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Background: Alley-cropping systems in the temperate zone are a type of agroforestry in which rows of fast-growing trees are alternated with rows of annual crops. With numerous environmental benefits, temperate agroforestry is considered a promising alternative to conventional agriculture and soil fungi may play a key in maintaining productivity of these systems. Agroforestry systems that are established for more than 10 years have shown to increase the fungal biomass and impact the composition of soil fungal communities. Investigations of soil fungi in younger temperate agroforestry systems are scarce and the temporal dynamic of these changes is not understood. Methods: Our study was conducted in a young poplar-based alley cropping and adjacent monoculture cropland system in an Arenosol soil in north-west Germany. We investigated the temporal dynamics of fungal populations after the establishment of agroforestry by collecting soil samples half, one, and one and a half years after conversion of cropland to agroforestry. Samples were collected within the agroforestry tree row, at 1, 7, and 24 m distance from the tree row within the crop row, and in an adjacent conventional monoculture cropland. The biomass of soil fungi, Asco-, and Basidiomycota was determined by real-time PCR. Soil fungal community composition and diversity were obtained from amplicon sequencing. Results: Differences in the community composition of soil fungi in the tree row and arable land were detected as early as half a year following the conversion of monoculture cropland to agroforestry. In the tree row, soil fungal communities in the plots strongly diverged with the age of the system. The presence of young trees did not affect the biomass of soil fungi. Conclusions: The composition of soil fungal communities responded rapidly to the integration of trees into arable land through agroforestry, whereas the fungal biomass was not affected during the first one and a half years after planting the trees. Fungal communities under the trees gradually diversified. Adaptation to spatially heterogeneous belowground biomass of the trees and understory vegetation or stochastic phenomena due to limited exchange among fungal populations may account for this effect; long-term monitoring might help unravelling the cause. [ABSTRACT FROM AUTHOR]

This account describes the context, history and outcomes of a series of studies into the ecology of slash-and-burn (S-B) agriculture in the world's humid tropics. These studies, which began in the mid-1980s, identified promising lines of research and continued to field trials, in Central America, of candidate agricultural systems as possible sustainable alternatives to the practice. The only system to emerge from 7 years' comparative trial with any promise of sustainability, in this context, was the agroforestry technique known as alley-cropping; but only with trees of the genus Inga. Inga alley-cropping then underwent field trials with subsistence farming families in northern Honduras. The system was aimed at the twin objectives of achieving food security in basic grains, on minimal inputs, and of providing the means of eliminating further S-B in the region. Since then, Inga alley-cropping has become the heart of a sustainable and integrated rural livelihood model (the Guama Model) which is being implemented successfully in northern Honduras with some 300 families. These families had been attempting to subsist on a few hectares of land degraded by decades or centuries of S-B. The development of Inga alley-cropping, supplemented by rock phosphate and other mineral supplements, as a sustainable subsistence and cash crop alternative means that land previously being held in reserve for subsequent S-B operations can now be planted to permanent forms of agroforestry. Entire landscapes can be re-greened by productive agroforest vegetation. Achieving this at scale will require the investment of huge extension effort and funds. However, the environmental, social and economic returns are also huge; and they are sustainable. In this programme,we are seeing the vitality and goodwill of hundreds of families focussed on the raising, planting and management of trees in ways that feed the living organisms of the soil and, hence, feed themselves. In so cheerfully planting out their own futures, they plant and reshape the future of their own country. Replicating this at scale, as Rattan Lal outlines below, could reshape the future of this planet. In the mid-1980s, progress on sustainable alternatives to S-B, especially in rain forests, was frustrated by a lack of conclusiveness in the literature as to why soil fertility fails so rapidly post-burn; but also by a degree of contradiction on the impacts of the burn on certain plant nutrients. Hands (Hands 1988 The ecology of shifting cultivation. MSc thesis, University of Cambridge) concentrated on the role of soil phosphorus and attempted to resolve these contradictions. The Cambridge Alley-cropping Projects (1988–2002) continued this theme and threw light on the question of sustainable food production in rain forest environments.

