Autoclaved citrate-extractable protein as a soil health indicator relates to soil properties and crop production

Nitrogen is an important and limiting nutrient for crop production, but its role as a soil health indicator relating to most soil properties and crop production needs further exploration. Our objectives were to examine the sensitivity of soil N fractions to management practices and their relationships to 60 soil physical, chemical, biological, and biochemical properties and mean crop yields in two long-term (14- and 36-year-old) experiments under dryland cropping systems in the northern Great Plains, USA. Nitrogen fractions were soil total N (STN), potential N mineralization (PNM), water-extractable N (WEN), autoclaved citrate-extractable protein (ACEP), NH 4 -N, and NO 3 -N. Management practices were no-till and tilled crop rotations of spring wheat ( Triticum aestivum L.), barley ( Hordeum vulgare L.), pea ( Pisum sativum L.), and fallow with and without N fertilization. Soil properties were analyzed from samples collected before farm operations in April 2019 and crop yields determined. Nitrogen fractions, except NH 4 -N and NO 3 -N, were greater with continuous cropping than crop-fallow. A principal component analysis (PCA) showed that PNM and ACEP were associated with most soil properties, followed by STN, WEN, NO 3 -N, and NH 4 -N. PNM, ACEP, and STN were more strongly related to mean crop yields across years in coarse- than medium-textured soil and other N fractions were weakly related. Because of its sensitivity to management practices, stronger relationships to most soil properties and crop yields, and rapid measurement, ACEP may be used as a promising N indicator of soil health in coarse- than medium-textured soil in dryland cropping systems in semiarid regions.