Golden harvest: Nitrogen’s impact on maize carotenoids

Abstract

Highly weathered tropical soils are deficient in nitrogen (N), phosphorus (P), and potassium (K), impacting maize yield and nutritional quality. The influence of soil N and P on maize carotenoid content remains poorly characterized, hindering nutritional advancements. This study examined how varying N fertilizer rates (0, 60, and 120 kg N/ha) affect provitamin A (proVA) carotenoid accumulation in different maize genotypes. proVA carotenoid components analyzed were alpha-carotene (αC), beta-carotene (βC), and beta-cryptoxanthin (βCr). The study also estimated proVA content among maize genotypes. The increasing N rates from 0 to 120 kg N/ha significantly (P < 0.05) enhanced proVA carotenoid content, as higher proVA content observed in higher N rates i.e., in 120 kg N/ha compared to low N rates (60 kg N/ha and 0 kg N/ha). The βC mean concentration ranged 0.42 to 13.08 µg/g, 0.56–11.17 µg/g and 0.38–11.99 µg/g for 120 kg N/ha, 60 kg N/ha, and 0 kg N/ha, respectively. While βCr concentration ranged 2.35 to 4.49 µg/g for 0 kg N/ha, 2.37–4.34 µg/g for 60 kg N/ha, and 2.35–4.69 µg/g for 120 kg N/ha. Whereas for αC content in studied maize genotypes ranged 0.38 to 13.08 µg/g and the highest value observed on high fertilizer rate (120 kg N/ha) where low content determined on low N rates (0 and 60 kg N/ha). The proVA ranged from 1.93 to 16.7 µg/g, the level of proVA in studied maize genotypes increased with increase in fertilizer rates. For instance, for 0 kg N/ha, proVA ranged from 2.03 to 12.3 µg/g), 60 kg N/ha (2.11–14.1 µg/g) and for 120 kg N/ha (1.99–16.7 µg/g). Genotype EE20 performed better in all the carotenoid components treated with 120 kg N/ha and the T4 had poor performance under no fertilizer plots. Indicating that N had a significant influence on proVA accumulation in maize kernels. The highest provitamin A concentration (16.7 µg/g) was observed on 120 kg N/ha, followed by 14.1 µg/g reported on 60 kg N/ha, and the lowest (12.3 µg/g) was observed on 0 kg N/ha. Thus, for enhancing carotenoid content in maize, N fertilization is crucial. This suggest that in low-N soils, biofortification of provA carotenoids efforts may not bring successful results.