Impacts of 4R Nitrogen Management and Water Optimization on Soil Health

Farmers in Utah and Idaho are facing growing challenges due to high fertilizer costs, limited irrigation water, and pressure to improve long-term soil health. To better understand current practices and grower attitudes, a survey was conducted in 2020 targeting 5,000 producers of small grains, corn, and potatoes. Although the response rate was low, 146 growers representing over 25,000 hectares of cropland participated. Survey results showed that most growers are open to improving nitrogen and irrigation practices and care about their soil health, even if not all are fully using 4R or precision agriculture methods. This thesis includes two field studies aimed at addressing those needs. The first study tested 4R nitrogen strategies, right rate, source, timing, and placement across cherry orchards, silage corn, potato, and wheat systems at four locations in Utah and Idaho from 2020 to 2023. Soil samples were analyzed for residual nitrate, soil respiration, ACE protein, aggregate stability, total nitrogen, and total carbon. Results showed that site-specific nitrogen management could reduce nitrate leaching and improve soil biological activity without harming soil productivity. Positive results were especially pronounced in Kaysville and Kimberly, where fertilizer timing, rate, and placement had the most significant effects. The second study evaluated how deficit irrigation combined with land management practices (no-tillage, cover cropping, and drought-tolerant hybrids) impacted soil health and water infiltration across three Utah sites between 2019 and 2023. A split-plot design tested full and 50% irrigation rates across five treatments. Results showed that the effects of deficit irrigation varied by site and soil type. In drier areas like Cedar City, reduced irrigation led to declines in biological soil health indicators, while other locations maintained or improved soil function when combined with conservation practices. Together, these studies show that integrating 4R nutrient strategies with water-saving practices can support healthier soils and more efficient resource use. However, successful outcomes depend on matching practices to local conditions.