Impact of nitrogen fertilizer timing on nitrate loss and crop production in northwest Iowa

Abstract

In the U.S. Midwest, nitrate in subsurface tile drainage from corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] systems is detrimental to water quality at local and national scales. The objective of this replicated plot study in northwest Iowa, performed in 2015–2020, was to investigate the influence of nitrogen (N) fertilizer timing on crop production and NO3 load in subsurface (tile) drainage discharge. Four treatments applied to corn included fall anhydrous ammonia with a nitrification inhibitor (F), spring anhydrous ammonia (S), split‐banded urea at planting and mid‐vegetative growth (SS), and no N fertilizer (0N). Across crops and years, NO3–N concentration in subsurface drainage discharge was the same at 11.7 mg L–1 for F and S applied anhydrous ammonia (AA). The NO3–N concentration was statistically lower with SS urea (10 mg L–1) than F and S, and 0N was lower than SS at 8.3 mg L–1. Average annual NO3–N loads were not different between any treatments due to plot variability in drainage discharge. Corn responded to N application, with overall mean yield the same for F, S, and SS. There were no agronomic or water quality benefits for applying AA in spring compared with fall, where the F included a nitrification inhibitor and was applied to cold soils. Split‐applied urea had a small positive water quality impact but no crop yield enhancement. This study shows that there were improvements to NO3–N concentration in subsurface drainage discharge, but more nutrient reduction practices are needed than fertilizer N management alone to reduce nitrate load to surface water systems.

Gulf of Mexico Hypoxia 2022: What’s the Role of Plant Nutrition?

“…The SPARROW modeling results in Table 1 suggest that neither the 59% nor the 45% nitrogen loading reduction targets can be achieved by better management of fertilizer alone. This is confirmed by in‐field experiments such as those in Iowa (Waring et al., 2022), which evaluated fertilizer application timing and concluded that while split application produced modest reductions in nitrate concentration in subsurface drainage discharge, fertilizer nitrogen management alone could not be enough to reduce nitrate load to surface water systems. Continued efforts to improve nitrogen use efficiency can nevertheless make further contributions to controlling the size of the hypoxic zone in the Gulf of Mexico.…”

Forecasting fish mortality from water and air quality data using deep learning models

“…Both the river pollution index (RPI) and the water quality index use the concentrations of NH 3 -N and DO as the primary indicators of river water quality (Fortuna et al, 2023;Tsai et al, 2021). NH 3 -N pollution mainly comes from anthropogenic sources such as the use of agricultural fertilizers on land (Dutra et al, 2016;Waring et al, 2022). WT significantly affects the inactivation/degradation of the physical, chemical, and biological processes within aquatic systems (Schijven et al, 2015).…”

Insights on agricultural nitrate leaching from soil block mesocosms

“…For example, measurements from tile lines that drain individual field research plots have long been utilized to study nutrient leaching (Baker et al., 1975). Although tile drainage studies have been crucial in helping to establish relationships between management practices and nutrient losses (Lawlor et al., 2008; Waring et al., 2022), there are several potential limitations.…”