Translocation of Nitrate in Rice Rhizosphere and Total Nitrogen Uptake Improvement under Interactive Effect of Water and Nitrogen Supply

Nitrogen, an essential macronutrient for rice (Oryza sativa L), mineral forms are extremely prone to leaching. In this study, pot experiment in a greenhouse was utilized to investigate the coupling effect of irrigation (W) and fertilizer (N) on nitrate (NO3-N) translocation in the soil-water-plant system, Total Nitrogen (TN) uptake. Three N levels (Low, Medium, High: N1, N2, N3) rated 25, 120, and 250 mg/kg similarly three W levels (Low, Medium, High: W1, W2, W3) 70%-80%, 80%-90% and 100% of field capacity (θf) +0.5 cm submergence depth were applied. Nine treatments (W1N1:T1, W1N2:T2, W1N3:T3, W2N1:T4, W2N2:T5, W2N3:T6, W3N1:T7, W3N2:T8 and W3N3:T9) with four replicates. To understand NO3-N distribution, six soil layers (1 cm width each) per treatment were generated making it 54 in total. T6 (69.2%) revealed the highest increment in NO3-N content followed by T7 (44.2%) and T8 (39%) compared to T1. Generally, Middle layers (3rd-4th) had the least NO3-N content compared to shallow (1st-2nd) and bottom (5th-6th) layers. Concerning TN, the highest was found in T3(63%), T2(45%) and T6(41.5%) and T7(-26%) with the highest decrement. Interacting W and N significantly affected means of NO3-N, TN, moisture content, and root shoot ratio (R/S) at 5% probability level. Results of this study suggested that proper W and N combination result in high rhizosphere NO3-N accumulation in shallow layers leading to high nitrogen uptake by plant thus N leaching reduction.