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Well-established perennial vegetation in riparian areas of agricultural lands can stabilize the end points of gullies and reduce their overall erosion. The objective of this study was to investigate the impacts of riparian land management on gully erosion. A field survey documented the number of gullies and cattle access points in riparian forest buffers, grass filters, annual row-cropped fields, pastures in which the cattle were fenced out of the stream, and continuously, rotationally and intensive rotationally grazed pastures in three regions of Iowa. Gully lengths, depths and severely eroding bank areas were measured. Gullies exhibited few significant differences among riparian management practices. The most significant differences were exhibited between conservation and agricultural management practices, an indication that conservation practices could reduce gully erosion. Changes in pasture management from continuous to rotational or intensive rotational grazing showed no reductions in gully erosion. It is important to recognize that more significant differences among riparian management practices were not exhibited because the conservation and alternative grazing practices had recently been established. As gully formation is more impacted by upland than riparian management, gully stabilization might require additional upland conservation practices. The existence of numerous cattle access points in pastures where cattle have full access to the stream also indicates that these could be substantial sources of sediment for streams. Finally, the gully banks were less important sediment contributors to streams than the streambanks. The severely eroding bank areas in streams were six times greater than those in the gullies in the monitored reaches. more...

In response to concern about the loss of ecosystem services once provided by natural riparian systems, state and federal agencies have established incentive programs for landowners to convert sensitive lands from agricultural to conservation uses. Enhancement of wildlife habitat, while identified as a function of such systems, has often been of secondary importance to soil conservation and water quality objectives. Though greatly important, little consideration has been given to how specific species will respond to the design and management of riparian buffers or other conservation lands. This study compared avian communities within a chronosequence of riparian buffers established on previously cropped or pastured land with those of the nearby matrix land cover types (row crop fields and an intensively grazed pasture). The riparian buffers consisted of native grasses, forbs, and woody vegetation established at three different times (2, 9, and 14+ years prior to survey). At each site, 10 min point counts for breeding birds were conducted using 50 m fixed radius plots, which were visited eight times between May 15 and July 10, 2008. A total of 54 bird species were observed over all of the study sites. The re-established riparian buffers in this study had higher bird abundance, richness, and diversity than the crop and pasture sites. These results suggest that re-establishing native riparian vegetation in areas of intensive agriculture will provide habitat for a broad suite of bird species, but that specific species will reflect successional stage, horizontal and vertical vegetative structure, and compositional diversity of the buffer vegetation. These results emphasize the importance of matching buffer design and management to species requirements if the objectives are to attract specific target species or species groups. more...

An enduring relationship developed between the University of Uppsala, Sweden, and the University of Illinois, Chicago, as a result of the author’s two opportunities to study and lecture in Uppsala through the auspices of the Fulbright Scholarship Awards, first at the invitation of Professor Tord Skoog in 1960, and then by Professor Valdemar Skoog in 2003. Some anecdotes and observations related to these dates and the 43-year interval are presented. more...

A major production constraint in arid and semiarid areas of Ethiopia is a lack of water for crop growth. Run off water can be harvested by channeling it into micro- catchments (MC) where it slowly infiltrates into the soil. The increased moisture provides more plant growth in these dry lands. An experiment using MC was conducted in eastern Ethiopia to study the growth of four multipurpose tree species intercropped with grass. Trees and grass were grown in 25 m2 and 100 m2 MC. Plant height, root collar diameter, and mortality rate of trees were determined 12 months after planting. Dry matter yield of grasses and trees were measured and nutrient analysis of plant tissues was determined. In a separate experiment the biomass of trees was determined after 2.5 years of continuous growth without grass competition. Soil moisture, organic matter, texture and bulk density of the soils were also determined. Mean tree height was 10% greater in the 100 m2 than in the 25 m2 MC. Root collar diameter and survival rate showed similar increase with 13% and 7.8% respectively. Acacia saligna and Leucaena leucocephala showed better growth in both plot sizes than the indigenous Acacia seyal and Acacia tortilis. The dry matter yield of grass (Panicum maximum) was over 12 tons/ha and 8 tons/ha in the 100 m2 and 25 m2 plots respectively. Soil moisture content was greater in MC than in control plots with no water harvesting structures with 31% and 24% during the wet and dry seasons respectively. The use of water harvesting can improve fodder production and carrying capacity of the dry lands of Ethiopia. more...

