RESUMO No cenário das mudanças climáticas, o estudo das emissões de gases do efeito estufa (GEE) e de medidas de mitigação na Caatinga são estratégicos e podem fornecer a base para planos de mitigação. Objetivou-se avaliar os fluxos de CO2, CH4 e N2O do solo, bem como determinar uma linha de base anual para as emissões de GEE, em um sistema de produção silvipastoril de referência no semiárido brasileiro, a fim de fornecer subsídios para estudos futuros de mitigação das emissões de GEE. Os fluxos de GEE foram monitorados durante um ano, em pastagem de capim buffel e em área de Caatinga pastejada e nativa, as quais são componentes de um sistema silvipastoril de longa duração. Os fluxos de CO2 variaram de -19,98 a 179,12 mg m-2 h-1 de C-CO2, os de CH4 de -76,21 a 113,87 µg m-2 h-1 de C-CH4, os de N2O de -1.043,12 a 471,37 µg m-2 h-1 de N-N2O e a umidade do solo foi o principal fator limitante para os fluxos de GEE. As emissões totais convertidas para CO2-equivalente nas áreas antropizadas foram menores que na área de vegetação nativa (65 % para o capim buffel e 741 % para a Caatinga pastejada). Portanto, pode-se afrmar que as emissões de GEE nas áreas pastejadas no bioma Caatinga não são tão altas quanto na Caatinga nativa, o que é um importante indicador da sustentabilidade ambiental do sistema silvipastoril avaliado.

ABSTRACT In the climate change scenario, studying greenhouse gases (GHG) emissions and measures of mitigation in the Caatinga biome are strategic and may provide a basis for mitigation plans. This study aimed to evaluate the soil CO2, CH4 and N2O fluxes, as well as determining an annual baseline for GHG emissions, in a reference site of silvopastoral production system in the Brazilian semiarid region, in order to provide subsidies for future studies on GHG emissions mitigation. The GHG fluxes were monitored over one year, in a buffel grass pasture and in grazed and native Caatinga areas, which are components of a long-term silvopastoral system. The CO2 fluxes ranged from -19.98 to 179.12 mg m-2 h-1 of CO2-C, CH4 fluxes from -76.21 to 113.87 µg m-2 h-1 of CH4-C, N2O fluxes from -1,043.12 to 471.37 µg m-2 h-1 of N2O-N and the soil moisture was the main factor limiting the GHG fluxes. The total emissions converted to CO2-equivalent in the anthropized areas were lower than in the native area (65 % for the buffel grass pasture and 741 % for the grazed Caatinga). Therefore, it is possible to afrm that the GHG soil emissions from grazed areas in the Caatinga biome are not as high as in the native Caatinga, what is an important indication of the environmental sustainability of the evaluated silvopastoral system.

ABSTRACT The use of irrigation can improve the productivity and nutritional quality of the forage cactus in environments with a water deficit, resulting in profit to the producer. The productive performance, bromatological composition and economic benefits of using irrigation were investigated in this study with forage cactus clones regulated deficit irrigation (RDI). The study was conducted in an experimental design of randomised blocks, in a factorial scheme with subdivided plots. The plots consisted of water regimes based on the crop evapotranspiration (ETc) (rainfed, 40, 80 and 120% ETc). The cactus clones [‘Miúda’ (MIU), ‘Orelha de Elefante Mexicana’ (OEM) and ‘IPA Sertânia’ (IPA)] comprised the subplots. The total number of cladodes per plant, the fresh and dry matter yields and the bromatological composition were evaluated. Economic viability was assessed using the net revenue and benefit to cost ratio (BCR). The irrigation depths did not increase the yield of the clones. The OEM clone showed 276 and 343% greater fresh and dry matter production, respectively, when compared to the IPA clone; however, when compared with the MIU clone, it was 63%, both on a fresh and dry matter production. The water regimes had no effect on the nutritional quality of the cactus. Only IPA showed no profit during the first cycle (BCR < 1). It can be concluded that planting one irrigated hectare with the OEM and MIU clones offer economic returns starting from the first production cycle (18 months).

