Xianjun Jiang

Combining Ridge with No-Tillage in Lowland Rice-Based Cropping System: Long-Term Effect on Soil and Rice Yield

Abstract A tillage method of combining ridge with no-tillage (RNT) was employed in lowland rice-based cropping system to study the long-term effects of RNT on soil profile pattern, soil water stable aggregate distribution, nutrients stratification and yields of rice and post-rice crops. After flooded paddy field (FPF) was practiced with RNT for a long time, soil profile changed from G to A-P-G, and horizon G was shifted to a deeper position in the profile. Also the proportion of macro- aggregate (> 2 mm) increased, whereas the proportion of silt and clay (

Observation of significant steric, valence and polarization effects and their interplay: a modified theory for electric double layers

Presented electric double layer theory achieves comparable results with experiments by including steric, polarization and valence effects and is applicable to all ions contrasting the classical theory only to hydrogen ions, which thus capably describes the selective adsorption on charged surfaces and is expected to clarify specific ion effects.

Effects of Fe oxide on N transformations in subtropical acid soils.

Subtropical ecosystems are often characterized by high N cycling rates, but net nitrification rates are often low in subtropical acid soils. NO3−-N immobilization into organic N may be a contributing factor to understand the observed low net nitrification rates in these acid soils. The effects of Fe oxide and organic matter on soil N transformations were evaluated using a 15N tracing study. Soil net nitrification was low for highly acidic yellow soil (Ferralsols), but gross ammonia oxidation was 7 times higher than net nitrification. In weakly acidic purple soil (Cambisols), net nitrification was 8 times higher than in Ferralsols. The addition of 5% Fe oxide to Cambisols, reduced the net nitrification rate to a negative rate, while NO3−-N immobilization rate increased 8 fold. NO3−-N immobilization was also observed in Ferralsols which contained high Fe oxides levels. A possible mechanism for these reactions could be stimulation of NO3−-N immobilization by Fe oxide which promoted the abiotic formation of nitrogenous polymers, suggesting that the absence of net nitrification in some highly acid soils may be due to high rates of NO3−-N immobilization caused by high Fe oxide content rather than a low pH.

Autotrophic and Heterotrophic Nitrification in a Highly Acidic Subtropical Pine Forest Soil

Abstract The occurrence of nitrification in some acidic forest soils is still a subject of debate. Identification of main nitrification pathways in acidic forest soils is still largely unknown. Acidic yellow soil (Oxisol) samples were selected to test whether nitrification can occur or not in acidic subtropical pine forest ecosystems. Relative contributions of autotrophs and heterotrophs to nitrification were studied by adding selective nitrification inhibitor nitrapyrin. Soil NH+4-N concentrations decreased, but NO−3-N concentrations increased significantly for the no-nitrapyrin control during the first week of incubation, indicating that nitrification did occur in the acidic subtropical soil. The calculated net nitrification rate was 0.49 mg N kg−1 d−1 for the no-nitrapyrin control during the first week of incubation. Nitrapyrin amendment resulted in a significant reduction of NO−3-N concentration. Autotrophic nitrification rate averaged 0.28 mg N kg−1 d−1 and the heterotrophic nitrification rate was 0.21 mg N kg−1 d−1 in the first week. Ammonia-oxidizing bacteria (AOB) abundance increased slightly during incubation, but nitrapyrin amendment significantly decreased AOB amoA gene copy numbers by about 80%. However, the ammonia-oxidizing archaea (AOA) abundance showed significant increases only in the last 2 weeks of incubation and it was also decreased by nitrapyrin amendment. Our results indicated that nitrification did occur in the present acidic subtropical pine forest soil, and autotrophic nitrification was the main nitrification pathway. Both AOA and AOB were the active biotic agents responsible for autotrophic nitrification in the acidic subtropical pine forest soil.

Manganese oxide affects nitrification and N2O emissions in a subtropical paddy soil with variable water regimes

Summary Crop management-induced redox cycles lead to the formation of distinct soil layers that characterize manganese (Mn) distribution or redistribution in rice (Oryza sativa L.) based ecosystems. We studied the effect of Mn oxides on soil nitrification and N2O emissions to validate the hypothesis that Mn oxides affect the soils nitrification and denitrification processes. Subtropical paddy soil with three different water regimes (50, 100 and 200% of soil water-holding capacity (WHC)) was treated with 3% birnessite (Mn oxide) or left untreated. The nitrification process was simulated with zero- or first-order kinetic models and N2O emissions were also measured. The maximum net rates of soil nitrification (Va1) decreased significantly with increasing soil moisture contents (F = 184.8; P < 0.001), and so did the average net rates of soil nitrification (Va2) (F = 6.96; P = 0.008). Manganese oxide significantly decreased Va1 (F = 474.7; P < 0.001), whereas it had no significant effects on Va2 (F = 0.26; P = 0.62). Manganese oxide changed the best fitting nitrification kinetic model from first- to zero-order for both 50 and 200% WHC, but it had no effect at 100% WHC. The maximum rates of emission of N2O significantly increased with increasing soil water contents (F = 15 007; P < 0.001). Manganese oxide retarded the maximum rate of N2O emission at 100% WHC, whereas it depressed the rate from 1084 to 225 μg N kg−1 day−1 at 200% WHC (F = 7494; P < 0.001). The results indicate that the effects of Mn oxide on regulating nitrification and N2O emissions are associated with water regime-dictated redox potential, and might have important implications for regulating N cycling in rice-based ecosystems. Highlights Effect of manganese oxide on nitrification and denitrification in a paddy soil. Mn oxide retarded nitrification in oxic conditions and enhanced it in anoxic conditions. Mn oxide decreased rate of emission of nitrous oxide in anoxic conditions. Manganese oxide might be able to regulate N cycling in rice paddy soil.

Soil Enzyme Activities and Organic Matter Composition Affected by 26 Years of Continuous Cropping

Abstract The study was to determine the long-term effects of subtropical monoculture and rotational cropping systems and fertilization on soil enzyme activities and soil C, N, and P levels. Cropping systems included continuous sorghum ( Sorghum bicolor L.), cotton ( Gossypium hirsutum L.), corn ( Zea mays L.), and cotton/sorghum rotations after 26 years of treatment imposition. Soil under continuous sorghum and continuous corn had 15% and 11%, respectively, greater C concentrations than soil under continuous cotton. Organic C was 10% higher at 0–7.5 cm than at 7.5–15 cm. Total N followed similar trends with soil depth as organic C. Continuous sorghum had 19% higher total N than other crop species and rotations. With fertilization, continuous cotton had the highest total P at 0–7.5 cm and sorghum had the highest at 7.5–15 cm. Soil total P was 14% higher at 0–7.5 than at 7.5–15 cm, and fertilization increased 15% total P compared to unfertilized soil. Arylsulfatase, alkaline phosphatase, and β-d-glucosidase activity were the highest for sorghum and the lowest for cotton. Rotation increased enzyme activities compared to continuous cotton but not for continuous sorghum. Of all crop species and rotations, continuous cotton generally showed the lowest levels of organic matter and enzyme activities after 26 years. Fertilization significantly increased the yields for all cropping systems, but rotation had no significant effect on either sorghum or cotton lint yield compared to each crop grown in monoculture. Long-term cropping did not increase soil organic matter levels beyond short-term gains, indicating the difficulty in promoting C sequestration in subtropical soils.