Agroforestry Research and Development
Researchers: Prof. Andrew M. Gordon, OAC, Principal Researcher, N. Kaushik, P.A. Williams, Dept. of Env. Biology, R. McBride, Dept. of Land Resource, W. Nickling, Dept. of Geography, M. Tollenaar, Dept. of Crop Science, P. Stonehouse, Dept. of Ag. Economics. Cooperating with Research Station Services, University of Guelph, Petawawa National Forestry Institute, Ontario Tree Improvement and Forest Biomass Institute
Several theses have been completed from funding of this project. Numerous articles have been published in professional journals, conference proceedings, lay journals and the media and many talks have been given at workshops and seminars to farm, professional and academic groups. Another highlight of the agroforestry research at Guelph during the contract was the First Conference on Agroforestry in North America, hosted by the University of Guelph. The following are abstracts from the theses done on this project.
The effects of corn row orientation and width on the growth of interplanted black walnut and red oak seedlings - This project was the subject of a M.Sc. thesis by Hugh McLean that was completed in September, 1990.
Studies were started in 1988 at the University of Guelph Agroforestry Research Station to investigate the effect of corn row width and orientation on the growth of interplanted black walnut (Juglans nigra L.) and red oak (Quercus rubra L.) seedlings. A split-split-plot design with four replications, four row orientations, (NS, EW, NE-SW, NW-SE) and two row widths (.75m and 1.5m) was utilized in the 1988 and 1989 growing seasons.
The orientation factor had a significant effect on seedling dieback in 1989 but not in 1988. Shoot regrowth analyses indicated that the ordering of the orientation treatments from most to least favourable was: NW-SE, NS, EW and NE-SW. The NW-SE and NS row treatments gave significantly greater regrowth than the NE-SW orientation treatment. A slight change in row orientation from NE-SW to NS results in significant increases in seedling growth.
The row width and species factors were significant only in 1988, due to differences in corn canopy leaf area index and height between the two seasons. Black walnut seedlings had significantly greater regrowth than red oak, and the wide row treatment had greater regrowth than the narrow row.
Investigations into seedling carbon assimilation in September 1989 found the greatest carbon assimilation response to the orientation treatments was, in descending order: NW-SE, NS, NE-SW and EW. On days of seedling stress, carbon assimilation trends in the orientation treatments were: NW-SE, EW, NE-SW and NS. Over the growing season, seedling growth in the various orientation treatments on unstressed and stressed days combines to give a growth response following the orientation height growth response.
Modelled light penetration and subsequent seedling carbon assimilation showed daily differences in time of initiation and duration of maximum seedling response to the orientation treatments. The narrow row light levels were found to limit carbon assimilation, in agreement with the results of the height growth analysis.
Economic analysis of intercropping as an alternative cropping system for tobacco farms - This project was the subject of a M.Sc. thesis by Dan Ball that was completed in September, 1991.
Declining income from tobacco production in southern Ontario has given rise to research on alternative crops for the tobacco belt. Nutcropping and the growing of hardwood tree species have been proposed as income generating activities and a potential diversification strategy for tobacco farmers. This is especially attractive in that Canada currently imports $150 million of nuts and much of its hardwoods from the United States and could displace some of these imports through local production. This study uses a multi-period linear programming model to determine resource allocations for tobacco farmers who may wish to diversify using agroforestry technologies such as nut production or intercropping with traditional field crops in a hardwood plantation of red oak (Quercus rubra L.). Initial capital outlays, potential cashflow problems and the long-term motivation process for farmers are major detractions for farm decision makers. Nut cropping is selected as the primary diversification enterprise due to, high commodity prices and low labour inputs. Red oak does not enter the optimal solution as the long-term nature of the enterprise is a major detraction to producers whose priorities are financial returns within their own lifespan. Sensitivity analysis shows that even if tobacco producers have to rely on lower export prices, they still have the capacity to carry the costs of establishing nut orchards.
Nitrogen cycling in a black locust/barley intercropping system - This project was the subject of a Ph.D. thesis by Phocus Ntayombya that is in its draft form.
The recent unprecedented interest in agroforestry is largely a response to the interrelated crises of food shortages, uncertainties of energy supply, and environmental degradation. As an integrated land use system, agroforestry presents many unique opportunities and advantages to meet these challenges. It provides the potential to diversify agricultural production, increase overall productivity and profitability from farming operations, and reduce ecological degradation. Intercropping systems involving multipurpose N2-fixing tree species have received much attention in recent years. Black locust (Robinia pseudoacacia L.) is the only important multipurpose N2-fixing tree legume adapted to cool-temperate climate. It can be put to various uses including fuelwood, fodder and fibre, and has great potential to improve soil fertility. Thus, intercropping practices using this species are considered viable agroforestry options in southern Ontario.
