Submitted to: Natural Resources Research Update (NRRU)
Publication Type: Research Technical Update
Publication Acceptance Date: 2/17/2010
Publication Date: 2/17/2010
Citation: Evans, R.G. 2010. Long-term Tillage influences on soil carbon, nitrogen, physical, chemical, and biological properties. Natural Resources Research Update (NRRU). Update #251349.
Technical Abstract: Long-term tillage influences physical, chemical, and biological properties of the soil environment and thereby crop production and quality. We evaluated the effect of long-term (>20 yrs) tillage no-till, spring till, and fall plus spring till under continuous spring wheat (Triticum aestivum L.) on soil penetration resistance, bulk density, gravimetric water content, and saturated hydraulic conductivity under dryland cropping systems in northeastern Montana, USA (1). Tillage frequency influences on these physical properties were evaluated on a Dooley sandy loam soil (fine-loamy, mixed Typic Argiborolls) in a randomized complete block design with four replications. Soil penetration resistance was measured using a digital penetrometer in 2.5-cm increments to a depth of 25 cm at three locations across each plot. Undisturbed soil cores were sampled at 0 to 5, 5 to 10, and 10 to 15 cm depths and were used to measure bulk density and particle size distribution. Soil penetration resistance was significantly greater in the no-till than in spring till and fall+spring till treatments at 0 to 10 cm depth, but was greater in fall+spring till than in no-till and spring till at a depth deeper than 10 cm. In all three treatments, soil penetration resistance generally increased to a depth of 10 to15 cm and then decreased beyond this depth. Long-term tillage reduced soil compaction in the surface (0 to 10 cm), but increased in the subsurface at a depth > 10 cm due to the traffic intensity induced by tillage. Soil bulk density was not affected by tillage and averaged 1.59, 1.58, and 1.61 Mg m-3 for no-till, spring till, and fall+spring till, respectively. Similarly soil gravimetric water content was not influenced by tillage and generally decreased with increased intensity of soil manipulation and tillage frequency. Soil saturated hydraulic conductivity at 15 to 20 cm depth generally decreased with increased tillage frequency. The results showed that soil bulk density, gravimetric water content, and saturated hydraulic conductivity were minimally influenced by tillage intensity after 22 year of treatment imposition. In dryland soils in the northern Great Plains, conventional farming systems, such as spring tillage with spring wheat-fallow, have resulted in a decline in soil aggregation and organic matter by 30 to 50% of their original levels in the last 50 to 100 yr. While tillage reduced soil organic C (SOC) and N concentrations, fallowing further decreased their levels by reducing the amount of crop residue returned to the soil and increasing the mineralization of soil organic matter during fallow. Therefore, improved management practices are needed to enhance soil aggregation and C and N fractions to reduce soil erosion and increase soil quality and productivity. We evaluated the 21-yr effect of tillage and cropping sequence combinations on C and N fractions in aggregates of a Dooley sandy loam at 0- to 20-cm depth in eastern Montana (2). Tillage and cropping sequences were no-till continuous spring wheat, spring-till continuous spring wheat, fall+spring-till continuous spring wheat, fall- and spring-till spring wheat-barley (1984-1999) followed by spring wheat-pea (2000-2004), and spring-till spring wheat-fallow. Carbon and N fractions were SOC, total N (STN), particulate organic C and N (POC and PON), microbial biomass C and N (MBC and MBN), potential C and N mineralization (PCM and PNM), NH4-N, and NO3-N. Aggregate proportion was greater in no-till continuous spring wheat than in fall+spring-till continuous spring wheat in 4.75-2.00 mm aggregate-size class at 0- to 5-cm but was greater in spring-till spring wheat-fallow than in spring-till continuous spring wheat in 2.00-0.25 mm size class at 5- to 20-cm. After 21 yr, spring-till spring wheat-fallow reduced SOC, STN, POC and PON concentrations in aggregates by 34 to 42% at 0- to 5-cm and by