Organic mulching promotes soil organic carbon accumulation to deep soil layer in an urban plantation forest

Background:Soil organic carbon(SOC)is important for soil quality and fertility in forest ecosystems.Labile SOC fractions are sensitive to environmental changes,which reflect the impact of short-term internal and external management measures on the soil carbon pool.Organic mulching(OM)alters the soil environment and promotes plant growth.However,little is known about the responses of SOC fractions in rhizosphere or bulk soil to OM in urban forests and its correlation with carbon composition in plants.Methods:A one-year field experiment with four treatments(OM at 0,5,10,and 20 cm thicknesses)was conducted in a 15-year-old Ligustrum lucidum plantation.Changes in the SOC fractions in the rhizosphere and bulk soil;the carbon content in the plant fine roots,leaves,and organic mulch;and several soil physicochemical properties were measured.The relationships between SOC fractions and the measured variables were analysed.Results:The OM treatments had no significant effect on the SOC fractions,except for the dissolved organic carbon(DOC).OM promoted the movement of SOC to deeper soil because of the increased carbon content in fine roots of subsoil.There were significant correlations between DOC and microbial biomass carbon and SOC and easily oxidised organic carbon.The OM had a greater effect on organic carbon fractions in the bulk soil than in the rhizosphere.The thinnest(5 cm)mulching layers showed the most rapid carbon decomposition over time.The time after OM had the greatest effect on the SOC fractions,followed by soil layer.Conclusions:The frequent addition of small amounts of organic mulch increased SOC accumulation in the present study.OM is a potential management model to enhance soil organic matter storage for maintaining urban forest productivity.

Fate of low-molecular-weight organic phosphorus compounds in the P-rich and P-poor paddy soils

Continuous application of organic fertilizers can cause accumulation of organic phosphorus(P)in soil,especially in the lowmolecular-weight organic phosphorus(LMWOP)forms.This organic P pool represents a potentially important source of P for both plants and microorganisms.To understand the effect of long-term fertilization(30 years)(P-rich soil)vs.fallowing(P-poor soil)on the bioavailability and fate of LMWOP in subtropical paddy soils,we determined the sorption and mineralization of 14 C-labeled adenosine,adenosine monophosphate(AMP),adenosine diphosphate(ADP),and adenosine triphosphate(ATP)in each soil.The contents of carbon,nitrogen,and P in the P-rich soil were more than two times greater than those in the P-poor soil.The mineralization rates of the LMWOP compounds were faster in the P-rich soil compared to the P-poor soil,and followed the order AMP>ADP>ATP.Using sterilized soil,all forms of adenosine-P were strongly sorbed to the solid phase and reached saturation in a short time,with the adsorbance increasing with the number of phosphate groups.We concluded that the mineralization of LMWOP compounds was repressed slightly by sorption to the solid phase,but only in the short term.Thus,LMWOP compounds serve as readily available sources of C for microorganisms,making P available for themselves as well as for the plants.However,P accumulation and the progressive saturation of the P sorption sites in highly fertile soils may increase the potential risk of P runoff.

Response of nitrogen fractions in the rhizosphere and bulk soil to organic mulching in an urban forest plantation

Nitrogen is an essential component in forest ecosystem nutrient cycling.Nitrogen fractions,such as dissolved nitrogen,ammonium,nitrate,and microbial biomass nitrogen,are sensitive indicators of soil nitrogen pools which affect soil fertility and nutrient cycling.However,the responses of nitrogen fractions in forest soils to organic mulching are less well understood.The rhizosphere is an important micro-region that must be considered to better understand element cycling between plants and the soil.A field investigation was carried out on the effect of mulching soil in a 15-year-old Ligustrum lucidum urban plantation.Changes in total nitrogen and nitrogen fractions in rhizosphere and bulk soil in the topsoil(upper 20 cm)and in the subsoil(20-40 cm)were evaluated following different levels of mulching,in addition to nitrogen contents in fine roots,leaves,and organic mulch.The relationships between nitrogen fractions and other measured variables were analysed.Organic mulching had no significant effect on most nitrogen fractions except for the rhizosphere microbial biomass nitrogen(MBN),and the thinnest(5 cm)mulching layer showed greater effects than other treatments.Rhizosphere MBN was more sensitive to mulching compared to bulk soil,and was more affected by soil environmental changes.Season and soil depth had more pronounced effects on nitrogen fractions than mulching.Total nitrogen and dissolved nitrogen were correlated to soil phosphorus,whereas other nitrogen fractions were strongly affected by soil physical properties(temperature,water content,bulk density).Mulching also decreased leaf nitrogen content,which was more related to soil nitrogen fractions(except for MBN)than nitrogen contents in either fine roots or organic mulch.Frequent applications of small quantities of organic mulch contribute to nitrogen transformation and utilization in urban forests.

