-Cowpea has great socioeconomic importance in the northeastern part of Pará state. However, in order to provide suitable irrigation management during the dry period this region requires solid information regarding water demand by regional crops. This research aims to determine the water demand, the crop coefficient (Kc) and the uncoupling factor during the different development stages of cowpea in the northeast of Pará. The crop evapotranspiration (ETc) was measured by drainage lysimeters. This information was coupled to the reference evapotranspiration (ETo) to obtain the crop coefficients, which were used to adjust the model function of accumulated degree-days and the leaf area index (LAI). The uncoupling factor was estimated to indicate the factors that control evapotranspiration. The ETc values reached a cumulative total of 267.73 mm ± 10.21 mm during the cowpea cycle. The average value of the uncoupling factor was 0.66. This indicates that the cowpea crop does not fully uncouple from the atmosphere underneath the climatic conditions in northeast Pará. The cowpea Kc values presented averages of 0.8, 1.4 and 0.8 in the vegetative phase, reproductive phase and final stage, respectively. The Gaussian model showed an excellent fit for the estimation of Kc values based on accumulated degree days and the LAI. These amounts differ from others found in the literature. Therefore, it reinforces the necessity for an assessment of crop coefficients under local conditions and for the employment of more precise methods.Keywords: Vigna unguiculata L. Walp. Penman-montheith. Lysimeters. Uncoupling factor. Evapotranspiration. DEMANDA HÍDRICA, COEFICIENTE DE CULTIVO E FATOR DE DESACOPLAMENTO DOFEIJÃO CAUPI NA AMAZÔNIA ORIENTAL RESUMO -O feijão caupi possui grande importância sócioeconômica para o nordeste paraense, porém, a região necessita de informações seguras quanto demanda hídrica, para promover um manejo adequado de irrigação no período considerado mais seco do ano. Assim, o objetivo da pesquisa foi determinar a demanda hídrica, coeficiente da cultura (Kc) e fator de desacoplamento nos diferentes estádios de desenvolvimento do feijão caupi no nordeste paraense. Com a evapotranspiração da cultura (ETc), obtida por meio de lisímetros de drenagem, e a evapotranspiração de referência (ETo) foram obtidos os coeficientes de cultura (Kc), utilizados posteriormente, para ajustar modelos em função dos graus dias acumulados (GD) e índice de área foliar (IAF), o fator de desacoplamento foi estimado para indicar os fatores que estão governando a evapotranspiração.

The state of Pará is the main regional producer of cowpea, but its yield is still low compared to other states of the Northern region such as Amazonas and Tocantins, due to the management adopted and the water regime during the cycle, since its cultivation is conducted on a rainfed basis. The objective of this study was to evaluate how water deficit imposed during reproductive stage interferes in the yield of cowpea and in its water use efficiency under the climatic conditions of Castanhal, Pará, Brazil, for agricultural planning purposes. The experiment was carried out in Castanhal, northeastern region of the Pará state during the dry season of 2014, 2015 and 2016. The experimental design was randomized blocks with six blocks and four treatments, corresponding to different irrigation depths in the reproductive stage, defined as 100, 50, 25 and 0% of the crop evapotranspiration. Water use efficiency (WUE) was determined by the ratio between total grain yield and total water used in each treatment. Maximum water availability led to an average increase in yield of 58% compared to the treatment without irrigation. Water depths below 260 mm limited yield to values lower than 1,000 kg ha-1. The cultivar adopted had WUE of 4.63 kg ha-1 mm-1, in response to the higher levels of water supply, but showed WUE of 4.31 kg ha-1 mm-1 under water depth of 50% of water demand.

