Towards applying N balance as a sustainability indicator for the US Corn Belt: realistic achievable targets, spatio-temporal variability and policy implications

Abstract

Gains in nitrogen use efficiency in the production of corn (Zea mays L.) remain low due to management constraints and difficulties in accurately predicting the optimum fertilizer application rate. Retailers and consumers are looking for robust sustainability indicators to help drive the industry towards more sustainable food production, including the simple input-output based 'N balance' metric. Seven-year simulations for 25 locations across five US Corn Belt States (NE, IA, MN, IL, IN) were conducted using the biogeochemical Adapt-N® model to determine (i) realistically achievable N balance values when N rates are optimized, (ii) the effects of climate and soil type on achievable N balance values, and (iii) the relative importance of N application timing (fall, spring, split in-season) and formulation (+/− nitrapyrin) in reducing N balance. Split in-season applications reduced N rates by 39% and 22% over fall and spring applications and N balance by 36% and 22%, respectively. Adding nitrapyrin to fall or spring preplant applications modestly reduced N inputs by 9% and 4% and N balance by 18% and 12%. Split N management reduced N losses by 52% and 31% of total areascaled N losses compared to fall and spring N applications and adding nitrapyrin by 13% and 10%, respectively. Benefits from improved timing and formulation were greater in the more humid eastern part of the region. Split in-season N management allows farmers to reach sustainable N balance levels in 88% of cases, with the remainder mostly affected by mid-season droughts. Economic assessment found partial profit to be enhanced with lower N balance, suggesting that N balance reductions may be achieved through voluntary approaches. The model simulations offered ranges of realistic N balance values that can be used to inform policy discussions. It appears that N balance is best applied when averaged over multiple seasons and threshold levels should be guided by characteristics of the production environment, including soil type and climate.

Relationship of in‐season soil nitrogen concentration with corn yield and potential nitrogen losses

“…There are growing efforts to use N balance as an indicator of potential N losses because it is a measure of anthropogenic N supply that exceeds crop N demand (McLellan et al., 2018; Sela et al., 2019; Tenorio et al., 2020). Recent studies have shown significant relationships between N balance and nitrous oxide and nitrate‐N leaching losses (McLellan et al., 2018; Omonode, Halvorson, Gagnon, & Vyn, 2017; Venterea, Coulter, & Dolan, 2016; Zhao, Christianson, Harmel, & Pittelkow, 2016).…”

“…the difference between N inputs and outputs) as an estimate of N losses to track changes in N fertilizer efficiency and decrease the environmental footprint of crop production (McLellan et al., 2018; Tenorio et al., 2020). Recent studies have shown that N balance is sensitive to changes in N rate and form in the U.S. Midwest (Sela, Woodbury, Marjerison, & van Es, 2019). However, little research has explored how N balance can be utilized within an integrated N management framework to help growers not only identify the potential for N deficiencies but also evaluate the risk of environmental N losses (Tenorio et al., 2020).…”

Quantifying Nutrient Budgets for Sustainable Nutrient Management

“…In contrast to the attempt in modeling the complex environmental impacts from nutrient budgets, several relatively simple indicators have been developed based on nutrient budgets. For example, N surplus (also called N balance) of the Soil‐Plant system is directly affected by farmers' management practices and is proven to be significantly related to yield‐scaled N losses when aggregated over multiple sites and years (McLellan et al, ; Sela et al, ). However, it should be recognized that the N surplus is not always the best predictor of the actual environmental impacts of an individual farm for a given year, which is also largely affected by factors such as year‐to‐year weather variations and the legacy effects of N in the soil.…”

A Pathway to Carbon Neutral Agriculture in Denmark

“…Another possibility is illustrated by a soil-based model for maize in the United States, which combines information on soils, yields, and each year's weather to inform farmers how much nitrogen to apply during the growing season. Papers have estimated potential reductions in nitrogen application using this model of 20-40 percent (Sela et al 2019(Sela et al , 2018. This model is commercially available to farmers in the United States today.…”