Alexandre Bryan Heinemann

The impact of potential errors in rainfall observation on the simulation of crop growth, development and yield

Abstract Precipitation is the source for almost all soil moisture available for plant extraction by crops that are grown in rainfed cropping systems. In many cases precipitation is measured using a tipping-bucket rain gauge (TBRG) or similar device. Most automated weather station (AWS) networks employ TBRG to observe rainfall, due to the need of automating the process of collecting rainfall data. However, it is known that these gages have some type of error due to aerodynamic effects, wetting losses and the actual design and operation of the tipping-bucket sensor. The data collected by AWS are frequently used as input for complex computer simulation models that predict crop yield as a function of weather and soil conditions and crop management scenarios. The objective of this study was to evaluate the impact of potential errors in rainfall observations on simulated growth, development and yield. The generic grain legume model cropgro and the generic cereal model ceres were used to simulate growth and development for soybean, peanut, wheat and maize under different precipitation scenarios. These crop models use daily weather data as inputs. In this study, 36 years of daily historical records from Tifton, Georgia were obtained and randomly modified with relative errors when the values for daily precipitation were greater than zero to emulate the inaccuracy of TBRG observations. Two approaches were considered: (a) rain gauges randomly underestimate (negative bias) rainfall and (b) rain gauges randomly overestimate (positive bias) rainfall. To account for the random variability of precipitation data and to avoid a trend that could affect crop growth and development, the random modifications were replicated 32 times for each individual weather year and for each inaccuracy case that was considered. In this study, the modifications in daily precipitation amounts did not impact crop phenology, but resulted in substantial changes in both the mean and the variability of simulated yield, biomass, evapotranspiration, and drainage. The underestimation, e.g. negative bias, of rainfall measurements had a larger impact on the simulated variables than an overestimation. This study showed that the accuracy of rainfall observations is critical for the simulation of yield and that the variability of the simulated outputs is directly correlated to the accuracy of model inputs. It also demonstrated that complex soil–plant–atmosphere models are sensitive to variation in precipitation and possibly other environmental inputs.

Nitrogênio e água como fatores de produtividade do trigo no cerrado

Two experiments were carried out at Embrapa Rice and Beans, located at the municipality of Santo Antonio de Goias, Goias state, Brazil, under no-tillage in the soybean straw, to evaluate the effects of irrigation management and nitrogen doses on the grain yield and its components of two wheat cultivars. In the first experiment, the irrigation was started at soil-water tension of 40 kPa, and in the second one, at soil-water tension of 60 kPa. For both experiments, a randomized block design with subdivided plots, with four replications, was used. In the plots were established five doses of nitrogen (0, 50, 100, 150, and 200 kg ha-1) and, in the subplots, the cultivars EMBRAPA 22 and EMBRAPA 42. Soil-water tension of 60 kPa was more adequate for management of irrigation in wheat, since it did not affect its grain yield and quality and used less water. The dose of nitrogen that promoted maximum technical efficiency was 73 kg ha-1. The crude protein content increased as nitrogen increased. The increase of irrigation frequency and nitrogen decreased the hectoliter-grain weight.

CENTER PIVOT IRRIGATION MANAGEMENT OPTIMIZATION OF DRY BEANS IN HUMID AREAS

During the spring growing season, periods of drought can cause a significant reduction in dry bean yield in Brazil. Therefore, irrigation is applied to reduce the risks associated with the variability in weather conditions. The common irrigation system in Brazil is a center pivot system. Irrigation managers usually operate a center pivot irrigation system in such a way that it requires more than one day to complete the irrigation of an entire field. In general, crop model simulations assume that irrigation of an entire field is completed in one day. This article presents modification made in the CROPGRO simulation model to provide irrigation managers with decision support information that is equivalent to their local conditions. The modified model takes into account the number of days that a center pivot irrigation system requires to complete one revolution. Different management regimes for three different water capacity center pivot systems were evaluated for dry bean as a function of net return for the State of Parana, Brazil. The management regimes that were evaluated included the completion of the center pivot revolution in either one, two or three days. Six different irrigation thresholds were applied, ranging from 40 to 90% of the remaining available soil water content, and three different commodity prices were analyzed. The center pivot system that showed the highest net return was the system that applied 6 mm/day. The irrigation management regime that resulted in the highest net return was to irrigate the entire field in one day (the highest frequency possible), when the soil water content in the top 30 cm of the profile dropped below 70 or 80% of available soil water, depending on the commodity price. Future research is needed to evaluate different weather conditions and soil types to make these modifications in the CROPGRO simulation model more widely applicable.

