Recent precision‐agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil‐sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal‐component analysis of landscape attributes and unsupervised classification of principal‐component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest‐ and lowest‐yielding MZ in three of five seasons, receiving average precipitation, less‐pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.

<p>Precision agriculture (PA) is growing considerably in Brazil. However, there is a lack of information regarding to PA adoption and use in the country. This study sought to: (i) investigate the perception of growers and service dealership about PA technologies; (ii) identify constraints to PA adoption; (iii) obtain information that might be useful to motivate producers and agronomists to use PA technologies in the crop production systems. A web-based survey approach method was used to collect data from farmers and services dealership involved with PA in several crop production regions of Brazil. We found that the growth of PA was linked to the agronomic and economic gains observed in the field; however, in some situations, the producers still can not measure the real PA impact in producer system. Economic aspects coupled with the difficulty to use of software and equipment proportioned by the lack of technical training of field teams, may be the main factors limiting the PA expansion in many producing regions of Brazil. Precision agriculture work carried out by dealership in Brazil is quite recent. The most services offered is gridding soil sampling, field mapping for lime and fertilizer application at variable rate. Many producers already have PA equipment loaded on their machines, but little explored, also restricting to fertilizers and lime application. Looking at the currently existing technologies and services offered by dealership, the PA use in Brazil could be better exploited, and therefore, a more rational use of non-renewable resources.</p>

Recent precision‐agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil‐sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal‐component analysis of landscape attributes and unsupervised classification of principal‐component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest‐ and lowest‐yielding MZ in three of five seasons, receiving average precipitation, less‐pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.

No abstract

Use of the combination model to predict evapotranspiration (ET) from a crop has been limited by uncertainty in the value and behavior of the bulk sulface resistance (rb). The purpose of this study was to characterize rb for irrigated wheat (Triticum aestivum L.) and evaluate its use for predictive purposes. Hourly Bowen ratio measurements were made over a field of irrigated ‘Anahuac’ wheat during the entire growing season of 1983. Data from 4 d were used to calculate rb using both the energy balance and residual methods. Crop surface temperatures predicted from measurement of wind speed and air temperature at one height above the canopy were within 0.4 °C of infrared measured canopy temperatures. Both the energy balance and residual methods gave similar values for rb. From 0830 h to 1430 h the day before irrigation, values for rb ranged from 50 to 100 s m−1 whereas after irrigation, rb for the same period ranged from 15 to 50 s m−1. In both cases, rb rapidly increased after 1430 h to values above 200 s m−1 by 1630 h. At the same time, latent heat loss in proportion to net radiation increased and canopy temperature decreased more rapidly than air temperature, suggesting that the increase in rb at this time is not due to a lag in the supply of water to the canopy. The combination model was used to predict ET on both an hourly and daily basis for several periods during another crop growing season. Mean predicted values were within 6% of Bowen ratio measurements and were highly correlated with hourly and daily measured rates of ET, suggesting that the combination model can be used for predictive purposes when rb is well characterized.

A agricultura é a atividade econômica mais dependente das condições climáticas e, em países tropicais, mais de 80% da variabilidade da produção agrícola pode ser explicada pelas condições meteorológicas. Nesse sentido, o uso contínuo de infor­mações relacionadas ao comportamento de variáveis meteorológicas para apoiar os processos de tomada de decisão gerencial em propriedades rurais permite mi­nimizar riscos e garantir a estabilidade dos níveis de produtividade das lavouras. Este trabalho descreve a experiência da Embrapa Informática Agropecuária, Uni­dade Descentralizada de Pesquisa da Empresa Brasileira de Pesquisa Agropecuária (Embrapa) e do Centro de Pesquisas Meteorológicas e Climáticas Aplicadas à Agri­cultura (CEPAGRI) da Universidade Estadual de Campinas (UNICAMP) no desenvol­vimento da plataforma web Sistema de Monitoramento Agrometeorológico (Agri­tempo), incluindo a geração de novas versões do sistema e novas funcionalidades a ele associadas.

To evaluate the water requirements for irrigated wheat, a micrometeorological study was conducted during the dry seasons of 1982 and 1983 at the Cerrados Agricultural Research Center, Brasilia-DF, Brazil The crop was irrigated when the soil water potential at 5 cm rached -60 to -70J/Kg.Bowen ratio measurements were made on an hourly basis during the entire crop season. Total amount of water evapotranspired during the crop cycle and the energy balance terms varied year to year due to regional advection; In 1982, a less advective year, the total amount of water evapotranspired was 345 mm, with approximately 80% of the net radiation dissipated as latent heat, 13% as a sensible heat and 7% as soil heat after the crop obtained a Leaf Area Index (LAI) of 1.5. In 1983, when advection was greater than 1982, total water evapotranspired increased to 385 mm. The partitioning of energy was similar to 1982 during periods of little or no advection. However, during periods of intense advection, latent heat was greater hi net radiation partitioning. Although regional advection increased the water used by the crop, irrigation scheduling based on soil tensiometers was considered adequate and efficient due to the low values of the Bowen ratio obtained.

Ao VIL. KlaU6 Rúehanclt, orientador e amigo, cuja experiência e incentivo possibilitaram a realização deste trabalho. -Aos professores VIL. AóonJ.io Ve.c,,foo, VIL. ]e/2U6 MMde.n. do.6 San.tal.> e VIL. Nfüon. AugU6to Vil.la Nova, pelas sugestões apresentadas durante a elaboração e revisão deste trabalho. --' Ao M.S. PÇLulo Le.on.e.l U.bCVl.cü, pelas críticas e sugestões apre sentadas durante a elaboração e revisão deste trabalho. -Aos colegas do Curso de Agrometeorologia e aos colegas orienta dos do Dr. Klaus Reichardt, pelo auxílio prestado nos lhos de campo. traba--Ã Emp1Le/2a BJz.MilúlLa de. Pe/2qul6a AglLope.euâkla ( EMBRAPA), pela oportunidade concedida. À Comi..61.>ão Naúon.al de. En.e.Jz.gia Nuele.CV!. (CNEN) pelo apoio finan ceiro através do Projeto Feijão do Centro de Energia Nuclear na Agricultura (CENA). Aos Sli6. Cle.U6val BJ.J.,1.>i, pelos serviços de datilografia e Be.ne. cüto He.lLeuia.no Vavan.zo, pelos serviços de imprensa. -Externamos ainda, nossos agradecimentos a todos aqueles que di_ reta ou indiretamente contribuíram para a realização deste tra balho. Página 5. CONCLUSÕES 6. RESUMO.