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Assessment of vine development according to available water resources by using remote sensing in La Mancha, Spain
Agricultural Water Management 40 (1999) 363±375
Assessment of vine development according to available water resources by using remote sensing in La Mancha, Spain F.J. Monteroa,*, J. MeliaÂb, A. Brasaa, D. Segarrab, A. Cuestaa, S. Lanjerib a
Department of Plant Production and Agricultural Technology, ETS Ingenieros Agronomos, University of Castilla-La Mancha, 02071, Albacete, Spain b Department of Thermodynamics, Facultad de Fisica, University of Valencia, Burjassot, 46100, Valencia, Spain
Abstract The relevance of growing vines under semiarid conditions is universally accepted because of its impacts on social, economic and environmental aspects. Improving the knowledge of the soil± plant±atmosphere system related to the expression of vine growth allows the study of vine cover in wide areas. Several aspects of vine growing under semiarid conditions, related to weather, soil, and plant cover are analysed in this paper. Once the ground truth is achieved, multitemporal studies by remote sensing are especially useful for vine growth monitoring. The purpose of this work is focussed on determining changes of vine cover development according to available water resources in relation to present remote sensing methods. The method is based on using multitemporal masking classification techniques based on the ground truth knowledge achieved during previous research. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Vine; Development; Remote sensing
1. Introduction The relevance of growing vines under semiarid conditions is universally accepted because of its impacts on social, economic and environmental aspects. Vine is the most common woody crop in Castilla-La Mancha, Spain, alternating high and low in harvest over the years, due to the pressing environmental influence on the one hand, and nutrient * Corresponding author. Tel.: +34-67-599239; fax: +34-67-599238; e-mail: [email protected] 0378-3774/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 9 9 ) 0 0 0 1 0 - 4
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Table 1 World-wide distribution of vine surface, yield and production Area
Yield
Production
(million ha)
(%)
(tm/ha)
Index
(million tm)
(%)
North and Central America South America Asia Europe Spain Italy France Others
0.36 0.47 1.34 4.39 1.20 0.94 0.90 1.40
5 6 17 55 15 12 11 17
16.2 11.0 7.7 6.2 2.6 10.0 7.7 ±
2.6 1.8 1.2 1 0.4 1.6 1.2 ±
6.0 5.2 10.4 27.2 3.2 9.4 6.9 10.5
10 9 17 46 5 16 12 18
Total
7.97
100
6.8
1.1
59.3
100
Own elaboration according to MAPA, 1997.
decrease in the soil as a consequence of years with high yield, on the other. The changing environmental conditions (soil, weather and water availability) make it difficult to promote any action to regularise annual yields, which could be a solution in a sector that represents one fifth of the total regional agrarian production and spreads over 609 000 ha surface in Castilla-La Mancha (MAPA, 1997). Table 1 shows that Europe has 55% of the world surface grown with vines and 46% of the world production (MAPA, 1997). Spain, France and Italy are the most producing countries, but in the case of Spain, the yield is much lower due to historical background and determining factors, resulting in paradoxical situations within the European framework (Montero, 1996). The vine in the Mediterranean Basin is preferentially grown in dry-farming conditions, establishing a strong environmental relationship that overcomes local, regional and national borders. Improper management of dry-farming systems under semiarid conditions enhance erosion and land degradation, waste rainfall resources and give rise to rural depopulation and land abandonment. Dry farming is so far the prevailing system of growing vines in Spain and even more in Castilla-La Mancha, where nearly 99% of the grape production is devoted to wine. The soils where vines are grown do not have much depth, little water retention capacity and there are few agricultural alternatives to grow any other crop. Under these conditions, the branching habit of vine stocks is creeping, the farmer tends to plant not more than 1500 plants haÿ1, the vineyards have a small size (4 ha), and the regime of tenancy is usually own property, and the main varieties are Airen and Tempranillo (Sotes, 1992). The process of reformation of the EU Common Agricultural Policy, (CAP), is outstandingly affecting the vine and wine sector in Spain (Salinas, 1996). The actions proposed are to decrease production in farms, root out a large surface of vine stocks, sustain vine growing in marginal areas, as well as facilitating training and research to improve the added value of vine products. Most of these proposals are negatively affecting vine growing in arid and semiarid regions because the accompanying financial measures hardly compensate for the socio-economic and environmental damage caused.