LOWLAND RICE GENOTYPES EVALUATION FOR PHOSPHORUS USE EFFICIENCY IN TROPICAL LOWLAND

Lowland rice is a staple food for more than 50% of the worlds population and phosphorus (P) deficiency is one of the main constraints in rice production in tropical lowlands. A field experiment was conducted for two years consecutive with the objective to evaluate 12 lowland rice genotypes for P use efficiency. The P rates used were 0, 22, 44, 66, and 88 kg P ha−1 (0, 50, 100, 150 and 200 kg P2O5 ha−1) applied to an Inceptisol. The genotypes used were BRS Jaçanã, CNAi 8860, BRS Fronteira, CNAi 8879, CNAi 8880, CNAi 8886, CNAi 8885, CNAi 8569, BRSGO Guará, BRS Alvorada, BRS Jaburu and BRS Biguá. There were significant and quadratic responses of genotypes to phosphorus fertilization. Adequate P rates for maximum grain yield varied from genotype to genotype. However, across 12 genotypes, maximum grain yield was obtained with the application of 54 kg P ha−1. Genotype BRS Jaçanã was most efficient and genotype CNAi 8569 was most inefficient in P use efficiency. Shoot dry weight and panicle number was also increased significantly and quadratically with increasing P rates in the range of 0 to 88 kg P ha−1. These two plant parameters were positively associated with grain yield. Agronomic efficiency (kg grain produced per kg P applied) was significantly decreased with increasing P rates in the range of 22 to 88 kg P ha−1.

Eficiência de uso da radiação solar na produtividade do trigo decorrente da adubação nitrogenada

An experiment was carried out at Embrapa Rice and Beans, Santo Antonio de Goias, Goias State, Brazil, under no-tillage in the soybean mulch to evaluate the effects of nitrogen doses on the solar radiation use efficiency, leaf area index in the anthesis, biomass in the anthesis, in the physiological maturation and grain yield of two wheat cultivars. A randomized block design in subdivided plots, with four replications was used. In the plots five nitrogen topdressing doses, 0, 50, 100, 150, and 200 kg ha-1 were established and in the subplots, the cultivars Embrapa 22 and Embrapa 42. The cultivars differed only in relation to biomass in anthesis. The analyzed variables showed a quadratic response to nitrogen doses. Wheat grain yield response to nitrogen was due to the effect of this nutrient in the leaf area index, that affected solar radiation use efficiency and biomass, which showed a positive correlation with grain yield. Under low nitrogen availability, grain yield showed higher correlation to biomass accumulated in the anthesis than to that accumulated in the physiological maturation.

Sensitivity of APSIM/ORYZA model due to estimation errors in solar radiation

Crop models are ideally suited to quantify existing climatic risks. However, they require historic climate data as input. While daily temperature and rainfall data are often available, the lack of observed solar radiation (Rs) data severely limits site-specific crop modelling. The objective of this study was to estimate Rs based on air temperature solar radiation models and to quantify the propagation of errors in simulated radiation on several APSIM/ORYZA crop model seasonal outputs, yield, biomass, leaf area (LAI) and total accumulated solar radiation (SRA) during the crop cycle. The accuracy of the 5 models for estimated daily solar radiation was similar, and it was not substantially different among sites. For water limited environments (no irrigation), crop model outputs yield, biomass and LAI was not sensitive for the uncertainties in radiation models studied here.

Calibração e avaliação do modelo ORYZA-APSIM para o arroz de terras altas no Brasil

Objetivou-se com este trabalho calibrar o modelo ORYZA-APSIM e avaliar o seu desempenho na simulacao do desenvolvimento, crescimento e produtividade da variedade cultivada de arroz de terras altas BRS-Primavera para as diferentes regioes produtoras dessa cultura. Na calibracao foram definidas: as unidades de calor efetivo diario (HU); as taxas de desenvolvimento fenologico para cada estadio (DVR); as fracoes da massa de materia seca das folhas (MSf), colmos (MSC) e orgaos armazenadores (paniculas) (MSp), e os parâmetros para calcular a area foliar especifica (AEF) simulada durante o ciclo da cultura. Na avaliacao foram comparados os valores simulados com os observados do desenvolvimento fenologico (numero de dias da emergencia ao florescimento) e do crescimento da cultura (massa de materia seca total da parte aerea (MSt) indice de area foliar (IAF)) e a produtividade (P). O modelo apresentou desempenho satisfatorio na simulacao do desenvolvimento fenologico para regioes proximas ao da calibracao. Para latitudes proximas ao equador, como Teresina, PI, o desempenho fenologico foi insatisfatorio. Para o crescimento, nos dois experimentos, o indice de area foliar (IAF) simulado diferiu do observado, e a MSt simulada foi semelhante a observada, mas diferiu entre o florescimento e a maturidade fisiologica. A MSf simulada foi satisfatoria no primeiro experimento e regular no segundo. Isso e devido ao modelo superestimar os efeitos da deficiencia hidrica que ocorreram durante a conducao do segundo experimento. Entretanto, o modelo ORYZA-APSIM apresentou bom desempenho na simulacao da ordem de produtividade ao nivel de significância de 5%.

