Impact of manure and biochar additions on annual crop growth, nutrient uptake, and fate of 15N-labelled fertilizer in two contrasting temperate prairie soils after four years

Liquid hog manure (LHM) and solid cattle manure (SCM) co-applied with biochar could beneficially influence soil nitrogen (N) and phosphorus dynamics. A split-plot design was used at two sites (Brown and Black) in Saskatchewan to assess LHM and SCM (100 kg N ha-1) applied alone or in combination with biochars (8 Mg carbon ha-1) produced using slow or fast pyrolysis. Crop growth and nutrient uptake, along with fertilizer 15N recovery were followed over four years in a cereal-oilseed rotation. Crop growth on the Brown soil was more responsive to the treatments than the Black soil, reflecting lower fertility of the Brown soil. The manure and biochar, applied alone or in combination, had little impact on available soil phosphorus. Manure and biochar effects on crop growth and nutrient uptake were attributed to temporal effects on soil N immobilization-mineralization influencing plant available soil N. A negative impact of the fast pyrolysis biochar on growth and plant uptake was observed and attributable to its greater labile-carbon content, which likely promoted soil N immobilization. Synergism observed between SCM and the slow pyrolysis biochar may reflect enhanced net SCM-N mineralization and increased water-holding capacity. The majority (55-80%) of plant 15N recovery occurred during the first year, with 86% of fertilizer 15N conserved within the soil-plant system after four years. Greater (40%) plant 15N recovery without biochar addition, coupled with increased (38%) soil 15N recovery with added biochar, suggests biochar-related immobilization and/or sorption in the biochar-amended soils.

Nitrogen Fertilization Management with Blends of Controlled-Release and Conventional Urea Affects Common Bean Growth and Yield during Mild Winters in Brazil

The common bean (Phaseolus vulgaris L.) requires nitrogen (N) during its vegetative and reproductive stages. A single application of a blend of polymer-sulfur coated urea (PSCU) and conventional urea (U) treated with NBPT (N-(n-butyl) thiophosphoric triamide) can meet that demand. Broadcast application could improve yield than other N management practices. This research evaluated two blends (70%PSCU + 30%U and 30%PSCU + 70%U) and three N fertilization managements (incorporated, broadcast, and split application) on soil ammonia volatilization (AV) and N mineral content (NM); plant N uptake (NU) and 15N recovery from U (NUR); and yield (GY). Irrigated field experiments were conducted in 2018 and 2019 in Rhodic Eutrustox soil. The N application rate was 90 kg ha−1. AV reached 12% (30%PSCU + 70%U, broadcast application) and 14% of the applied N (split application at the third trifoliate leaf unfolded stage (V4)). The incorporated application resulted in higher NM in the vegetative and reproductive stages than the other management practices. Broadcast application resulted in higher NU than split application at physiological maturity. Split application resulted in higher NUR (grain) and GY than broadcast application. There was a positive correlation between NUR (grain) and GY in all N fertilization management treatments. The NUR values reached 48% (30%PSCU + 70%U) and 18% (70%PSCU + 30%U). Split N application using these blends can improve NUR in grain and GY compared to broadcast application in Rhodic Eutrustox soil. This information can help farmers improve the fertilization management practices used with these blends, and thereby avoid economic losses and environmental pollution.

Management Intensity Controls Nitrogen-Use-Efficiency and Flows in Grasslands—A 15N Tracing Experiment

The consequences of land use intensification and climate warming on productivity, fates of fertilizer nitrogen (N) and the overall soil N balance of montane grasslands remain poorly understood. Here, we report findings of a 15N slurry-tracing experiment on large grassland plant–soil lysimeters exposed to different management intensities (extensive vs. intensive) and climates (control; translocation: +2 °C, reduced precipitation). Surface-applied cattle slurry was enriched with both 15NH4+ and 15N-urea in order to trace its fate in the plant–soil system. Recovery of 15N tracer in plants was low (7–17%), while it was considerably higher in the soil N pool (32–42%), indicating N stabilization in soil organic nitrogen (SON). Total 15N recovery was only 49% ± 7% indicating substantial fertilizer N losses to the environment. With harvest N exports exceeding N fertilization rates, the N balance was negative for all climate and management treatments. Intensive management had an increased deficit relative to extensive management. In contrast, simulated climate change had no significant effects on the grassland N balance. These results suggest a risk of soil N mining in montane grasslands under land use intensification based on broadcast liquid slurry application.

Biological nitrogen fixation and urea-N recovery in 'Coastcross-1' pasture treated with Azospirillum brasilense

The objective of this work was to quantify the inoculation effect of Azospirillum brasilense (Ab-V5 and Ab-V6 strains) on the forage yield, biological nitrogen fixation (BNF), and urea-15N recovery of the forage grass 'Coastcross-1'. The experiment was carried out in a 2 (with or without inoculation) × 2 (without N fertilizer and with 100 kg ha-1 N per year as urea) × 7 (cuts) factorial arrangement. The natural 15N abundance method was used to determine BNF; to determine urea-N recovery, 15N-labeled urea was applied in microplots. Forage yield was higher in grasses subjected to inoculation, with 7.4 Mg ha-1 dry matter per year, for the treatment without N fertilizer, and 8.0 Mg ha-1 dry matter per year for the treatment with 100 kg ha-1 N per year, respectively, which shows an additive effect of inoculation and N fertilization. The contribution of BNF was 23.0 and 53.8 kg ha-1 per year for the unfertilized treatment, both in uninoculated and inoculated plants, respectively. Urea-15N recovery was 13.7 and 16.5 kg ha-1 per year for uninoculated and inoculated treatments, respectively, corresponding to 13.7 and 16.5% of the urea-N applied. Inoculation with A. brasilense increases forage yield and the contribution of BNF to grass nutrition with N, as well as urea-N recovery by the forage grass.