Search

In recent years there has been an increasing spread of photovoltaic greenhouses, especially in southern European countries, due to the higher incentives recognized to solar photovoltaic (PV) panels integrated on the greenhouse roofs and/or to local laws which limit the photovoltaic systems on the ground. To maximize the income from the production of electricity, often solar panels cover 50% or more of the roof, but the shading caused by these elements on the growing surface seriously limits the productivity and affects crop development. In order to assess the effects of the spatial distribution of the solar radiation inside these structures on yield and quality of leaf vegetable crops, the response of lettuce, grown in two cycles (autumn and winter-spring), in an east-west oriented photovoltaic greenhouse with the 50% of the roof covered by PV modules was analysed. The influence of span orientation, plant position (under plastic or PV roof) and cultivar were analysed as experimental treatments in a split-split plot design with two replications. Total and marketable yield of the lettuce heads and some quality parameters (dry matter and nitrate content) were evaluated. A significant variability of the total and marketable yield due to the plant position and as consequence to the solar radiation distribution inside the structure during the growing cycle was observed. Furthermore, ranges and variability of the nitrate content of lettuce (expressed as NO(3) mg kg(‑1) of fresh weight) were affected by the plant position and harvest season. In order to maximize yield and quality of the crops, the arrangement of plant rows and transit areas, as well as the management of nutrition, should be optimized in relation to the shading caused by the PV roof during the growing cycle.

The cultivation of the horticultural crops inside photovoltaic greenhouses (PVG) should be studied in relation to the shading cast by the photovoltaic (PV) panels on the roof. This work evaluated the green bean cultivation inside PVGs with a percentage of the greenhouse area covered with PV panels (PV cover ratio, PVR) ranging from 25 to 100%. Three dwarf green bean cycles (Phaseolus vulgaris L., cv. Valentino) were conducted inside an iron–plastic PVG with a PVR of 50%. The average yield was 31% lower than a conventional greenhouse. Adverse effects on quality were noticed under the PV roof, including a reduction of pod weight, size, and caliber. Negative net photosynthetic assimilation rates were observed on the plants under the PV roof, which adapted by relocating more resources to the stems, increasing the specific leaf area (SLA), leaf area ratio (LAR), and the radiation use efficiency (RUE). The fresh yield increased by 0.44% for each additional 1% of cumulated PAR. Based on the linear regressions between measured yield and cumulated PAR, a limited yield reduction of 16% was calculated inside a PVG with maximum PVR of 25%, whereas an average yield loss of 52% can occur with a PVR of 100%. The economic trade-off between energy and green bean yield can be achieved with a PVR of 10%. The same experimental approach can be used as a decision support tool to identify other crops suitable for cultivation inside PVGs and assess the agricultural sustainability of the mixed system.

The aim of this work was to calibrate CROPGRO-Tomato model, included in the Decision Support System for Agrotechnology Transfer (DSSAT) software, for a cherry tomato genotype grown in a photovoltaic greenhouse in southern Europe (39°19'59”N; 8°59'19”E). The experiment was carried out in Decimomannu, Sardinia, in an East-West oriented pitched-roof greenhouse with two spans (50×9.6 m each) covering an area of 960 m2. Silicon photovoltaic panels were used to completely replace the south-oriented roof of each span, resulting in a 50% roof cover ratio. Tomato was grown hydroponically with a plant density of 2.3 plants m-2. An autumn-winter tomato crop cycle was carried out from August 2011 to January 2012. Microclimatic conditions were monitored for the whole lifespan of the experiment (e.g., internal global and PAR radiation and greenhouse internal temperature). Phenology was monitored at weekly interval. Leaf area, aboveground biomass, and fresh fruit production was determined at fifteen day interval. CROPGRO-Tomato model was calibrated over the uncovered roof data and it was evaluated over the covered roof data. The genotype file (cultivar), including the main parameters of crop phenology and plant growth, was adapted to the cherry tomato cultivar 'Shiren'. The first flowering date showed a good agreement between simulated and observed data. The model fitted well the observed leaf area index data with an index of agreement (D-Index) of 0.87 and an average root mean square error (RMSE) of 0.53. Good agreement was observed between the measured and simulated plant development parameters as biomass and fresh weight yield. Overall, the CROPGRO-Tomato model proved to be suitable for predicting tomato growth and yields inside PV greenhouses and under different light intensity conditions. However, model validation is also necessary to show how the model works under a spring-summer cycle and with supplementary lighting system.