Agroforestry, which is the integration of trees into monoculture cropland, can alter soil properties and nutrient cycling. Temperate agroforestry practices have been shown to affect soil microbial communities as indicated by changes in enzyme activities, substrate-induced respiration, and microbial biomass. Research exploring soil microbial communities in temperate agroforestry with the help of molecular tools which allow for the quantification of microbial taxa and selected genes is scarce. Here, we quantified 13 taxonomic groups of microorganisms and nine genes involved in N cycling (N2 fixation, nitrification, and denitrification) in soils of three paired temperate agroforestry and conventional monoculture croplands using real-time PCR. The agroforestry croplands were poplar-based alley-cropping systems in which samples were collected in the tree rows as well as within the crop rows at three distances from the tree rows. The abundance of Acidobacteria, Actinobacteria, Alpha- and Gammaproteobacteria, Firmicutes, and Verrucomicrobia increased in the vicinity of poplar trees, which may be accounted for by the presence of persistent poplar roots as well as by the input of tree litter. The strongest population increase was observed for Basidiomycota, which was likely related to high soil moisture, the accumulation of tree litter, and the absence of tillage in the tree rows. Soil microorganisms carrying denitrification genes were more abundant in the tree rows than in the crop rows and monoculture systems, suggesting a greater potential for nitrate removal through denitrification, which may reduce nitrate leaching. Since microbial communities are involved in critical soil processes, we expect that the combination of real-time PCR with soil process measurements will greatly enhance insights into the microbial control of important soil functions in agroforestry systems. [ABSTRACT FROM AUTHOR]

In the current context of climate change, tree–crop combinations in agroforestry systems are suggested to mitigate water and heat stresses, particularly in semi-arid environments of the Mediterranean area. In this framework, a 3-year trial was conducted at the French National Research Institute for Agriculture, Food and the Environment (INRAE) in Mauguio (Southern France) in order to investigate the response of twenty-five durum wheat genotypes under a yearly pruned (AF) and a never-pruned alley olive orchard (AF+), in comparison with an open field without trees (control, C). The grain yield of wheat was markedly reduced in both the agroforestry systems AF (average −43%) and AF+ (−83%), according to the shading level. Among the yield components, the plant density at harvest was enhanced in AF (+22%) and AF+ (+3%), although with a significant reduction in the number of grains per spike (−37% in AF and −62% in AF+), and the number of spikes per plant (−32% in AF and −52% in AF+). The thousand-grain weight (TGW) and harvest index (HI) were slightly higher under moderate shade (AF; +12% vs. C) and severe shading (AF+; +6%). Plant biomass and spike size were significantly reduced in both agroforestry systems, while the flag leaf–spike distance (last internode) increased in AF. It was concluded that the moderate shading conditions of AF may create a sustainable agricultural system, and the wide intraspecific variability suggested a large scope for screening suitable genotypes, helping to produce ideotypes to implement agroforestry-oriented breeding programs.

Land management in Germany has been characterised by a continued intensification in recent decades. This development has come along with the replacement of landscape elements like hedges, bushes and single trees. Despite the high relevance of food supply, further social claims and requirements with regard to agricultural have land gained in importance over time. These include for example ecological aspects and the enhancement of the appearance of the landscape. Alley cropping systems with short-rotation wood can contribute to an increase of biodiversity and improved landscapes. Furthermore, the simultaneous growing of wood and crops can bring about economic benefits as well. Despite their ecological, social and economic advantages, only a very limited number of agroforestry systems has been established in Germany, mostly on experimental sites. Reasons for this may be economic disadvantages. This paper presents a comprehensive literature review about the economic effects of alley cropping agroforestry in comparison to traditional cropping. The results show that from an economic point of view agroforestry systems most is preferable for medium quality agricultural sites. Results also show that three to ten percent higher yields due to synergy effects between tree crops and field crops are needed to make alley cropping systems financially attractive. Furthermore, liquidity has to be taken into account due to the relatively high investment costs of the trees and delayed returns moreover. The results provide manifold starting for measures to increase the attractiveness of alley cropping systems. [ABSTRACT FROM AUTHOR]

