The analysis of gross primary production (GPP) is crucial to better understand CO₂ exchanges between terrestrial ecosystems and the atmosphere, while the quantification of water-use efficiency (WUE) allows for the estimation of the compensation between carbon gained and water lost by the ecosystem. Understanding these dynamics is essential to better comprehend the responses of environments to ongoing climatic changes. The objective of the present study was to analyze, through AMERIFLUX and LBA network measurements, the variability of GPP and WUE in four distinct tropical biomes in Brazil: Pantanal, Amazonia, Caatinga and Cerrado (savanna). Furthermore, data measured by eddy covariance systems were used to assess remotely sensed GPP products (MOD17). We found a distinct seasonality of meteorological variables and energy fluxes with different latent heat controls regarding available energy in each site. Remotely sensed GPP was satisfactorily related with observed data, despite weak correlations in interannual estimates and consistent overestimations and underestimations during certain months. WUE was strongly dependent on water availability, with values of 0.95 gC kg⁻¹ H₂O (5.79 gC kg⁻¹ H₂O) in the wetter (drier) sites. These values reveal new thresholds that had not been previously reported in the literature. Our findings have crucial implications for ecosystem management and the design of climate policies regarding the conservation of tropical biomes, since WUE is expected to change in the ongoing climate change scenario that indicates an increase in frequency and severity of dry periods.

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.

The cowpea bean presents low productivity in the Pará state, Brazil, due to low soil fertility and climatic adversity, mainly water deficiency. The aim of this study was to evaluate the yield gap of cowpea bean in northeast of Para state in response to water deficit during its reproductive phase. The experiment was carried out in Castanhal, PA, Brazil, during 2015 and 2016. A randomized block design with six repetitions and four treatments was used; where T1 consisted of 100% replacement of the crop evapotranspiration (ETc), T2 to 50%, T3 to 25% and T4 without irrigation, in the reproductive phase. The yield was determined at R9 stage. The simulations with the SARRAZON model were carried out with different sowing dates. The total deficiencies in the reproductive phase were spatialized considering the 30 locations in order to assess the temporal and spatial seasonality of water availability and the sowing period in the study region. The cowpea bean was sensitive to soil water availability with considerable reductions in productivity due to the increase in water deficit compared to the treatment T1 (100% ETc). When water deficits reached more than 47 mm, there were yield gaps over 20%. According to the spatial variability of simulated water deficiency, the sowing of cowpea bean in regions located above 2° latitude may extend until June 20 without showing high yield gaps.

O extrativismo de produtos florestais não madeireiros na Amazônia é uma atividade que expõe o trabalhador a riscos ambientais que podem afetar sua saúde e sua segurança no trabalho. O objetivo deste estudo foi identificar os riscos ambientais e os impactos psicofisiológicos e físicos da coleta do fruto do açaizeiro no trabalhador da Amazônia Oriental. O Estudo foi realizado pela aplicação de questionários semiabertos e entrevistas estruturadas baseadas a partir de protocolos do software Ergolândia versão 6.0 a 33 coletores na Ilha do Combú, Belém/PA. Os riscos físicos identificados foram: radiação ultravioleta (12 h de sol), umidade relativa média anual de 71,9% e calor com IBUTG de 24,4ºC. O medo da queda do açaizeiro, animais peçonhentos, altura e o alto esforço físico requerido para escalar a palmeira foram as principais dificuldades apontadas pelos extrativistas. Foram identificados os riscos de acidentes: cobra, maribondo, escorpião, aranha, queda do açaizeiro, cortes, arranhões e torção muscular. A carga de 30 quilos, transportada pelos coletores, atende ao estabelecido pela legislação vigente. As partes do corpo que os extrativistas sentem dores com frequência durante e após a atividade foram: a parte inferior das costas, pés e dedos, mãos e dedos, membros superiores, ombro, punho, trapézio, cabeça e peito, pescoço, antebraço, cotovelo, panturrilha, tornozelo e joelho. O protocolo de Moore e Garg classificou a atividade como de alto risco para o desenvolvimento de doenças ocupacionais com Strain Index de 13,5 e 10,12 na safra e entressafra, respectivamente, e o protocolo de Lehmann como um trabalho fatigante. A OWAS indicou a categoria de ação 4 com adoção de correções imediatas na postura da coluna, membros superiores e pernas dos extrativistas.

Cowpea (Vigna unguiculata (L.) Walp.) is a leguminous species widely cultivated in northern and northeastern Brazil. In the state of Pará, this crop still has low productivity due to several factors, such as low soil fertility and climatic adversity, especially the water deficiency. Therefore, the present study aimed at evaluating the physiological parameters and the productivity of cowpea plants under different water depths. The experiment was conducted in Castanhal/Pará between 2015 and 2016. A randomized block design was applied with six replications and four treatments, represented by the replacement of 100%, 50%, 25% and 0% of the water lost during crop evapotranspiration (ETc), starting from the reproductive stage. The rates of net photosynthesis (A), stomatal conductance (gs), leaf transpiration (E_leaf), substomatal CO₂ concentration (Ci), leaf temperature (T_leaf) and leaf water potential (Ψ_w) were determined in four measurements at the R5, R7, R8 and R9 phenological stages. Cowpea was sensitive to the water availability in the soil, showing a significant difference between treatments for physiological variables and productivity. Upon reaching a Ψ_w equal to −0.88 MPa, the studied variables showed important changes, which allows establishing this value as a threshold for the crop regarding water stress under such experimental conditions. The different water levels in the soil directly influenced productivity for both years, indicating that the proper water supply leads to better crop growth and development, increasing productivity.

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.