A “MANAGE”ed Approach for 4R Nutrient Stewardship on Drained Land

As agriculture in the 21^st century faces increasing pressure to reduce negative environmental impacts while continuing to efficiently produce food, fiber, and fuel, it becomes increasingly important to reflect upon more than half a century of drainage water quality research to identify future paths towards sustainability. Nearly 400 drainage water quality studies were reviewed to create a publically available database that compiles site, climate, cropping, and agronomic management information across more than 50 years of drainage research. The data were pared to 91 individual journal publications, representing 1,279 site-years from 1961 to 2012, each with sufficient study design and management detail to investigate the impact of controllable factors (cropping management such as the 4R practices: right source, rate, time, and place of nutrient application) and uncontrollable factors (wet and dry years) on total, dissolved, and particulate N and P loads. This new “Drain Load” table in the “Measured Annual Nutrient loads from AGricultural Environments” (MANAGE) database was then used to compare drainage water quality and crop yield based on this pooled dataset.

Wetter years predictably resulted in more drainage and greater N and P loads in drainage waters. Nutrient loads also increased at increasing N and P application rates. However, increased N and P application rates also improved crop yield across this large dataset, which indicates that new approaches and trade-offs may be required to balance agronomic and environmental goals. Optimal nutrient application timing and placement are generally known to be important strategies for improving agronomic performance and water quality, but these two approaches showed no significant impact on dissolved N or total/dissolved P loads here. This may have been complicated by a lack of P drainage studies.

This work provided an important opportunity to identify gaps in drainage nutrient research. More drainage studies are needed focused on newly drained areas, on ditch-drained areas, and on factors affecting P in drainage water. This review and meta-analysis strongly indicated the pressing need for more long-term studies with coordinated controls across multiple sites and years. The MANAGE database primarily focuses on North America, but suggested future directions include addition of international drainage studies as well as creation of a “Drain Concentration” table to complement this new “Drain Load” table.