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Plant can directly take up the intact amino acids, thus bypass the microbial mineralization of organic nitrogen. As an excellent carbon and nitrogen source, there exists competition for amino acid absorption between plant roots and soil microorganisms. And the total flux of amino acids in soil may be enormous due to the extensive sources and short hall-life. Studies on amino acid nitrogen nutritional contribution for plant by the technique of nitrogen isotopic tracer, has become a research topic in recent years, which will help us better understand the principle of soil fertility. This paper summarized the recent researches on amino acid morphological characteristics in soil and its metabolic mechanism and nitrogen nutritional contribution for plant in different ecosystems, and discussed the present status and development trend of the amino acid circulation mechanism in the plant-soil-microorganism ecosystem and its bioavailability for plant. Finally, the topics of environmental regulating mechanism of amino acid bioavailability, amino acid carbon-nitrogen metabolism, and how to improve the field organic nitrogen management were all the core issues to be resolved. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to study the effect of spent mushroom compost ( SMC) in alleviating greenhouse soil secondary salinization and cabbage salt stress. With the amendment of SMC, the salinized soil after 60 day cabbage cultivation had a pH value close to 7. 0, its organic matter and available phosphorous contents increased significantly, and the increment of total water-soluble salt content reduced, compared with the control. When the amendment amount of SMC was 10 g ∙ kg-1 the increment of soil water soluble salt content was the least, suggesting that appropriate amendment with SMC could reduce the salt accumulation in greenhouse soil. Amendment with SMC increased the cabbage seed germination rate, plant height, plant fresh mass, chlorophyll SPAD value, and vitamin C content, and decreased the proline content significantly. All the results indicated that SMC could improve the growth environment of greenhouse cabbage, and effectively alleviate the detrimental effect of salt stress. [ABSTRACT FROM AUTHOR]

With two rice genotypes (cv. Zhongbu 51 and Azucena) differing in their root-secreted acid phosphatase activity (APA) under low P condition as test materials, an agar culture experiment was conducted to investigate their P utilization from myo-inositol hexaphosphate (IHP) under conditions of sterilization and inoculating with soil microorganisms. Under sterilization, the shoot dry mass, P absorption and P concentration of test genotypes supplied with hexaphosphate (IHP) as the P source were significantly higher than those with no P supply, but significantly lower than those supplied with inorganic P, indicating that rice plants could partly acquire P from IHP under sterilized condition. The root-secreted APA of the two genotypes was significantly higher under low P than under sufficient P supply, and the higher APA of Zhongbu 51 under low P could be one of the mechanisms of higher P utilization capability of Zhongbu 51 than Azucena under deficient P supply. When supplied with high level IHP (0.96 mmol P · L-1), the shoot dry mass, P absorption and P concentration of both Zhongbu 51 and Azucena were higher than those when supplied with low level IHP (0.16 mmol P · L-1), indicating that substrate availability could be one of the limiting factors to the utilization of phytate by rice. Inoculation with soil microorganisms had no significant effects on the shoot dry mass, P absorption and P concentration of rice plants, regardless of IHP level and rice genotypes, implying that the utilization of IHP by rice could not be improved via inoculation with soil microorganisms. [ABSTRACT FROM AUTHOR]

The influence of nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) on nitrate accumulation in greengrocery (Brassica campestris L. ssp. chinensis) and vegetable soil at surface layer were investigated in field experiments in 2002 and 2003. Results showed that NI DMPP took no significant effect on yields of edible parts of greengrocery, but it could significantly decrease NO_3^--N concentration in greengrccery and in vegetable soil at surface layer. In addition, NI DMPP could reduce the NO_3^--N concentration during the prophase stage of storage. [ABSTRACT FROM AUTHOR]

