Preventing nitrogen loss in maize

By John Bakum

The widespread availability of chemical nitrogen fertilizers is a prime driver of the vast improvement of crop yields over the past 50 years. However, their use has come with a price, as nitrogen escaping into surrounding soil and air has negative impacts on the environment and human health, including water pollution, depletion of soil-fertility, and greenhouse gas emissions.

Researchers from CIMMYT and JIRCAS (Japan International Research Center for Agricultural Science) examined ways to curtail the leakage of nitrogen into ecosystems, through a process called biological nitrification inhibition (BNI) in the paper ″Genetic variation among elite inbred lines suggests potential to breed for BNI-capacity in maize,″ published in the journal Scientific Reports on August 17, 2023.

BNI is a plant-based natural process that reduces nitrogen losses, which can reduce fertilizer demand while sustaining agricultural systems. In BNI, a plant’s root system releases antibiotic compounds specifically aimed at suppressing the action of nitrifying microbes in soil, and consequently, the amount of nitrogen lost to the surrounding ecosystem is reduced.

Maize productivity remains below its potential, due partly to inefficient management of nitrogen fertilizer. Synthetic, chemical nitrification inhibitors can reduce nitrogen losses in maize farming, but the high costs of this approach have limited its adoption.

Giant Jala landrace maize growing alongside modern variety. (Photo: Eloise Phipps/CIMMYT)

Many plant species have BNI activity in their roots. Because plant BNI activity delivers nitrification inhibitors from root systems directly to the soil, breeding to increase BNI activity can offer a practical and economical approach to reduce nitrogen fertilizer need and waste. But both genetics and environmental interactions influence its effectiveness.

″We are in the discovery phase regarding BNI activity and its determining traits for maize. Such information is crucial to pave the way for breeding programs and genetic improvement efforts,″ said Kevin Pixley, co-author of the paper and former director of CIMMYT’s Genetic Resources Program. ″We need to identify genetic markers for BNI compounds including ‘zeanone’, which will enable breeders to develop maize varieties that require and waste less nitrogen fertilizer, while achieving high yields.″

This research identified 18 single nucleotide polymorphisms (SNP) that act as genetic ″signposts″ for breeders to use to accelerate and increase the accuracy of breeding to increase BNI activity for maize. The researchers also identified six ″candidate genes″ associated with BNI activity and related to nitrogen use efficiency, thereby enhancing the understanding of the genetics controlling BNI activity.

″Our identification of SNPs and genes that regulate how maize processes nitrogen begins to draw a road map for scientists, facilitating the development of molecular markers to guide the breeding for BNI in maize, creating in the future maize varieties which meet farmer and consumer needs at a lower environmental,″ said senior author Cesar Petroli. ″Based on the results obtained, we are developing maize haploid double lines that will be used as population linkage mapping in our next analysis″.

The research was done in collaboration with partners at the JIRCAS and the Universidad de la República, Uruguay.