[Effects of different cultivation patterns on soil aggregates and organic carbon fractions].

Combined with the research in an organic farm in the past 10 years, differences of soil aggregates composition, distribution and organic carbon fractions between organic and conventional cultivation were studied by simultaneous sampling analysis. The results showed that the percentages of aggregates (> 1 mm, 1-0.5 mm, 0.5-0.25 mm and < 0.25 mm) in the conventional cultivation were 23.75%, 15.15%, 19.98% and 38.09%, while those in organic cultivation were 9.73%, 18.41%, 24.46% and 43.90%, respectively. The percentage of < 0.25 mm micro-aggregates was significantly higher in organic cultivation than that in conventional cultivation. Organic cultivation increased soil organic carbon (average of 17.95 g x kg(-1)) and total nitrogen contents (average of 1.51 g x kg(-1)). Among the same aggregates in organic cultivation, the average content of heavy organic carbon fraction was significantly higher than that in conventional cultivation. This fraction accumulated in < 0. 25 mm micro-aggregates, which were main storage sites of stable organic carbon. In organic cultivation, the content of labile organic carbon in > 1 mm macro-aggregates was significantly higher than that in conventional cultivation, while no significant difference was found among the other aggregates, indicating that the labile organic carbon was enriched in > 1 mm macro-aggregates. Organic cultivation increased the amounts of organic carbon and its fractions, reduced tillage damage to aggregates, and enhanced the stability of organic carbon. Organic cultivation was therefore beneficial for soil carbon sequestration. The findings of this research may provide theoretical basis for further acceleration of the organic agriculture development.

[Emission inventory of greenhouse gases from agricultural residues combustion: a case study of Jiangsu Province].

Burning of agricultural crop residues was a major source greenhouse gases. In this study, the proportion of crop straws (rice, wheat, maize, oil rape, cotton and soja) in Jiangsu used as household fuel and direct open burning in different periods (1990-1995, 1996-2000, 2001-2005 and 2006-2008) was estimated through questionnaire. The emission factors of CO2, CO, CH4 and NO20 from the above six types of crop straws were calculated by the simulated burning experiment. Thus the emission inventory of greenhouse gases from crop straws burning was established according to above the burning percentages and emission factors, ratios of dry residues to production and crop productions of different periods in Jiangsu province. Results indicated that emission factors of CO2, CO, CH4 and N2O depended on crop straw type. The emission factors of CO2 and CH4 were higher for oil rape straw than the other straws, while the maize and the rice straw had the higher N2O and CO emission factor. Emission inventory of greenhouse gases from agricultural residues burning in Jiangsu province showed, the annual average global warming potential (GWP) of six tested crop straws were estimated to be 9.18 (rice straw), 4.35 (wheat straw), 2.55 (maize straw), 1.63 (oil rape straw), 0.55 (cotton straw) and 0. 39 (soja straw) Tg CO2 equivalent, respectively. Among the four study periods, the annual average GWP had no obvious difference between the 1990-1995 and 2006-2008 periods, while the maximal annual average GWP (23.83 Tg CO2 equivalent) happened in the 1996-2000 period, and the minimum (20.30 Tg CO2 equivalent) in 1996-2000 period.

[Effects of bio-fertilizer on organically cultured cucumber growth and soil biological characteristics].

Field trials of organic farming were conducted to examine the effects of different bio-fertilizers on the organically cultured cucumber growth, soil enzyme activities, and soil microbial biomass. Four treatments were installed, i. e., organic fertilizer only (CK), bio-fertilizer "Zhonghe" combined with organic fertilizer (ZHH), bio-fertilizer "NST" combined with organic fertilizer (NST), and bio-fertilizer "Bio" combined with organic fertilizer (BIO). Bio-fertilizers combined with organic fertilizer increased the cucumber yield significantly, and improved the root growth and leaf chlorophyll content. Comparing with that in CK, the cucumber yield in treatments ZHH, NST, and BIO was increased by 10.4%, 12.4%, and 29.2%, respectively. At the seedling stage, early flowering stage, and picking time of cucumber, the soil microbial biomass C and N in treatments ZHH, NST, and BIO were significantly higher than that in CK, and the activities of soil urease, acid phosphatase, and catalase were also higher.

[Extraction of Cd by ramie from soils as affected by applications of chelators and peat].

Pot experiments were performed to study the effectiveness of chelators (EDTA, citric acid) and peat in enhancing phyremediation of heavy metal Cd by ramie. The results showed that peat increased the ramie's biomass by improving soil's physical and chemical properties, and the relative yields of peat alone, chelators(EDTA, citric acid) combined with peat were 1.23, 1.13 and 1.41 respectively. So the combination of citric acid and peat was more useful for growth of the ramie. As far as improving Cd uptake was concerned, it seemed that the combination of chelators with peat significantly promoted Cd uptake by the plant, and the percent of changeable Cd in soil were 61.6% and 58.3% . In addition, it had better bioaccumulation effects to combine with chelators and peat, of which Cd bioaccumulation coefficients were 1.33 and 1.32, compared to 1.11, 1.11 and 1.05 in application of peat, EDTA and citric acid respectively. What's more, cadmium removal rates in soil were up to 1.13% and 1.22% respectively in applications of two kinds of chleators (EDTA, citric acid) combined with peat. Therefore, it had better effects of phytoremediation to accumulate more cadmium amounts by combining with citric acid and peat because of more biomass. In conclusion, the phytoremediation by ramie can be more effective when chelators and peat were combined and added to soils.

