**5. References**

FAO, (2006). World Reference Base of Soil Resources. Rome, Italy.


**7** 

*1P.R. China 2Korea* 

**Effect of Mixed Amino Acids on Crop Growth** 

*College of Agriculture and Life Sciences, Chungnam National Univeristy, Taejon,* 

Among the mineral nutrient elements, nitrogen is a kind of macronutrient. Most plant species are able to absorb and assimilate nitrate (NO3–), ammonium (NH4+), urea and amino acids as nitrogen sources. Most soils do not have sufficient N in available form to support desired production levels. Therefore, addition of N from fertilizer is typically needed to maximize crop yields. Many kinds of N fertilizers are used which contain varying forms of

form of N absorbed by plants, regardless of the source of applied N (Breteler and Luczak, 1982). This preference is due to several autotrophic soil bacteria, which rapidly oxidize NH4+

available form of N to plants, it can be more readily lost from the root zone because it is very mobile and easy to leach. This economically and environmentally undesirable process perpetuates a large amount of the uncertainty associated with N fertilizer management

In the soil solution, nitrate is carried towards the root by bulk flow and is absorbed into the epidermal and cortical symplasm. Within the root symplasm, nitrate has four fates: (1) reduced to nitrite by the cytoplasmic enzyme nitrate reductase; (2) efflux back across the plasma membrane to the apoplasm; (3) influx and stored in the vacuole; or (4) transported to the xylem for long−distance translocation to the leaves (Andrews, 1986; Ashley et al., 1975; Black et al., 2002; Cooper and Charkson, 1989). Translocated from the xylem, nitrate enters the leaf apoplasm to reach leaf mesophyll cells, where nitrate is again absorbed and either

Nitrate translocated from the roots through the xylem is absorbed by a mesophyll cell via one of the nitrate−proton symporters into the cytoplasm, reduced to nitrite by nitrate reductase (NR) in the cytoplasm, and then reduced to ammonium by nitrite reductase (NiR)

––N, NH4+–N and urea. However, NO3

**1. Introduction** 

N such as NO3

(Pessarakli, 2002).

Corresponding author

 \*

to NO2–, and then to NO3

**1.1 Nitrogen uptake and assimilation** 

reduced to nitrite or stored in the vacuole.

Xing-Quan Liu1 and Kyu-Seung Lee2\* *1School of Agriculture and Food Science,* 

*2Department of Bio-Environmental Chemistry,* 

– form of nitrogen is the predominant

*Zhejiang Agriculture and Forestry University, Hangzhou,* 

– in warm, well–aerated soils. Even though NO3– is the most

