Robert L. McGraw

Shade effects on forage crops with potential in temperate agroforestry practices

Thirty forages, including eight introduced cool-season grasses, four native warm-season grasses, one introduced warm-season grass, eight introduced cool-season legumes, five native warm-season legumes, and four introduced warm-season legumes, were grown in 7.6 L (two gallon) pots in full sun, 50%, and 80% shade created by shade cloth over a greenhouse frame. Experiments were conducted during summer--fall 1994, spring--early summer 1995, and summer--fall 1995. A complete randomized experimental design was used and above ground dry weight was measured in each shade environment. Tukeys studentized range test was used to compare mean dry weights (MDW) within a species. Warm-season grasses displayed significant reductions in MDW under shade regardless of growing season. All cool-season forages grown during spring--early summer showed a decrease in MDW under shade; however, the reductions in dry weights of ‘Benchmark’ and ‘Justus’ orchardgrass, ‘KY 31’ tall fescue, Desmodium canescens and D. paniculatum were not significant under 50% shade. Cool-season grasses showed more shade tolerance when grown during the summer--fall than when grown during the spring--early summer. Seven of the selected cool-season grasses grown during the summer--fall did not display significant reductions in MDW under 50% shade as compared to full sun. Smooth bromegrass grown under 50% shade showed a significantly increased MDW production compared to growth in full sun. With the exception of Justus orchardgrass and smooth bromegrass, growth of cool-season grasses was inhibited at 80% shade. Among the legumes harvested during the fall, the dry weights of both Desmodium species tested and hog peanut (Amphicarpaea bracteata L.) increased significantly under 50% and 80% shade. In addition, ‘Cody’ alfalfa, white clover, slender lespedeza and ‘Kobe’ lespedeza showed no significant reductions in MDW under 50% shade.

Forage legumes as living mulches for trees in agroforestry practices - preliminary results

Successful establishment and growth of tree seedlings in an agroforestry practice is dependent on the control of competing herbaceous vegetation. Conventional weed control methods (i.e., chemical, mechanical, and physical suppression) are effective but can be costly in terms of time, damage to non-target vegetation, or increased soil erosion. Alternatively, some living mulches can exclude undesirable vegetation, protect the soil, compete minimally with associated trees, and supplement soil nitrogen. In this study, small and large white clover (Trifolium repens L.), red clover (T. pratense L.), kura clover (T. ambiguum Bieb.), strawberry clover (T. fragiferum L.), birdsfoot trefoil (Lotus corniculatus L.), hairy vetch and ’AU Early‘ hairy vetch (Vicia villosa Roth) were selected for evaluation as living mulches. These species were established in 9 m ×9 m replicated plots along with two controls [tall fescue (Festuca arundinacea Schreb.) and bare soil kept vegetation free using glyphosate]. The controls represent ’high competition‘ and ’no competition‘, respectively. Eastern black walnut (Juglans nigra L.), honeylocust (Gleditsia triacanthos L.), and hybrid pitch × loblolly pine (Pinus rigida L. × P. taeda L.) seedlings were planted in association with each living mulch. Tree seedling heights and diameters were measured during the first two years and forage performance evaluated. All seedlings grew better in the absence of competition. Tall fescue greatly reduced the growth of hardwood seedlings. Red clover and ladino clover showed the greatest promise as living mulches for use with the hardwood and pine seedlings, respectively.

Evaluation of Native Legume Species for Forage Yield, Quality, and Seed Production

Illinois bundleflower (Desmanthus illinoensis (Michaux) MacMillan ex Robinson & Fern.) appears to have the greatest potential as a forage species among 15 species of native legumes (Fabaceae) evaluated for forage yield, quality, and seed production. It ranked among the top five for all agronomic characteristics measured. Hoary tick clover (Desmodium canescens [L.] DC.), panicled tick clover (Desmodium paniculatum [L.] DC.), and roundhead lespedeza (Lespedeza capitata Michaux), ranked among the top five for grams per plant of forage and seed. All of the native legumes contained greater concentrations of crude protein and lower concentrations of neutral detergent fiber than typically found in the native warm-season grasses commonly sown for pasture, suggesting that these native legumes should improve forage quality in mixed pastures. Only white prairie clover (Dalea candida Michaux ex Willd.), purple prairie clover (Dalea purpurea Vent.), and Illinois bundleflower had lower concentrations of acid detergent fiber than that typically found in native warm-season grasses.