Climate change will pose a major threat to food supply worldwide. Agroforestry has been proposed as an effective approach to minimize its effects on crops. However, to design sustainable and productive agroforestry systems, net responses of crops to trees need to be clarified, particularly in regions where competitive interactions will outweigh facilitative ones. The study of plant traits has become a useful approach to select best-adapted plants, yet the sensitivity of yield components to agroforestry and their relationship with plant traits needs investigation. In this experiment, we assess the phenological, morphological and physiological responses of shade-adapted cultivars of winter wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.), growing in an agroforestry system (AF) with walnut trees (Juglans x intermedia Mj209xRa), as compared to cereal monocrops (MC). Agroforestry reduced the light intercepted by crops by 58 %, buffered extreme temperatures at the crop canopy level and increased air relative humidity, advancing plant development for wheat and barley. Major tree effects on crops were observed after walnut budburst. Under trees, crops increased the relative water content (RWC), Photochemical Reflectance Index (PRI) and P content of both wheat and barley leaves, increased Normalized Difference Vegetation Index (NDVI) of barley leaves, and reduced leaf mass area (LMA) in wheat and cell membrane damage in both species. In agroforestry, crops also reduced plant growth, leaf area (LA), leaf area index (LAI) and grain yield in both wheat and barley. Drivers of grain yield differed among agroforestry and open conditions in both species, showing for the first time that the selection of cereal cultivars for specific conditions could be based on plant traits, along with the shade tolerance, to establish successful agroforestry systems. • Trees buffered air temperature and humidity in Southwestern Mediterranean area. • Agroforestry advanced winter cereal development compared to open fields. • Trees altered physiological and morphological parameters of both wheat and barley. • Agroforestry reduced cereal grain yield because nutrient competition. • Agroforestry modified how plant traits ultimately affected grain yield. [ABSTRACT FROM AUTHOR]

In temperate regions, short rotation woody crops cultivated as tree strips in alley-cropping agroforestry systems (ACS) can provide economic benefits by producing an additional commodity, and environmental benefits, e.g., soil erosion control, protection against evaporation and increased biodiversity. Moreover, compared to agrisivilcutural systems incorporating noble trees, ACS with short rotation coppice (SRC)-strips provide periodically high energy outputs and could help to answer environment and energetic political objectives in Germany. However, limited data are available in such systems concerning biomass production of different strip designs. An ACS incorporating poplar SRC has been established near Braunschweig in Lower Saxony (Germany) in 2008. Two harvest cycles (a coppiced 3-year rotation cycle and a un-coppiced 6-year rotation cycle) and two strip designs ('SRC': 6 poplar rows; 'Combined': 4 poplar rows and 1 aspen row in the centre) were compared. Diameters at breast height, tree heights, shoot numbers and mortality rates were measured to describe growth and estimate yield of outer and middle poplar rows within a tree strip. Concerning the 3-year rotation cycle, higher numbers of shoots per tree as well as higher biomass yields compared to the control field were measured in outer rows, both leeward and windward. With the 6-year rotation cycle, all leeward rows and the middle rows of the combined design showed larger diameters and higher biomass yields. Middle rows of the SRC design, in both rotation cycles, revealed a quicker height growth than outer rows, but a reduced biomass production. Both rotation cycles showed similar yearly biomass production. The results can contribute to improve the design of poplar SRC-strips in ACS in order to optimize biomass production. We recommend reducing the number of rows within SRC-strips, while increasing their total length. Further research is however needed to determine effects of increased biomass in outer tree rows on adjacent crop fields, which influences the whole system productivity. [ABSTRACT FROM AUTHOR]