Intensive agriculture can result in increased runoff of sediment and agricultural chemicals that pollute streams. Consensus is emerging that, despite our best efforts, it is unlikely that significant reductions in nutrient loading to surface waters will be achieved through traditional, in-field management alone. Riparian forest buffers can play an important role in the movement of water and NPS (non-point source) pollutants to surface water bodies and ground water. Riparian buffers are linear in nature and because of their position in the landscape provide effective connections between the upland and aquatic ecosystems. Present designs tend to use one model with a zone of unmanaged trees nearest the stream followed by a zone of managed trees with a zone of grasses adjacent to the crop field. Numerous variations of that design using trees, shrubs, native grasses and forbs or nonnative cool-season grasses may provide better function for riparian forest buffers in specific settings. Properly designed riparian buffers have been shown to effectively reduce surface NPS pollutant movement to streams and under the right geological riparian setting can also remove them from the groundwater. Flexibility in design can also be used to produce various market and nonmarket goods. Design flexibility should become more widely practiced in the application of this agroforestry practice. more...

This study was conducted to determine biomass dynamics, carbon sequestration and plant nitrogen immobilization in multispecies riparian buffers, cool-season grass buffers and adjacent crop fields in central Iowa. The seven-year-old multispecies buffers were composed of poplar (Populus×euroamericana ‘Eugenei’) and switchgrass (Panicum virgatum L.). The cool-season grass buffers were dominated by non-native forage grasses (Bromus inermis Leysser., Phleum pratense L. and Poa pratensis L). Crop fields were under an annual corn-soybean rotation. Aboveground non-woody live and dead biomass were determined by direct harvests throughout two growing seasons. The dynamics of fine (0–2 mm) and small roots (2–5 mm) were assessed by sequentially collecting 35 cm deep, 5.4 cm diameter cores (125 cm deep cores in the second year) from April through November. Biomass of poplar trees was estimated using allometric equations developed by destructive sampling of trees. Poplar had the greatest aboveground live biomass, N and C pools, while switchgrass had the highest mean aboveground dead biomass, C and N pools. Over the two-year sampling period, live fine root biomass and root C and N in the riparian buffers were significantly greater than in crop fields. Growing-season mean biomass, C and N pools were greater in the multispecies buffer than in either of the crop fields or cool-season grass buffers. Rates of C accumulation in plant and litter biomass in the planted poplar and switchgrass stands averaged 2960 and 820 kg C ha−1 y−1, respectively. Nitrogen immobilization rates in the poplar stands and switchgrass sites averaged 37 and 16 kg N ha−1 y−1, respectively. Planted riparian buffers containing native perennial species therefore have the potential to sequester C from the atmosphere, and to immobilize N in biomass, therefore slowing or preventing N losses to the atmosphere and to ground and surface waters. more...

We quantified rates of soil respiration among sites within an agricultural landscape in central Iowa, USA. The study was conducted in riparian cool-season grass buffers, in re-established multispecies (switchgrass + poplar) riparian buffers and in adjacent crop (maize and soybean) fields. The objectives were to determine the variability in soil respiration among buffer types and crop fields within a riparian landscape, and to identify those factors correlating with the observed differences. Soil respiration was measured approximately monthly over a two-year period using the soda-lime technique. Mean daily soil respiration across all treatments ranged from 0.14 to 8.3 g C m−2 d−1. There were no significant differences between cool-season grass buffers and re-established forest buffers, but respiration rates beneath switchgrass were significantly lower than those beneath cool-season grass. Soil respiration was significantly greater in both buffer systems than in the cropped fields. Seasonal changes in soil respiration were strongly related to temperature changes. Over all sites, soil temperature and soil moisture together accounted for 69% of the seasonal variability in soil respiration. Annual soil respiration rates correlated strongly with soil organic carbon (R = 0.75, P < 0.001) and fine root ( more...

