L. H. Bassoi

Contribution of water content and bulk density to field soil penetration resistance as measured by a combined cone penetrometer–TDR probe

Abstract Soil strength as measured by cone penetrometers depends on several parameters, but it is mostly affected by the soil water content ( θ ) and bulk density ( ρ ). In order to better understand the effect of the water content and bulk density on soil strength we developed a combined penetrometer–coiled TDR probe to determine simultaneously the depth distribution of penetration resistance and water content in a soil profile. Field experiments carried out for a Yolo soil allowed the fitting of the effect of θ and ρ using a combined power–exponential equation. Using the combined cone penetrometer–TDR probe data, the fitted equation may be used to estimate soil bulk density.

Grapevine root distribution in drip and microsprinkler irrigation

ABSTRACT: Grape ( Vitis vinifera L.) yield and its quality are dependent of the status of the root system.Root distribution information is also valuable for soil and water management. An analysis of methods toevaluate the root distribution of grapevines for both, drip and microsprinkler irrigation in a Typic Acrustoxis presented for the table grape cv. Italia grafted on the rootstock IAC-313, in northeastern Brazil. Measuredroot parameters using the monolith method were root dry weight (D w ) and root length density (L v ), while rootarea (A p ) was estimated using the soil profile method in combination with digital image analysis. For bothirrigation systems, roots were present to the 1 m soil depth and extended laterally to 1 m distance from thetrunk, but grapevines irrigated by microsprinkler showed greater root presence as the distance from the trunkincreased. Values of A p were reasonably well correlated to D w and L v . However, correlation values werehigher when fractional root distribution was used. The soil profile method in combination with image analysistechniques, allows proper grapevine root distribution evaluation.Key words:

Economic impacts of regional water scarcity in the Sao Francisco River Basin, Brazil: an application of a linked hydro-economic model

This paper presents a linked hydro-economic model and uses it to examine the regional effects of water use regulations and product price changes on the agriculture of the Sao Francisco River Basin, Brazil. The effects of weather on surface water availability are explicitly addressed using the hydrological model MIKE-Basin. Farmers’ adjustments to changes in precipitation, surface water availability, and other factors are quantified using an economic model based on non-linear programming techniques. The models are externally linked. Results show that regional impacts, at the sub-basin level, vary depending on the location of each sub-basin relative to river flows. The effects of water use regulations and of exogenous price shocks on agriculture depend on weather, location, product mix and production technology. Implications of these results for policies designed to manage agriculture and water use are discussed.

Soil moisture calibration of TDR multilevel probes

Time domain reflectometry (TDR) probes are increasingly used for field estimation of soil water content. The objective of this study was to evaluate the accuracy of the multilevel TDR probe under field conditions. For this purpose, eight such TDR probes were installed in small plots that were seeded with beans and sorghum. Data collection from the probes was such that soil moisture readings were automated and logged using a standalone field unit. Neutron probe measurements were used to calibrate the TDR probes. Soil-probe contact and soil compaction were critical to the accuracy of the TDR, especially when a number of TDR probes are combined for a single calibration curve. If each probe is calibrated individually, approximate measurement errors were between 0.005 and 0.015 m3 m-3. However, measurement errors doubled to approximately 0.025 to 0.03 m3 m-3, when TDR probes were combined to yield a single calibration curve.

Water relations of field-grown grapevines in the São Francisco Valley, Brazil, under different rootstocks and irrigation strategies

ABSTRACT: There is an increased demand for high quality winegrapes in the Sao Francisco Valley, anew wine producing area in Brazil. As the grape quality is closely linked to the soil water status,understanding the effects of rootstock and irrigation management on grapevine water relations isessential to optimize yield and quality. This study was carried out to investigate the effects of irrigationstrategies and rootstocks on water relations and scion vigour of field-grown grapevines in Petrolina,Pernambuco state, Brazil. The cultivars used as scions are Moscato Canelli and Syrah, both graftedonto IAC 572 and 1103 Paulsen rootstocks. The following water treatments were used: deficit irrigation,with holding water after veraison; and partial root-zone drying, supplying (100% of cropevapotranspiration) of the water loss to only one side of the root system after fruit set, alternating thesides periodically (about 24 days). In general, all treatments had values of pre-dawn leaf water potentialhigher than –0.2 MPa, suggesting absence of water stress. The vine water status was more affectedby rootstock type than irrigation strategies. Both cultivars grafted on IAC 572 had the highest valuesof midday leaf water potential and stem water potential, measured on non-transpiring leaves, whichwere bagged with both plastic sheet and aluminum foil at least 1 h before measurements. For bothcultivars, the stomatal conductance