Padrões de deficiência hídrica para a cultura de milho (safra normal e safrinha) no estado de Goiás e suas conseqüencias para o melhoramento genético

Deficiencia hidrica e considerada a maior restricao na producao e estabilidade da produtividade de culturas em muitas regioes do mundo. No Estado de Goias, regiao na qual predomina a producao em sequeiro, para a cultura do milho (Zea mays L.) implantada na safra normal e na safrinha, e comum sofrer periodos de estresse por deficiencia hidrica intermitente ou terminal, que reduzem o rendimento de graos. No processo de desenvolvimento de novos hibridos e variedades cultivadas, genotipos sao selecionados em funcao de sua adaptabilidade em um determinado ambiente alvo. Assim, programas de melhoramento vegetal, com o objetivo de desenvolver hibridos e variedades cultivadas mais adaptados a um determinado ambiente, requerem informacoes sob a probabilidade de ocorrencia dos diferentes tipos de deficiencia hidrica, como tambem, suas caracteristicas, intensidade e tempo, em funcao da fase fenologica da cultura. Um modelo de simulacao de culturas foi utilizado para determinar os padroes de deficiencia hidrica no estado de Goias, considerando 12 locais e 6 diferentes datas de semeadura para a cultura do milho semeada na safra normal e na safrinha. Para a cultura do milho semeado na safra normal, a perda na produtividade decorrente do estresse por deficiencia hidrica foi menor que 50%, sendo que os tipos de deficiencia hidrica que provocam um maior impacto na produtividade iniciam-se no comeco do periodo reprodutivo. Para o milho semeado na safrinha, a perda na produtividade e superior a 50%, sendo mais comum o estresse terminal, que tem sua maior intensidade no enchimento de graos.

Utilization of the cropgro-soybean model to estimate yield loss caused by Asian rust in cultivars with different cycle

In recent years, crop models have increasingly been used to simulate agricultural features. The DSSAT (Decision Support System for Agrotechnology Transfer) is an important tool in modeling growth; however, one of its limitations is related to the unac- counted-for effect of diseases. Therefore, the goals of this study were to calibrate and validate the CSM CROPGRO-Soybean for the soybean cultivars M-SOY 6101 and MG/BR 46 (Conquista), analyze the performance and the effect of Asian soybean rust on these cultivars under the environmental conditions of Vicosa, Minas Gerais, Brazil. The experimental data for the evaluation, testing, and adjustment of the genetic coefficients for the cultivars, M-SOY 6101 and MG/BR 46 (Conquista), were obtained during the 2006/2007, 2007/2008 and 2009/2010 growing seasons. GLUE (Generalized Likelihood Uncertainty Estimation) was used for the estimation of the genetic coefficients, and pedotransfer functions have been utilized to estimate the physical characteristics of the soil. For all of the sowing dates, the early season cultivar, M-SOY 6101, exhibited a lower variance in yield, which represents more stability with regard to the interannual climate variability, i.e., the farmers who use this cultivar will have in 50% of the crop years analyzed, a higher yield than a late-season cultivar. The MG/BR 46 (Conquista) cultivar demonstrated a greater probability of obtaining higher yield in years with favorable weather conditions. However, in the presence of the Asian soybean rust, yield is heavily affected. The early cultivar, M-SOY 6101, showed a lower risk of being affected by the rust and consequently exhibited less yield loss considering the scenario D90 (condensation on the leaf surface occurs when the relative humidity is greater than or equal to 90%), for a sowing date of November 14.

Environmental group identification for upland rice production in central Brazil

Upland rice (Oryza sativa L.) production is basically concentrated in four central Brazilian States, Mato Grosso, Goias, Rondonia and Tocantins. To reduce the genotype and environment (G × E) interactions, the classification of environment groups was proposed. The goal of this study explores possibilities to adjust the upland rice regional breeding systems to optimally fit to the range of environments they are targeting, based on a historical yield data set of the Brazilian Geographic and Statistics Institute (IBGE, www.ibge.gov.br/home/) from 54 microregions. The specific objectives of this study were: (i) to identify and classify environmental groups in the Brazilian upland rice production area; (ii) to validate these environmental groups using yield data set from the upland rice multi-trial experiments (MTEs); (iii) and to identify the most representative site for each environmental group. For this the historical upland rice yield data from 54 microregions were detrented from the effects of technological advances and adjusted to the reference year, 2006. The adjusted yield data were used to build a matrix, which was submitted to a cluster analysis allowing the identification of three different environmental groups. These groups were classified as: highly favorable environment (HFE); favorable environment (FE); and less favorable environment (LFE). The HFE is less affected by inter-annual rainfall variability than the other two groups. The upland rice breeding programs must take into account the differences among the environmental groups to conduct their trials and suggest genotypes for the upland production area.