Temperate Tree-based Intercropping System Research Articles

Nitrogen leaching and soil nutrient supply vary spatially within a temperate tree-based intercropping system

Nitrogen leaching and soil nutrient supply vary spatially within a temperate tree-based intercropping system

Soybean performance under moisture limitation in a temperate tree-based intercropping system

CONTEXTTree-based intercropping (TBI) systems show promise in reducing the vulnerability of field crops to increasing water stress. TBI can generate several above- and belowground interactions between trees and crops. These interactions remain poorly documented, especially in the context of moisture limitation. OBJECTIVEThe objective of this study was to determine the performance of soybean within a TBI system under moisture limitation. We hypothesized that TBI generates both positive (near the alleyway centre) and negative (near the trees) effects on soybean performance and that these effects are accentuated when moisture availability decreases. METHODSA partial rainfall interception treatment (50% of the soil surface) in a soybean crop (stages R1 to R7) was installed for two years (2018 and 2019) in a TBI (50 trees/ha planted in 2012) in southern Quebec. TBI was composed of hybrid poplars (Populus deltoides × P. nigra) and different high-value hardwood species that were planted alternately within rows. A tree root-pruning treatment was also applied to understand belowground effects of tree roots on soybean growth under moisture limitation. Various microclimatic (light availability, wind speed and soil moisture) and soybean performance variables (leaf traits, 100-grain weight and yield) were measured at four distances from the tree row (4, 12 and 20 m, and control). RESULTS AND CONCLUSIONSRainfall exclusion decreased soil moisture and had a negative effect on soybean yield (−14%). The effect of the rain exclusion treatment on soybean performance was similar across all tree row distances and in both root-pruning treatments, which is contrary to our prediction. In 2018, an abnormally dry and warm season, yield near the alley centres was higher than near the tree row and tended to outperform the control. In 2019, a season with normal rainfall and temperature, soybean yield within the alleys was consistent among the different measured distances and did not differ from that in the control. Moderate shading at 4 m (−26% of PAR) was not associated with a change in soybean yield or leaf traits compared to other distances where shading was negligible or absent. Root pruning negatively affected soybean yield in 2018 (−14%) and 2019 (−22%), which is contrary to our prediction. SIGNIFICANCEThis case study adds to our knowledge regarding interactions between crops and trees in widely spaced TBI systems. TBI effects on spatial patterns of crop yield may vary substantially depending upon inter-annual variation in climatic conditions. This study suggests that more facilitative effects would prevail in dryer and warmer years, in contrast to near neutral effects in normal years.

Soybean Performance Under Moisture Limitation in a Temperate Tree-Based Intercropping System

Soybean Performance Under Moisture Limitation in a Temperate Tree-Based Intercropping System

Light availability, weed cover and crop yields in second generation of temperate tree-based intercropping systems

An experimental network representing a new generation of widely spaced tree-based intercropping (TBI) systems, which are more adapted to large-scale annual crops than narrowly spaced ones, was established in southern Quebec. Over two consecutive growing seasons (2016-2017), we determined effects of these TBI systems on percent total light transmittance (PTLT), soil moisture, weed cover and crop yield. We studied six experimental sites that included different annual crops (maize, soybean, wheat, black bean) or forage crops. Age of TBI systems varied between 3 and 22 years, and spacing between tree rows ranged from 25 to 90 m. Variables were measured in control (non-tree) farm plots and in TBI alleys at four distances from the row of trees. Spatial variation in crop yield in TBI alleys was crop-specific. Yield reductions for maize, soybean and black bean were observed at the closest distance to the tree row (½H, where H = tree height). These yield reductions were associated with a decrease in PTLT or an increase in weed cover. Soil moisture changed little with distance from the row of trees and no significant relationship between crop yield and soil moisture was measured, which suggested that competition for water between trees and crops was marginal. Our results indicate that forage crops are less sensitive than annual crops to changes in environmental conditions that were incurred by TBI systems. Overall, the second-generation TBI systems under study exerted neutral net effects on integrated crop yields (i.e., all distances combined), except for black bean in 2016. Second-generation TBI agricultural yields appear to be more promising than those obtained in first-generation TBI systems.

