Shaojun Qiu

Effects of applied urea and straw on various nitrogen fractions in two Chinese paddy soils with differing clay mineralogy

Combined application of synthetic nitrogen (N) fertilizers and organic materials can enhance soil quality, but little is known about the distribution of fertilizer N among different soil fractions after crop harvest. A pot experiment using 15N tracer was employed to address this question with three treatments, i.e., labeled urea-only (15NU), labeled urea + rice straw (15NU-S) and labeled rice straw + urea (15NS-U) applied to a Ferallic Cambisol (1:1 type soil clay mineral) and a Calcaric Fluvisol (2:1 clay mineral). Soil microbial biomass N, fixed ammonium (fixed NH4+), exchangeable ammonium and soil organic N fractions by hydrolysis (6 N HCl) and their isotope abundance were determined after the rice harvest. Soil newly formed N in urea + straw (U-S) treatments (15NU-S, 15NS-U) was the sum of labeled urea-N in 15NU-S and labeled straw-N in 15NS-U. Compared with 15NU, U-S significantly (Pu2009<u20090.05) increased the content and percentage of newly formed total soil N, acid insoluble N, amino acid N, and hydrolysable unknown N in both soils. In U-S treatment, straw amendment significantly (Pu2009<u20090.05) reduced the content and percentage of newly formed fixed-NH4+-N in Fluvisol as compared with 15NU treatments. Soil microbes contributed to the larger percentage of newly formed amino acid N (Pu2009<u20090.01) in Cambisol as compared with Fluvisol. Fertilizer N in various soil fractions was therefore strongly affected by clay mineral type and microbes after the combined application of organic materials and synthetic N fertilizer.

Yield Gap, Indigenous Nutrient Supply and Nutrient Use Efficiency for Maize in China.

Great achievements have been attained in agricultural production of China, while there are still many difficulties and challenges ahead that call for put more efforts to overcome to guarantee food security and protect environment simultaneously. Analyzing yield gap and nutrient use efficiency will help develop and inform agricultural policies and strategies to increase grain yield. On-farm datasets from 2001 to 2012 with 1,971 field experiments for maize (Zea mays L.) were collected in four maize agro-ecological regions of China, and the optimal management (OPT), farmers’ practice (FP), a series of nutrient omission treatments were used to analyze yield gap, nutrient use efficiency and indigenous nutrient supply by adopting meta-analysis and ANOVA analysis. Across all sites, the average yield gap between OPT and FP was 0.7 t ha-1, the yield response to nitrogen (N), phosphorus (P), and potassium (K) were 1.8, 1.0, and 1.2 t ha-1, respectively. The soil indigenous nutrient supply of N, P, and K averaged 139.9, 33.7, and 127.5 kg ha-1, respectively. As compared to FP, the average recovery efficiency (RE) of N, P, and K with OPT increased by percentage point of 12.2, 5.5, and 6.5, respectively. This study indicated that there would be considerable potential to further improve yield and nutrient use efficiency in China, and will help develop and inform agricultural policies and strategies, while some management measures such as soil, plant and nutrient are necessary and integrate with advanced knowledge and technologies.

Role of Carbon Substrates Added in the Transformation of Surplus Nitrate to Organic Nitrogen in a Calcareous Soil

Abstract Excessive amounts of nitrate have accumulated in many soils on the North China Plain due to the large amounts of chemical N fertilizers or manures used in combination with low carbon inputs. We investigated the potential of different carbon substrates added to transform soil nitrate into soil organic N (SON). A 56-d laboratory incubation experiment using the 15N tracer (K15NO3) technique was carried out to elucidate the proportion of SON derived from accumulated soil nitrate following amendment with glucose or maize straw at controlled soil temperature and moisture. The dynamics and isotopic abundance of mineral N (NO−3 and NH+4) and SON and greenhouse gas (N2O and CO2) emissions during the incubation were investigated. Although carbon amendments markedly stimulated transformation of nitrate to newly formed SON, this was only a substitution effect of the newly formed SON with native SON because SON at the end of the incubation period was not significantly different (P > 0.05) from that in control soil without added C. At the end of the incubation period, amendment with glucose, a readily available C source, increased nitrate immobilization by 2.65 times and total N2O-N emission by 33.7 times, as compared with maize straw amendment. Moreover, the differences in SON and total N2O-N emission between the treatments with glucose and maize straw were significant (P 0.05) greater than that in the control. Straw amendment may be a potential option in agricultural practice for transformation of nitrate N to SON and minimization of N2O emitted as well as restriction of NO3-N leaching.