This study introduces a novel algorithm to estimate the cumulated global radiation inside photovoltaic (PV) greenhouses at the desired time interval. The direct and diffuse radiation were calculated on several observations points (OPs) inside the PV greenhouse. The PV panels were assimilated to polygons that can overlap the sun path seen from a specific OP. The algorithm was tested in a greenhouse with 50% PV cover ratio on the roof. The results were showed as the percentage ratio of the cumulated yearly global radiation with and without PV array on the roof (GGR), and used to draw maps of light distribution on different canopy heights (from 0.0 to 2.0 m). The maps displayed the variability of the light distribution and the most adversely affected zones inside the PV greenhouse. The yearly GGR increased with the canopy height on the zones under the plastic cover (GGR from 59% at 0.0 m to 73% at 2.0 m), and decreased under the PV cover (GGR from 57% at 0.0 m to 40% at 2.0 m). Most zones close to the side walls and the gable walls were the least affected by shading on all canopy heights. The different light distribution on the canopy heights showed that the incident solar energy on the crop changes consistently, according to the growth stage of the plants. The algorithm can be applied to several PV greenhouse types and may provide a decision support tool for the identification of the most suitable plant species, based on their light requirements.

International audience; AbstractThe conventional cultivation of globe artichoke causes high nitrogen (N) balance surpluses. The planning of more sustainable open-field horticultural systems (with no synthetic fertilizer supply) can contribute to the reduction of the nutrient surplus. We hypothesized that an artichoke conventional system could be shifted to a sustainable system through mineral fertilizer supply based on expected plant nutrient uptake, return of crop residues in well-defined growth phases, use of fertility-building crops, and crop rotations. Over a 10-year field experiment, three management systems, differing in fertilizer rates, crop sequence (monoculture/rotation with cauliflower), and legume cover crop adoption and management, were compared: (i) improved conventional, (ii) alternative monoculture, and (iii) biannual rotation. We monitored soil conditions at a sampling interval of approximately 3 years. We calculated gross N, P, and K balances for each growing season, and we also monitored soil respiration over the last two growing seasons. On average, the biannual rotation resulted in a well-balanced N budget (72 kg ha−1 N surplus) compared with improved conventional (160 kg N ha−1 N surplus) and alternative monoculture (− 34 kg ha−1 deficit) systems. By contrast, compared with the improved conventional system (133 and 116 kg ha−1 for P and K budgets, respectively), alternative monoculture and biannual rotation systems had negative budgets for P (− 9 kg ha−1 for both alternative systems) and K (− 58 and − 51 kg ha−1 for alternative monoculture and biannual rotation systems, respectively) in nine of ten growing seasons. Our results show for the first time that long-term biannual rotation with cauliflower coupled with cover crop use can optimize nutrient fluxes of conventionally grown globe artichoke. Overall, the study proposes a re-design of artichoke cropping systems, provides novel information useful for growers, and verifies that introducing a legume species cover crop is also the most promising approach to foster long-term sustainability.

Due to the complexity of soil organic carbon (SOC), models have proved very useful in helping to improve our understanding of the soil–plant–atmosphere system. In this study we used the Rothamsted carbon model (RothC), which considers the effect of climate (temperature, rainfall and evaporation), soil texture (clay content) and crop management on the decomposition processes, to predict changes in SOC under different land uses and the different climate that may occur in the future. SOC turnover was evaluated in land uses under different levels of agricultural intensification. The agriculture of the study-area is mainly extensive and markedly agro-silvo-pastoral, and is typical of north-eastern Sardinia (Italy) and similar areas of the Mediterranean basin. The following land uses were considered: vineyards, hay crops, pastures, semi-natural systems (formerly vineyards) and cork oak forests. Since the study-area is characterized by the same soil type (Haplic Endoleptic Cambisols, Dystric) derived from granitic rocks and potential native vegetation (Quercus suber L.), this was considered as the model baseline to study soil organic carbon dynamics. Climate change scenarios for 90 yr were generated from the baseline climate with two Global Climate Models: GISS (Goddard Institute of Space Studies, USA), and HadCM3 (Met Office, Hadley Centre, UK), for two of the Intergovernmental Panel on Climate Change (IPCC) emission scenarios (SRES A2 and B2). Land uses at low cropping intensity were more efficient than intensive agricultural systems in terms of SOC storage in the order: hay crop > pasture > cork oak forest > semi-natural systems. Land use change to vineyards decreased the carbon balance significantly between 0.09 and 0.15 t C ha−1 yr−1. However, former vineyards have almost recovered from soil disturbance following the establishment of the vineyards.