Spatial and temporal variations in nitrogen retention effects in a subtropical mountainous basin in Southeast China

Nitrogen retention within a watershed reduces the amount of N exported to the ocean;however, it worsens environmental problems, including surface water eutrophication, aquifer pollution, acid rain, and soil acidification. Here, we adopted the Soil and Water Assessment Tool(SWAT) model to describe the riverine N output and retention effects in the Shanmei Reservoir Basin, a subtropical mountainous basin located in Quanzhou City, Southeast China. The results revealed that farmlands and orchards in the upstream and central parts of the basin were the dominant land use types, which contributed large N yields. Fertilizer application was the key source of riverine N output and N retention within the basin. On average, approximately 64% of anthropogenic N inputs were retained within the basin, whereas 36% of total N was exported to the downstream and coastal areas. The average N retention efficiency was 80% in a dry year, and within the year, N retention occurred in spring and summer and N release occurred in autumn and winter. The annual variation in N retention within the basin was largely dominated by changes in rainfall and runoff, whereas the seasonal characteristics of N retention were mainly affected by fertilization. Even with a large decrease in fertilizer application, owing to the contributions of the residual N pool and river background, the riverine N output still maintained a certain base value. The effects of precipitation, land use types, and agricultural fertilizer on N retention should be comprehensively considered to implement reasonable N management measures.

Effect of exogenous additives on heavy metal passivation and nitrogen retention in pig manure composting

The widespread use of feed additives in intensive and large-scale pig farming has resulted in high levels of heavy metals in pig manure.The long-term application of organic fertilizers containing high levels of heavy metals leads to the accumulation of heavy metals in the soil,which not only causes heavy metal pollution in the soil,and also affect food safety and endanger human health.Composting is an economical and effective technical measures to achieve environmentally-sustainable treatment of pig manure and is a practical method to reduce the problem of heavy metals and to improve the resource value of pig manure.The composting process is accompanied by high temperatures and the production and emission of gases,and also lead to changes in the nitrogen content of the compost and provide opportunity for heavy metal passivation additives.This paper summarizes the forms and types of heavy metals present in pig manure and reviews the progress of research as well as the techniques and problems of in the composting process,and provides recommendations for research on heavy metal passivation and nitrogen retention in pig manure composting.

Magnetized Water Improves Digestion and Growth of Lambs

Twelve of weaned Small-tail Han male lambs,with body weight of(7.99±1.04)kg,at 30 days of age,were divided into two groups to study the effect of drinking magnetized water(MW)on digestion and metabolism of lambs.The voluntary intake and ADG from 30 to 240 days of age were measured,twice of digestion and metabolism trial were carried out,and at the age of 240 days slaughter test was conducted.The results showed that drinking MW significantly increased voluntary feed intake(27.2%),ADG(27.4%)and apparent digestibility of DM(17.9%),OM(20.2%),CP(22.8%),and energy(12.7%),respectively.The nitrogen retention in two experimental trials significantly increased by 43.9%and 28.9%,respectively.Drinking MW significantly increased live body weight(24.5%),carcass weight(28.2%),carcass net meat weight(25.5%),carcass lean weight(32.5%)and carcass fat weight(31.3%),respectively.The fresh weights of liver,kidney,rumen,longissimus dorsi and leg muscle of lambs drinking MW increased significantly,but there was no significant difference in their contents of DM,OM and CP.It is concluded that drinking MW is beneficial for increasing voluntary feed intake,digestibility,and ADG,and improving slaughter performance of lambs.

Nitrogen-retaining property of compost in an aerobic thermophilic composting reactor for the sanitary disposal of human feces

Aerobic composting is a method for the sanitary disposal of human feces as is used in bio-toilet systems.As the products of composting can be utilized as a fertilizer,it would be beneficial if the composting conditions could be more precisely controlled for the retention of fecal nitrogen as long as possible in the compost.In this study,batch experiments were conducted using a closed aerobic thermophilic composting reactor with sawdust as the bulk matrix to simulate the condition of a bio-toilet for the sanitary disposal of human feces.Attention was paid to the characteristics of nitrogen transformation.Under the controlled conditions of temperature at 60°C,moisture content at 60%,and a continuous air supply,more than 70%fecal organic removal was obtained,while merely 17%fecal nitrogen loss was observed over a two-week composting period.The nitrogen loss was found to occur mainly in the first 24 h with the rapid depletion of inorganic nitrogen but with an almost unchanged organic nitrogen content.The fecal NH4-N which was the main component of the inorganic nitrogen(>90%)decreased rapidly in the first day,decreased at a slower rate over the following days,and finally disappeared entirely.The depletion of NH4-N was accompanied by the accumulation of NH3 gas in the ammonia absorber connected to the reactor.A mass balance between the exhausted NH3 gas and the fecal NH4-N content in the first 24 hours indicated that the conversion of ammonium into gaseous ammonia was the main reason for nitrogen loss.Thermophilic composting could be considered as a way to keep a high organic nitrogen content in the compost for better utilization as a fertilizer.

