Derived Humic Acids And Its Effects On Soil Environment And Growth Of Plants

Plants need significant amounts of fertilizers to produce high yield, however, intensive use of chemical fertilizers has caused environmental pollution. For the last two decades,reducing applications of synthetic chemicals to the soil has arose as a vital necessity and become a goal for environmental activists,as well as government and the agricultural industry who mainly concerned crop productivity. For this reason, the study of humic acid(HA) have received considerable attention. These studies discovered that HAs can improve the biological, chemical, and physical properties of soils. Low molecular size HA endowing with a high aromatic and carboxyl C content, and while high molecular size HA with a peptidic and Carbohydratic C positively influence the metabolic parameters of plants.Leonardite is a natural form of humates with the appearance of coal, but a much lesser density than coal. It is rich in organic matter (50-75%), and its HA contents range from 30 to 80%. Using Leonardite or its derived HAs as soil amendments or plant promoter is expected to improve the properties of soil and growth of plants as well as reduce air and water pollution. Humic substances can serves as nitrogen, phosphorus and sulfur reservoirs,improve soil structure, aeration and drainage, and increase buffering and exchange capacities. Leonardite has potential as soil amendment and had beneficial effects on bean growth. Applications of HA also showed to be able to improve plant growth, seed germination, and fruit quality. However, little research has been done on how fractions of HA from Leonardite affect plant growth. Therefore, this study is to investigate effects of fractions of HA derived from Leonardite based on molecular weight on the growth of plants and soil environment. The experimental results provide valuable information for the wide utilization of the Leonardite for sustainable production of crops.1. Effect of different levels of humic acids on nutrient content and enzymatic activities of horticultural soil: In this study, HA extracted from Leonardite with different molecular weight were tested for their effects on the activities of four soil enzymes. Six organic materials were applied in horticultural soil with six different levels to test whether or not molecular weight and level of HA would alter soil enzyme activity and soil nutrient content.Different molecular weight humus similarly and, as a group, had greater effects on soil enzyme activity than blank experiment and leonardite. It reflects humic substances strongly affect the acid and alkaline phosphatase activity, especially the low molecular weight humus (HS1). Also, it indicated that humus can affect the phosphodiesterase availably, but the influence of the molecular weight was not so obvious. However, high molecular weight humic substance significantly inhibited the activity of urease in the soil, and the optimal application rate is 600 kg/hm2. Concentration of NH4+-N tended to decrease with the application of humus and all treatments didn't affect the content of Ca,but the concentration of K, P, Cu, Zn in the soil was increased significantly when applied with small molecular weight humus (HS1).2. Effect of different levels of humic acids and fulvic acid sources on nutrient content and enzymatic activities of horticultural soil: Fulvic acid (FA) and humic acid (HA)extracted from soils formed under widely different pedologic and geographic environments had similar analytical characteristics and chemical structures. Humic extracts with distinct,obtained by various coal extracts and from different sources, were used to study their effect on soil nutrient content and enzymatic activities of horticultural soil. HA and FA can improve the physical and chemical nature of soil and promote the growth of plant. We find that OMRI has the best inhibition on urease activity of soil and the strongest effect on Alkaline Phosphatase and Phosphodiesterase ,HS the highest promotion on the Acid Phosphatase of soil.3. Humic acids derived from Leonardite affected growth and nutrient uptake of snap bean seedlings: Understanding chemistry and the effects of humic substances on plant growth is important for employing organic fertilizer or soil amendment for sustainable snap bean production. This study was to characterize different factions of HA derived from Leonardite and evaluate their effects on seedling growth and nutrient uptake of snap bean.HA extracted from Leonardite were separated according to molecular weights into three fractions (HS1,HS2, HS3) plus sediment (SED). With direct polarization combined with spectral-editing techniques, functional groups of humic acids were quantified and the results indicated that HAs with low molecular weights had more O-alkyl, carboxyl C groups than those with large molecular sizes. The results show that addition of HAs was beneficial to leaf and root growth of snap bean compared with the control (no humic acid).The root length and surface were significantly higher treated by treatments with low molecular weight HAs, while leaf growth was affected mainly by high molecular weight.Plants treated with HAs containing low molecular weights also improved uptake of potassium by shoot, but not by roots.4. Humic acids derived from Leonardite affected growth and nutrient uptake of corn seedlings: Using organic fertilizer or soil amendment such as humic substances is an important component for sustainable agriculture. This study was to determine the effects of different factions of HA on corn seedling growth and nutrient uptake. The experiment was carried out with both an agar culture in root boxes and a hydroponic culture to which 400 mg/L of different factions of humus acids, mixed HA, and raw Leonardite were added. The results showed that applications of HA were significantly improved leaf and root growth of corn seedlings compared with the control (no humic acid addition). In the agar culture,seedlings treated with HA with relatively low molecular weights had more leaves and twice long of roots compared to control and other treatments. In the hydroponic culture, the mixture of three factions was the best treatment for both shoot and root growth of seedlings.5. Ractions of humic substances affected growth and nutrient uptake of lettuce: It is well known that humic materials in soil may affect the growth or nutrient uptake of root and shoot of plants, but existing results have been long reported about direct effects of humic substances, nevertheless, there isn't to date the certainty over the different molecular weight humus made by sedimentation separation. To investigate how different molecular weights of HA alter on the growth of lettuce, we germinated lettuce seed exposed to mixed solution containing rates of organic substances solution. It showed that incorporation of different molecular weight HA with the increasing of applying concentration of HA can enhance the fresh weight of lettuce significantly, and all of these indicated that humic acids with both small and medium molecular can promote the growth and nutrient uptake of lettuce compared with dry matter accumulation at the low, middle, high rate.6. Different chemical activation of humic acid from weathered coal affect the growth of tomatoes and cabbage: Crop productivity is the basis of certain nutrients for human life which depends on amount of available nutrient in the soil. HA (HA ) are the major constituent of organic oxidation products and are formed on coal surface with various molecular weights for different oxidation conditions, and they are soluble in alkaline solutions but become insoluble in acidic solutions. HA activated coal is the new production of humic preparations to be used in the branch of agriculture in recent years. Two commonly used methods (Nitric acid oxidation method and Potassium hydroxide extraction method) were used to activate the weathered coal to find out the best method of making humic acid. We find that coals of Inner Mongolia and Shanxi after activation have more strong effect than raw materials.