ABSTRACT Discussions on desertification frequently highlight soil erosion as a striking feature of this phenomenon. In particular, the high spatial density of gullies represents a strong indication of the formation of desertification hotspots. In this study, through field activities and Monte Carlo simulations, we estimated the volume of soil loss by linear erosion on the slopes of the middle course of the Salitre river in the North of Bahia State. This estimative contributes to the recognition of a desertification process in the studied local. The lengths of the gullies and rills, visible through high-spatial-resolution satellite images, were vectorized. The width and depth of the Linear Erosion Features (LEFs) were measured through field study and recorded via geoprocessing. Statistical treatment was applied to the data to indicate the probability of occurrence of the width and depth classes. Subsequently, the Monte Carlo simulation was used to indicate the volume of soil removed from the slopes by the linear erosion process. Several ramified systems of LEFs are identified and mapped. Monte Carlo simulation fits the measured data well. Estimates indicate that linear erosion event eroded approximately 450,000 m3 of soil in an area of 2,000 hectares, which indicates extreme land degradation.

ABSTRACT Soil physical-hydraulic properties are among the most important indicators for evaluating soil quality. This study aimed to experimentally demonstrate how the construction of terraces can affect physical-hydraulic properties of a soil degraded by water erosion on the banks of the Salitre river, tributary of the São Francisco river. An area in advanced stage of degradation by water erosion was delimited for the construction of a level bench terrace. The experiment was conducted for two years. Soil physical-hydraulic properties were determined before and after terracing. Time-domain reflectometry (TDR) was used to measure soil water storage (mm). This study demonstrated that terracing positively affected soil physical-hydraulic properties in the previously degraded area, allowed the increase in the retention and availability of water in the soil, thus is an ecologically beneficial practice for recovery of degraded soils on the banks of the Salitre river.

ABSTRACT A detailed knowledge of the soil water storage variability in the root zone can promote recommendations regarding the ideal positioning of sensors, as well as make the calculation of soil water balance more precise and accurate. This study aimed to assess soil water storage variability in the melon root zone and indicate – based on spatial variation of soil water storage – the regions of highest rootactivity of the melon crop in different development stages. Soil waterstorage was measured using time domain reflectometry (TDR) in 40 monitoring points. The data were daily collected in two periods: (i) immediately before irrigation and (ii) 30 min after irrigation. The soil water storage variation in the melon root zone occurs with greater intensity throughout the time of vegetative growth and the highest values are always observed in the same distances and depths of the soil in all phases of growth. The region indicated as of greatest root activity of the melon crop under drip irrigation is delimited, inrelation to the stem, by the radial distance of 0.36 m and depth of0.3 m, for all development stages.

ABSTRACT: The knowledge on spatial and temporal variations of soil water storage in the root zone of crops is essential to guide the studies to determine soil water balance, verify the effective zone of water extraction in the soil and indicate the correct region for the management of water, fertilizers and pesticides. The objectives of this study were: (i) to indicate the zones of highest root activity for banana in different development stages; (ii) to determine, inside the zone of highest root activity, the adequate position for the installation of soil moisture sensors. A 5.0 m3 drainage lysimeter was installed in the center of an experimental area of 320 m2. Water extraction was quantified inside the lysimeter using a 72 TDR probe. The concept of time stability was applied to indicate the position for sensor installation within the limits of effective water extraction. There are two patterns of water extraction distribution during the development of banana and the point of installation of sensors for irrigation management inside the zone of highest root activity is not constant along the crop development.

Spatial and temporal variability of soil water extraction from the root zone affect soil water balance determination. The number of sensors installed in the root zone in studies addressing water balance is still set arbitrarily. This study provided an investigation of the water extraction process by banana (Musa spp.) roots by (i) determining the variability of water extraction from the banana tree root zone, (ii) detecting differences in the estimation of evapotranspiration (ET) by the soil water balance method when the number of soil profiles monitored in the roots zone varies, (iii) and; determining the minimum number of Time Domain Reflectometry (TDR) probes needed to obtain ET precision and accuracy similar to that determined by a drainage lysimeter. The field experiment was conducted in Cruz das Almas, in the state of Bahia, Brazil, where a drainage lysimeter was installed on a banana plantation. The water extraction in the banana root zone was quantified by the water content variations monitored in 72 points by TDRs, with measurements at 15-min intervals. The variability of water extraction in the banana root zone was medium to high. The range of variability affects the reliability of the crop evapotranspiration calculation by the soil water balance method. To prevent an overestimation of banana evapotranspiration, the water extraction in the soil profile must be monitored with at least 16 TDR probes installed at a minimum distance of 0.9 m and a minimum depth of 0.7 m.

