Introduction
In living mulch (LM) systems, cash crops are intercropped with one (or more) cover crop(s), introduced with the main aim to provide ecological services to the agro-ecosystem (Willey, Reference Willey1990; Masiunas, Reference Masiunas1998; Adamczewska-Sowińska et al., Reference Adamczewska-Sowińska, Kołota and Winiarska2009). Therefore, overall management is optimized in such systems to reduce competition between the cover crops and the cash crops, in order to eliminate or reduce any detrimental effect of the LM introduction while promoting the cover crops to provide ecological services at field/farm level (i.e., increase nutrient availability, contribute to management and control of weed, pest and diseases, conserve biodiversity, reduce NO3 − leaching) (Swenson et al., Reference Swenson, Walters and Chong2004; Vanek et al., Reference Vanek, Wien and Rangarajan2005; Båth et al., Reference Båth, Kristensen and Thorup-Kristensen2008; Thériault et al., Reference Thériault, Stewart and Seguin2009). For their ability to provide such a wide range of services, recent scientific literature defined cover crops as Agro-ecological Service Crops (ASC) (Kremen and Miles, Reference Kremen and Miles2012; Canali et al., Reference Canali, Diacono, Campanelli and Montemurro2015). Accordingly, this terminology, where appropriate, is sometimes used in the present paper as synonymous of LM.
Many attempts to use LM in cropping systems have resulted in reduced yields for the cash crops (Hiltbrunner et al., Reference Hiltbrunner, Streit and Liedgens2007; Chase and Mbuya, Reference Chase and Mbuya2008). Detriment of product quality is also an issue, especially for vegetable production in which the relation between quality and product value along the supply chain is not linear and a slight reduction in quality may greatly impact on product value (Maggio et al., Reference Maggio, De Pascale, Paradiso and Barbieri2013). Therefore, with the aim of seeking the trade-off among yield, quality and the ecological services provided by the ASC, a range of different options to manage the LM system have been identified (Reeve et al., Reference Reeve, Black, Ransom, Culumber, Lindstrom, Alston and Tebeau2013; Ziyomo et al., Reference Ziyomo, Albrecht, Baker and Bernardo2013). However, vegetable crops are commonly weak competitors in comparison with arable and fruit crops, then fewer options are feasible (Baumann et al., Reference Baumann, Kropff and Bastiaans2000; Leary and DeFrank, Reference Leary and DeFrank2000). Indeed, in vegetable cropping systems, LM can be permanently kept present in the field spatially separated from the cash crop, in minimally- or no-tilled strips. The growth of the intercropped ASC can then be controlled by mowing and/or root pruning (Båth et al., Reference Båth, Kristensen and Thorup-Kristensen2008; Thorup-Kristensen et al., Reference Thorup-Kristensen, Dresbøll and Kristensen2012). Differently, in non permanent LM systems, ASC are sown during the season, in advance, at the same time or later than the planting of the vegetable cash crops (Adamczewska-Sowińska et al., Reference Adamczewska-Sowińska, Kołota and Winiarska2009). This strategy is thought to be particularly powerful in vegetable systems where the cash crop's cropping cycle is generally not so long as in field crops. Therefore, even the shift of few days of the ASC sowing in respect to the vegetable crop planting may greatly affect the competition relationship between the LM and the cash crop (Chase and Mbuya, Reference Chase and Mbuya2008).
Competition between the cash crop and the ASC can also be managed by modifying the spatial distribution and/or modulating their density. In this context, two main approaches are described in the scientific literature: the additive and substitutive design. In the additive design, two (or more) species are grown together and the density of one species is the same as in the sole system, while the density of the other species is allowed to vary. Conversely, in the substitutive (or replacement) design, the density of one species is modified (i.e., reduced) relative to the sole cropping system in order to leave space and resources available to the other species (Shaxson and Tauer, Reference Shaxson and Tauer1992; Li and Hara, Reference Li and Hara1999; Rusinamhodzi et al., Reference Rusinamhodzi, Corbeels, Nyamangara and Giller2012). This terminology, generally used for systems in which two or more cash crops are intercropped, is used here to define LM systems where the cash crop spatial distribution and density is maintained equal to the one of the sole system or is reduced when the ASC is introduced.