Neotropical Legume Tree Inga edulis Forms N2-fixing Symbiosis with Fast-growing Bradyrhizobium Strains

Inga edulis Mart. is a tropical legume tree used for shade in coffee and cacao plantations and as a hedgerow in alley-cropping practices. Little information can be found concerning N2 fixation in this species. This study was conducted to characterize the rhizobia of I. edulis and determine if it is capable of fixing substantial amounts of N2. Four strains of fast-growing, Gram-negative rhizobia-type bacteria were isolated from I. edulis nodules. The strains were identified by sequencing of partial 16S–23S rDNA internal spacer region. Nitrogenase activity was determined using acetylene reduction assay (ARA). Dinitrogen fixation was measured under controlled conditions by the 15N isotope dilution technique using two non-N2-fixing reference species, Vochysia guatemalensis Donn. Sm, and Gmelina arborea Roxb. ex. Sm. Seedlings were grown in three growth media: native soil and naturally N-depleted sand amended to a low and high N level. The four strains of symbiotic bacteria were closely related to Bradyrhizobium japonicum and to Bradyrhizobium liaoningense. Nodules demonstrated nitrogenase activity as measured by ARA. Vochysia guatemalensis was a better non-N2-fixing reference than G. arborea. When V. guatemalensis was used as the non-N2-fixing reference, the estimate of the percentage of N fixed from atmosphere out of total N in I. edulis seedlings was ca. 40 in the two sand media treatments and 10 in the native soil.

COMPARISON OF CONTINUOUS AND ROTATIONAL SILVOPASTORAL SYSTEMS FOR ESTABLISHED WALNUT PLANTATIONS IN SOUTHWEST MISSOURI, USA

Forty-eight Holstein steers (average weight 243 kg ± 11.8) were utilized to study the performance of cattle grazing a mature walnut stand. Steers were grazed for 56 days in either a continuous (C) or rotational (R) silvopastoral system. Four 0.81 ha pastures were assigned to either the C or R system (two replications per treatment). Initial stocking rates for both treatments were 14.8 animals/ha which was reduced at the mid-point to 7.4 animals/ha. Forage quality, yield, and plant composition were measured weekly throughout the trial. Forage quality differences were determined by neutral detergent fiber (NDF), acid detergent fiber (ADF), and crude protein (CP) measurements. Forage composition was determined by separating material into four categories: grass, legume, weed and dead plant material. Tree response (diameter at breast height and height growth) was measured prior to and following the grazing period. No significant differences were observed for cattle average daily gain between treatments. Forage availability was higher (P > 0.05) for the R treatment. There were no differences for %NDF (P < 0.10) while %ADF was lower (P > 0.10) and %CP tended (P = 0.12) to be higher for R when compared to C. Rotational pastures had higher (P > 0.10) percentages of grass and legume with lower (P > 0.10) percentage dead material. There were no treatment differences (P < 0.10) for tree diameter at breast height. The average height growth for C was 1.67 m while R was 1.19 m which was only numerically different (P = 0.13). It is postulated that differences in height growth were due to increased water competition in R due to increased soil moisture loss by vegetative growth and transpiration.

