Organic nitrogen components in soils from southeast China

Area of Science:

• Soil Science
• Agricultural Chemistry
• Plant Nutrition

Background:

• Extractable organic nitrogen (EON) constitutes a substantial fraction of total extractable nitrogen (TEN) in soils.
• Understanding the composition and dynamics of EON, especially amino acids (AAs), is crucial for soil fertility and plant nutrition.
• The rhizosphere, the soil zone directly influenced by plant roots, plays a vital role in nutrient cycling.

Purpose of the Study:

• To quantify extractable organic nitrogen (EON) and total extractable nitrogen (TEN) in typical Southeast China soils.
• To investigate the relationships between EON, TEN, and soil amino acids (AAs).
• To evaluate the role of EON and AAs in the rhizosphere and bulk soil under traditional agricultural practices.

Main Methods:

• Pot experiments were conducted using pakchoi and rice.
• Organic nitrogen components were extracted using distilled water, 0.5 mol/L K2SO4, or acid hydrolysis.
• Analysis focused on EON, TEN, and AAs in both rhizosphere and bulk soil.

Main Results:

• K2SO4-extractable EON comprised over 30% of TEN pools.
• K2SO4-extractable AAs represented 25% of EON and nearly 10% of TEN in rhizosphere soils.
• Positive correlations were observed between K2SO4-EON, extractable AAs, and TEN pools.

Conclusions:

• EON is a major component of TEN in garden and paddy soils under traditional cultivation.
• The release of AAs from soil exchangeable sites may be a key source of organic nitrogen for plants.
• Most organic nitrogen forms were higher in the rhizosphere than in bulk soil, though total TEN was lower in the rhizosphere without added nitrogen.