Jong-Bae Chung

Effects of Long-Term Compost and Fertilizer Application on Soil Phosphorus Status Under Paddy Cropping System

Abstract External phosphorus (P) fertilization in intensive cropping systems often exceeds P demand by crops, which leads to P accumulation in soils. Levels of different pools of soil P have been affected not only by soil properties and climatic condition but also by rate and type of P applied. This experiment was conducted to investigate the long-term applications of compost and chemical fertilizer on soil phosphorus status in paddy cropping system after addition of compost and chemical fertilizers for 34 years in rice monoculture production at National Youngnam Agricultural Experiment Station, Miryang, Korea. Four different treatments of soil amendments were selected in this study: control, compost application, NPK (nitrogen–phosphorus–potassium) fertilizer application, and compost plus NPK fertilizer application. Phosphorus status varied with the long-term applications of compost and fertilizers, and the compost plus NPK fertilizer treatment significantly increased total P in soil. Available P was increased in the treatments that received chemical fertilizers. Applications of compost and chemical fertilizers increased organic P fraction but the ratio of organic P to total P declined with application of compost or chemical fertilizers. Phosphorus-fixation was significantly increased due to the long-term application of compost and chemical fertilizers. The P fixation was highest with iron (Fe) than with aluminum (Al) and calcium (Ca) in the paddy soil. The highest Fe-P content occurred in the compost plus NPK fertilizer treatment. These results represented that the higher level of P remaining in the soil is accumulated by long-term annual application of compost and chemical fertilizers than by that of chemical fertilizer, and P accumulation might be a gradual saturation of the P-sorption capacity.

Chromium Oxidation Potential and Related Soil Characteristics in Arable Upland Soils

Oxidation of Cr(III) to Cr(VI) can increase availability and toxicity of chromium. In this study, the potential of chromium oxidation in arable upland soils was evaluated with a quick test and its relationships with some soil characteristics were investigated. Also, the possibility of Cr(VI) generation was tested in arable upland soils amended with Cr-containing sludge. Thirty-seven out of the forty-five arable upland soils tested could oxidize Cr(III) to Cr(VI). Since manganese (Mn)-oxide is the only known oxidant of chromium in natural conditions, oxidation potential was directly related with Mn-oxide content in the soils. Also, soil pH and organic matter content had a very significant relationship with chromium oxidation in soil. As the pH was higher and the organic matter content lower, the chromium oxidation potential was higher. Soil pH and organic matter seem to be important controlling factors for Mn-oxide content in soils. Manganese-oxides can be dissolved reductively at lower pH and higher organic matter conditions. Soils of high chromium oxidation potential amended with Cr-containing sludge could generate Cr(VI) in laboratory incubation. However, oxidation of the amended Cr(III) was not found in soils of low chromium oxidation potential. In land application of sewage sludges, care should be taken with soil types, because the soils high in Mn-oxides and low in organic matter are able to oxidize chromium. By controlling organic matter content and pH of soils, the risk from oxidized chromium would be reduced in agricultural environments amended with chromium containing wastes.

Low Water Potential in Saline Soils Enhances Nitrate Accumulation of Lettuce

Abstract The relationship between nitrate accumulation of lettuce and soil salinity in plastic film house was investigated, and the effect of water stress on the nitrate accumulation in lettuce was further examined in nutrient solutions of different water potentials. Nitrate contents in fresh lettuce were in the range of 85–2510 mg kg−1, and the content increased as soil electrical conductivity increased up to 5 dS m−1. Nitrate content in lettuce increased significantly as water potential in the nutrient solution decreased under low light intensity and an ample supply of nitrate. Soluble sugar and oxalate contents also increased with water stress. However, the changes of nitrate contents in response to the water potential changes were more significant than those of organic compounds. These results confirm the osmotic regulatory function of nitrate in replacement of organic compounds in lettuce grown in plastic film house where light intensity and soil water potential are low.

