plant: soil interactions in temperate multi-cropping ...· marschner review plant: soil interactions
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Plant: soil interactions in temperate multi-croppingproduction systems
Jrgen Ehrmann & Karl Ritz
Received: 23 February 2013 /Accepted: 25 September 2013 /Published online: 6 November 2013# Springer Science+Business Media Dordrecht 2013
AbstractBackground and scope Multi-cropping approaches inproduction systems, where more than one crop cultivaror species are grown simultaneously, are gaining in-creased attention and application. Benefits can includeincreased production, effective pest, disease and weedcontrol, and improved soil health. The effects of suchpractices on the range of interactions within the plant-soilsystem are manifest via plant interspecific competition,pest and disease attenuation, soil community composi-tion and structure, nutrient cycling, and soil structuraldynamics. Interplant diversity and competition effective-ly increases the nature and extent of root networks,tending to lead to more efficient resource use in timeand space. Increased competitive ability at a system level,and allelopathic interactions, can reduce weed, pest anddisease severity. Soil biotic communities are affected byplant diversity, which can increase abundance, diversityand activity of functional groups. Attendant rhizosphere-located processes can facilitate nutrient uptake betweencomponent crops.Whilst there are few studies into multi-cropping effects on soil structure, it is hypothesised thatsuch processes are manifest particularly via the role
which the belowground biota play in soil structural dy-namics. A deeper understanding of eco-physiologicalprocesses affecting weed, pest and disease dynamics inthe context of multiple cropping scenarios, and breedingcultivars to optimise mutualistic and allelopathic traits ofcrop mixtures could significantly increase productivityand adoption of more sustainable farming practices.Conclusions Wider consideration needs to be given toplant: soil interactions when crop plants are grown inthe context of mixtures, i.e. as communities as opposedto monotonous populations. In particular, a better un-derstanding is required of how root systems develop inthe context of mixtures and the extent to which resul-tant interactions with the soil biota are context-dependent. A significant challenge is that crop culti-vars or production systems optimised for monoculturalcircumstances should not be assumed to be most suitedfor multi-cropping scenarios, and hence alternativestrategies for developing new production systems needto take this into account.
Keywords Intercropping . Plant interspecificcompetition . Soil biotic communities . Biologicalweed, pest and disease control . Nutrient facilitation .
Traditional farming practices, particularly in temperateregions, have largely been replaced with intensified andhighly-mechanised systems founded upon monocultures
Plant Soil (2014) 376:129DOI 10.1007/s11104-013-1921-8
Responsible Editor: Philippe Hinsinger.
J. Ehrmann :K. Ritz (*)Environmental Science and Technology Department,School of Applied Sciences, Cranfield University,Cranfield, MK43 0AL, UKe-mail: firstname.lastname@example.org
J. Ehrmanne-mail: email@example.com
both at the field and regional-scale (Whitmore andSchrder 2007; Malzieux et al. 2009; Lithourgidis et al.2011). Modern agricultural systems greatly depend onmanaging soils using external inputs and soil disturbanceregimes. By simplifying structurally diverse natural sys-tems and by replacing the services these ecosystems pro-vide (e.g. nutrient cycling, water regulation, micro-climateregulation, detoxification) with chemical and fossil-fuelbased inputs and farming operations, and by depletingnatural soil resources, intensive agricultural systems arearguably less resilient, compromising sustainability, aswell as posing threats to the natural environment (Altieri1999; de Vallavieille-Pope 2004; Malzieux et al. 2009).
Multi-cropping, also referred to as intercropping ormixed cropping, is the agricultural practice of growingmultiple cultivars or crop species simultaneously in thesame field for a significant part of their life cycle(Vandermeer 1989; Lithourgidis et al. 2011). Mixedcropping can be applied to field-crop species, pasturespecies, trees, or a combination thereof. Tree basedintercropping systems (TBIs) are referred to as alley-cropping or agroforestry. Vegetables have long beenintercropped in horticultural systems, but have alsobeen trialled in agricultural settings (Motisi et al.2009; Kluth et al. 2010; Zhou et al. 2011).