Simulated rainfall and runoff were used to compare the effectiveness of 6 m and 3 m wide filter strips of switchgrass (Panicum virgatum) and cool-season filter strips consisting of bromegrass (Bromus inermis), timothy (Phleum pratense) and fescue (Festuca spp.) in reducing sediment, nitrogen and phosphorus in surface runoff from adjacent crop fields. The 6 m and 3 m wide strips represented 20:1 and 40:1 area ratios, respectively. Twelve plots, six each, in the switchgrass and cool-season grass strips, were laid out on Coland soil, having an average slope of 3%. Plots received simulated rainfall of 5.1 cm hr1 intensity and simulated runoff containing known quantities of sediment and nutrients. Three runon samples, each integrated over 15 minutes, and nine runoff samples, each integrated over five minutes, were collected from each plot and analyzed for sediment, total-N, \({\text{NO}}_{\text{3}}^{\text{ - }} \)-N, total-P and \({\text{PO}}_{\text{4}}^{\text{ - }} \)P. The 6 m wide filter strips removed 77% while the 3 m removed 66% of the incoming sediment from surface runoff. The 6 m filter strips removed 46% of total-N, 42% of \({\text{NO}}_{\text{3}}^{\text{ - }} \)-N, 52% of total-P, and 43% of \({\text{PO}}_{\text{4}}^{\text{ - }} \)-P; and the 3 m filter strips removed 28% of total-N, 25% of \({\text{NO}}_{\text{3}}^{\text{ - }} \)-N, 37% of total-P and 34% of \({\text{PO}}_{\text{4}}^{\text{ - }} \)-P. Differences between 6 m and 3 m filter strips were significant (P < 0.05) for sediment and nutrient removal. Switchgrass filter strips removed significantly more total-N, \({\text{NO}}_{\text{3}}^{\text{ - }} \)-N, total-P and \({\text{PO}}_{\text{4}}^{\text{ - }} \)-P than cool-season grass filter strips (P < 0.05). more...

A multispecies riparian buffer strip (MRB) was established along Bear Creek in central Iowa by the Agroecology Issues Team at Iowa State University (ISU) in order to assess the ability of the MRB to positively impact soil erosion and process non-point source pollutants to improve water quality. Soil organic matter (SOM), and especially biologically-active soil organic matter, is considered to be an important soil quality indicator variable because of it has relationship to critical soil functions like erodibility and the capacity of the soil to act as an environmental buffer. The objectives of this study were to examine trends in SOM C accrual and to quantify intra-seasonal changes in SOM C and particulate organic matter (POM) C for each vegetation zone of a MRBS seven years after establishment on previously cultivated or heavily grazed soil. Total SOM C and POM C in soil under perennial vegetation (poplar, switch- grass and cool season grass) were significantly higher than under cropped soil. Total POM C changed within vegetation type over the four month study period, whereas total SOM C did not. After six growing seasons, SOM C increased 8.5% under poplar grown in association with cool season grass, and 8.6% under switchgrass. The results are very promising and suggest that changes in SOM C can occur in a relatively short time after the establishment of perennial vegetation in a MRB. These changes should increase the ability of MRB soil to process non- point source pollutants. more...

By influencing belowground processes, streamside vegetation affects soil processes important to surface water quality. We conducted this study to compare root distributions and dynamics, and total soil respiration among six sites comprising an agricultural buffer system: poplar (Populus × euroamericana‘ Eugenei), switchgrass, cool-season pasture grasses, corn (Zea mays L.), and soybean (Glycine max (L.) Merr.). The dynamics of fine (0--2 mm) and small roots (2--5 mm) were assessed by sequentially collecting 35 cm deep, 5.4 cm diameter cores from April through November. Coarse roots were described by excavating 1 × 1 × 2 m pits and collecting all roots in 20 cm depth increments. Root distributions within the soil profile were determined by counting roots that intersected the walls of the excavated pits. Soil respiration was measured monthly from July to October using the soda-lime technique. Over the sampling period, live fine-root biomass in the top 35 cm of soil averaged over 6 Mg ha-1 for the cool-season grass, poplar, and switchgrass sites while root biomass in the crop fields was < 2.3 Mg ha-1 at its maximum. Roots of trees, cool-season grasses, and switchgrass extended to more than 1.5 m in depth, with switchgrass roots being more widely distributed in deeper horizons. Root density was significantly greater under switchgrass and cool-season grasses than under corn or soybean. Soil respiration rates, which ranged from 1.4--7.2 g C m-2 day-1, were up to twice as high under the poplar, switchgrass and cool-season grasses as in the cropped fields. Abundant fine roots, deep rooting depths, and high soil respiration rates in the multispecies riparian buffer zones suggest that these buffer systems added more organic matter to the soil profile, and therefore provided better conditions for nutrient sequestration within the riparian buffers. more...

