Organic nitrogen components in soils from southeast China.

OBJECTIVE: To investigate the amounts of extractable organic nitrogen (EON), and the relationships between EON and total extractable nitrogen (TEN), especially the amino acids (AAs) adsorbed by soils, and a series of other hydrolyzed soil nitrogen indices in typical land use soil types from southeast China. Under traditional agricultural planting conditions, the functions of EON, especially AAs in the rhizosphere and in bulk soil zones were also investigated. METHODS: Pot experiments were conducted using plants of pakchoi (Brassica chinensis L.) and rice (Oryza sativa L.). In the rhizosphere and bulk soil zone studies, organic nitrogen components were extracted with either distilled water, 0.5 mol/L K2SO4 or acid hydrolysis. RESULTS: K2SO4-EON constituted more than 30% of TEN pools. K2SO4-extractable AAs accounted for 25% of EON pools and nearly 10% of TEN pools in rhizosphere soils. Overall, both K2SO4-EON and extractable AAs contents had positive correlations with TEN pools. CONCLUSIONS: EON represented a major component of TEN pools in garden and paddy soils under traditional planting conditions. Although only a small proportion of the EON was present in the form of water-extractable and K2SO4-extractable AAs, the release of AAs from soil exchangeable sites might be an important source of organic nitrogen (N) for plant growth. Our findings suggest that the content of most organic forms of N was significantly greater in rhizosphere than in bulk soil zone samples. However, it was also apparent that the TEN pool content was lower in rhizosphere than in bulk soil samples without added N.

Effects of a new nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on nitrate and potassium leaching in two soils.

In this study, soil column was used to study the new nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on nitrate (NO3(-)-N) and potassium (K) leaching in the sandy loam soil and clay loam soil. The results showed that DMPP with ammonium sulphate nitrate (ASN) ((NH4)2SO4 and NH4NO3) or urea could reduce NO3(-)-N leaching significantly, whereas ammonium (NH4(+)-N) leaching increased slightly. In case of total N (NO3(-)-N+NH4(+)-N), losses by leaching during the experimental period (40 d) were 37.93 mg (urea), 31.61 mg (urea+DMPP), 108.10 mg (ASN), 60.70 mg (ASN+DMPP) in the sandy loam soil, and 30.54 mg (urea), 21.05 mg (urea+DMPP), 37.86 mg (ASN), 31.09 mg (ASN+DMPP) in the clay loam soil, respectively. DMPP-amended soil led to the maintenance of relatively high levels of NH4(+)-N and low levels of NO3(-)-N in soil, and nitrification was slower. DMPP supplementation also resulted in less potassium leached, but the difference was not significant except the treatment of ASN and ASN+DMPP in the sandy loam soil. Above results indicate that DMPP is a good nitrification inhibitor, the efficiency of DMPP seems better in the sandy loam soil than in the clay loam soil and lasts longer.

[Effects of DMPP-compound fertilizer on greenhouse celery growth and nutritional quality].

A field study with greenhouse celery (Apium graveolens L. ) showed that compared with basal application of ordinary compound fertilizer, one-time basal application of DMPP-compound fertilizer ( ENTEC , 12-12-17) at the rates of 67. 5 kg N x hm(-2) and 54. 0 kg N x hm(-2) increased the yield by 5. 78% and 10. 14% , respectively. The application of ENTEC also improved the nutritional quality of edible parts, e. g. , the Vc, amino acid, soluble sugar, N and P contents increased, while nitrate content decreased. Compared with basal plus side dressing applications, appropriately reducing the application rate and times of ENTEChad more beneficial effects on celery yield and quality, and reduced the production costs. ENTEC could suppress the transformation of soil NH4+ -N to NO3 - -N effectively, and thus, its application could retain soil residual N more in NH4+ -N than in NO3- -N form after celery harvested, resulting in a reduction of nitrate leaching.