The effects of black locust on productivity and nitrogen nutrition of barley (Hordeum vulgare L.) were evaluated under various management scenarios (i.e., two soil types, 3 levels of N fertilizer, and 3 cropping systems - barley alone, barley intercropped with trees pruned or unpruned). The evidence to support the hypothesis that intercropping would not affect productivity of intercropped barley was not conclusive. Productivity was not affected when the trees were small, but there was a significant yield decline as they grew bigger, especially when they were not pruned. Competition for water was considered the major constraint. Nonetheless, the overall productivity from the intercropped systems was much higher than that from sole cropping.
The hypothesis that intercropping with black locust has the potential to improve N nutrition of barley and soil fertility were well demonstrated. Intercropped barley had higher grain and straw N. concentrations than the sole crop. Intercropping and removal of the trees also resulted in significant crop and N yield increases in subsequent barley compared to continuous barley cropping. This was attributed to enhanced N mineralization and nutrient cycling, and N2-fixation. In situ soil incubations showed much higher nitrification potentials in intercropped systems vs. sole cropping. Additionally, nitrate-N leaching losses were reduced in the intercropped systems compared to sole cropping in three main ways: the frequency of leaching declined; the volume of leachate lost decreased; and nitrate-N concentration in the leachate dropped. The ability of black locust to fix N2 was estimated using the C2H2-reduction activity (ARA) assay. Mean ARA rates were low 5-8 µmole N2g-1h-1), possibly because assays are conducted late in the season. The results showed that the potential to fix N2 may be affected by tree pruning mainly due to a reduction in nodule mass and leaf biomass yield compared to non-coppiced trees. In contrast, addition of N fertilizer had little effect. These experiments showed a real potential to create low-input, sustainable agricultural practices through intercropping using black locust.
The thesis discussed opportunities offered by agroforestry in meeting societal needs, and it outlined some of the challenges to be overcome and the strategies to enchance its development and adoption.
Effect of three crop-types on tree growth in an intercropping system - Methodology and preliminary results of this project were reported in the 1990/91 report and it is the subject of an ongoing Ph.D. project by Peter Williams. Soil moisture, crop growth and microclimate data were collected during 1991 and 1992 but have not been analyzed as yet.
Site index curves and site factors affecting the growth of white pine and Norway spruce in southern Ontario - This work applies to species suitability for plantation establishment on marginal or abandoned lands. Data was collected for the Ministry of Natural Resources and part of the analysis and reporting was conducted under this contract.
Effects of free carbonates in the soil on red pine growth - This work applies to species suitability for plantation establishment on marginal or abandoned lands. The project was also supported by the Ministry of Natural Resources and part of the analysis and reporting was conducted under this contract.
The decline of red pine (Pinus resinosa Ait.) on calcareous soils in Ontario has been widely observed. The decline symptoms are similar to those exhibited in red pine growing on poorly drained sites and/or suffering micronutrient deficiency: chlorosis, reduced height and diameter increment, rosetting, mortality. This problem is generally associated with free carbonates at or near the soil surface. This paper will report on chemical and physical soil properties from 40 sample plots across a variety of site types as well as elemental foliar nutrient levels. The results do not indicate acute nutrientdeficiency as a probable cause. Two measured growth variables, site index (base age 25) and age at which three consecutive years of declining current annual increment were more highly correlated with depth to free carbonates than visual symptoms of decline. Foliar copper content was correlated (a=0.03) to the interaction between depth to free carbonates and soil texture. This indicated improved copper nutrition is associated with coarser textured soils and greater depth to free carbonates.
Establishment of tree seedlings on marginal pasture in an agro-silvo-pastoral system - This project was the subject of an M.Sc. thesis by Peter Bezkorowajnyj that was completed in July, 1990.
Trees growing concurrently with grazing cattle may increase the economic productivity of pasture land with the additional benefit of wood production and other tree products. To increase survival of planted seedlings, however, it has been suggested that cattle be allowed to graze on planted land only after the trees have established themselves: approximately 5 years or when the terminal leaders are beyond the reach of the browsing animals. This is an impractical length of time for most cattle farmers who depend on the pasture for fresh forage during the growing season. This study investigates the use of manure slurry as a repellent to cattle, and its effectiveness in deterring cattle from browsing young seedlings in planted areas.
It was hypothesized that if a manure slurry is sprayed onto or around tree seedlings before cattle are allowed into pasture, then the natural aversion exhibited to excreta by cattle will help to reduce browsing of the seedlings and encourage proper seedling establishment with a minimum amount of seedling damage. The objectives of the experiment were to determine the effects of cattle grazing and foliar application of manure slurry on growth and survival of red oak (Quercus rubra L.), hybrid poplar (Populus spp. x), silver maple (Acer saccharinum L.), and white pine (Pinus strobus L.) seedlings planted on marginal pasture. Also investigated were the effects of manure slurry application around planted poplar seedlings upon associated grazing of pasture grasses, the dietary preference of stall-fed cattle for poplar leaves either slurry treated or not treated, and the effects of soil compaction on both tree growth and manure nitrogen uptake.
