Effects Of Biochar Application On C,N, And P Cyclings And Soil Ouality In Highly Weathered Acidic Ferralsols

Ferralsols are highly weathered soils. They have a high potential productivity; however their long-term inappropriate management together with the inherent properties such as low pH, high content of exchangeable Al3+, and deficiencies of organic matter and nutrients, has caused severe degradation. Liming and application of adequate organic matter and fertilization are important management practices to improve or obtain good crop yields on these soils. However, Chinese agriculture has intensified greatly on a limited land area with large inputs of chemical fertilizers and other resources. These have exacerbated the degradation of the soil and environmental quality such as release of N and P from agricultural fields to surface and ground water. Therefore, it is better to develop a technique which holds nutrients in soil and ameliorate the degradation.Soil organic matter has an important role in soil fertility and agricultural productivity. Many practices have been used to increase organic carbon in soil, particularly nitrogen fertilization, zero-tillage agriculture, and the addition of large amounts of manure to soil. These practices do not sequester significant quantities of carbon into soil because most of the organic matter is not stable and is mineralized very fast. In recent years, there has been considerable interest in the use of biochar from pyrolysis of renewable biomass to sequester carbon and improve soil productivity. Much of the stimulus for this interest has come from research on the soils of the Amazon basin, known as Terra Preta de Indio, that contain variable quantities of organic black carbon considered to be of anthropogenic origin. Biochar can improve nutrient availability, cation exchange capacity, bulk density, and water-holding capacity, but these effects depend on the feedstock, prolysis conditions. It is important to evaluate the effects of biochar on soil fertility under different soil and climatic regimes to increase our understanding of potential interactions before widespread use of biochar in agricultural systems. Although biochar has been shown to increase soil fertility and productivity in the tropics, there is limited information about influences of biochar on transformation and chemical forms of C, N and P in soils. Therefore, series of incubation experiments were conducted to study the effects of biochars (oak wood biochar and bamboo biochar) application on microbial activities, biomass and communities, carbon fractions and enzyme activity, fractions and sorption of nitrogen and phosphorus, and growth of rye grass in a highly weathered acidic Ferralsols. The study was emphasized on the C, N and P cyclings in the soil.The experiments included four treatments, ie., control without application of any biochar, application of0.5%oak wood biochar (W0.5) or bamboo biochar (B0.5), application of1.0%oak wood biochar (W1.0) or bamboo biochar (B1.0), and application2.0%oak wood biochar (W2.0) or bamboo biochar (B2.0). After mixing the soil and the biochar thoroughly, they were wetted with deionized water to about saturation of the experimental soil. All pots were covered with plastic film and then a small hole was made to allow gaseous exchange. The treated soils were incubated at a constant temperature of25℃for372days. Based on evaporation loss, the soil moisture was kept constant by regular weighing of the pots. After week1,8,16, and53(372days) the incubated soils were taken and separated into three groups:The first group samples were air dried and sieved with2mm and0.25mm. These samples used for analysis of chemical properties. The second groups were sieved with2mm to determine soil microbial biomass C and N and enzymatic activities. The third group were freeze-dried and preserved at-70℃in refrigerator, these group used to determine phospholipid fatty acids for microbial communities in soil. The main results are as follows:(1) Effects on microbial activities, biomass and communitiesSoil microbial activities are responsible for the cycles of bio-elements (C, N and P). We hypothesized that application of biochar affects activities of extracellular enzymes involved in the soil C (β-glucosidase), N (urease) and P (acid phospahtase) cycling. Accordingly, to study the effect of biochar treatments across time, the amended soil properties were evaluated after the1st,8th and16th weeks of the incubation. It was found that soil pH, total organic carbon (TOC) and urease increased significantly with increasing biochar rate while the activity of acid phosphatase decreased, the reason can be the inverse correlation of this enzyme with soil pH. TOC had positive correlation with urease, indicating that organic matter plays vital role in protecting this enzyme. The β-glucosidase correlated positively with dissolved organic carbon (DOC) and negatively with C/N, suggesting that mineralization of organic matter provides substrates for this enzyme. The highest microbial biomass C and N as well as total PLFA was observed at the lowest rates, particularly the treatment of W0.5had higher relative abundance of soil bacteria, fungi and gram-positive bacteria. Our results suggest that biochar application improve the fertility of acidic Ferralsols by increasing soil pH, TOC and DOC which, in turn, enhance soil enzymes, microbial biomass and community.