Field experiments were conducted to investigate the effects of four fertilization treatments, that is, controlled-release fertilizer (CRF), biochar combined with controlled-release fertilizer (BC+ CRF), biochar combined with stabilized fertilizer (BC+ SF), and biochar combined with controlled-release fertilizer and stabilized fertilizer (BC+ CRF+ SF), on the dynamics of the pH and nitrogen mass concentration and runoff losses of nitrogen in paddy field surface water in the Taihu Lake Basin. The results show that the average pH of the surface water decreases by 3.16%-4.48% for BC+ CRF+ SF and is in the range of 5.64-8.15. The average total nitrogen (TN) mass concentration of surface water ranges from 19.05 to 25.23 mg·L -1 . A significant decrease of 4.75%-6.58% in the TN mass concentration of surface water was observed for BC+ CRF+ SF. The average ammonium (NH 4 + -N) and nitrate (NO 3 - -N) mass concentration of the surface water vary from 0.01-17.26 mg·L -1 and from 0.24-3.11 mg·L -1 , respectively. Inorganic nitrogen is dominated by NH 4 + -N in surface water. Compared with individual CRF, other treatments significantly reduce the NH 4 + -N mass concentration of surface water by 35.89%-48.78% and the NO 3 - -N mass concentration of surface water by 20.54%-37.01%. The BC+ SF combination shows a significant reduction in the NH 4 + -N and NO 3 - -N mass concentration of the surface water, which greatly lowers the risk of inorganic nitrogen loss via runoff. The runoff losses of TN, NH 4 + -N, and NO 3 - -N are in the range of 16.24-18.09, 1.76-2.22 and 0.76-1.38 kg·hm -2 , respectively. Compared with the individual CRF, the runoff loss of TN, NH 4 + -N, and NO 3 - -N of other treatments is reduced. The BC+ CRF+ SF combination shows a significant reduction in the runoff losses of nitrogen, which greatly lowers the risk of nitrogen nonpoint source pollution from paddy fields.

Currently, reasonable disposal of municipal sewage sludge is one of the important issues in the field of resources and environmental science. Sludge is rich in large amounts of organic matter and available nutrients, promoting soil fertility, soil physical structure and biological properties. However, sludge contains a variety of heavy metals, organic contaminants and other hazardous substance, especially heavy metals, which are the bottlenecks of agricultural application of sludge. To improve the sewage sludge utilization efficiency and decrease the effect on soil, this essay made a summary on domestic and foreign studies on plant-soil interaction ecosystem with sewage sludge to provide a theoretical basis and scientific guidance for advancing sewage sludge utilization efficiency.

Organic nitrogen can play an important role in plant growth, and soil pH changed greatly due to the over-use of chemical fertilizers, but the effects of soil pH on the competitive uptake of amino acids by plants and rhizosphere microorganisms are lack of detailed research. To study the effects of soil pH on the uptake of amino acids by maize and soil microorganisms, two soils from Hangzhou and Tieling were selected, and the soil pH was changed by the electrokinesis, then the 15 N-labeled glycine was injected to the centrifuge tube with a short-term uptake of 4 h. Soil pH had a significant effect on the shoot and root biomass, and the optimal pH for maize shoot growth was 6.48 for Hangzhou red soil, while it was 7.65 for Tieling brown soil. For Hangzhou soil, the 15 N abundance of maize shoots under pH=6.48 was significantly higher than under other treatments, and the uptake amount of 15 N-glycine was also much higher. However, the 15 N abundance of maize shoots and roots under pH=7.65 Tieling soil was significantly lower than it under pH=5.78, but the uptake amount of 15 N-glycine under pH=7.65 was much higher. The microbial biomass C was much higher in pH=6.48 Hangzhou soil, while it was much lower in pH=7.65 Tieling soil. According to the results of root uptake, root to shoot transportation, and the competition with microorganisms, we suggested that although facing the fierce competition with microorganisms, the maize grown in pH=6.48 Hangzhou soil increased the uptake of glycine by increasing its root uptake and root to shoot transportation. While in pH=7.65 Tieling soil, the activity of microorganisms was decreased, which decreased the competition with maize for glycine, and increased the uptake of glycine by maize.

