Amanda Heemann Junges

Modelo agrometeorológico-espectral de estimativa de rendimento de grãos de trigo no Rio Grande do Sul

Este trabalho teve como objetivo construir uma regressao linear multipla, empregando variaveis agrometeorologicas e espectrais, para estimativa de rendimento de graos de trigo, em municipios pertencentes a regiao de atuacao da Cooperativa Cotrijal (norte do Rio Grande do Sul). Para isso, foram empregados dados de rendimento (1991 a 2006), dados agrometeorologicos mensais (1991 a 2006) e dados espectrais (imagens NDVI/MODIS, 2000 a 2006). Foi analisada existencia de aumento significativo no rendimento de graos, decorrente da incorporacao de novas tecnologias (tendencia tecnologica). Para escolha das variaveis independentes da regressao linear, foi analisada a correlacao dos dados agrometeorologicos e espectrais com os dados de rendimento. Definidas as variaveis, foi construida uma regressao linear multipla de estimativa de rendimento de graos de trigo. Os resultados mostraram que nao houve aumento significativo no rendimento de graos de trigo da Cotrijal, no periodo analisado. Foram escolhidas as seguintes variaveis independentes para construcao da regressao linear multipla: precipitacao pluvial (outubro), indice de dano por geadas (setembro), graus-dia (acumulados de maio a outubro) e indice de vegetacao por diferenca normalizada (integrado de junho a outubro). As regressoes lineares multiplas apresentaram resultados satisfatorios, com erros de estimativa inferiores a 10%, na maior parte dos anos analisados. As caracteristicas de precisao, facil execucao e baixo custo das regressoes apontaram para possibilidade de uso conjunto de dados agrometeorologicos e espectrais, na estimativa de rendimento de graos de trigo. Mais estudos sao necessarios para verificacao dos resultados dos modelos, quando da incorporacao de uma serie mais longa de dados espectrais.

Desenvolvimento das culturas de cereais de inverno no Rio Grande do Sul por meio de perfis temporais do índice de vegetação por diferença normalizada

This research aimed to elaborate temporal NDVI profiles through the crop masks building, and find the interannual variations of profiles associated with variation of wheat grain yield in Rio Grande do Sul, Brazil. The data set were composed by MODIS13 images (NDVI product from May to November, 2000 to 2006), ground control points (collected in wheat, oat and barley fields) and official wheat grain yield (IBGE and Cotrijal). The results showed that using the proposed methodology for crop masking it is possible to generate consistent NDVI temporal profiles, which allows monitoring the development of winter cereal crops and can be used to evaluate the interannual variations of grain yield. The profiles showed that wheat grain yield was related to the maintenance of high NDVI values (above 0.7) for a larger period of time. However, the methodology did not allow the wheat, oats and barley discrimination, pointing for subsequent studies.

Temporal profiles of vegetation indices for characterizing grazing intensity on natural grasslands in Pampa biome

The Pampa biome is an important ecosystem in Brazil that is highly relevant to livestock production. The objective of this study was to analyze the potential use of vegetation indices to discriminate grazing intensities on natural grasslands in the Pampa biome. Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) images from Jan to Dec, 2000 to 2013 series, were analyzed for natural grassland experimental units managed under high (forage allowance of 5 ± 2 % live weight – LW), moderate (13 ± 5 % LW) and low grazing intensity (19 ± 7 % LW). Regardless of intensity, the temporal profiles showed lower NDVI and EVI during winter, increased values in spring because of summer species regrowth, slightly decreased values in summer, especially in years when there is a water deficit, and increased values in the fall associated with the beginning of winter forage development. The average temporal profiles of moderate grazing intensity exhibited greater vegetation index values compared with low and high grazing intensities. The temporal profiles of less vegetation index were associated with lower green biomass accumulation caused by the negative impact of stocking rates on the leaf area index under high grazing intensity and a floristic composition with a predominance of tussocks under low grazing intensity. Vegetation indices can be used for distinguishing moderate grazing intensity from low and high intensities. The average EVI values can discriminate moderate grazing intensity during any season, and the NDVI values can discriminate moderate grazing intensity during spring and winter.

