Effect of Composts Combined with Chemical N Fertilizer on Nitrogen Uptake by Italian Ryegrass and N Transformation in Soil

Combining compost with sufficient chemical N fertilizer (CF) in agricultural lands is a popular practice to reduce the amount of inorganic nitrogen and accumulation of non-nutrient constituents in soils. A pot culture experiment was conducted to study the effects of 130 mg N of either solids waste compost (Scomp) or biosolids waste compost (Bcomp) complemented with 130 mg (CF, 1N) and 260 mg·N·pot-1 (CF, 2N) as 15N labeled (NH4)2SO4 (13.172 atom %) on growth and N uptake by Italian ryegrass. A separate soil incubation without plants was set up by only blends of Scomp and CF. The results from pot culture experiment show that total plant biomass and N uptake from Bcomp were significantly higher than Scomp alone. Scomp combined with CF improved yield and N uptake over those of Scomp alone. For Scomp + 1N treatment, plant nitrogen uptake derived from compost and CF accounted for 29% and 56% of added N from Scomp and CF, respectively. The incubation study indicates that 16.08 - 29.62 mg·N·kg-1·soil·day-1 from inorganic-N were immobilized into organic pools, while only 0.40 - 0.66 mg·N·kg-1·soil·day-1 from organic-N were mineralized to inorganic pools. Because a part of additional N could be tied up in organic form, combining solids compost with chemical N fertilizer therefore need to consider the effective use of compost-N.

In-Field Corn Residue Management for Bioenergy Use: Potential Effects on Selected Soil Health Parameters

In the U.S. biofuel industry is using corn (Zea mays L.) residue mix (CRM) consisting of corncob and stover for cellulosic ethanol and biogas production. The field storage method left different depths of CRM on the field after its removal, where negative effects on plant growth were observed. The objective of this study is to evaluate the CRM effect on selected soil health indicators. The field study conducted with four different depths of CRM, two tillage systems (no-till (NT) and chisel plow (CP), and three nitrogen (N) rates (0, 180, and 270 kg⋅N⋅ha−1) in a randomized complete block design with split-split arrangements in three replications in a continuous corn system from 2010 to 2012 at the Agronomy Research Farm at Iowa State University. The findings of this study showed a negative effect on soil organic carbon (SOC) change across all treatments at 0 - 15 cm (−0.35 to −0.03 Mg⋅ha−1⋅yr−1), while at 15 - 30 cm there was an increase in SOC rate (0.13 to 0.40 Mg⋅ha−1⋅yr−1) after 2-yr. In addition, soil aggregate-associated C of macro-aggregates decreased by 8%, while micro-aggregates increased by 2%. Soil microbial biomass carbon (MBC) across tillage and N rates for 2.5 & 7.5 CRM treatments increased by 14% in June to July 2011, while in 2012 increased by 9%. However, at the 15 cm soil depth, soil bulk density (ρb), soil penetration resistance (SPR), and soil pH showed no significant differences among CRM treatments. The findings of this study showed that in-field CRM management can affect certain soil health parameters in the short term.