Advancing Intercropping of Drought-Resistant Oilseed Crops: Mechanized Harvesting

Abstract

Adverse climatic dynamics in recent years have intensified the need for resilient and multifunctional agricultural systems that integrate productivity, ecological sustainability, and socio-economic viability. This study evaluates the harvesting performance of three cropping systems: intercropping of cardoon and safflower (IT) and monocultures of cardoon (DC) and safflower (DS). Field trials were conducted during three following growing seasons to assess key harvesting parameters, including working speed, effective field capacity, harvesting costs, biomass yield, seed yield, seed losses, and seed moisture content. DC demonstrated the better performance, with a working speed of 6.35 ha h⁻¹ and a field capacity of 2.56 ha h⁻¹, also resulting in the lowest harvesting cost (EUR 70.24 ha⁻¹). In contrast, IT exhibited the lowest performance and the highest cost (EUR 98.61 ha⁻¹). DS achieved the highest effective seed yield (1.394 Mg ha⁻¹), while IT produced the greatest biomass (22.96 Mg ha⁻¹). Seed losses were lowest in DS (0.020 Mg ha⁻¹) and highest in IT (0.425 Mg ha⁻¹). Moisture content ranged from 5.82% in DC to 9.40% in DS. These findings highlighted the trade-offs between productivity, efficiency, and system complexity, offering valuable insights into the comparative performance and sustainability of innovative cropping systems under changing climatic conditions.

1. Introduction

In the past, agricultural systems had only the principal objectives of yield maximization and the cost reduction [1,2,3]. To achieve this goal, monospecific agricultural systems have been used for years, which have led to various problems such as loss of biodiversity at all scales and economic risks for producers in case of production issues [4]. However, this has led to prioritizing agricultural systems that maximize yields and minimize production costs. Significant technological innovation has been implemented for the most widely cultivated species, resulting in increased productivity and mechanical efficiency [5,6,7,8].

Today, agriculture is no longer understood solely as a productive activity as in the past, but rather as a multifunctional system that must also meet ecological and social needs [9,10,11]. In addition to multifunctionality, today’s agricultural systems must cope with more adverse climatic phenomena due to climate change, and it has been observed that having monocultural production can put agricultural enterprises at risk of income loss [12,13,14]. Possible solutions to these production risks are provided by the use of crops that can withstand the adverse climatic conditions or the use of mixed cropping systems, where the coexistence of multiple productive species within the same field offers greater production guarantees compared to monocultures due to the higher number of products/services available for sale by the farm [15,16,17]. Crop diversification is recognized as a strategy for sustainable land management [18]. It aims to increase the productivity and resilience of cropping systems to weather variability over the long term [19,20,21]. Examples of these practices include agroforestry and intercropping systems [22,23,24]. There is accumulating evidence that intercropping can confer multiple agronomic benefits, including enhanced yield, stabilized food production, and reduced input consumption [22,23,25,26].

Increasing interest in the potential of intercropping is reflected in the growing body of scientific literature on the subject [27,28,29]. Despite the growing interest, there are gaps in both scientific research and dedicated technologies for the mechanical harvesting of these systems. The development of specialized harvesting equipment may significantly reduce seed loss and increase yield and profit, as demonstrated by the dedicated technologies for industry (First2Run project: flagship demonstration of an integrated biorefinery for dry crops sustainable exploitation towards biobased materials production) or food crops [30]. Despite this, industrial crops often lack dedicated technologies due to the current absence of a well-established value chain. However, as demonstrated in several studies, an adequate machinery setup can achieve optimal efficiencies similar to those of the crops for which the machines were originally developed [31,32,33]. The Marginal land Industrial Crops and Innovative Biobased Value Chains project (MIDAS), with the aim to provide a comprehensive view of applicability within multifunctional and climate-resilient agricultural systems, selected some crops with high adaptability and drought-resistant characteristics [34,35,36,37] to be tested. The selected crops were cardoon (Cynara cardunculus L.), as s perennial multipurpose species, and safflower (Carthamus tinctorius L.), as an annual oilseed species, both characterized by high industry interest, good adaptation to drought environments [38,39,40,41,42], and good results in terms of mechanical harvesting [43,44]. Prior to this research, the intercropping of these two species and the possibility of simultaneous harvesting had never been studied.

