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Nodulation and N Fixation of Field‐Grown California Cowpeas as Influenced by Well‐Irrigated and Droughted Conditions 1
Author(s) -
Zablotowicz Robert M.,
Focht Dennis D.,
Cannell Glen H.
Publication year - 1981
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1981.00021962007300010003x
Subject(s) - nitrogenase , vigna , point of delivery , irrigation , agronomy , nitrogen fixation , biology , rhizobium , horticulture , water stress , inoculation , bacteria , genetics
The cowpea, ( Vigna unguiculata (L.) Walp.), is considered a drought‐tolerant legume. The N fixation process, however, is sensitive to water stress. This study was conducted to describe the development of nodulation and N fixation of field‐grown Californian cowpeas as influenced by stage of growth and drought. California No. 5 blackeyes were evaluated for nodulation and N fixation (as measured by acetylene reduction assay) utilizing four strains of Rhizobium sp. applied as seed inoculum. Two water regimes were utilized in this study: 1) the well‐watered regime was irrigated when the soil matric potential reached ‐0.6 bars at a depth of 20 cm, 2) the droughted regime received sufficient irrigation to allow good seed emergence, followed by a 42‐day period free of rain or irrigation. Maximum nodulation of 175 mg/plant was observed at flowering in the well‐watered plots versus 15 mg/plant in the droughted plants. Following this development stage, there was no significant difference in nodulation between water regimes. Maximum total nitrogenase activity was 22.5 and 18.8 µmoles of ethylene/plant/hour, respectively at flowering and pod‐fill in the well‐watered plants. The dry regime by contrast achieved a maximum nitrogenase activity of 5.3 and 4.5 µmoles ethylene/plant/hour at pod‐fill and pod yellowing stages of maturity, respectively. Consequently, there was a significant reduction in total nitrogenase activity (mmoles of ethylene/plant/growing season) averaged over four Rhizobium strains from 14.5 in the well‐watered to 3.7 in the droughted regime. This decrease in N fixation capacity did not decrease seed yields of droughted plants below those of well‐watered plants.