Adding polyethylene glycol to steer ration containing sorghum tannins increases crude protein digestibility and shifts nitrogen excretion from feces to urine

The objectives of the experiment were to study the effects of adding polyethylene glycol(PEG)to steer ration containing high sorghum tannins on rumen fermentation,nutrient digestion,nitrogen(N)balance and plasma biochemical parameters.Eight growing steers at 16 months of age were allotted to a replicated 4×4 Latin square design with 4 treatments and 4 periods(19 d each).Polyethylene glycol at 0,1.75,3.50 and 7.00 g/kg dry matter(DM)were added to a basal ration containing 27.82%DM of sorghum grain(total tannins 3.3 g/kg DM)as the treatments.The results indicated that adding PEG quadratically increased the ruminal pH(P=0.049),tended to linearly increase the ruminal concentration of total volatile fatty acids(P=0.070),increased the molar proportion of acetate(P=0.016),linearly decreased the molar proportion of butyrate(P=0.015),and tended to increase the molar proportion of iso-valerate(P=0.061)and the ruminal concentration of ammonia N(P=0.092).Adding PEG tended to quadratically decrease the relative abundance of methanogenic archaea(P=0.082),linearly decreased the relative abundance of Fibrobacter succinogenes(P=0.008)and decreased the relative abundance of Butyrivibrio fibrisolvens(P=0.048)at 7.00 g/kg DM.Dietary addition with PEG increased the crude protein(CP)digestibility(P<0.001)and tended to increase the neutral detergent fiber digestibility(P=0.066)in a linear manner.Adding PEG to basal ration also increased the plasma globulin concentration(P=0.029)and tended to linearly increase the plasma total protein concentration(P=0.069).Adding PEG linearly decreased the fecal N excretion(P<0.001)and the fecal N-to-total N excretion ratio(P=0.004)and increased the urinary N-to-total N excretion ratio(P=0.004)and urinary urea excretion(P=0.010)without affecting the urinary N and total N excretions(P>0.05).It was concluded that adding PEG effectively improved the CP digestibility of the ration containing high sorghum tannins but increased the urinary urea excretion without improving the N retention and N retention rate in steers.

Soil fauna accelerated litter C and N release by improving litter quality across an elevational gradient

Background Soil fauna is an important driver of carbon(C)and nitrogen(N)release from decomposing litter in forest ecosystems.However,its role in C and N cycling concerning climate and litter traits remains less known.In a 4-year field experiment,we evaluated the effects of soil fauna on litter C and N release across an elevation gradient(453,945,3023,and 3582 m)and litter traits(coniferous vs.broadleaf)in southwestern China.Results Our results showed that N was retained by–0.4%to 31.5%,but C was immediately released during the early stage(156–516 days)of decomposition for most litter species.Soil fauna significantly increased the peak N content and N retention across litter species,but reduced the C/N ratio for certain species(i.e.,Juniperus saltuaria,Betula albosinensis,Quercus acutissima,and Pinus massoniana litter),leading to more C and N being released from decomposing litter across the elevation gradient.Contributions of soil fauna to C and N release were 3.87–9.90%and 1.10–8.71%,respectively,across litter species after 4 years of decomposition.Soil environment and initial litter quality factors caused by elevation directly affected litter C and N release.Changes in soil fauna resulting from elevation and fauna exclusion factors had a direct or indirect impact on C and N release during litter decomposition.Conclusions Our findings suggest that soil fauna promote C and N release from decomposing litter in different magnitudes,mainly controlled by environmental conditions(i.e.,temperature and moisture),litter quality(i.e.,lignin and cellulose content,and lignin/cellulose),and its diversity across the elevation gradient.