Influence of Long-Term Localized Fertilizer Applications on Soil Organo-Mineral Complexes in a Sheltered Vegetable Field

Organo-mineral interactions are considered to play a relevant role in organic matter (OM) protection against biodegradation in regard to soil developed under sheltered vegetable conditions. However, little is known about the effect of fertilizer applications on the composition of organo-mineral interactions. A long-term (16 years) fertilizer experiment was carried out in a sheltered vegetable field at Shenyang Agricultural University, Shenyang, China, in order to study the effects of different fertilizer applications on organo-mineral complexes. It was found that a long-term application of a combination of organic plus chemical fertilizers induced a higher concentration of OM than applying chemical fertilizers alone, and loosely bound humic (LB-H) slightly increased with application of a combination of organic and chemical fertilizers. No significant influence on firmly bound humic (FB-H) was found among the chemical fertilizer treatments, whereas the application of organic fertilizer slightly decreased the content of FB-H compared to chemical fertilizer treatments. More tightly bound humic (TB-H) was observed in organic fertilizer treatments than in chemical fertilizer treatments, and its highest concentration (11.53 g kg-1) was in the treatment of organic fertilizer plus nitrogen (N)-phosphorus (P)-potassium (K) chemical fertilizers. The ratio of LB-H/TB-H tended to decrease after a long-term application of organic fertilizer, being the lowest (1.10) in the treatment of organic fertilizer plus P-K chemical fertilizer.