Dipartimento di Economia e Sistemi Arborei

Sezione di AgroEcosistemi Arborei

Pubblicazioni Scientifiche

Titolo dell'articolo Model for estimating evaporation and transpiration from row crops
Anno di pubblicazione 2001
ISSN: 0733-9437
N Volume 127
Pagine 339 - 345
Abstract Accurate estimates of crop evapotranspiration (ETc), that quantify the total water used by a crop, are needed to optimize irrigation scheduling for horticultural crops and to minimize water degradation. During early growth, accurate assessments of ETc are difficult in vegetable crops because of high soil evaporation due to frequent irrigation. A model to estimate ETc for vegetable crops, using only daily reference evapotranspiration data as an input parameter, was developed. It calculates crop transpiration and soil evaporation based on ground cover and daily radiation intercepted by the canopy. The model uses a two-stage soil evaporation method adapted to conditions of variable reference evapotranspiration. The model was evaluated against data using measurements from two seasons of lettuce crop, two tomato fields in the same season, and one season of broccoli crop production. Using all of the crop data, the root-mean-square error for measured versus modelled daily ETc was 0.72 mm/day, indicating that the model works well

Titolo dell'articolo Temperature Data for Phenological Models
Anno di pubblicazione 2001
ISSN: 0020-7128
N Volume 45
Pagine 178 - 183
Abstract In an arid environment, the effect of evaporation on energy balance can affect air temperature recordings and greatly impact on degree-day calculations. This is an important consideration when choosing a site or climate data for phenological models. To our knowledge, there is no literature showing the effect of the underlying surface and its fetch around a weather station on degree-day accumulations. In this paper, we present data to show that this is a serious consideration, and it can lead to dubious models. Microscale measurements of temperature and energy balance are presented to explain why the differences occur. For example, the effect of fetch of irrigated grass and wetting of bare soil around a weather station on diurnal temperature are reported. A 43-day experiment showed that temperature measured on the upwind edge of an irrigated grass area averaged 4% higher than temperatures recorded at 200 m inside the grass field. Using the single triangle method and with a 10oC threshold and starting on May 19, the station on the upwind edge reached 900 degree days on June 28, whereas the interior station reached 900 degree-days on July 1. Clearly, a difference in fetch can lead to big errors for large degree-day accumulations. Immediately after wetting, the temperature over a wet soil surface was similar to that measured over grass. However, the temperature over the soil increased relative to over the grass as the soil surface dried. Therefore, the observed temperature difference over bare soil and grass increases with longer periods between wettings. In most arid locations, measuring temperature over irrigated grass gives lower mean annual temperature, resulting in lower annual cumulative degree-days. This was verified by comparing over grass and over-bare-soil measurements from several weather stations in a range of climates. To eliminate the effect of rainfall frequency, using temperature data collected only over irrigated grass is recommended for long term assessment of climate change effects on degree-day accumulation. In high evaporative conditions, a fetch of at least 100 m of grass is recommended. Our results clearly indicate that weather stations sited over bare soil have consistently higher degree-day accumulations. Therefore, especially in arid environments, phenology models based on temperature collected over bare soil are not transferable to those based on temperature recorded over irrigated grass. At a minimum, all degree-day based phenology models reported in the literature should clearly describe the weather station site.

Autore/i dell'articolo CESARACCIO C; SPANO D; DUCE P; SNYDER R. L
Titolo dell'articolo An improved model for determining degree-day values from daily temperature data
Anno di pubblicazione 2001
ISSN: 0020-7128
N Volume 45
Pagine 161 - 169
Abstract Although using hourly weather data offers the greatest accuracy for estimating growing degree-day values, daily maximum and minimum temperature data are often used to estimate these values by approximating the diurnal temperature trends. This paper presents a new empirical model for estimating hourly mean temperature. The model describes the diurnal variation using a sine function from the minimum temperature at sunrise until the maximum temperature is reached, another sine function from the maximum temperature until sunset, and a square-root function from then until sunrise the next morning. The model was developed and calibrated using several years of hourly data obtained from five automated weather stations located in California and representing a wide range of climate conditions. The model was tested against an additional data-set at each location. The temperature model gave good results, the root-mean-square error being less than 2.0C for most years and locations. The comparison with published models from the literature showed that the model was superior to the other methods. Hourly temperatures from the model were used to calculate degree-day values. A comparison between degree-day estimates from the model and those obtained from other selected methods is presented. The results showed that the model had the best accuracy in general regardless of the season.

Autore/i dell'articolo MULAS M; CAULI E; FRANCESCONI A.H.D
Titolo dell'articolo Advances in the study of wild olive genetic resources
Anno di pubblicazione 2002
ISSN: 0567-7572
N Volume 586
Pagine 121 - 123
Abstract A study of the wild olive (Olea europaea L. var. oleaster Hoff. et Lk.) genetic resources widely spred in Sardinia was carried out to evaluate their potential use for cultivated olive breeeding. General morphological and ecological observations of 74 mother plants were performed in situ. The following biometrical characters were determined on shoot samples: fruit-bearing shoot and internode length; number of inflorescences and fruit per shoot; number of secondary ramifications and small leaves per inflorescence; and inflorescence, leaf, fruit and seed size. Rooting ability of softwood cuttings and in vitro seed germinability were also evaluated. High variability for many of the studied traits was observed, which represents a good availability of genetic resources for breeding.

Autore/i dell'articolo MULAS M; FRANCESCONI A. H.D; PERINU B
Titolo dell'articolo Myrtle (Myrtus communis L.) as a new aromatic crop: cultivar selection.
Anno di pubblicazione 2002
ISSN: 1049-6475
N Volume 9(2/3)
Pagine 127 - 131
Abstract Myrtus communis L. (Myrtaceae) is a typical shrub of the Mediterranean maquis which grows spontaneously in Sardinia. It is used in the drug, perfume and food industries. Intensive myrtle cultivation systems should be developed. In order to assure both a constant supply of good quality material for the liqueur industry and the preservation of natural myrtle populations. Cultivar selection is essential for the successful cultivation of this new aromatic crop and has been the main goal of our research. The main morphological and phenological characters of 16 cultivars selected for fruit and biomass production are presented here.

Autore/i dell'articolo BARBERIS A; DETTORI S; FILIGHEDDU M.R
Titolo dell'articolo Management problems in Mediterranean cork oak forests: post-fire recovery
Anno di pubblicazione 2003
Rivista JOURNAL OF ARID ENVIRONMENTS (Impact Factor: .596)
ISSN: 0140-1963
N Volume 54
Pagine 565 - 569
Abstract The objective of this paper is to present the results of a long-term research project carried out in north-east Sardinia, which aims to evaluate the effects of three different kinds of forest management (traditional trunk coppicing, branch pruning, and no sylvicultural practice) on the post-fire recovery of a cork oak (Quercus suber L.) stand. The most and the least effective forestry operations appeared to be traditional trunk coppicing and the branch pruning, respectively. Where traditional trunk coppicing is considered strictly necessary, the opportunity of thinning some of the new suckers should be carefully considered, as modern harvesting techniques should be combined with appropriate strategies to protect the soil from erosion.

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