Stratification of soil acidity derived from nitrogen fertilizaton in winter wheat tillage systems

Abstract

Conservation tillage systems have varying degrees of mechanical soil mixing which may result in stratification of soil properties. This study was conducted to determine the change in soil acidity due to surface N applications (0, 56, 112,168, 224, and 280 kg N/ha) in recently initiated continuous winter wheat (Triticum aestivum L.) clean‐till (CT), reduced‐till (RT), and not‐ill (NT) systems. Experiments were conducted three consecutive years on Grant silt loam (fine‐silty, mixed, thermic Udic Argiustoll) and Norge clay loam (fine‐silty, mixed, thermic Udic Paleustoll) soils. Soil samples were taken after harvest and separated into 0 to 2.5, 2.5 to 7.5, 7.5 to 15, 15 to 30, and 30 to 60 cm depth increments after the second, third, and fourth cropping seasons. Reduced‐till and NT systems developed increased acidity in the top 7.5 cm of soil compared to CT. Tillage system trends were not expressed as dramatically as the N contribution to soil acidification. Application of only 56 kg N/ha significantly decreased soil pH in the top 15 cm of soil 60% of the time, while the 112 kg N/ha rate decreased soil pH in nearly 90% of the observations considering all years and locations. Acidification from N fertilization was restricted to the top 15 cm of soil. Pooled pH changes due to N fertilization across two locations and three years resulted in a 0.42,0.42, and 0.17 pH unit decrease for the 0 to 2.5, 2.5 to 7.5, and 7.5 to 15 cm depths, respectively. Nitrogen fertilization in conservation tillage systems quickly resulted in modest soil pH decreases which can impact future fertilizer, pesticide, cultivar, and other decisions whose effectiveness is influenced by soil pH.

Notes

Published by the Director of the Oklahoma Agricultural Experiment Station as Journal No. 5074.

Assistant Professor of Soils, Montana State University, Bozeman, MT 59717, and Reagents Professor of Soil Fertility and Plant Nutrition, Oklahoma State University, Stillwater, OK 74078.