Erratum to: Avian diversity in a temperate tree-based intercropping system from inception to now

Erratum to: Avian diversity in a temperate tree-based intercropping system from inception to now

Avian diversity in a temperate tree-based intercropping system from inception to now

Migratory bird populations in North America have been declining over the last several decades, largely due to habitat loss and forest cover fragmentation in both their summer breeding ranges and overwintering territories. Tree-based intercropping (TBI), which is a land-use system incorporating trees with agricultural crops on the same unit of land, is an alternative to conventional agriculture that provisions many ecological and environmental benefits in conjunction with agricultural production. This study seeks to assess the contributions of temperate TBI systems on avian biodiversity, and to quantify these changes as they develop in time. Standard bird monitoring protocols were used to examine avian communities in a TBI system at the University of Guelph’s Agroforestry Research Site in 2014 and compared to a similar study completed by Williams et al. in 1995 at the same site. The TBI system surveys were then compared to present (2014) and past (1995) avian communities living in other nearby agro-ecosystems including an abandoned field, conventional monocrop field, a willow plantation and a mature woodlot. The avian species richness and diversity at the TBI site was higher in 2014 (32 species; diversity index of 2.9) than in 1995 (17 species; diversity index of 2.2). Among land-use types, avian species richness was highest at the TBI site in both 2014 (32 species vs. 26, 24, 21, and 15) and 1995 (17 species vs. 7 and 4). The results of this study suggest that TBI systems may help to maintain and even enhance avian diversity in North America.

Measurements and economics of carbon sequestration in temperate tree-based intercropping systems

The paper aims to quantify and monetise carbon sequestration potential of temperate Tree-Based Intercropping (TBI) systems in Canada. The net carbon sequestration potential is estimated to be 2.26 Mg C ha−1y−1 that represents an immobilisation of 8.3 ton CO2 ha−1y−1. In economic terms this amount of sequestered carbon represents $24,383 per hectare of societal benefits over a rotation period of 40 years. This means 137 million dollars per year of climate regulation services could be achieved through establishment of TBI systems on 1.93 million hectares of land areas in the province of Quebec in Canada. Government incentives, however, are needed to interest farmers in adopting practices that reduce farmers' private profits yet benefit society as a whole.

Determining tree water acquisition zones with stable isotopes in a temperate tree-based intercropping system

Tree-based intercropping (TBI) systems induce microclimate modifications that can enhance crop performance through water use efficiency. However, the extent of this efficiency is dependent on water acquisition strategies of trees in such agroforestry systems. Charting water uptake zones at the tree-crop root interface in TBI systems is essential for managing water resources, particularly with increasing water stress from a changing climate. In this study, we identify the water uptake zones of Juglans nigra (walnut) and Populus sp. (hybrid of Populus deltoids X Populus nigra clone DN-177) (poplar) intercropped with winter barley (Hordeum vulgare) in a temperate TBI system. Water isotopic analysis using δ18O was conducted on paired soil water and tree xylem water samples in early season (pre-crop) and late season (with crop) collected from the Agroforestry Research Station in Guelph, Ontario, Canada. Two approaches for identifying the water uptake zones were used: direct inference and multiple source mass-balance analysis. Both approaches showed that poplar exhibits a dominant soil water uptake zone at 20 cm in the soil profile in the early season, while the dominant walnut uptake zone was higher in the soil profile at 10 cm. Depth of water uptake was lower in the soil profile (40–70 cm) in the late season for both species. This study indicates: (i) tree species dependent water acquisition zones, and (ii) a shift in tree water acquisition to deeper in the soil profile over the growing season. Using isotopic techniques, we suggest that poplar and walnut root activity stratify below the crop root zone later in the growing season, potentially reducing competition for water resources.