AGRONOMIC AND ENVIRONMENTAL BENEFITS OF REINTRODUCING HERB-AND LEGUME-RICH MULTISPECIES LEYS INTO ARABLE ROTATIONS:A REVIEW

Agricultural intensification and the subsequent decline of mixed farming systems has led to an increase in continuous cropping with only a few fallow or break years,undermining global soil health.Arable-ley rotations incorporating temporary pastures(leys) lasting 1–4 years may alleviate soil degradation by building soil fertility and improving soil structure.However,the majority of previous research on arable-ley rotations has utilized either grass or grassclover leys within ungrazed systems.Multispecies leys,containing a mix of grasses,legumes,and herbs,are rapidly gaining popularity due to their promotion in agri-environment schemes and potential to deliver greater ecosystem services than conventional grass or grass-clover leys.Livestock grazing in arable-ley rotations may increase the economic resilience of these systems,despite limited research of the effects of multispecies leys on ruminant health and greenhouse gas emissions.This review aims to evaluate previous research on multispecies leys,highlighting areas for future research and the potential benefits and disbenefits on soil quality and livestock productivity.The botanical composition of multispecies leys is crucial,as legumes,deep rooted perennial plants(e.g.,Onobrychis viciifolia and Cichorium intybus) and herbs(e.g.,Plantago lanceolata) can increase soil carbon,improve soil structure,reduce nitrogen fertilizer requirements,and promote the recovery of soil fauna(e.g.,earthworms) in degraded arable soils while delivering additional environmental benefits(e.g.,biological nitrification inhibition and enteric methane reduction).Multispecies leys have the potential to deliver biologically driven regenerative agriculture,but more long-term research is needed to underpin evidence-based policy and farmer guidance.

REINTEGRATION OF CROP-LIVESTOCK SYSTEMS IN EUROPE:AN OVERVIEW

Ongoing specialization of crop and livestock systems provides socioeconomic benefits to the farmer but has led to greater externalization of environmental costs when compared to mixed farming systems.Better integration of crop and livestock systems offers great potential to rebalance the economic and environmental trade-offs in both systems.The aims of this study were to analyze changes in farm structure and review and evaluate the potential for reintegrating specialized intensive crop and livestock systems,with specific emphasis on identifying the co-benefits and barriers to reintegration.Historically,animals were essential to recycle nutrients in the farming system but this became less important with the availability of synthetic fertilisers.Although mixed farm systems can be economically attractive,benefits of scale combined with socio-economic factors have resulted in on-farm and regional specialization with negative environmental impacts.Reintegration is therefore needed to reduce nutrient surpluses at farm,regional and national levels,and to improve soil quality in intensive cropping systems.Reintegration offers practical and cost-effective options to widen crop rotations and promotes the use of organic inputs and associated benefits,reducing dependency on synthetic fertilisers,biocides and manure processing costs.Circular agriculture goes beyond manure management and requires adaptation of both food production and consumption patterns,matching local capacity to produce with food demand.Consequently,feed transport,greenhouse gas emissions,nutrient surpluses and nutrient losses to the environment can be reduced.It is concluded that reintegration of specialized farms within a region can provide benefits to farmers but may also lead to further intensification of land use.New approaches within a food system context offer alternatives for reintegration,but require strong policy incentives which show clear,tangible and lasting benefits for farmers,the environment and the wider community.

