Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/20/2004
Publication Date: 9/1/2004
Citation: Burner, D.M., Belesky, D.P. 2004. Diurnal effects on nutritive value of alley-cropped orchardgrass herbage. Crop Science. 44(5):1776-1780. Interpretive Summary: Quality assessments of grass forage often are based on agronomic studies conducted under high levels of environmental control in conventional systems. Agroforestry systems, however, tend to have more environmental variation because of intermittent illumination of understory plants, and tree-crop competition for soil moisture and soil nutrients. We sought to determine whether the nutritive value of orchardgrass had daily variation in pine agroforestry plots and unshaded plots. Carbohydrate levels had cyclical daily variation in unshaded plots but not in pine plots. This demonstrated that orchardgrass responded differently in agroforestry and conventional systems. These results should be of interest to producers, scientists, and extension agents because they demonstrate that orchardgrass in agroforestry systems needs to be managed differently to optimize nutritive value and livestock production.
Technical Abstract: Nonstructural carbohydrates, crude protein, and in vitro dry matter digestibility (IVDMD) are important indices of herbage nutritive value and can exhibit diurnal variation in 'conventional' agronomic systems. Our objective was to determine diurnal trends of nutritive value components in alley cropped orchardgrass (Dactylis glomerata L.) herbage harvested daily from 1-15 June 2001 and 2002 at three time intervals (0500, 1100, and 1700h, CST), from three environments: unshaded control, loblolly (Pinus taeda L.) pine alleys, and shortleaf (P. echinata Mill.) pine alleys. Diurnal responses were defined as a regression response (P<0.10) with time. Total nonstructural (TNC) and water soluble carbohydrates (WSC) increased linearly in the control environment, but not in pine alleys. Starch increased curvilinearly in loblolly pine alleys but not in the control environment. Crude protein and IVDMD did not have diurnal responses within or among environments. However, mean crude protein decreased and IVDMD increased in AM- vs. PM-herbage. Compared to the unshaded control, pine shading increased crude protein and IVDMD, but decreased yield and nonstructural carbohydrates of orchardgrass herbage. Differential responses of nutritive value components in pine alleys compared to the control were attributed to altered amount and temporal distribution of solar irradiance. The study shows that herbage nutritive value is affected by fundamental, spatio-temporal effects in conventional and alley crop environments.