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365
Vine growing plays an important role in the region of Castilla-La Mancha as a permanent plant cover in terms of protection (from erosion), sustainable use of resources (land and water), defence (against desertification), and settling population in rural areas (instead of urban unemployment). A great deal of experimental research has been carried out in Castilla-La Mancha in recent years. The regional and the national government have participated in projects and ongoing initiatives related to vine growing. From 1991 to 1995, the EU promoted the EFEDA project (ECHIVAL Field Experiment in a Desertification-threatened Area) as a part of the IV framework Programme in the field of the Environment (Bolle et al., 1993). The advances achieved by this project during the phases I and II (EPOC-CT90-0030 and EV-5V-CT93-0272), concerning the plant cover behaviour in vineyards of desertification-threatened areas (Castilla-La Mancha), pointed out two facts of enormous importance. Firstly, soil is a key element that allows enough water storage for proper vine development under conditions of high evapotranspiration, and secondly, the density and layout of vine root system enhance the plants ability to explore deeper zones looking for soil water. Under the environmental conditions of La Mancha, the behaviour of vine in terms of wine production and vegetative development must be understood as a result of the close linkage between these two facts. The exploring capability of vine roots and the soil water storage buffering capacity of the petrocalcic layer lead us to estimate that actual water available resources comprise the reserve from the last years as well as the annual rainfall. Improving the knowledge of the soil±plant±atmosphere system and its interactions allows the expression of vine growth, aiming to study the ground truth in vine areas, as a part of the research developed in the Remote Sensing of Mediterranean Desertification and Environmental Stability (RESMEDES) (ENV4-CT-95-0094) project. Multitemporal studies by remote sensing are especially useful for vine growth monitoring. The changes in vine cover development are analysed through an interannual study, which includes periods of severe drought and others with enough rainfall. The historical series of annual rainfall was analysed in the study area. 2. Materials and methods 2.1. The study area The study area selected for this work is placed near Tomelloso (UTM coordinates are 4331130 N, 30506090 E), 670 m above sea level in Castilla-La Mancha. This area covers 260 000 ha with one of the higher concentration of vineyards in the world: 130 000 ha of vines (MAPA, 1995), which implies strong social, economic and environmental dependence on the crop. Although generally soils are not extremely suitable for agricultural use, the quality of substrates highly enriched with pebbles is adequate enough for vine growing. But there exist other woody species such as olive trees, natural forests and herbaceous crops, mainly dry-farming cereals and fallow lands, which hardly reach 20% of area. The variety used in 93% of the vineyards is AireÂn, a white variety grown over 32% of the Spanish surface. The plant growth habits and techniques used provide vine shoots with a creeping
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Fig. 1. Evolution of temperatures along the year in the study area (1984±1991).
appearance invading nearby rows in the maximum growth stages, keeping the soil free from weeds. The environmental conditions of vine growing in Castilla-La Mancha, particularly soil and weather, are restrictive, forcing vines to adapt and take profit of them extraordinarily. The study site was selected according to criteria based on plant material, planting age, farming techniques, as well as other remote sensing criteria (flat relief, homogeneous soil, farm size, etc.). 2.2. Weather conditions The climate is a Mediterranean type showing high continentality, with sudden changes from cold months to warm months and high thermal oscillations in all seasons between the maximum and minimum daily temperatures. The mean annual temperature is 14.68C. July is the warmest month (26.48C) and January the coldest one (4.88C). Temperatures play an important role in the productive scheme of vineyards. Temperatures are above mean annual values in the summer period from May to September, which produces a great vegetative activity. Mean temperatures in July and August reach 258C, whilst maximum values are over 348C. Fig. 1 shows the evolution of temperatures along the year for the period 1984±1991. 2.3. Water resources The rainfall in Castilla-La Mancha is also seasonal and subject to great oscillations from one year to another. Fig. 2 shows the changes of total annual rainfall for the period 1984±1996. Years with low values can be observed between 1990 and 1995, whose average is 284 mm, together with years with higher values as in 1989 and 1996. The mean annual rainfall is 427 mm (1984±1996). The mean daily rainfall intensity is 4.2 mm dayÿ1, meaning that water is infiltrated when reaching the ground, and there is not much runoff. Fig. 3 shows the mean monthly averaged values of rainfall and evapotranspiration according to the Penman±Monteith method (Doorenbos and Pruitt, 1984), as well as the number of rain days for the period 1996±1997. The months with less precipitation are those of largest evapotranspiration and more vegetative development of vines that results
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367
Fig. 2. Annual rainfall in the study area in the period 1984±1996.