Growing multiple crops simultaneously is a centuries-old practice and is still widely applied around the world,in contemporary terms mainly in tropical, small-scalesubsistence farming (Lithourgidis et al. 2011). In temper-ate zones multi-cropping is receiving greater attention,particularly in forage production, in grass-clover/legumepasture mixtures (Anil et al. 1998; Whitmore andSchrder 2007; Lithourgidis et al. 2011) and in organicfarming, where multi-cropping is considered to provide abiological means of maintaining soil health (Altieri1995a; Malzieux et al. 2009), and reducing the frequen-cy and severity of pest infestations (Trenbath 1993; deVallavieille-Pope 2004; Saucke and Ackermann 2006).
Practical issues, such as drilling, sowing, spraying andharvesting, pose problems when adapting multiple-cropping in highly mechanised agricultural systems.Differing growth cycles and requirements for nutrientsand pesticides make it difficult for growers to adapt newsystems in order tomanage and harvest mixed crops (Anilet al. 1998; Tosti and Guiducci 2010; Lithourgidis et al.2011). Such issues can be more easily overcome whencrops are grown for forage or grazing where the market-ability of the end product is of no concern (Anil et al.1998). Crop models will also need to be adapted.
Multiple-crop models are challenged by the complexplant-soil interactions, which are key in understandingnutrient dynamics, interplant competition and disease re-sistance (Malzieux et al. 2009). Suchmodels also need toaccommodate soil processes and include concepts ofcommunity ecology (population dynamics, epidemiology,and the role of soil micro- and macro-organisms).
Numerous studies have reported how yield advantagesin mixed cropping systems compared to sole crops areprovided for by ecological processes. These include: (i)more efficient and complementary use of available re-sources and niches (Malzieux et al. 2009; Tosti andGuiducci 2010); (ii) facilitation via the roots (Vandermeer1989; Hauggaard-Nielsen and Jensen 2005); (iii) enhancedsoil fertility by intercropping nitrogen-fixers (Hauggaard-Nielsen and Jensen 2005); (iv) increased resilience againstpests and diseases (Trenbath 1993); (v) increased abioticstress resistance due to higher levels of functional diversitywithin the system and resultant complex interactions be-tween associated ecological and biochemical processes(Eisenhauer 2012; George et al. 2012).
More recently, attention has shifted towards thepotential of mixed cropping in soil conservation andthe ecosystem services that soils provide (Altieri 1999;Whitmore and Schrder 2007; Malzieux et al. 2009).By intercropping trees and by increasing soil cover androot presence in the topsoil; run-off rates, the risk ofsoil erosion, salinity and nitrate leaching are reduced(Wang et al. 2011; George et al. 2012), while keynutrients are being restored (Altieri 1999; Whitmoreand Schrder 2007). Further, agroforestry systems se-quester more carbon through crop stands and affectorganic matter inputs (Malzieux et al. 2009;Oelbermann and Echarte 2011; George et al. 2012).
Although the majority of research on multiple-cropsystems has focused on aboveground effects on thecomponent crops, belowground interactions have farmore significant impacts on combined plant develop-ment (Martin and Snaydon 1982; Hauggaard-Nielsenand Jensen 2005; Thorsted et al. 2006). Only recentlyattention has shifted towards the complexity of below-ground interactions between crops and the soil system(Tosti and Thorup-Kristensen 2010). A framework forlinkages between the individual interacting below-ground components is given in Fig. 1.
The aim here is to review the effects of temperatearable multiple-crop systems on belowground processeswithin the plant-soil system, considering competition,soil microbial composition and structure, weed, pest
2 Plant Soil (2014) 376:129
and disease control, nutrient cycling, organic matter andsoil structural dynamics. Gaps in knowledge are identi-fied and recommendations for further research are made,which could potentially offer significant insight into howsuch plant-soil systems can be managed more produc-tively and sustainably. We confine the scope of thisreview to arable farming systems in temperate regions,which include common cereal-legume intercrops, cerealvariety mixtures and agroforestry, but examples frompastures will also be drawn upon, where similarities exist.
We further confine this review to the belowground com-ponents influencing agricultural production systems, andthe interactions and physical, chemical and ecologicalsoil processes linking them.
Range and types of multiple-crop systems
Malzieux et al. (2009) proposed the following criteriato classify mixed cropping arrangements: (i) the
Table 1 Different forms of species mixtures in agricultural systems. Systems are classified according to a gradient of complexity,including the number and type of plant species (annual vs. perennial), the horizontal and vertical structure of the mixture
Type of system No. ofspecies
Combination (intraspecific mixture) 1 1 Cereals variety mixtures and populations (Europe)
Relay cropping (time overlay only during on