Impact of Nitrogen Fertilization and Cropping System on Carbon Sequestration in Midwestern Mollisols

Growing interest in the potential for agricultural soils to provide a sink for atmospheric C has prompted studies of effects of management on soil organic carbon (SOC) sequestration. We analyzed the impact on SOC of four N fertilization rates (0–270 kg N ha−1) and four cropping systems: continuous corn (CC) (Zea mays L.); corn–soybean [Glycine max (L.) Merr.] (CS); corn–corn–oat–alfalfa (oat, Avena sativa L.; alfalfa, Medicago sativa L.) (CCOA), and corn–oat–alfalfa–alfalfa (COAA). Soils were sampled in 2002, Years 23 and 48 of the experiments located in northeast and north-central Iowa, respectively. The experiments were conducted using a replicated split-plot design under conventional tillage. A native prairie was sampled to provide a reference (for one site only). Cropping systems that contained alfalfa had the highest SOC stocks, whereas the CS system generally had the lowest SOC stocks. Concentrations of SOC increased significantly between 1990 and 2002 in only two of the nine systems for which historical data were available, the fertilized CC and COAA systems at one site. Soil quality indices such as particulate organic carbon (POC) were influenced by cropping system, with CS \u3c CC \u3c CCOA. In the native prairie, SOC, POC, and resistant C concentrations were 2.8, 2.6, and 3.9 times, respectively, the highest values in cropped soil, indicating that cultivated soils had not recovered to precultivation conditions. Although corn yields increased with N additions, N fertilization increased SOC stocks only in the CC system at one site. Considering the C cost for N fertilizer production, N fertilization generally had a net negative effect on C sequestration

Long‐term phosphorus accumulation and removal efficiency in a land‐based wastewater treatment system in the UK

The study aims to assess the long‐term phosphorus (P) removal in a land treatment system (LTS) in the UK. Different sections of the site have been irrigated with wastewater effluent for different periods of time for up to 85 years. The amounts of P discharged and accumulated were calculated from historical data, estimations of water consumption, composition and soil measurement. The total P input during the study period was estimated to be 90 010 kg, the average P removal was 4% and there was no significant difference in the total P accumulated between plots irrigated for different periods, indicating that the sorption capacity of the soil might be saturated. Despite the low P retention rates in the LTS, there is no evidence that emissions from this system are affecting P concentrations in either the nearby river or the local chalk aquifer. Gaps remain, however, in performance optimisation and longevity forecasting

Nitrogen Fertilization and Cropping System Impacts on Soil Quality in Midwestern Mollisols

High grain production of corn (Zea mays L.) can be maintained by adding inorganic N fertilizer, and also by using crop rotations that include alfalfa (Medicago sativa L.), but the relative impact of these management practices on soil quality is uncertain. We examined the effects on soil of N fertilization rate (0, 90, 180, 270 kg ha−1, corn phase only) in four cropping systems: CC, continuous corn; CS, corn–soybean [Glycine max (L.) Merr.]; CCOA, corn–corn–oat (Avena sativa L.)–alfalfa; and corn–oat–alfalfa–alfalfa (COAA). The 23- and 48-yr-old experimental sites, situated in northeast (Nashua) and north central (Kanawha) Iowa, were in a replicated split-plot design and managed with conventional tillage. At Nashua, we measured available N, potential net N mineralization and microbial biomass C (MBC) throughout the growing season; all were significantly higher in the CCOA system. At both sites, post-harvest N stocks, and soil organic C (SOC) concentrations were significantly higher in systems containing alfalfa. Grain yield was most strongly correlated with soil N properties. At Nashua, N fertilizer additions resulted in significantly lower soil pH (0- to 15-cm depth) and lower exchangeable Ca, Mg, and K and cation exchange capacity (CEC) in the CC and CCOA systems. In an undisturbed prairie reference site for Nashua, low available N, low pH, and high CEC suggested a strong influence of the vegetation on nutrient cycling. In terms of management of soil fertility, inclusion of alfalfa in the rotation differed fundamentally from addition of N fertilizer because high yield was maintained with fewer adverse effects on soil quality.This article is from Soil Science Society of America Journal 70 (2006): 249, doi:10.2136/sssaj2005.0058.</p