| Fertilization is an important measure in agricultural production, and meanwhile crop rotation is the essence of traditional agriculture. Long-term rotation and fertilization is of great significance in soil improving fertility and soil quality. Based on the long-term rotation and fertilization experiment on loess plateau set by Chinese Academy of Sciences, this paper studied the effect of long-term rotation and fertilization on soil microbiological properties and evaluated the biological fertility. The experiment including eight cropping systems and eight fertilization treatments, and 29 treatments were used in the study. All the soil samples determined physical and chemical properties, cultivable microorganisms, microbial biomass and enzyme activities in 2011, physical and chemical properties, microbial biomass and soil respiration in 2012. In this paper, the effects of crop rotation, fertilization, stubbles and cropping years on soil physical, chemical and microbial properties were analyzed and the biological fertility was evaluated. The results and conclusions were as following:(1) Compared with the other cropping systems, continuous cropping of alfalfa(AC) significantly improved the concentration of the organic matter, total nitrogen and alkali-hydrolyzale nitrogen, and significantly reduced the soil pH value. Continuous cropping of maize(MC) consumed more total nutrients relative to the other cropping systems, and consumed more available nutrient than grain-legume rotation(GLR) and grain-maize rotation(GMR). In different cropping systems, P fertilization significantly increased the concentration of total phosphorus and available phosphorus relative to unfertilized control(CK), while the concentration of total phosphorus increased 10.95%-61.76% and the concentration of available phosphorus increased 3.42-12.65 times, in which GLR-P increased most. Compared with CK, N fertilization only had a significant influence on soil total nitrogen and alkali-hydrolyzale nitrogen. Organic fertilization improved soil nutrients, and a combined application of N, P and manure(NPM) had better effect on improving soil nutrient. Compared with fallow control(FW) and continuous cropping of winter wheat cropping(WC), the concentrations of organic matter, total nitrogen and alkali-hydrolyzale nitrogen increased and the soil pH value reduced in eight-years grain-grass rotation(ER) and three-years grain-grass rotation(TR). Planting alfalfa in ER and sainfoin in TR had higher concentration of organic matter, total nitrogen and available nitrogen than the other plants in the same rotation system. TR was more advantageous in improving soil nutrients and reducing pH value than ER. With the cropping year increased, the concentration of soil total nitrogen of AC-CK increased, and which of WC-CK and GLR-CK decreased. With NPM fertilization, the concentration of organic matter, total nitrogen and available phosphorus increased in AC, WC, GLR and GMR, and the concentration of available phosphorus decrease in continuous cropping of maize(MC).(2) Compared with FW, planting crops increased soil bacteria amount, fungi amount and actinomyces amount. AC stimulated the growth of fungi. The fungi amount and proportion of total culturable microorganism of AC were higher than GLR and GMR. Compared with continuous cropping, rotation created the beneficial conditions for the growth of bacteria. The bacteria amount and total culturable microorganism amount of GMR were 34.03×106 cfu/g and 42.58×106 cfu/g. Compared with FW, organic fertilization had positive effects on the growth of bacteria, fungi and actinomyces, and NPM also had higher bacteria proportion of total culturable microorganism than CK. Compared with FW, N fertilization and P fertilization were unfavorable for the increase of bacteria amount and proportion of total culturable microorganism. However, the fungi amount of P fertiliazation in GLR increased 1.55×103 cfu/g and the fungi proportion of total culturable microorganism inceased 0.03%. N fertilization and P fertilization were unfavorable for the healthy community structure formed. ER and TR had higher proportion of total culturable microorganism than WC, and TR had higher total culturable microorganism amount than ER. Planting potato in ER stimulated the growth of fungi, the fungi amont increased at most 2.12 times and the fungi proportion of total culturable microorganism increased at most 6.00 times relative to the other plants in ER. All the cropping systems with NPM fertilization promoted the growth of bacteria amount after long-term cropping, the bacteria amount after 27 years cropping increased 53.73—176.80×106 cfu/g than after 15 years cropping. After 27 years cropping, the fungi amount of NPM fertilization in AC increased 19.02×103 cfu/g than after 15 years cropping, which reflected long-term continuous cropping of alfalfa with fertilizers result in soil unhealthy development.