Fig. 3. Monthly values of evapotranspiration according to Penman±Monteith method, rainfall and number of rainfall days in the period 1996±1997.
in water stress negatively affecting the physiological functions of the plants, and subsequently, decreasing production. 2.4. Soil characteristics and vine root distribution The landscape is mainly flat with slight slopes, generally less that 5%. The soils are formed over limestone material, with pH values of 8, its upper horizon being poorly developed and the underlying ones presenting a content in calcium carbonate of 52% and 10% of active limestone. They contain more stones and are very suitable for growing
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Fig. 4. Schematic soil profile and root density distribution of vines in the study area.
vines. The soils belong to the calcisols groups (petric-calcisols), in terms of soil taxonomy. The presence of the petrocalcic horizon determines that vines (Vitis vinifera L.) should be planted by breaking through the impervious layer which prevents evaporation losses. Other soils present in the area are lithic and eutric-leptosols. One of the key elements to understand how vine performs under these semiarid conditions is the root system development. Fig. 4 shows the distribution of the roots in depth as a function of the distance to the vine stock in terms of root density (cm dmÿ3). Vine roots collected in cross and logitudinal sections at five depths were measured by using digital image processing and subsequently, isolines of root density were mapped by applying kriging techniques (Honrubia, 1997). 2.5. Field monitoring of vegetation parameters One of the main purposes of many recent agronomy studies is to determine the behaviour of the plant canopy. By studying and monitoring characteristic parameters of vegetation along its vegetative cycle, we can simulate its growth and development and predict its behaviour, as well as the interaction with the soil and the atmosphere around it (MartõÂn de Santa Olalla and de Juan, 1993). The plant parameters most used to monitor the plant cover and compare it with those acquired by remote sensing methods are surface cover, leaf area index (LAI), height and above-ground biomass. Besides, a monitoring of the plant development has to be defined to allow assessment of the changes of the different parameters studied along the cycle.
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369
Fig. 5. Distribution of rainfall according to the phenological stage of vines.
Baillod and Baggiolini (1993) phenology code is mostly used to monitor the vine cycle, estimating the stage by means of field sampling in different periods of the vegetative cycle. Fig. 5 shows the distribution of rainfall according to the phenological stages of the vine. It is clear that the soil is a reservoir that operates as a buffer of water availability, especially during periods of maximum evaporation. The plant parameters selected to show the development of vines were readily studied by remote sensing. Crop height (m), vine surface cover (%) and LAI (m2 mÿ2) of individual plants were measured through the different phenological stages of vine (AndreÂs et al., 1994) following statistical sampling procedures. Changes in vine cover development are analysed through an interannual study, which includes periods of drought and others with enough rainfall (see Fig. 2). The years selected to be studied are: 1991: dry year (264 mm) following a wet period (1989±1991): start of drought. 1994: dry year (214 mm) following a dry period (1992±1994): drought. 1996: wet year (511 mm) after a dry period (1994±1996): end of drought. 2.6. Remote sensing monitoring The seasonal combination of the vegetative cycle of vines and that of crops like cereals and olive trees present in the area along with natural vegetation allows us to identify the
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Fig. 6. Evolution of vine development according to the phenological cycle (Baillod and Baggiolini, 1993) in two different years (1991 and 1994), and the Landsat overpasses (1996) over the study area, outlining the period between flowering (May) and grape toning (July).
vine cover by using Landsat-5 TM images. As a result of the inventory, monitoring of its growth cycle can be undertaken. Nine images have been used in this study: five in 1991 (9 April, 27 May, 12 June, 28 June and 14 July) and four in 1996 (24 May, 25 June, 11 July and 29 September). The images were geometrically corrected following the control point method and interpolated by cubic convolution. The distance fitness with less than one pixel error ensures that all the nine images overlap. After georeferencing, all the images were radiometrically normalised to correct the atmospheric effects. The normalisation functions were obtained by relating the radiometric response of several zones of the reflectance image that were time invariant and covered the whole reflectances range in each day, to that corresponding to 9 April 1991, where the disturbing effects of the atmosphere were smaller (Segarra et al., 1997). Vineyard satellite monitoring was limited to the growing period in between May and July, when the vine plants show fastest growth. Before May the ground coverage is too small, and after July the changes are not significant. Fig. 6 states the importance of this period in remote sensing studies monitoring vine changes because of the sudden change of slope in the curves of vine development. 3. Results and discussion Fig. 7 shows the evolution curves of vine height, surface cover and LAI from ground means. It can be noticed that crop height does not seem to be affected by changes in water availability (R2 0.92), whilst vine cover (R2 0.63) and LAI (R2 0.53) show changes. It can be concluded that the growth behaviour of Airen variety in Castilla-La Mancha is limited by the water availability and its expression may be mostly linked to the above-
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371
Fig. 7. Evolution of vine height, surface cover and leaf area index, measured on the study area in 1991, 1994 and 1996.
ground biomass production. The relationship between vine cover, LAI and water availability in terms of rainfall series of mean monthly accumulated values confirms that plant growth is assured by the effect of a positive soil water balance, and less by seasonal rainfall. In order to be able to delimit the vine zones, we carried out a land use classification by using masks and supervised multitemporal classifications, removing step by step already
372
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Fig. 8. Land use classification of the study area (%) by remote sensing methods (Landsat) and by information acquired in the field (ground truth).