Abstract The vegetation structure is a good indicator of the conservation condition of an ecosystem, since it reflects alterations caused by anthropic action. This study proposes to analyze the phytosociological aspects of the Caatinga domain under anthropic disturbance and their correlations with hydrological variables. Twenty-five 400 m 2 plots were sampled in the municipality of Floresta - PE, Brazil. Phytosociological parameters such as density, frequency and dominance were calculated. The seasonality of plant area index was analyzed for six species. The association between structural characteristics and hydrological variables (throughfall, stemflow and interception loss) in the species was evaluated by multivariate analysis. A total of 930 individuals, six families and 10 species were recorded. The abundance of the species Cenostigma pyramidale in the area may be an indicator of the degree of change in the vegetation. The structural characteristics of the species revealed little association with rainfall partitioning.

Abstract This study investigated the water and radiation use efficiencies by Erythrina velutina and Enterolobium contortisiliquum under four water regimes. The experiment was carried out in the municipality of Serra Talhada, PE, Brazil. The experimental design was completely randomized with a 2 x 4 factorial arrangement and three replications. The water regimes were imposed from water replenishments based on the reference evapotranspiration (25, 50, 75 and 100% ET0). Water and radiation use efficiencies were calculated to the 120 days of growth. E. velutina showed a greater accumulated dry biomass (4.89 g pl-1) than E. contortisiliquum (2.22 g pl-1). The 75% ET0 water regime can be adopted without damage to the growth of both species. E. velutina was more efficient in the conversion of water (0.42 g l-1) and radiation in dry biomass (0.028 g MJ-1), indicating high environmental resilience, which is important features to choose species more adequate for reforestation activities.

ABSTRACT It was evaluated how straw management modifies the development, growth, nutrient cycling and crop water productivity of sugarcane in the semiarid region of Brazil. The experiment was carried out using two plots with 5 ha each, being one without straw on the soil surface and one with 26 Mg·ha-1 covering the soil. Sugarcane growth and development and straw decomposition coefficient were evaluated, whereas the industrial yield, juice quality, dry matter partitioning, and crop water productivity were determined at harvesting. The straw decomposition coefficient was 0.0049 Mg·ha-1·day-1, and the remaining dry mass was equal to 24%. The straw affected the sugarcane growth and development until the first 100 days. The individual internode volume can be adopted as an indicator of the effect of straw on sugarcane growth because the internode volumes up to the sixth position in the with-straw treatment crop were lower than in the no-straw treatment, which was not observed in other variables of the stalks. Keeping straw on the soil surface reduced the crop lodging. Yield and juice quality were not affected, but crop water productivity was increased by keeping sugarcane straw in the field.

Resumo Nas últimas décadas houve mudança no sistema de colheita e manejo da palhada em canaviais de todo o Brasil, visando atender a legislação vigente e reduzir custos. A deposição de resíduos culturais sobre o solo, contudo, modifica as características micrometeorológicas do ambiente. Este trabalho reporta um estudo conduzido em Juazeiro-BA, para avaliar o efeito da manutenção da palhada no balanço de energia, emissão foliar e eficiência do uso da radiação da cana-de-açúcar. Medidas micrometeorológicas e da cultura foram feitas entre setembro de 2015 e julho de 2016. A magnitude e sazonalidade dos fluxos de calor latente, sensível e no solo foram afetadas pela presença da palhada (p<0,0001) com alteração na partição do LE/Rn de 84% para 64%, do H/Rn de 12% para 35% e do G/Rn de 4% para 2%, nessa ordem, para o cultivo sem e com palhada. A temperatura do ar foi maior no cultivo com palhada após o fechamento do dossel, enquanto, a umidade relativa do ar foi acrescida apenas nos primeiros meses. A modificação do microclima por causa da manutenção da palhada em campo alterou a velocidade de emissão foliar da cana-de-açúcar, mas, pouco afetou a eficiência do uso da radiação (~ 2,51 g MJ-1).

Abstract In recent decades there has been a change in the system of harvesting and management of straw in sugarcane fields all over Brazil, aiming to comply with current legislation and reduce costs. The crop residues deposition on the soil, however, modifies the micrometeorological characteristics of the crop environment. This work reports a study conducted in Juazeiro-BA to evaluate the effect of field straw maintenance on the energy balance, development and radiation use efficiency by sugarcane. Micrometeorological and crop measurements were made between September 2015 and July 2016. The magnitude and seasonality of the latent, sensible and soil heat fluxes were affected by the presence of straw (p < 0.0001) with a change in the LE/Rn from 84% to 64%, H/Rn from 12% to 35% and G/Rn from 4% to 2%, in that order, for the cultivation without and with straw. The air temperature was higher in the straw crop after the canopy closure, while the air relative humidity was increased only in the first months. The modification of the microclimate due to the maintenance of the straw altered the leaf emission speed of the sugarcane, but little affected the radiation use efficiency by crop (~ 2.51 g MJ-1).