The Hardwood Quality Nursery Cooperative (bareroot forest nurseries in 5 midwestern states) initiated a series of studies in 1987 to evaluate red oak (Quercus rubra L.), and black walnut (Juglans nigra L.) seedling performance as a function of cultural treatments and seedling root system morphology. Seedlings were grown at three densities (32, 64, and 128 stems m-2for red oak; 32, 64, and 96 stems m-2for black walnut), and half of the density plots were undercut. Seedlings received fertilizer, weeding, and irrigation treatments customary to their respective nurseries. Seedlings were lifted, measured, and outplanted in their respective states as completely random individual tree plots during spring 1988. Survival, height, and diameter were evaluated annually through 1992. Seedling height, diameter, and number of permanent first-order lateral roots (FOLR) decreased with increasing bed density. At a given density, undercutting produced smaller seedlings (for both height and diameter) that had greater numbers of FOLR. Numbers of FOLR influenced seedling performance after outplanting. Red oak seedlings with at least 5 FOLR and black walnut with at least 7 FOLR had better survival and growth than seedlings with fewer roots. more...

Agriculture in the United States makes intensive use of large portions, of the nation's arable landscape. This landscape is dominated by large fields of annual crops with few perennial buffering communities within them. Agroforestry systems such as riparian buffers, alleycropping, windbreaks, tree/pasture systems, and forest farming provide buffering opportunities within these landscapes. Riparian buffers and alleycropping systems provide two unique opportunities toward sustainable production by reducing nonpoint source pollution while increasing ecological diversity. The major impediment to agroforestry in the United States is a lack of identity. Agroforestry as a practice is not officially recognized by federal and most state agencies and thus does not qualify for cost-share support or funding for research and establishment of demonstrations. A recent white paper, prepared by representatives from government agencies, academic institutions, and nongovernment organizations, identified eight major actions that could provide the support, for making agroforestry an acceptable alternative to nonsustainable agriculture. Ames, Iowa. Project No. 3209. more...

On 3 sites, 3-year performance of 1+0 northern red oak (Quercus rubra L.) seedlings was evaluated with respect to initial root system grade. Seven hundred twenty nursery-run bareroot northern red oak seedlings were graded according to numbers of large (>1mm) first-order lateral roots and outplanted in spring 1987 on eight 90-tree plots distributed among three sites in central Iowa. Survival, height growth, and diameter growth were significantly greater for seedlings with 10 or more large first-order lateral roots than for seedlings with 4 or fewer. Seedling survival and growth were significantly and positively related to initial root grade. First-year height growth, however, was significantly and negatively correlated with initial height. Combined results for seedling survival and growth indicated that red oak seedlings with five or more large first-order lateral roots have a greater probability of success both in terms of survival and early growth than do those with four or fewer first-order lateral roots. more...