A wide range of plant species belonging to different botanical families can be utilized as ASC in LM systems. However, most of them belong to three families: Graminaceae (grasses), Brassicaceae (brassicas) and Leguminosae (legumes), and only a minor number of species belong to other families (i.e., Polygonaceae or Boraginaceae). Since plants of the different families or species show differences in terms of physiology and agronomic features, they have different abilities to provide agro-ecological services (Ramírez-García et al., Reference Ramírez-García, Carrillo, Ruiz, Alonso-Ayuso and Quemada2015). Adamczewska-Sowińska et al. (Reference Adamczewska-Sowińska, Kołota and Winiarska2009) reported the criteria to select LM species on the basis of favorable traits or attributes. Leary and DeFrank (Reference Leary and DeFrank2000) also underlined the need to implement specific breeding programs for ASC species to be used as LM. However, also the cash crops to be cultivated in diversified and competitive environments, as the LM systems are, should present specific characteristics and traits. Wezel et al. (Reference Wezel, Casagrande, Celette, Vian, Ferrer and Peigné2014) contributed to identify plant breeding strategies for crops to be cultivated in systems designed in accordance to cropping practices based on agro-ecology. Vegetable cash crop hybrid genotypes and open pollinated locally adapted cultivars may differ in terms of biomass production, growth rate and root system architecture (Jackson, Reference Jackson1995). These traits may greatly influence their competitive ability and, consequently, their adaptability to intercropped and LM systems (Singh and Partap, Reference Singh and Partap2011). However, complete information about breeding programs and/or evaluation schemes to improve or to test the performances of vegetable genotypes when cultivated in LM systems are not available at present.
Also cost and energy consumption are important when assessing an agro-ecological sound technique. The change of system energy consumption can strongly influence the farmers’ decision in choosing a specific technique for both economic and environmental reasons (Wezel et al., Reference Wezel, Casagrande, Celette, Vian, Ferrer and Peigné2014). Indeed, the application at farm level of the LM is often constrained because it is perceived by farmers as a costly and energy consuming operation. Moreover, the potential impact of the LM technique on energy consumption is often pinpointed in the scientific literature. Despite that, detailed information about the use of human labor (HL) and consumption of fossil fuel (FF) energy in vegetable LM systems is not available and the assessment of their energetic performances compared with the sole ones have not been deeply studied so far.
Overall, organic farmers are demonstrating a proactive stance on development and practice of innovative production techniques based on agro-ecological principles (Leary and DeFrank, Reference Leary and DeFrank2000) as a holistic approach to manage agricultural ecosystems, their processes and impacts. According to this concept, even though farmers desire cropping systems that maximize profits, the variability of profits and/or risks, can influence the level of acceptance by farmers of the cropping systems themselves or that of the different practices or techniques (Lu et al., Reference Lu, Teasdale and Huang2003).
Based on the considerations above, we carried out a study in a range of different vegetable cropping systems, climatic and soil conditions and ASC species. The aim was to assess the effect of the introduction and management strategies of LM on cash crop yield and product quality. In more detail, we wanted to test the hypothesis that, in vegetable cropping systems, the introduction and optimized management of LM do not reduce cash crop yield or product quality. We compared the introduction of the substitutive and the additive spatial design in cropping systems; and the effect of ASC sowing time relative to cash crop transplanting. Our objective was also to verify if the effect of LM introduction varied between cash crop genotypes, testing the hypothesis that hybrid cultivars perform better than open pollinated/local cultivars in LM systems compared with sole ones.
An additional aim of the present study was to evaluate if the introduction of LM in the vegetable farming systems could significantly change the amount and the pattern of energy consumption of human and fossil origin. Finally, in order to assess the farmers’ endorsement of the LM technique, through a questionnaire, we tested farmers’ perception of LM feasibility and applicability in their own farms/systems.
Materials and Methods
Field experiments
In order to test the above hypotheses, a number of field experiments were carried out each for 2 subsequent years in the period from 2011 to 2014 in different areas of Europe, where open field organic vegetable production is important. In more detail, seven experiments (Experiment 1–7) were carried out in long term organically managed research farms and three experiments (Experiment A–C) were carried out in commercial organic farms.
Experiments 1 and 2 were carried out at the Hessian State Estate Frankenhausen, belonging to Kassel University and located in Grebenstein (latitude 51°4′N, longitude 9°4′E), in Germany. The annual precipitation and average air temperature during the vegetable growing seasons were 293 mm and 11.9°C (first year) and 257 mm and 13.5°C (second year). Experiment 1 and 2 had a randomized block design with two factors (i.e., LM introduction strategy and cash crop genotype) and three replicates, the cash crop, namely cauliflower (Brassica oleracea L. var. botrytis) for experiment 1 and leek (Allium ampeloprasum L.) for experiment 2, was grown within June and September in 2012 and 2013. The cash crop was intercropped with annual white clover (Trifolium repens L.) sown 2 weeks after transplanting at seeding rate of 8 kg ha−1. For the first factor, three treatments were compared, namely: (i) control (no LM), (ii) LM introduced according to the additive approach (Ad, ls LM) and (iii) LM introduced according to the substitutive approach by replacing every third row of vegetables a row of LM (Su, ls LM), thus entailing a reduction of 1/3 of cash crop density. Moreover, as far as the genotype factor was concerned, the Chambord and Belot HF1 hybrid and the White ball open pollinated cultivar for cauliflower and the Axima and Catcher HF1 hybrids and the Hannibal open pollinated cultivar for leek were compared.
