1. Introduction
Changing climate conditions coupled with the transformations in cultivation practices and land use in sole cropping sunflower (
Helianthus annuus L.) production may significantly decline yield stability of this important oilseed crop. More than 80% of this crop is mainly grown in just 10 world countries, primarily in Ukraine, Russia, and Argentina, and two-thirds of the world’s production is concentrated in Europe
[1]. Considering the global significance of sunflower, it is essential to test the methods of its sustainable production in the times of population growth and accelerated climate change characterized by higher average temperatures, extreme climatic hazards, reduced water availability and water logging, and so forth
[2]. Despite the constant improvement of genetic yield potential in the recent years, most of the mentioned sunflower production countries have experienced yield gaps, between 1.1 and 2.4 t ha
−1 at a national level
[1]. Along with inadequately performed agro-technical measures, a considerable number of resistant weed species, nutrient uptake inefficiency, drought, poor disease, weed and pest control also affect the reduction of yield. Thus, modification and improvement of cropping practices suitable for the changing climate will have a major role in the achievement of sustainable sunflower production and global food security
[3].
Diversity at all levels, from genetic to the ecosystem, enhances the ability of cropping systems to overcome and adapt to the forthcoming changes. According to the EU Biodiversity Strategy for 2030, biodiversity is fundamental in preserving the EU and world food safety
[4]. Along with food safety, biodiversity supports healthy and nutrient-rich diets, enhances the efficiency of agroecosystems, and boosts resilience to the changing environmental conditions, climate risks and socioeconomic challenges. In addition to the EU Biodiversity Strategy for 2030, the Farm to Fork Strategy, and the new Common Agricultural Policy (CAP) are also encouraging eco-schemes development and sustainable systems implementation.
Many alternative cultivation practices can be applied in order to adapt crop production to climate change and variability. Although it is a centuries-old farming system, intercropping can be considered as one of the solutions for 21st century agriculture, and applied in order to improve resource use efficiency and yield stability. Some of the reasons for intercropping are increased yields of crops by more efficient utilization of soil and rainfall in a growing area, better disease, pest, and weed control, more uniform distribution of labour and saleable produce over a calendar year, greater stability of annual yields compared to sole-cropping, more effective control of erosion, decrease or elimination of the need for commercial fertilizers, reduced risk of crop failure, and many others
[5][6][7][8][9][10][11].
Intercropping has been widely used in some countries. Over 40% of maize (
Zea mays L.) in the Dominican Republic, 50% of maize in Jamaica, and 60% of beans (
Phaseolus vulgaris L.) in Brazil is intercropped, while 50% of the Zimbabwe growing area is cultivated with mixed crops
[12]. In Latin America, small-scale farmers grow between 70–90% of beans intercropped with maize, potatoes (
Solanum tuberosum L.), and other crops, whereas maize is intercropped at 60% of the maize-growing areas
[13]. However, in Europe, intercropping disappeared from many systems and currently remains in agroforestry, orchard, or vegetable production. Intercropping is a sporadic growing technology in industrial agriculture and intensive production systems, yet its use is expanding in organic production systems
[14].
Research on intercropping has shown that the best combination is when one of the species is from the
Fabaceae family. Species from this family are “expected” to be able to create a large aboveground mass, have a strong root system with high absorption capacity, and have moderate nutrition requests, for example, they should be more adaptable to poorer soils and shaded conditions, with high weed suppression and an ability to fix atmospheric nitrogen even in competition conditions, as in intercropping
[15][16][17]. Driven by photosynthesis, biological nitrogen fixation by legumes is a significant ecosystem service, which can partially meet the nitrogen needs of other crops in the system, and improve their overall productivity
[18]. According to the Food and Agriculture Organization of the United Nations (FAO), the present global use of N fertilizer is assessed at around 110 Tg of N year
−1 [19]. The N
2 fixed by grain legumes is assessed at around 22 Tg N and by forage legumes around 20 Tg N year
−1, which is low given the fact that, prior to the mass introduction of N fertilizers, 25–50% of agricultural land was commonly cropped on a legume base using cover crops and animal manure
[20]. Regarding the effect of main species in intercropping on legumes, it is highly possible that legumes’ biomass and biomass-related traits will be affected in the year of the establishment. However, bearing in mind the above-mentioned legume characteristics, after the main crop harvest, legumes usually rapidly regenerate
[16][18][20].
With all of the above-mentioned factors in mind, the goal of this research is to:
- Analyse and recommend sustainable production technology of sunflowers in intercropping systems. The research considered sunflowers as the main cash crop, and investigated different legumes as complementary crops;
- Define the most suitable legumes for intercropping with sunflowers. The aim is to determine how legumes affect sunflower production, qualitative, physiological and morphological traits:
- Analyse how this system affects perenniallegumes as crops that remain for exploration in the second year after the sunflower harvest (in the first year).
2. ExpMaterimental Deals and Methodsign
2.1. Experimental Design
For the purpose of our study, a four-year trial was conducted from 2017 to 2020 at the experimental fields of the Institute of Field and Vegetable Crops, Novi Sad, Serbia at Rimski šančevi (45°34′23.2″ N 19°86′18.9″ E). Prior to the trial establishment, the selected plot was divided into four parts in order to respect the sunflowers’ requirement for crop rotation. Three hybrids of sunflower, two oil types (Rimi PR and Dukat), and one confectionary type (NS Gricko) were intercropped with forage legumes (Vicia sativa L., Novi Beograd variety; Trifolium pratense L., Una variety; Medicago sativa L., Banat vs. variety), whereas sole cropping of sunflower and legumes was used as the control treatment (Figure 1). A rain-fed experiment was established using a split-plot design in four repetitions (Figure 2). All plant varieties were created and produced at the Institute of Field and Vegetable Crops, Novi Sad. The implemented cultivation practices were the same in the production area of the Republic of Serbia, by using mouldboard ploughing at 27–30 cm soil depth in autumn. Grain sorghum was used as the preceding crop to ensure a neutral impact on the main crop, and legumes as the complementary crop. Mouldboard ploughing ensured sorghum residue incorporation into the soil. Pre-sowing seedbed preparation and cultivation was carried out by the System Kompactor at optimal soil moisture. Sunflower hybrids were sown as the main crop in the first half of April, while legumes, as a supplementary crop, were sown a day before. Sunflower was sown with a Wintersteiger PSP Single Disk seeder in six rows, with a row spacing of 70 cm and a 25 cm spacing of plants in a row, and the sowing rate was the same in the sole crop and in intercropping treatments. Legumes were sown with anAmazone 08–30 Super seed drill (seeder). The sowing rate of red clover and alfalfa was 18 kg/ha and the common vetch 120 kg/ha, the same as in biomass production. The sowing rate of the legumes was the same in sole crop and in intercropping treatments, with a row spacing of 12.5 cm. The size of the single plot was 9×3.5 m, with 1.5 m spacing between treatments, that is, legumes, and repetitions. In the autumn before winter ploughing, basic macronutrients were supplied to the soil in the form of double NP (11:52) fertilizer MAP with high phosphorus content and sufficient amounts of nitrogen, in the amount of 220 kg ha-1. Before sowing, the soil was rolled to provoke the initial emergence of weeds, which were then destroyed by interrow cultivation. After the emergence of crops, two hand weedings were applied in the row area. After the sunflower harvest, red clover and alfalfa were left for exploitation in the following year.