RESUMO Conhecer a umidade de solo disponível para as plantas é preponderante para o manejo adequado do uso da água nas propriedades agrícolas, sendo os métodos automatizados os mais precisos. Entretanto, os custos de aquisição são elevados e a maioria dos controladores de irrigação ainda trabalha com tempos pré-definidos. Assim, o estudo teve por objetivo desenvolver e calibrar um tensiômetro automatizado de baixo custo e alta eficiência no controle da irrigação, baseado em monitoramento em tempo real. A pesquisa foi conduzida nos Laboratórios de Hidráulica e Relação Água-Solo-Planta-Atmosfera pertencentes à Universidade Federal da Grande Dourados (UFGD), em Dourados, MS, com solo classificado como Oxisol. Foram utilizados transdutores de pressão e um microcrontrolador capazes de assimilar a pressão no interior dos tensiômetros e transformá-la em leituras de potencial matricial de água no solo - Ψm. Desta forma, realizou-se a calibração comparando as diferentes leituras do transdutor e do tensímetro digital de agulha. Foram aplicadas diferentes tensões para obtenção da curva de umidade do solo, partindo do ponto mais úmido (saturado) para o mais seco (solo seco em estufa), coletando 20 pontos válidos. Posteriormente, os dados foram submetidos ao teste de normalidade, com posterior análise estatística e modelos de curva de regressão. Foram verificados ajustes lineares com altos valores de coeficiente de determinação (R2 = 0,99), sendo o sistema automatizado construído, capaz de monitorar a tensão de água do solo em tempo real.

ABSTRACT Knowing the soil moisture available to plants is important for adequate management of water use in agricultural farms, with automated methods being the most accurate. However, acquisition costs are high and most of the commercially available irrigation controllers still work using pre-set times. This study aimed to develop and calibrate a low-cost automated tensiometer with high efficiency in irrigation control, based on real-time monitoring. The research was conducted at the Laboratories of Hydraulics and of Water Soil Plant and Atmosphere Relationship, which belong to the Federal University of Grande Dourados (UFGD), in Dourados, MS, Brazil, with soil classified as an Oxisol. Pressure transducers and a microcontroller were used to assimilate the pressure inside tensiometers and transform it into readings of soil water matric potential (Ψm). Thus, the calibration was carried out by comparing the different readings of the transducer and digital tension meter. Different tensions were applied to obtain a soil moisture curve, starting from the most humid point (saturated) to the driest one (oven-dried soil), collecting 20 valid points. Subsequently, the data were subjected to the normality test, with subsequent statistical analysis and regression curve models. Linear adjustments with a high coefficient of determination (R2 = 0.99) were observed, with the automated system built in this study being capable of monitoring soil water tension in real-time.

RESUMO O direcionamento dos renques das árvores em sistema silvipastoril, associados a diferentes estações do ano, permite maior ou menor penetração de luz solar, resultando em expressiva modificação da composição do microclima e das condições térmicas a serem propiciadas aos animais. Neste sentido, objetivou-se avaliar as variáveis microclimáticas e índices de conforto térmico em sistemas silvipastoris orientados na direção leste-oeste e norte-sul, comparados ao sistema sem sombra nas estações de verão e inverno. O estudo foi realizado na Fazenda Modelo II (21° 08’ S 53º 17’ O, e altitude de 354 m). O delineamento adotado foi em blocos casualizados em esquema de parcelas sub-subdivididas, com cinco repetições. Nas parcelas foram avaliadas duas direções de plantio e controle (sem sombra). Nas sub-parcelas foram avaliados os horários de coleta e nas sub-subparcelas as distâncias em relação ao renque das árvores de eucalipto. As direções leste-oeste e norte-sul não promoveram alterações nas variáveis climáticas, bem como nos índices de conforto térmico durante o verão. Entretanto, diferenciaram-se para temperatura e umidade relativa do ar, temperatura do globo negro e carga térmica radiante durante o inverno. Os sistemas silvipastoris proporcionam melhoria no ambiente e concomitantemente no conforto térmico animal quando comparados ao sistema sem sombra. Todavia, mesmo na presença de árvores, ocorrem situações de estresse térmico, dependendo do horário do dia e da distância em relação aos renques de eucalipto.

ABSTRACT The orientation of tree-rows in a silvopastoral system associated with different seasons of the year allows more or less sunlight penetration, resulting in deliberate modification of the microclimate composition and thermal conditions provided to animals. In this sense, the aims of this study were to evaluate microclimatic variables and thermal comfort indices for east-west and north-south oriented silvopastoral systems, compared to unshaded systems during summer and winter. The study was conducted at the Modelo II Farm (21° 08’ S 53° 17’ W) at an altitude of 354 m. A randomized block design in scheme of split-split plots with five repetitions was adopted. Two planting directions and a control treatment (unshaded) were evaluated in the plots. Collection times were evaluated in sub-plots, and the distance from eucalyptus trees was evaluated in sub-sub-plots. Changes in the east-west and north-south planting directions did not promote changes in climate variables, nor did they change the thermal comfort indices during summer. There were differences, however, in temperature and relative humidity of the air, black globe temperature, and radiant heat load during winter. Silvopastoral systems provide improvements in the environment and, concomitantly, to the thermal comfort of animals, when compared to unshaded systems. However, thermal stress situations occur despite the presence of trees, depending on the time of the day and the distance from the rows of eucalyptus trees.

ABSTRACT One of the limitations to producing irrigated forages is setting suitable biometric parameters to establish the entrance of animals to grazing areas. Such parameters can be measured or even estimated. Estimates are advantageous for being practical and able to be used for grazing optimization. This study aimed to evaluate the correlation among growing degree-days (GDD), canopy height (CH), leaf area index (LAI), and number of cycle days (NCD) of Guinea grass (Panicum maximum cv. Mombaça) and Bermuda grass (Cynodon spp. Tifton 85) single cropped for one year and overseeded with black oat and ryegrass in the autumn-winter season. The study was carried out from February 2016 to February 2017, and forage crops were sprinkle irrigated. LAI and CH were measured twice a week, at intervals of 3 and 4 days. These parameters were correlated to GDD accumulation at each cutting cycle (CC). All the correlations showed high coefficients in linear fits. For spring-summer cycles, Guinea grass in exclusive cultivation showed the highest averages for CH and LAI, being 102.3 cm and 5.93, respectively. For autumn- winter cycles, when this grass was overseeded, it showed an LAI value similar to that when single cropped, which was of about 5.6. Yet single Bermuda grass presented lower values of LAI (one unit lower) and CH (16.4 cm lower) in the autumn-winter season when compared to that overseeded. The spring-summer cycles of Guinea grass had a duration of 24 days, after which no increase in leaf production was registered.