ABSTRACT The accumulation of dry biomass, its partitioning and the adjustment of equations were assessed for the initial growth of Piptadenia stipulacea (Benth) Ducke and Anadenanthera colubrina (Vell.) Brenan under water availability variation. The experiment was conducted in pots arranged in a completely randomized design with three replicates. Water conditions were evaluated using the percentages of reference evapotranspiration. Samples of the biomass were taken at 10-day intervals and used for the achievement of partitioning data and model adjustments. The short period of water scarcity in the initial growth phase of P. stipulacea and A. colubrina does not affect the establishment of these species, but different water regimes alter their root growth dynamics. The A. colubrina allocates more dry matter to the roots, while P. stipulacea sends more dry matter to the aerial part. The Gaussian, Lorentzian, Log-Normal and Gompertz models had excellent adjustments for the biomass variables of the P. stipulacea species, whereas for A. colubrina, we recommend the Exponential model.

Resumo Objetivou-se comparar os fluxos de radiação e de energia entre uma área de caatinga preservada e um cultivo de cana-de-açúcar irrigada no Semiárido brasileiro. Para tanto, foram analisados os componentes dos balanços de radiação e de energia, os dados ambientais (umidade, temperatura do solo, e regime hídrico) e o índice de cobertura vegetal, entre junho de 2015 e maio de 2016. No centro de cada área foi instalada uma torre micrometeorológica equipada com sensores eletrônicos. Como resultados, constatou-se que as principais diferenças no balanço de radiação entre a caatinga e a cana-de-açúcar estão associadas ao albedo e a emissão de radiação de ondas longas pelas superfícies. O fluxo de calor sensível (H) foi sempre maior na caatinga, enquanto o fluxo de calor latente (LE) foi superior na cana-de-açúcar (p < 0,05). Na caatinga, as partições de energia para o H, LE e fluxo de calor no solo (G) foram 64%, 34%, e 2%, nessa ordem; enquanto na cana-de-açúcar, foi de 12% para o H, 85% para o LE e 3% para o G; com diferenças significativas entre as superfícies (p < 0,05). Essas diferenças podem acarretar modificações no clima local e/ou regional, logo, devem ser consideradas nos modelos de simulação hidrológicos e climáticos.

Abstract The objective of this study was to compare the radiation and energy fluxes between an area of preserved caatinga and an irrigated sugarcane crop in the Brazilian semi-arid region. The radiation and energy components, the environmental data (soil moisture and temperature, water regime) and the vegetation cover index were analyzed between June 2015 and May 2016. In each area was installed a micrometeorological tower equipped with electronic sensors. As results, it was verified that the main differences in the radiation balance between caatinga and sugarcane are associated to the albedo and the emission of long-wave radiation on the surfaces. The sensible heat flux (H) was always higher in the caatinga, while the latent heat flux (LE) was higher in sugarcane (p < 0.05). In the caatinga, the energy partitions for H, LE and soil heat flux (G) were 64%, 34% and 2%, in that order; while in sugarcane, it was 12% for H, 85% for LE and 3% for G; with significant differences between the surfaces (p < 0.05). These differences can lead to modifications in the local and / or regional climate, so they should be considered in hydrological and climatic simulation models.

