ROOTING ACTIVITY AND WATER-USE DURING VEGETATIVE DEVELOPMENT OF CRESTED AND WESTERN WHEATGRASS

Crested wheatgrass [Agropyron desertorum (Fisch. ex. Link) Schult] and western wheatgrass [Pascopyrum smithii Rybd, (Love)] are important cool-season forage species that have contrasting growth patterns. Knowledge of relationships among plant development stage, water use, and rooting activity would aid in understanding the responses of these species to stresses and defoliation. Our objectives were to compare evapotranspiration (ET), rooting activity, and plant water status in relation to Haun development stage of 'Nordan' crested wheatgrass 'Rodan' western wheatgrass. These species were grown at three water treatments (50, 100, and 150% of 1 April to 31 October monthly rainfall) and two N fertilizer (11 and 110 kg N ha-1) rates in a rain-out shelter at Mandan, ND for a 3-yr period. The soil was a Parshall fine sandy loam (coarse-loamy, mixed Pachic Haploborolls). Cumulative ET through early boot stage averaged 133 and 170 mm for crested and western wheatgrass, respectively. Maximum ET rate occurred at Haun stage 5 to 6 for both species. Crested wheatgrass rooting activity averaged over three water treatments increased about 4.4 cm d-1 compared to 3.7 cm d-1 for western wheatgrass. Both species exhibited rooting activity to 1.2 m by mid-May when western wheatgrass had developed to Haun stage 4.9 and crested wheatgrass to 5.7. Water use-efficiency of crested wheatgrass decreased as water treatment and Haun stage increased, but western wheatgrass did not change with either. Water use-efficiency of crested wheatgrass, but not of western wheatgrass, was greater at 110 than at 11 kg fertilizer N ha-1. Information on the simultaneous development of plant aerial parts and rooting activity contributes to an understanding of the water-use relations of these species and has application in development of growth and yield simulation models.