Effects of shade on growth and nodulation on three native legumes with potential for use in agroforestry

In the Midwest US, native legume species adapted to savanna environments may grow well under varying shade conditions. These species may be ideal for use within tree rows in alley-cropping practices and on tree plantations by providing biologically fixed nitrogen, ground cover, and wildlife food and habitat. A greenhouse experiment was conducted to evaluate the effect of 3 different light levels (100%, 45%, 20%) on the growth and nodulation of 3 Desmodium (Fabaceae) species: Hoary ticktrefoil (D. canescens (L.) DC.), Showy ticktrefoil (D. canadense (L.) DC.), and Illinois ticktrefoil (D. illinoense A. Gray). All species produced equal amounts of dry matter at 45% and 100% light, but significantly less dry matter at 20% light. All species had greater or equal concentrations of nitrogen (N) at 20% light compared with 45% or 100% light. The number of nodules per gram of plant dry weight and nodule dry weight was similar at all light levels within each species. A significant species x light interaction was found for the number of nodules per plant because nodule number decreased in both D. canescens and D. canadense but not in D. illinoense for plants grown at 20% in comparison with 45% light. The number of nodules per plant and the number of nodules per gram of plant dry weight were lower under all light conditions for D. illinoense compared with the other species. Results indicate that these native legumes grow as well at 45% light as they do at 100% light, and shade does not reduce N concentration.Houx JH III, McGraw RL, Fritschi FB, Navarrete-Tindall NE. 2009. Effects of shade on growth and nodulation of three native legumes with potential for use in agroforestry. Native Plants Journal 10(3): 232–238.

Growth and nutrient concentration of two native forage legumes inoculated with Rhizobium and mycorrhiza in Missouri, USA

The Center for Agroforestry at the University of Missouri has tested numerous native legumes for potential use in agroforestry and selected Illinois bundleflower (Desmanthus illinoensis (Michaux) MacMillan ex Robinson and Fern.) and panicled tick clover (Desmodium paniculatum (L.) DC.) for further testing. Our objective was to document the effect of arbuscular mycorrhizae (AM) (Glomus spp.) and Rhizobium on growth and nutrient concentration of these legumes. Seeds were planted in a greenhouse and inoculated with one of two species of AM and/or one of two strains of Rhizobium. Plants were harvested after 80 d and data taken on leaf and stem dry weight, root fresh weight, stem height, nodulation, AM colonization, and N, P, K, Ca, and Mg concentration. Inoculation with Rhizobium did not affect plant growth in Illinois bundleflower, but colonization by Glomus intraradices increased all plant growth variables except stem height. Nutrient concentration was unaffected by the presence of either endophyte. In contrast, inoculation of panicled tick clover with Rhizobium str. 41Z10 increased leaf dry weight (32%) compared to the control and root fresh weight (41%) compared to str. 32Z3, and colonization by G. intraradices increased leaf dry weight (35%) and stem height (26%). Both species of AM increased P and K concentration (41% and 55%, respectively) in panicled tick clover. Our results suggest that the growth of these legumes can be improved by the use of proper AM species and/or Rhizobium strains. However, additional research to identify the best Rhizobium and AM inoculates for these plant species is important in developing strategies for their use in agroforestry.

Cattle Preferentially Select Birdsfoot Trefoil from Mixtures of Tall Fescue and Birdsfoot Trefoil

When birdsfoot trefoil (Lotus corniculatus L.) is interseeded into tall fescue (Festuca arundinacea Schreb.) pastures, animal performance often exceeds that expected based on forage samples taken from the pasture. This may be due to cattle (Bos taurus) preferentially selecting birdsfoot trefoil from mixed pastures. Our objective was to investigate the selectivity for birdsfoot trefoil by cattle grazing tall fescue-birdsfoot trefoil pastures. Treatments were ‘Phyter’ tall fescue sown in a monoculture and in mixtures with ‘ARS-2622’ and ‘Norcen’ birdsfoot trefoil. Beef heifers fitted with esophageal cannulas grazed pastures in the spring and autumn of 1998 and again in spring 1999. In the tall fescue-birdsfoot trefoil mixtures, the amount of birdsfoot trefoil on-offer showed a 73% reduction during the study, but the amount of birdsfoot trefoil in esophageal samples declined by an average of only 22%. Although the percentage of birdsfoot trefoil in mixed pastures often declines over time, its value may be underestimated because animals selectively graze this species when its proportion in pastures is low.