Estimating coarse root biomass with ground penetrating radar in a tree-based intercropping system

Conventional measurements of tree root biomass in tree-based intercropping (TBI) systems can be inadequate in capturing the heterogeneity of rooting patterns or can be highly destructive and non-repeatable. In this study, we estimated coarse root biomass using ground penetrating radar (GPR) of 25-year-old trees inclusive of five species (Populus deltoides × nigra clone DN-177, Juglans nigra L., Quercus rubra L., Picea abies L. Karst, and Thuja occidentalis L.) at a TBI site in Southern Ontario, Canada. Subsurface images generated by GPR were collected in grids (4.5 × 4.5 m) centred on tree stems. The predictive relationship developed between GPR signal response and root biomass was corrected for species effects prior to tree-scale estimates of belowground biomass. Accuracy of the tree-scale estimates was assessed by comparing coarse root biomass measured from complete excavations of the corresponding tree. The mean coarse root biomass estimated from GPR analysis was 54.1 ± 8.7 kg tree−1 (mean ± S.E.; n = 12), within 1 % of the mean coarse root biomass measured from excavation. Overall there was a root mean square error of 14.4 kg between measured and estimated biomass with no detectable bias despite variable conditions within the in-field and multi-species study. Root system C storage by species, calculated with species-specific root carbon concentrations, is estimated at 5.4 ± 0.7–34.8 ± 6.9 kg C tree−1 at this site. GPR is an effective tool for non-destructively predicting coarse root biomass in multi-species environments such as temperate TBI systems.

Vertical root separation and light interception in a temperate tree-based intercropping system of Eastern Canada

We analysed the spatial distribution of fine roots and light availability in a tree-based intercrop system (TBI) composed of Quercus rubra L. (QUR), hybrid poplar (Populus deltoides × Populus nigra—HYP) and hay (CROP) in southern Quebec (Canada) to evaluate interactions between trees and crop. Trees in the 8-year-old TBI system had superficial fine root profiles, which is common in tree species grown in conventional plantations and natural forests. More than 95 % of fine roots were found within the first 25 and 45 cm for QUR and HYP, respectively, and 35 cm for CROP. However, vertical separation between the fine root systems of QUR and CROP was evident, as QUR allocated less fine roots to the top 10 cm of soil, and more to depths between 10 and 30 cm, as opposed to CROP which had a greater proportion of fine roots in the top 10 cm. HYP fine roots showed no adaption when intercropped with hay. High tree fine root length density (FRLD) in the top soil layer was observed near the tree stems while hay FRLD was reduced by 45 %, suggesting strong competition for resources. Hay yield analysis revealed significant reduction near trees, particularly HYP. However, light did seem to be the main driver of intercrop yield, as it not only accounted for the effect of competition by roots (being correlated), but also had a singular effect.

Carbon sequestration potential of five tree species in a 25-year-old temperate tree-based intercropping system in southern Ontario, Canada

Carbon (C) sequestration potential was quantified for five tree species, commonly used in tree-based intercropping (TBI) and for conventional agricultural systems in southern Ontario, Canada. In the 25-year-old TBI system, hybrid poplar (Populus deltoides × Populus nigra clone DN-177), Norway spruce (Picae abies), red oak (Quercus rubra), black walnut (Juglans nigra), and white cedar (Thuja occidentalis) were intercropped with soybean (Glycine max). In the conventional agricultural system, soybean was grown as a sole crop. Above- and belowground tree C Content, soil organic C, soil respiration, litterfall and litter decomposition were quantified for each tree species in each system. Total C pools for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and a soybean sole-cropping system were 113.4, 99.4, 99.2, 91.5, 91.3, and 71.1 t C ha−1, respectively at a tree density of 111 trees ha−1, including mean tree C content and soil organic C stocks. Net C flux for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and soybean sole-crop were 2.1, 1.4, 0.8, 1.8, 1.6 and −1.2 t C ha−1 year−1, respectively. Results presented suggest greater atmospheric CO2 sequestration potential for all five tree species when compared to a conventional agricultural system.