The experimental hypothesis of intercropping cardoon arises from the characteristics of its growing cycle, which generally, after the first year of cultivation, show variable and lower plant densities [45,46]. Therefore, the experimental hypothesis aimed to exploit this characteristic of the cardoon’s production cycle by evaluating an intercropping system with another resilient species, such as safflower, which shares the same harvest period and seed size. This similarity potentially allows both species to be harvested using identical settings on standard harvesting machinery when sown in the same field. The objective was to evaluate the impact on harvesting efficiency and overall crop yield.

The advantages and disadvantages of using non-specific equipment in a large-scale trial of intercropping were compared with a dedicated field of the same crops, aiming to provide technical data regarding performance, costs, and seed losses.

2. Materials and Methods

2.1. Study Area

Tests of mechanical harvesting were carried out on the same field located in Maccarese (Fiumicino, Lazio, Italy) (WGS84-UTM33T coordinates 271167 E, 4633933 N; 0 m a.s.l.) during three seasons (2022–2023–2024). The overall surface of the field was 18.32 ha, but the effectively sown area corresponded to 17.67 ha, considering that no planting was performed into the ditches (Figure 1). Before the first growing season, the soil was cultivated with Triticale.

Before starting the test, five samples of 500 g of soil were collected from the field and shipped to the lab in order to study soil characteristics. Each sample was collected following the soil sampling methodology [47]. The physical characteristics were classified according to the GEPPA soil texture classification system (i.e., clay 44%, sand 37%, silt 19%, organic matter 2.6%, N 0.15%, pH 7.9, P₂O₅ Olsen 18 mg kg⁻¹, K₂O 807 mg kg⁻¹). Weather data of the entire study period (i.e., March 2022–September 2024) were acquired with a station Davis Vantage Pro2™ 6152 located in the study area. The system included a Weather Link that let the weather station interface with a computer to log weather data and to upload weather information to the internet [48]. The mean monthly weather data of the three growing seasons are reported in the diagram below (Figure 2).

2.2. Cardoon (Cynara cardunculus L.), 2022

Cardoon (Trinaseed variety) was cultivated in the first season of the experiment in 2022. Soil preparation was carried out in October 2021 and included subsoiling to a depth of 30 cm, followed by harrowing with a rotary implement. Fertilization was conducted prior to seeding the 5 March 2022, at rate of 160 kg ha⁻¹ of slow-release nitrogen fertilizer (Urea, 46% N). This dose was selected based on agronomic recommendations for Cynara cardunculus in Mediterranean environments, where nitrogen rates between 120 and 180 kg ha⁻¹ have been shown to support optimal biomass production and crop performance [49]. The crop was cultivated under rainfed conditions, without irrigation. Harvesting was carried out on 11 August 2022.

2.3. Intercropping, 2023

Cardoon cultivation typically involves multi-annual cycles due to the species’ extreme hardiness. In this case, the characteristic hardiness of cardoon was utilized to establish an intercropping system with safflower. After harvesting cardoon (August 2022), in October 2022, minimum tillage was performed, involving only superficial harrowing, followed by fertilization at rate of 75 kg ha⁻¹ of diammonium phosphate (18% N, 46% P₂O₅) and 75 kg ha⁻¹ of urea fertilizers (46% N) and sowing only safflower at a density of 24 kg ha⁻¹ on the 8 March 2023. The crops were cultivated under rainfed conditions, without irrigation. Harvesting of the intercropped field was carried out on 8 August 2023.

2.4. Safflower (Carthamus tinctorius L.), 2024

Soil preparation was conducted in October 2023, involving deep tillage with a ripper and superficial chisel ploughing before seeding safflower (CW99OL variety). Fertilization was performed before sowing at rate of 75 kg ha⁻¹ of urea (46% N) and 75 kg ha⁻¹ of diammonium phosphate (18% N, 46% P₂O₅), resulting in a total nitrogen input of approximately 69 kg ha⁻¹. This rate was selected based on agronomic studies indicating that nitrogen levels between 50 and 150 kg ha⁻¹ are effective in enhancing safflower growth and yield under Mediterranean conditions [50,51]. The sowing was performed on 29 February 2024 with a rate of 30 kg ha⁻¹. The crop was cultivated under rainfed conditions, without irrigation. Harvesting was carried out on the 3 August 2024.

