NODULATION, DRY MATTER PRODUCTION, AND N₂ FIXATION BY FABABEAN AND CHICKPEA AS AFFECTED BY SOIL MOISTURE AND POTASSIUM FERTILIZER

Abstract

The impact of three rates of potassium (K) fertilizer (0, 75, and 150 kg K₂O/ha) on nodulation, dry matter production, and nitrogen (N₂) fixation by fababean (Vicia faba L.) and chickpea (Cicer arietinum L.) was evaluated in a pot experiment. The plants were subjected to three soil moisture regimes (low, 45–50%; moderate, 55–60%; and high, 75–80% of field capacity). The ¹⁵N-isotope dilution method was employed to evaluate N₂ fixation using a non-fixing chickpea genotype as a reference crop. Water restriction drastically affected dry matter production, nodulation, and N₂ fixation by both plant species. The negative effect of water stress on %N₂ fixed was more prominent in chickpea (11–58%) than in fababean (68–81%) under low and high % of field capacity, respectively. Plant species differed in their response to K fertilizer as a means of enhancing growth and overcoming the stress conditions. The higher level of K fertilizer increased both dry matter production and total N₂ fixed in fababean, but did not have any impact on chickpea. Percent N₂ fixed, however, appeared to be unaffected by K fertilizer as a means of alleviating drought stress in both plant species. Therefore, it appears that under the experimental conditions the beneficial effect of potassium on water-stressed fababean resulted from stimulating the growth rather than improving the N₂ fixation efficiency. However, in well-watered plants, a high requirement of the symbiotic system for potassium is needed to ensure an optimal growth and N₂ fixation.

ACKNOWLEDGMENTS

We would like to thank Professor I. Othman, General Director of AECS, for his support, and Professor N. E. Sharabi for his remarks.