[Show abstract][Hide abstract] ABSTRACT: The differences in soil inorganic-nitrogen (N) concentration and distribution, plant biomass, and root growth in the presence or absence of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) under different urea-application methods (placement versus homogeneously applied) were explored in a short-term microcosm experiment. Spring wheat (Triticum aestivum L.) was grown in a microcosm with six different treatments: no amendment (CK), DMPP homogeneously applied (DMPP-hom), urea homogeneously applied (Urea-hom), urea with DMPP homogeneously applied (Urea + DMPP-hom), urea placement (Urea-place), and urea with DMPP placement (Urea + DMPP-place). After 28 d, plant biomass, soil inorganic nitrogen content, distribution of soil inorganic nitrogen and plant roots in the soil were analyzed. The soil inorganic N and plant roots tended to be distributed asymmetrically in the placement treatment but were distributed symmetrically in the homogeneous treatment. DMPP addition significantly increased the soil NH-N content and decreased the NO-N content, especially near the fertilized zones in the placement treatment. Compared to the urea-only treatments, DMPP application significantly increased the shoot biomass and root lengths of the wheat in the homogeneous treatment but decreased them in the placement treatment. Therefore, homogeneously applied urea and DMPP may produce a more uniform nutrient distribution, leading to greater nitrogen retention in the soil and thus accelerating wheat growth.
Journal of Plant Nutrition and Soil Science 04/2014; 177(2). DOI:10.1002/jpln.201100390 · 1.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Annual production of crop residues has reached nearly 4 billion metric tons globally. Retention of this large amount of residues on agricultural land can be beneficial to soil C sequestration. Such potential impacts, however, may be offset if residue retention substantially increases soil emissions of N2O, a potent greenhouse gas and ozone depletion substance. Residue effects on soil N2O emissions have gained considerable attention since early 1990s; yet, it is still a great challenge to predict the magnitude and direction of soil N2O emissions following residue amendment. Here, we used a meta-analysis to assess residue impacts on soil N2O emissions in relation to soil and residue attributes, i.e., soil pH, soil texture, soil water content, residue C and N input, and residue C:N ratio. Residue effects were negatively associated with C:N ratios, but generally residue amendment could not reduce soil N2O emissions, even for C:N ratios well above ca. 30, the threshold for net N immobilization. Residue effects were also comparable to, if not greater than, those of synthetic N fertilizers. In addition, residue effects on soil N2O emissions were positively related to the amounts of residue C input as well as residue effects on soil CO2 respiration. Furthermore, most significant and stimulatory effects occurred at 60-90% soil water-filled pore space and soil pH 7.1-7.8. Stimulatory effects were also present for all soil textures except sand or clay content 10%. However, inhibitory effects were found for soils with >90% water-filled pore space. Altogether, our meta-analysis suggests that crop residues played roles beyond N supply for N2O production. Perhaps, by stimulating microbial respiration, crop residues enhanced oxygen depletion and therefore promoted anaerobic conditions for denitrification and N2O production. Our meta-analysis highlights the necessity to connect the quantity and quality of crop residues with soil properties for predicting soil N2O emissions.
Global Change Biology 06/2013; 19(10). DOI:10.1111/gcb.12274 · 8.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Soil N2O emissions can affect global environments because N2O is a potent greenhouse gas and ozone depletion substance. In the context of global warming, there is increasing concern over the emissions of N2O from turfgrass systems. It is possible that management practices could be tailored to reduce emissions, but this would require a better understanding of factors controlling N2O production. In the present study we evaluated the spatial variability of soil N2O production and its correlation with soil physical, chemical and microbial properties. The impacts of grass clipping addition on soil N2O production were also examined. Soil samples were collected from a chronosequence of three golf courses (10, 30, and 100-year-old) and incubated for 60 days at either 60% or 90% water filled-pore space (WFPS) with or without the addition of grass clippings or wheat straw. Both soil N2O flux and soil inorganic N were measured periodically throughout the incubation. For unamended soils, cumulative soil N2O production during the incubation ranged from 75 to 972 ng N g−1 soil at 60% WFPS and from 76 to 8842 ng N g−1 soil at 90% WFPS. Among all the soil physical, chemical and microbial properties examined, soil N2O production showed the largest spatial variability with the coefficient of variation ~110% and 207% for 60% and 90% WFPS, respectively. At 60% WFPS, soil N2O production was positively correlated with soil clay fraction (Pearson's r = 0.91, P < 0.01) and soil NH4+–N (Pearson's r = 0.82, P < 0.01). At 90% WFPS, however, soil N2O production appeared to be positively related to total soil C and N, but negatively related to soil pH. Addition of grass clippings and wheat straw did not consistently affect soil N2O production across moisture treatments. Soil N2O production at 60% WFPS was enhanced by the addition of grass clippings and unaffected by wheat straw (P < 0.05). In contrast, soil N2O production at 90% WFPS was inhibited by the addition of wheat straw and little influenced by glass clippings (P < 0.05), except for soil samples with >2.5% organic C. Net N mineralization in soil samples with >2.5% organic C was similar between the two moisture regimes, suggesting that O2 availability was greater than expected from 90% WFPS. Nonetheless, small and moderate changes in the percentage of clay fraction, soil organic matter content, and soil pH were found to be associated with large variations in soil N2O production. Our study suggested that managing soil acidity via liming could substantially control soil N2O production in turfgrass systems.