Experimental strategies to measure the microbial uptake and mineralization kinetics of dissolved organic carbon in soil

Soil organic matter turnover rates are typically estimated from mass loss of the material over time or from on rates of carbon dioxide production.In the study,we investigated a new way to characterize the concentration-dependent kinetics of amino acids used by measuring microbial uptake and mineralization of ^(14)C-alanine.We measured the depletion from soil solution after additions ^(14)C-alanine.The microbial uptake of ^(14)C-alanine from soil solution was concentration-dependent and kinetic analysis indicated the operation of at least three distinct alanine transport systems of differing affinities.Most of the ^(14)C-alanine depletion from the soil solution occurred rapidly within the first 10-30 min of the incubation after 10μM to 1 mM substrate additions.At alanine concentrations less than 250μM,the kinetic parameters for K_(m) and V_(max) of the higher-affinity transporter were 60.0μM and 1.32μmol g^(-1) DW soil h^(-1),respectively.The mineralization of alanine was determined and the half-time values for the rapid mineralization process were 45 min to 1.5 h after the addition at alanine concentrations below 1 mM.The time delay after its uptake into microbial biomass suggested that alanine uptake and subsequent respiration were uncoupled pattern.The microbial N uptake rate was calculated by microbial mineralization,and an estimated K_(m) value of 1731.7±274.6μM and V_(max )value of 486.0±38.5μmol kg^(-1)DW soil h^(-1).This study provides an alternative approach for measuring the rate of turnover of compounds that turnover very rapidly in soil.

Effects of 7 years of field weathering on biochar recalcitrance and solubility

How weathering affects the physiochemical properties of biochar and its long-term carbon(C)sequestration potential remains unclear.In this study,we measured changes in biochar recalcitrance and solubility after 7 years of weathering in a cultivated field.Biochar recalcitrance and biodegradability of weathered and unweathered hardwood biochar mixtures were determined by thermal analysis(differential scanning calorimetry)and evolved gas analysis.Differences in biochar solubility and the chemical composition of biochar-derived dissolved organic carbon(DOC)were determined by repeated laboratory leaching and UV-Vis spectroscopy.The surface carbon-oxidation state(Cox)of biochar increased by 117.6-158.2%with weather-ing in the field,and there was an average of 0.9-1.2%decrease in biochar C contents per year.However,thermal indices of biochar recalcitrance and biodegradability,which suggested intermediate C sequestration potential,were not significantly different between weathered and unweathered biochars.The O:C ratio increased with weathering suggesting an increase in biodegradability,however,both weathered and unweathered biochars were still estimated to have half-lives of over 1000 years.Water-soluble organic carbon(WSOC)concentrations from the unweathered biochar rapidly decreased during laboratory leaching to levels similar to the field-weathered biochars,and aromaticity(SUVA_(254))of WSOC increased from 5.9%in the unweathered biochar to 42%aromaticity in the biochars weathered for 7 years.We conclude that during short-term(years)weathering under field conditions,there is continued solubilization of increasingly aromatic biochar-C compounds,however,this accounts for a relatively small proportion of biochar C such that there is little-to-no change in biochar stability or C sequestration potential after field application.

Biochar application to temperate grasslands:challenges and opportunities for delivering multiple ecosystem services

Grasslands(natural,semi-natural and improved)occupy approximately one-third of the terrestrial biosphere and are key for global ecosystem service provision,storing up to 30%of soil organic carbon(SOC).To date,most research on soil carbon(C)sequestration has focused on croplands where the levels of native soil organic matter(SOM)are typically low and significant potential exists to replenish SOM stocks.However,with the renewed push to achieve“net zero”C emissions by 2050,grasslands may offer an additional C store,utilising tools such as biochar.Here,we critically evaluate the potential for biochar as a technology for increasing grassland C stocks,identifying a number of practical,economic,social and legislative challenges that need to be addressed before the widescale adoption of biochar may be achieved.We critically assess the current knowledge within the field of grassland biochar research in the context of ecosystem service provision and provide opinions on the applicability of biochar as an amendment to different types of grassland(improved,semi-improved and unimproved)and the potential effect on ecosystem provision using a range of application techniques in the topsoil and subsoil.We concluded that the key question remains,is it possible for managed grasslands to store more C,without causing a loss in additional ecosystem services?To address this question future research must take a more multidisciplinary and holistic approach when evaluating the potential role of biochar at sequestering C in grasslands to mitigate climate change.