TheCONero project is designed to achieve society’s challenges related to the sustainability of agricultural land and to design an improvement in the land use and land management of agricultural land in citrus plantations. The main objective is to achieve a sustainable agriculture based on organic farming, improve agriculture management, and advance the sustainability of primary production. The main mission is to achieve sustainable management that will accomplish the UN Sustainable Development Goals (SDGs) and the EU Green Deal. Here are the main challenges:
1. The measurements and experiments carried out will bring new sustainable agriculture management strategies to farmers. We will inform how much soil is preserved due to the new proposed management strategies, and how much water is preserved because of the catch crops and straw mulches that reduce runoff discharge.
2. The socio-economic research will link the economic and social issues to the changes in the expansion of citrus plantations. Relevant data about the expansion of citrus plantations, and how this is related to the changes in the economy of the region and the social characteristics will be made available to society.
3. There is a lack of information about the perception of stakeholders; the CONero project will interview farmers, citizens, managers, and technicians to get insights into the management strategies they use and prefer. This is relevant as the agricultural land is in private hands and their owners are the ones who mainly decide the management. Moreover, the perception of the society will induce changes in soil management.
4. The expected results will allow a change in management once the impact of the new strategies is tested. This will foster their use by the farmers upon our dissemination.
5. CONero‘s impact on soil conservation and its acceptance by society and managers and farmers. This will bring us into a trajectory towards sustainable land and soil management as a key contribution to a green transition.
The characteristics of the project covering the research on national citrus production areas request to apply a multidisciplinary and interdisciplinary approach with colleagues from different backgrounds that will bring different skills and views during the 4 years of research.
Background
The need for sustainable soil management.
Soil conservation is the key to maintaining food production, soil health, and the functionality of terrestrial ecosystems, to enable the achievement of the Sustainable Development Goals of the United Nations, specifically SDG15.3: the Land Degradation Neutrality challenge, and deliver associated ecosystem services (Keesstra et al., 2016; 2018; Lal et al., 2019). In addition, the European Commission has set the target that by 2030 75% of all European soils will be healthy and 25% of all agriculture to be under organic management by 2030 (Veerman et al., 2020). However, so far, in agricultural land, chemical fertilizers, herbicides and pesticides, and intense tillage has led to severe soil degradation, especially in the Mediterranean region (Kamau et al., 2017; Guillaume et al., 2016; Kuzyakow and Zamanian, 2019). Far too often 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 (Trivedi et al., 2016). For example, intensive, high chemical input agricultural systems can seriously increase soil erosion processes (Nearing et al., 2017; Borrelli et al., 2020; Guerra et al., 2020; Katra et al., 2020). A new soil management framework is necessary to control the accelerated erosion rates and maintain agricultural sustainability and the functions and services the soil system provides to society and nature (García-Ruiz et al., 2020; Liu et al., 2020).
Accelerated soil erosion in Spain.
Spain is severely affected by soil degradation and high soil erosion rates. In Spain, agriculture has been the cause of onsite soil degradation on arable land and the source of the sediments that reach rivers, reservoirs, and wetlands (Taguas and Gómez, 2015; Bayat et al., 2019). This is due to the steep slopes, poor soils, heavy rains, and the eradication of all vegetation other than the crop itself (García Ruiz, 2010). Until the 1960s, the plow affected soil structure and facilitated the mineralization of organic matter. Since then, the use of high-horsepower tractors has caused soil disturbance deeper in the profile causing compaction and even more organic matter depletion than traditional ploughing. In recent years, herbicide use has increased in non-irrigated crops, which has led to less vegetation cover and soil surface crusting and compaction (Keesstra et al., 2019). This practice provides the right conditions to generate high rates of soil erosion. Casalí et al., (1999) measured soil losses of 13.3 Mg ha-1 year-1 on gullied agricultural land in Navarre, Rodríguez Martínez-Conde (1998) measured a high erosion rate in Galicia, where 17.58 Mg ha-1 year-1 in 1996 and 15.81 Mg ha-1 year-1 in 1997 were registered. Martínez Casasnovas et al., (2002) reported a 207 Mg ha-1 soil loss in Lérida after a 205 mm rainfall event in 135 minutes. Studies at the Pyrenean Institute of Ecology demonstrated that the greatest soil loss (15 Mg ha-1 year-1) was from fallow fields that were ploughed but not sown after 2- or 3-years