Effect of nitrogen, phosphorus and seed inoculation on dry matter partitioning and enzymatic activities in french bean (Phaseolus vulgaris L)

To examine the effect of nitrogen, phosphorus and seed inoculation on dry matter partitioning and enzymatic activities in French bean, a field experiment was conducted in partially reclaimed salt affected soil of eastern Uttar Pradesh with 32 treatments and 3 replications. Both, dry matter accumulation and enzymatic activities were influenced by the levels of nitrogen and phosphorus and inoculation of seeds with Rhizobium tropici. The highest amount of dry matter accumulation at 30 and 75 day stages of plant growth (1460.6 mg and 13.086g plant⁻¹ respectively) were recorded with 120 Kg N ha⁻¹ + 120 Kg P₂O₅ ha⁻¹ especially under non- inoculated conditions. However, starter dose of nitrogen (40 Kg ha⁻¹) along with 120 Kg P₂O₅ ha⁻¹ was found significantly superior to rest of the treatments to augment dry matter accumulation. The highest fraction of dry matter accumulated in leaf and the lowest in root at 30 day stage of plant, however, pattern of dry matter partitioning changed to Pod • Stem • Leaf • Root at 75 day stage. The contents of nitrite reductase (5.52 μmol NO₂ reduced g⁻¹ fresh wt. h⁻¹) and nitrate reductase (3.32 μmol NO₃ reduced g⁻¹ fresh wt. h⁻¹) were found to be the highest in non-inoculated plants treated with 120 Kg N ha⁻¹ + 120 Kg P₂O₅ ha⁻¹, whereas, the highest content of these enzymes in inoculated plants were recorded with N₄₀P₁₂₀S₁. Leg haemoglobin, an indicator of biological N₂-fixation was found only in inoculated plants and the highest amount (205 n mol g⁻¹ nodules) was recorded in root nodules of French bean plants treated with N₄₀P₁₂₀S₁. Increasing levels of nitrogen improved nitrite and nitrate reductase status of inoculated plants, but decreased leg haemoglobin content in root nodules. Phosphorus application found to be beneficial to increase enzymatic activities in both inoculated and non-inoculated plants. Protein content and grain yield of French bean were also influenced by the application of nitrogen and phosphorus and inoculation of seeds with Rhizobium tropici. The highest grain protein (23.3%) and seed yield (1.73 t ha⁻¹) were recorded with N₄₀P₁₂₀S₁.