Effects of ammonium-nitrate ratios on the nutrient absorption characteristics of mango (Mangifera indica L.)

Objectives The ammonium-nitrate ratio is an important factor to affect the nutrient absorption of mango (Mangifera indica L.). The ammonium nitrogen (AN), nitrate nitrogen (NN), P, K, Ca, and Mg uptake of mango with varied ammonium-nitrate ratios was explored, aiming to screen the most suitable ammonium-nitrate ratio and provide a basis for rational fertilization in mango.

Methods An hydroponic experiment was conducted using mango seedlings of cultivar ‘Golek’ as test materials. Based on the Hoagland nutrition solution, five ammonium-nitrate ratios was setup, i.e. 0∶1 (T1), 3∶7 (T2), 1∶1 (T3), 7∶3 (T4), and 1 : 0 (T5). The mango seedlings had cultured for 48 h under no nitrogen supply before grown in the treatment nutrient solutions. At 0, 1, 2, 3, 4, 6, 8, 10, 12, and 24 hours of culture, nutrient solution samples were collected for determination of ammonia, nitrate, total nitrogen (TN), P, K, Ca, and Mg concentrations. Michaelis-Menten kinetics equations were adapted to measure the kinetic parameters of the ion uptake.

Results The absorption pattern of NO₃⁻, NH₄⁺, and TN uptake by mango root followed the Michaelis-Menten kinetics equation under different ammonium-nitrate ratios. The maximum absorption rate, affinity and flow velocity of NO₃⁻ were higher than those of NH₄⁺ under all treatments, while the absorption capacity and poorness-resistance of NO₃⁻were higher than those of NH₄⁺ under T4 treatment. The flow rate of NO₃⁻ and NH₄⁺ continued change with the prolongation of ammonium-nitrate ratios and NO₃⁻ changed more easily than NH₄⁺ under T2, T3, and T4, whereas the maximum absorption rate and flow rate of TN continued reducing, and the affinity, absorption capacity and poorness-resistance of TN were highest at T3 treatment. The absorption rates of NO₃⁻ and NH₄⁺ by the mango roots treated with different ammonium-nitrate ratios increased first and then decreased with the extension of culture time, while the absorption rates of H₂PO₄⁻, K⁺, Ca²⁺, and Mg²⁺ continued to decrease and tended to stabilize at 10 h. Additionally, the affinity of K⁺ and Ca²⁺ as well as the poorness-resistance of H₂PO₄⁻, K⁺, Ca²⁺, and Mg²⁺ were highest at T1; the maximum absorption rate and absorption capacity of K⁺ reached the peak at T2; the affinity and absorption capacity of H₂PO₄⁻ were highest at T3; and the maximum absorption rate of H₂PO₄⁻, Ca²⁺ and Mg²⁺, the affinity of Mg²⁺, the absorption capacity of H₂PO₄⁻and Mg²⁺, and flow rate of H₂PO₄⁻, K⁺, Ca²⁺ and Mg²⁺ reached their maximums at T5.

Conclusions Mango has a preference for absorbing NO₃⁻, however, the combined application of ammonia and nitrate nitrogen is more conducive to the absorption of N and other nutrients by mango. In order to improve the absorption of P, Ca, and Mg, phosphate, calcium, and magnesium fertilizers should be applied in conjunction with an appropriate amount of ammonium nitrogen fertilizer in mango production.