The effect of growth temperature, level of ammonium nitrate, and light intensity on the growth and nodulation of cowpea (Vigna sinensis endl. ex hassk.)

Abstract

The nodulation and growth of cowpea plants (Vigna sinensis Endl. ex Hassk. var. Poona), grown in the CERES phytotron glasshouses, were examined. The plants were grown under six controlled temperature regimes (21, 24, 27, 30, 33, or 36°C day temperature) with ammonium nitrate (NH₄N0₃) additions of 0, 10, 30, and 90 mg nitrogen per pot of six plants; and were grown either under natural daylight or under natural daylight reduced in intensity by one-third by mesh screens.

Primary root nodulation was significantly affected by temperature, NH₄NO₃ level, and light intensity, with an optimum temperature of 24°C. Secondary root nodulation was also affected by light intensity and temperature, but the nodulation pattern (with an optimum temperature of 33°) was almost the inverse of the primary root pattern. Temperature significantly influenced the fresh weight of nodules per plant and the nodule size, with a lesser effect of the NH₄NO₃ level.

Plant dry weight production (tops and roots) was governed by the temperature, NH4NO3 level, and light intensity, the maximum total dry weight being produced at 27°C.

Temperature, light intensity, and NH₄NO₃ level all influenced the plant combined- nitrogen uptake. The nodule leghaemoglobin concentration was significantly reduced at the two extreme temperatures 21° and 36°C. Temperature also markedly affected the nodule structure – particularly the distribution of starch within the nodule.