Items

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  Effects and mechanism of microplastics on organic carbon and nitrogen cycling in agricultural soil: a review

  At present, microplastics (MPs) are a kind of emerging pollutants of concern in the environment, and have a wide and far-reaching impact on terrestrial ecosystems. This paper summarizes the latest research progress of the impact of MPs pollution on the biogeochemical cycle of carbon (C) and nitrogen (N), and summarizes the current situation of MPs pollution in agricultural soil. On the basis of summarizing the effects of MPs on soil physicochemical properties, soil microorganisms, and soil plants and animals, this paper focuses on how soil MPs affect the C and N cycles by changing these factors. MPs can alter organic matter degradation and C and N cycles by changing the soil physicochemical properties, as well as the soil microbial and enzymatic activities. MPs may alter plants’ nutrient uptake processes, which in turn affects the ability of plants to photosynthesize and absorb C and N elements. MPs can affect the survival rate, the growth rate, and intestinal injury of soil animals, therefore indirectly affecting the soil C and N cycles. At the same time, this paper compares the different effects of conventional plastics and biodegradable plastics on soil, and looks forward to the current research deficiencies and the future research directions of ecotoxicology of MPs on C and N cycle.
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  Long-term tillage, residue management and crop rotation impacts on N2O and CH4 emissions from two contrasting soils in sub-humid Zimbabwe

  The respective contribution of conservation agriculture (CA) principles (no-tillage, permanent soil cover/mulch and crop rotations) on greenhouse gas (GHG) emissions is still unclear. This study was conducted at two long-term experimental sites established in 2013 in Zimbabwe, on an abruptic Lixisol at Domboshava Training Center (DTC) and on a xanthic Ferralsol at the University of Zimbabwe Farm (UZF). The purpose of the study was to unravel the individual and combined effects of tillage, mulching and rotation on N2O and CH4 emissions in low nitrogen (N) input maize-based cropping systems (< 60 kg N ha−1) and to compare emissions within maize rows and between maize rows. We hypothesised that integrating no tillage, mulch and cereal-legume rotation would enhance N2O emissions. Six treatments, replicated four times were investigated: conventional tillage, conventional tillage with rotation, no-tillage, no-tillage with mulch, no-tillage with rotation, no-tillage with mulch and rotation. The main crop was maize (Zea mays L.) and treatments with rotation included cowpea (Vigna unguiculate L. Walp.). Gas samples were regularly collected using the static chamber method in the maize row and inter-row spaces during the 2019/20 and 2020/21 cropping seasons and during the 2020/21 dry season. Soil moisture and mineral N were measured in the 0–20 cm soil depth. In 2019/20, cumulative total N2O emissions were significantly higher in mulch treatments at DTC, while at UZF N2O emissions were higher with cowpea rotation. Cumulative total N2O emissions ranged from 215 to 496 g N2O-N ha−1 yr−1 and from 226 to 395 g N2O-N ha−1 yr−1, at DTC and UZF, respectively. In 2020/21, N2O emissions were much lower and no differences were found between treatments on both sites (145 to 179 g N2O-N ha−1 yr−1 and 83 to 136 g N2O-N ha−1 yr−1 at DTC and UZF, respectively). A significant relationship was found between soil nitrate and daily N2O emissions. At UZF, highest N2O emissions were observed at a water-filled pore space of 60–70%. There were no significant differences in yield-scaled N2O emissions between treatments at both sites for the two seasons. DTC was a net source of CH4 (694 g CH4-C ha−1 yr−1 on average), while UZF was a net sink of CH4 (−494 g CH4-C ha−1 yr−1 on average). No evidence was found for in situ CH4 production at DTC, and an external source is most likely. Our study indicates that for low N input cropping systems in the sub-humid tropics, N loss through N2O is low.
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  A Paradigm Shift to CO2 Sequestration to Manage Global Warming – With the Emphasis on Developing Countries

  Global land use changes that tend to satisfy the food needs of augmenting population is provoking agricultural soils to act as a C source rather than sink. Agricultural management practices are crucial to offset the anthropogenic C emission; hence, Carbon sequestration (CS) in agriculture is a viable option for reversing this cycle, but it is based on hypotheses that must be questioned in order to contribute to the development of new agricultural techniques. This review summarizes a global perspective focusing on 5 developing countries (DC) (Bangladesh, Brazil, Argentina, Nigeria and Mexico) because of their importance on global C budget and on the agricultural sector as well as the impact produced by several global practices such as tillage, agroforestry systems, silvopasture, 4p1000 on CO2 sequestration. We also discussed about global policies regarding CS and tools available to measure CS. We found that among all practices agroforestry deemed to be the most promising approach and conversion from pasture to agroforestry will be favorable to both farmers and in changing climate, (e.g., agroforestry systems can generate 725 Euroeq C credit in EU) while some strategies (e.g. no-tillage) supposed to be less promising and over-hyped. In terms of conservative tillage (no-, reduced-, and minimal tillage systems), global and DC’s land use increased. However, the impact of no-tillage is ambiguos since the beneficial impact is only limited to top soil (0-10 cm) as opposed to conventional mechanisms. Grasses, cereals and cover crops have higher potential of CS in their soils. While the 4p1000 initiative appears to be successful in certain areas, further research is needed to validate this possible mode of CS. Furthermore, for effective policy design and implementation to obtain more SOC stock, we strongly emphasize to include farmers globally as they are the one and only sustainable driver, hence, government. and associated authorities should take initiatives (e.g., stimulus incentives, C credits) to form C market and promote C plantings. Otherwise, policy failure may occur. Moreover, to determine the true effect of these activities or regulations on CS, we must concurrently analyze SOC stock adjustments using models or direct measurements. Above all, SOC is the founding block of sustainable agriculture and inextricably linked with food security. Climate-smart managing of agriculture is very crucial for a massive SOC stock globally especially in DC’s.