Índice de colheita de arroz de terras baixas irrigado por aspersão

Abstract

Harvest Index (HI) is the measurement of the plant eficiency in the photoassimilates division. An increase in the HI means an increase in the economically important portion of the plant. The objective of this study was to quantify the Harvest Index of lowland rice cultivars in different irrigation layers by sprinkling. Three experiments were conducted at the experimental area of the Universidade Federal do Pampa – Campus Itaqui, in the 2014/2015, 2015/2016 and 2016/2017 growing seasons. In the 2014/2015 growing season, the treatments were composed by three lowland rice cultivars (XP 102, IRGA 428 and IRGA 429), under five irrigation layers by sprinkling, 0%, 50%, 100% e 150% and 200% crop evapotranspiration (ETc), with four repetitions. In the 2015/2016 growing season, the treatments were composed by four lowland rice cultivars (BR IRGA 409, IRGA 428 e Puitá INTA CL and IRGA 424), five irrigation layers by sprinkling, 0%, 50%, 100% e 150% e 200% of the ETc, with four repetitions. In the 2016/2017 growing season, the cultivar used was the IRGA 424 RI, submitted to five irrigation layers by sprinkling, 50%, 100%, 150%, 200% e 250% of the (ETc), with four repetitions. The above ground dry mass (AGDM) and grain yield measurements were performed when the plants reached R9. The harvest index was calculated according to the following equation, HI = Harvest index/ above ground dry mass, with the final result expressed in kg kg-¹. The ANOVA was performed by the software SISVAR, and the statistical analyzes and graphs were performed by the software SIGMAPLOT 10.0. The 2014/2015 growing season recorded the highest values of AGDM and grain yield. However, the 2015/2016 growing season were injured due to a record El niño that occurred during this growing season. In the 2014/2015 and 2015/2016 growing seasons, the treatment without irrigation did not complete its cycle, so its HI was 0, this resulted in the substitution of this treatment for the 250% ETc irrigation layer in the 2016/2017 growing season. In most treatments, the HI presented a logistic growth, but, in the 2015/2016 growing season, two cultivars showed a quadratic response curve as a function of the irrigation layer. Irrigation layers above 100% of the ETc were enough to reach HI greater than 0,50. However, the plants submitted to water stress showed a lower HI value. The highest HI value reached was 0,56. This value is similar to the highest values found in the literature.