Soil Erosion and Degradation Research Group (SEDER).
Departament de Geografia. Universitat de València. Blasco Ibàñez, 28, 46010, Valencia, Spain
Soil conservation and orchard production
Soil conservation is the key to maintaining the food production, soil sustainability, and the functionality of terrestrial ecosystems. However, chemical agriculture, based on synthetic chemical fertilizers, herbicides and pesticides, has led to soil degradation where soil quality became secondary to other agricultural factors, such as water, microclimate, and the variety of the crop. In too many instances soils are not properly managed, despite their key role in the functioning of terrestrial biogeochemical cycles, plant and animal nutrition, and the success of human societies. And one of those instances is chemically farming orchards.
Although soil erosion problems have been present in Spain since the Neolithic period due to human impact and enviromental conditions (droughts, high rainfall intensities, steep slopes), farmers developed agricultural systems to control the soil and water losses by means of terracing (García Ruiz, 2010).
Citrus production in Spain
Spanish citrus production has grown from sustainable management in the traditional orchards of alluvial plains and fluvial terraces of Júcar, Turia and Segura basin in Murcia and Valencia, to plantation on slopes without terraces. These new mechanized production systems have replaced the traditional production systems that were based on flood irrigation and dry farming on terraced hillsides.
New citrus plantations results in extreme erosion rates
The consequences of this new intensive monoculture of citrus plantation management and high chemical usage have been an increase in erosion rates, as demonstrated by the SEDER research group (www.soilerosion.com) (Cerdà et al., 2007; Cerdà and Jurgensen, 2008; Cerdà et al., 2009a; 2009b; 2009c). Soil erosion measured during a single rainfall event (180 mm day-1) resulted in soil erosion rates higher than 50 Mg ha-1 y-1. Deep rill and gully formation damaged the farms and the roads, with a high economic lost.
Most of these new orchards are located on slopes to avoid the frosts caused by temperature gradient inversions that often develop during the coldest days in winter. In addition, urbanisation of the traditional citrus production zones near the Mediterranean Coast (traditional flooding irrigation) has pushed the new orange orchards to steeper slopes in order to find cheaper land. These changes in land management and population distribution has resulted in the establishment of new orange, lemon and clementine orchards on steeper soils, which use drip-irrigation systems and the pumping of groundwater for summer irrigation. An example of this change in land use is the traditional “huertas” of the Júcar River and the Coastal Plain of Castellón, where the amount of agricultural land has decreased, while the area of citrus plantations in Valencia, Murcia and Huelva have increased (Cerdà and Doerr, 2007).
Citrus fruits are a crop of great economic importance in Spain, and one of the stalwarts of the economy in Valencia, which produced over 70 % of the total Spanish citrus crop in 1997-1998 (5,461,000 Mg). In addition, the area of land in citrus orchards has increased by 20 % since 1982 to 2002, and new non-registered citrus establishments likely double this figure. Other Mediterranean regions of Spain, such as Murcia and Andalucía, show similar increases as in the Valencia Region (MAPA, 2004). However, the new production system by means of monoculture on steep slope resulted in low prices of oranges in the market due to the over-production, a landscape change and extreme soil erosion rates.
Cerdà, A. & Doerr, S.H. 2007. Soil wettability, runoff and erodibility of major dry-Mediterranean land use types on calcareous soils. Hydrological Processes, 21, 2325. 2336. DOI: 10.1002/hyp.6755.
Cerdà, A. & Jurgensen, M.F. 2008. The influence of ants on soil and water losses from an orange orchard in eastern Spain. Journal of Applied Entomology-Zeitschrift für Angewandte Entomologie. 132, 306-314. DOI: 10.1111/j.1439-0418.2008.01267.x.
Cerdà, A., Bodí, M. B. & Hevilla-Cucarella, E.B. 2007. Erosión del suelo en plantaciones de cítricos en laderas. Valle del riu Canyoles, Valencia. Agroecología, 2, 12-33.
Cerdà, A., Jurgensen, M.F. & Bodí, M.B. 2009a. Effects of ants on water and soil losses from organically-managed citrus orchards in eastern Spain. Biologia, 3, 527-531. DOI: 10.2478/s11756-009-0114-7.
Cerdà, A., Giménez-Morera, A. & Bodí, M.B. 2009b. Soil and water losses from new citrus orchards growing on sloped soils in the western Mediterranean basin. Earth Surface Processes and Landforms, 34, 1822-1830. DOI: 10.1002/esp.1889.
García Ruiz, J.M. 2010. The effect of land uses on soil erosion in Spain. A review. Catena, 81, 1-11. DOI: 10.1016/j.catena.2010.01.001.
González-Peñaloza, F.A., Cerdà, A., Zavala, L.M., Jordán, A., Giménez-Morera, A., & Arcenegui, V. 2012. Do conservative agriculture practices increase soil water repellency? A case study in citrus-cropped soils. Soil and Tillage Research, 124, 233-239. DOI: 10.1016/j.still.2012.06.015.