The authors tested two harvesting systems especially designed for mallee agroforestry plantations on farmland. Both systems were based on versatile forest technology commonly used for conventional logging operations. They differed especially for the felling technology: small-scale drive-to-tree or industrial swing-to-tree equipment. Both systems were tested side-to-side on 12 experimental plots each. The resulting harvesting cost was 22 and 27 AU$ t, for the industrial and the small scale system, respectively. Chipping represented between 60 and 80 % of the overall harvesting cost, and offered much room for improvement. The industrial system always offered the lowest harvesting cost, regardless of annual usage, when equipment mobilisation costs were not considered. The productivity of conventional forestry equipment was strongly dependent on belt stocking and tree size. If the diameter at ankle height dropped below 10 cm, economic viability decreased very rapidly. [ABSTRACT FROM AUTHOR]

Alley-cropping has successively been overestimated and despised, due to unrealistic expectations of this “more natural” type of agriculture and the disappointment thereafter, when the negative effects of trees on crops became evident over time. In this paper we examine the performance and underlying mechanisms of a Calliandra (Calliandra calothyrsus Meissn.)–maize (Zea mays L.) alley-cropping system on a phosphorus (P) limiting Ferralsol in Western Kenya. The system performance analysis methods of [The ‘dark side’ of intercropping: manipulation of soil resources. In: Sinoquet, H., Cruz, P. (Eds.), Proceedings of the International Conference on Ecophysiology of Intercropping. INRA, Paris, France, pp. 45–66] and [Agric. Ecosyst. Environ. 80 (2000) 87] were used as well as mechanistic research into availability, uptake and balances of below ground resources. The Calliandra–maize system performed worse than sole maize (I=-66%, according to Ong’s method) Calliandra affected the less limiting resource nitrogen (N) positively, but the negative effect of Calliandra on P-availability, the main limitation of the environment outweighed the positive or fertility effect, according to Kho’s performance analysis method. However, after P application, when the main limiting resource for maize in our environment shifted to N, the Calliandra had still only a marginal positive effect on maize yields (insignificant 5% increase of alley-cropping compared to sole maize). This was explained by a negative total N balance in the soil of -30 kg ha-1, and a negative inorganic N balance in the soil of -277 kg ha-1 over the seven seasons. The difference between total and inorganic N balance was due to a mineralisation of only 20% of the N in all the Calliandra mulch applied over the seven seasons. Net negative nutrient balances also explain the general trend of decreasing yields of 40–90% over the seven seasons. We conclude that the combination of Ong’s simple method, Kho’s resource-base explanation and further investigation of long-term supply and availability of the resources that are the main limitation(s) of an environment can give an understanding needed to create productive and sustainable alley-cropping systems. [Copyright &y& Elsevier]

In the current context of climate change, tree–crop combinations in agroforestry systems are suggested to mitigate water and heat stresses, particularly in semi-arid environments of the Mediterranean area. In this framework, a 3-year trial was conducted at the French National Research Institute for Agriculture, Food and the Environment (INRAE) in Mauguio (Southern France) in order to investigate the response of twenty-five durum wheat genotypes under a yearly pruned (AF) and a never-pruned alley olive orchard (AF+), in comparison with an open field without trees (control, C). The grain yield of wheat was markedly reduced in both the agroforestry systems AF (average −43%) and AF+ (−83%), according to the shading level. Among the yield components, the plant density at harvest was enhanced in AF (+22%) and AF+ (+3%), although with a significant reduction in the number of grains per spike (−37% in AF and −62% in AF+), and the number of spikes per plant (−32% in AF and −52% in AF+). The thousand-grain weight (TGW) and harvest index (HI) were slightly higher under moderate shade (AF; +12% vs. C) and severe shading (AF+; +6%). Plant biomass and spike size were significantly reduced in both agroforestry systems, while the flag leaf–spike distance (last internode) increased in AF. It was concluded that the moderate shading conditions of AF may create a sustainable agricultural system, and the wide intraspecific variability suggested a large scope for screening suitable genotypes, helping to produce ideotypes to implement agroforestry-oriented breeding programs. [ABSTRACT FROM AUTHOR]