Intercomparison of sugarcane simulation models and its use to evaluate yield gap and irrigation impacts in different Brazilian regions

Author(s)

Henrique Boriolo Dias

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2016-07-07

Examining board members

Paulo Cesar Sentelhas; Rubens Duarte Coelho

• Advisor: Paulo Cesar Sentelhas

Abstract

The sugarcane production system is highly complex and the expansion of this crop is occurring to areas with expressive water deficit (WD). In this context, WD and crop management (CM) are the main determining factors of yield gaps (YG). Irrigation is an alternative to reduce YG of this crop. Crop simulation models can be used to evaluate the YG and irrigation impacts on sugarcane production. Based on that, this study aimed: i) to evaluate and adjust the MZA-FAO, DSSAT/CANEGRO and APSIM-Sugarcane models and propose a management factor (kdec) to improve the performance of these models; ii) to assess the YG magnitude and its causes (WD and CM); iii) to evaluate the impacts of irrigation on sugarcane yield and; iv) to estimate the drying-off days before harvest for different locations. When comparing 12-month cane data with several cuts in rainfed and irrigated systems, the performance of all models was poor with high mean absolute error (MAE > 29 t ha-1) and low precision (R2 < 0.54), once the models does not take into account crop management aspects. The introduction of kdec increased the models\' performances, with MAE < 14 ta ha-1 and R2 &ge; 0.63. When the average yield of the three models was used, the precision and accuracy improved and MAE decreased. The YG was calculated by the difference between simulated values of 12-months plant cane under optimum management in a multi-model approach and data from IBGE for 30 locations. The average YG total (YGT) was 121 t ha-1, which were mainly caused by WD (YGWD), followed by sub-optimal CM (YGCM). The YGWD accounted for about 72% of YGT (&sim; 87 t ha-1). The YGCM is dependent on the region and practices adopted by growers, and it represents, in average, 28% of the YGT (34 t ha-1). YGCM can be related mainly to monoculture and mechanization of high impact. Since the WD is the main cause of YG, the impact of irrigation on sugarcane yield was estimated by simulating 12-month plant cane in three soil types and 12 planting dates with MZA-FAO model for a long-term period (30 years). The results showed that the yield increases depend on the interaction between weather conditions, soil type, planting date and irrigation level. The simulations showed that irrigation is a practice with great potential to increase the sugarcane yield in several Brazilian locations. When sugarcane is irrigated, the drying-off is a strategy to increase sucrose content and yield; however, there are no recommendations about it for Brazilian conditions. In order to address this issue, simulations were conducted with APSIM-Sugarcane model for 12-month plant cane under optimum management in three soil types and 12 Brazilian locations for a long-term period (30 years). The harvest dates were simulated from May to November, which is the common harvesting season in sugarcane mills in the evaluated regions. The number of drying-off days varies according to location, soil type and harvest date, with the median ranging from 15 to 115 days. (AU)

• FAPESP's process: 14/05173-3 - Intercomparison of sugarcane simulation models and use these in assessing the productivity and quality of the crop in rainfed and irrigated conditions
• Grantee: Henrique Boriolo Dias
• Support Opportunities: Scholarships in Brazil - Master