(2) Effects on carbon fractions and enzyme activityTo evaluate the changes in the pool of organic carbon fractions, aggregate stability and activity of enzymes, after the53rd weeks of the incubation, the treated soils were analyzed for total organic C (TOC), potassium permanganate oxidizable C (POXC), light fraction organic C (LFOC), water soluble organic C (WSC), hot-water extractable C (HWC) and microbial biomass C (MBC), macroaggregates (>0.25mm), dehydrogenase,(3-glucosidase and urease. The highest values of>0.25mm, POXC, LFOC, HWC, MBC and enzyme activities were measured in the lowest rates (Wo5and B0.5). MBC positively correlated with all labile organic carbon fractions and macroaggregates, indicating microbial activities result in mineralization of organic matter (OM) and contribute on bonding agent for macroaggregation. The C/N of the experimental soil negatively correlated with most of labile organic carbon fractions and macroaggregates, which could be the effect of limited N availability on labile organic carbon fraction and aggregation. As compared to the control, lability index (LI)(changes in the lability of soil carbon) in the treatments of W0.5and B0.5increased by4and6%, respectively, whereas the carbon management index (CM I)(changes of the total carbon in the soil and its lability) increased by ranges of50to286%in the treatments, implies sequestration of organic C in soil. The high CMI is largely caused by high C sequestration and low lability differences between the treatments. Our results suggest that biochar application increase total organic carbon, stimulate microbial activities, in turn increase macroaggregation, and thus soil quality.(3) Effects on fractions and sorption of N and PWhen applied to soil, biochar has the ability to absorb ions as compared to other forms of soil organic matter, due to its surface chemistry. The forms of N and P would also be affected by incorporation of biochar into soil. In view of that, after16weeks, the incubated soils were analyzed for N forms (NO3--N, NH4+-N, and organic N), P fractions (water-soluble P (H2O-P), bioavailable inorganic P (NaHCO3-IP), readily mineralizable organic P (NaHCO3-OP), potentially bioavailable inorganic P (NaOH-IP), potentially bioavailable organic P (NaOH-OP), acid-soluble P (Ca-bound P/HC1-P), and residual P), and sorption of nitrate (NO3’-N), ammonium (NH4+-N) and phosphate (PO43--P). The results showed that ammonium (NH4--N) concentration decreased with increasing rates of biochar application, the highest was recorded in control (6.31mg kg-). It indicates biochar application reduce NH4+-N in soil. The lowest biochar rates showed the highest nitrate (NO3--N) concentration, the maximum were measured in the treatment of B0.5(98.61mg kg-1). The total nitrogen positively correlated with organic N (r=0.99, p<0.001), indicating that the N accumulation due to biochar application occurred mainly in organic N forms. Both biochars sorbed more NH4+-N and NO3--N as compared to the control. Bamboo biochar sorbed more NO3-N as compared to the oak wood biochar with the highest was measured in the treatment of B2.0(47.07mg kg-1). Both biochars had no significant effect on sorption of phosphate. Soil total P positively correlated with residual P (r=0.86, p<0.001) indicates that the P accumulation in this soil by biochar addition occurred mainly in the forms of residual P. While, the labile P (NaHCO3-P) and potentially labile P (NaOH-P) were significantly and positively correlated with microbial biomass C (4=0.58,p<0.01and r=0.73, p<0.001, respectively). It indicates that biochar may have indirect effect on P availability by providing a beneficial environment for microorganisms that in turn produce and recycle a highly labile pool of organic P.(4) Respones of rye grass to nutrient properties of biochars In this experiment, two biochars were used:Oak wood biochar (WB) and bamboo biochar (BB), which were produced at600℃, had no significant differences in pH, C content and morphology. However, the WB had higher surface area, pore volume and oxygen containing functional groups. These are non-nutritional properties that modify the bulk density (BD), water holding capacity (WHC) and cation exchange capacity (CEC) of the amended soils. On the contrary, the BB was significantly higher in nutrient content (nutritional properties) as compared to WB. These biochars were used to study their influence on properties of soil, growth and nutrient uptake of rye grass (Lolium perenne L.) on acidic Ferralsol. Application of both biochars increased organic C, soil pH, CEC, base saturation and WHC, but decreased exchangeable Al and BD of the soil. These modified growth environments of ryegrass and thus improved the soil quality. Principal component analysis showed that available N and P had significant correlation (r=0.92) with shoot biomass, suggesting N and P are the main factor that determine productivity of the tested soil. As compared to WB treated soils, significant increases in shoot and root biomass, and uptake of nutrients occurred in ryegrass in BB treated soil, particularly for the treatment of B0.5. This is due to the BB had higher innate nutrient value, indicating that the nutritional properties had significant impact on growth of rye grass than the non-nutritional properties.In general, we conclude that biochar addition to acidic Ferralsols improves the soil quality and increase plant growth, particularly when applied at low rates (0.5%). However, our findings show that short-term effects of biochar on plant growth, and C, N and P cyclings reported from green house and laboratory studies, respectively. Future works should focus on long term field trials to help inform soil management decisions involving biochar.