Chemical Insecticide Effects on Growth and Nitrogenase Activity of Azospirillum sp. OAD-2

Abstract The growth and nitrogenase activity of Azospirillum OAD-2 were examined in presence of five insecticides at recommended dose (RD), half dose (HD), and double recommended dose (DRD). The growth of the Azospirillum sp. OAD-2 in Luria agar plates was inhibited in descending order by chlorpyrifos, fenvalerate, quinalphos, monocrotophos, and endosulfan. The inhibition zone of Azospirillum sp. OAD-2 ranged from 2.6 to 13.2 mm and 5 to 20 mm at RD (2 mL L−1) and DRD (4 mL L−1) of insecticides, respectively. The growth of Azospirillum sp. OAD-2 in semisolid N free medium was not affected by endosulfan and monocrotophos, but inhibited by chlorpyrifos, fenvalerate, and quinalphos. However, Azospirillum sp. OAD-2 growth in malate liquid medium plus endosulfan or monocrotophos, was initially decreased (lag phase), increased after 24 h and cell growth attained a stationary phase after 48 h. Two organophosphorus insecticides, chlorpyrifos and quinalphos, and a pyrethroid, insecticides fenvalerate inhibited growth and nitrogenase activity of Azospirillum OAD-2 at all concentrations. Conversely, endosulfan (organoclorine) and monocrotophos (organophosphorus) had no detrimental effect on growth and nitrogenease activity of Azospirillum OAD-2 at RD (2 mL L−1).

Availability of Silicate Fertilizer and its Effect on Soil pH in Upland Soils

Although silicon (Si) has been Down to be an essential element fer rice growth, the optimum soil level of Si for upland crops remains unestablished. This study was conducted to estimate the availability of Si fertilizer in upland soils, and also effect of the Si fertilizer on soil pH was examined. Different application rates of Si fertilizer were tested using faur soils of different available Si levels and pHs in a series of laboratory incubation study. The treatments included Si fertilizer levels of 100, 200, and 300 kg/10a. Also to examine the effects of compost and lime on the availability of Si fertilizer in upland soil, treatment of silicate fertilizer 200 kg/10a + compost 1,000 kg/10a and lime alone treatment were included. Changes of Si availability in the soils during the incubation period were measured by 1 N NaOAc extraction procedure. Availability of Si fertilizer was different among the tested soils, and about of the applied Si fertilizer was extracted after 60 days laboratory incubation. Application rate could not influence the availability of Si fertilizer. Application of compost with Si fertilizer could not increase Si availability in upland soils, but lime treatment could increase Si availability. Soil pH increased by application of Si fertilizer, but the effect of Si fertilizer on soil pH was minimal. When Si fertilizer is applied on the purpose of Si nutrition in acid upland soils, lime treatment should be coupled with the Si fertilizer for remediation of soil acidity.

Suppression of Powdery Mildew Development in Oriental Melon by Silicate Fertilizer

Silicon is known to accumulate in plants and results in greater resistance to diseases and insect pests. In this study, we investigated the effect of silicate fertilizer applied in soil on the development of powdery mildew of oriental melon. Oriental melon seedlings of four-leaf stage were transplanted and grown in a plastic film house. Silicate fertilizer was applied to maintain soil available level of 200 mg/kg one week before transplanting. Fungicide triflumizol was sprayed three times; one, two, and three weeks after transplanting. Sphaerotheca fuliginea was inoculated 2 weeks after transplanting. The number of infected leaf and the number of fungal colony in leaves were measured one, two, and three weeks after the inoculation. Three weeks after the fungal inoculation, in the treatment of fungicide triflumizol. infected leaf numbers and number of colony per leaf were reduced by 10 and 58%, respectively. In the silicate fertilizer treatment, infected leaf numbers and numbers of colony per infected leaf were suppressed only by 6 and 16%, respectively, and the efficacy was lower than that of the fungicide triflumizol. The combined treatment of silicate fertilizer and the fungicide suppressed powdery mildew more effectively, and infected leaf numbers and numbers of colony per leaf were reduced by 31 and 80%, respectively. These results indicate that although silicate fertilizer itself is not much effective in the suppression of powdery mildew, it can significantly enhance the efficacy of the fungicide.

Comparison of Nitrate Accumulation in Lettuce Grown under Chemical Fertilizer or Compost Applications

Accumulation of nitrate in green vegetables is undesirable due to potential risks to human health. Lettuce was cultivated in pots under greenhouse conditions with compost applications of 2,000 and 4,000 kg/10a, and the growth and nitrate accumulation of lettuce were compared with those found in the lettuce cultivated with chemical fertilizers of recommended levels. Content of in the soils of compost applications were much lower than those found in the soil of chemical fertilizer application. Two weeks after lettuce transplant was not found in the soils of compost applications, and in the soils of chemical fertilizers application was not found three weeks after lettuce transplant. One week after lettuce transplant content of was much higher in the soils of compost applications, and the contents were rapidly decreased. While, the content of in the soil of chemical fertilizers application was rapidly increased due to the nitrification of released from the applied urea. At the time of harvest contents of in the soils of compost applications were less than 1.4 mg/kg, but in the soil of chemical fertilizers application the content of was 54.2 mg/kg. Contents of in lettuce were about 20 mg/kg FW and were not much different among the treatments. However, contents of in lettuce were significantly different between the treatments of chemical fertilizer and compost. There were significant differences in fresh and dry weights, and growth of lettuce in the compost treatment of 4,000 kg/10a was highest among the treatments. These results indicate that the cultivation with compost only as N source can produce higher yield of lettuce and significantly reduce nitrate accumulation as compared to the conventional cultivation with chemical fertilizers.

