Influence of Alley Crop Environment on Orchardgrass and Tall Fescue Herbage

unshaded sites in southern USA when exposed to high summer temperatures (Van Santen and Sleper, 1996). The design of agroforestry systems requires a thorough understandNeither orchardgrass nor tall fescue had significant ing of biological interactions that might complement or constrain yield reduction in pots exposed to 50% shade, and orproduction. The objective of this study was to examine effects of alley chardgrass yield was not significantly reduced in 80% crop environment on persistence, herbage yield, nutritive value, and gas exchange (CO2 exchange rate, transpiration, and stomatal conducshade compared with unshaded growth (Lin et al., 1999). tance) of two shade-tolerant herbage grasses. The experiment was When grown at 14% ambient photosynthetically active conducted for 3 yr in orchardgrass (Dactylis glomerata L.), tall fescue radiation, orchardgrass produced more tillers per plant (Festuca arundinacea Schreb.), and a 1:1 binary mixture (tall fescue than most other grasses tested (Devkota et al., 1997). and orchardgrass) in 4.9-m-wide alleys of 10-yr-old loblolly pine (PiWhen grazed, however, orchardgrass did not persist well nus taeda L.) and shortleaf pine (P. echinata Mill.), and the unshaded in conifer-shaded pasture in West Virginia (Belesky et control at Booneville, AR. Loblolly pine was 1.5 m taller and had al., 2001). twice the canopy cover as shortleaf pine (52 and 25% canopy cover, Overstory trees can either complement or constrain respectively). Averaged across harvests, orchardgrass persisted better understory herbage production and nutritive value. in loblolly pine alleys (72% stand) than in the control (44% stand) Trees can favorably alter the understory microclimate while tall fescue persisted better in the control (30% stand) than in (Feldhake, 2001) and protect herbage by reducing loblolly pine (13% stand). Persistence in shortleaf pine alleys was evapotranspiration during drought (Frost and McDouintermediate for both herbage treatments. Yields of orchardgrass and the binary mixture did not differ in pine alleys (1300 kg ha 1) and gald, 1989), minimizing deleterious interactions of heat were usually greater than tall fescue yields ( 700 kg ha 1). Crude stress and high light intensity on photosynthesis of C3 protein was higher in loblolly pine alleys (172 g kg 1) than in the species (Lin et al., 1999) and reducing radiation frost control (141 g kg 1). Gas exchange parameters were similar for tall damage (Feldhake, 2002) compared with unshaded fescue and orchardgrass across a range of volumetric soil moisture herbage. Conversely, trees can reduce herbage produc(15–30%), indicating little difference in drought response. Producers tion through shade, competition for soil moisture and should consider using orchardgrass monocultures or binary mixtures nutrients, and allelopathy (Clason and Sharrow, 2000; with tall fescue for pine alleys in the midsouth USA. Garrett and McGraw, 2000). The objective of this study was to examine effects of alley crop environment on persistence, herbage yield, nutritive value, and gas exT use of land resources can be increased when change of two shade-tolerant herbage grasses. herbage, livestock, and wood fiber production are integrated in maturing loblolly pine plantations (Clason, MATERIALS AND METHODS 1999). Alley crop productivity is influenced by many factors, including the interaction of crop and tree species Site Description in space and time. Potential herbage species for alley The experimental area was located near Booneville, AR crop systems have been discussed (Clason and Sharrow, (35 05 N, 93 59 W; 152 m above sea level), on Linker fine 2000; Garrett and McGraw, 2000), but further research sandy loam (fine-loamy, siliceous, thermic Typic Hapludults). is needed to assess alley crop productivity and susLoblolly, longleaf (Pinus palustris Mill.), and shortleaf pines tainability in specific systems. were planted in a north–south orientation in spring 1992 in four-row blocks 30 m long, spaced 1.2 m within rows and 4.9 m Tall fescue and orchardgrass have substantial shade between rows (Pearson, 1994). tolerance and silvopastoral value (Blake et al., 1966; Tree survival was 72 and 77% for loblolly and shortleaf Clason and Sharrow, 2000). Tall fescue has broad adaptpine, respectively, in 1999. Branches were pruned in 1999 to ability, persistence, and nutritive value (Burns and a minimum stem diameter of 8.5 cm (a height of about 2.3 m) Chamblee, 1979) and is the predominant cool-season and 9.0 cm (a height of about 3 m) for shortleaf and loblolly herbage grass in the central highlands of Arkansas. Orpine, respectively. This left about 40 to 50% of the canopy chardgrass has a more narrow range of adaptation than unpruned. Pruning debris was removed from the site. Trees tall fescue and is a minor pasture component in much were not thinned, except that a few broken trees were removed following a December 2000 ice storm. Longleaf pine survival of the USA. Orchardgrass is at its extreme southwestern was only about 20%, so survivors were removed in 1999 to range in the central highlands of Arkansas (Jung and create the unshaded control treatment (Fig. 1). Baker, 1973) and is at a competitive disadvantage in Alleys were sprayed with glyphosate [N-(phosphonomethyl)glycine] at 1.06 kg a.i. ha 1 three times in summer 1999 to kill the existing sod of tall fescue and bermudagrass [Cynodon USDA-ARS, Dale Bumpers Small Farms Res. Cent., 6883 S. State dactylon (L.) Pers.]. Topsoil sampled to 15-cm depth had a Hwy. 23, Booneville, AR 72927. Received 7 Oct. 2002. *CorrespondpH range of 5.3 to 5.7 and 8.5 and 92 mg kg 1 available P and ing author ([email protected]). Published in Agron. J. 95:1163–1171 (2003).  American Society of Agronomy Abbreviations: CER, CO2 exchange rate; IVDMD, in vitro dry matter digestibility; PLS, pure live seed. 677 S. Segoe Rd., Madison, WI 53711 USA