Effects of Microplastic Fibers on Soil Aggregation and Enzyme Activities Are Organic Matter Dependent

Microplastic as an anthropogenic pollutant accumulates in terrestrial ecosystems over time, threatening soil quality and health, for example by decreasing aggregate stability. Organic matter addition is an efficient approach to promote aggregate stability, yet little is known about whether microplastic can reduce the beneficial effect of organic matter on aggregate stability. We investigated the impacts of microplastic fibers in the presence or absence of different organic materials by carrying out a soil incubation experiment. This experiment was set up as a fully factorial design containing all combinations of microplastic fibers (no microplastic fiber addition, two different types of polyester fibers, and polyacrylic) and organic matter (no organic matter addition, Medicago lupulina leaves, Plantago lanceolata leaves, wheat straw, and hemp stems). We evaluated the percentage of water-stable aggregates (WSA) and activities of four soil enzymes (β-glucosidase, β-D-celluliosidase, N-acetyl-b-glucosaminidase, phosphatase). Organic matter addition increased WSA and enzyme activities, as expected. In particular, Plantago or wheat straw addition increased WSA and enzyme activities by 224.77 or 281.65% and 298.51 or 55.45%, respectively. Microplastic fibers had no effect on WSA and enzyme activities in the soil without organic matter addition, but decreased WSA and enzyme activities by 26.20 or 37.57% and 23.85 or 26.11%, respectively, in the presence of Plantago or wheat straw. Our study shows that the effects of microplastic fibers on soil aggregation and enzyme activities are organic matter dependent. A possible reason is that Plantago and wheat straw addition stimulated soil aggregation to a greater degree, resulting in more newly formed aggregates containing microplastic, the incorporated microplastic fibers led to less stable aggregates, and decrease in enzyme activities This highlights an important aspect of the context dependency of microplastic effects in soil and on soil health. Our results also suggest risks for soil stability associated with organic matter additions, such as is common in agroecosystems, when microplastics are present.

Soil fertility status and sweet potato cultivation in composted mounds under humid lowland tropical climatic conditions

<p>The importance of organic matter addition in composted mounds in terms of nutrients status, nutrient uptake, and environmental impact under different climatic conditions need to be studied. This study was conducted to assess the importance of Cogon grass materials addition as organic matter in composted mounds used for sweet potato cultivation on selected sandy loam soil properties under humid lowland, tropical climatic conditions. A replicated trial with four treatments with or without organic matter or sweet potato plants was set in a completely randomized design. After 6 months, soil samples were collected from two profiles in each treatment and analyzed for selected soil physiochemical properties. Data collected from each profile was pooled, averages taken, and statistically analyzed. The results showed organic matter addition increased water holding capacity and electrical conductivity, lowered soil bulk density, pH, and soil organic carbon content. Cultivation of sweet potato in soil with or without organic matter amendment, in general, depleted nitrogen, potassium, and magnesium contents and increased phosphorous availability. This study showed the addition of Cogon grass materials as organic matter in composted mounds has implications for the production of sweet potato in sandy loam soil in the tropics.</p>

Developing reservoir sediment ceramsite as a novel growing medium: I low temperature and anaerobic production

&lt;p&gt;Ceramsite is a typical substrate used in soilless culture systems. It is clean and durable but usually shows poor performance in water and nutrient retention capacity. In this study, we used reservoir sediment as the material to produce ceramsite to use as a growing medium. We sintered it under relatively low temperature (600&amp;#176;C, 800&amp;#176;C, and 1000&amp;#176;C) and anaerobic conditions with and without organic matter addition (5%, 10%, and 15%). We examined their water holding capacity, bulk density, mechanic strength, and pH, which were related to the essential characteristics using the growing media. The results showed that organic matter addition decreased bulk density and mechanic strength but increased water holding capacity and pH. The sintering temperature has less influence on bulk density and water holding capacity but increased mechanic strength and pH with the increasing sintering temperature. Compared with the commercial high-temperature ceramsite and lava rock, the water holding capacity in our ceramsite can be three times higher than those. The microstructure from scanning electronic microscopy indicated the rough surface in ceramsite at 600&amp;#176;C and 800&amp;#176;C but became glassy surface at 1000&amp;#176;C which was similar to the commercial ceramsite and lava rock that showed more glassy and non-porous surface. The addition of organic matter maintained rough surfaces at 1000&amp;#176;C, which can be the mechanism to have higher water and nutrient retention. Our results suggest that the ceramsite produced from reservoir sediment under lower temperature and anaerobic conditions with organic matter addition can be used as a growing medium to replace commercial ceramsite with its better water retention capability.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;