Enhanced maize yield and nitrogen efficiency with low molecular weight fulvic acid: insights into chlorophyll a/b ratio and nitrogen metabolising enzyme activity

Abstract

This study investigates the impact of various molecular weights (MWs) of fulvic acid (FA) on maize growth, grain yield, and nutrient uptake under different nitrogen levels (NLs). A 2 × 3 balanced design was employed, with high (0.2 g N/kg) and low (0.05 g N/kg) NLs, and three FA MW ranges (W1 ≤ 3 000 D, 3 000 < W2 ≤ 10 000 D, W3 > 10 000 D) were applied at 25 mg/kg in soil. Significant interactions between NLs and FA MWs were observed in chlorophyll a/b ratio, nitrate reductase and glutamate dehydrogenase activities, nitrogen content, and nitrogen uptake efficiency. Overall, under different NLs, FA application reduced chlorophyll a/b ratio, increased nitrogen metabolism enzyme activities, promoted maize growth, and thereby improved grain yield and nitrogen fertiliser uptake efficiency. Additionally, the promotion effect of low MW FA on these indicators outweighed that of high MW FA, yet the latter exhibited a more pronounced effect on increasing grain nitrogen concentration. Structural equation model analysis revealed direct effects of chlorophyll content, nitrogen accumulation, nitrogen uptake efficiency, NLs and FA MWs on maize grain yield, with FA MWs negatively impacting yield.

Keywords

• low nitrogen stress
• nitrogen utilisation
• plant growth
• zea mays l