classified zones (Lanjeri, 1996). We also chose five training areas where the plant parameters were measured on the ground trying to keep close to dates of Landsat overpasses. Fig. 8 shows the total results calculated for each class, along with the ground truth known for the study area. Differences are due to confusion between young vineyards (younger than four years old) and fallow, as well as abandoned vineyards classified as vineyard on the ground and not so recognised on the satellite image. Multitemporal evolution of the NDVI for vine fields in 1991 at the Tomelloso field site is shown in Fig. 9, masking in white crops different from vines. Landsat TM images have been obtained for those dates more representative of the vineyard evolution. Plant parameters were related to the Normalised Difference Vegetation Index (NDVI) obtained from TM3 and TM4 band reflectances. Fig. 10 shows the relation between relevant plant parameters measured on the ground and NDVI values, showing that NDVI correlates well with LAI of individual plants through a linear relationship, since we are not close to the saturation zone expected when analysing LAI of the whole vine field. It also correlates well with vine surface cover and biomass. Since height is colinear with biomass it is not surprising that although with more scattering it correlates well with NDVI, it is much easier to measure on the ground. Plant parameters maps were produced based on the fitness functions between those parameters and NDVI. Some areas with very small values for these parameters could be explained by an irregular development of the vegetation due to external factors such as drought or spring frost.
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373
Fig. 9. Evolution of the NDVI vineyard inventory along four Landsat-5 TM images in the area of Tomelloso. The images cover the whole phenological cycle of the crop.
4. Conclusions The NDVI of vineyard varies slightly with the plant development of the crop, as can be observed from Fig. 9, due to the low cover of the vineyard. Vine cover values above 15% are very rare. Only the second half of June, with vine cover values higher than 5%, is useful for vineyard monitoring. Previous dates exhibit values of NDVI lower than 0.08 and are mainly due to the soil contribution. Moreover, in the NDVI image corresponding to 14 July 1991, there exists some areas with very small values of NDVI that could be explained by an irregular development of some vineyards due to external factors such as drought or spring frost that occurred that year. Unusually high NDVI values may be due to additional irrigation applied in some parcels leading to the development of spontaneous vegetation.
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Fig. 10. Relation between NDVI values and vegetation cover (1991, 1996), height (1991, 1996), Biomass (1991) and LAI (1996) measured in the field.
Acknowledgements The work was partly funded by the Commission of the European Communities (contracts EPOC-CT90-0030, EV5V-CT93-0272 and ENV4-CT-95-0094), by the Spanish government through CICYT contract: AMB93-1413-C05-04-CE, and by the regional government of Castilla-La Mancha. The support given by the Centre for Vine Growing Training and Research of Tomelloso is most gratefully acknowledged, as well as the comments from the editor.
References AndreÂs, M., Brasa, A., del Cerro, A., Legorburo, A., LoÂpez, F.R., MartõÂn de Santa Olalla, F., Montero, F.J., Rubio, M., 1994. VegetacioÂn. In: F. Martin de Santa Olalla (Ed.), DesertificacioÂn en Castilla-La Manch, El Proyecto EFEDA, Universidad de Castilla-La Mancha, Cuenca, pp. 143±168. Baillod, M., Baggiolini, M., 1993. Les stades reÁperes de la vigne. Rev. Suisse Vitic. Arboric. Hort. 28, 7±9.
