Abstract:
Fertilizer application positively affects yield of most crops but needs special attention in root crops, including turnip (Brassica rapa)because of direct accumulation of nutrients, particularly nitrates, in root that can be harmful to consumers. So, determination of fertilizer dose that can give high yield, while avoiding nitrate accumulation, is very important. This experiment was carried out to find the best combination of nitrogen (N= 75 and 100 kg ha-1) and phosphorus (P= 50 and 75 kg ha-1), with respect to agronomic and physiological efficiency, apparent recovery of nutrients, and yield response, in comparison with control (recommended dose of N-P i.e., 50:50 kg ha-1) for getting high yield of turnip roots, while keeping the nitrogen accumulation within permissible limits.Results revealed that high dose of nitrogen with moderate level of phosphorus (N-P@100-50 kg ha-1) proved the best in promoting the growth (leaf and root size), leaf chlorophyll contents, fresh and dry weight of leaves and roots,and yield of turnip. But, further increase in dose of phosphorus (N-P@100-75 kg ha-1) did not improve the values of these parameters. Nitrogen contents of leaves and root were highest in response to N-P @100-50 kg ha-1. While, highest concentration of phosphorus in leaves and roots was recorded for N-P@100-75 kg ha-1. Interestingly, the value of yield response (60.4%), agronomic efficiency (109 kg of root per kg of N and 218 kg root per kg of P), and physiological efficiency of phosphorus (296 kg of root per kg of P) were also higher for N-P@100-50 kg ha-1than N-P@100-75 kg ha-1, which also implies more efficient use of fertilizer applied @ 100-50 kg ha-1. Moreover, apparent recovery of nitrogen was also greatest for N-P@100-50 kg ha-1but, apparent recovery of phosphorus was highest for N-P@100-75 kg ha-1.Furthermore, total nitrogen concentration in the roots was within permissible range even for the highest level of fertilizers. Therefore, farmers can use N-P @100-50 kg ha-1to get high yield at a high benefit:cost ratio, while keeping nitrate nitrogen within non-toxic range.