2.5. Pre-Harvest Tests and Biomass Caracterization

Before each harvesting operation of the three growing seasons, 5 sample plots of 1 m² each were randomly selected to study the overall aerial biomass. Plants were cut at the ground level and brought outside the field to be counted and measured in both weight and height and shipped to the laboratory of the Research Centre for Engineering and Agro-Food Processing (CREA-IT) for further investigations. In particular, the number of plants for each sample, potential seed yield (PSY), dry weight (DW), and moisture content were evaluated. Dry weight and moisture content were estimated according to EN ISO 18134-2:2017 [52], while PSY was measured using a stationary thresher (PLOT 2375 Thresher, Cicoria Company, San Gervasio, Italy).

2.6. Combine Harvesting

A local contractor provided a combine harvester with a 176 kW diesel engine (Figure 3). The combine was equipped with different headers: a 4.8 m wide sunflower header for the cardoon in 2022 and a 5.5 m wide cereal header for safflower in 2024. Based on previous studies which showed that using a cereal header for safflower resulted in lower seed losses compared to using a sunflower header for cardoon, the cereal header system was selected for the intercropped field as well [43,53]. This approach, applied and verified by several studies, is used when dedicated machines are not available [53,54,55,56]. The combine settings were the same across the different treatments, because the weights and dimensions of the two crop’s seeds are very similar: concave clearance of 23.7 mm, thresher speed of 800 rpm, fan speed of 420 rpm, upper sieve clearance of 5 mm, and lower sieve clearance of 4 mm. These settings were maintained constantly throughout the test.

2.7. Evaluation of the Harvesting Performance and Costs

Harvesting performance and cost analysis of the different crops under evaluation were assessed using the parameters and the methodology suggested by Reith et al., 2017, and Pari et al., 2013 [57,58]. The parameters considered were working speed (km h⁻¹), theoretical field capacity (TFC, ha h⁻¹), effective field capacity (EFC, ha h⁻¹), and field efficiency (FE, %).

The various parameters were calculated as follows:

• TFC: Working speed × cutting bar width.
• EFC: Harvested surface/working times (effective working time + maneuvers time, avoidable delay time + unavoidable delay time + accessory time).
• FE: (Harvested surface/working times)/(working speed × cutting bar width).

The time required to discharge the combine harvester was recorded as accessory time.

Starting with the initial cost of the combine harvester and the operating expenses verified by the contractor, the machine’s performance was derived from field test results and utilized as input data. Standard calculation values were sourced from the CRPA (Research Centre on Animal Productions) methodology [59], consistent with previous studies on similar topics [60]. The price of the machine was discounted through the application of a lending rate of 3% provided by the Banca d’ Italia Institute [61]. Fuel consumption was measured by filling the tank before the harvesting and refilling it at the conclusion of the operation. Consumption of the lubricant was calculated according to the ASAE standard D497.4 [62]. The applied parameters for the economic evaluation are reported in

Table 1. Parameters and values used for economic evaluation. The various parameters were given by the mean value of the three study years.

