Soil water use by diploid and tetraploid Russian wildrye

Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] is an important co ol-season forage grass for the Northern Great Plains, but it exhibits poor seedling vigor. Tetraploid (2n=4x=28) plants hare improved seedling vigor o ver diploid (2n=2x=14) plants, but data is lacking on plant-soil-water rela tions. Objectives of this research were to compare water-use efficiency (WU E), evapotranspiration (ET), rooting activity, and water extraction in rela tion to Ham stage for diploid and tetraploid Russian wildrye. A diploid and tetraploid entry were evaluated for 3 yr under two water treatments (50 an d 150% of monthly average precipitation for 1 April to 1 November) and two fertilizer rates (10 and 134 kg N ha(-1)) in a rain shelter. The soil was a Parshall fine sandy loam (Coarse-loamy, mixed, superactive, frigid Pachic Haplustoll). Cumulative ET averaged across the 50 and 150% water treatments was 138 and 141 mm for the diploid and tetraploid, respectively. Rate of r oot activity progression was linear with Haun to the 1.2-m depth and ranged from 0.148 to 0.163 m per Haun stage for the diploid and tetraploid, respe ctively, at 50% water, Forage yield of the tetraploid was greater than the diploid at the 50%, but not at the 150% water treatment. Water-use efficien cy was higher for the tetraploid (3.8 g kg(-1)) than the diploid (3.1 g kg( -1)) at the 50% water treatment, but at 150% water the entries were not dif ferent. Overall, the tetraploid entry exhibited a more favorable WUE and ot her soil mater relations than did the diploid entry.