjuna, G. arborea, C. siamea, and H. tiliaceus on wetland paddy field boundaries is a promising strategy for improving on-farm nutrient self-reliance, enhancing soil fertility, boosting rice productivity, and contributing to climate change mitigation. Such boundary agroforestry systems represent a sustainable, multifunctional alternative to intensive fertilizer input use, aligning well with national priorities on organic farming and agroecological intensification. The results provide a scientific basis for recommending suitable species for scaling out tree-based green leaf manuring in Kerala’s rice ecosystems. However, long-term studies are required to get more conclusive results on tree growth and biomass production, crop productivity and soil fertility changes. |
