Although diazotrophs are important in the nitrogen (N)-cycle and contribute to the pool of plant available N, the population response to long-term inorganic fertilization is largely unknown. Here, we ...investigated the diazotrophic populations in both the bulk and rhizosphere soils of maize grown in an acidic farmland soil that experienced 25 years of inorganic fertilization. The fertilization regimes included unfertilized control, N fertilizer alone, N fertilizer with quicklime, phosphorus (P) and potassium (K) fertilizers, N + P + K fertilizers, and N + P + K fertilizers with quicklime. Quantitative PCR and high-throughput pyrosequencing of the nifH gene were used to analyze diazotrophic abundance and community composition. All of the fertilizer treatments improved soil nutrient availability, but those without quicklime caused soil acidification. Maize biomasses and nifH copy numbers were significantly lower under N and N + P + K treatments but increased under P + K fertilization. Quicklime applications effectively alleviated the inhibitory effect of N input. Fertilization led to decreases in operational taxonomic unit richness and shifts in diazotrophic community composition. Soil pH and nutrient availability had a cooperative effect on diazotrophic abundance, while soil nutrient availability appeared to be the main factor shaping diazotrophic community structure. Rhizosphere effects increased the nifH gene copy number but did not obviously change the diazotrophic community composition on the current research scale. Overall, the long-term inorganic fertilization affected both diazotrophic abundance and community composition, and the fertilizer treatment had a greater influence than quicklime remediation or crop cultivation on community composition.
•Long-term N fertilization decreased soil diazotrophic abundance and OTU richness.•Both maize cultivation and PK fertilization increased soil diazotrophic abundance.•Soil pH and nutrient availability had a cooperative effect on diazotrophic abundance.•Fertilization had a greater influence on diazotrophic community composition.•Soil nutrient rather than pH influenced diazotrophic community composition.
No fertilized soils (unfertilized and fallow treatments) and soils subjected to 28-year fertilization regimes, including mineral fertilization (PK and NPK) and manure amendments (NPKM and M), were ...incubated with or without
13
C - glucose. Results showed that compared to mineral fertilization (0.64 − 0.69), the manure amendments significantly increased microbial C use efficiency (CUE) (0.76 − 0.79), mainly due to higher soil pH, lower resource stoichiometric ratios of dissolved organic C (DOC): mineral N, DOC: available P and mineral N: available P, and lower specific activities (per microbial biomass C unit) of β-1,4-glucosidase, N-acetyl-glucosaminidase and acid phosphatase. Glucose addition increased SOC mineralization, inducing positive priming effect (PE) with lower values in the manure amendments (0.11 − 0.12 mg C g
−1
SOC) relative to mineral fertilization (0.25 − 0.55 mg C g
−1
SOC). The PE was negatively correlated with soil pH and positively associated with resource stoichiometric ratios of DOC: mineral N, DOC: available P and mineral N: available P, mainly due to microbes mineralizing SOM to release nutrients, as indicated by the positive relationships between PE and the specific activities of N-acetyl-glucosaminidase and acid phosphatase. Concluding, relative to mineral fertilization, long-term manure amendment could increase CUE and decrease PE via alleviated soil acidifi
c
ation and resource limitation, thus facilitating soil C sequestration.
Understanding the processes that regulate communities of microorganisms is a key issue and focus in microbial ecology. Although fungi play a critical role in soil biogeochemical cycling, their ...community assembly processes remain largely unknown, especially in agricultural soils. In this study, we investigated the relative importance of five community assembly processes (variable selection, homogeneous selection, homogeneous dispersal, dispersal limitation and an undominated process) in soil fungal communities under long‐term (28 years, 1990–2018) fertilization management consisting of 12 different treatments in triplicate field plots. Using Illumina MiSeq sequencing of the 18S rRNA eukaryotic gene, we observed that fungal communities in manure treatments were all structured primarily by homogeneous dispersal, whereas the communities in chemical fertilizer treatments were structured primarily by homogeneous dispersal and an undominated process. Soil calcium played an important role in shaping the soil fungal community, whereas soil organic matter concentrations had a considerable impact on the soil fungal phylogenetic community composition. Overall, our results suggest that fertilization management should be considered as a key factor driving microbial community assembly processes in farmed soils.
Highlights
Soil Ca played a key role in shaping eukaryotic microbial community
Chemical fertilization resulted in homogenous selection and undominated processes.
