A dataset of the effect of different maize residue on soil organic nitrogen cycling in Li Shu, China

Our data contains three parts: nitrogen cycling enzymes, soil organic nitrogen fractions and other soil properties. In the first part, the data of five nitrogen cycling enzymes (protease, N-acetyl-β-D-glucosaminidase (NAG), amidase, urease, and peptidase) were shown with different treatments (RT, NT, TT and PT) and different soil depths (0-10cm, 10-20cm, 20-35cm). Each treatment has four replicates. The methods that obtained these data were as follows: Protease activity was measured as described by Ladd and Butler (1972). Field moist soil samples were incubated with 0.05 M Tris buffer (pH 8.10) and 2 % sodium caseinate (w/v) for 2 h at 50 ℃. The tyrosine produced was determined using the colorimetrical method at 700 nm, and the protease activity was expressed as µg tyrosine g−1 soil 2 h−1. Amidase activity was assayed using the method described by Frankenberger and Tabatabai (1980). Field moist soil samples were incubated with 0.1 M sodium borate buffer (pH 8.50) and 0.5 M formamide for 2 h at 37 ℃. The ammonium released was determined using the colorimetrical method at 660 nm, and amidase activity was expressed as µg NH4+ g−1 soil 2 h−1. Soil NAG activity was measured using field moist soil incubated with 0.1 M acetate buffer (pH 5.50) and N-acetyl-β-D-glucosaminide solution at 37 ℃ for 1 h. The nitrophenol produced was measured using the colorimetrical method at 405 nm, and the activity of NAG was expressed as mg ρ-nitrophenol kg−1 soil h−1 (Parham and Deng, 2000). Soil urease activity was assayed by determining the amount of urea remaining after incubation (Tabatabai, 1994). Field moist soil was incubated with 2 mg mL−1 of urea solution at 37 ℃ for 5 h. The residual urea was determined using a colorimetric method at 527 nm. Soil urease activity was expressed as mg urea kg−1soil 5 h−1 (Douglas and Bremner, 1970). Soil peptidase activity was measured using a fluorescent substrate (7-amino-4-methylcoumarin). A total of 2.00 g of field-moist soil was weighed and mixed with 200 mL NaN3 to produce soil suspension, 50 μL acetate buffer (pH 5.0), 100 μL substrates, and 50 μL soil suspension was then added to a 96-well flat-black-bottomed microplate (NUNC, Denmark) before being incubated for 3 h at 30 ℃.In this study, soil peptidase activity was the sum of the activity of leucine aminopeptidase, glutamate aminopeptidase, and aspartate aminopeptidase. The substrates of these enzymes were L-leucine-AMC, L-glutamic acid-γ-AMC, and aspartic acid-AMC, respectively. The soil peptidase activity was expressed as nmol AMC g−1 soil h−1 (Marx et al., 2001; Frossard et al., 2012).In the second part, the data of five organic nitrogen fractions (hydrolyzable NH4+-N, amino acid N, amino sugar N, hydrolyzable unknown N and acid-insoluble N) were shown with different treatments (RT, NT, TT and PT) and different soil depths (0-10cm, 10-20cm, 20-35cm). Each treatment has four replicates. The methods that obtained these data were as follows: Organic nitrogen fractions were determined by hydrolyzing the soil sample with 6 M HCl in an autoclave at 121 ℃ for 6 h (Stevenson, 1982). Total hydrolyzable N was measured using steam distillation with 10 M NaOH after digestion with sulfuric acid and a K2SO4 -catalyst mixture. Amino acid N was determined using steam distillation with a phosphate–borate buffer after treatment with NaOH at 100 ℃ and ninhydrin powder. Hydrolyzable NH4+-N was measured via steam distillation using MgO. Amino sugar N was calculated as the difference between the amount of N evaporated by steam distillation with phosphate-borate at pH 11.2 and hydrolysable NH4+-N. Hydrolysable unknown-N was calculated as the difference between total hydrolyzable-N and N accounted for as hydrolyzable NH4+ + amino acid + amino sugar) − N. The amount of acid-insoluble N was calculated as the difference between soil TN and total hydrolyzable N. In the third part, the data of other soil properties (MBC, MBN, SOC, SOM, DHA, NH4+, soil pH, Total N of maize straw) were shown with different treatments (RT, NT, TT and PT) and different soil depths (0-10cm, 10-20cm, 20-35cm). Each treatment has four replicates. The methods that obtained these data were as follows: Soil microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were extracted by 0.5 M K2SO4 and were determined using a C and N analyzer (VarioTOC Analyzer, Elementar, Germany) (Mulvaney, 1996). Soil organic carbon (SOC) was determined by chemical oxidation using K2Cr2O7 solution, the SOC oxidized by 0.8 M K2Cr2O7 was measured by titrating the remaining K2Cr2O7 with 0.2 M FeSO4 (Nelson and Sommers, 1982). Soil dehydrogenase (DHA) activity was measured using field moist soil incubated with 2,3,5-Triphenyltetrazolium chloride solution at 37 °C for 24 h. The produced 1,3,5-Triphenylformazan was extracted by CH3OH and measured using the colorimetrical method at 485 nm (Tabatabai, 1994).Soil NH4+-N were extracted by 1 M KCl (Mulvaney, 1996) and were determined using a colorimetric method with an AutoAnalyser III continuous flow analyzer (Bran & Luebbe, Norderstedt, Germany).Soil pH was determined in a 1:2.5 soil/water suspension by a digital pH meter (pH 700 Bench Meter, Eutech Instruments).Total N of maize straw was determined using a Vario MACRO cube analyzer (Elementar Analysensysteme Vario MACRO cube, German).ReferenceLadd, J.N., Butler, J.H.A., 1972. Short-term assays of soil proteolytic enzyme activities using proteins and dipeptide derivatives as substrates. Soil Biol. Biochem. 4, 19–30. Frankenberger, W.T., Tabatabai, M.A., 1980. Amidase activity in soils: I. Method of assay. Soil Sci. Soc. Am. J. 44, 282–287.Parham, J.A., Deng, S.P., 2000. Detection, quantification and characterization of beta- glucosaminidase activity in soil. 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