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Bolle, H.J., Andre, J.C., ArruÂe, J.L., Barth, H.K., Bessemoulin, P., Brasa, A., De Bruin, H.A.R., Cruces, J., Dugdale, G., Engman, E.T., Evans, D.L., Fantechi, R., Fiedler, F., Van de Griend, A., Imeson, A.C., Jochum, A., Kabat, P., Kratzsch, T., Lagouarde, J.P., Langer, I., Llamas, R., Lopez-Baeza, E., Melia Miralles, J., Muniosguren, L.S., Nerry, F., Noilhan, J., Oliver, H.R., Roth, R., Saatchi, S.S., Sanchez Diaz, J., Martin de Santa Olalla, F., Shuttleworth, W.J., Sùgaard, H., Stricker, H., Thornes, H., Vauclin, M., Wickland, D., 1993. EFEDA, European field experiment in a desertification-threatened area. Annales Geophysicae 11, 173±189. Doorenbos, J., Pruitt, W.O., 1984. Crop Water Requirements. Irrigation and Drainage, Paper 24, FAO, Rome. Honrubia, F.T., 1997. DistribucioÂn espacial del sistema radicular del cultivar AireÂn en la zona de Tomelloso (Ciudad Real), Trabajo Fin de Carrera, Departamento de ProduccioÂn Vegetal y TecnologõÂa Agraria, Universidad de Castilla-La Mancha. Lanjeri, S., 1996. Estudio y seguimiento por teledeteccioÂn del vinÄedo en la zona experimental EFEDA (CastillaLa Mancha), Tesis de Licenciatura, Universidad de Valencia. MAPA, 1997. Anuario de EstadõÂstica Agraria, Ministerio de Agricultura, Pesca y AlimentacioÂn, Madrid, 710 pp. MAPA, 1995. Registro Viticola. Secretaria General de Alimentacion. Direccion General de Politica Alimentaria, Subdireccion General del Instituto Nacional de Denominaciones de Origen. Ministerio de Agricultura, Pesca y AlimentacioÂn, Madrid. MartõÂn de Santa Olalla, F., de Juan, J.A. (Eds.), 1993. AgronomõÂa del Riego, Ediciones Mundi-Prensa, Madrid, 732 pp. Montero, F.J., 1996. PanoraÂmica general. In: F. Montero (Ed.), La Vid y el Vino en Castilla-La Mancha, Junta de Comunidades de Castilla-La Mancha, Toledo, pp. 15±25.. Salinas A., 1996. El sector vitivinõÂcola regional y futuro dentro del marco europeo. In: F. Montero (Ed.), La Vid y el Vino en Castilla-La Mancha, Junta de Comunidades de Castilla-La Mancha, Toledo, pp. 145±152. Segarra, D., Lanjeri, S., Brasa, A., Montero, F., MeliaÂ, J., 1997. El vinÄedo en Castilla-La Mancha y su seguimiento mediante imaÂgenes Landsat-5 TM, VII ReunioÂn Bienal de la AsociacioÂn EspanÄola de TeledeteccioÂn, Santiago de Compostela, pp. 70±73. Sotes, V., 1992. Criterios de diferenciacioÂn, delimitacioÂn de comarcas y regiones vitivinõÂcolas. Vitivinicultura 5, 29±39.
Assessment of vine development according to available water resources by using remote sensing in La Mancha, Spain F.J. Monteroa,*, J. MeliaÂb, A. Brasaa, D. Segarrab, A. Cuestaa, S. Lanjerib a
Department of Plant Production and Agricultural Technology, ETS Ingenieros Agronomos, University of Castilla-La Mancha, 02071, Albacete, Spain b Department of Thermodynamics, Facultad de Fisica, University of Valencia, Burjassot, 46100, Valencia, Spain
Abstract The relevance of growing vines under semiarid conditions is universally accepted because of its impacts on social, economic and environmental aspects. Improving the knowledge of the soil± plant±atmosphere system related to the expression of vine growth allows the study of vine cover in wide areas. Several aspects of vine growing under semiarid conditions, related to weather, soil, and plant cover are analysed in this paper. Once the ground truth is achieved, multitemporal studies by remote sensing are especially useful for vine growth monitoring. The purpose of this work is focussed on determining changes of vine cover development according to available water resources in relation to present remote sensing methods. The method is based on using multitemporal masking classification techniques based on the ground truth knowledge achieved during previous research. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Vine; Development; Remote sensing
1. Introduction The relevance of growing vines under semiarid conditions is universally accepted because of its impacts on social, economic and environmental aspects. Vine is the most common woody crop in Castilla-La Mancha, Spain, alternating high and low in harvest over the years, due to the pressing environmental influence on the one hand, and nutrient * Corresponding author. Tel.: +34-67-599239; fax: +34-67-599238; e-mail: [email protected] 0378-3774/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 9 9 ) 0 0 0 1 0 - 4
364
F.J. Montero et al. / Agricultural Water Management 40 (1999) 363±375
Table 1 World-wide distribution of vine surface, yield and production Area
Yield
Production
(million ha)
(%)
(tm/ha)
Index
(million tm)
(%)
North and Central America South America Asia Europe Spain Italy France Others
0.36 0.47 1.34 4.39 1.20 0.94 0.90 1.40
5 6 17 55 15 12 11 17
16.2 11.0 7.7 6.2 2.6 10.0 7.7 ±
2.6 1.8 1.2 1 0.4 1.6 1.2 ±
6.0 5.2 10.4 27.2 3.2 9.4 6.9 10.5
10 9 17 46 5 16 12 18
Total
7.97
100
6.8
1.1
59.3
100
Own elaboration according to MAPA, 1997.
