Influence of Slope Position on Nitrogen Fixation and Yield of Dry Peas¹

Abstract

Abstract Slope position and aspect are known to influence soil temperature and moisture which have a direct bearing on yield of agronomic crops. The objectives of this study were to determine the influence of soil slope on yield and N 2 fixation by dry peas ( Pisum sativum L.) in the field and to determine the effectiveness of isolates of Rhizobium leguminosarum taken from various slopes on N 2 fixation by peas in the greenhouse. From N 2 (C 2 H 2 )‐fixation rates conducted weekly in three positions of a Palouse catena; bottomland (Xeric Argialbolls) south slope, (Ultic Argixerolls), and ridgetop (Pachic Haploxerolls), total seasonal N 2 (C 2 H 2 ) fixed was estimated at 69, 22, and 17 kg/ha of N, respectively. For peas growing on the bottomland, south slope and ridgetop, plant N uptake was 210, 99, and 75 kg/ha of N, respectively. Pea seed yields of 2,106, and 480 kg/ha on the bottomland and ridgetop, respectively, were related to the amount of water depleted in the soil profile of 21.6 and 8.9 cm, respectively. Higher yield and greater N 2 fixation by peas growing on the bottom slope were apparently related to greater root penetration and removal of water. Greater plant N and dry matter were obtained in the greenhouse when peas were inoculated with isolates from the north slope when compared with isolates from other slopes. No differences were noted in pea growth and N 2 fixation between isolates from the bottomland, south slope and ridgetop, which suggested that differences in N 2 fixation and yield observed in the field were not related to efficiency of the microsymbiot