Studies On Soil Microbial Properties And Their Seasonal Variations Of Different Long-term Fertilization Regimes

Soil quality and soil health are important for the sustainable development of terrestrial ecosystem, and soil microbial properties are important characterizations of soil quality. In this paper, we studied the relationship between soil quality and soil microbial properties such as soil microbial biomass carbon (SMBC),soil microbial biomass nitrogen (SMBN), soil basal respiration, soil enzyme activities and soil microbial diversity (structural diversity and functional diversity) in order to illustrate the function of soil microbial properties as bio-indicators of soil health. Studies, related to these microbial properties, soil fertility and crop production with different fertilization regimes were carried out based on a 15-year long-term fertilizer experiment in Drab Fluvo-aquic soil in Changping County, Beijing, China. At this site, seven different treatments were established in 1991. They were in a wheat-maize rotation receiving either no fertilizer (CK), mineral fertilizers (NPK), mineral fertilizers with wheat straw incorporated (NPKW), mineral fertilizers with 50% more wheat straw incorporated (NPKW+), mineral fertilizers plus swine manure (NPKM), mineral fertilizers plus 50% more swine manure (NPKM+) or mineral fertilizers with maize straw incorporated (NPKS). The amount of mineral fertilizer per year was N160 kg·hm^-2, P35 kg·hm^-2, K 49.8 kg·hm^-2, and they were applied twice annually in early summer after wheat is harvested and fall after maize is harvested. The amount of organic manure or crop straw were swine manure 22.5 t?hm^-2, wheat straw 2.17t·hm^-2 and maize straw 2.17t·hm^-2 reapectively and they were applied once a year in fall after maize is harvested. In this study, we also select four different sampling stages (12^th, April, 2006, wheat-shooting stage; 13^th, June, 2006, wheat-harvest stage; 22^nd, August, 2006, maize-tasselling stage and 29^th, September, 2006, maize-harvest stage) to explore seasonal variation of soil microbial properties in different long-term fertilization regimes. In conclusion, the objective of our study is to investigate the effects of seven long-term (15 years) different fertilization regimes and four different sampling stages on soil microbial properties. The main results are as follows:(1) It was found that the long-term application of NPK gave higher values for the soil total nitrogen (STN), soil total phosphorous (STP), soil organic matter (SOM) than CK, and have 307.4% more wheat yield than CK. The values for the measured soil nutrients and wheat yield were much higher under long-term combined application of NPK plus swine manure or crop straw than under NPK. Meantime, NPK could significantly decrease the ratio of soil carbon to nitrogen (C/N) and the soil pH under Fluvo-aquic soil (the pH around 8.00 in this experimental soil), and long-term combined application of NPK plus swine manure or crop straw decreased soil C/N and pH more obviously than NPK.(2) At wheat-shooting stage, long-term fertilization regimes greatly increased the soil microbial properties (SMBC, SMBN, qMB, soil basal respiration, urease activities, invertase activities and alkaline phosphatase activities). Long-term combined application of NPK plus swine manure or crop straw had a significantly greater impact on the above measured soil microbial properties compared with NPK. The measured parameters increased with increasing application rates of swine manure or wheat straw. Long-term NPK plus swine manure gave higher values for soil microbial properties compared with long-term NPK plus crop straw. But the performance of qCO2 was on the contrary in these fertilization regines. There was no obvious correlation between the soil nutrients and wheat yield, but most of above measured soil microbial properties were positively correlated with soil nutrients and wheat yield, qCO2 was negatively correlated with wheat yield.(3) At wheat-shooting stage, long-term application of NPK plus swine manure or crop straw increased the numbers of bacteria, fungi, Actinomycete and Abiogenous Azotobacter more obviously than CK. NPK plus swine manure had much higher numbers of bacteria, fungi, Actinomycete and Abiogenous Azotobacter than NPK plus crop straw. There were no significantly different numbers of bacteria between under NPK and under CK.(4) Denaturing gradient gel electrophoresis (DGGE) based on 16S rRNA gene was used to determine the bacterial community composition structure and BIOLOG method was used to study the functional diversity of microbial communities. The results indicated that long-term fertilization regimes had greater effects on both bacterial structure composition and microbial functional diversity compared with CK at wheat-shooting stage in April. Bacterial community composition, microbial metabolic activities, and functional diversity indexes of microbial communities from treatments of NPK plus swine manure or crop straw were much higher than those from NPK only. The composition of the bacterial community, microbial metabolic activities and functional diversity indexes in NPKM+ treatment were the highest. Unweighted Pair Group Method Clustering (UPGMC) analysis of the DGGE banding patterns indicated that NPK plus the same organic matters treatments had the highest similarity coefficient. Profiles of NPKS and NPKM (M+) were separated into one group and profiles of NPK and NPKW (W+) into another group. CK and the other 6 fertilization treatments had the lowest similarity coefficient. BIOLOG showed that different carbon types were used by soil microorganisms in different treatments.(5) The above microbial properties such as SMBC, SMBN, soil enzyme activities showed significant seasonal variation, with the highest value being from June to August of the growing season. SMBC changed from 96.49 mg·kg^-1 to 567.36 mg·kg^-1, and SMBN changed from 35.89 to 132.41 mg·kg^-1. Although the seasonal variation, the different fertilization regimes predominated the influence. NPK plus swine manure showed higher values for the soil microbial properties than NPK plus crop straw, and the values in NPK plus crop straw were higher than in NPK. NPKM+ showed the most influence.Fertilization regimes and seasonal variation had obvious influence on the soil microbial diversity separately, and fertilization regimes influenced soil microbial diversity much heavier than seasonal variation. Long-term fertilization regimes increased the soil bacterial composition, improved the microbial functional activity and the ability of using carbon more significantly in September than in April. But in September, NPK showed significantly lower metabolic ability of using carbon than other treatments.