Experiments 3 and 4 were carried out at the Research Centre Aarslev, Department of Food Science, Aarhus University and located at mid Funen (latitude 55°18′N, longitude 10°27′E) in Denmark. The annual precipitation and average air temperature during the vegetable growing seasons were 441 mm and 14°C (first year) and 167 mm and 16°C (second year). Experiment 3 had a randomized block design with three factors (i.e., LM management, cash crop genotype and nitrogen fertilization dose) and three replicates. Cauliflower was grown within May and August in 2012 and 2013, and it was alternated with LM permanent strips (p) according to a substitutive design by replacing every third row of vegetables with a row of LM, thus entailing a reduction of 1/3 of cauliflower density. LM strips were root pruned at cauliflower transplanting in accordance to Båth et al. (Reference Båth, Kristensen and Thorup-Kristensen2008) and in 2013 an additional time during the growth season to control LM competition. The LM consisted of an overwintering mix of grass and legumes (Lolium perenne L., Trifolium repens L., Medicago lupulina L. at seeding rates of 5, 3 and 3 kg ha−1, respectively). Two levels were compared for the LM management factor, namely: (i) control (no LM) and (ii) LM (Su, p LM). Moreover, as far as the genotype factor is concerned, an HF1 hybrid (Chambord) and an open pollinated cultivar (Goodman) were compared. In this paper the effect of the third factor (N fertilization dose) is not presented. Experiment 4 had a randomized block design with two factors (i.e., LM introduction strategy and cash crop genotype) and three replicates. Leek was grown within June and October in 2012 and 2013, and it was intercropped with annual dyers woad (Isatis tinctoria L.) introduced in the system according to the substitutive design by replacing every third row of vegetables with a row of LM (seeding rate 100 seeds m−2), thus entailing a reduction of 1/3 of leek density relative to the sole crop system (control). As far as the first factor was concerned, three treatments were compared, namely: (i) control (no LM), (ii) LM sown 5 weeks after leek transplanting (early sown; Su, es LM) and (iii) 7 weeks after leek transplanting (late sown; Su, ls LM). Two cash crop genotypes (second factor) were compared: Runner, an HF1 hybrid and Hannibal, an open pollinated cultivar.
Experiment 5 was carried out at the Agricultural Centre of the University of Maribor located in Pivola near Hoče (latitude 46°28′N, longitude 15°38′E) in Slovenia. The annual precipitation and average air temperature during the vegetable growing seasons was 430 mm and 18.1°C (first year) and 230 mm and 18.4°C (second year). In a randomized block design with two factors (i.e., LM management and cash crop genotype) and three replicates, cauliflower was grown within June and October in 2012 and 2013. The cash crop was intercropped with white clover (Trifolium repens L.) as LM, introduced in the system in an additive design at seeding rate of 18 kg ha−1. Three treatments were compared: (i) control (no LM), (ii) LM sown at cauliflower transplanting (early sown; Ad, es LM) and (iii) LM sown 3 weeks delayed after cauliflower transplanting (late sown; Ad, ls LM). Two cash crop genotypes (second factor) were compared: Chambord, an HF1 hybrid and Snow ball, an open pollinated, locally adapted cultivar.
Experiments 6 and 7 were carried out at the Vegetable Research Unit of the Consiglio per la Ricerca e la Sperimentazione in Agricoltura (CRA-ORA) in Monsampolo del Tronto (AP), (latitude 42°53′N, longitude 13°48′E), along the coastal area of the Marche Region, Central Italy. The annual precipitation and average air temperature during the vegetable growing seasons was 272 mm and 13.4°C (first year) and 634 mm and 13.5°C (second year). Experiment 6 had a strip plot experimental design with two factors (i.e., LM management and cash crop genotype) and three replicates, cauliflower was grown within August and January in 2012 and 2013 and it was intercropped with Burr medic (Medicago polimorpha L. var anglona) used as living mulch, introduced into the system in accordance to the additive design at seeding rate of 80 kg ha−1. As far as the first factor is concerned, three treatments were compared: (i) control (no LM), (ii) LM sown at cauliflower transplanting (early sown; Ad, es LM) and (iii) LM sown three weeks delayed after the cauliflower transplanting (late sown; Ad, ls LM). Three cash crop genotypes (second factor) were compared: Emeraude, an HF1 hybrid, ORA1 and ORA2, two patented cultivars obtained by breeders of the CREA-ORA research station derived from locally adapted, heterogeneous genetic materials. Experiment 7 had a strip plot experimental design with two factors (i.e., LM management and cash crop genotype) and three replicates, in a 3-years-old artichoke (Cynara cardunculus subsp. scolymus L.) plantation an annual LM was sown in February, approximately 5 months after the annual starting of re-growth (i.e., September) of the artichoke, and terminated in May, in both 2012 and 2013. The LM, introduced in the system in accordance to the additive design, was a mixture of species, namely (seeding rates between brackets): Pisum sativum L. (25 kg ha−1), Vicia faba var minor Beck (25 kg ha−1), Trifolium incarnatum L. (4 kg ha−1), Vicia villosa L. (8 kg ha−1), Brassica rapa L. (0.2 kg ha−1), Alyssum spp. (1 kg ha−1), Coriandrum sativum L. (1.5 kg ha−1), Phacelia tanacetifolia Benth (1.3 kg ha−1) and Fagopyron esculentum Moench (13.5 kg ha−1). Two levels were compared for the first factor: (i) control (no LM) and (ii) LM (Ad LM). Moreover, two open pollinated, locally adapted cultivars (Iesino and Mazzaferrata) were compared.