Results indicate that oak was the most suitable, and white pine the least suitable species for the selected site. Application of manure slurry reduced consumption of both pasture grasses and poplar leaves, and differences in browsing damage, seedling growth, and soil compaction between "slurry" and "no slurry" treatments were indicated. In addition, artificial soil compaction reduced the rate of water infiltration and increased soil dry bulk density around tree saplings. It is hypothesized that this resulted in denitrification of soil nitrates and a subsequent reduction in the rate of seedling growth. The application of manure slurry increased the height growth of the saplings in the compacted soils to the same rate as those saplings planted in the non-compacted soils.
Riparian reforestation of agricultural fields to reduce inorganic nitrogen leaching into streams - This project was the subject of a M.Sc. thesis by Greg O'Neill that was completed in August, 1991.In agricultural watersheds riparian zones act as a buffer between intensively cultivated land and the watercourse. Riparian vegetation, specially trees, may improve water quality by shading the watercourse, stabilizing the bank, providing detrital inputs to maintain the aquatic food web and filtering nutrients leaching into the watercourse. It was hypothesized that riparian trees would act as a filter for NO3-N leaching in the saturated soil zone.
An artificial riparian zone was constructed in a plywood box that was divided into six compartments, set on a 4% slope, lined with 6-mm plastic and filled with loam soil. A mariotte container supplied a concentrated NO3-N source and maintained a saturated soil zone the length of the compartment. Carolina poplar whips Populus × euramericana Dode (Guinier)) and Shrub willow cuttings (Salix spp.) were planted in the artificial riparian zone. The Carolina poplar trees were effective in lowering the NO3-N concentration from the saturated zone. An increase in tree density further the NO3-N concentration.
The Shrub willow trees were not effective in lowering the NO3-N concentration. It is believed this result is due to reduced root growth of the willows (16.5 g) compared to the poplin (274.4 g), since the former were grown from 18 cm long cuttings and the latter from 1 m whips.
Also investigated was the growth response of two hybrid polar clones DN2 (Populus × euramericana Dode (Guinier)) and IH214 (Populus × euramericana Dode (Gunier)) to conditions typical of a riparian zone in a predominantly agricultural watershed; high watertable and high concentration of dissolved nitrogen. Both clones had a cubic growth response of most tree parameters to increasing NH4NO3 concentrations. However, clone DN2 appeared better adapted to the riparian conditions.
Establishment of demonstration windbreaks at the Cambridge Research Station - Four windbreaks have been established at the Cambridge Research Station, with assistance from this contract and the Environmental Youth Corps. The primary objectives for the plantings were functional for the station and for demonstration purposes. Different species compositions and arrangements were made in the plantings.
Using optical porosity to evaluate the shelter effectiveness of windbreaks in southern Ontario - This project was the subject of a M.Sc. thesis by Anne Loeffler that was completed in May, 1990.
This thesis is an investigation of the relationship between the optical porosity of a windbreak and the shelter effect found behind it. Relative windspeed reduction was measured behind nine relatively narrow, homogenous windbreaks to assess whether any characteristics of the windspeed reduction curve generated could be predicted from optical porosity. The latter was determined for each of the windbreaks by digitizing high contrast black and white photographic silhouettes using the Oculus digitizing system. Various structural and environmental parameters were also measured.
Minimum windspeeds behind the windbreaks ranged from 29 to 70% of open windspeed; these minima were located 2 to 6 multiples of windbreak height away from the windbreak. Optical porosities of the bottom half of the windbreak ranged from 0 to 31%. Multiple regression of the shelter parameters (minimum relative windspeed, location of minimum) on the independent variables (optical porosity, open windspeed, surface roughness, approaching wind direction relative to the windbreak, average tree diameter, average tree spacing) showed that minimum relative windspeed could be predicted from the optical porosity of the bottom-half of the windbreak.
The digitizing technique for measuring optical porosities was tested by analyzing windbreak silhouettes previously published in the literature. The digitizing technique gave slightly higher optical porosities than the dot grid technique for any given windbreak.
Using equations from a recent numerical model of air flow through a windbreak, minimum relative windspeed values were used to calculate resistance coefficients for each windbreak in this study. The model was further used to estimate aerodynamic porosities from the resistance coefficients.
The results suggest that optical porosity can be used to predict minimum relative windspeeds and may therefore be useful as a guide in the field evaluation of windbreaks. The regression results suggest that greater predictive accuracy could be achieved if enough data were obtained to develop species- specific predictive equations. The relationship derived in this study should be applied only to those windbreaks with characteristics similar to those described above.