decrease in the soil as a consequence of years with high yield, on the other. The changing environmental conditions (soil, weather and water availability) make it difficult to promote any action to regularise annual yields, which could be a solution in a sector that represents one fifth of the total regional agrarian production and spreads over 609 000 ha surface in Castilla-La Mancha (MAPA, 1997). Table 1 shows that Europe has 55% of the world surface grown with vines and 46% of the world production (MAPA, 1997). Spain, France and Italy are the most producing countries, but in the case of Spain, the yield is much lower due to historical background and determining factors, resulting in paradoxical situations within the European framework (Montero, 1996). The vine in the Mediterranean Basin is preferentially grown in dry-farming conditions, establishing a strong environmental relationship that overcomes local, regional and national borders. Improper management of dry-farming systems under semiarid conditions enhance erosion and land degradation, waste rainfall resources and give rise to rural depopulation and land abandonment. Dry farming is so far the prevailing system of growing vines in Spain and even more in Castilla-La Mancha, where nearly 99% of the grape production is devoted to wine. The soils where vines are grown do not have much depth, little water retention capacity and there are few agricultural alternatives to grow any other crop. Under these conditions, the branching habit of vine stocks is creeping, the farmer tends to plant not more than 1500 plants haÿ1, the vineyards have a small size (4 ha), and the regime of tenancy is usually own property, and the main varieties are Airen and Tempranillo (Sotes, 1992). The process of reformation of the EU Common Agricultural Policy, (CAP), is outstandingly affecting the vine and wine sector in Spain (Salinas, 1996). The actions proposed are to decrease production in farms, root out a large surface of vine stocks, sustain vine growing in marginal areas, as well as facilitating training and research to improve the added value of vine products. Most of these proposals are negatively affecting vine growing in arid and semiarid regions because the accompanying financial measures hardly compensate for the socio-economic and environmental damage caused.
F.J. Montero et al. / Agricultural Water Management 40 (1999) 363±375
365
Vine growing plays an important role in the region of Castilla-La Mancha as a permanent plant cover in terms of protection (from erosion), sustainable use of resources (land and water), defence (against desertification), and settling population in rural areas (instead of urban unemployment). A great deal of experimental research has been carried out in Castilla-La Mancha in recent years. The regional and the national government have participated in projects and ongoing initiatives related to vine growing. From 1991 to 1995, the EU promoted the EFEDA project (ECHIVAL Field Experiment in a Desertification-threatened Area) as a part of the IV framework Programme in the field of the Environment (Bolle et al., 1993). The advances achieved by this project during the phases I and II (EPOC-CT90-0030 and EV-5V-CT93-0272), concerning the plant cover behaviour in vineyards of desertification-threatened areas (Castilla-La Mancha), pointed out two facts of enormous importance. Firstly, soil is a key element that allows enough water storage for proper vine development under conditions of high evapotranspiration, and secondly, the density and layout of vine root system enhance the plants ability to explore deeper zones looking for soil water. Under the environmental conditions of La Mancha, the behaviour of vine in terms of wine production and vegetative development must be understood as a result of the close linkage between these two facts. The exploring capability of vine roots and the soil water storage buffering capacity of the petrocalcic layer lead us to estimate that actual water available resources comprise the reserve from the last years as well as the annual rainfall. Improving the knowledge of the soil±plant±atmosphere system and its interactions allows the expression of vine growth, aiming to study the ground truth in vine areas, as a part of the research developed in the Remote Sensing of Mediterranean Desertification and Environmental Stability (RESMEDES) (ENV4-CT-95-0094) project. Multitemporal studies by remote sensing are especially useful for vine growth monitoring. The changes in vine cover development are analysed through an interannual study, which includes periods of severe drought and others with enough rainfall. The historical series of annual rainfall was analysed in the study area. 2. Materials and methods 2.1. The study area The study area selected for this work is placed near Tomelloso (UTM coordinates are 4331130 N, 30506090 E), 670 m above sea level in Castilla-La Mancha. This area covers 260 000 ha with one of the higher concentration of vineyards in the world: 130 000 ha of vines (MAPA, 1995), which implies strong social, economic and environmental dependence on the crop. Although generally soils are not extremely suitable for agricultural use, the quality of substrates highly enriched with pebbles is adequate enough for vine growing. But there exist other woody species such as olive trees, natural forests and herbaceous crops, mainly dry-farming cereals and fallow lands, which hardly reach 20% of area. The variety used in 93% of the vineyards is AireÂn, a white variety grown over 32% of the Spanish surface. The plant growth habits and techniques used provide vine shoots with a creeping
366
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Fig. 1. Evolution of temperatures along the year in the study area (1984±1991).