O conhecimento acurado da percolação de água no solo é crucial para resolução de problemas de drenagem, recarga e poluição de aquíferos subterrâneos. O objetivo deste trabalho foi avaliar a percolação estimada com TDR em lisímetro de drenagem. Utilizou-se da Lei de Darcy com funções K(θ) determinadas por métodos de campo e laboratório, bem como pela variação de armazenagem de água no perfil do solo com 16 pontos de medidas de umidade em diferentes intervalos de tempo. Um solo de textura argiloarenosa foi saturado e coberto com lona plástica para evitar a evaporação, procedendo-se um ensaio de drenagem interna em um lisímetro de drenagem. A avaliação da relação entre os valores de percolação estimados e observados foi feita mediante análise de regressão linear. Os resultados sugerem que a estimativa da percolação em nível de campo ou laboratório pode ser realizada a partir do monitoramento contínuo e em curtos intervalos de tempo da variação de armazenagem de água no solo com TDR. Esse método apresentou precisão e acurácia próxima a de lisímetro e algumas vantagens sobre os demais avaliados, como a possibilidade de estimativas de percolação em curtos intervalos de tempo e a não necessidade da predeterminação de propriedades hidráulicas do solo como curva de retenção e condutividade hidráulica. Verificou-se que o uso da equação de Darcy-Buckingham para estimativa das lâminas de percolação com uso da função K(θ) predita pelo método de Hillel et al. (1972) proporcionou estimativas de percolação de água com valores compatíveis aos obtidos no lisímetro de drenagem para intervalos de tempo maior que 1 h. Os métodos de Libardi et al. (1980), Sisson et al. (1980) e van Genuchten (1980) subestimaram os valores de percolação de água estimados.

Detailed knowledge on water percolation into the soil in irrigated areas is fundamental for solving problems of drainage, pollution and the recharge of underground aquifers. The aim of this study was to evaluate the percolation estimated by time-domain-reflectometry (TDR) in a drainage lysimeter. We used Darcy's law with K(θ) functions determined by field and laboratory methods and by the change in water storage in the soil profile at 16 points of moisture measurement at different time intervals. A sandy clay soil was saturated and covered with plastic sheet to prevent evaporation and an internal drainage trial in a drainage lysimeter was installed. The relationship between the observed and estimated percolation values was evaluated by linear regression analysis. The results suggest that percolation in the field or laboratory can be estimated based on continuous monitoring with TDR, and at short time intervals, of the variations in soil water storage. The precision and accuracy of this approach are similar to those of the lysimeter and it has advantages over the other evaluated methods, of which the most relevant are the possibility of estimating percolation in short time intervals and exemption from the predetermination of soil hydraulic properties such as water retention and hydraulic conductivity. The estimates obtained by the Darcy-Buckingham equation for percolation levels using function K(θ) predicted by the method of Hillel et al. (1972) provided compatible water percolation estimates with those obtained in the lysimeter at time intervals greater than 1 h. The methods of Libardi et al. (1980), Sisson et al. (1980) and van Genuchten (1980) underestimated water percolation.

Em razão da dificuldade em se estimar a percolação de água em solos não saturados, realizou-se este trabalho com o objetivo de examinar a estimativa da percolação de água, utilizando TDR. Em dois lisímetros de drenagem com solos de texturas diferentes, instalaram-se sondas de TDR para formar baterias de monitoramento de água compostas por diferentes números de sondas. Os solos foram saturados e cobertos com lona plástica para evitar a evaporação. Assim, procedeu-se a um ensaio de drenagem interna, utilizando-se de uma TDR 100 programada para realizar leituras de constante dielétrica a cada 15 min. Para testar a adequação dos valores de laminas de percolação estimada pela TDR aos valores observados na coleta de drenos dos lisímetros de drenagem, utilizou-se do teste da hipótese da nulidade conjunta com 5 % de probabilidade. O incremento da quantidade de sondas no perfil de monitoramento de água aproximou os valores das laminas de percolação estimada por TDR aos valores das laminas observadas nos lisímetros. A definição do número de sondas necessárias para o monitoramento de água com fins de estimar a percolação por TDR depende das propriedades físicas do solo. Para solos de textura argiloarenosa, três baterias com quatro sondas às profundidades 0,10; 0,30; 0,50; e 0,70 m a 0,20; 0,40; e 0,60 m do centro do lisímetro são suficientes para estimar a percolação equivalente à observada. Em solos de textura areia-franca, não há equivalência entre as laminas de percolação estimadas e observadas, mesmo para quatro baterias de quatro sondas cada, nas profundidades 0,10; 0,30; 0,50; e 0,70 m.

