Pedotransfer functions (PTF) were developed to estimate the parameters (α, n, θr and θs) of the van Genuchten model (1980) to describe soil water retention curves. The data came from various sources, mainly from studies conducted by universities in Northeast Brazil, by the Brazilian Agricultural Research Corporation (Embrapa) and by a corporation for the development of the São Francisco and Parnaíba river basins (Codevasf), totaling 786 retention curves, which were divided into two data sets: 85 % for the development of PTFs, and 15 % for testing and validation, considered independent data. Aside from the development of general PTFs for all soils together, specific PTFs were developed for the soil classes Ultisols, Oxisols, Entisols, and Alfisols by multiple regression techniques, using a stepwise procedure (forward and backward) to select the best predictors. Two types of PTFs were developed: the first included all predictors (soil density, proportions of sand, silt, clay, and organic matter), and the second only the proportions of sand, silt and clay. The evaluation of adequacy of the PTFs was based on the correlation coefficient (R) and Willmott index (d). To evaluate the PTF for the moisture content at specific pressure heads, we used the root mean square error (RMSE). The PTF-predicted retention curve is relatively poor, except for the residual water content. The inclusion of organic matter as a PTF predictor improved the prediction of parameter a of van Genuchten. The performance of soil-class-specific PTFs was not better than of the general PTF. Except for the water content of saturated soil estimated by particle size distribution, the tested models for water content prediction at specific pressure heads proved satisfactory. Predictions of water content at pressure heads more negative than -0.6 m, using a PTF considering particle size distribution, are only slightly lower than those obtained by PTFs including bulk density and organic matter content.

We developed a computer program for life table analysis using the open source, free software programming environment R. It is useful to quantify chronic nonleth

The corn leafhopper, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae), is one of the most important pests of corn, Zea mays L. (Poaceae), in Latin America. We assessed the seasonal and vertical distribution of D. maidis in corn fields in Brazil, in addition to describing the effect of 2 types of yellow traps positioned at 2 heights on the capture of this leafhopper. Sampling was conducted using yellow pan traps and yellow sticky cards throughout the cropping period, in both the rainy and dry seasons. The population of D. maidis in the dry season was much larger than in the rainy season. During both the rainy season and dry seasons, the greatest abundance of D. maidis was observed at 77 d post emergence of the corn, which corresponded to physiological maturity. Greater numbers of insects were captured with yellow cards than with pan traps, at both heights and in both cropping seasons. Also, more insects were captured at the 1.5 m than at the 0.5 m sampling height. The corn leafhopper w... Resumen La chicharrita del maíz, Dalbulus maidis (DeLong y Wolcott) (Hemiptera: Cicadellidae), es una de las plagas más importantes del maíz, Zea mays L. (Poaceae), en América Latina. Se evaluó la distribución estacional y vertical de D. maidis en campos de maíz en Brasil, además de describir el efecto de las 2 clases de trampas amarillas colocadas en 2 alturas sobre la captura de este saltahoja. Se realizó el muestreo utilizando trampas de paila amarillas y tarjetas amarillas pegajosas durante todo el período de cultivo, tanto en la estación lluviosa y seca. La población de D. maidis en la estación seca fue mucho más grande que en la época de lluvias. Tanto durante la época de lluvias y la estación seca, se observó la mayor abundancia de D. maidis a los 77 días pos-emergencia del maíz, lo que correspondía a la madurez fisiológica. Un mayor número de insectos fueron capturados con las tarjetas amarillas que con las trampas de paila, tanto por alturas y en ambos ciclos de cultivo. También, más insectos fue...

The rice stem stink bug, Tibraca limbativentris Stål (Hemiptera: Pentatomidae), is a primary insect pest of paddy rice in South America. Knowledge of its spatial distribution can support sampling plans needed for timely decisions about pest control. This study aimed to investigate the spatial distribution of adults and nymphs of T. limbativentris and determine the spatial coexistence of these stages of development. Fifteen paddy rice fields were scouted once each season to estimate insect densities. Scouting was performed on regular grids with sampling points separated by ∼50 m. Moran’s I and semivariograms were used to determine spatial distribution patterns. Spatial coexistence of nymphs and adults was explored via spatial point process. Here, adults and nymphs had typically contrasting spatial distribution patterns within the same field; however, the frequency of aggregation was not different between these developmental stages. Adults and nymphs were aggregated in seven fields and randomly distributed in the other eight fields. Uniform distribution of adults or nymphs was not observed. The study-wide semivariogram ranges were ∼40 m for adults and ∼55 m for nymphs. Nymphs and adults spatially coexisted on 67% of the fields. Coexisting patterns were classified using one of the following processes: stage-independent, bidirectional attractive, unidirectional attractive, bidirectional inhibiting, or unidirectional inhibiting. The information presented herein can be important for developing sampling plans for decision-making, implementing tactics for site-specific management, and monitoring areas free of T. limbativentris .