Estimation of nitrogen use efficiency by mango seedlings under nano and convention calcium fertilization using the enriched stable isotope (N-15)

Abstract

This study aimed to investigate the effect of nano-Ca fertilizer on nitrogen uptake, nitrogen use efficiency and determine the best calcium form and dose for mango.  A pot experiment was conducted using two year old mango seedlings (cv. Zebda). The pots were filled with sandy soil (8 kg per pot) and one seedling was transplanted into each pot. Four treatments including nano-Ca, convention Ca, soil application and foliar application have been formulated. Calcium was applied as CaO for both the convention and nanoforms. The enriched (15NH4)2SO4 was applied at a rate of (5g per pot). Plants were harvested at the end of the fall, spring, and summer growth cycles and dried at 70 oC. The dried plant is used for making fine powder and to determine total nitrogen, calcium, and %15N atom excess. Results of the study revealed that in all growth cycles, the 15N translocation was higher under foliar nano-Ca treatment than under convention Ca at a 100% rate. The highest uptake, translocation, and nitrogen use efficiency were observed at 50% (250 mg. L-1) foliar nano-Ca treatment in all cycles. In the Fall growth cycle, the values for nitrogen fertilizer use efficiency at 50% nano-Ca rate was 81.8%, while it recorded 64.9% for 25% rate and 51.2% for 100% rate.  Calcium concentration, in shoot and roots, was also higher under nano-calcium (for fall cycle = 3.0 for the shoot and 2.8 for root) than the convention calcium (for fall cycle = 2.7% for the shoot and 2.2 for root) for all cycles. The summer growth cycle recorded the highest total biomass under all treatments compared with the fall or spring growth cycles. Allocation of biomass to the shoot was also reported higher under nano-Ca foliar application than that of soil application in all cycles. The best treatment is 50% (250 mg.L-1) foliar nano-Ca as it resulted in the highest N-15 uptake, translocation, and nitrogen use efficiency. Nano calcium proves to be more efficient as fertilizer than conventional calcium.