Methods for Measuring Nutrient Uptake in Maize Using Nitrogen Stable Isotopes

Nitrogen is a key nutrient for plant growth and development, and understanding nutrient uptake is central to improving nitrogen use efficiency in crops, including maize. Reducing the need for fertilizer without reducing yield is extremely important, as nitrogen fertilizers come with a high environmental cost, in terms of both emissions from manufacturing and losses to waterways or volatilization off fields. Maize develops multiple different root types, including primary, seminal, crown, and brace roots. Part of improving efficiency in maize involves understanding the differences in nutrient uptake via each distinct root type, but these differences have been largely ignored to date. Here, we describe a protocol that uses stable isotopes for determining nitrogen uptake rates by maize root types. We describe the steps both for intact roots, for which we use rhizoboxes with openable front windows that allow access to the roots without disturbing the rest of the plant, and for field-grown plants, for which intact analysis is not feasible and requires excising the roots. The methods described here can also be modified to measure uptake kinetics and for monitoring nutrient translocation between roots and shoots. Advancing our understanding of root physiology and nutrient dynamics will improve breeding opportunities for efficient nutrient uptake varieties, reducing the need for fertilizer additions.