Assessing agriculture–water links at the basin scale: hydrologic and economic models of the São Francisco River Basin, Brazil

This article uses a basin-wide hydrologic model to assess the hydrologic and economic effects of expanding agriculture in the São Francisco River Basin, Brazil. It then uses a basin-wide economic model of agriculture to examine the effects of implementing water use regulations. Preliminary results suggest that substantially expanding agriculture would put pressure on some of the rivers environmental flows. Agricultural output and rural employment would increase, though not in spatially uniform ways. The economic model demonstrates how cropping area, crop mix and production technology respond simultaneously to water shortages. While farmers can adjust, the costs of doing so may be beyond the reach of resource-poor farmers.

Guidelines for irrigation scheduling of banana crop in São Francisco Valley, Brazil . II - Water consumption, crop coefficient, and physiologycal behavior

The water consumption and the crop coefficient of the banana cv. Pacovan were estimated in Petrolina County, northeastern Brazil, in order to establish guidelines to irrigation water management. Evaluations were carried out since planting in January 1999 to the 3rd harvest in September 2001 on a microsprinkler irrigated orchard, with plants spaced in a 3 x 3 m grid. Average daily water consumption was 3.9, 4.0, and 3.3 mm in the 1st, 2nd and 3rd growing seasons, respectively. Crop coefficient values increased from 0.7 (vegetative growth) to 1.1 (flowering). Even with high soil water availability, transpiration was reduced due to high evaporative demand.

Root distribution of irrigated grapevine rootstocks in a coarse texture soil of the São Francisco Valley, Brazil

An experiment was carried out to determine the root distribution of four grapevine rootstocks (Salt Creek, Dogridge, Courdec 1613, IAC 572) in a coarse texture soil of a commercial growing area in Petrolina County, Sao Francisco Valley, Brazil. Rootstocks were grafted to a seedless table grape cv. Festival, and irrigated by microsprinkler. Roots were quantified by the trench wall method aided by digital image analysis. Results indicated that roots reached 1 m depth, but few differences among rootstocks were found. All of them presented at least 90 % of the roots distributed until 0.6 m depth, with a greater root presence in the first 0.4 m. The upper 0.6 m can be taken into account as the effective rooting depth for soil and water management.

Soil spatial variability and the estimation of the irrigation water depth

A influencia da variabilidade espacial da umidade do solo em uma situacao pre-irrigacao e da capacidade de campo e avaliada no calculo da lâmina de irrigacao. O experimento constou de cultura de feijao (Phaseolus vulgaris L.) estabelecida em um ARGISSOLO da regiao de Piracicaba, SP, irrigada por pivo central, tendo as medidas de umidade sido feitas com sonda de neutrons, em uma malha de 20x4 pontos, espacados de 0.5 m. Em determinada situacao, os 80 valores de lâmina de irrigacao calculados apresentaram um coeficiente de variacao de 29.3%, para uma media de 18 mm, com valor minimo de 9 mm e maximo de 41mm. E concluido que a unica forma pratica de irrigacao e o uso de uma lâmina media devido a variabilidade inerente ao solo, e que a procura de melhores valores para a capacidade de campo nao implica em melhores estimativas da lâmina de irrigacao.

Assessment on nutrient levels in the aerial biomass of irrigated guava in São Francisco Valley, Brazil

A aplicacao de fertilizantes em culturas perenes baseia-se na reposicao das quantidades de nutrientes removidas pelos frutos, mas a imobilizacao de nutrientes deve ser tambem considerada. Assim, foram determinadas as concentracoes de nutrientes nas folhas e nos frutos da goiabeira cv.Paluma, irrigada, em Petrolina-PE, bem como as quantidades de nutrientes removidas pelos frutos e pela poda de frutificacao do ciclo seguinte. Entre os macronutrientes, o N e o K foram os mais removidos pelos frutos, enquanto o Fe , o Zn e Mn apresentaram maiores valores entre os micronutrientes. No minimo, 60% das quantidades totais de N,P,K,Fe e B removidas pela poda estavam imobilizadas na folha e no fruto nao-comerciavel.