RESUMO Informações confiáveis sobre a cobertura vegetal e sua dinâmica ao longo do tempo são essenciais para a gestão de vidas, recursos, e apoio a políticas. Embora muitas iniciativas tenham sido realizadas no Brasil desde a década de 1980, o conhecimento sobre suas florestas secas ainda é limitado. Neste estudo, abordamos os moduladores do desmatamento e sua ameaça à floresta seca brasileira chamada Caatinga. Avaliamos a dinâmica da cobertura da terra e métricas de paisagem na bacia do rio Pontal, a qual se tornou uma das áreas mais socialmente e ambientalmente importantes do Brasil. O processo em geral consiste em uma amostragem sistemática baseada em características hidrológicas, onde imagens Landsat (1975 a 2013) combinadas com o software FRAGSTATS foram utilizadas para avaliar índices de métricas de paisagem para a Caatinga. Os dados mostraram que a área relativa (RA) diminuiu de 90,25% para 60,98% ao longo do período de 38 anos, enquanto que a fragmentação (PD) apresentou uma tendência crescente. Além disso, a distribuição espacial de ambos os índices se tornou mais heterogênea e agrupada ao norte. Sugerimos que a aptidão da terra para a agricultura foi a principal causa do desmatamento. A chuva é 112% mais intensa no norte da bacia do que no sul. Portanto a fauna e flora ao norte foram significativamente alteradas e reduzidas. A relação entre desmatamento e tempo mostrou uma ameaça crescente. Outros estudos que avaliem essas causas são necessários para melhorar a compreensão da dinâmica da vegetação nesta região.

ABSTRACT Reliable information on vegetation cover and its dynamics over time is essential for managing life, resources, and supporting policies. Although many related initiatives have been undertaken in Brazil since the 1980s, knowledge about its dry forests is still limited. In this study, we address the drivers of deforestation and their threat to the Brazilian dry forest called Caatinga. We evaluated the land cover dynamics and landscape metrics in the watershed of the Pontal River, as it has become one of the most socially and environmentally important areas in Brazil. The overall process consists of a systematic sampling grid of hydrological samples, where Landsat images (1975 to 2013) combined with the FRAGSTATS package were used to evaluate landscape metrics indices for the Caatinga. Data showed that the relative area (RA) decreased from 90.25% to 60.98% over the 38-year period, while fragmentation (PD) presented an increasing bias. In addition, the spatial distribution of both indices became more heterogeneous and clustered in the north. We suggest that appropriateness of land for farming was the leading cause of deforestation; rainfall is 112% more intense in the north of the watershed than in the south. Therefore, the northern fauna and flora have been significantly altered and reduced. The relationship between deforestation and time shows an increasing threat. Further studies evaluating these causes are needed to improve our understanding of the vegetation dynamics in this region.

Resumo Diante do aumento das emissões dos gases do efeito estufa, o presente estudo analisou o sequestro de carbono em áreas de caatinga do município de Petrolina – PE, por meio de técnicas de sensoriamento remoto. Foram utilizadas imagens do sensor MODIS, referentes ao produto MOD17, o qual contém a estimativa da Produção primária bruta (GPP) e da Produção primária líquida (NPP). A coleta das imagens ocorreu para os anos de 2011 e 2012. No período chuvoso, as áreas de caatinga preservada apresentaram maiores valores de assimilação total (até 160 g C/m2 em janeiro de 2011) e sequestro de carbono, enquanto no final do período seco foram registrados valores inferiores a 20 g C/m2. Quanto ao total anual, em 2011 as áreas de caatinga preservada juntamente com a agricultura irrigada apresentaram os maiores valores de GPP (> 900 g C/m2), enquanto que em 2012 a GPP das áreas de caatinga variaram, em geral, de 500 a 600 g C/m2, com algumas áreas chegando a 700 g C/m2. A NPP, ou seja, o sequestro de carbono, variou de 500 a 700 g C/m2 em 2011 e de 100 a 400 g C/m2 em 2012. Desse modo, são necessárias medidas e elaboração de instrumentos políticos que visem à preservação dos remanescentes de caatinga do município de Petrolina, como forma de contribuir com mitigação do aquecimento global.

Abstract Given the increasing emissions of greenhouse gases, the present study analyzed the carbon sequestration in savanna areas of the city of Petrolina - PE, via remote sensing techniques. Images from the MODIS sensor, for the product MOD17, which contains an estimated gross primary production (GPP) and net primary production (NPP). The collection of images was for the years 2011 and 2012. During the rainy season, the preserved savanna areas had higher overall assimilation of values (up to 160 g C/m in January 2011) and carbon sequestration, however the dry season stood out areas of irrigated agriculture. As the annual total in 2011 the areas of savanna preserved along with irrigated agriculture had the highest GPP values (> 900 g C/m2), while in 2012 the GPP of savanna areas ranged generally from 500 to 600 g C/m2, with some areas reaching 700 g C/m2. The NPP, ie carbon sequestration, ranged 500-600 g C/m2 in 2011 and 400 g C/m2 in 2012. Thus, measures are needed and development of policy instruments aimed at the conservation of remaining to scrub the city of Petrolina, in order to contribute to mitigating global warming.