Parameters		Measures Unit		Value
Combine Harvester	Power		kw	176
	Investment		EUR	250,000
	Service life		year	10
	Service life		h	3000
	Inflation	(1 + i)n		5.22
	Resale		%	60.34
	Resale		EUR	47,157.71
	Depreciation		EUR	202,842.3
	Annual usage		h/year	300
	Interest rate		%	2.5
	Worker salary		EUR× h−1	12.19
	Manpower		n°	1
Fixed costs	Ownership costs	(V0 − Vr)/n	EUR yr−1	20,284.23
	Interests	Mean (V0;Vr) × r	EUR yr−1	3714.47
	Value of the shelter		EUR yr−1	30
	Insurance costs	0.25%	EUR yr−1	625
	Various expenses *		EUR yr−1	655
	Total annual fixed costs	Qr + Qi + Qv	EUR yr−1	24,653.7
	Total fixed costs	Qfa/Ui	EUR h−1	82.18
Variable costs	Repair factor		%	60
	Repairs and maintenance		EUR h−1	50
	Fuel cost		EUR lt−1	0.91
	Fuel consumption		lt h−1	26.6
	Fuel consumption		EUR h−1	24.21
	Lubricant cost		EUR lt−1	3.03
	Lubricant consumption		lt h−1	0.32
	Lubricant consumption		EUR h−1	0.97
	Manpower costs		EUR h−1	12.19
	Total variable costs		EUR h−1	87.37
	Total annual costs	Ui × qu + Qfa	EUR yr−1	50,863.89
	Total hourly costs		EUR h−1	169.55

* Various expenses include costs related to documentation management, maintenance records, insurance paperwork, and other bureaucratic procedures.

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2.8. Crop Yield and Seed Losses Evaluation

Crop yield was assessed for each growing season and crop by weighing all seeds harvested at the conclusion of the harvesting process. Total harvesting losses (THL) were considered as the sum of seed losses due to the inefficiency of the header to correctly collect the capitula (CHL—capitula harvesting losses) and the ineffectiveness of the cleaning system of the combine harvester (IHL—ineffectiveness harvesting losses).

To summarize, CHL is the loss of not-threshed capitula laying on the ground or standing on plants not correctly cut by the header, and IHL corresponds to the seeds discharged from the rear of the combine harvester instead of being collected in its grain tank.

To evaluate CHL, 10 sample plots of 1 m² each were randomly established in the lateral areas of the harvesting roadway (Figure 4b). To evaluate IHL, a wooden tray of 0.027 m² (0.3 × 0.9 m), corresponding to the width of the rear expeller of the combine, was randomly placed on the path of the harvester at various locations within the field for a total of 10 times during each harvesting process (Figure 4a). All collected material was sealed in plastic bags to be brought to the CREA-IT laboratory for further processing.

As an additional method to evaluate the harvesting losses, the effective seed losses (ESL) were estimated by calculating the difference between the potential seed yield (PSY), measured in the pre-harvesting plot, and effective seed yield (ESY), measured by weighing the trailer with the harvested seeds at the farm scale. The ESY specific composition of IT was obtained from 10 random sampling of the seeds collected in the combine trailer.

2.9. Land Equivalent Ratio (LER)

To better quantify the efficiency of the intercropping system, the Land Equivalent Ratio (LER) of biomass and seed was calculated using the following formula [63]:

$$\mathrm{L}\mathrm{E}\mathrm{R}=({\displaystyle \frac{Y_{IS}}{Y_{DS}}})+\left({\displaystyle \frac{Y_{IC}}{Y_{DC}}}\right)$$

where

• Y_IS = yield of intercropped safflower;
• Y_DS = yield of monoculture safflower;
• Y_IC = yield of intercropped cardoon;
• Y_DC = yield of monoculture cardoon.

2.10. Statistical Analysis

The analysis of variance (ANOVA) was performed using the R 3.6.1 software to separate statistically different means among the groups; when a significant effect was found, the means of the treatments were compared by the Tukey test (p ≤ 0.05). Previously, all data were tested for normality and homoscedasticity. Furthermore, when significant differences among treatments were detected (p ≤ 0.05), pairwise comparisons were performed using the Least Significant Difference (LSD) test. The LSD was calculated using the standard error of the mean and the critical value of the t-distribution at the 5% significance level, providing a sensitive method for detecting differences between treatment means.

3. Results

3.1. Pre-Harvest Tests

Table 2. Plant characteristics in function of different cropping systems (mean of five repetitions ± SD). Values within the same column followed by a different letter are statistically different at the level of p ≤ 0.05 according to Tukey’s HSD test.