(3) Planting crops increased the concentration of microbial biomass carbon(C), microbial biomass nitrogen(N) and microbial quotient relative to FW. Compared with the other cropping systems, the concentration of microbial biomass C and microbial biomass N increased in AC and decreased in MC. In all the cropping systems, P fertilization increased the concentration of microbial biomass N relative to CK, the concentration of microbial biomass C increased or decreased in different cropping system. Compared with CK, Organic fertilization increased the input of organic matters, stimulated the growth of organism, and then increased the concentration of microbial biomass C and microbial biomass N. ER and TR promoted the increase of microbial biomass C and microbial biomass N relative to FW and WC. The concentration of microbial biomass C, microbial quotient and microbial biomass C/ microbial biomass N(Cmic/Nmic) of TR were higher than ER. In all the cropping systems with fertilizer treatments, the concentration of microbial biomass C and microbial biomass N increased with the cropping years increasing. In different systems, the annually increase of microbial biomass C ranged from 1.85 to 69.08 mg/kg, the annually increase of microbial biomass N ranged from 1.45 to 10.15 mg/kg.(4) The activity of sucrase, urease and alkaline phosphatase of AC were higher relative to the other cropping systems. MC decreased the activity of sucrase, alkaline phosphatase and catalase, in which the alkaline phosphatase significantly decreased 32.87%—51.78%. In all the cropping systems, P fertilization increased the activity of sucrase relative to CK, N fertilization decreased enzyme activity and in which the activity of sucrase decreased 7.92%. Compared with CK, NPM fertilization increased the activity of urease, alkaline phosphatase and catalase. ER and TR increased the activity of urease, alkaline phosphatase relative to FW and WC. Planting potato in ER increased the activity of urease, and the value increased 4.36% relative to the former alfalfa planting. Planting winter wheat increased the activity of sucrase, urease and alkaline phosphatase relative to planting alfalfa in ER. ER was more favorable for the increase of enzyme activity than TR. After 27 years cropping, the activity of catalase of fertilization treatments increased than after 15 years cropping, the activity of sucrase, urease and alkaline phosphatase ranged differently in different cropping systems.(5) The soil basal respiration of FW was higher than the other cropping systems, the soil potential respiration of AC and WC increased 22.52%—87.23%. The soil microbial metabolic quotient and microbial potential metabolic quotient of MC, GLR and GMR decreased than WC and GMR, which was benefit for the improvement of carbon utilization efficiency by microorganism and the activity of microorganism. Compared with CK, organic fertilization promoted the soil basal respiration and soil potential respiration. N fertilization and P fertilization had no promotion on soil respiration relative to CK, and N fertilization even inhibited soil respiration. In the meantime fertilization decreased the metabolic quotient. ER and TR stimulated the soil potential respiration, and increased 29.66% and 11.33% respectively relative to FW. The metabolic quotient and potential metabolic quotient of ER and TR decreased 45.78%—73.68% relative to FW. Planting alfalfa in ER decreased soil respiration, metabolic quotient, and potential metabolic quotient relative to other crops planting in the same system. Planting sainfoin in TR increased soil respiration relative to planting winter wheat in the same system. The soil basal respiration of TR increased 2.67 mg CO2/(kg·h), the metabolic quotient decreased 0.01 d-1 and the potential metabolic quotient decreased 0.46 d-1 relative to ER. The grain-grass rotation had well potential mineralization and carbon utilization efficiency by microorganism, and TR had better activity of microorganism than ER. Correlation relationship showed that the metabolic quotient and the potential metabolic quotient had more close relations to microbial biomass C, microbial biomass N, organic matter and total nitrogen relative to soil respiration, which means the metabolic quotient and the potential metabolic quotient are more suitable microbial index for soil fertility evaluation relative to soil respiration.(6) As the response of different biological fertility factor to long-term rotation and fertilization was different, single index was hardly to evaluate soil biological fertility. In order to well analyze the effect of long-term rotation and fertilization on heilu soil biological fertility on loess plateau, ten biological fertility factors were used as the indexes of biological fertility evaluation. Cumulated frequency method was used to determine the threshold value of subordinating degree function and weighted sum method was used to evaluate the soil biological fertility. The soil biological fertility of AC was higher than the other cropping systems under different fertilization, and the soil biological fertility of MC was the lowest among cropping systems. In all the cropping systems, application of NPM increase soil biological fertility relative to CK and P fertilization, and the increase of soil biological fertility of GLR was higher than the other cropping systems, which means the effect of NPM fertilization on soil microorganism activity was stronger in GLR. The effect of stubble was weaker than rotation and fertilization. Planting different crops in ER has no significant effect on soil biological fertility and planting sainfoin decreased soil biological fertility relative to winter wheat and winter wheat + sainfoin. Long-term rotation and fertilization maintained or improved soil biological fertility, and the increase of soil biological fertility of NPM fertilization in MC, GLR and GMR were higher than the other treatments. In conclusion, AC, GLR and GMR with NPM fertilization can significantly improve soil biological fertility, and MC, GLR and GMR with NPM fertilization had tremendous potential to improve soil biological fertility... |
PDF Full Text Request