Inferências sobre o calendário agrícola a partir de perfis temporais de NDVI/MODIS

A major challenge for grain yield modeling in the context of estimates made operationally for large areas is related to the identification of periods in which annual crops show greater susceptibility to environmental stress. For soybean grown in the spring-summer period in southern Brazil, the main risk factor is the occurrence of water stress during flowering and grain filling. These subperiods occur at different times across the production region due to differences in management practices of each farmer. This study aimed to relate the soybean crop calendar to the temporal profiles of normalized difference vegetation index (NDVI/MODIS), in order to present/validate a low cost technology with adequate accuracy for crop monitoring and harvest prediction. Thus, we analyzed data from soybean crop calendar (subperiods of flowering, grain filling and maturation) from EMATER (RS) regions and NDVI MODIS images. The NDVI temporal profiles allow monitoring the development of the soybean crop biomass and determining the occurrence of subperiods. Differences in NDVI values between harvests, regions and subperiods demonstrate the sensitivity of this index in detecting the responses of soybean plants to environmental conditions. Because NDVI data are generated from MODIS images, it is possible to create maps with information about the subperiods for all harvests and throughout the State, which enables greater temporal and spatial details compared to data currently available.

Normalized difference vegetation index obtained by ground-based remote sensing to characterize vine cycle in Rio Grande do Sul, Brazil

The normalized difference vegetation index (NDVI) obtained by remote sensing is widely used to monitor annual crops but few studies have investigated its use in perennial fruit crops. The aim of this study was to determine the temporal NDVI profile during grapevine cycle in vineyards established in horizontal training systems. NDVI data were obtained by the ground-based remote sensing Greenseeker in Chardonnay and Cabernet Sauvignon vineyards located in the Serra Gaúcha region, Rio Grande do Sul, Brazil, from September to June in the 2014/2015 and 2015/2016 vegetative seasons. The grapevine canopies were managed in horizontal training systems (T-trellis and Y-trellis). The results indicated that the temporal NDVI values varied during the grapevine cycle (0.33 to 0.85), reflecting the changing in vigor and biomass accumulation that resulted from the phenological stages and management practices. The temporal NDVI profiles were similar to both horizontal training systems. The NDVI values were higher throughout the cycle for Cabernet Sauvignon compared to Chardonnay indicating Cabernet Sauvignon as the cultivar with greater vegetative vigor. The NDVI obtained by ground-based remote sensing is a fast and non-destructive tool to monitor and characterize the canopy in real time, compiling into a single data several parameters related to vine development, like meteorological conditions and management practices that are difficult to be quantified together.

NDVI and meteorological data as indicators of the Pampa biome natural grasslands growth

The present study aimed to characterize the dynamics of NDVI and meteorological conditions, relating both to the annual dynamics of biomass accumulation in natural pastures of the Pampa biome as a way of subsidizing growth modeling. Forage accumulation rate data from a long-term experiment, NDVI data from the MODIS images, and meteorological data measured at the surface were used. We verify that the agrometeorological element associated to the accumulation of forage in the natural grasslands is different according to the season, which is typical of the subtropical climate. Winter is the critical season for livestock production due to the lower forage accumulation rate and lower IRRIGATION AND AGROMETEOROLOGY Article NDVI and meteorological data as indicators of the Pampa biome natural grasslands growth Denise Cybis Fontana1*, Amanda Heemann Junges2, Carolina Bremm2, Laura Pigatto Schaparini1, Vagner Paz Mengue3, Ana Paula Luz Wagner4, Paulo Carvalho1 1.Universidade Federal do Rio Grande do Sul Faculdade de Agronomia Porto Alegre (RS), Brazil. 2.Fundação Estadual de Pesquisa Agropecuária Porto Alegre (RS), Brazil. 3.Universidade Federal do Rio Grande do Sul Centro Estadual de Pesquisas em Sensoriamento Remoto e Meteorologia Porto Alegre (RS), Brazil. 4.University of Florida Institute of Food and Agricultural Sciences Agricultural and Biological Engineering Department Gainesville (FL), United States. *Corresponding author: dfontana@ufrgs.br Received: Jul. 5, 2017 – Accepted: Oct. 24, 2017 values of NDVI, conditioned by the decrease of solar radiation and air temperature. In the summer, the limiting factor to forage accumulation is the hydric condition. It was also verified that the variability in the growth of grasslands can be associated with the ENSO phenomenon, being the El Niño favorable and the La Niña unfavorable, especially in the spring-summer period. Considering the verified associations, spectral indices combined with agrometeorological elements are recommended to the adjustment of models of forage accumulation in the Pampa biome natural grasslands.

Relation between temperature and relief through NOAA images

This work analyze the temperature and relief relationship duringthe 2006 frosts happened in the main producer winter cereals region,through the characteristics of regional relief and minimum surfacetemperatures obtained of satellite NOAA-12 images. The results showedthat the well-known relationship between surface temperature and altitudecan be represented throughout NOAA-12 images.