A method for estimating crop actual evapotranspiration

The reliability of Rhenals and Bras (1981) model in estimating actual evapotranspiration in Samaru for a wheat crop was tested and result is herein presented. This model incorporates climate, crop and soil characteristics factors in estimating actual evapotranspiration. Actual evapotranspiration values estimated using the model were compared with actual evapotranspiration amounts estimated from open pan evaporation data. The mean difference between the average aily evapotranspiration obtained by Rhenals and Bras (1981) model and those from open pan evaporation data was 0.20 mmday-1 and was not statistically significant at 0.05 level of significance. The tested model is found reliable in estimating the crop actual evapotranspiratio

Performance evaluation of selected crop yield-water use models for wheat crop

Crop yield-water use models that provide useful information about the exact form of crop response to different amounts of water used by the crop throughout its growth stages and those that provide adequate information for decisions on optimal use of water in the farm were evaluated. Three crop yield models: Jensen (1968), Minhas et al., (1974) and Bras and Cordova (1981) additive type models were studied. Wheat (Triticum aestivum) was planted at the Institute for Agricultural Research Farm during the 1995/96 and 1996/97 irrigation seasons of November to March. The data collected from the field experiments during the 1995/96 planting season were used to calibrate the models and their stress sensitivity factors estimated for four selected growth stages of the wheat crop. The ability of the model to predict grain yield of wheat with the estimated stress sensitivity factors was evaluated by comparing predicted grain yields by each model with those obtained in the field during the 1996/97 season. The three models performed fairly well in predicting grain yields, as the predicted results were not significantly different from the field measured grain yield at 5% level of significance

Brazilian maize genotypes sensitivity to water deficit estimated through a simple crop yield model Sensibilidade de genótipos brasileiros de milho ao deficit hídrico, estimada por um modelo simples de produtividade

The objective of this work was to determine the sensitivity of maize (Zea mays) genotypes to water deficit, using a simple agrometeorological crop yield model. Crop actual yield and agronomic data of 26 genotypes were obtained from the Maize National Assays carried out in ten locations, in four Brazilian states, from 1998 to 2006. Weather information for each experimental location and period were obtained from the closest weather station. Water deficit sensitivity index (Ky) was determined using the crop yield depletion model. Genotypes can be divided into two groups according to their resistance to water deficit. Normal resistance genotypes had Ky ranging from 0.4 to 0.5 in vegetative period, 1.4 to 1.5 in flowering, 0.3 to 0.6 in fruiting, and 0.1 to 0.3 in maturing period, whereas the higher resistance genotypes had lower values, respectively 0.2-0.4, 0.7-1.2, 0.2-0.4, and 0.1-0.2. The general Ky for the total growing season was 2.15 for sensitive genotypes and 1.56 for the resistant ones. Model performance was acceptable to evaluate crop actual yield, whose average errors estimated for each genotype ranged from -5.7% to +5.8%, and whose general mean absolute error was 960 kg ha-1 (10%).<br>O objetivo deste trabalho foi determinar a sensibilidade de genótipos de milho (Zea mays) ao deficit hídrico, pelo uso de um modelo agrometeorológico simples de estimativa de produtividade. Dados de produtividade real e agronômicos de 26 genótipos foram obtidos dos Ensaios Nacionais de Milho, em dez localidades, em quatro estados brasileiros, entre 1998 e 2006. Os dados meteorológicos, para cada experimento e período, foram obtidos das estações mais próximas de cada local. O índice de sensibilidade ao deficit hídrico (Ky) dos genótipos foi determinado por meio do modelo de depleção da produtividade. Os genótipos de milho podem ser classificados em dois grupos de resistência ao deficit hídrico. Os de resistência normal tiveram Ky entre 0,4 e 0,5 no período vegetativo, 1,4 e 1,5 no florescimento, 0,3 e 0,6 na frutificação, e 0,1 e 0,3 no período de maturação, enquanto os genótipos de maior resistência tiveram, respectivamente, os seguintes valores de Ky: 0,2-0,4; 0,7-1,2; 0,2-0,4; e 0,1-0,2. Em todo o ciclo, o Ky geral foi 2,15 nos genótipos mais sensíveis, e 1,56 nos de maior resistência ao deficit hídrico. O desempenho do modelo foi aceitável para a avaliação da produtividade real, cujos erros médios estimados para cada genótipo variaram de -5,7 a +5,8%, e cujo erro absoluto médio geral foi de 960 kg ha-1 (10%)