appearance invading nearby rows in the maximum growth stages, keeping the soil free from weeds. The environmental conditions of vine growing in Castilla-La Mancha, particularly soil and weather, are restrictive, forcing vines to adapt and take profit of them extraordinarily. The study site was selected according to criteria based on plant material, planting age, farming techniques, as well as other remote sensing criteria (flat relief, homogeneous soil, farm size, etc.). 2.2. Weather conditions The climate is a Mediterranean type showing high continentality, with sudden changes from cold months to warm months and high thermal oscillations in all seasons between the maximum and minimum daily temperatures. The mean annual temperature is 14.68C. July is the warmest month (26.48C) and January the coldest one (4.88C). Temperatures play an important role in the productive scheme of vineyards. Temperatures are above mean annual values in the summer period from May to September, which produces a great vegetative activity. Mean temperatures in July and August reach 258C, whilst maximum values are over 348C. Fig. 1 shows the evolution of temperatures along the year for the period 1984±1991. 2.3. Water resources The rainfall in Castilla-La Mancha is also seasonal and subject to great oscillations from one year to another. Fig. 2 shows the changes of total annual rainfall for the period 1984±1996. Years with low values can be observed between 1990 and 1995, whose average is 284 mm, together with years with higher values as in 1989 and 1996. The mean annual rainfall is 427 mm (1984±1996). The mean daily rainfall intensity is 4.2 mm dayÿ1, meaning that water is infiltrated when reaching the ground, and there is not much runoff. Fig. 3 shows the mean monthly averaged values of rainfall and evapotranspiration according to the Penman±Monteith method (Doorenbos and Pruitt, 1984), as well as the number of rain days for the period 1996±1997. The months with less precipitation are those of largest evapotranspiration and more vegetative development of vines that results
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Fig. 2. Annual rainfall in the study area in the period 1984±1996.
Fig. 3. Monthly values of evapotranspiration according to Penman±Monteith method, rainfall and number of rainfall days in the period 1996±1997.
in water stress negatively affecting the physiological functions of the plants, and subsequently, decreasing production. 2.4. Soil characteristics and vine root distribution The landscape is mainly flat with slight slopes, generally less that 5%. The soils are formed over limestone material, with pH values of 8, its upper horizon being poorly developed and the underlying ones presenting a content in calcium carbonate of 52% and 10% of active limestone. They contain more stones and are very suitable for growing
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Fig. 4. Schematic soil profile and root density distribution of vines in the study area.
vines. The soils belong to the calcisols groups (petric-calcisols), in terms of soil taxonomy. The presence of the petrocalcic horizon determines that vines (Vitis vinifera L.) should be planted by breaking through the impervious layer which prevents evaporation losses. Other soils present in the area are lithic and eutric-leptosols. One of the key elements to understand how vine performs under these semiarid conditions is the root system development. Fig. 4 shows the distribution of the roots in depth as a function of the distance to the vine stock in terms of root density (cm dmÿ3). Vine roots collected in cross and logitudinal sections at five depths were measured by using digital image processing and subsequently, isolines of root density were mapped by applying kriging techniques (Honrubia, 1997). 2.5. Field monitoring of vegetation parameters One of the main purposes of many recent agronomy studies is to determine the behaviour of the plant canopy. By studying and monitoring characteristic parameters of vegetation along its vegetative cycle, we can simulate its growth and development and predict its behaviour, as well as the interaction with the soil and the atmosphere around it (MartõÂn de Santa Olalla and de Juan, 1993). The plant parameters most used to monitor the plant cover and compare it with those acquired by remote sensing methods are surface cover, leaf area index (LAI), height and above-ground biomass. Besides, a monitoring of the plant development has to be defined to allow assessment of the changes of the different parameters studied along the cycle.
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Fig. 5. Distribution of rainfall according to the phenological stage of vines.
Baillod and Baggiolini (1993) phenology code is mostly used to monitor the vine cycle, estimating the stage by means of field sampling in different periods of the vegetative cycle. Fig. 5 shows the distribution of rainfall according to the phenological stages of the vine. It is clear that the soil is a reservoir that operates as a buffer of water availability, especially during periods of maximum evaporation. The plant parameters selected to show the development of vines were readily studied by remote sensing. Crop height (m), vine surface cover (%) and LAI (m2 mÿ2) of individual plants were measured through the different phenological stages of vine (AndreÂs et al., 1994) following statistical sampling procedures. Changes in vine cover development are analysed through an interannual study, which includes periods of drought and others with enough rainfall (see Fig. 2). The years selected to be studied are: 1991: dry year (264 mm) following a wet period (1989±1991): start of drought. 1994: dry year (214 mm) following a dry period (1992±1994): drought. 1996: wet year (511 mm) after a dry period (1994±1996): end of drought. 2.6. Remote sensing monitoring The seasonal combination of the vegetative cycle of vines and that of crops like cereals and olive trees present in the area along with natural vegetation allows us to identify the
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Fig. 6. Evolution of vine development according to the phenological cycle (Baillod and Baggiolini, 1993) in two different years (1991 and 1994), and the Landsat overpasses (1996) over the study area, outlining the period between flowering (May) and grape toning (July).