A combination of chemical and manure fostered homogenous selection processes.
The phosphorus activation coefficient (PAC, the ratio of available P to total P) is an important indicator of soil P availability and the transformation of P fractions. Understanding the details of ...the PAC is useful to estimate soil available P status and to provide P management guidance. In this research, soils from five long-term (23 years) fertilization treatments in three croplands were selected to examine the relationships between the PAC and P fractions and to analyse the influencing factors. PAC was affected by both soil types and fertilization treatments. Compared to the unfertilized control (CK) treatment, long-term P application significantly increased the PAC, all of the inorganic P (Pi) fractions and most of the organic P (Po) fractions in all the three soils, particularly in chemical fertilizer combined with manure treatment (NPKM). The PAC was significantly correlated to all of the Pi fractions proportions (P<0.05) except for Dil. HCl-Pi and Conc. HCl-Pi. Compared with CK, the chemical P and chemical P combined with manure treatments increased the ratio of total Pi fractions to total Po fractions (Pit/Pot); furthermore, NPKM significantly increased the organic C (Co) content and decreased the Co/Pot ratio. Stepwise multiple regressions showed that PAC = 0.93 Co+0.69 Pit/Pot-0.07 Co/Pot-0.27CaCO3-3.79 (R2 = 0.924, P<0.001). In addition, the variance partitioning analysis showed that more variance of PAC is explained by soil factors (29.53%) than by P input (0.19%) and climate (0.25%) factors. Our findings demonstrate that P application increased the PAC by changing the Co content and the proportion of P fractions. Moreover, soil factors were the most important drivers of P transformations, and NPKM was optimal for improving soil fertility in Chinese croplands.
The Olsen phosphorus (Olsen-P) concentration of soil is generally a good indicator for estimating the bioavailability of P and environmental risk in soils. To maintain soil Olsen-P at adequate levels ...for crop growth and environmental sustainability, the relationship between soil Olsen-P and the P budget (the P input minus the output) as well as the variations of soil Olsen-P and P budget were investigated from three long-term (22 years) experiments in China. Five treatments were selected: (1) unfertilized control (CK); (2) nitrogen and potassium (NK); (3) nitrogen, phosphorous, and potassium (NPK); (4) nitrogen, phosphorous, potassium and straw; (5) nitrogen, phosphorous, potassium and manure. The results showed that without P fertilizers (CK, NK), there was a soil P deficit of 75-640 kg ha-1, and the lowest P deficit (mean of CK and NK) was in Eutric Cambisol. Soil Olsen-P decreased by 0.11-0.39 mg kg-1 year-1 in the order of Luvic Phaeozems > Eutric Cambisol > Calcaric Cambisol. Soil Olsen-P and the P deficit had a significantly (P<0.01) positive linear relationship. For every 100 kg of P ha-1 of deficit, soil Olsen-P decreased by 0.44-9.19 mg kg-1 in the order of Eutric Cambisol > Luvic Phaeozems > Calcaric Cambisol. Under the P fertilizer treatments (NPK, NPKS, and NPKM), soil Olsen-P showed an obvious surplus (except the NPK and NPKS in Luvic Phaeozems) of 122-2190 kg ha-1, and the largest P surplus was found under the NPKM treatment at each site. The relation between soil Olsen-P and the experimental years could be simulated using quadratic equation of one unknown in Calcaric Cambisol for the lower P input after 14 years of fertilization. And soil Olsen-P increased by 1.30-7.69 mg kg-1 year-1 in the order of Luvic Phaeozems > Eutric Cambisol. The relation between soil Olsen-P and the P surplus could be simulated by a simple linear equation except under NPK and NPKS in Luvic Phaeozems. With 100 kg ha-1 P surplus, soil Olsen-P increased by 3.24-7.27 mg kg-1 in the order of Calcaric Cambisol (6.42 mg kg-1) > Eutric Cambisol (3.24 mg kg-1). In addition, the change in soil Olsen-P with a 100 kg P ha-1 surplus (soil Olsen-P efficiency) was affected by the soil organic matter (SOM), pH, and CaCO3 content, etc. In the practice of fertilization, it's not necessary to increase the amount of P fertilizers, farmers should take measure to solve the local problem, for adjust the soil pH of Eutric Cambisol and Calcaric Cambisol, and apply more nitrogen in Luvic Phaeozems. In the area of serious soil P surplus, it is encouraged to stop applying P fertilizers for a few years to take advantage of soil accumulated P and make the high Olsen-P content decrease to a reasonable level.
