Agroecosystem Stability In Spring Wheat Crops With The Application Of Fertilizers And Microbial Biological Products

The formation of spring wheat biomass on sod-podzolic soil is carried out mainly due to soil nitrogen, the share of which reaches 1/3 of the total removal of the element when using mineral fertilizers. Inoculation of spring wheat seeds with biologics of rhizosphere microorganisms increases the nitrogen content of fertilizers to 7.3%, increases its immobilization by 5.9-6.7% and reduces losses by 7.4-13.9%. The stability of the agroecosystem is characterized by nitrogen flows. During the growing season of spring wheat with a hydrothermal coefficient of 1.55-1.72, the amount of mineralized nitrogen (mineralization (M)), depending on fertilizers, reaches 9.4-11.1 g/m2, while the reimobilized nitrogen (reimobilization (RI)) – 2.2-3.1 g/m2, net-mineralized (net-mineralization (N-M)) – 6.8 - 8.0 g/m2. The use of nitrogen fertilizers and biological products leads the agroecosystem to the resistance mode (the maximum permissible level of exposure) (RI : M = 27-28%, N-M : RI = 2.5-2.7).

Soil nitrogen dynamics during an oilseed rape (Brassica napus L.) growing cycle in a humid Mediterranean climate

Nitrogen budgets help explain the supply pattern of N from the soil to the crop. Through budgeting, an improvement of the N fertilization strategy can be achieved. The objective of the present study, which was carried out under humid Mediterranean climate conditions, was to assess the influence of N fertilization, temperature and soil humidity on soil N dynamics during a whole oilseed rape growing cycle. A field experiment was conducted with two treatments: without N (0 N) and with application of 180 kg N ha−1(180 N). Mineralization was calculated from N balances made throughout the growing cycle, all while taking into account measured N uptake by oilseed rape and N losses by leaching and N2O emissions. Nitrogen net mineralization was negative after fertilization, reaching –6.73 kg N ha−1, day−1, but total net mineralization over the year was similar for the 0 N and 180 N treatments (21 and 8 kg N ha−1, respectively). Temperatures over 5 °C were sufficient for initiating the mineralization processes. In the summer, when the soil water content was below the wilting point, immobilization took place; however, there is a risk of N leaching if rainfall occurs thereafter, mainly in the 180 N treatment.

Sustainability of the agroecosystem in the application of fertilizers and biopreparations

The formation of biomass of spring wheat on sod-podzolic soil is mainly due to soil nitrogen, the share of which reaches 4/5 of the total removal of the element when using mineral fertilizers. Inoculation increases the nitrogen content of fertilizers by 4.5%, reduces losses by 7%; there is some tendency to increase the immobilization of N fertilizers. The sustainability of the agroecosystem is characterized by nitrogen flows. During the growing season of spring wheat, the amount of mineralized nitrogen depending on the fertilizer reached 17.4-18.0 g/m2, while the amount of remobilized nitrogen was 4.4-4.9 g/m2, net-mineralization (N-M) – 13.1 g/m2. The inoculation of RA seeds does not significantly affect the processes of mineralization (M) and remobilization (RI), only a positive trend of growth of mineralization and remobilization of nitrogen in the soil is observed. The use of nitrogen fertilizer leads agroecosystem in a resistant state-the zone of the maximum permissible level of exposure (RI:M=25%, N-M:RI=3.0). On average, over the years of research, inoculation of RA seeds does not change the indicators of sustainability of agroecosystem when applying fertilizers.

Wildfire effects on ecosystem nitrogen cycling in a Chinese boreal larch forest, revealed by ¹⁵N natural abundance

Wildfire is reported to exert strong influences on N cycling, particularly during the early succession period immediately after burning (i.e., < 1 year). Previous studies have mainly focused on wildfires influences on inorganic N concentrations and N mineralization rates; but plant and soil 15N natural abundance (expressed by δ15N), as a spatial-temporal integrator of ecosystem N cycling, could provide a more comprehensive understanding of wildfire on various N cycling processes at a relatively broader time scale. In this study, we attempted to evaluate legacy effects of wildfire on nitrogen cycling using δ15N in a boreal forest of northeastern China, which is an important yet understudied ecosystem. We measured inorganic N concentrations (NH4+ and NO3−) and net N transformation rates (net ammonification, net nitrification, and net mineralization) of organic and mineral soil 4 years after a wildfire and compared with unburned area. We also measured δ15N of plant and soil samples in 4 and 5 years after the fire. We found that even 4 years after burning, wildfire still increased net mineralization and net ammonification in the organic soil and increased NH4+ and total inorganic N (TIN) concentrations in the mineral soil. Organic soil and foliar δ15N were significantly higher (by 2.2 ‰ and 7.4 ‰, respectively) in the burned area than the unburned area. Five years after fire, plant tissues such as foliar, branch, fine roots and moss in the burned area were increased significantly (by 1.7 ‰ to 6.4 ‰) greater than that in unburned area. The wildfire also significantly increased the δ15N of Oi, Oa+e and 0–10 cm mineral soil, but had no significant effects on deeper layer of mineral soil. These results indicate the wildfire had a strong legacy effect on N cycling. We suggest that the change of abiotic environment was the primary mechanism determining inorganic nitrogen transformation rates, and the NH3 volatilization might play a key role in severe N losses and thereby affect soil and plant 15N in this ecosystem.

Short-Term Effects of Biogas Digestates and Pig Slurry Application on Soil Microbial Activity

The effect of four biogas digestates (BD-A, BD-B, BD-C, and BD-D) and pig slurry (PS) on soil microbial functions was assessed at application rates corresponding to 0–1120 kgNH4+-N ha−1. At dose corresponding to 140 kgNH4+-N ha−1, 30.9–32.5% of the carbon applied in BD-A, BD-C, and PS was utilized during 12 days, while for BD-B and BD-D corresponding utilization was 19.0 and 16.9%, respectively. All BDs resulted in net nitrogen assimilation at low rates (17.5–140 kgNH4+-N ha−1) but net mineralization dominated at higher rates. PS resulted in net mineralization at all application rates. All residues inhibited potential ammonium oxidation (PAO), with EC50-values ranging between 45 and 302 kgNH4+-N ha−1. Low rates of BDs appeared to weakly stimulate potential denitrification activity (PDA), while higher rates resulted in logarithmic decrease. The EC50-values for PDA were between 238 and 347 kgNH4+-N ha−1. No inhibition of PDA was observed after amendment with PS. In conclusion, biogas digestates inhibited ammonia oxidation and denitrification, which could be an early warning of potential hazardous substances in the digestates. However, this effect can also be regarded as positive, since it may reduce nitrogen losses.