Critical nitrogen content and nitrogen nutrition index for sweetpotato crop

Abstract

Sweetpotato is an important tuber crop for the food security in Island countries of the South Pacific. The allometric relationship between tissue nitrogen (N) concentration and aerial dry matter is unknown. We determined critical N (N_c) content from vegetative stage to harvesting, and estimated the range of variation in N nutrition index (NNI) from two field experiments with varied rates of N (0, 25, 60, 125 and 180 kg N ha⁻¹ in 2015 and 0, 50, 125, 175 and 250 kg N ha⁻¹ in 2017). A unified critical N curve (N_c = 3.338 W^−0.307) where W = aerial dry matter with W ≥ 1.38 t ha⁻¹, was constructed based on the N concentration in the aerial dry matter. The calculated NNI ranged from 0.69 to 1.23 in 2015 and 0.54 to 1.17 in 2017. The preliminary N_c dilution curve and NNI determined could potentially be used as a parameter for N management.

Keywords:

• aerial dry matter
• critical nitrogen concentration
• nitrogen nutrition index

Acknowledgement

The Research Committee, PNG University of Technology is thankfully acknowledged by the first author that enabled the author to carry out a trial in 2015.

Disclosure statement

No potential conflict of interest was reported by the authors.