Relationships between Micronutrient Contents in Soils and Crops of Plastic Film House

Micronutrient status in soils and crops of plastic film house and their relationship were investigated. Total 203 plastic film houses were selected (red pepper, 66; cucumber, 63; tomato, 74) in Yeongnam region and soil and leaf samples were collected. Hot-water extractable B and 0.1 N HCl extractable Cu, Zn, Fe, and Mn in soil samples and total micronutrients in leaf samples were analyzed. Contents Zn, Fe, and Mn in most of the investigated soils were higher than the upper limits of optimum level for general crop cultivation. Contents of Cu in most soils of cucumber and tomato cultivation were higher than the upper limit of optimum level, but Cu contents in about 30% of red pepper cultivation soils were below the sufficient level. Contents of B in most soils of cucumber and tomato were above the sufficient level but in 48% of red pepper cultivation soils B were found to be deficient. Micronutrient contents in leaf of investigated crops were much variable. Contents of B, Fe, and Mn were mostly within the sufficient levels, while in 71% of red pepper samples Cu was under deficient level and in 44% of cucumber samples Cu contents were higher than the upper limit of sufficient level. Contents of Zn in red pepper and cucumber samples were mostly within the sufficient level but in 62% of tomato samples Zn contents were under deficient condition. However, any visible deficiency or toxicity symptoms of micronutrients were not found in the crops. No consistent relationships were found between micronutrient contents in soil and leaf, and this indicates that growth and absorption activity of root and interactions among the nutrients in soil might be important factors in overall micronutrient uptake of crops. For best management of micronutrients in plastic film house, much attention should be focused on the management of soil and plant characteristics which control the micronutrient uptake of crops.

Tertiary Treatment of Municipal Wastewater Using Unsaturated Sandy Soil

Treatment of secondary effluent was investigated using sandy soil as a possible alternative to the tertiary treatment of municipal wastewater. Secondary effluent was applied with three different flow rates to the surface of pilot scaled lysimeters, which were filled with sandy soil. Some of the lysimeters were covered with osd, while others were kept bare in order to investigate the role of plantation on the treatment. The concentration changes in COD and nitrogen were measured along the unsaturated soil depth. The same set of experiment as with the secondary effluent was performed using tap water to investigate the dissolution of the contaminants from the soil. from the results it was found that when sandy soil was used for tertiary treatment of municipal wastewater COD removal efficiency reached about 70% regardless of the application rate. The soil depth needed to obtain such efficiency increased along with the application rate, which was about 60 cm at the application rate of 50 L/day. Results also showed that nitrification occurred rapidly. The process was completed in soil depth of first . Nitrogen removal efficiency was as low as about 20% regardless of the application rate. Some supplementary means should be considered to improve the efficiency. Sod on the soil surface had no significant influence on the contaminant treatment but was helpful to keep the infiltration rate undiminished. Finally, the organic soil was found to release significant amount of contaminants when it was in contact with soil water.

Extractable Heavy Metals in Phosphogypsum

In addition to supplying the essential elements, Ca and S, phosphogypsum can have profound effect on both the physical and chemical properties of certain soils. However, no widespread use of by-product phosphogypsum will be made unless such uses pose no threat to the public health and soil contamination. In this study, the extractability of As, Cd, Cu, and Pb with water and DTPA solution from phosphogypsum samples of pH 3, 5, and 7 were investigated to estimate the availability of those metals. Contents of water extractable metals in ohosphogypsum were less than 5 mg/kg for all the heavy metals investigated. The extractability of metals in DTPA solution was not quite different but a little higher in comparison to the water extraction. And the extractability was decreased as the pH of phosphogypsum increased. In the phosphogypsum of pH 7, amounts of water extractable metals were nearly zero. There was no significant difference in the amount of extractable metals during the extraction period of 5 weeks. The length of extraction time did not affect heavy metal extractability. Therefore there may be small fractions of easily soluble or extractable forms of metals in the phosphogypsum and most of the metals would be present in very insoluble forms. These results suggest that the application of phosphogypsum at appropriate rates on agricultural lands appears of no concern in terms of hazardous element contamination in soil.