Characterizing soil surface structure in a temperate tree-based intercropping system using X-ray computed tomography

The objective of this work was to characterize differences in the soil surface (top 3.5 cm) microstructure, as influenced by four tree species, within a temperate tree based intercropping (TBI) system. Soils adjacent to walnut (Juglans nigra), poplar (Populus spp.), red oak (Quercus rubra), Norway spruce (Picea abies), as well as three types of ground cover [row crop, willow (Salix spp.), and perennial grass tree rows] were analyzed. X-ray computed micro –tomography (µCT) was employed to evaluate soil void phase characteristics, as well as heterogeneity of soil matrix radiodensity. X-ray µCT identified void phase parameters were not affected by tree species due to confounding effects caused by perennial vegetation and mixed leaf litter inputs.. A positive correlation was found between traditionally measured soil bulk density and bulk X-ray radiodensity (rs = 0.53, p < 0.01) and a negative correlation between mean intra-aggregate X-ray radiodensity and soil organic carbon (rs = −0.48, p = 0.03). It was determined, through the use of geostatistics, that there were no distinct or consistent anisotropic structures, in directional semivariograms, evident for the various species. However, the semivariograms revealed greater variability, correlated with less directional anisotropy within the tree row as compared to cropping alley soils. It was interpreted that processes within soils in the tree rows were leading to a homogenous type of structure, and that soils under row crops exhibited a greater tendency for destruction of surface structure, leading to more directional anisotropy (trends).

Influence of trees on the spatial structure of arbuscular mycorrhizal communities in a temperate tree-based intercropping system

Tree-based intercropping (TBI) is an ecologically sustainable agricultural practice that may promote a more diverse arbuscular mycorrhizal (AM) fungal community compared to conventional systems, but the influence of the dynamics of these systems on AM fungi has not been established. Soil and root samples were collected in the intercropping alleys along transects perpendicular to tree rows occupied by white ash ( Fraxinus americana), poplar ( Populus deltoids × nigra), Norway spruce ( Picea abies), and rows without trees (control). Molecular analysis of the AM fungal community at the TBI site revealed 17 phylotypes belonging to the Glomeraceae. Overall, the AM fungal community in the TBI site was comparable to other conventional agricultural systems; with the majority of phylotypes belonging to Glomus group A. AM fungal phylotype richness and community composition significantly differed among the treatments in the TBI site. AM fungal communities were more diverse in cropping alleys adjacent to trees that associate with AM fungi than trees that do not associate with AM fungi. Norway spruce had a negative influence on the AM fungal community as tree rows and bordering intercropping alleys had a significantly lower phylotype richness and different community composition. These results suggest that to maintain a diverse AM fungal community throughout TBI systems, it may be best to incorporate tree species that associate with AM fungi.

Potential Greenhouse Gas Mitigation through Temperate Tree-Based Intercropping Systems

Increasing awareness of global climate change has pressured agricultural producers to reduce greenhouse gas (GHG) emissions while at the same time encouraging them to maintain food production needed for an increasing population. Tree-based intercropping (TBI) systems are believed to be useful in climate change mitigation, especially in temperate regions, due to their potential to reduce GHG emissions from agricultural practices. The purpose of this paper is therefore to review some of the research conducted on GHG mitigation in TBI in southern Ontario and Quebec, Canada. Research conducted at the University of Guelph Agroforestry Research Station (GARS) indicated that TBI systems had the potential to lower N2O emissions by 1.2 kg ha-1 y-1 compared to a conventional agricultural field cropping system. Trees can assimilate residual nitrate (NO3-) left from nitrogen (N) fertilizer applications, thereby leaving less NO3- available for denitrification and subsequently reducing N2O losses. Carbon sequestration is also enhanced in TBI systems as carbon (C) is stored in both above and below ground tree components. Soil Organic Carbon (SOC) is higher in systems incorporating trees because tree litter decomposes slowly, therefore reducing CO2 loss to the atmosphere. The C sequestration potential of TBI systems and the possibility to include fast-growing tree species for bioenergy production in TBI systems make it a valid solution to mitigate climate change in temperate regions. The opportunity of C trading credits to offset the costs of implementing a TBI system and provide additional income to farmers could facilitate the adoption of TBI amidst agricultural producers in temperate regions.