Resumo: O objetivo deste trabalho foi avaliar o desempenho produtivo, a eficiência biológica e a habilidade competitiva do consórcio palma-sorgo sob irrigação com diferentes lâminas de água salina, no Semiárido brasileiro. O experimento foi realizado em Serra Talhada, PE, entre 2014 e 2015, em delineamento de blocos ao acaso, com quatro repetições, em arranjo fatorial 5x3, com parcelas subdivididas, tendo sido um ano de ciclo de palma e dois ciclos de sorgo. As parcelas foram compostas por quatro lâminas de irrigação com base nas frações de 25, 50, 75 e 100% da evapotranspiração de referência, além das condições de sequeiro, e as subparcelas consistiram de três sistemas de plantio (palma solteira, sorgo solteiro e consórcio palma-sorgo). O aumento das lâminas de água incrementou a produtividade do sorgo e do consórcio palma-sorgo. O consórcio promoveu estabilidade na produção, com índice de produtividade do sistema (IPS) palma-sorgo (6.279,02 kg ha-1 MS) maior que o de palma em cultivo solteiro (4.626,98 kg ha-1 MS). O coeficiente de adensamento relativo (12,33) foi indicativo de ótima compatibilidade do consórcio. A associação palma-sorgo apresenta vantagem biológica e capacidade competitiva com maior índice produtivo que os dos seus monocultivos.

Abstract: The objective of this work was to evaluate the productive performance, biological efficiency, and the competitive ability of the forage cactus-sorghum intercropping under different irrigation depths with saline water in the Brazilian Semiarid Region. The experiment was carried out in Serra Talhada, in the state of Pernambuco, between 2014 and 2015, in a randomized complete block design, with four replicates, and a 5x3 factorial arrangement in split plots, with one year of forage cactus cycle and two years of sorghum cycles. The plots were composed by four irrigation water depths based on the fractions of 25, 50, 75, and 100% of the reference evapotranspiration, besides dry conditions; and the subplots consisted of three cropping systems (single crop of forage cactus, single crop of sorghum, and intercropping of forage cactus-sorghum). The increase of water irrigation depths increased the yields of sorghum in single crop and of the forage cactus-sorghum intercropping. The intercropping system promoted production stability with a higher system productivity index (SPI) for forage cactus-sorghum intercropping (6,279.02 kg ha-1 DM) than for forage cactus in single crop (4,626.98 kg ha-1 DM). The relative density coefficient (12.33) was indicative of the great compatibility of the intercropping system. The forage cactus-sorghum association shows biological advantage and competitiveness capacity, with a higher productive index than their monocultures.

RESUMO: Objetivou-se determinar a necessidade de água e o coeficiente de cultura para as diferentes fases fenológicas do milho ( Zea mays L) e do feijão-caupi ( Vigna unguiculata (L) Walp) em sistemas de plantio exclusivo e consorciado sob as condições climáticas do Semiárido brasileiro. O experimento foi conduzido no município de Petrolina, PE. Foram monitorados o rendimento de matéria seca total da parte aérea e a radiação fotossinteticamente ativa interceptada para ambas as culturas. Além disso, obteve-se a evapotranspiração da cultura (ETc) por meio do método do balanço de água no solo. Com estes dados e a evapotranspiração de referência foi obtido o coeficiente de cultura (Kc), os quais foram utilizados, posteriormente, para ajustar modelos em função dos graus dias acumulados. Com os resultados, constatou-se que o requerimento hídrico do milho e feijão-caupi no sistema de plantio consorciado foi maior que no sistema exclusivo. Os valores de Kc no consórcio foram de 0,90, 1,30, 1,20 e 0,72 para o milho, e 0,86; 1,30, 1,21 e 0,91 para o feijão-caupi, respectivamente, para as fases vegetativa, floração, enchimento de grãos e maturação. No sistema exclusivo esses valores foram de, 0,86, 1,23, 0,97 e 0,52 para o milho e de 0,68; 1,02, 1,06 e 0,63 para o feijão-caupi, nesta ordem. As variações dos valores de Kc para ambos os sistemas e culturas estiveram associadas ao incremento de biomassa e a interceptação da radiação. O modelo Gaussiano ajustado descreveu adequadamente a relação entre os valores de Kc e dos graus dias acumulados.

