Wu Zj

Changes in Soil Carbon and Enzyme Activity As a Result of Different Long-Term Fertilization Regimes in a Greenhouse Field

In order to discover the advantages and disadvantages of different fertilization regimes and identify the best management practice of fertilization in greenhouse fields, soil enzyme activities involved in carbon (C) transformations, soil chemical characteristics, and crop yields were monitored after long-term (20-year) fertilization regimes, including no fertilizer (CK), 300 kg N ha-1 and 600 kg N ha-1 as urea (N1 and N2), 75 Mg ha-1 horse manure compost (M), and M with either 300 or 600 kg N ha-1 urea (MN1 and MN2). Compared with CK, fertilization increased crop yields by 31% (N2) to 69% (MN1). However, compared with CK, inorganic fertilization (especially N2) also caused soil acidification and salinization. In the N2 treatment, soil total organic carbon (TOC) decreased from 14.1±0.27 g kg-1 at the beginning of the long-term experiment in 1988 to 12.6±0.11 g kg-1 (P<0.05). Compared to CK, N1 and N2 exhibited higher soil α-galactosidase and β-galactosidase activities, but lower soil α-glucosidase and β-glucosidase activities (P<0.05), indicating that inorganic fertilization had different impacts on these C transformation enzymes. Compared with CK, the M, MN1 and MN2 treatments exhibited higher enzyme activities, soil TOC, total nitrogen, dissolved organic C, and microbial biomass C and N. The fertilization regime of the MN1 treatment was identified as optimal because it produced the highest yields and increased soil quality, ensuring sustainability. The results suggest that inorganic fertilizer alone, especially in high amounts, in greenhouse fields is detrimental to soil quality.

Biochar Improves Soil Aggregate Stability and Water Availability in a Mollisol after Three Years of Field Application

A field experiment was carried out to evaluate the effect of organic amendments on soil organic carbon, total nitrogen, bulk density, aggregate stability, field capacity and plant available water in a representative Chinese Mollisol. Four treatments were as follows: no fertilization (CK), application of inorganic fertilizer (NPK), combined application of inorganic fertilizer with maize straw (NPK+S) and addition of biochar with inorganic fertilizer (NPK+B). Our results showed that after three consecutive years of application, the values of soil bulk density were significantly lower in both organic amendment-treated plots than in unamended (CK and NPK) plots. Compared with NPK, NPK+B more effectively increased the contents of soil organic carbon, improved the relative proportion of soil macro-aggregates and mean weight diameter, and enhanced field capacity as well as plant available water. Organic amendments had no obvious effect on soil C/N ratio or wilting coefficient. The results of linear regression indicated that the improvement in soil water retention could be attributed to the increases in soil organic carbon and aggregate stability.

Effects of the nitrification inhibitor DMPP on soil bacterial community in a Cambisol in northeast China

A long-term experimental site was built to study effects of the nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) on a bacterial populations diversity and activity in a Cambisol in northern China. Treatments included no fertilization (CK), application of urea alone (U), and application of urea plus DMPP (UD). The annual application rate for the urea was 180 kg N ha -1 , and that of the DMPP was 1.8 kg ha -1 . The diversity and composition of the overall soil bacterial community were analyzed using pyrosequencing, and the abundances of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) were analyzed using a real-time polymerase chain reaction (RT-PCR) assay. The dominant phyla were Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, Gemmatimonadetes, Chloroflexi, Firmicutes, and Planctomycetes in all of the samples. However, compared with treatment U, the relative abundance and identities of the dominant phyla that were increased in treatment UD were more similar to those of the CK treatment. DMPP significantly reduced the targeted ammonia oxidizing bacterial abundance, and the soil potential nitrification rate had a significant positive correlation with the amoA gene copy number of the AOB (r=0.685, n=9, p<0.05) but not of the AOA. The results suggested that long-term application of DMPP to this agricultural soil was relatively beneficial for both urea application and soil bacterial ecosystem reversion.

The activity and kinetic parameters of oxidoreductases in phaeozem in response to long-term fertiliser management

This study describes the effects of balanced versus nutrient-deficient fertilisation on soil nutrient content and selected oxidoreductase activity and kinetic parameters in a long-term (28 years) field experiment conducted using a phaeozem type soil in the Jilin Province of northeast China. As compared to no or unbalanced fertilisation, balanced fertilisation improved the overall chemical fertility of the soil and sig- nificantly increased the activities and Vmax values of soil dehydrogenase and cata- lase. Compared with control (CK), unbalanced fertilisation (with the exception of P deficiency) significantly increased the total carbon content and soil dehydrogenase activity but had less of an effect on the Vmax of the enzyme, whereas the soil cata- lase activity and its Vmax were less affected under unbalanced fertilisation condi- tions. The Km value of soil dehydrogenase increased with the application of chemi- cal NPK combined with farmyard manure but decreased under the application of NPK, NP, and PK. The Km value of soil catalase decreased under the application of NK and showed little difference between CK and the other fertilisation treatments. The variations in the activities and kinetic parameters of the enzymes revealed the benefits of long-term balanced fertilisation, particularly the combined application of chemical and organic fertilisers, by improving the chemical and biological fertility of phaeozem. The results also indicated that unbalanced fertilisation with P deficiency (NK) could enhance phaeozem quality, but this effect was limited.

Nitrogen Fertilizer and Straw Applications Affect Uptake of 13C,15N-Glycine by Soil Microorganisms in Wheat Growth Stages

This study investigated the influence of nitrogen (N) fertilizer and straw on intact amino acid N uptake by soil microorganisms and the relationship between amino acid turnover and soil properties during the wheat growing season. A wheat pot experiment was carried out with three treatments: control (CK), N fertilizer (NF) and N fertilizer plus rice straw (NS). We used stable isotope compound-specific analysis to determine the uptake of 13C,15N-glycine by soil microorganisms. In the NF treatment, microbial 13C,15N-glycine uptake was lower compared with CK, suggesting that inorganic N was the preferred N source for soil microorganisms. However, The application of straw with N fertilizer (in NS treatment) increased microbial 13C,15N-glycine uptake even with the same amount of N fertilizer application. In this treatment, enzyme activities, soil microbial biomass C and microbial biomass N increased simultaneously because more C was available. Soil mineral N and plant N contents all decreased substantially. The increased uptake of intact 13C,15N-glycine in the NS treatment can be attributed to direct assimilation by soil microorganisms to satisfy the demand for N when inorganic N was consumed.