[Show abstract][Hide abstract] ABSTRACT: It is a common agricultural practice for crop residues to be plowed into the soil or left on the soil surface. Soil addition of crop residues can considerably modify soil microbial activity and net N mineralization, and in general such modifications are negatively related to the C:N ratios of crop residues. Yet, little is known on the impacts of crop residues of different C:N ratios on soil nitrous oxide (N2O) production under different aeration conditions via nitrification and denitrification. In this study, an 84-day laboratory incubation was conducted under aerobic and O2-limited conditions and soil N2O production was measured every 3 days after the addition of plant materials with a wide range of C:N ratios from 14 to 297. Two aerobic conditions were created by adjusting the water content of soil at a bulk density of 1.1 g cm−3 to 30% water-filled pore space (WFPS) and 60% WFPS, and two O2-limited conditions were made by 90% WFPS and fluctuation between 90% and 30% WFPS. Each fluctuation cycle lasted 9 days and soil water content was readjusted to 90% WFPS at the end of each cycle. We also measured microbial respiration activity and net N mineralization periodically (i.e., 3, 7, 14, 28, 42, 56, 70, and 84 days) during the incubation and microbial biomass C at the end of incubation. At aerobic conditions, soil amendments of plant materials, regardless of their C:N ratios, all enhanced soil N2O production. However, net N mineralization was dependent on plant material C:N ratios, being significantly higher or lower than the control for C:N ratios ∼15 and C:N ratios ≥44, respectively. Such inconsistent responses indicated that nitrifiers mediating nitrification and therefore byproduct N2O production could strongly compete with heterotrophic microbes for NH4+ and therefore net N mineralization was not a good predictor for nitrification-associated N2O production. Interestingly, plant material additions reduced soil N2O production by up to ∼95% at O2-limited conditions, perhaps due to NO3− limitation. Soil NO3− production via nitrification could be low at O2-limited conditions, and soil NO3− availability could be further reduced due to increases in microbial biomass and thus microbial N assimilation after plant material additions. This NO3− limitation might enhance N2O reduction to N2, by which denitrifiers could harvest more energy from the consumption of limited NO3−. Nonetheless, our results revealed contrasting differences in N2O production between aerobic and O2-limited conditions following soil amendments of plant materials.
[Show abstract][Hide abstract] ABSTRACT: The effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N transformations and composition of ammonia-oxidizing bacteria (AOB) communities was investigated at the centimeter scale in a microcosm experiment under laboratory conditions. After 28 days, samples were collected from soil treated with urea or urea and DMPP at increasing distance from the fertilizer zone; this distance ranged from 0 to 5 cm in both horizontal and vertical directions. The results showed that DMPP application significantly increased soil pH and NH 4 + -N and mineral N (NH 4 + -N, NO 3 − -N, and NO 2 − -N) concentrations but decreased (NO 3 − + NO 2 − )-N concentration, and such effect was decreased by increasing the distance from the fertilizer zone. Fingerprint profiles of denaturing gradient gel electrophoresis showed that the number of bands decreased by increasing the distance from the fertilizer zone due to decreasing NH 4 + -N concentrations in the urea treatment. Compared to urea applied alone, DMPP application increased NH 4 + -N concentrations and decreased AOB diversity from 0 to 3 cm but promoted diversity from 3 to 5 cm distance from the fertilizer zone. A phylogenetic analysis showed that AOB communities were dominated by Nitrosospira cluster 3. Therefore, the nitrification inhibitor DMPP modified the composition of AOB communities by increasing the distance from the fertilizer zone and this probably was related to the changes in soil pH and inorganic N concentration.
Biology and Fertility of Soils 01/2013; DOI:10.1007/s00374-012-0692-3 · 3.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Microcosm experiments were carried out to study the effects of bacterial-feeding nematodes and indigenous microbes and their interactions on the degradation of prometryne and soil microbial activity in contaminated soil. The results showed that soil indigenous microbes could degrade prometryne up to 59.6-67.9%; bacterial-feeding nematodes accelerated the degradation of prometryne in contaminated soil, and prometryne degradation was raised by 8.36-10.69%. Soil microbial biomass C (C(mic)), basal soil respiration (BSR), and respiratory quotient (qCO(2)) increased in the beginning of the experiment and decreased in the later stage of the experiment. Nematodes grew and reproduced quite fast, and did increase the growth of soil microbes and enhance soil microbial activity in prometryne contaminated soil during the incubation period.