vine cover by using Landsat-5 TM images. As a result of the inventory, monitoring of its growth cycle can be undertaken. Nine images have been used in this study: five in 1991 (9 April, 27 May, 12 June, 28 June and 14 July) and four in 1996 (24 May, 25 June, 11 July and 29 September). The images were geometrically corrected following the control point method and interpolated by cubic convolution. The distance fitness with less than one pixel error ensures that all the nine images overlap. After georeferencing, all the images were radiometrically normalised to correct the atmospheric effects. The normalisation functions were obtained by relating the radiometric response of several zones of the reflectance image that were time invariant and covered the whole reflectances range in each day, to that corresponding to 9 April 1991, where the disturbing effects of the atmosphere were smaller (Segarra et al., 1997). Vineyard satellite monitoring was limited to the growing period in between May and July, when the vine plants show fastest growth. Before May the ground coverage is too small, and after July the changes are not significant. Fig. 6 states the importance of this period in remote sensing studies monitoring vine changes because of the sudden change of slope in the curves of vine development. 3. Results and discussion Fig. 7 shows the evolution curves of vine height, surface cover and LAI from ground means. It can be noticed that crop height does not seem to be affected by changes in water availability (R2 0.92), whilst vine cover (R2 0.63) and LAI (R2 0.53) show changes. It can be concluded that the growth behaviour of Airen variety in Castilla-La Mancha is limited by the water availability and its expression may be mostly linked to the above-
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Fig. 7. Evolution of vine height, surface cover and leaf area index, measured on the study area in 1991, 1994 and 1996.
ground biomass production. The relationship between vine cover, LAI and water availability in terms of rainfall series of mean monthly accumulated values confirms that plant growth is assured by the effect of a positive soil water balance, and less by seasonal rainfall. In order to be able to delimit the vine zones, we carried out a land use classification by using masks and supervised multitemporal classifications, removing step by step already
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Fig. 8. Land use classification of the study area (%) by remote sensing methods (Landsat) and by information acquired in the field (ground truth).
classified zones (Lanjeri, 1996). We also chose five training areas where the plant parameters were measured on the ground trying to keep close to dates of Landsat overpasses. Fig. 8 shows the total results calculated for each class, along with the ground truth known for the study area. Differences are due to confusion between young vineyards (younger than four years old) and fallow, as well as abandoned vineyards classified as vineyard on the ground and not so recognised on the satellite image. Multitemporal evolution of the NDVI for vine fields in 1991 at the Tomelloso field site is shown in Fig. 9, masking in white crops different from vines. Landsat TM images have been obtained for those dates more representative of the vineyard evolution. Plant parameters were related to the Normalised Difference Vegetation Index (NDVI) obtained from TM3 and TM4 band reflectances. Fig. 10 shows the relation between relevant plant parameters measured on the ground and NDVI values, showing that NDVI correlates well with LAI of individual plants through a linear relationship, since we are not close to the saturation zone expected when analysing LAI of the whole vine field. It also correlates well with vine surface cover and biomass. Since height is colinear with biomass it is not surprising that although with more scattering it correlates well with NDVI, it is much easier to measure on the ground. Plant parameters maps were produced based on the fitness functions between those parameters and NDVI. Some areas with very small values for these parameters could be explained by an irregular development of the vegetation due to external factors such as drought or spring frost.
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Fig. 9. Evolution of the NDVI vineyard inventory along four Landsat-5 TM images in the area of Tomelloso. The images cover the whole phenological cycle of the crop.
4. Conclusions The NDVI of vineyard varies slightly with the plant development of the crop, as can be observed from Fig. 9, due to the low cover of the vineyard. Vine cover values above 15% are very rare. Only the second half of June, with vine cover values higher than 5%, is useful for vineyard monitoring. Previous dates exhibit values of NDVI lower than 0.08 and are mainly due to the soil contribution. Moreover, in the NDVI image corresponding to 14 July 1991, there exists some areas with very small values of NDVI that could be explained by an irregular development of some vineyards due to external factors such as drought or spring frost that occurred that year. Unusually high NDVI values may be due to additional irrigation applied in some parcels leading to the development of spontaneous vegetation.
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Fig. 10. Relation between NDVI values and vegetation cover (1991, 1996), height (1991, 1996), Biomass (1991) and LAI (1996) measured in the field.
Acknowledgements The work was partly funded by the Commission of the European Communities (contracts EPOC-CT90-0030, EV5V-CT93-0272 and ENV4-CT-95-0094), by the Spanish government through CICYT contract: AMB93-1413-C05-04-CE, and by the regional government of Castilla-La Mancha. The support given by the Centre for Vine Growing Training and Research of Tomelloso is most gratefully acknowledged, as well as the comments from the editor.
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