Summary
Different fertilization managements of red soil, a kind of Ferralic Cambisol, strongly affected the soil properties and associated microbial communities. The association of the soil microbial ...community and functionality with long‐term fertilization management in the unique low‐productivity red soil ecosystem is important for both soil microbial ecology and agricultural production. Here, 454 pyrosequencing analysis of 16S recombinant ribonucleic acid genes and GeoChip4‐NimbleGen‐based functional gene analysis were used to study the soil bacterial community composition and functional genes involved in soil organic carbon degradation. Long‐term nitrogen‐containing chemical fertilization‐induced soil acidification and fertility decline and significantly altered the soil bacterial community, whereas long‐term organic fertilization and fallow management improved the soil quality and maintained the bacterial diversity. Short‐term quicklime remediation of the acidified soils did not change the bacterial communities. Organic fertilization and fallow management supported eutrophic ecosystems, in which copiotrophic taxa increased in relative abundance and have a higher intensity of labile‐C‐degrading genes. However, long‐term nitrogen‐containing chemical fertilization treatments supported oligotrophic ecosystems, in which oligotrophic taxa increased in relative abundance and have a higher intensity of recalcitrant‐C‐degrading genes but a lower intensity of labile‐C‐degrading genes. Quicklime application increased the relative abundance of copiotrophic taxa and crop production, although these effects were utterly inadequate. This study provides insights into the interaction of soil bacterial communities, soil functionality and long‐term fertilization management in the red soil ecosystem; these insights are important for improving the fertility of unique low‐productivity red soil.
Purpose
Soil acidification from chemical N fertilization has worsened and is a major yield-limiting factor in the red soil (Ferralic Cambisol) of southern China. Assessment of the acidification ...process under field conditions over a long term is essential to develop strategies for maintaining soil productivity. The objective of this study was to quantify soil acidification rates from chemical fertilizers and determine the amount of manure needed to inhibit the acidification process.
Materials and methods
A long-term experiment with various fertilizations was carried out during 1990–2008 in a wheat–corn cropping system in the red soil of southern China. Treatments included non-fertilized control, chemical N only (N), chemical N and P (NP), chemical N, P and K (NPK), pig manure only (M), and NPK plus M (NPKM; 70 % total N from M). All N treatments had an input of 300 kg N ha
−1
year
−1
. Annual soil sampling was carried out for pH measurement and acidity analysis.
Results and discussion
Soil pH decreased sharply from an initial pH of 5.7 and then stabilized after 8 to 12 years of fertilization in the N, NP, and NPK treatments with a final pH of 4.2, 4.5, and 4.5, respectively. These three treatments significantly increased soil exchangeable acidity dominated by Al, decreased soil exchangeable base cations (Ca
2+
and Mg
2+
), and elevated acidification rates (3.2–3.9 kmol H
+
ha
−1
year
−1
). In contrast, the manure applications (M or NPKM) showed either an increase or no change in soil pH and increases in soil exchangeable base cations.
Conclusions
Urea application to the intensive cropping system accelerated acidification of the red soil during the 18-year field experiment. As 70 % or more total N source, continuous manure application can fully prevent or reverse red soil acidification process. As an effective animal waste management tool, manure incorporation into the acidic soil can promote the overall agricultural sustainability.
A long-term experiment with various fertilizations was carried out during 1990-2006 in a double cropping system rotated with wheat (Triticum Aestivium L.) and corn (Zea mays L.) in the red soil of ...southern China. The experiment consisted of eight treatments: non-fertilization (CK), nitrogen-phosphorus fertilization (NP), phosphorus-potassium fertilization (PK), nitrogen-phosphorus-potassium fertilization (NPK), pig manure (M), pig manure and NPK fertilization (NPKM), high rates of NPKM (hNPKM), and straw returned with inorganic fertilizers (NPKS). Applications of manure (i.e., M, NPKM and hNPKM) significantly increased soil organic carbon (SOC) and total nitrogen contents. Applications of inorganic fertilizers without manure showed small influences on SOC, but resulted in declines of soil total nitrogen over the long-term experiment. Grain yields were more than doubled under fertilizations for both wheat and corn, with the highest under the NPKM and hNPKM treatments and the lowest under non-fertilization. Long-term cropping practices without fertilization or with unbalanced fertilizations (e.g., NP and PK) caused low grain yields. The balanced fertilization of NPK increased grain yields. However, such practice was not able to maintain high grain yields during the last few years of experiment. Our analyses indicate that both wheat and corn grain yields are significantly correlated with SOC, total and available nitrogen and phosphorus. However, the relationships are stronger with total nitrogen (r = 0.5-0.6) than with available nitrogen (r = 0.26-0.3), indicating the importance of maintaining soil total nitrogen in agricultural practice.
