The expansion of renewable energies aims at meeting the global energy demand while replacing fossil fuels. However, it requires large areas of land. At the same time, food security is threatened by the impacts of climate change and a growing world population. This has led to increasing competition for limited land resources. In this context, the combination of photovoltaics and plant productionoften referred to as agrophotovoltaic (APV) or agrivoltaic systemshas been suggested as an opportunity for the synergistic combination of renewable energy and food production. Although this technology has already been applied in various commercial projects, its practicability and impact on crop production have hardly been investigated. In this review, we give a short summary of the current state of the art and prospective opportunities for the application of APV systems. In addition, we discuss microclimatic alterations and the resulting impacts of APV on crop production. Our main findings are that (1) crop cultivation underneath APV can lead to declining crop yields as solar radiation is expected to be reduced by about one third underneath the panels. However, microclimatic heterogeneities and their impact on crop yields are missing reference and thus, remain uncertain. (2) Through combined energy and crop production, APV can increase land productivity by up to 70%. (3) Given the impacts of climate change and conditions in arid climates, potential benefits are likely for crop production through additional shading and observed improvements of water productivity. (4) In addition, APV enhances the economic value of farming and can contribute to decentralized, off-grid electrification in developing and rural areas, thus further improving agricultural productivity. As such, APV can be a valuable technical approach for more sustainable agriculture, helping to meet current and prospective needs of energy and food production and simultaneously sparing land resources.

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Abstract:Soybean field experiments were performed to investigate the weed-suppressing effects of different tillage systems and cover crop mulches at two locations in southwest Germany during 2014 and 2015. The influence of three different tillage systems on weed control efficacy, soybean plant density, and crop yield was determined. In the no-till system (NT), two different cover crops, (rye and barley), were treated by a roller-crimper before soybean sowing. For the reduced tillage system (RT), shallow soil cultivation (7.5 cm depth) using a cultivator after cover crop harvest was performed. The third system was conventional tillage (CT), which used a plow (25 cm depth) without any previous cover crop treatment. Finally, a CT system without weed control was used as a control treatment (C). Weed densities in the field experiments ranged from 1 to 164 plants m −2 with Chenopodium album (L.), Echinochloa crus-galli (L.) P. Beauv., and Sonchus arvensis (L.) as the predominant weed species. No difference in weed suppression was found between the two cover crops. The highest cover crop soil coverage was measured in the NT treatment. The greatest weed density (164 plants m −2 ) was measured in the untreated control. CT, RT and NT reduced weed density up to 71%, 85%, and 61%, respectively, to C, across both locations and years. Soybean plant density was reduced in NT (−36%) and CT (−18%) based on aimed sown plant density. Highest crop yields up to 2.4 t ha −1 were observed in RT, while NT resulted in lower yields (1.1 t ha −1 ). Our work reveals the importance of cover crops for weed suppression in soybean cropping systems without herbicide application.

Weathering and initial soil formation was investigated on 5 sites of lignite ash disposal differing in age (5 to 30 years) and methods of disposal (landfills and sluicing to settling ponds). Soils developed on lignite ash derived substrates were characterized by low bulk densities (< 0.85 g cm—3), high contents of gypsum (maximum 27%) and calcium carbonate (maximum 46%), high pH values (7—9), very high contents of organic carbon (about 20%), and high contents of ammonium oxalate soluble Si, Al, and Fe containing compounds. These features depended on the constitution of the lignite and the burning conditions. As the substrates were initially in disequilibrium with their environmental surroundings, they were subjected to rapid weathering. Typical features were the depletion of gypsum and decarbonatization in the topsoils of the profiles. Furthermore, pedogenic organic carbon became enriched by ruderal vegetation despite low contents of plant available P and K and high pH values. The C : N ratios increased with profile depth, which indicated the input of pedogenic OM with low C : N ratios into topsoils and the predominance of lignite with a wide C : N ratio (> 100) in subsoils.