Due to the sensitivity of the cowpea to water deficit during the dry season in the Amazonian environment, there is a need for studies related to water management and the optimization of annual yield. Thus, the objective was to estimate the crop evapotranspiration (ETc) and the actual evapotranspiration (ETr), whilst also evaluating the effect of different irrigation depths on the yield response factor (Ky) and dry biomass (Kss) of the cowpea cultivar BR3-Tracuateua under edaphoclimatic conditions in the Amazon region. The experiment was carried out in randomized blocks, with six replicates and four treatments: T1 (100% ETc), T2 (50% ETc), T3 (25% ETc), and T4 (0% ETc), commencing in the reproductive phase with a drip irrigation system. The total evapotranspiration recorded for the cowpea cultivar BR3-Tracuateua across the four treatments was 337.5, 284.35, 258.62, and 219.82 mm with an average consumption of 4.6, 3.90, 3.54, and 3.01 mm d-1 for T1, T2, T3, and T4, respectively. The emergence phase showed evaporation rate of 5.19 mm d-1 and the reproductive, vegetative, and senescence ETc phases showed evaporation of 4.87, 4.84, and 3.32 mm d-1, respectively. The flowering stage had the greatest water demand (5.88 mm d-1). There was a significant difference in the crop yield among all treatments, with decreases of 18.91, 33.12 and 57.17% for T2, T3 and T4 in the grain yield, with a Ky of 1.48, and Kss of 2.03, 1.08, and 0.87 for the flowering, grain filling, and physiological maturation stages, respectively.

This study aims to determine the cowpea efficiency in absorbing and using solar radiation according to different irrigation depths under the climatic conditions of the northeast of Pará State. The experiment was carried out on 2014 and 2016 in an experimental design of randomized blocks, which consisted in six blocks with four treatments, in which different irrigation depths the reproductive phase were applied, as follows: T100, T50, T25 e T0, that corresponded to 100%, 50%, 25% e 0% of the crop evapotranspiration, respectively. The absorbed photosynthetically active radiation, leaf area index (LAI), total aerial dry matter (TADM) and grain yield were measured. The extinction coefficient (k) was obtained by nonlinear regression between the fraction of absorbed PAR (fPARinter) and the LAI. The radiation use efficiency (RUE) was calculated by linear regression between the TADM and the accumulated absorbed PAR. The water deficit imposed by the treatments had a significant influence on the LAI, TADM and cowpea yields. The water deficit did not significantly influenced k À it ranged between 0.83 for T100 and 0.70 for T0. The RUE showed significant behaviors regarding the treatments with adequate water supply and treatments under water deficit, ranging from 2.23 to 1.64 g·MJ -1 , respectively. ResumoObjetivou-se neste trabalho determinar a eficiência do feijão-caupi em interceptar e usar a radiação solar quando submetido a diferentes lâminas de irrigação nas condições climáticas do nordeste paraense. O experimento foi realizado em 2014 e 2016 em delineamento experimental de blocos casualizados, com seis blocos e quatro tratamentos, que consistiram diferentes laminas de irrigação na fase reprodutiva, sendo T100, T50, T25 e T 0 correspondente a 100%, 50%, 25% e 0% da evapotranspiração da cultura. Realizou-se medição da radiação fotossinteticamente ativa (PAR) interceptada, do índice de área foliar (LAI), da matéria seca total da parte aérea (TADM) e produtividade. O coeficiente de extinção (k) foi obtido através de regressão não linear entre a fPARinter e o LAI. A eficiência de uso da radiação (RUE) foi obtida pela regressão linear entre a TADM e a radiação PARinter acumulada. O déficit hídrico imposto pelos tratamentos influenciou significativamente as respostas no LAI, TADM e produtividade do feijão-caupi. O k não foi influenciado significativamente pelo déficit hídrico, apresentando variação de 0,83 no T100 e 0,70 no T 0. A RUE apresentou resposta significativa entre os tratamentos com suprimento hídrico adequado e os tratamentos sob déficit hídrico, variando de 2,23 a 1,64 g·MJ -1 , respectivamente.Palavras-chave: vigna unguiculata, radiação interceptada, coeficiente de extinção, déficit hídrico.

The present work evaluated the Aquacrop model as a tool for climate risk analysis and yield prediction of cowpea, cultivated in a dystrophic yellow oxisol. The model was previously calibrated and validated for two harvests, in order to simulate the biomass and yield of cowpea, considering four applied water blades over its reproductive period. The good achieved results prove the model’s efficiency for this kind of simulation. After validation, the yield simulation of cowpea based on the meteorological data (2003 to 2014), soil and crop management of 12 harvests was performed. Two scenarios were given: the potential yield without water restrictions; and the actual yield, considering to pluvial availability conditions of the inserted series. The results suggested that the optimum sowing dates are between April 1st and 20th, in which there was a low yield loss (< 10 %) considering the potential yield, high probability (> 90 %) of achieving high yields (above 1300 kg ha-1) and a low risk of getting crop harvesting in the rainy period. After all, the model proved to be a feasible tool for predicting cowpea yield in the region and also over regions with similar characteristics.