Background and aims Sufficient soil phosphorus (P) is important for achieving optimal crop production, but excessive soil P levels may create a risk of P losses and associated eutrophication of ...surface waters. The aim of this study was to determine critical soil P levels for achieving optimal crop yields and minimal P losses in common soil types and dominant cropping systems in China. Methods Four long-term experiment sites were selected in China. The critical level of soil Olsen-P for crop yield was determined using the linear-plateau model. The relationships between the soil total P, Olsen-P and CaCl₂-P were evaluated using two-segment linear model to determine the soil P fertility rate and leaching change-point. Results The critical levels of soil Olsen-P for optimal crop yield ranged from 10.9 mg kg⁻¹ to 21.4 mg kg⁻¹, above which crop yield response less to the increasing of soil Olsen-P. The P leaching change-points of Olsen-P ranged from 39.9 mg kg⁻¹ to 90.2 mg kg⁻¹, above which soil CaCl₂-P greatly increasing with increasing soil Olsen-P. Similar change-point was found between soil total P and Olsen-P. Overall, the change-point ranged from 4.6 mg kg⁻¹ to 71.8 mg kg⁻¹ among all the four sites. These change-points were highly affected by crop specie, soil type, pH and soil organic matter content. Conclusions The three response curves could be used to access the soil Olsen-P status for crop yield, soil P fertility rate and soil P leaching risk for a sustainable soil P management in field.
Purpose
Crop straws and animal manure have the potential to ameliorate acidic soils, but their effectiveness and the mechanisms involved are not fully understood. The aim of this study was to ...evaluate the effectiveness of two crop (maize and soybean) straws, swine manure, and their application rates on acidity changes in acidic red soils (Ferralic Cambisol) differing in initial pH.
Materials and methods
Two red soils were collected after 21 years of the (1) no fertilization history (CK soil, pH 5.46) and (2) receiving annual chemical nitrogen (N) fertilization (N soil, pH 4.18). The soils were incubated for 105 days at 25 °C after amending the crop straws or manure at 0, 5, 10, 20, and 40 g kg
−1
(
w
/
w
), and examined for changes in pH, exchangeable acidity, N mineralization, and speciation in 2 M KCl extract as ammonium (NH
4
+
) and nitrate plus nitrite (NO
3
−
+ NO
2
−
).
Results and discussion
All three organic materials significantly decreased soil acidity (dominated by aluminum) as the application rate increased. Soybean straw was as effective (sometimes more effective) as swine manure in raising pH in both soils. Soybean straw and swine manure both significantly reduced exchangeable acidity at amendment rate as low as 10 g kg
−1
in the highly acidic N soil, but swine manure was more effective in reducing the total acidity especially exchangeable aluminum (e.g., in the N soil from initial 5.79 to 0.50 cmol
(+)
kg
−1
compared to 2.82 and 4.19 cmol
(+)
kg
−1
by soybean straw and maize straw, respectively). Maize straw was less effective than soybean straw in affecting soil pH and the acidity. The exchangeable aluminum decreased at a rate of 4.48 cmol
(+)
kg
−1
per pH unit increase for both straws compared to 6.25 cmol
(+)
kg
−1
per pH unit from the manure. The NO
3
−
+ NO
2
−
concentration in soil increased significantly for swine manure amendment, but decreased markedly for straw treatments. The high C/N ratio in the straws led to N immobilization and pH increase.
Conclusions
While swine manure continues to be effective for ameliorating soil acidity, crop straw amendment has also shown a good potential to ameliorate the acidity of the red soil. Thus, after harvest, straws should preferably not be removed from the field, but mixed with the soil to decelerate acidification. The long-term effect of straw return on soil acidity management warrants further determination under field conditions.
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