Treatment	Plant Density (N × m2)	Biomass * (Mg ha−1)	Straw * (Mg ha−1)	Seed Moisture (%)	Straw Moisture (%)
DC	14.20 ± 3.27 a	21.47 ± 4.43 a	20.02 ± 4.10 a	5.82 ± 0.04 a	26.75 ± 10.10 a
IC	11.20 ± 1.64 a	14.49 ± 3.16 b	13.32 ± 1.47 b	5.91 ± 0.27 a	26.36 ± 11.58 a
DS	46.20 ± 8.70 b	13.08 ± 4.09 a	11.67 ± 3.97 b	9.40 ± 0.29 b	34.70 ± 2.95 a
IS	9.00 ± 4.30 a	8.47 ± 1.97 b	8.22 ± 1.10 b	8.62 ± 0.77 b	34.46 ± 5.98 a
IT	20.20 ± 3.27 a	22.96 ± 2.23 a	21.53 ± 2.57 a	7.27 ± 0.35 b	30.41 ± 5.68 a
LSD (α = 0.05)	6.26	4.27	3.75	0.54	10.18

Note: (*) fresh matter; the LSD (α = 0.05) row indicates the Least Significant Difference for each parameter.

represents a comparative analysis of the parameters collected before the harvesting of the different analyzed systems: dedicated cardoon (DC), intercropped cardoon (IC), dedicated safflower (DS), intercropped safflower (IS), and intercropping (IT), i.e., composed of IS and IC.

Regarding plant density, safflower in monoculture (DS) exhibited the highest number of plants per m² (46.2), with statistically significant differences compared to its intercropped counterpart (IS, 9.0 plants m²) and other treatments. Similarly, cardoon in monoculture (DC) had a density of 14.2 plants m², slightly higher than in intercropping (IC, 11.2 plants m²), though without statistically significant differences.

When evaluating biomass production, cardoon showed a reduction in intercropping (14.49 Mg ha⁻¹) compared to monoculture (21.47 Mg ha⁻¹), with statistically significant differences. Also, safflower experienced a decrease, from 13.08 Mg ha⁻¹ of DS to 8.47 Mg ha⁻¹ of IS with statistically significant differences. The total intercropping (IT) recorded the highest value of total biomass (22.96 Mg ha⁻¹).

Straw production followed a similar trend, with higher values in monoculture respect to intercropping. Cardoon straw yield decreased from 20.02 Mg ha⁻¹ in monoculture to 13.32 Mg ha⁻¹ in intercropping, while safflower straw dropped from 11.67 Mg ha⁻¹ (DS) to 8.22 Mg ha⁻¹ (IS). The straw yield in the intercropping system (21.53 Mg ha⁻¹) remained high and statistically comparable to cardoon monoculture. Seed moisture content was affected by the cropping system, with significantly higher values in DS, IS, and IT compared to DC and IC. Cardoon showed moisture content values around 6% while safflower reached approximately 9%. The intercropping treatment (IT) recorded an intermediate value of 7.27%, falling between the two crops. DS and IS were statistically significantly higher compared to DC and IC. Straw moisture content remained relatively stable across treatments (26–34%), with no significant differences observed.

3.2. Harvesting Performance and Costs

The results of the harvesting performance and cost analysis are reported in

Table 3. Evaluation of the working performance and associate costs of the machineries used for the harvesting (mean of ten repetitions ± SD). Values within the same column followed by a different letter are statistically different at the level of p ≤ 0.05 according to Tukey’s HSD test. Cost analysis was performed relying on average working times per treatment, therefore statistical analysis was not applied.

Treatment	Working Speed (ha h−1)	Theoretical Field Capacity (ha h−1)	Effective Field Capacity (ha h−1)	Cutting Height (cm)	Field Efficiency (FE %)	Harvesting Cost (EUR ha−1)	Total Cost (EUR)
DC	6.35 ± 2.11 a	3.05 ± 1.01 a	2.56 ± 0.65 a	57.42 ± 2.62 a	85 ± 0.06 a	70.24	1241.19
DS	3.92 ± 0.11 b	2.35 ± 0.06 a	1.98 ± 0.06 ab	45.10 ± 2.75 b	84 ± 0.01 a	90.66	1602.04
IT	3.81 ± 0.66 b	2.09 ± 0.36 a	1.82 ± 0.26 b	49.20 ± 3.09 b	87 ± 0.04 a	98.61	1742.52
LSD (α = 0.05)	1.25	0.72	0.61	3.85	1.02	/	/

The LSD (α = 0.05) row indicates the Least Significant Difference for each parameter, which helps assess whether differences between treatment means are statistically meaningful. Harvesting cost and total cost were not subjected to statistical analysis; they are reported as mean values only.