ABSTRACT: In order to determine the water requirement and crop coefficient for the different phenological stages on corn plants ( Zea mays L.) and cowpea plants ( Vigna unguiculata (L.) Walp) in intercropping and sole cropping systems under the climatic conditions of the Brazilian semiarid. The experiment was conducted in the city of Petrolina, PE. Shoots total dry mass and photosynthetically active radiation intercepted for both crops were monitored. Furthermore, it was obtained the evapotranspiration (ETc) by the soil water balance method. With these data and reference evapotranspiration it was obtained crop coefficient (Kc), which were subsequently used to adjust models as a function of accumulated degree days. With the results, it was found the water requirements from maize and cowpea intercropped system were greater than the sole system. Kc in the intercropped system was 0.90, 1.30, 1.20 and 0.72 for maize and 0.86, 1.30, 1.21 and 0.91 for cowpea, respectively, for the vegetative, flowering, grain filling and ripening stages. In the sole system, these values were, 0.86, 1.23, 0.97 and 0.52 for maize and 0.68, 1.02, 1.06 and 0.63 for cowpea in those phases mentioned. The variations of the Kc values for both systems and cultures have been associated to the increase of biomass and light interception. The Gaussian model adjusted properly described the relationship between Kc and accumulated degree days.

Resumo:O objetivo deste trabalho foi determinar a variação sazonal dos componentes do balanço de energia e avaliar o controle biofísico da evapotranspiração, em área de Caatinga preservada, em condições de seca intensa. O experimento foi conduzido em 2012, tendo-se utilizado o sistema "eddy covariance", instalado a 16,9 m acima da superfície do solo. Além disso, foram realizadas medidas de temperatura, umidade, radiação solar, saldo de radiação, fluxo de calor no solo e temperatura do solo. Os dados dos fluxos de calor sensível e latente foram processados com o programa Alteddy e analisados em escalas diária e sazonal. Com os dados do fluxo de calor latente, foram determinados os valores da evapotranspiração, bem como os indicadores da sua sensibilidade às condições ambientais: fator de desacoplamento, e resistências aerodinâmica e da superfície. O saldo de radiação apresentou forte sazonalidade, com comportamento dependente da radiação solar. A partição dos componentes do balanço de energia revelou que a ocorrência de seca intensa maximiza a destinação da energia disponível ao fluxo de calor sensível, e que a evapotranspiração nessa condição é especialmente dependente do deficit de pressão de vapor e da resistência da superfície.

Abstract:The objective of this work was to determine seasonal variation in energy balance components and to evaluate the biophysical control of evapotranspiration in a preserved Caatinga area, under intense drought conditions. The experiment was conducted in 2012, using the eddy covariance system, installed at 16.9 m above soil surface. In addition, temperature, humidity, solar radiation, net radiation, soil heat flux, and soil temperature were measured. Data on the sensible and latent heat fluxes were processed with the Alteddy software and analyzed on daily and seasonal scales. Using the latent heat flux data, the evapotranspiration rates were determined, as well as the indicators of their sensitivity to environmental conditions: decoupling factor, and aerodynamical and surface resistances. The net radiation showed a strong seasonality, with behavior dependent on solar radiation. The partition of the energy balance components revealed that the occurrence of intense drought maximizes the destination of the available energy to sensible heat flux, and that evapotranspiration under this condition is specifically dependent on the vapor pressure deficit and on the surface resistance.

