Abstract
With increasing economic and environmental costs associated with fertilizer use, the need for low-input agroecological systems is on the rise. It is well documented that intercropping legumes can increase the supply of nutrients, through N2-fixation and P mobilization. Concurrently, the integration of trees in the agricultural landscape shows increasing evidence of nutrient inputs through efficient biogeochemical cycles. However, little is known about the effects shade has on legume-crop performance. This research aims to determine whether intercropping of the legumes soybean (Glycine max L. Merr.) and alfalfa (Medicago sativa) with wheat (Triticum turgidum durum) is beneficial for performance, particularly under shady conditions associated with tree-based intercropping. Test species were cultivated in hydroponics with a broad nutrient solution and steady state addition of N for 3 weeks. Individual plants were transferred to rhizoboxes with a 2 mm zone of soil for 16 days under (i) full sun or (ii) shade to mimic light levels at the tree-crop interface. Under monocropping, shading was found to significantly decrease wheat biomass. Intercropping wheat with alfalfa under full sun had no negative effect on growth but did increase wheat P uptake as compared to monocropped wheat. In contrast, intercropping wheat with soybean under full sun decreased wheat biomass, suggesting competition. However, under shade, this competitive effect was mitigated, as wheat exhibited similar biomass and higher N and P shoot concentration when associated with soybean as compared to monocropped wheat under lower light levels. This effect may be attributed to reduced biomass of soybean combined with higher soybean N2-fixation under shade. Legume-based intercrops may increase nutrient supply and growth but these beneficial effects will be dependent on matching species selection to light levels under tree-based intercropping.
Highlights
As conventional agriculture systems become dominated by monospecific crops, nutrient cycles become more open and more susceptible to losses through leaching, run off and volatilization [1,2,3]
Wheat performance was highest under full sun in monocropping; dry weight of shoot, root, and total wheat biomass was significantly greater in full sun as compared to under shade
Intercropped with soybean under the no shade treatment, wheat shoot mass was significantly smaller (p = 0.042) as compared to monocropped wheat (Table 1). Overall, this significant negative intercropping effect on companion wheat was not observed when intercropped with alfalfa (Table 1)
Summary
As conventional agriculture systems become dominated by monospecific crops, nutrient cycles become more open and more susceptible to losses through leaching, run off and volatilization [1,2,3]. It is vital that sustainable agriculture practices be developed to decrease inputs of synthetic fertilizers into ecosystems. Intercropping annual crops within tree-based systems can reduce nutrient leaching and increase nutrient cycling, through complementarity of resource partitioning [1,4,5,6]. This in turn can decrease the amount of external fertilizer inputs. In single species cropping systems, individuals can be expected to have adapted similar strategies to fulfill those requirements, whereas plants in a multi-species system can have different resource requirements, and possess different biological and physical strategies for acquiring nutrients [7,8].
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