Bok-Jin Kim

Estimating nitrogen and phosphorus contents using model integrated in small agricultural watersheds.

Abstract The Agricultural Nonpoint Source Pollution Model (AGNPS) was applied to estimate the loads of nitrogen and phosphorus according to antecedent soil moisture conditions (AMC) using probable rainfall in a stream draining small agricultural watersheds. Calibration and verification of the model were performed using observed data collected from rainfall events in the Imgo watersheds during 1997–1998. Evaluation of model outputs was based on graphical displays contrasting observed and simulated values for each rainfall-runoff event, and standard statistics such as coefficient of efficiency. The coefficient of efficiency of peak flow, total N, and total P in the estimation were 0.97, 0.93, and 0.74, respectively. Probable rainfall of Imgo watersheds was computed for several return periods using the frequency analysis of Gumbels extreme value distribution. As the probable flood increase, concentrations of total N and total P generally decrease. Loss of N and P was proportional to the preceding soil water content in the same probable rainfall. The excessive fertilization under AMC-III condition can cause relatively higher outflow of N and P from the soil. It can be concluded that surface runoff and sediment transport influence soil quality and the quality of water absorption and AGNPS can provide realistic estimates of nonpoint source nutrient yields.

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.