Addition of urease inhibitors is one of the important measures to increase nitrogen (N) use efficiency of crop, due to retardant of urea hydrolysis and reduction of ammonia volatilization loss. An incubation experiment was conducted to investigate the urease inhibition effect of a new phosphoramide urease inhibitor, NPPT (N-(n-propyl) thiophosphoric triamide) in different texture soils under dark condition at 25 ℃, and NBPT (N-(n-butyl) thiophosphoric triamide) was obtained to compare the inhibition effect on urease in different soil textures by different dosages of urea adding. Results showed that the effective reaction time of urea was less than 9 d in the loamy and clay soil. Addition of inhibitors for retardation of urea hydrolysis was more than 3 d. In sandy soil, urea decomposition was relatively slow, and adding inhibitor significantly inhibited soil urease acti-vity, and reduced NH 4 + -N content. During the incubation time, the inhibition effect of high dosage urea in the soil was better than that of low dosage. At day 6, the urease inhibition rate of NBPT and NPPT (N 250 mg·kg -1 ) were 56.3% and 53.0% in sandy soil, 0.04% and 0.3% in loamy soil, 4.1% and 6.2% in clay soil; the urease inhibition rate of NBPT and NPPT (N 500 mg·kg -1 ) were 59.4% and 65.8% in sandy soil, 14.5% and 15.1% in loamy soil, 49.1% and 48.1% in clay soil. The urease inhibition effects in different texture soil were in order of sandy soil > clay soil> loamy soil. The soil NH 4 + -N content by different inhibitors during incubation time increased at first and then decreased, while soil NO 3 - -N content and apparent nitrification rate both showed rising trends. Compared with urea treatment, addition of urease inhibitors (NBPT and NPPT) significantly increased urea-N left in the soil and reduced NH 4 + -N content. In short, new urease inhibitor NPPT in different texture is an effective urease inhibitor.

On the basis of field soil sampling, this paper investigated the distribution characteristics of soil different nitrogen (N) forms and its influence factors in the different typical zonal soils. The results showed that the concentrations of soil extractable total N, extractable organic N and adsorbed amino acids extracted with 0.5 mol·L -1 K 2 SO 4 significantly increased along the altitudinal gradient in the different vertical soils, and their mean concentrations were greater than that in the horizontal soils. The concentrations of soil different N forms widely varied with the soil type in the different horizontal soils. On average, the concentration of soil adsorbed amino acids was approximately 5-fold greater than that of the free amino acids, representing 21.1% of soil extractable organic N. It indicated that the soil adsorbed amino acids extracted with the strong salt solution could serve as an important form of soil organic N. Pearson correlation analysis showed that extractable total N, extractable organic N, ammonium and amino acids in vertical soils were positively correlated with soil organic matter and total N (r=0.57-0.93, P<0.05), but negatively correlated with soil pH and nitrate (r=-0.37--0.91, P<0.05). In the horizontal soils, soil extractable total N, nitrate, organic matter, total N, alkali-hydrolyzable N and cation ions (e.g. K + , Ca 2+ , Mg 2+ ) were all positively correlated with soil pH (r=0.36-0.85, P<0.05), whereas negatively correlated with soil ammonium and amino acids (r=-0.39--0.81, P<0.05).

Plant can directly take up the intact amino acids, thus bypass the microbial mineralization of organic nitrogen. As an excellent carbon and nitrogen source, there exists competition for amino acid absorption between plant roots.and soil microorganisms. And the total flux of amino acids in soil may be enormous due to the extensive sources and short half-life. Studies on amino acid nitrogen nutritional contribution for plant by the technique of nitrogen isotopic tracer, has become a research topic in recent years ,which will help us better understand the principle of soil fertility. This paper summarized the recent researches on amino acid morphological characteristics in soil and its metabolic mechanism and nitrogen nutritional contribution for plant in different ecosystems, and discussed the present status and development trend of the amino acid circulation mechanism in the plant-soil-microorganism ecosystem and its bioavailability for plant. Finally, the topics of environmental regulating mechanism of amino acid bioavailability, amino acid carbon-nitrogen metabolism, and how to improve the field organic nitrogen management were all the core issues to be resolved.