Resumo: O objetivo deste trabalho foi avaliar a dinâmica de água no solo em áreas cultivadas com clones de palma forrageira, e determinar como as condições ambientais e o crescimento da cultura afetam a evapotranspiração. O estudo foi conduzido no Município de Serra Talhada, no Estado de Pernambuco. O crescimento da cultura foi monitorado por meio da evolução do índice de área do cladódio (IAC) e da fração de cobertura do solo calculada ao final do ciclo. A evapotranspiração real (ET) dos três clones avaliados foi obtida como resíduo do método do balanço hídrico do solo. Não foi observada diferença entre os componentes do balanço hídrico do solo, embora os clones pertencessem a gêneros diferentes e apresentassem diferentes incrementos do IAC. A ET acumulada foi de 1.173 mm durante os 499 dias experimentais, com média diária de 2,35 mm. O IAC aumenta o consumo de água do clone Orelha de Elefante Mexicana. Em condições de seca, o consumo de água do clone Miúda responde mais lentamente à variação no armazenamento de água no solo. A menor evolução do IAC do clone IPA Sertânia, durante o período chuvoso, induz à maior contribuição do componente de evaporação na ET. A demanda atmosférica controla a ET dos clones apenas quando há maior disponibilidade de água no solo; nesta condição, o consumo de água do clone Miúda diminui mais rapidamente com o aumento da demanda atmosférica.

Abstract: The objective of this work was to evaluate soil water dynamics in areas cultivated with forage cactus clones and to determine how environmental conditions and crop growth affect evapotranspiration. The study was conducted in the municipality of Serra Talhada, in the state of Pernambuco, Brazil. Crop growth was monitored through changes in the cladode area index (CAI) and through the soil cover fraction, calculated at the end of the cycle. Real evapotranspiration (ET) of the three evaluated clones was obtained as the residual term in the soil water balance method. No difference was observed between soil water balance components, even though the evaluated clones were of different genus and had different CAI increments. Accumulated ET was of 1,173 mm during the 499 days of the experiment, resulting in daily average of 2.35 mm. The CAI increases the water consumption of the Orelha de Elefante Mexicana clone. In dry conditions, the water consumption of the Miúda clone responds more slowly to variation in soil water availability. The lower evolution of the CAI of the IPA Sertânia clone, during the rainy season, leads to a higher contribution of the evaporation component in ET. The atmospheric demand controls the ET of clones only when there is higher soil water availability; in this condition, the water consumption of the Miúda clone decreases more rapidly with the increase of atmospheric demand.

RESUMO Métodos de determinação do índice de área foliar têm sido aplicados a várias culturas agrícolas. Todavia, os seus usos limitam-se a plantas folhosas, não havendo registro para a palma forrageira, em que a interceptação da radiação é realizada pelo cladódio. Assim, este estudo objetivou analisar o uso de diferentes métodos indiretos na estimativa do índice de área do cladódio da palma forrageira. Foram utilizados cladódios dos clones Nopalea cochenillifera Salm Dyck, Nopalea cochenillifera Salm Dyck e Opuntia stricta (Haw) Haw, dos quais se amostraram sessenta plantas por clone, distribuídas em cinco subáreas com 12 plantas. Foram avaliados métodos de interceptação de luz com diferentes técnicas de medida, bem como os métodos planimétrico, discos foliares e modelagem. A estimativa do índice de área do cladódio da palma forrageira pelo método da modelagem foi considerada a mais precisa, por apresentar valores de coeficiente de precisão e de acurácia acima de 0,90, bem como desempenho de muito bom a ótimo. Porém, a sua aplicabilidade depende do uso de parâmetros ou equações de ajuste dos valores estimados. Os métodos da interceptação de luz e de suas derivações, discos foliares do cladódio médio e da planimetria do cladódio médio não são recomendados, devido à baixa precisão e acurácia dos mesmos.

ABSTRACT Methods for determining leaf area index have been applied to various agricultural crops. However, their uses are limited to broadleaf plants, with no record for forage cactus, whose radiation interception is performed by the cladode. This study aimed to evaluate the use of different indirect methods to estimate the area index of forage cactus cladode. Cladodes from clones of Nopalea cochenillifera Salm Dyck, Nopalea cochenillifera Salm Dyck and Opuntia stricta (Haw) Haw were used, being sampled sixty plants per clone, distributed in five sub-areas with 12 plants. Light interception methods with different measurement techniques were evaluated, as well as the planimetric, leaf discs and modeling methods. The estimate of area index of the forage cactus cladode by the modeling method was considered the most accurate one, for presenting precision coefficient values and accuracy above 0.90, as well as a performance varying from very good to excellent. However, its applicability depends on the use of estimated parameters or adjusted value equations. The methods of light interception and its derivations, leaf discs of medium cladodes and planimetry of medium cladodes are not recommended, due to their low precision and accuracy.