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Rice phenology and development are events controlled by environmental and genetic factors, and the yield potential of the crop is defined by their interaction. This study aimed at analyzing the performance of irrigated rice genotypes in contrasting ecosystems and their effects on morphophysiological characteristics. Two ecosystems (tropical and subtropical) were analyzed, as well as cultivars recommended for tropical (BRS Catiana and BRS Jaçanã) and subtropical (BRS Pampa, BRS 7 Taim and IRGA 424) regions. The experiments were arranged in a complete randomized block design, with four replicates, being the factors the genotypes, sowing times and sites. The phenological development, biomass dynamics, radiation use efficiency and grain yield were evaluated. The accumulated degree-days demand for flowering decreased faster in the tropical ecosystem than in the subtropical ecosystem for late sowing. The radiation use efficiency values were similar in the subtropical ecosystem and yield was high for all sowing dates. On the other hand, the tropical ecosystem showed a high variation for radiation use efficiency values and yield. The higher accumulation of degree-days and solar radiation during the reproductive and grain-filling phases contributed to increase yield in both ecosystems.

O avanço do conhecimento da variabilidade espacial dos atributos do solo, por meio do uso de ferramentas da agricultura de precisão e geoestatística, tem sido considerado como uma estratégia de manejo que visa maximizar a produtividade agrícola. Objetivo foi avaliar a eficiência de malhas amostrais na caracterização da variabilidade espacial dos atributos físicos do solo na cultura do fumo. O trabalho foi desenvolvido na Fazenda Capivari, no município de Governador Mangabeira, Bahia. Avaliou-se: resistência do solo à penetração de raízes e condutividade hidráulica em duas malhas regulares, de 15x15 e 25x25 m, georreferenciadas. A resistência à penetração foi avaliada mediante o uso de penetrômetro de impacto. A determinação da condutividade hidráulica foi realizada por meio de ensaios em permeâmetro de carga constante. Os valores de resistência à penetração da malha 1 (15x15m) concentraram-se na faixa de pouca limitação a penetração de raízes, enquanto que na malha 2 (25x25m) no perfil abaixo dos 0,40 m valores superiores a 2,6 MPa, o que já implica em algumas limitações à penetração de raízes. Os dados demonstram que a malha amostral de maior dimensão apresenta grande potencial em detectar diferentes escalas de variabilidade espacial dos atributos físicos avaliados em Latossolos sob cultivo de fumo.

Abstract The objective of this study was to evaluate the use of estimated global solar radiation data in the simulations of potential yield of irrigated rice. Global solar radiation was estimated by four empirical models, based on air temperature, and a meteorological satellite derivated. The empirical models were calibrated and validated for 10 sites, representative of the six rice regions of the State of Rio Grande do Sul - Brazil. To evaluate the impact of the radiation estimates on irrigated rice yield simulations, the CERES-Rice model, calibrated for four cultivars, was used. The estimates of global solar radiation of the empirical models based on the air temperature showed deviations, from the observed values, of 20 to 30% and the estimated by satellite deviations of more than 30%. The global solar radiation data estimated by the Hargreaves and Samani, Donatelli and Campbell and derived satellite (PowerNasa) type air temperature-based empirical models can be used as input data in simulation models of crop growth, development and productivity of irrigated rice.