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.

Objetivou-se determinar os modelos que melhor descrevem a relação entre as dimensões lineares e a área foliar da mangueira, cultivar Tommy Atkins, além de estabelecer o fator de correção. A pesquisa foi conduzida na Fazenda Experimental da Universidade Federal Rural da Amazônia, na vila de Cuiarana, município de Salinópolis. Foram analisadas de 90 a 150 folhas, em 11 árvores de um campo experimental, determinando-se o comprimento e a largura máxima das folhas. A área foliar real foi determinada usando o integrador de área foliar "Area Meter" (AM 300). O fator de correção foi obtido pela divisão da área foliar real pela área foliar calculada. A área foliar foi também estimada por meio de modelos linear e não linear. Os modelos gerados apresentaram ótimo desempenho, com valores de R² entre 90 e 97%. O fator de correção de 0,71 pode ser utilizado para estimar a área foliar real da mangueira, multiplicado pelas medidas lineares. Os modelos que utilizaram o produto das dimensões como variável independente apresentaram valores de R² superiores aos que utilizaram apenas uma das dimensões, sendo o tipo cúbico o mais preciso.

This work evaluated the effect of soil water availability on growth and productivity variables of cowpea in northeastern Pará, Brazil. The experiment was carried out in a field of 2,100 m2 at the experimental site of the Federal Rural University of Amazon, during the driest season of the years 2011, 2012 and 2013, in a completely randomised design with two treatments (irrigated and non-irrigated), both with 12 replications in the reproductive phase (2012 and 2013). Growth and productivity data were submitted to analysis of variance with two variation factors (water regime and experimental year) at 5% probability. Student's t -test at 5% probability was used in the means of the stomatal conductance data, since this was monitored only in 2012. Final biomass production presented a reduction of 54.3% in 2012 and 26.4% in 2013 as a result of water deficit (DEF) of 76 and 26 mm, respectively. Mean stomatal conductance was reduced by 73% in the grain-filling stage as a result of the lower water availability during this period. Average cowpea productivity under water deficit reached 1,257 kg ha-1 in 2012 and 1,396 kg ha-1 in 2013. The reduction in water supply over the reproductive period significantly decreased production by 72 and 41% (F test, p < 0.05) in 2012 and 2013, respectively. An accumulated water deficit during the reproductive phase caused a maximum LAI reduction of 47% in 2012 (DEF of 76 mm) and of 13% in 2013 (DEF of 26 mm).

RESUMO A condutância estomática (gs) é uma variável fisiológica que faz referência ao fluxo gasoso (CO2 e H2O) entre folha e atmosfera, portanto, representa um processo fundamental para as pesquisas agrometeorológicas. O objetivo deste estudo foi ajustar e validar um modelo descritivo, para quantificar o efeito das variáveis meteorológicas que modulam a gs como: temperatura do ar (T), irradiância solar (Io), déficit de pressão de vapor no ar (DPV) e umidade no solo. O modelo, proposto neste estudo foi calibrado com dados experimentais realizados em blocos casualizados. A gs potencial (gsp) (condições ótimas de água no solo) foi estimada a partir do produto das variáveis meteorológicas (T×DPV×Io -1). Na sequência a gsp foi corrigida para a condição atual de água no solo, utilizando um fator de estresse hídrico. As estimativas de gs obtidas pelo modelo foram comparadas com dados experimentais independentes. Os testes de validação indicaram que o modelo foi satisfatoriamente sensível às variações meteorológicas e aos teores de água disponíveis no solo, a julgar pelo baixo erro absoluto médio das estimativas (<15%) e pela alta concordância entre os dados observados e simulados (d = 0,82).

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.

The objective of this work was to deter mine the base temperatures, thermal time requirements, and length of the main reproductive growth stages of acai palm (Euterpe oleracea) in the northeast of the state of Pará, in eastern Amazon, Brazil. The experiment was carried out from 2017 to 2019 in a 10 ha acai plantation, using the time-series analysis. Plant phenology was monitored weekly, and local weather conditions were monitored daily. The lower and upper base temperatures were of 12.92 and 32.46°C, respectively, for pre-flowering; 13.50 and 32.23°C for flowering; 12.14 and 32.55°C for green fruit stage; 11.64 and 32.78°C for fruit color-changing stage; and 11.23 and 32.94°C for maturation. The thermal time requirement and the average cycle length for the ideal harvest time of acai palm were 3,893.15 degree-days and 283 days, respectively. The thermal time requirement and the duration of the reproductive growth stage for acai palm are influenced by the period of the year and the variability of air temperature, which, when high, reduces the cycle of the crop, and when mild, increases it.