years of crop production, a practice that is traditionally done in the Mediterranean Region (García Ruiz, 1996). The pioneering work of Lasanta and Sobrón (1984) on traditional plowing practices in the vineyards of La Rioja showed soil erosion rates < 1 Mg ha-1 year-1. López Bermúdez (2002) reported ploughed fields averaged 1.84 Mg ha-1 year-1 of soil loss in Murcia, but values were lower when cereal crops were planted (barley – 1.04 Mg ha-1 year-1), and very low on scrubland (0.05 Mg ha-1 year-1). This demonstrates that vegetation cover is the key factor that controls soil loss and explains the soil loss reductions found by Francis (1990) and Ruiz Flaño et al., (1992) in the north and south-eastern Spain after land abandonment. In Andalucía, Cuadros et al., (1993) measured soil losses of 10.9 Mg ha-1 yr-1 in citrus orchards using traditional ploughing methods, while soil loss was reduced to 2.9 Mg ha-1 yr-1 under non-tillage conditions. De Alba (1998) found soil losses of 2.4 Mg ha-1 year-1 when cereal fields in the Castilla-La Mancha region are fallow, 0.48 Mg ha-1 year-1 when a crop is present, 0.67 Mg ha-1 yr-1 when no-tillage is applied, and only 0.17 Mg ha-1 year-1 on abandoned land. Bienes and Torcal (1997) found similar results in Central Spain. The available data confirm that agricultural lands contribute to soil exhaustion (Lasanta et al., 2001). In addition, soil erosion rates on agricultural land in Mediterranean environments depend on the type of crop that is grown. Giráldez et al., (1989) used the Universal Soil Loss Equation to show that no-tillage practices reduced the soil losses in all crops they studied (sunflower, wheat, sugar beet, beans) except in olive orchards. However, no-tillage practices aimed to reduce soil losses are not always the most sustainable land management system. Francia et al., (2000) found that no-tillage increased the soil erosion rates (5.2 Mg ha-1 year-1), as compared to traditional tillage (1.3 Mg ha-1 year-1), and areas with vegetation cover (0.41 Mg ha-1 year-1). Martínez-Raya et al., (2001) also found a no-tillage strategy for an Andalucía olive orchard increased the soil losses to 28.03 Mg ha-1 year-1, as compared to traditional plowing of 9.08 Mg ha-1 year-1, and 1.56 Mg ha-1 year-1 in soil with vegetation cover. Soil losses are usually low or negligible where vegetation cover is present or surface mulches are used (Bienes et al., 2000). The latest research findings on soil erosion for agricultural land in Spain show that non-sustainable soil losses are widespread (Gómez et al., 2004; Arnáez et al., 2006; De Santisteban et al., 2006) and more research is necessary on control of soil erosion by water and tillage. The non-sustainable soil erosion rates in Spain found by the pioneers mentioned here were confirmed along the last decades by many other researchers such as Sastre et al. (2017); Rodrigo-Comino et al. (2018); Merchán et al. (2019); Rodríguez Sousa et al. (2019) and Zuazo et al. (2020).
Changes in citrus production. New plantations accelerate soil losses.
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 unsustainable plantations on slopes without terraces. These new mechanized production systems have replaced the traditional production systems that were based on flood irrigation in the valley bottoms and dry farming on terraced hillsides. These new farming systems are widespread in provinces such as Málaga, Seville, Huelva, Badajoz, Murcia, Alicante, Valencia, and Castellón. Similar changes were found also in other regions of the world (Chenoweth, 2003; Xu et al., 2018; Tercan and Dereli, 2020). The consequences of this intensive citrus plantation management, that is combined with high chemical usage have brought an increase in erosion rates and soil degradation, as was demonstrated by the SEDER research group (Cerdà et al, 2009; Holdenbrink et al., 2017; Di Prima et al., 2018; Keesstra et al., 2019; Rodrigo-Comino et al., 2020).
Accelerated soil erosion has indeed been present in Spain since the Neolithic period due to the environmental conditions (droughts, high rainfall intensities, steep slopes), combined with the abuse of the soil resources by humans (grazing, tillage, fire, and mining). However, the recent mechanization of agriculture has increased the rates and extent of the area affected. Soil erosion has been deeply studied in Spain, but now it is time for the next step: to find strategies to reduce soil losses (García-Ruiz et al., 2017; van Leeuwen et al., 2019; Calatrava and Franco, 2020). Scientific research studies so far have mostly concentrated on characterizing and understanding the mechanisms and processes of soil erosion. This is also the case of the citrus plantations (Cerdà et al., 2009). Now, based on a good understanding of the soil erosion process, it is necessary to design soil conservation strategies to achieve sustainable environmental management. The research on citrus orchards proposed in this project is novel and will focus on management that will reduce soil losses and induce recovery of soil health. The research developed here can be applied to other citrus production regions where soil erosion rates are also found unsustainable (Yang et al., 2012; Niu et al., 2020; Duan et al., 2020; Zhang et al., 2020).