In addition to the experiments carried out in the research farms, four field experiments were conducted in organic farms using an on-farm research approach to measure energy consumption. These experiments were also carried out for 2 subsequent years (2013 and 2014) and were designed in accordance to a simple layout, which was agreed with the farmers on the basis of the preliminary results obtained from experiments carried out in the research farms in 2012. The simplified design of these experiments was also aimed to keep the pilot farm operations manageable by farmers, who operated in collaboration with the researchers.
In particular, Experiment A was conducted in an organic farm located in Hrastje Mota, a village in North East Slovenia (latitude 46°36′N, longitude 16°4′E) in 2013 and 2014. It consisted of two fields (500 m2 each) where cauliflower (Snow ball, open-pollinating cultivar) was plastic mulched using a black foil and living mulched with white clover (Trifolium repens L. cv. Huia), sown 3 weeks after transplanting.
Experiments B and C were conducted in an organic farm located in Spoltore (latitude 42°28′N, longitude 14°09′E), a village about 10 km from the Adriatic coast of Central Italy in 2013 and 2014. Experiment B consisted of two fields (500 m2 each) where cauliflower (Emeraude, hybrid HF1) was grown as sole crop and living mulched (additive design) with Burr medic (Medicago polimorpha L. var anglona). In Experiment C artichoke (Iesino and Mazzaferrata local cultivars) was grown, in two separate fields of about 1000 m2 each, as sole crop and living mulched (additive design) with the mixture of species already described for experiment 7.
In all the experiments but that where black foil was used, the no LM treatment was managed and weeded in accordance to the standard agronomic practices, commonly used by organic farmers in the area.
Measurements
Cash crop yield and quality were assessed, according to the local market standards, in the experiments carried out in the research farms (experiments 1–7). In more detail, for cauliflower, total and marketable yield (Mg ha−1), head diameter (m) and head weight (Kg) were measured at harvest. Similarly, for leek, total and marketable yield (Mg ha−1), diameter (m) and weight (Kg) were recorded. Artichoke was harvested in accordance to the globes ripening and marketability, collecting heads weekly during the whole harvesting period (mid April—beginning of June). Measurements were also taken separately by head order, which were classified in accordance to local standard in 1st, 2nd, 3rd and auxiliary order. Total yield (Mg ha−1) and total number of head (n ha−1) were then calculated as the sum of the different harvests. Head weight (g), diameter and length were also measured. In the experiments where the yield comparison between additive and substitutive systems were performed, the results of the substitutive systems were reported either as the real plant density and corrected to take into account the crop density difference of 1/3 between the compared systems. Moreover, in experiments 3–7, the products of all the cash crops (cauliflower, leek and artichoke) were evaluated including damages and faults due to diseases, pests or other biotic and non-biotic agents in accordance to Table 1. The evaluation was carried out by visual estimation using four classes as follows: 0 = no damage; 1 = light damage; 2 = intermediate damage; 3 = heavy damage.
Table 1. Agents/factors of the observed damages and faults (i.e., diseases, pests, other biotic and non-biotic agents).
Data about energy consumption were collected in experiment A–C following a similar standardized procedure. During the cash crop cycle, all the field operations were recorded and the consumption of variable energy (fossil fuel and human power) was calculated. Neither the energy embedded in the machinery, which represents a fixed component, nor the differences in the type of HL, depending on the worker age, gender and on the type of operation done were taken into account (Giampietro and Pimentel, Reference Giampietro and Pimentel1990). Both fuel and human power were converted in MJ: the energy equivalent of human power used was 2.3 MJ man*hour−1 (Ozkan et al., Reference Ozkan, Kurklu and Akcaoz2004) and of 47.8 MJ kg−1 for diesel fuel (Ortiz-Cañavate and Hernanz Reference Ortiz-Cañavate and Hernanz1999).
Questionnaire structure and administration
For the specific purpose of this study, a questionnaire for farmers was developed (Mellenbergh, Reference Mellenbergh2008). It consisted of eight questions, clustered in three groups. The first one had the aim to classify the respondents according to the nationality and to the typology of farming activity in which he/she was involved. The second cluster started with a typical ‘skip’ question, to let only the respondents who had experience on LM go through the entire questionnaire (Foddy, Reference Foddy1994). Accordingly, questions from 3 to 5 were targeted only to the respondents familiar with LM and were aimed to analyze their expectations towards the LM technique and to investigate their motivation. The third cluster (questions from 6 to 8) represented the core of the questionnaire, containing questions meant to capture the perception of the effectiveness of the LM technique in terms of ecological services, yield and quality provided. Two of these questions were ‘closed-ended’, nominal-polytomous, as the respondent had more than two unordered options and was allowed to provide more than one answer. Finally, an open ended question (Gillham, Reference Gillham2008) was addressed to collect farmers’ opinion on the weaknesses and strength of the LM technique.
