Soybean rust (SBR), caused by the fungus Phakopsora pachyrhizi, is the most damaging disease of soybean in Brazil. Effective management is achieved by means of calendar-timed sprays of fungicide mixtures, which do not explicitly consider weather-associated disease risk. Two rain-based action thresholds of disease severity values (DSV50 and DSV80) were proposed and compared with two leaf wetness duration-temperature thresholds of daily values of infection probability (DVIP6 and DVIP9) and with a calendar program, with regard to performance and profitability. An unsprayed check treatment plot was included for calculating relative control. Disease severity and yield data were obtained from 29 experiments conducted at six sites across four states in Brazil during the 2012–13, 2014–15, and 2015–16 growing seasons, which represented different growing regions and climatic conditions. The less conservative rainfall action threshold (DSV80) resulted in fewer fungicide sprays compared with the other treatments, and the more conservative one (DSV50) resulted in fewer sprays than the DVIP thresholds. Yield was generally higher with the increase in spray number, but the economic analysis showed no significant differences in the risk of not offsetting the costs of fungicide sprays regardless of the system. Therefore, based on the simplicity and the profitability of the rain-based model, the system is a good candidate for incorporating into the management of SBR in soybean production fields in Brazil.

Evapotranspiration depends primarily on the local energy balance, which is the most important variable of the physical environment when it comes to irrigation scheduling, especially throughout the production formation stages that are limited by water factors. The current manuscript will verify the applicability of estimates of grass net radiation to the performance of estimation methods of potential evapotranspiration under the climatic conditions in Piracicaba, Sao Paulo, Brazil. In order to proceed to simple linear regression studies, meteorological data were monitored by an automatic weather station throughout a period of 87 days for the calculation of potential evapotranspiration, taking into account both the estimated and calculated grass net radiation values. The use of grass net radiation estimated by a model based on the local energy balance showed an excellent performance for estimating potential evapotranspiration by means of the Penman–Monteith, adjusted Priestley–Taylor, and simplified Penman approaches, along with a good agreement (R² > 0.91) related to the potential demand values obtained with grass net radiation measured by net radiometers. Copyright © 2012 Royal Meteorological Society

The potential yield of annual crops is affected by management practices and water and energy availabilities throughout the crop season. The current work aimed to assess the effects of plant population, planting dates and soil covering on yield components of maize. Field experiments were carried out during the 2014–2015 and 2015–2016 growing seasons at areas grown with oat straw, voluntary plants and bare soil, considering five plant populations (40,000, 60,000, 80,000, 100,000 and 120,000 plants ha⁻¹) and three sowing dates (15 September, 30 October and 15 December) for the hybrid P30F53YH in Ponta Grossa, State of Paraná, Brazil. Non-impacts of soil covering or plant population on plant height at the flowering phenological stage were observed. Significant effects of soil covering on yield components and final yield responses throughout the 2014–2015 season were detected. An influence of plant populations on yield components was evidenced, suggesting that, from 80,000 plants ha⁻¹, the P30F53YH hybrid performs a compensatory effect among assessed yield components in such a way as to not compromise productivity insofar as the plant population increases up to 120,000 plants ha⁻¹. It was noticed, a positive trend of yield components and crop final yield as a function of plant density increments.

A irradiância solar global (Qg) é uma variável física importante que vem sendo constantemente empregada em modelos agrometeorológicos, tanto para caracterização climática, como para dar suporte a estudos radiométricos voltados ao planejamento da irrigação e à previsão de safras agrícolas. O trabalho teve como objetivo comparar medidas diárias de Qg com estimativas dessa variável obtidas por quatro diferentes métodos de cálculo. Para tanto, no período compreendido entre 28/03/2008 a 24/08/2011, no município de Ponta Grossa, PR, procedeu-se ao estudo de análise de regressão linear simples mediante o confronto entre medidas radiométricas realizadas por piranômetro e estimativas de Qg. A transmitância global foi condicionada pela nebulosidade atmosférica. Os modelos baseados na transmitância global média diária estimaram de forma mais satisfatória os valores de Qg, face aos coeficientes estatísticos calculados para validação dos critérios de estimativa propostos por Angström-Prescott. Entretanto, o desempenho dos modelos baseados na determinação da transmitância global média sob condições atmosféricas extremas, considerando dias totalmente ensolarados e nublados, revelou coeficientes de Willmott mais elevados, os quais se aproximaram muito de 1, refletindo exatidão e confiabilidade dos valores calculados de Qg, quando comparados aos valores observados em estação meteorológica automática.

The potential yield of annual crops is affected by management practices and water and energy availabilities throughout the crop season. The current work aimed to assess the effects of plant population and soil covering on yield components of maize. Field experiments were carried out during 2014-15 and 2015-16 growing seasons at areas grown with oat straw, voluntary plants and bare soil, considering five different plant populations (40,000, 60,000, 80,000, 100,000 and 120,000 plants ha-1) and three sowing dates (15 Sep., 30 Oct., 15 Dec.) for the hybrid P30F53YH in Ponta Grossa, State of Parana, Brazil. Non-impacts of soil covering or plant population on plant height at the flowering phenological stage were observed. Significant effects of soil covering on crop physiological and yield components responses throughout the 2014-15 season were detected. Influence of plant populations on yield components was evidenced, suggesting that from 80,000 plants ha-1 the P30F53YH hybrid performs a compensatory effect among assessed yield components in such a way as to not compromise productivity insofar as plant population increases up to 120,000 plants ha-1. It was noticed a positive trend of yield components and crop final yield as a function of plant density increments.