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Results of working speed and field capacity, and both TFC and EFC, followed the same trend, with higher values for cardoon, followed by safflower and IT. Regarding working speed, the value of cardoon (6.35 ha h⁻¹), was statistically significant higher respect to safflower (3.92 ha h⁻¹) and the IT (3.81 ha h⁻¹). Concerning TFC, no statistically significant differences were found between the treatments, while for EFC, the value of cardoon was significantly higher than IT. The cutting height of cardoon (57.42 cm) was significantly higher than IT (49.20 cm) and safflower (45.10 cm). Concerning FE, the highest value was recorded in the IT system (87%) followed by cardoon (85%) and safflower (84%), with no statistically significant differences. The harvesting cost was highest for the IT with EUR 98.61 ha⁻¹, followed by safflower and cardoon (EUR 90.66 and 70.24 ha⁻¹, respectively). These data are also reflected in the total costs of the study field (17.67 ha) that was EUR 1742.52 for the IT system, EUR 1602.04 for safflower and EUR 1241.19 for cardoon.

3.3. Crop Yield and Seed Losses

The results of crop yield and seed losses are reported in

Table 4. Assessment of seed loss during combine harvesting (mean of ten repetition ± SD). Values within the same column followed by a different letter are statistically different at the level of p ≤ 0.05 according to Tukey’s HSD test.

Treatment	PSY (Mg × ha−1)	CHL (Mg × ha−1)	IHL (Mg × ha−1)	THL (Mg × ha−1)	ESY* (Mg × ha−1)	ESL* (Mg × ha−1)
DC	1.448 ± 0.710 a	0.106 ± 0.158 a	0.007 ± 0.003 a	0.114 ± 0.158 a	1.247	0.201
IC	1.175 ± 0.233 a	0.260 ± 0.137 b	0.080 ± 0.036 b	0.340 ± 0.142 c	0.748	-
DS	1.415 ± 0.161 a	-	0.011 ± 0.001 a	0.011 ± 0.001 b	1.394	0.02
IS	0.247 ± 0.109 b	0.009 ± 0.001 c	0.020 ± 0.006 a	0.029 ± 0.006 b	0.249	-
IT	1.422 ± 0.325 a	0.269 ± 0.136 b	0.100 ± 0.037 b	0.369 ± 0.143 c	0.997	0.425
LSD	0.682	-	0.042	0.208	-	-

Note: (*) this value was not replicated since all seeds were collected within one trailer and weighed only once at the end of the harvesting. PSY—potential seed yield; CHL—capitula harvesting losses; IHL—impact harvesting losses; THL—total harvesting losses; ESY—effective seed yield; ESL—effective seed losses.

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The results highlighted how the value of PSY for IT was 1.42 Mg ha⁻¹ with a lower fraction of IS (0.25 Mg ha⁻¹) with respect to the cardoon that accounted for 1.17 Mg ha⁻¹. The dedicated crops were in the range of IT with values of 1.41 Mg ha⁻¹ for DS and 1.45 Mg ha⁻¹ for DC. The value of IS was significantly lower than all other treatments.

Considering CHL, the DC showed values of 0.106 Mg ha⁻¹, while for DS, these losses were no detected. The value of CHL of IT, 0.269 Mg ha⁻¹, was characterized by a minimal amount of IS (0.009 Mg ha⁻¹) and a bigger fraction of IC (0.260 Mg ha⁻¹). Differences between the values of IT and IC with respect to DC and IS were statistically significant, as well as between DC and IS.