The questionnaire was administrated to farmers of four different nationalities (namely: Italy, Slovenia, Denmark and Germany; n = 19), using a ‘paper and pencil’ administration model (Lavrakas, Reference Lavrakas, Pau and Lavrakas2008). The questionnaire was filled in mainly as complementary activity, during workshops, field days and other events organized in the frame of extension activities to share knowledge among farmers and scientists promoting innovation knowledge exchange. For sake of clarity, a questionnaire proponent remained available while the farmer filled it in to elucidate possible obscure elements, yet without interfering whatsoever with the respondent.
Data handling and statistical analysis
Yield and quality parameters were analyzed by analysis of variance (ANOVA) using LM management and cash crop genotype as fixed factors and the year as random factor. The Least Significant Difference (LSD) and the Duncan Multiple Range Test (DMRT) were performed for treatment mean comparisons for two and more than two comparisons, respectively (P ≤ 0.05 probability level). We chose to present main effects of fixed factors due to lack of significant LM management × genotype interaction and, in most of cases, for the year factor.
In the experiments where the LM was introduced according to the substitutive design, in order to directly compare the LM treatments with the control (no LM), yield results were corrected to take into account the difference of crop density. Corrected and not-corrected mean values are presented and discussed.
The Kruskal–Wallis H-test, based on rank transformation, was applied for the analysis of damages and faults. The pairwise comparisons per LM management factor were processed by the Mann–Whitney post hoc test.
The above described analyses were performed with the SPSS 16.0 package.
As far as the questionnaire is concerned, for each question, the percentage of the answers was calculated. In more detail, for some questions the respondents were allowed to give more than one answer, therefore the total of the percentage may exceed 100%.
Questionnaire data were analyzed through Excel™.
Results and Discussion
Effect of system design
Tables 2 and 3 report the yield and quality parameters for cauliflower and leek obtained respectively in experiment 1 and 2 (non-permanent LM sown 2 weeks after the cash crop transplanting). Both cauliflower and leek total and marketable yield were significantly lower in the substitutive system in comparison with either the additive system and the control (no LM). However, when the two parameters were corrected to take into account the difference of the cash crop density (number of plants * unit area−1) the total and the marketable yield were slightly higher (no significant difference) than the other treatments. Therefore, the yield reduction of the substitutive system was due only to the different cash crop density and we excluded relevant changes in the rate of the main physiological processes (i.e., photosynthesis) and resource use efficiency (i.e., water and nutrient use) of cauliflower and leek in the compared treatments. The effect of permanent LM substitutive design on cauliflower yield and quality was assessed in experiment 3 (Table 4). The obtained results, similarly to those obtained in experiments 1 and 2, evidenced that yield reduction of LM system was due to the cash crop density and not to interspecific competition (Xie and Kristensen, Reference Xie and Kristensen2016).
Table 2. Effect of non-permanent LM design on cauliflower yield and quality (Experiment 1).
Note: no, sole crop system (control); ad, additive system; su, substitutive system; su_c, substitutive system with results corrected to take into account the crop density difference between the compared systems; ls, late sown LM.
The mean values in each column followed by a different letter are significantly different according to Duncan Multiple Range Test at the reported probability level.
n.s., not significant; ***P ≤ 0.001; **P ≤ 0.01; *P ≤ 0.05.
Table 3. Effect of non-permanent LM design on leek yield and quality (Experiment 2).
Note: no, sole crop system (control); ad, additive system; su, substitutive system; su_c, substitutive system with results corrected to take into account the crop density difference between the compared systems; ls, late sown LM.
The mean values in each column followed by a different letter are significantly different according to Duncan Multiple Range Test at the reported probability level.
n.s., not significant; ***P ≤ 0.001; **P ≤ 0.01; *P ≤ 0.05.
Table 4. Effect of permanent LM design on cauliflower yield and quality (Experiment 3).
Note: no, sole crop system (control); ad, additive system; su, substitutive system; su_c, substitutive system with results corrected to take into account the crop density difference between the compared systems; p, permanent LM. The mean values in each column followed by a different letter are significantly different according to Duncan Multiple Range Test at the reported probability level.
n.s., not significant; ***P ≤ 0.001; **P ≤ 0.01; *P ≤ 0.05.
On the basis of the above reported results, we argue that LM systems designed in accordance to the substitutive approach are effectively implementable in vegetable production only if the value of the ecological services (positive externalities) delivered by LM to the system is of the same order of magnitude or higher as the value of the yield loss due to the cash crop density reduction (Crowder and Reganold, Reference Crowder and Reganold2015).