Abstract: A 2-year field experiment with a yellow-clay paddy soil in Zhejiang Province was conducted to study the effects of different planting measures combined with different fertilization practices on rice yield, soil nutrients, microbial biomass C and N and activities of urease, phosphatase, sucrase and hydrogen peroxidase at the maturity stage. Results showed that mechanical transplanting of rice with controlled release bulk blending (BB) fertilizer (BBMT) could achieve a significantly higher mean yield than traditional manual transplanting with traditional fertilizer (TFTM) and direct seeding with controlled release BB fertilizer (BBDS) by 16.3% and 27.0%, respectively. The yield by BBMT was similar to that by traditional manual transplanting with controlled release BB fertilizer (BBTM). Compared with TFTM, BBMT increased the contents of soil total-N, available N, available P and microbial biomass C, and the activities of urease, sucrase and hydrogen peroxidase by 21.5%, 13.6%, 41.2%, 27.1%, 50.0%, 22.5% and 46.2%, respectively. Therefore, BBMT, a simple high-efficiency rice cultivation method with use of a light-weighted mechanical transplanter, should be widely promoted and adopted.

A pot experiment was conducted to study the effect of spent mushroom compost (SMC) in alleviating greenhouse soil secondary salinization and cabbage salt stress. With the amendment of SMC, the salinized soil after 60 day cabbage cultivation had a pH value close to 7.0, its organic matter and available phosphorous contents increased significantly, and the increment of total water-soluble salt content reduced, compared with the control. When the amendment amount of SMC was 10 g x kg(-1), the increment of soil water soluble salt content was the least, suggesting that appropriate amendment with SMC could reduce the salt accumulation in greenhouse soil. Amendment with SMC increased the cabbage seed germination rate, plant height, plant fresh mass, chlorophyll SPAD value, and vitamin C content, and decreased the proline content significantly. All the results indicated that SMC could improve the growth environment of greenhouse cabbage, and effectively alleviate the detrimental effect of salt stress.

With two rice genotypes (cv. Zhongbu 51 and Azucena) differing in their root-secreted acid phosphatase activity (APA) under low P condition as test materials, an agar culture experiment was conducted to investigate their P utilization from myo-inositol hexaphosphate (IHP) under conditions of sterilization and inoculating with soil microorganisms. Under sterilization, the shoot dry mass, P absorption and P concentration of test genotypes supplied with hexaphosphate (IHP) as the P source were significantly higher than those with no P supply, but significantly lower than those supplied with inorganic P, indicating that rice plants could partly acquire P from IHP under sterilized condition. The root-secreted APA of the two genotypes was significantly higher under low P than under sufficient P supply, and the higher APA of Zhongbu 51 under low P could be one of the mechanisms of higher P utilization capability of Zhongbu 51 than Azucena under deficient P supply. When supplied with high level IHP (0.96 mmol P x L(-1)), the shoot dry mass, P absorption and P concentration of both Zhongbu 51 and Azucena were higher than those when supplied with low level IHP (0.16 mmol P x L(-1)), indicating that substrate availability could be one of the limiting factors to the utilization of phytate by rice. Inoculation with soil microorganisms had no significant effects on the shoot dry mass, P absorption and P concentration of rice plants, regardless of IHP level and rice genotypes, implying that the utilization of IHP by rice could not be improved via inoculation with soil microorganisms.

With hydroponic culture, this paper studied the effects of different nitrogen (N) supply levels (0, 0.15, 0.3, 0.45, 0.6, 0.75 g N x L(-1)) on the seedling morphology and N allocation of Parthenocissus tricuspidata. The results showed that lower N supply retarded the development of P. tricuspidata seedling's branch; while higher N supply had significant effects in promoting the seedling's early branching and lowering the branching position on the main stem. Supplying higher amount of N increased the plant biomass and the N concentration in root, leaf and stem significantly. Compared with stem and root, leaf had the highest biomass, accounting for 50% of the total biomass, and the highest N accumulation, accounting for 60%-70% of the total accumulated N.

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.

The influence of nitrification inhibitor (NI) 3, 4-dimethylpyrazole phosphate (DMPP) on nitrate accumulation in greengrocery (Brassica campestris L. ssp. chinensis) and vegetable soil at surface layer were investigated in field experiments in 2002 and 2003. Results showed that NI DMPP took no significant effect on yields of edible parts of greengrocery, but it could significantly decrease NO(3-)-N concentration in greengrocery and in vegetable soil at surface layer. In addition, NI DMPP could reduce the NO(3-)-N concentration during the prophase stage of storage.