Regarding the IHL, value of DC accounted to 0.007 Mg ha⁻¹ while for DS accounted to 0.011 Mg ha⁻¹. IT recorded values of IHL equal to 0.100 Mg ha⁻¹, with IS contributing for 0.020 and IC for 0.080 Mg ha⁻¹. Differences among values of IT and IC with respect to the other treatments were statistically significant.

Values of THL, being the sum of CHL and IHL, were consistent with what was previously reported. Higher values were recorded by IT (0.37 Mg ha⁻¹), with a specific THL of 0.34 Mg ha⁻¹ for IC and 0.03 Mg ha⁻¹ for IS. Dedicated crops showed values of THL equal to 0.114 Mg ha⁻¹ for DC and 0.011 Mg ha⁻¹ for DS.

Regarding ESY, DS reported the highest value of 1.394 Mg ha⁻¹ followed by the DC (1.247 Mg ha⁻¹) and IT (0.997 Mg ha⁻¹). Lower values were recorded by IC (0.748 Mg ha⁻¹) and IS 0.249 Mg ha⁻¹. The ESL showed values of 0.02 Mg ha⁻¹ for DS, 0.201 Mg ha⁻¹ for DC, and 0.455 Mg ha⁻¹ for IT.

The Land Equivalent Ratio (LER) analysis revealed contrasting outcomes across yield components [64]. The results of LER are presented in the

Table 5. Land Equivalent Ratio (LER) values for different yield components under intercropping and monoculture systems.

Parameter	LER
Biomass	1.32
Potential Seed Yield (PSY)	0.99
Effective Seed Yield (ESY)	0.77

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The LER for total biomass was 1.32, indicating a clear land-use advantage of the intercropping system (IT) over monoculture, as values above 1.0 reflect more efficient resource utilization. However, the LER for potential seed yield (PSY) was 0.99, suggesting that intercropping did not provide a yield benefit in terms of seed production potential. Similarly, the LER for effective seed yield (ESY) was 0.77, indicating a reduced efficiency of the intercropping system for this specific component compared to monoculture.

4. Discussion

In this study the mechanical harvesting of an intercropping field of two oilseed crops was studied and compared with the corresponding dedicated fields in order to give new insights on related performance, cost, and seed losses.

The results of pre-harvesting highlighted how the natural reduction in plant density of cardoon in the second year was 22%. Taking advantage of this process, safflower was also cropped in the same field. The plant density of safflower was 80% higher when cultivated in monoculture compared to intercropping, emphasizing the difference in development of this crop according to the management system, considering that the variation in sowing rate was only of 20%. The plant density of intercropping was 30% higher compared to dedicated cardoon while 57% lower than dedicated safflower. This result is in line with the natural potential reduction in monoculture of cardoon in the second year of cultivation and confirmed the opportunity of cultivating a further crop in IT [64,65,66]. Despite the difference in plant density, the biomass and straw yield of safflower were reduced by only 35% and 23% in intercropping compared to the monoculture. Regarding cardoon, the reduction amounted to 33% and 40% for biomass and straw, respectively. These results are confirmed by other authors that stated how inter-specific competition between the species of the mixture may affect several agronomic parameters [65].

Concerning seed and straw moisture content, the values of cardoon were lower than safflower, regardless of the management of the field (i.e., monoculture or intercropping). Both crops, in monoculture or intercropping, exhibited optimal moisture content, with no problems for storage and processing and higher production possibility due to a longer shelf life and better storage properties or preservation [67,68]. Based on an agronomic perspective, it can be asserted that intercropping showed intermediate results between the two dedicated crops. These results are in line with those of other authors that studied the dedicated crops in terms of plants density and total biomass as also in this case, the intercropping was intermediate between monoculture crops [69,70].

The harvesting performance and cost analysis showed that lower working speeds were applied while harvesting dedicated sallower, due to high plant density, and intercropping, due to different size and shape of the crops. The forward speed was also reduced because by applying low cutting height (< 50 cm for DS and IT), more biomass must be processed by the combine while harvesting. Alternatively, for dedicated cardoon, the lower plant density combined with higher cutting height allowed for faster progress and resulted in better theoretical and effective field capacity despite the lower width of the header used. Interestingly, regarding field efficiency, there were no significant differences between treatments, indicating how slower forward speed allowed a reduction in maneuvers and delay and accessory times. Harvesting and total cost of the intercropping were 29% and 9% higher with respect to cardoon and safflower as a consequence of the low performance of the previous parameters. This result is common in mixed systems, as already mentioned by [71], who stated how the higher complexity of intercropped/mixed systems required more time to manage the different crops simultaneously.