No significant differences were observed for the main cauliflower and leek quality parameters (diameter and weight of head and stem, respectively) in all the compared treatments, thus indicating that neither the introduction of LM in the system nor the type of system design determined a quality loss or improvement compared with the sole crop system. This confirmed that the tested technique could be used in vegetable production with the aim to exploit its potential to deliver agro-ecological services (i.e., weed control, soil erosion protection, enhancement of beneficial arthropods activity).
Effect of LM sowing time
Yield and quality effects of LM sowing time in respect of the transplanting of the vegetable cash crop are reported in Tables 2, 3, 5, 6 and 7.
Table 5. Effect of LM sowing time on cauliflower yield and quality (Experiment 5).
Note: no, sole crop system (control); ad, additive design; es, early sown LM; ls, late sown LM. Note.
The mean values in each column followed by a different letter are significantly different according to Least Significant Difference at the reported probability level.
n.s., not significant; ***P ≤ 0.001; **P ≤ 0.01; *P ≤ 0.05.
Table 6. Effect of LM sowing time on cauliflower yield and quality (Experiment 6).
Note: no, sole crop system (control); ad, additive design; es, early sown LM; ls, late sown LM. Note. The mean values in each column followed by a different letter are significantly different according to Duncan Multiple Range Test at the reported probability level.
n.s., not significant; ***P ≤ 0.001; **P ≤ 0.01; *P ≤ 0.05.
Table 7. Effect of LM sowing time on leek yield and quality (Experiment 4).
Note: no, sole crop system (control); su, substitutive design; es, early sown; ls, late sown; _c, results corrected to take into account the crop density difference between the compared systems.
The mean values in each column followed by a different letter are significantly different according to Duncan Multiple Range Test at the reported probability level.
n.s., not significant; ***P ≤ 0.001; **P ≤ 0.01; *P ≤ 0.05.
In the case of additive design, when LM was sown with 2–3 weeks delay in respect to the transplanting of the cash crop, we observed similar or lower total and marketable yield in comparison to the control (no LM) in experiments 1 and 2 (Tables 2 and 3) and in experiments 5 and 6 (Tables 5 and 6), respectively. These findings, which did not allow us to reach a clear conclusion, can be explained considering that our experiments were carried out in very different pedoclimatic environments and in different seasons (summer and winter, respectively). It is likely that the available resources for the crops (i.e., water and light) were very different and influenced the results. On the other hand, in experiments 5 and 6 (Tables 5 and 6), despite the different pedo-climatic conditions, total and marketable yield significantly decreased when the LM was early sown (simultaneously to the cash crop transplanting), both in comparison with the control (no LM) and the late sown LM (Ad, ls LM). In particular, in the experiment 5 (Table 5), due to the strong competition between LM and cash crop, the cauliflower completely succumbed. These results are in accordance with Adamczewska-Sowińska et al. (Reference Adamczewska-Sowińska, Kołota and Winiarska2009) who observed a yield reduction if the LM sowing was not delayed in respect to the cash crop transplanting and attributed the yield reduction to the competition for nutrients, water and light between the two components of the system (i.e., the cash crop and the LM).
When non-permanent LM was introduced according to the substitutive design in Experiment 4, we did not observe significant differences on yield between the early and the late sown treatments (Table 7). These results demonstrated that, as expected, the density of the system and the length of the period in which the cover and the cash crop coexist in the same area are oppositely related in terms of competition and yield. Therefore, if the LM has to be established in advance of the cash crop in order to deliver its agro-ecological services to the system, it is preferable to use the substitutive design instead of the additive one. Moreover, the LM often reduced the head size and weight of cauliflower when it was introduced as additive design (Table 5 and 6). Conversely, we observed no differences on the quality of leek between early and late sown LM when the substitutive design was used (Table 7). This achievement was in agreement to several studies (Bottenberg et al., Reference Bottenberg, Masiunas, Eastman and Eastburn1997; Leary and DeFrank, Reference Leary and DeFrank2000; Hartwig and Ammon, Reference Hartwig and Ammon2002; Adamczewska-Sowińska et al., Reference Adamczewska-Sowińska, Kołota and Winiarska2009), which reported a quality detriment of yields in additive LM systems.
Effect on damages and faults
In all the experiments, none of the measurements carried out for assessing damages and faults of the products (Table 1) showed significant differences between the living mulch and the sole cropping system (results not reported). Our results, obtained irrespective of the cash crop species studied, its growing season and the experimental site, further confirmed that the introduction of LM did not influence the quality of vegetables.
Effect of cash crop genotype
The effect of the genotype on yield and quality is reported in Tables 8–10 for cauliflower, leek and artichoke, respectively. Table 8 shows that the hybrid genotypes of cauliflower performed better than the open pollinated cultivars in 3 out of 4 experiments (namely, experiments 1, 3 and 6). However, in experiment 1, the White ball open pollinated cultivar showed intermediate values compared to the two hybrid genotypes tested, the Belot hybrid being the less performing genotype. Only in experiment 5, Snow ball, an open pollinated cultivar yielded more and showed a better quality response than the correspondent hybrid genotype. As far as leek was concerned, the hybrid genotypes did not perform better than the correspondent open pollinated cultivar (Table 9). Hannibal (open pollinated) performed best in both the experiments, which were carried out in very different pedological and climatic European regions.
