Doug-Young Chung

Changes of the Physical Structure and Chemical Properties of Cocopeat Influenced by the Changes of the Components of Cocopeat

To verify the effective usage period of cocopeat as a growth media for plants growing in a greenhouse, we conducted this investigation by observing the changes of physical and chemical properties of cocopeat used as the bag culture substrate of greenhouse tomatoes for three years. The results showed that the organic matter contents and the EC were increased from 82.0 to 96.2% and from 53.5 to 22.2 dS m-1, respectively. Also, cation exchange capacity was significantly increased from 71.0 to 191.7 cmol kg-1, indicating the surface charges were developed by the breakdown of the cocopeat. The surface structure observed with electrical microscope showed that the number of large pores decreased with increasing cultivating time with increasing the proportion of smaller pores within the cocopeat body, indicating that the decomposition of substances inside the cocopeat structures. Also we found that the content of cellulose was rapidly decreased with increasing usage period contrary to the increase in CEC. With these results, we could conclude that these changes of all physical and chemical properties of the cocopeat might strongly influence CEC due to decomposition of lignin within the cocopeat and increasing periods of usage as the substrate of growth media for tomato.

Assessing the Limits of Agricultural Situation for the Food Security in North Korea

Received: August 8, 2017 Revised: August 30, 2017 Accepted: August 31, 2017 The food situation in North Korea (Democratic People’s Republic of Korea, DPRK) has been in difficulty situation because of a shortage of energy, and of raw materials such as fertilizer and agricultural chemicals. The international agricultural aid programs can alleviate some difficulties in the agricultural areas, but the policies and measures in North Korea can not help difficulties in the agriculture due to the institutional obstacles enforced by DPRK. The arable area of DPRK is approximately 20,000 km2, of which 14,000 km2 is well for cereal cultivation. Fertilizer supplies in recent years between 700,000 and 750,000 tons annually were less than 50% of the normal requirement. Also, North Korea strongly needed to inject phosphorus fertilizer and lime to increase the fertility. Soil degradation in DPRK was characterized by physical and chemical changes caused by rapid loss of clay particles and organic matter. Intensive ploughing and tilling to grow crops may lead to massive soil degradation and declining yields. Although farmers in the DPRK have faced numerous challenges, not least of which are soil erosion, scarce inputs and extreme weather like drought, flooding and cold spells. Therefore farmers should be encouraged to adopt more environmentally sound cropping practices, to access quality seeds and planting materials and to reduce losses after the harvest.

Changes in Physical and Chemical Properties of Coir Used as the Bag Culture Substrate of Greenhouse Tomatoes for Three Years

To identify causes for drastic decrease in yield of tomato with repeated culturing number of the bag culture substrate of greenhouse tomatoes we investigated the physical and chemical properties of a coir used as the bag culture substrate to grow tomato at the Booyeo tomato experimental institute located in Booyeo, Chungnam Province for three years from 2012 to 2014. The results showed that total porosity ranged from 65.4 to 73.1% for the bulk densities of coir ranging from 0.12 to 0.14 g cm -3 . The volumetric water contents measured at 0.01 bar as air entry point were 25% (before), 33% (1 st yr), 45% (2 nd yr), and 37% (3 rd yr). Organic matter contents ranged from 82.0 to 96.2% (highest in 1 st yr). pH and EC ranged from 4.47 to 6.47 (highest in 2 nd yr), and from 22.2 to 53.5 dS m -1 (highest in 1 st yr) and cation exchange capacity ranged from 71.0 to 191.7 cmol kg -1 (highest in 3 rd yr). The surface structure observed with electrical microscope showed that the number of large pores decreased with increasing cultivating time while the proportion of smaller pores increased, indicating that the coir was consistently decomposed. Therefore, we could conclude that these changes of all physical and chemical properties of the coir may influence the holding capacities of water and nutrients, resulting in deterioration of quality of culture substrate of greenhouse tomatoes.

Competitive Adsorption and Subsequent Desorption of Sulfate in the Presence of Various Anions in Soils

In this experiment we investigated the influence of various anions including oxalic acid encountered as solution phase in soil on the adsorption and desorption of sulfate in Chungwon Bt soil. The effect of chloride and nitrate on the adsorption of sulfate was not significant, suggesting that sulfate was better able to compete for adsorption sites at concentrations studied, in contrast to the large reduction in the amount of chloride adsorbed in the presence of sulfate. The results of competition for sorption sites between sulfate and anion showed that the simultaneous presence of two anions in solution was effective in reduction of competing anion at a maximum value of adsorption, due to the similar adsorption mechanism for anion competition. Therefore, the variation in the buffer power of the acids will produce a change in the strength and amount of adsorption and the competitive ability.

Leaching of Arsenic in Soils Amended with Crushed Arsenopyrite Rock

Arsenic and its compounds which is one of the most toxic elements that can be found naturally on earth in small concentrations are used in the production of pesticides, herbicides, and insecticides. Most arsenic that cannot be mobilized easily when it is immobile is also found in conjunction with sulfur in minerals such as arsenopyrite (AsFeS), realgar, orpiment and enargite. In this investigation we observed the leaching of arsenic in soils amended with several levels of gravel size of arsenopyrite collected from a road construction site. Soil and gravel size of arsenopyrite were characterized by chemical and mineralogical analyses. Results of XRF analysis of arsenopyrite indicated that the proportion of arsenate was 0.075% (wt wt -1 ) while the maximum amount of arsenic in soil samples was 251.3 mg kg -1 . Cumulative amounts of effluent collected from the bottom of the soil column for different mixing rate of the gravel were gradually increased where proportion of the gravel mixed was greater than 70% whereas the effluent was stabilized to the maximum after approximately 45 pore volumes of effluent or greater were collected. The arsenic in the effluent was recovered from the soil columns in which the proportion of arsenopyrite gravel was 60% or greater. The total amount of arsenic recovered as effluent was increased with increasing proportion of gravel in a soil, indicating that the arsenic in the effluent was closely related with gravel fraction of arsenopyrite.