Abelardo A. A. Montenegro

Improving agricultural water management in the semi-arid region of Brazil: experimental and modelling study

Agricultural practice in the semi-arid region of Brazil is highly dependant on irrigation. As access to water is limited in the region, there is a need to guarantee its efficient use, especially in small-scale farming schemes. Models adequately calibrated for semi-arid conditions and for typical crops are useful tools for analysis of on-farm strategies to improve water use efficiency. A physically based agrohydrological model, SALTMED, is calibrated and validated for carrots (Daucus carota L., Brasília variety) and cabbage (Brassica oleracea var. capitata), two of the main crops in small-scale irrigated agriculture in the northeast of Brazil. SALTMED is also calibrated for castor beans (Ricinus communis L.) under rainfed conditions. The results demonstrated the suitability of the SALTMED model for simulating soil water dynamics and crop yield in the area. Predicted time series of soil water content and matric potential of root zone showed good agreement with observed values, as shown graphically and statistically. Using the calibrated and validated model, management scenarios were analysed in terms of applied irrigation water, irrigation frequency, soil and crop types. Impact of climate change on the irrigation water requirements was also briefly analysed for possible changes in annual temperature using two different emission scenarios. Analysis of possible impact of climate change on temperature related to two emission scenarios on the area showed an increase around 11% of the crop water requirement for carrots and cabbage, for the low emission scenario, and around 17% for the high emission scenario. The analysis of management scenarios indicated possible over-irrigation in the area. The simulation showed that the deficit irrigation was a useful water-saving strategy for the region. The simulations also indicated that irrigation frequency affected crop water use and differed according to the soil type.

FITORREMEDIAÇÃO DE SOLO SALINO SÓDICO POR Atriplex nummularia E GESSO DE JAZIDA (1)

The cultivation of Atriplex nummularia on saline-sodic soils is economically attractive because it can be used as a forage crop as well as in landscape projects. The potential of Atriplex nummularia for phytoextraction of Na+ from a saline-sodic soil irrigated with saline water was evaluated. Additionally, gypsum was tested for improving phytoremediation. The experiment was set up as a randomized block design, in a 2 x 3 factorial scheme. The treatments consisted of: no gypsum and 50 % of the regularly recommended gypsum dose, and three salinity levels of irrigation water: C1 = 175 μS cm -1; C2 = 500 μS cm -1; C3 = 1,500 μS cm -1. The Na concentration in plant tissues and soil were evaluated 40, 70, 100 and 130 days after A nummularia transplanting. The results showed that there was a 96 % increase in root dry matter as a result of gypsum application. Sodium accumulation in shoots increased significantly in the third (90.1 g kg-1) and fourth (109.7 g kg-1) sampling period. This effect was magnified by gypsum application. After 100 days, the soil Na+ content had decreased by 31 and 26 %, with and without gypsum addition, respectively. Our results indicate that A. Nummularia is a Na+ accumulator species. Gypsum was effective as a phytoextraction enhancer. A. nummularia irrigation aiming at Na phytoremediation is possible with saline water varying from 175 to 1,500 μS cm-1.

Desempenho de lisímetro de pesagem hidráulica de baixo custo no semi-árido nordestino

Direct evapotranspiration measurements are important to the calibration of indirect methods. The performance of a low cost hydraulic weighing lysimeter was evaluated, aiming to estimate the reference evapotranspiration (ETo) in a settlement area in the Semi Arid Brazilian northeast. The lysimeter presents a simplified design, with loading cells of butyl internally covered with nylon, connected to a manometric system with mercury and water. The lysimeter equilibrium was stable, with the largest positional average error of 3.93%. Calibrations produced correlation coefficients higher than 0.9993, and reading resolutions between 0.095 and 0.134 mm. Lysimeter readings were compared to ETo estimate Penman-Monteith, Blaney-Criddle FAO, Jensen-Haise, and Class A methods. Additionally, the performance of a simplified evaporimetric tank was evaluated, built with recycled material, which has been used for irrigation management in communal areas. All the considered methods produced good results, well correlated to the readings from the lysimeter, for the studied period.

Umidade do solo no semiárido pernambucano usando-se reflectometria no domínio do tempo (TDR)

Present study aimed to investigate the temporal variability of surface water content in soil by time domain reflectometry (TDR), as consequence of precipitation characteristics of Pernambuco semiarid, studying such dynamics under different types of the soil cover. The study was conducted in a slope of a representative catchment, in a Typic Hapludalf soil, where four experimental plots were installed with two TDR probes for soil moisture investigation as well as monitoring the runoff. Treatments were natural cover (CN), bare soil (SD), cactus (P) and microdams associated with mulch (B + CM). From the results obtained during a period with erosive rainfall, it was found that soil moisture observed during the experimental period showed high variability in time, related to different types of coverage and soil properties. Mulching was the most appropriate conservation practice for maintaining soil moisture.

Variabilidade espacial de atributos físicos em solos de vale aluvial no semiárido de Pernambuco 1

Soil physical and hydraulic characteristics are relevant for agricultural management, particularly at irrigation districts. The objective of this study was to evaluate the spatial variability of physical attributes of soil in an alluvial valley in the semiarid region of Pernambuco State, at the Ipanema River Watershed. Statistical techniques and geostatistics were applied to observe the degree of dependence and the spatial variability of soil physical properties, in plots adopted for communal agriculture. The coefficient of variation for the hydraulic conductivity was high, medium for soil resistance to root penetration and for sand, clay and silt. For bulk density, particle density and porosity, however, such coefficient was low. Spatial dependence structures were investigated, with ranges spanning from 135 m, for soil hydraulic conductivity, to 465 m, for silt content. Contour map was produced by kriging interpolation, representing the spatial variability of hydraulic conductivity, which showed moderate spatial dependence. Resistance to root penetration, soil density and particle distribution presented spatial random behavior, for the adopted spatial scale. It was possible to identify regions with higher agricultural potential. From the produced map, it was highlighted that loam soils usually present higher resistance to root penetration, and low hydraulic conductivity.