Table 8. Effect of genotype on cauliflower yield and quality.
Note. The mean values in each column followed by a different letter are significantly different according to Least Significant Difference and Duncan Multiple Range Test (two and more than two comparisons, respectively) at the reported probability level.
n.s., not significant; ***P ≤ 0.001; **P ≤ 0.01; *P ≤ 0.05.
Table 9. Effect of genotype on leek yield and quality.
Note. The mean values in each column followed by a different letter are significantly different according to Least Significant Difference and Duncan Multiple Range Test (two and more than two comparisons, respectively) at the reported probability level.
n.s., not significant; ***P ≤ 0.001; **P ≤ 0.01; *P ≤ 0.05.
The two open pollinated artichoke cultivars grown in the experiment 7 yielded very differently, the Mazzaferrata being the most productive (Table 10). This result was mainly determined by the total number of heads, which was dramatically higher in the Mazzaferrata compared with the Iesino. However, the Iesino first order head weight was greater than the Mazzaferrata one. This is a relevant aspect since, in artichoke, generally most of the yield value is related to the market quality (i.e., size and shape) of the first order head. Therefore, the information achieved might be useful to guide farmers’ decisions in regard to the choice of cultivar.
Table 10. Effect of genotype on artichoke yield and quality.
Note. The mean values in each column followed by a different letter are significantly different according to Least Significant Difference at the reported probability level.
n.s., not significant; ***P ≤ 0.001; **P ≤ 0.01; *P ≤ 0.05.
However, it is noticeable that, irrespectively to which was the best performing genotype in each of the experiments, we never observed a significant LM management × genotype interaction (results not reported). These results did not confirm our hypothesis that hybrids and open pollinated/local cultivars of the studied vegetable cash crops perform differently in the LM systems in comparison with the sole ones. The results demonstrated that the effect of LM introduction did not vary with respect to the cash crop genotype. Consequently, the findings indicated that farmers can select the genotype to grow on the basis of other conditions than the LM introduction and management (i.e., their own preference and/or market request).
Effect on energy consumption
Energy consumption derived from HL and FF in the LM and sole cropped cauliflower and artichoke were studied in the experiments A, B and C. In experiment A (Table 11), the sole cropping system had an higher energy consumption for soil tillage than the living mulched treatment, which instead had preparation of ridges, necessary when LM is used. Cauliflower transplanting was done by hand in the sole crop and by machinery (tractor and planter) in the LM system and, for this reason, the LM treatment showed a higher FF energy consumption. Conversely, energy spent for irrigation was considerably higher in the sole crop system. This last result was likely due to the different soil temperature that might be higher in the control, because of the plastic mulch, than the LM treatment and, consequently, influenced the soil evaporation and water consumption of the crop (Xu et al., Reference Xu, Li, Liu, Zhou, Tao, Wang, Meng and Zhao2015). However, this evidence need to be further verified in different climatic and soil conditions. Moreover, the LM system required more effort than the control in term of HL and FF consumption because of the soil tillage needed to prepare the LM sowing bed. The energy spent for hoeing and mowing in the control treatment were due to the weeding operation carried out between the black foiled ridges. The slight difference observed in the two treatments for the harvest (which was done manually) was due to the yield differences between the two treatments, which was lower in the LM system (results not shown). The energy consumption in the LM system was 9.5% lower and 14.5% higher than the sole crop one, for HL and FF, respectively.
Table 11. Human labor and fossil fuel energy consumption in cauliflower (Mj ha−1) in experiment A and B.
Note: no LM, sole crop system, control; LM, living mulched system; PPP, plant protection products.
In experiments B (Table 11) and C (Table 12), the only difference observed between the two treatments was due to the LM sowing operations, which were done by hand. Consequently, energy consumption of HL in the LM system showed an increase in respect to the sole one (9 and 17.5% for cauliflower and artichoke, respectively).
Table 12. Human labor and fossil fuel energy consumption in artichoke (Experiment C; Mj ha−1).
Note: no LM, sole crop system, control; LM, living mulched system.
Overall, in all the three experiments, the total energy consumption for HL and FF consumption was higher in the LM systems in respect to the sole crop ones, having the highest difference (11%) in the cauliflower of experiment A, the lowest (2%) in the cauliflower of experiment B and intermediate (7%) in the artichoke of experiment C. The increase of energy use due to the introduction of living mulches in cropping systems was also reported by Wezel et al. (Reference Wezel, Casagrande, Celette, Vian, Ferrer and Peigné2014). These results should be evaluated taking into account that, in vegetable crops, the energy of human and FF accounted for between 30 and 50% of the total energy used, while the amount of energy contained in the off-farm inputs (i.e., fertilizers and plant production products) and that embedded in the machinery have the largest share (Ozkan et al., Reference Ozkan, Kurklu and Akcaoz2004; Gomiero et al., Reference Gomiero, Pimentel and Paoletti2008). Moreover, in two out of three cases, the measured differences were only due to the HL, confirming that the implementation of agro-ecological practices may determine a shift in the proportion of FF and human energy consumption (Smith et al., Reference Smith, Williams and Pearce2015).
