Soil physicochemical properties influenced by nitrogen sources and rates in the central Great Plains

Abstract

Land application of beef cattle (Bos turus) manure is a management strategy that can supply essential plant nutrients, enhance land sustainability, and maintain environmental quality. The objectives of this study were to evaluate (1) soil chemical properties and (2) temporal changes in soil nutrient dynamics as influenced by tillage practices (no-tillage [NT] and conventional tillage [CT]) and nitrogen (N) sources (manure and commercial fertilizer; urea) at two application rates (high 134 kg N ha⁻¹ y⁻¹ [120 lb ac⁻¹ yr⁻¹] and low 67 kg N ha⁻¹ y⁻¹ [60 lb ac⁻¹ yr⁻¹]) for both N sources. An unfertilized control treatment with no N added was also included within each tillage treatment. The study was conducted on an Armo silt loam (fine-loamy, mixed, mesic Entic Haplustolls) at Kansas State University Agriculture Research Center near Hays, Kansas, from 2006 to 2016. Soil samples were taken annually at 0 to 15 cm (0 to 6 in) depth prior to spring field operations. Across tillage, soil pH, total N (TN), extractable phosphorus (P), potassium (K), and sodium (Na) were influenced by N source, N rate, and sampling time. The high manure rate treatments increased soil TN by an average of 19% compared with the commercial N fertilizer and control treatments. Eliminating tillage enhanced soil TN accumulation in the top 15 cm of soil by approximately 9% more than CT. Extractable soil P measured in 2016 increased by approximately 401% compared with 2006. Similarly, soil P increased by approximately 331% with high manure and by 66% with low manure compared with commercial fertilizer treatments. Manure addition at high and low rates had 43% and 20% increase in soil available K, respectively, compared with commercial fertilizer treatments. The observed temporal variability in soil extractable P, K, and Na were mostly related to manure addition. The increase in N rates strengthens the relationship between soil electrical conductivity (EC) and soil nitrates (NO₃), especially with commercial fertilizer where the changes in soil EC were 2.8-fold greater than the manure treatments. The significant (p < 0.05) changes in soil chemical properties influenced by the management interaction throughout the years (time × tillage × N sources) may take longer than 10 years to be observed in the dryland cropping system of the Great Plains region. However, growers should take extra care to prevent soil P and Na accumulation, specifically when cattle manure is being added to meet the N requirement for crop production.