A multi-species riparian buffer strip (MSRBS) system was designed and placed along a Central Iowa stream in 1990. Bear Creek, is typical of many streams in Central Iowa where the primary land use along the stream's length is row crop (corn and soybeans) production agriculture or intensive riparian zone grazing. The Bear Creek watershed is long (∼ 35 km), narrow (3–6 km), and drains 7,661 ha of farmland. The MSRBS system is a 20 m wide filter strip consisting of four or five rows of fast-growing trees planted closest to the stream, then two shrub rows, and finally a 7 m wide strip of switchgrass established next to the agricultural fields. The 1.0 km long system, is located on an operational farm and is laid out in a split block design on both sides of Bear Creek. An integral part of this system is a streambank stabilization soil bioengineering component and a constructed wetland to intercept NPS pollutants in field drainage tile water flow. It is hypothesized that this system will function effectively as a nutrient, pesticide, and sediment sink for NPS pollutants coming from the upslope agricultural fields. Prior to establishment of the MSRBS system, the riparian zone along Bear Creek was grazed and row cropped to the stream edge. Since 1990 there has been dramatic alteration in the appearance and functioning of this riparian zone. After four growing seasons, the fast-growing tree species (cottonwood, silver maple, willow, and green ash) range in height from 2.4 m to over 5.5 m. Mean (four-year) biomass production of silver maple was 8.4 dry Mg ha−1, more than twice to seven times the yield from other silver maple research plots in Central Iowa. The shrub species, selected because of desired wildlife benefits, have done well in terms of survival and growth with ninebark, Nannyberry viburnum and Nanking cherry doing the best. The switchgrass grass has developed into a dense stand that effectively stops concentrated flow from the agriculture fields and allows for infiltration rates well above the field rate. Early root biomass data indicate significantly more roots below the MSRBS than agricultural fields. This suggests better soil stabilization, absorption of infiltrated water, and soil-root-microbe-NPS pollutant interaction characteristics within the MSRBS system than the cropped fields. Nitrate-nitrogen concentrations in the MSRBS never exceed 2 mg l−1 whereas the levels in the adjacent agricultural fields exceed 12 mg l−1. The water quality data collected suggest that the MSRBS is effective in reducing NPS pollutants in the vadose and saturated zone below the system. The soil bioengineering revetments have stabilized the streambank and minimized bank collapse. Initial results (from 4 months of operation) from the constructed wetland (built in summer 1994) indicate nitrate-nitrogen concentrations of the tile inflow water >15 mg l−1 whereas, the outflow water had a nitrate-nitrogen concentration of more...

A survey, conducted in 1990–1991 on agroforestry and forestry-related systems in eight Midwestern states, showed that three traditional and three nontraditional agroforestry systems are practiced in the region. Of 46 traditional systems reported, most common was agrisilviculture (28), then silvipasture (12) and agrisilvipasture (6). These systems often involved corn, soybeans, and hay planted with tree species for nut, timber, or Christmas tree production, and cattle. Non-traditional agroforestry systems were field windbreaks/shelterbelts (29), treeshrub intercropping systems (21), and boundary plantings (11). These systems involved a variety of northern hardwood species evergreens, and shrubs. There was also a preponderance of specialized systems (97) of growing trees with the production of mushrooms, nuts, syrup, wildlife, and other nonwood products. The survey is exploratory in nature and, although the results may not represent a complete count of people involved with agroforestry in the region, the numbers reported may indicate where a practice may be prevalent. The results reflect the fact that much work still needs to be done by agroforesters in this region. They also provide some basis for further research on more suitable systems, and for identifying other researchable questions on agroforestry for the region. The methodology also made possible a bigger nucleus for networking of agroforesters and other interested people in the Midwest. Finally, although not normally considered as agroforestry, the significance of the other specialized systems reported in this survey is that they offer varied ways of connecting forestry with other activities in a largely agricultural landscape, and that they may even be seen as opportunities for easier transition into agroforestry. more...

Zeatin-9-riboside was identified in shoots and roots of Pinus resinosa by GC-MS analysis of its permethyl derivative. Based on their chromatographic properties on Sephadex LH-20 and C18 HPLC, and their susceptibility to enzymatic degradation, several other cytokinins have been tentatively identified. The basic fraction of both the roots and shoots contained zeatin, whereas the shoots contained dihydrozeatin-O-glucoside and the roots contained zeatin-O-glucoside. Zeatin-9-riboside monophosphate, isopentenyladenosine monophosphate ([9R-5′P]iP) and glucosyl phosphate derivatives were detected in the acidic fractions from both roots and shoots. There were equivalent amounts of [9R-5′P]iP in both roots and shoots. The presence of equivalent amounts of [9R-5′P]iP in both the roots and shots suggests that cytokinin biosynthesis may be occurring in both locations. more...