Evaluating Shade Tolerance of Cover Crops, Forages and Woodland Forbs: Facility Design and Preliminary Results


Kejia Pang, J.W. Van Sambeek, H.E. Garrett, and Shibu Jose

Postdoctoral Research Associate (KP), Professor Emeritus (GG), and Center for Agroforestry Director (SJ), 203 Natural Resources Building, and Research Plant Physiologist (JVS), USDA Forest Service Northern Research Station, University of Missouri, Columbia, MO 65211. KP is corresponding author, to contact email pangk@missouri.edu.

Abstract – An artificial shade facility was constructed in 1996 at the Horticulture and Agroforestry Research Center (HARC) in New Franklin, Missouri. Nine shade structures, 14.6 m long (south to north) × 4.9 m wide, where laid out on 2.4 m tall posts on a 4.9 m square spacing connected with high tensile wire. Each structure was designed to hold 120 pots with a 0.7 m × 0.7 m spacing connected to a drip irrigation system. Shade cloth with different densities was placed on both top and sides of the structures to emulate three light levels: full sun, 45% of full sun (medium shade), and 20% of full sun (dense shade). Experimental design is a split plot randomized block with three blocks with three light levels and six replications (pots) of fifteen different cover crops, forages, or woodland forbs nested within each shade. Seedlings were established in 10-L plastic pots with a well-drained potting medium supplemented with controlled released nitrogen and micronutrient fertilizers to minimize nutrient deficiencies. Annual biomass yields average 220 g, 369 g, and 286 g, respectively, for 15 species under 20, 45, and 100% of full sunlight. Average annual biomass yields for 1997, 1998, and 1999 ranged from 396 g, 279 g, and 200 g, respectively. Several improvements have been made to the initial design. Elevating the shade cloth on the sides of structures to the same height as the pots and removal of shade cloth on the north end reduced temperature differences of 3.5 to 4.2 ˚C inside structure covered with dense shade cloth compared to open structure. Using either white pots or white sleeves placed around each black pot minimized high soil temperatures on the south side of black pots exposed to full sun. The relative distance plasticity index (RDPI) is a promising parameter to quantify the capacity of a species to sustain forage quantity and quality through physiologically and morphologically adaptations under different light levels. Woodland forbs usually have low RDPI values suggesting a high degree of shade tolerance. Forage grasses tend to have lower RDPI values for biomass production than forage legumes. Our results suggest that many herbaceous species that can be use in agroforestry systems have the capacity to sustain high forage quantity and quality under moderate shade when tree root competition is controlled.