The potential seed yield of cardoon was reduced by 19% in intercropping compared to the dedicated field, consistent with the reduction in plant density. Although the reduction of 83% of potential seed yield of intercropped safflower compared to the dedicated field, the value of total intercropping was in line with the monocultures, highlighting the potential of mixed systems [64,65]. Alternatively, values of effective and total harvesting losses were higher in intercropping compared to the dedicated fields for each crop and each parameter (i.e., CHL and IHL). Capitula harvesting losses of cardoon accounted for 70% of total harvesting losses of intercropping, highlighting how this was the critical phase when using a cereal header for combining the mixed system, as also observed in other studies [31,72,73]. Moreover, values of THL and ESL were equal to 25 and 30% of the potential seed yield for the total intercropping. These values, that were higher compared to monoculture fields and other studies conducted on industrial crops, can influence the profitability of the crop, also considering the higher harvesting cost. Alternatively, values of THL were equal to 7% and 1%, while ESL were equal to 13% and 1% of the potential seed yield for dedicated cardoon and safflower, respectively. The values of effective seed yield of total intercropping were lower than the two dedicated crops, being lower than 1 ton ha⁻¹.

The results indicated that to harvest the mixed system, too much material had to be collected, which did not allow for adequate conveyance into the combine harvester even when the same header was used (safflower). Regarding cardoon, the header was changed between dedicated and intercropping, influencing the value of seed losses and confirming that the mixed crop composition may pose challenges for the harvesting operation and crop profitability. The Land Equivalent Ratio (LER) values obtained in this study further highlight the variable performance of intercropping depending on the yield component considered. The LER for total biomass was 1.32, indicating a clear land-use advantage of the intercropping system over monoculture. This result aligns with the findings of [74], who reported biomass increases of up to 21% in intercropped systems compared to monocultures, supporting the idea that species complementarity can enhance resource use efficiency. On the contrary, the LER value for Potential Seed Yield was very close to 1 (0.99), indicating a low impact of intercropping on this parameter. Notably, the LER value for Effective Seed Yield (0.77) indicates that intercropping reduced seed yield efficiency, primarily due to the impact of mechanical harvesting. These outcomes emphasize the need for careful selection of crop combinations and spatial arrangements to optimize both vegetative and reproductive performance in intercropping systems. The overall results of the intercropped system harvested with a cereal header indicate that better solutions must be sought, despite the choice of harvesting method following the process generally used for crops for which dedicated technologies do not exist [54,75].

5. Conclusions

This study highlights the multifaceted performance of intercropping versus monocropping systems, considering agronomic, mechanical, and operational parameters. While dedicated cropping systems demonstrated strong outcomes, the intercropping of cardoon and safflower presented both opportunities and challenges.

Cardoon emerged as the dominant species in the intercropped system, particularly in terms of biomass and seed yield. However, significant harvesting inefficiencies, especially capitula losses due to unsuitable header design, substantially reduced the seed yield in the mixed system. These mechanical limitations underscore the critical role of harvesting technology in determining the profitability of intercropping systems.

Beyond yield, the study also revealed important differences in plant density, straw production, and moisture content. Intercropping influenced seed and straw moisture levels, which have implications for post-harvest processing and storage. Field efficiency metrics, including working speed, effective field capacity, and cutting height, further illustrated the operational constraints and potential of each system.

Despite the current limitations, intercropping remains a promising strategy due to its environmental and ecosystem service benefits.

Although the study examined several relevant parameters, we adopt a cautious approach in drawing conclusions due to the absence of a comparative analysis of header performance. Future experiments should prioritize exploring strategies to reduce seed loss, such as optimizing cutting height, adjusting crop density, and developing or adapting harvesting equipment specifically tailored to mixed cropping systems.