ORIGINAL ARTICLE Financial support: None. Conflict of interest: Nothing to declare. Corresponding author: rodrigo_hakamada@yahoo.com.br Received: 25 May 2022. Accepted: 1 January 2023. Editor: Mauro Valdir Schumacher. This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original scientific article is properly cited. Scientia Forestalis, 51, e3917, 2023 | https://doi.org/10.18671/scifor.v51.07 1/15 3-PG model enhancement by modifying soil water availability in a tropical Eucalyptus urophylla plantation Aprimoramento do modelo 3-PG pela modificação da disponibilidade de água no solo em Eucalyptus urophylla Cristiane Zani de Lemos 1 , Omar Carrero 2 , Rodrigo Hakamada 3,4,5 , Luis Fernando Silva 6 , Karina Ferreira 7 , José Luiz Stape 8 1 Agriflora, Ibaté, SP, Brasil 2 Consultor independente, Porto Alegre, RS, Brasil 3 Universidade Federal Rural de Pernambuco – UFRPE, Recife, PE, Brasil 4 Instituto de Pesquisas e Estudos Florestais – IPEF, Piracicaba, SP, Brasil 5 Universidad de Guadalajara – UDG, Guadalajara, Jalisco, México 6 Paper Excellence, São Paulo, SP, Brasil 7 Sylvamo, Mogi Guaçu, SP, Brasil 8 Departamento de Ciência Florestal, Universidade Estadual Paulista “Júlio de Mesquita Filho” – UNESP, Botucatu, SP, Brasil How to cite: Lemos, C. Z., Carrero, O., Hakamada, R., Silva, L. F., Ferreira, K., & Stape, J. L. (2023). 3-PG model enhancement by modifying soil water availability in a tropical Eucalyptus urophylla plantation. Scientia Forestalis, 51, e3917. https://doi.org/10.18671/scifor.v51.07 Abstract 3-PG is a widely process-based model used to estimate forest growth. After 20 years of use, along with progress in scientific knowledge, some model processes can be improved, such as soil water balance. The objective of this study was to assess the enhancements in the 3-PG model for Eucalyptus urophylla by changing the soil water availability, which considers the depth of the root system in the soil profile as stand ages. To set up the model and assess the improvement, a site in Sao Paulo state, Brazil, was used. From this trial two treatments were selected: 1) control (operational fertilization, without irrigation) and 2) fertilized and irrigated. The model enhancement for rooting depth and the maximum amount of water available was based on a measured relationship between the above-ground height and below-ground root depth, by replacing the constant value of the available soil water in the original 3-PG with a dynamic amount that increases as the root system grows. This modification increased the model efficiency to estimate the stem biomass and the leaf area index. This work can be used by researchers and forest managers using the 3PG model, as there was a significant improvement in stem biomass estimates, where the root mean square error (RMSE) decreased from 18.22 (original) to 12.16 (increased) Mg ha -1 yr -1 for non-irrigated treatment, increasing the model accuracy in forest biomass estimates Keywords: Eco-physiological modeling; Process-based modelling; Forest modelling; Forest growth. Resumo O 3-PG é um modelo baseado em processos amplamente difundido, usado para estimar o crescimento florestal. Após 20 anos de uso, juntamente com o avanço do conhecimento científico, alguns processos dentro do modelo podem ser aprimorados, como o balanço hídrico do solo. O objetivo deste estudo foi avaliar uma potencial melhoria no modelo 3-PG em termos de disponibilidade de água no solo considerando a profundidade de raiz que varia com a idade do povoamento. Para configurar o modelo e avaliar a melhoria, foi utilizado um sítio no Estado de São Paulo, Brasil. Deste ensaio foram selecionados dois tratamentos: 1) testemunha (adubação operacional, sem irrigação) e 2) adubado e irrigado. O aprimoramento do modelo para a profundidade de enraizamento e a quantidade máxima de água