Microplastic pollution on the soil and its consequences on the nitrogen cycle: a review.

Microplastics (MPs) correspond to plastics between 0.1 µm and 5 mm in diameter, and these can be intentionally manufactured to be microscopic or generated from the fragmentation of larger plastics. Currently, MP contamination is a complicated subject due to its accumulation in the environment. They are a novel surface and a source of nutrients in soils because MPs can serve as a substrate for the colonization of microorganisms. Its presence in soil triggers physical (stability of aggregates, soil bulk density, and water dynamics), chemical (nutrients availability, organic matter, and pH), and biological changes (microbial activity and soil fauna). All these changes alter organic matter degradation and biogeochemical cycles such as the nitrogen (N) cycle, which is a key predictor of ecological stability and management in the terrestrial ecosystem. This review aims to explore how MPs affect the N cycle in the soil, the techniques to detect it in soil, and their effects on the physicochemical and biological parameters, emphasizing the impact on the main bacterial groups, genes, and enzymes associated with the different stages of the N cycle.

Biochar impacts on soil chemical properties, greenhouse gas emissions and forage productivity: A field experiment.

Biochar is a promising alternative to agricultural productivity and climate change mitigation. However, quantitative data are needed to better understand the productivity and greenhouse gas (GHG) emissions from agricultural fields amended with biochar. To assess the impacts of the four biochars on soil properties, forage productivity, and GHG emissions, a 1-year field experiment was conducted in a Humic Haploxerands (Andisol). Three manure-derived biochars and one wood residue biochar (all pyrolyzed at 550 °C) were applied at rates of 1% (equivalent to 11 t ha-1) in two parallel and independent experiments. The changes in (i) soil chemical properties and yield of Sorghum sudangrass (S. bicolor×S. bicolor var. Sudanese) and (ii) soil CO2 and N2O emissions were monitored. Two controls, with and without NPK, were included. The added amendments produced from residues of poultry and pig systems increased soil pH by 0.73 and 0.19 units, respectively. Increased sorghum yield were associated with fertilizer and the liming potential of the added biochar. Soil total carbon (TC) increased with the addition of different biochars, especially during the wood biochar treatment. Biochar application, regardless of the feedstock, had no significant impact on the cumulative soil CO2 emitted after a year. Soil N2O fluxes decreased (23%-50%) in treatments containing biochars with low mineral N contents and high C stability (i.e., low H:OC and Cox:TC ratios). NPK treatment resulted in the highest N2O emissions. Wood residue-derived biochar has a great potential in mitigating climate change, reducing soil N2O emissions, and promoting soil C storage. Manure-derived biochars could be instrumental in circular economy livestock systems, where pyrolyzed animal manure can satisfy the demand for nutrients and/or liming of Andisols under sustainable forage models.

Effects of Wood Ash on Nutrients and Heavy Metal(oid)s Mobility in an Ultisol.

Wood ash produced through cellulose manufacturing has agricultural uses due to its neutralizing power, like that of commercial products, in addition to providing key soil nutrients such as Ca, Mg, K, and P. However, this industrial waste can possess heavy metal(oid)s that bioaccumulate in the food chain. The objective of this study was to determine the effect of wood ash (WA) on the physicochemical properties of an Ultisol, the mobility of heavy metal(oid)s (As, Cd, Cr, Pb, and Ni) in the soil-plant-water system, and the nutritional response (N, P, and K) of ryegrass (Lolium perenne L.). The experiment was conducted in pots, under greenhouse conditions, using a completely randomized design. Ryegrass was grown in pots containing mixtures of WA plus soil at 7.5, 15, 30, and 75 g kg-1, commercial lime plus soil at 1.5 g kg-1, and unamended soil as a control. Heavy metal(oid)s were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES). All WA doses favored an increase in pH and the availability of P, Ca, Mg, Na, K, Cu, and Zn in soil and N, P, and K absorption in ryegrass. WA favored the availability and later absorption of heavy metal(oid)s by ryegrass (staying mainly in the roots). Heavy metal(oid)s mobility in the soil-plant-water system was as follows: Cr > Pb > Ni > As.