Nereu Augusto Streck

Improving predictions of developmental stages in winter wheat: a modified Wang and Engel model ☆

Accurate simulations of plant development is an important component in crop simulation models and for use in managerial decisions, such as fertilizer applications or pest control. The three major environmental factors that control development in winter wheat (Triticum aestivum L.) are temperature, photoperiod, and vernalization. Results from a previous study showed that the prediction of several developmental stages from booting to physiological maturity were better with the Wang and Engel (WE) model compared to CERES-Wheat, but not for the prediction of terminal spikelet initiation (TS). In the WE model, the vernalization function [f(V)] is a three-stage linear function and the life cycle of the wheat crop is divided into two phases, vegetative (emergence–anthesis) and reproductive (anthesis–physiological maturity). The objective of this study was to modify the WE model by introducing a nonlinear f(V), and dividing the vegetative phase into two sub-phases (emergence–terminal spikelet initiation and terminal spikelet initiation-anthesis). A series of field experiments were carried out at Lincoln, NE, USA, to provide independent data on the date of developmental stages of two winter wheat cultivars (Arapahoe and Karl 92) for evaluating the original and the modified WE model. The root mean square error (RMSE) with the modified WE model was 5 days for Arapahoe and 6 days for Karl 92 for all developmental stages, which corresponds to a 45% decrease in the RMSE compared with the original WE model.

Energy Partitioning and Evapotranspiration over a Rice Paddy in Southern Brazil

AbstractDuring approximately 80% of its growing season, lowland flooded irrigated rice ecosystems in southern Brazil are kept within a 5–10-cm water layer. These anaerobic conditions have an influence on the partitioning of the energy and water balance components. Furthermore, this cropping system differs substantially from any other upland nonirrigated or irrigated crop ecosystems. In this study, daily, seasonal, and annual dynamics of the energy and water balance components were analyzed over a paddy rice farm in a subtropical location in southern Brazil using eddy covariance measurements. In this region, rice is grown once a year in low wetlands while the ground is kept fallow during the remaining of the year. Results show that the energy budget residual corresponded to up to 20% of the net radiation during the rice-growing season and around 10% for the remainder of the year (fallow). The energy and water balance analysis also showed that because of the high water table in the region, soil was near sat...

Desempenho de cultivares de mandioca em ambiente subtropical

The objective of this study was to evaluate and compare variables of growth, development and yield components of roots and stems of five cassava cultivars in subtropical environment in Rio Grande do Sul, Brazil. A field experiment was conducted in the 2010-2011 and 2011-2012 growing seasons at Santa Maria, RS, with five cassava cultivars, Fepagro - RS 13, Fepagro - RS 13, Fepagro - RS 14, Estrangeira, Fecula Branca and Cascuda in a randomized block design with four replicates and a two factor scheme. Variables of growth and development such as leaf area, plant height and leaf number and yield components of roots and stems were collected. The cultivars Fepagro - RS 13 and Fepagro - RS 14 have the highest LAI, above-ground biomass and height compared to the cultivars Estrangeira, Fecula Branca and Cascuda, because the former have greater sympodial branching. Cultivars Fepagro – RS13 and Fepagro – RS 14 have high production of both above-ground and tuber roots whereas cultivars Estrangeira, Cascuda and Fecula Branca are adapted for tuber roots production in subtropical environment of Rio Grande do Sul, Brazil.

ACOMPANHAMENTO DA SAFRA 2012/2013 DE ARROZ IRRIGADO NO RIO GRANDE DO SUL POR MODELAGEM NUMÉRICA

O objetivo deste trabalho foi realizar o acompanhamento de safra de arroz irrigado durante o ano agricola 2012/2013 para o estado do Rio Grande do Sul. Para o acompanhamento de safra, foi utilizado o modelo SimulArroz. Foi utilizado o grupo de maturacao precoce de cultivares de arroz, com simulacoes nos niveis de tecnologia alto, medio e baixo. A media de produtividade observada foi de 7481,7 kg/ha, enquanto que a media de produtividade simulada com o SimulArroz nos niveis de tecnologia alto, media e baixo foi de 8732,0 kg/ha, 7041,7 kg/ha e 5597,9 kg/ha respectivamente. O modelo demonstrou boa sensibilidade as variacoes meteorologicas entre as regioes do RS, demonstrando maior potencial produtivo de arroz para as regioes da Fronteira Oeste e da Campanha. Portanto, o modelo SimulArroz simulou de forma satisfatoria a produtividade de arroz irrigado para os municipios em que foi testado, podendo ser utilizado no acompanhamento de safra.

O POTENCIAL EROSIVO DAS CHUVAS EM SANTA MARIA, RS E O FENÔMENO EL NIÑO OSCILAÇÃO SUL

O fenomeno El Nino Oscilacao Sul (ENOS) afeta o tempo e oclima de diferentes locais, influenciando os elementos meteorologicos,principalmente a chuva, nas diferentes regioes do Brasil. Entre os metodosde determinacao da erosividade das chuvas, o indice de erosividadeEI30 e o mais usado no Rio Grande do Sul (RS). O objetivo deste trabalhofoi determinar e associar o indice EI30 com o fenomeno ENOS paraSanta Maria, RS. Usaram-se os dados diarios de chuva retirados depluviogramas a partir de 01 de julho de 1978 a 30 de junho de 2008 eclassificados em anos de El Nino, La Nina e Neutros, posteriormentecalculado o seu indice EI30. O potencial erosivo das chuvas em SantaMaria e afetado pelo fenomeno ENOS, de modo que um maior numerode chuvas tem maior potencial erosivo em anos de El Nino e em anosNeutros