Rhizobium inoculation and phosphate fertilization effects on productive and qualitative traits of guar (Cyamopsis tetragonoloba (L.) Taub.)

Guar (Cyamopsis tetragonoloba (L.) Taub.), a grain legume grown in India, Pakistan and the United States, draws interest for irrigated environments in the Mediterranean areas. A limitation to widespread guar adaptation in this environment is its low capability to develop N-fixing Rhizobium nodulation. A study was conducted in South- Eastern Sicily, Italy in 2005 and 2006, to examine three levels of Rhizobium inoculation (non-inoculated, inoculated at sowing, inoculated at sowing plus at the third true leaf) and two levels of applied phosphorus fertilizer (0 and 40 kg ha-1 P). Plant height, pods per plant, seed yield, number of nodules per plant and seed galactomannan content were measured. No significant difference was found due to year of cultivation. Plant height was not significantly affected by Rhizobium or P fertilizer. Phosphorus fertilizer promoted the number of pods per plant, especially when bacteria inoculation was applied. Seed yield was significantly increased by inoculation and phosphorus levels. Inoculant caused a significant increase in seed yield (by 34%) from 2.2 t ha-1 (I0) to 3.4 t ha-1 (I2), whereas phosphorus application enhanced yields by 18% when P0 (2.7 t ha-1) were compared with P40 plots (3.3 t ha-1). Without inoculant there was no nodulation, whereas the number of nodules per plant increased to 14 in plots with the highest level of inoculation. Fertilizer P application did not affect Rhizobium nodulation. Galactomannan content was not influenced by inoculation and P fertilization, however increased seed yield resulting from inoculation and P fertilization led to increased galactomannan production per hectare.