Abundance and Dynamics of Soil Labile Carbon Pools Under Different Types of Forest Vegetation

Soil organic matter (SOM) in forest ecosystems is not only important to global carbon (C) storage but also to sustainable management of forestland with vegetation types, being a critical factor in controlling the quantity and dynamics of SOM. In this field experiment soil plots with three replicates were selected from three forest vegetation types: broadleaf, Masson pine (Pinus massoniana Lamb.), and Chinese fir (Cunninghamia lanceolata Hook.). Soil total organic C (TOC), two easily oxidizable C levels (EOC1 and EOC2, which were oxidized by 66.7 mmol L-1 K_2Cr_2O_7 at 130-140℃and 333 mmol L-1 KMnO4 at 25℃, respectively), microbial biomass C (MBC), and water-soluble organic C (WSOC) were analyzed for soil samples. Soil under the broadleaf forest stored significantly higher TOC (P (?) 0.05). Because of its significantly larger total soil C storage, the soil under the broadleaf forest usually had significantly higher levels (P (?) 0.05) of the different labile organic carbons, EOC1, EOC2, MBC, and WSOC; but when calculated as a percentage of TOC each labile C fraction of the broadleaf forest was significantly lower (P (?)0.05) than one of the other two forests. Under all the three vegetation types temperature as well as quality and season of litter input generally affected the dynamics of different organic C fractions in soils, with EOC1, EOC2, and MBC increasing closely following increase in temperature, whereas WSOC showed an opposite trend.

Short-term impacts of biochar and manure application on soil labile carbon fractions,enzyme activity,and microbial community structure

Biochar is known to ameliorate soil fertility and increase crop yield;however,information regarding its effects on soil chemical and biological properties remains limited.The experiment was conducted to study the short-term impacts of dif-ferent types of biochar on soil C fractions,enzyme activities,and microbial community structure at depositional and eroded landscape positions at different sampling times[before planting,after planting,and after harvesting of soybean(Glycine max L.)].Three biochar materials,produced from C-optimized gasification of corn(maize,Zea mays L.)stover(CS),pon-derosa pine(Pinus ponderosa Lawson and C.Lawson)wood residue(PW),and switchgrass(Panicum virgatum L.)(SG),and dairy manure(DM)and mixture of dairy manure and pinewood biochar(DMP),were applied at a rate of 10 Mg ha^(−1) to depositional and eroded landscape positions.Data showed that the application of DMP and sole application of DM treat-ments significantly increased the labile C fractions at the depositional and eroded landscapes.The addition of DM and DMP increased the activities ofβ-glucosidase and urease enzymes,and those are involved in C and nitrogen cycling at depositional and eroded landscape positions.There were no significant differences between different biochar materials.However,there was an increase in soil microbial community structure in the DM and DMP treatments at both the landscape positions.In conclusion,our study revealed that DMP and sole application of DM influenced the soil labile C pool,enzyme activities,and microbial community structure at both the landscape positions for different sampling times.

Fractionation of soil organic carbon in a calcareous soil after longterm tillage and straw residue management

No-tillage(NT)and straw return(S)collectively affect soil organic carbon(SOC).However,changes in the organic carbon pool have been under-investigated.Here,we assessed the quantity and quality of SOC after 11 years of tillage and straw return on the North China Plain.Concentrations of SOC and its labile fractions(particulate organic carbon(POC),potassium permanganate-oxidizable organic carbon(POXC),microbial biomass carbon(MBC),and dissolved organic carbon(DOC)),components of DOC by fluorescence spectroscopy combined with parallel factor analysis(PARAFAC),and the chemical composition of SOC by 13C NMR(nuclear magnetic resonance)spectroscopy were explored.Treatments comprised conventional tillage(CT)and NT under straw removal(S0),return of wheat straw only(S1),or return of both wheat straw and maize residue(S2).Straw return significantly increased the concentrations and stocks of SOC at 0–20 cm depth,but NT stratified them with enrichment at 0–10 cm and a decrease at 10–20 cm compared to CT,especially under S2.Labile C fractions showed similar patterns of variation to that of SOC,with POC and POXC more sensitive to straw return and the former more sensitive to tillage.Six fluorescence components of DOC were identified,mainly comprising humic-like substances with smaller amounts of fulvic acid-like substances and tryptophan.Straw return significantly decreased the fluorescence index(FI)and autochthonous index(BIX)and increased the humification index(HIX).No-tillage generally increased HIX in topsoil but decreased it and increased the FI and BIX below the topsoil.Relative abudance order of the chemical composition of SOC was:O-alkyl C>alkylC>aromatic-C>carbonyl-C.Overall,NT under S2 effectively increased SOC and its labile C forms and DOC humification in topsoil and microbially-derived DOC below the topsoil.Return of both wheat and maize straw was a decisive factor in promoting SOC in the plow layer.The stratification of SOC under NT may confer a long-term influence on carbon sequestration.