[Impact of different levels of nitrogen fertilizer on N2O emission from different soils].

To investigate the effect of different urea incorporation amount in different soils on N2O emission, a pot experiment was carried in 2002-2003. Four treatments were designed as the control (without urea incorporation); low N fertilizer level (334 kg/hm2); middle N fertilizer level (670 kg/hm); high N fertilizer level (1004 kg/hm2). In rice growing season, compared to control, the increment of N2O emission accumulation flux of each soil has no obviously differences among three N fertilizer levels. Contrarily, in wheat-planted soils, there are remarkably differences among three N fertilizer levels. Without urea incorporation, there are no differences among N2O accumulation emission flux of three soils. During the rice growing season, N2O accumulation emission flux of F soil (jiangsu province, lishui), G soil (jiangsu province, lianshui) and H soil (jiangsu province, agriculture academy) are 168, 127 and 146 mg/m2, respectively. N2O accumulation emission flux of F soil, G soil and H soil is 134, 124 and 168 mg/m2, respectively, during wheat growing season. Incorporation of urea into different soils yielded different influence on N2O emission. For example, at middle-N fertilizer, N2O accumulation emission flux from F soil, G soil and H soil is 976, 744 and 626 mg/m2, respectively. During rice-wheat rotation period, significance differences exists among N2O emission factors of three soils, with the value of (1.1 +/- 0.23)%, (0.75 +/- 0.17%) and (1.01 +/- 0.11)%. Furthermore, under the high N fertilizer level, N2O emission factors of three soils had no significantly difference (p = 0.3); while, the N2O emission factors existed difference among three soils under the low and middle N fertilizer level (F = 6.25, p = 0.01).

[Effect of organic material incorporation in rice season on N2O emissions from following winter wheat growing season].

In a field experiment, five fertilizer treatments including chemical fertilizer (CF), rapeseed cake + chemical fertilizer (RC + CF), wheat straw + chemical fertilizer (WS + CF), cow manure + chemical fertilizer (CM + CF), and pig manure + chemical fertilizer (PM + CF), were dedicated to examine the effect of organic materials incorporation in the rice season on N2O emissions from the following winter wheat season and to assess the climatic impacts from CH4 and N2O emissions in a rice-wheat rotation. Organic material was incorporated at the same rate (225 g x m(-2)) for organic treatments at the depth of 10 cm in the soil as the basal fertilizer just before rice transplanting. An identical synthetic nitrogen fertilizer was adopted for all treatments. Results show that the seasonal amount of N20 emissions from the following wheat season differed with organic material applied in rice season. No pronounced difference in N20 emissions was found between the CF and RC + CF treatments. In contrast with the CF treatment, however, N2O emission was decreased by 15% for the WS + CF treatment, but increased by 29% and 16% for the CM + CF and PM + CF treatments, respectively. Over the entire annual rotation cycle, N2O amount was increased by 17% for the CM + CF treatment, 7% for the PM + CF treatment, and 6% for the RC + CF treatment, but decreased by 16% for the WS + CF treatment in comparison with the CF treatment. Based on total emissions of CH4 in rice season and N2O over the entire rotation cycle, the estimation of combined Global Warming Potentials (GWPs) for CH4 and N20 shows that over a 20 years horizon or a 500 years horizon, the value of annual total GWPs was ranked in the order of RC + CF > WS + CF > CM + CF > PM + CF > CF or RC + CF > CM + CF > PM + CF > WS + CF > CF. The highest, middle and the lowest value of the GWPs per unit crop grain yield occurred for the crop residue, farmyard manure and pure synthetic fertilizer treatments, respectively. Compared to the chemical fertilizer treatment, accordingly, organic material combined with chemical fertilizer application in rice season increased climatic impacts from CH4 and N20 emissions in a rice-winter wheat rotation system.

[Impact of different levels of nitrogen fertilizer on CH4 emission from different paddy soils].

To investigate the effect of different urea incorporation amount in different soils on CH4 emission, a pot experiment was carried in 2002. Four treatments were designed as the control (without urea incorporation); low N fertilizer level (0.64 g urea/pot); middle N fertilizer level (1.28 g urea/pot); high N fertilizer level (1.93 g urea/pot). During rice growing season, incorporation of urea into different soils yielded different influence on CH4 emission. Without urea incorporation, significance differences existed among CH4 emission flux of three soils, with the values of 6.7 g/m2, 12.6 g/m2 and 8.3 g/m2, respectively. Incorporation of urea reduced considerably CH4 emission of three soils. A further investigation indicate that CH4 emission of three soils largely decreased and three soils NH4(+)-N content obviously increased from low N fertilizer level to middle N fertilizer level. It concluded that soil NH4(+)-N content is a key influence factor on CH4 emission after incorporation of urea into soils. From middle N level to high N level, CH4 emision of soil G (Lianshui, Jiangsu) and H (Jiangsu Academy of agricultural sciences) reduced, while CH4 emission of soil F (Lishui, Jiangsu) had no obvious significance with the value of 3.0 g/m2 and 3.4 g/m2.