No abstract

Indicators of soil quality associated with N‐cycling were assessed under different land‐use systems (native forest – NAT, reforestation with Araucaria angustifolia or Pinus taeda and agricultural use – AGR) to appraise the effects on the soil potential for N supply. The soil total N ranged from 2 to 4 g/kg (AGR and NAT, respectively), and the microbial biomass N ranged from 80 to 250 mg/kg, being higher in NAT and A. angustifolia, and lower in P. taeda and AGR sites. Activities of asparaginase (ca. 50–200 mg NH4+‐N/kg per h), glutaminase (ca. 200–800 mg NH4+‐N/kg per h) and urease (ca. 80–200 mg NH4+‐N/kg/h) were also more intense in the NAT and A. angustifolia‐reforested soils, indicating greater capacity for N mineralization. The NAT and AGR soils showed the highest and the lowest ammonification rate, respectively (ca. 1 and 0.4 mg NH4+‐N/kg per day), but the inverse for nitrification rate (ca. 12 and 26%), indicating a low capacity for N supply, in addition to higher risks of N losses in the AGR soil. A multivariate analysis indicated more similarity between NAT and A. angustifolia‐reforested sites, whilst the AGR soil was different and associated with a higher nitrification rate. In general, reforestation with the native species A. angustifolia had less impact than reforestation with the exogenous species P. taeda, considering the soil capacity for N supply. However, AGR use caused more changes, generally decrease in indicators of N‐cycling, showing a negative soil management effect on the sustainability of this agroecosystem.

Neglected Glyphosate-resistant (GR) crops are common in agro-ecosystems mainly due to its benefits of weed management. However, the effect of GR crops on soil ecosystem and on non-target soil organisms need to be monitored. The effect of two transgenic soybeans GR on soil microorganisms, soil enzymes, microbial biomass and plant growth were evaluated. The experimental design was conducted as factorial arrangement with two GR soybean varieties, the Londrina (RR 59) and its near isogenic non-GM 59 Londrina called VAR 1; the second was Valiosa soybean (RR Conquista) and its near isogenic non-GM Conquista - Uberaba soybean called VAR 2. The plants were inoculated with arbuscular mycorrhiza fungi and rhizobia. The results showed that significant differences were observed among GM plants and their parental non-GM only for N biomass, AM colonization and cellulase activity. The presence of AM fungi had great influence on the functional groups of microorganisms while some enzymes activity decreased.