Carbon Sequestration Potentials in Temperate Tree-Based Intercropping Systems, Southern Ontario, Canada

Carbon (C) sequestration was quantified in two tree-based intercropping and in conventional agricultural systems in southern Ontario, Canada. In the intercropping systems, 13-year-old hybrid poplar (Populus deltoides × Populus nigra clone DN-177) and Norway spruce (Picea abies L.) were intercropped with barley (Hordeum vulgare L. cv. OAC Kippen). In the conventional agricultural system, barley was grown as a sole crop. Above- and below-ground carbon in trees, soil C, soil respiration and C leaching from each system were determined in situ. These data coupled with complementary data obtained from the literature were compiled and used to construct C cycle models, C pools and fluxes for each system. The total mean above- and below-ground C sequestered in permanent tree components was 15.1 and 6.4 t C ha−1 for poplar and spruce trees, respectively at 111 stems ha−1. Soil C pools were 78.5, 66 and 65 t C ha−1 in poplar, spruce intercropping and in barley sole cropping systems, respectively. Soil respiration rates were 3.7, 4.5 and 2.8 t C ha−1 y−1 in poplar, spruce intercropping and barley sole cropping systems, respectively. Carbon leaching within the intercropping systems was greater below the tree row compared to the middle of the alley, but average values differed little from the sole cropping system. Total C pools (including an assumed barley C pool of 3.4 and 2.9 t C ha−1 within the sole cropping and the intercropping systems respectively) were 96.5, 75.3, and 68.5 t C ha−1 within poplar, spruce intercropping and in barley sole cropping systems, respectively. Estimated net C fluxes for the poplar and spruce intercropping systems and for the barley sole cropping system in 2002 were +13.2, +1.1, and −2.9 t C ha−1 y−1, respectively. These results suggest that intercropping systems have a greater potential in reducing the atmospheric carbon dioxide concentration compared to sole cropping systems.

Biophysical and Ecological Interactions in a Temperate Tree-Based Intercropping System

SUMMARY Tree-based intercropping is considered an excellent farming system and can contribute much to our understanding of sustainable agriculture practices. Our current research goals are to address and quantify the numerous biophysical interactions that occur at the tree-crop interface in order to enhance our understanding of the ecology of tree-based intercropping (a form of agroforestry). In 1987, the University of Guelph established a large field experiment on 30 ha of prime agricultural land in Wellington county southern Ontario, Canada to investigate various aspects of intercropping trees with agricultural crops. A variety of spacing, crop compatibility and tree growth, and survival experiments were initiated at that time, utilizing 10 tree species within the genera Picea, Thuja, Pinus, Juglans, Quercus, Fraxinus, Acer, and Populus. Two between row-spacings (12.5 m or 15 m) and two within row-spacings (3 m, or 6 m) were utilized in conjunction with all possible combinations of three agricultural crops (soybean, corn, and either winter wheat or barley). Investigations over the last decade have documented several complementary biophysical interactions. Nitrogen (N) transfer from fall-shed leaves to adjacent crops with enhanced soil nitrification as the proposed mechanism was estimated to be 5 kg N ha−1. Soil organic carbon (C) adjacent to tree rows has increased by over 1%, largely as a result of tree litterfall inputs and fine root turnover. It is estimated that intercropping has reduced nitrate loading to adjacent waterways by 50%, a hypothesized function of deep percolate interception by tree roots. We have also noticed increased bird diversity and usage within the intercropped area as compared to mono-cropped adjacent agricultural areas, and have recorded increases in small mammal populations. Earthworm distribution and abundance was also found to be higher closer to the tree rows when compared to earthworm numbers in the crop alleys. We speculate that these are indicative of major changes in the flow of energy within the trophic structure identified with intercropping systems. In light of climate change mitigation processes, C sequestration and NO2 reduction potentials in tree-based intercropping systems were studied and compared to conventional agricultural systems. The results suggest that sequestration of C was 5 times more in the former system than in the latter. Competitive interactions between trees and crops for nutrients, moisture and light were also studied. The tangible benefits that are derived from properly designed and managed tree-based intercropping systems place this land management option above conventional agriculture in terms of long-term productivity and sustainability.