Due to the difficulty of estimating water percolation in unsaturated soils, the purpose of this study was to estimate water percolation based on time-domain reflectometry (TDR). In two drainage lysimeters with different soil textures TDR probes were installed, forming a water monitoring system consisting of different numbers of probes. The soils were saturated and covered with plastic to prevent evaporation. Tests of internal drainage were carried out using a TDR 100 unit with constant dielectric readings (every 15 min). To test the consistency of TDR-estimated percolation levels in comparison with the observed leachate levels in the drainage lysimeters, the combined null hypothesis was tested at 5 % probability. A higher number of probes in the water monitoring system resulted in an approximation of the percolation levels estimated from TDR - based moisture data to the levels measured by lysimeters. The definition of the number of probes required for water monitoring to estimate water percolation by TDR depends on the soil physical properties. For sandy clay soils, three batteries with four probes installed at depths of 0.20, 0.40, 0.60, and 0.80 m, at a distance of 0.20, 0.40 and 0.6 m from the center of lysimeters were sufficient to estimate percolation levels equivalent to the observed. In the sandy loam soils, the observed and predicted percolation levels were not equivalent even when using four batteries with four probes each, at depths of 0.20, 0.40, 0.60, and 0.80 m.

Further food production may be limited by the reduced availability of water resources. Since irrigated agriculture is the productive sector that presents a higher demand of water, this sector has been under intense pressure in order to ensure food production with improved efficiency of water use. This study aimed to use the Time Domain Reflectometry (TDR) technique to measure percolation losses and to determine water application efficiency of banana (Musa spp.) trees using microsprinkler irrigation systems. Three systems were studied: (i) one 32 L h-1 microsprinkler for four plants; (ii) one 60 L h-1 microsprinkler for four plants; and (iii) one 60 L h-1 microsprinkler for two plants. Systems that replace water to the soil with the lowest variation of infiltrated water depths at different distances from plant pseudostem were the most efficient. The water application efficiency of microsprinkler irrigation systems using the (i), (ii), and (iii) microsprinkler systems were 85%, 80 % and 90 % respectively.

O objetivo deste trabalho foi avaliar a distribuição de água e raízes de bananeira (Musa sp.) irrigada, para determinar a eficiência de aplicação de água por diferentes sistemas de irrigação por gotejamento. Foram estudados três sistemas de gotejamento: T1, dois emissores de 4 L h-1 por planta; T2, quatro emissores de 4 L h-1 por planta; e T3, cinco emissores de 4 L h-1 por planta. Os emissores foram dispostos em uma linha lateral. No tratamento T3, os emissores formaram uma faixa contínua. A área de cultivo foi plantada com bananeira cultivar BRS Tropical com espaçamento de 3 m entre fileiras e de 2,5 m entre plantas. Dados de umidade e comprimento de raízes foram coletados durante o primeiro ciclo da cultura, em cinco distâncias radiais e profundidades, em uma malha vertical de 0,20x0,20 m. O solo da área experimental era um Latossolo Amarelo franco-argilo-arenoso. Os dados de umidade foram coletados em intervalos de 10 min por um período de cinco dias com uso de sondas de TDR. A eficiência de aplicação de água foi de 83, 88 e 92% para os sistemas com dois, quatro e cinco emissores por planta, respectivamente. O incremento no número de emissores na linha lateral promove melhor distribuição radicular, maior extração de água e menores perdas por percolação profunda.

The objective of this work was to evaluate root and water distribution in irrigated banana (Musa sp.), in order to determine the water application efficiency for different drip irrigation emitter patterns. Three drip emitter patterns were studied: two 4-L h-1 emitters per plant (T1), four 4-L h-1 emitters per plant (T2), and five 4-L h-1 emitters per plant (T3). The emitters were placed in a lateral line. In the treatment T3, the emitters formed a continuous strip. The cultivated area used was planted with banana cultivar BRS Tropical, with a 3-m spacing between rows and a 2.5-m spacing between plants. Soil moisture and root length data were collected during the first production cycle at five radial distances and depths, in a 0.20x0.20 m vertical grid. The experiment was carried out in a sandy clay loam Xanthic Hapludox. Soil moisture data were collected every 10 min for a period of five days using TDR probes. Water application efficiency was of 83, 88 and 92% for the systems with two, four and five emitters per plant, respectively. It was verified that an increase in the number of emitters in the lateral line promoted better root distribution, higher water extraction, and less deep percolation losses.