Acceptability of the LM technique by farmers
Nineteen questionnaires (1 from Denmark, 8 from Germany, 5 from Italy and 5 from Slovenia) about perception of the LM technique were gathered from organic farmers running either open field specialized (16%) and non-specialized (84%) vegetable farms. Indeed, in addition to the open field activities, the other productions operated by the non-specialized farmers were: greenhouse vegetables (26% of farmers), field crops (42%), animal husbandry (11%), others (16%).
Results revealed a quite positive judgment of farmers on the effectiveness of the technique to provide proper yields and acceptable quality standards (Fig. 1). However, more than 1/4 of farmers were not satisfied with the performance of the LM systems, indicating that this technique is widely perceived as not effective and/or risky.
Figure 1. Perception of farmers on the effect of living mulch on yield (a) and quality (b) of vegetable crops (% of respondent for each level of satisfaction1; n = 19). Note: 0 = low (not satisfied); 4 = high (fully satisfied).
Perceptions of farmers of the ecological services provided by LM in the vegetable cropping systems are reported in Figure 2. Contributions of the LM technique to control weeds and improve soil fertility were the most positively perceived services (i.e., 32 and 47% of farmers scored 4 for these services). Conversely, the promotion of insect pest–beneficial interaction was not clearly perceived as a relevant service by all interviewed famers, their answers being distributed over a wider range of scores. Also, the respondents had the perception that the LM technique is only able to a low or medium extent to reduce costs, energy consumption and the risk of nitrate losses from the vegetable cropping systems. In Table 13, selected farmers’ opinions on LM are reported. It is remarkable that the positive statements include relevant ecological services as ‘biodiversity conservation’ and ‘soil erosion protection’, demonstrating a high familiarity of some of the interviewed organic farmers with the potential agro-ecological benefits of living mulch. At the same time, concerns about the feasibility of the technique as well as the incommensurability between costs and resources used, on one hand and product quality and environmental benefits on the other, clearly emerged. Overall, the farmers’ acceptance of the LM techniques was quite high, even though their critical considerations about yield quality and quantity have to be taken into consideration in order to set up future research and implementation activities based on LM.
Figure 2. Perception of farmers on the ecological services provided by living mulch in the vegetable cropping systems (% of respondent for each level of contribution1; n = 19). Note: 0 = low (no contribution); 4 = high contribution; 2) since the respondents could check no or more than one option, the total of the percentage may exceed 100%.
Table 13. Selected farmers’ statements related to living mulch (LM).
Conclusions
This study allowed to assess the effect of the introduction and management strategies of LM on cash crop yield and product quality, in a range of different vegetable cropping systems, climatic and soil conditions and crop genotypes. The LM systems designed in accordance to the substitutive approach should be implemented in vegetable production only if the value of the agro-ecological services (i.e., weed control, soil erosion protection, enhancement of beneficial arthropods activity, reduction of nitrate leaching) delivered by LM to the system is of the same order of magnitude as the yield loss due to the cash crop density reduction. Further study aimed to identify the breakeven point between the impact of LM on farming output and positive externalities in the different cropping systems should be encouraged in order to set a suite of agro-environmental policy measures.
It was confirmed that the crop density of the system and the length of the period in which the ASC used for LM and the cash crops coexist in the same area are oppositely related for competition and yield. Therefore, if the ASC has to be established early in advance to the cash crop cycle in order to deliver its agro-ecological services to the system, it is preferable to use the substitutive design instead of the additive one.
If the additive design is preferred, the LM should be established several weeks after the cash crop. However, since we observed that the responses of the LM introduction were both crop (system) and site specific, farmers should verify the effectiveness of the technique under their local conditions.
Our results indicated that the cash crop genotype did not affect the performance of the LM vegetable systems and, consequently, farmers can select the genotypes to grow in accordance to their own preferences and/or the market request.
In general, human labor and FF energy use slightly increased in LM systems and the implementation of this practice may determine a shift in the proportion of FF and human energy consumption.
The on-farm research carried out in the framework of this specific study, has played an important role for validating and developing the findings about LM. Moving to farmers’ fields and interacting with them allowed the researchers to have a real appraisal of the farmers’ conditions and problems. Indeed, combining research evidence and farmers’ perception, this study represented a great opportunity for the identification of problem areas and issues that arise from both the scientists’ and farmers’ perspective, thus promoting a continuous process of refining, improving and re-testing the experimental and practical technique.
Acknowledgements
This study has been carried out in the frame of the InterVeg research project: Enhancing multifunctional benefits of cover crops—vegetables intercropping (Core Organic II ERA-NET).