Allocation of photosynthestically-fixed carbon in plant and soil during growth of reed (Phragmites australis) in two saline soils

AimsTerrestrial carbon (C) sequestration is derived mainly from plant photosysthetically-fixed C deposition but soil organic C (SOC) content in saline soils is generally low due to low deposition of C from restricted plant growth. It is important to explore the effects of soil salinity on the allocation of photosynthetically-fixed C to better understand C sequestration in saline wetland soils.MethodsWe conducted a pot experiment in which reed (Phragmites australis) was grown in a low salinity (LS) soil and a high salinity (HS) soil from the Yellow River Delta under flooded conditions. The allocation of photosynthetically-fixed C into plant tissues, SOC, dissolved organic C (DOC), microbial biomass C (MBC), particulate organic C (POC), and mineral-associated organic C (MAOC) was determined using a 13C pulse-labeling method after four labeling events during the 125-day-long reed growing season and destructive sampling immediately at the end of six hours of pulse labeling (end 6-h) and on the final harvest day (final day).ResultsIn most cases soil salinity, reed growth stage, or reed biomass significantly (Pxa0<xa00.05) affected the deposition of photosynthetically-fixed C into the plant-soil system. At all four pulses at end 6-h the high salinity soil had significantly (Pxa0<xa00.05) lower percentage net assimilated 13C in the roots and significantly higher (Pxa0<xa00.05) percentage net assimilated 13C in the soil than did the low salinity soil. At both end 6-h and on the final day the high salinity soil had significantly (Pxa0<xa00.05) lower SO13C, and significantly (Pxa0<xa00.05) higher DO13C/SO13C ratio than the low salinity soil except for pulses 3 and 4 on the final day. The majority of photosynthetically-fixed C in soil was deposited into MAOC pools and >80xa0% of deposited SO13C was present as MAOC in the high salinity soil due to its significantly (Pxa0<xa00.05) higher clay content compared with the low salinity soil.ConclusionsSoil salinity affected the allocation of photosynthetically-fixed C in the plant-soil system, and soil texture altered the allocation of rhizodeposition C in different soil particles.

Nitrate Transformation and N2O Emission in a Typical Intensively Managed Calcareous Fluvaquent Soil: A 15-Nitrogen Tracer Incubation Study

A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO3-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N2O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO3-N decreased. When 15NO3-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg−1 only 1.1 ± 0.4 mg kg−1 NO3-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly (P < 0.05) with increasing amount of straw. Total N2O-N emissions were at levels of only micrograms kg−1 soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N2O.

Changes of heavy metals in soil and wheat grain under long-term environmental impact and fertilization practices in North China

Abstract We evaluated the effects of long-term fertilization on heavy metals in soil and wheat grain under no-fertilizer control (CK), nitrogen, phosphorus, and potassium fertilizers (NPK), NPK plus straw (NPKS), and NPK plus manure (NPKM) treatments. Total lead (Pb) significantly increased in the CK over the initial soil. All fertilization treatments increased soil total arsenic (As) than CK, and the NPKM increased total cadmium (Cd), copper (Cu), and zinc (Zn) than NPK. All fertilization treatments increased soil available As and Cd than CK, and the NPKM increased available As and chromium (Cr) than NPK. The NPKS decreased grain As, Cd, Cu, and bran Cr, Zn, and Pb; but the NPKM increased grain Cr, Pb, and bran As, and Cu than NPK. Under current manure fertilization systems, the maximum bearing year of soil for As, Cr, Cd, Cu, Zn, and nickel (Ni) was 1136, 2990, 694, 1530, 910, and 1555u2009years, respectively.