Características hidráulicas e perdas de solo e água sob cultivo do feijoeiro no semi-árido

The semiarid zone presents scarce and irregular rainfall with frequent droughts, with the occurrence of high intensity events being usual. The soils are shallow and stony, which limits regular agriculture practice, usually reducing productivity and turning this environment susceptible to erosion. The objective of this study was to evaluate the influence of conservation practices, under bean crop, upon soil and water losses by the hydric erosion, in a Fluvic Neossol in the semiarid zone, with rainfed crop. Simulated rainfall has been applied with 60 mm h-1 intensity under the following treatments: cultivation in contour lines (N1) with rock barriers between each row of plantation, spacing 0.5 m; cultivation in contour lines (N2) with rock barriers between each row of plantation, spacing 1.0 m; downslope cultivation (DS); cultivation in contour lines with mulch cover (MC), using bean straws; cleared bare soil (CB) and natural covering (CN). Among the used treatments, the mulch cover option allowed, on average, a soil loss reduction of 86.91% in relation to the plot with cleared bare soil, with values close to the ones for the ideal condition of covering, which is the natural condition, during whole crop cycle.

Avaliação de parâmetros hidráulicos e manejo da irrigação por microaspersão em área de assentamento

: Este trabalho foi desenvolvido em solo aluvial do semi-arido de Pernambuco, suscetivel asalinizacao, visando a orientar agricultores de assentamento para instalar, avaliar e manejarracionalmente sistemas de irrigacao por microaspersao, para atender ao plantio da cultivar de repolhoMidori. Adotando-se percentagem de area molhada igual a 100%, foram avaliados nos setores daunidade operacional a variacao de vazao e pressao, os coeficientes de uniformidade (CU) e a eficienciade aplicacao (EA). A uniformidade da irrigacao apresentou valores elevados, superiores a 93%. Aeficiencia de aplicacao foi boa, com valores maiores que 80%. O sistema foi entao utilizado nairrigacao, utilizando como controle o tanque “Classe A”, durante um periodo de 75 dias, e conduzidopor um agricultor local. Considerando os riscos de salinizacao na area, promoveu-se lavagem continuado solo. Foi adotado um coeficiente de lixiviacao medio de 1,21, com desvio-padrao de 0,45, para operiodo sem precipitacao. Praticamente em todo o experimento, o sentido do gradiente de potencialtotal da agua do solo foi ascendente, com media de 1,14 e 0,21 de desvio-padrao. Preveniu-se com issoa ocorrencia de ascensoes capilares, estabelecendo-se um perfil drenante, bem como se manteve acondutividade eletrica da zona saturada em equilibrio. Nao foi observada a saturacao do solo na zonaradicular.

Mapping Soil Surface Macropores Using Infrared Thermography: An Exploratory Laboratory Study

Macropores and water flow in soils and substrates are complex and are related to topics like preferential flow, nonequilibrium flow, and dual-continuum. Hence, the quantification of the number of macropores and the determination of their geometry are expected to provide a better understanding on the effects of pores on the soils physical and hydraulic properties. This exploratory study aimed at evaluating the potential of using infrared thermography for mapping macroporosity at the soil surface and estimating the number and size of such macropores. The presented technique was applied to a small scale study (laboratory soil flume).

Variabilidade espaço-temporal da condutividade elétrica da água subterrânea na região semiárida de Pernambuco

RESUMO Quando mal-conduzida, a irrigacao pode causar degradacao dos solos e da agua subterrânea, por potencializar o risco de salinizacao. Este problema e mais evidente em regioes semiaridas, nas quais as caracteristicas fisico-climaticas contribuem para seu agravamento. Uma das variaveis mais utilizadas para avaliar a concentracao de sais soluveis na agua de irrigacao e no solo, e a condutividade eletrica. Neste trabalho, buscou-se avaliar a variabilidade espacial e temporal da condutividade eletrica da agua subterrânea utilizada para irrigacao em um assentamento rural, no semiarido pernambucano. Tecnicas estatisticas descritivas e geoestatisticas foram aplicadas para identificacao dos padroes de variabilidade e dependencia espacial da condutividade eletrica, visando ao mapeamento da salinidade da agua subterrânea. Verificou-se que a condutividade eletrica possui variabilidade media a alta, com dependencia espacial moderada, em que a textura do solo e o regime pluviometrico influenciam na variacao espacial e temporal da condutividade eletrica, que vem aumentando ao longo dos anos, na area estudada.

Caracterização física e hidráulica de solos em bacias experimentais do semiárido brasileiro, sob manejo conservacionista

For the study involving the water movement in soil, it becomes imperative to know their physical and hydraulic properties and their correlations. Both are of fundamental importance in the storage and transport of water and nutrients and in controlling infiltration, being influenced by the conditions of the soil surface. In this context, this study aimed to perform physical and hydraulic characterization of the soil in two experimental basins (Jatoba and Mimoso/Pesqueira, PE), in the brazilian semiarid, at different depths and vegetation cover conditions (natural vegetation, bare soil, cultivation downhill, palm contour and stone micro walls with mulching). High variability of hydraulic conductivity was observed in layers up to 50 cm. Besides this there was a decrease in sand content, organic matter, and hydraulic condutivity with depth, the soil profile in the studied basins. On the other hand, with respect to different vegetation cover, it was observed that there was no significant difference in mean hydraulic conductivity among the different evaluated conservation treatments, for the analysed depths.