Resumo O feijão-caupi é uma leguminosa bastante cultivada no Norte e Nordeste do Brasil, mas no Pará, a cultura apresenta baixa produtividade, devido à baixa fertilidade dos solos e especialmente à deficiência hídrica. O trabalho teve como objetivo avaliar o efeito de distintos níveis de deficiência hídrica acumulada durante a fase reprodutiva nas trocas gasosas do feijão-caupi. O experimento foi conduzido em Castanhal-Pa, em 2015 e 2016, em um delineamento de blocos ao acaso, com seis repetições e quatro tratamentos correspondentes à reposição de 100% da água perdida pela evapotranspiração da cultura (T1), a 50% de reposição (T2), a 25% de reposição (T3) e sem irrigação (T4). As trocas gasosas foram medidas no estádio fenológico R9, correspondente aos 64 dias após a semeadura (28 dias após o inicio dos tratamentos). A deficiência hídrica foi calculada pelo balanço hídrico diário considerando a capacidade de água disponível (CAD) e a profundidade efetiva do sistema radicular observada em campo. Não houve diferença significativa entre os anos experimentais além do próprio efeito dos tratamentos. O feijão-caupi mostrou-se sensível ao aumento da deficiência hídrica acumulada, diminuindo sua condutância estomática e taxa de fotossíntese, as quais diferiram significativamente entre os 4 tratamentos. Para o potencial hídrico foliar e carbono interno houve diferença significativa apenas entre os tratamentos extremos. Tal comportamento sugere que o feijão-caupi consegue preservar o potencial hídrico foliar mesmo em condições cumulativas de deficiência hídrica agindo como uma espécie conservadora ao priorizar a manutenção de seu status hídrico ao invés da sua atividade fotossintética. As menores produtividades ocorreram em função do déficit hídrico imposto pelos tratamentos com menores lâminas de irrigação.

The acai palm (Euterpe oleracea Mart.) is a fruit from the Amazon that is originally found in flooded areas. Over recent years, its marketability has gained significant interest in Brazil and abroad because of its agronomic, nutritional and economic potential. However, there is a lack of technical-scientific information about crop water requirements for irrigation management during the reproductive phase of acai palm. Therefore, the aim of this research was to estimate the water requirements (crop evapotranspiration (ET c ), single (Kc) and dual (Kcb + Ke) crop coefficients) of acai palm in the Eastern Amazon (Brazil) using the Bowen ratio system. A micrometeorological tower was installed in the center of an experimental area to monitor ET c and meteorological variables. Phenological development was monitored during two growing seasons. Soil water evaporation was determined on a daily scale using weighing microlysimeters. Ke and Kcb values were calculated by the ratio of soil surface evaporation and transpiration to reference evapotranspiration (ET o ), respectively. Total water requirements of the acai palms were 1165 mm, with a daily average of 3.49 mm day −1 for the growing season. The average values of Kc, Ke and Kcb for the acai palm were 1.08; 0.21 and 0.84, respectively. The findings will assist the design of irrigation management protocols for acai trees that are better tailored to satisfy crop water requirements. This will allow improved water use efficiency, ensuring tree crop sustainability.

Energy and water dynamics are crucial for citrus development in the Eastern Amazon. This study aimed to determine the energy balance, water demand, and crop coefficient of acid lime in the northeast region of Pará. A micrometeorological tower was installed in the center of the experimental area to monitor meteorological variables between October 2020 and December 2021. The energy balance and water demand were obtained by the Bowen ratio method. Kc was determined by the ratio between crop and reference evapotranspiration. The results obtained indicate that 63% of the available energy was used by latent heat in the rainiest period, while 60% was used during the less rainy period. Sensible heat used 32% and 34% during the most and least rainy periods, respectively. Soil heat presented a low variation, with an average of 5% for the entire period. Water consumption of the acid lime during the experiment was 1599 mm, with a daily mean of 3.70 mm day−1, while the mean value of Kc was 1.4. These results allow for the design of adequate water supply protocols for the crop in the main citrus pole in the Amazon region.