Nitrogen use efficiency and critical leaf N concentration of in urea and diammonium phosphate amended soil.

L is widely cultivated in many countries due to its importance as an all-purpose herbal or medicinal plant. The growth and yield of this plant can be enhanced by application of fertilizer. It is expected that a higher and balanced nutrient supply will result in higher crop production maintaining soil health, which is possible when the applied fertilizers are done in way that is efficient. So, there is a need to understand the amount of applied and type of fertilizer that will give the best output for farmers and to formulate economical market products. This study was conducted to investigate the effect of N fertilizer on leaf yield, its uptake and requirement, critical concentration, use efficiency and economics of L. Plants were grown at six levels of N: 0, 40, 80, 100, 150 and 200 kg ha from urea and diammonium phosphate (DAP) following completely randomized design with three replicates under field condition. The highest values of yield and yield attributes and profit based on benefit cost ratio (3.81 for urea and 2.91 for DAP) were obtained with 150 kg N ha (urea) and 100 kg N ha (DAP). Leaf biomass yield increased by 18-128 % in urea-N and 30-139 % in DAP-N fertilized plant over control while DAP > urea by 7.59 %. Sucker production (mean number) was urea-N (4.95 Plant) > DAP-N (2.28 Plant). Both gel and leaf N concentration and uptake was highest at 200 kg ha for both sources. For 80 % leaf biomass yield, minimum requirement of N was 74.90 (urea) and 89.60 kg ha (DAP). Growth and yield parameters to N application exhibited significant and positive correlations. Critical leaf N concentration was 0.88% (DAP) and 0.90% (urea) while mean and maximum NUE was 34% and 64 % (urea) and 43% and 69% (DAP), respectively. Farmers can be advised to apply N at the rate of 150 kg ha from urea for producing economically higher yield and better-quality leaves.