Impacts of 4R nitrogen management on soil health and residual soil nitrate across annual and perennial cropping systems

Abstract

Nitrogen (N) is one of the most important and expensive inputs for crop production. Inefficient N management reduces profitability and contributes to nitrate (NO ₃ ⁻ ) accumulation in groundwater, posing risks to environmental quality. The 4R nutrient stewardship framework aims to optimize fertilizer management by applying four components: right rate, source, time, and place. However, few studies have evaluated the combined effects of all four components across diverse cropping systems. This study quantified how individual and integrated 4R N practices influence soil health and residual soil nitrate (RSN) across four major western crop systems—tart cherry ( Prunus cerasus ), potato ( Solanum tuberosum ), silage corn ( Zea mays ), and wheat ( Triticum aestivum ). Field experiments were conducted from 2020 to 2023 at four sites in southern Idaho and northern Utah. Treatments included combinations of N rate (50%, 75%, 100%, and 200% of yield goal), source (urea [46% N]), environmentally smart nitrogen (42% N), urea ammonium nitrate (32% N)], timing (preplant, planting, and in‐season), and placement (broadcast, banded, and fertigation). Soil health indicators (organic matter, respiration, autoclave citrate extractable [ACE] protein, permanganate oxidizable carbon, and aggregate stability), soil nitrate (0–120 cm), and total N and C (0–60 cm) were measured after 4 years. In the tart cherry orchard, the right time treatment increased soil respiration and ACE protein, while the combined rate and time improved aggregate stability. In the silage corn–wheat rotation, N placement, especially banding, substantially reduced RSN, and several 4R treatments increased aggregate stability. These findings highlight that 4R N management practices have site‐specific impacts, and most 4R practices alone or combined can sometimes increase aggregate stability and microbial respiration and reduce RSN.