Effect of Combined Application of Organic Farming Aid (OFA) and Inorganic Fertilizers on the Growth and Yield of Maize and Soil Microbial Properties in the Guinea Savannah Agro-Ecological Zone of Ghana

The aim of the study was to evaluate the effect of different rates of organic farming aid (OFA) and inorganic fertilizer on the productivity of maize, chemical and microbial properties of soil for higher economic value. Field experiments were conducted during the 2020 and 2021 cropping seasons at the research fields of CSIR-Savanna Agricultural Research Institute located at Nyankpala in the Guinea savannah agroecology of Ghana. The study consisted of five treatment combinations: full rate of OFA, full rate of NPK, 1/2 OFA + 1/2 NPK, full OFA + 1/2 NPK and a control (no OFA and no NPK) which were arranged in a randomized complete block design with four replications. Analysis of variance indicated significant (P 0.05) treatment and year interaction effect for all the growth parameters except for plant height, leaf area and leaf area index. Apart from hundred seed weight, treatment and year interaction effect for all the yield and yield components was significant (P 0.05). Application of full rate of NPK (90:60:60) resulted in the highest grain yield of 4960 kg·ha-1, however it was statistically similar to those obtained by the combined application of full rate of OFA (250 ml·ha-1) + 1/2 NPK and 1/2 OFA + 1/2 NPK with grain yield of 4856 kg·ha-1 and 4639 kg·ha-1 respectively. There was also a yield advantage of 197. 5%, 191.3%, 178.3 and 79.1% over the control for full NPK rate, full OFA rate + 1/2 NPK rate, 1/2 OFA rate + 1/2 NPK and full OFA rate respectively. Application of full OFA rate + 1/2 NPK enhanced soil basal respiration (evolved CO2) and mineralizable C, implying that, combination of full OFA rate and NPK fertilizer would be necessary to boost soil microbial activity and soil labile nutrient pool (labile C pool). This suggests that combined use of full OFA rate + 1/2 NPK fertilizer can be a better strategic tool for improving soil quality. The highest benefit cost ratios (BCR) of 2.58 and 3.77 were obtained following the application of full OFA rate + 1/2 NPK and 1/2 OFA rate + 1/2 NPK respectively. Hence, it could be concluded that complementary use of OFA and NPK is more profitable than using single inputs (either OFA or NPK). Thus, in promoting technology packages to farmers, development practitioners must carefully consider the complementary of inputs that are cost-effective but economically rewarding.

Soil Organic Carbon Mineralization as Affected by Cyclical Temperature Fluctuations in a Karst Region of Southwestern China

The diurnal fluctuation in soil temperature may influence soil organic carbon （SOC） mineralization, but there is no consensus on SOC mineralization response to the cyclical fluctuation in soil temperature. A 56-d incubation experiment was conducted to investigate the effects of constant and variable temperatures on SOC mineralization. Three soils were collected from the karst region in western Guizhou Province, southwestern China, including a limestone soil under forest, a limestone soil under crops and a yellow soil under crops. According to the World Reference Base （WRB） classification, the two limestone soils were classified as Haplic Luvisols and the yellow soil as a Dystric Luvisol. These soils were incubated at three constant temperatures （15, 20 and 25 ℃） and cyclically fluctuating temperatures （diurnal cycle between 15 and 25 ℃）. The results showed that the 56-d cumulative SOC mineralized （C56） at the fluctuating temperatures was between those at constant 15 and 25 ℃, suggesting that the cumulative SOC mineralization was restricted by temperature range. The SOC mineralization responses to the fluctuating temperatures were different among the three soils, especially in contrast to those at constant 20 ~C. Compared with constant 20 ℃, significant （P 〈 0.05） decreases and increases in C56 value were found in the limestone soil under forest and yellow soil under crops at the fluctuating temperatures, respectively. At the fluctuating temperatures, the forest soil with lower temperature coefficient Q10 （the relative change in SOC mineralization rate as a result of increasing the temperature by 10 ℃） had a significantly （P 〈 0.05） lower SOC mineralization intensity than the two cropland soils. These indicated that differences in temperature pattern （constant or fluctuating） could significantly influence SOC mineralization, and SOC mineralization responses to the fluctuating temperatures might be affected by soil characteristics. Moreover, the warmer temperatures might improve the ability of soil microbes to decompose the recalcitrant SOC fraction, and cyclical fluctuations in temperature could influence SOC mineralization through changing the labile SOC pool size and the mineralization rate of the recalcitrant SOC in soils.

Correlation Between CO_2 Efflux and Net Nitrogen Mineralization and Its Response to External C or N Supply in an Alpine Meadow Soil

In nutrient-limited alpine meadows,nitrogen(N) mineralization is prior to soil microbial immobilization;therefore,increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils.In addition,low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization.A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau.Two levels of NH4NO3(N) or glucose(C) were added,with a blank without addition of C or N as the control,before incubation at 5,15,or 25 ℃ for 28 d.CO2 efflux was measured during the 28-d incubation,and the mineral N was measured at the beginning and end of the incubation,in order to test two hypotheses:1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive.The results showed a negative correlation between CO2 efflux and net N immobilization in the control.External inorganic N supply did not change the negative correlation.The external labile C supply shifted the linear correlation from negative to positive under the low C addition level.However,under the high C level,no correlation was found.These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures.Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.