The State-of-the-Art of soil erosion in citrus plantations shows that there are few studies done targeted on citrus erosion and that the current situation shows unsustainable soil erosion rates. In Spain, these studies have shown high erosion rates in the orchards of Eastern Spain. However, there are no measurements in other regions such as Andalusia, Extremadura, and Murcia. Spain is the largest citrus producer and has the largest citrus crop area in Europe (Bono, 2010). The lack of sustainable management occurs even though the production of citrus fruits is of great economic importance in Spain, and one of the stalwarts of the economy of some regions, such as Valencia, which produces over 70 % of the total Spanish citrus yield. In addition, the area of land in citrus orchards has increased by 20 % from 1982 to 2002, and new non-registered citrus establishments likely double this figure. Other Mediterranean regions of Spain, such as Extremadura, Murcia, and Andalucía, show similar increases as in the Valencia Region.
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, urbanization of the traditional citrus production zones near the Mediterranean Coast (traditional flooding irrigation) has pushed the new orange orchards out of these now valuable peri-urban areas to find cheaper land. These changes in land management and population distribution have resulted in the establishment of new orange, lemon, and clementine orchards on steeper soils, that use drip-irrigation systems and pump-up groundwater for summer irrigation. An example of this change in land use is the traditional «Huertas» of the Jucar River and the Coastal Plain of Castellón, where the amount of agricultural land has decreased, while the area of citrus plantations in Valencia, Extremadura, Murcia, and Andalucía regions have increased in plantations located in sloping terrain.
Since 1781, when the first sweet orange was planted in Carcaixent (Valencia), the citrus orchards were located on alluvial plains, terraces, or alluvial fans. This is due to the need to be irrigated, and flood irrigation was only available in the low and flat terrains. Beginning in the 1950 citrus orchards could be planted on slightly higher land and irrigated by groundwater pumping using water vapor engines. These new orchards expanded citrus production to the inland districts, but the fields were always level flooding terraces and soil loss from water erosion was avoided. During the 1970s citrus orchards spread inland from the Mediterranean coast, and since 1980 the expansion of citrus orchards reached steeper mountain slopes, which used drip irrigation systems instead of flood irrigation. Terracing and land leveling were not necessary anymore. Since the 1990s, citrus orchards have been established on slopes >20 %, and therefore, have high soil erosion risks. Therefore, overall citrus production has moved from valley bottom sites to steeper soils, and from a traditional flooding system to a modern, high-technology drip irrigation system.
Although citrus plantations moved from the alluvial plains to sloping terrains, land management practices have failed to adapt to the new topography. The newly rugged terrains that have been taken into use ask for new, sustainable strategies to reduce or avoid the associated soil erosion, which so far has not been developed. Consequently, intensive tillage and high herbicide use on these citrus orchards are causing the largest soil losses measured in Spain (De Santisteban et al., 2006; Cerdà and Doerr, 2007; García Ruiz, 2010) and Europe (Panagos et al., 2020). Traditional citrus orchards on flat land in river basins have negligible soil losses, or they accumulate sediments during the river flooding. This process of sedimentation on the traditional Mediterranean «Huertas» during floods contributed to soil development and the maintenance of soil fertility. However, the detachment of soil particles by water erosion processes on slopes is now contributing to soil degradation on the new citrus plantations, damage in the infrastructures, and enhancement floods.
Land management practices on citrus orchards planted on steep soils are similar, or identical, to the ones applied on the flat traditional irrigated «Huertas». Tillage and the recurrent use of herbicides (No-Tillage) are increasing, which results in bare soils and high soil erosion rates. Catch crops or allowing weeds to grow is rarely used in Spanish citrus orchards as a means to reduce soil erosion. Today’s aggressive land management practice results in soil degradation, as the organic matter turnover is negligible, and the soil organic matter content is below 1 % in many citrus orchard soils (Cerdà and Jurgensen, 2008; Novara et al., 2019). During high-intensity rainfall events, which are typical in Mediterranean environments, the surface wash can result in high erosion rates, soil nutrient removal, and lower citrus orchard productivity. Eroded soils have lower water infiltration rates, greater runoff discharge, and greater flood risk. High runoff from citrus orchards can reduce water quality, increase sediment in the fluvial system, and disturb river biota. These sediments accelerate the siltation of reservoirs, which affect urban water supply, irrigation, and flood control. High use of agrochemicals in citrus orchards also increases water, soil, and air pollution, and impact roads and other infrastructures. Moreover, the use of agrochemicals induces a reduction in soil biota, depletion of organic matter, and degradation of the soil structure. This will result in a loss of soil health. CONero will contribute to traverse this unsustainable situation.
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