Labile soil organic carbon pools are valuable indicators of soil quality, early changes in soil total organic carbon (TOC) stocks, and (hence) changes in soil carbon sequestration pools and dynamics ...induced by changes in soil management practices. To improve the management of loess soils in China, we have examined effects of soil and nutrient management treatments applied in a 20-year experiment on TOC and the following fractions: particulate organic carbon (POC), light fraction organic carbon (LFOC), microbial biomass carbon (MBC) and permanganate oxidizable carbon (KMnO4 C). The soil management regimes were cropland abandonment (Abandonment), bare fallow without vegetation (Fallow) and a wheat-maize cropping system (Cropping). Cropping was combined with the following nutrient management treatments: control (CK, no nutrient input), nitrogen only (N), nitrogen and potassium (NK), phosphorus and potassium (PK), NP, NPK, straw plus NPK (SNPK) and two levels of manure (M, 13.7 and 20.6tha−1) plus NPK (M1NPK and M2NPK). After 20years, the Fallow treatment resulted in significantly lower TOC by 22% and labile C fractions by 29%–43% except MBC than Cropping, while Abandonment markedly increased all labile C fractions by 43%–64% except POC relative to Cropping, but the Abandonment and Cropping regimes resulted in similar TOC contents (10.75gkg−1 and 10.16gkg−1, respectively). Of the four C fractions, LFOC and KMnO4 C were the most sensitive indicators of changes in TOC induced by the soil management regimes. Under Cropping, TOC contents were similar in NP, NPK and SNPK plots, and significantly higher than those in CK plots (by 34%, 32% and 45%, respectively). Manure addition further enhanced TOC contents, which were highest following the M2NPK treatment (13.88gkg−1). Labile C fractions were also significantly higher following the treatments including organic amendment than following applications solely of chemical fertilizers, except that the SNPK, NP and NPK treatments resulted in similar LFOC contents. Application solely of chemical fertilizers had no significant effects on LFOC and KMnO4 C fractions compared with CK. Nevertheless, application of NP or NPK significantly increased contents of POC and MBC relative to CK (by 115% and 90% or 31% and 53%, respectively). Thus, LFOC and KMnO4 C fractions were not sensitive indicators of changes in TOC induced by mineral nutrient management practices under current conditions. Overall, given the minor differences between the effects of the NP and NPK treatments, application of manure and NP appears to be the most suitable management practice for improving TOC sequestration in the loess soil.
► Soil management regimes had significant effects on TOC and its fractions. ► Bare fallow resulted in significantly lower labile C fractions than Cropping. ► Abandonment markedly increased labile C fractions except POC relative to Cropping. ► Integrated application of manure and NPK greatly improved TOC and its labile pools.
Understanding organic carbon (OC) sequestration in aggregates and OC stability under different fertilization practices is of key importance in improving soil quality and crop productivity and in ...mitigating the causes of climate change. A long-term field experiment established in 1990 was used to assess the influence of organic and inorganic fertilizers on aggregate-associated OC and its mineralization and on the SOC stock at a soil depth of 0–20cm under an intensive wheat-maize cropping system on Anthrosol in North China. The study involved three treatments: CK, control without fertilization; NPK, nitrogen (N), phosphorus (P) and potassium (K) fertilizers; MNPK, manure (M) combined with N, P and K fertilizers. Soil samples were collected and analyzed to determine the size distribution of aggregates, which were separated by dry sieving; the concentrations of OC and N in aggregates (>2, 0.25–2 and <0.25mm) and bulk soils; and respiration from aggregates and bulk soils in the 0–10 and 10–20cm layers after 21years. Fertilization did not affect the size distribution of aggregates in the surface soil layer, but there was a significant change in the subsurface layer in response to manure addition. Application of NPK and MNPK significantly and evenly augmented OC and N sequestration in the three aggregate classes tested. However, the OC mineralization rate was substantially higher in micro- than in macro-aggregates. Application of NPK and MNPK considerably increased OC mineralization in both aggregates and bulk soils; MNPK yielded the highest values. OC mineralization rates in bulk soils were comparable among the three treatments for the surface layer, but they increased in the subsurface layer because of adding manure. Overall, soils treated for 21years with NPK and MNPK showed increases in the OC pools in the top 20cm of 7.42 and 22.83MgCha−1, respectively, compared with the control treatment, and had average sequestration rates of 353 and 1087kgCha−1yr−1 respectively. Thus, appropriate application of NPK, alone or in combination with manure, can lead to improved OC sequestration by evenly augmenting aggregate-associated OC and providing the same degree of protection for OC in both macro-aggregates and micro-aggregates under a winter wheat-summer maize rotation on Anthrosol.
•Fertilization evenly augmented OC and N sequestration in all aggregates.•OC respiration rate was markedly higher in micro- than in macro-aggregates.•SOC respiration rates in bulk soil were same among treatments at 0–10cm layer.•SOC sequestration rates were 353kgCha−1yr−1 under NPK treatment.•SOC sequestration rates were 1087kgCha−1yr−1 under MNPK treatment.
▶ No-tillage combined with crop residue mulching was not recommended for spring maize cultivation in the study area. ▶ Ridges covered by plastic film combined with bare furrow may not sustain maize ...productivity in the long run. ▶ Ridges covered by plastic film combined with furrow mulched by crop residue could be a suitable measure for sustaining maize productivity and maintaining soil fertility.
The large dryland area of the Loess Plateau is subject of developing strategies for a sustainable crop production, e.g. by modifications of field management affecting soil water status and crop productivity. A three-year field experiment was conducted to investigate the effects of field management practices on soil water, maize development and yield on the Loess Plateau of China. The field management practices included traditional tillage (CK), no-till with crop residue mulch (SM), alternating ridges mulched with plastic film and bare furrows (PM) and alternating ridges mulched with plastic film and furrows mulched with crop residue (PSM). The soil water storage was higher under SM than the other treatments, except in the first half of the first maize growing season. Higher soil water stimulated maize growth, as indicated by a higher leaf area index and greater biomass accumulation, and thus the highest grain yield (7251
kg
ha
−1) and water use efficiency (2.41
kg
m
−3) in the first experimental season was recorded in SM plots. Maize growth and grain yield did not benefit in the other two seasons. Although soil water storage was similar between PM or PSM and CK treatments at sowing and harvest time, consistently better maize development and higher grain yield were observed through three seasons in PM and PSM plots. Under the PM and PSM treatments grain yield was 8–24% and 13–24% higher, respectively, than under the CK treatment, indicating that utilization of water and other resources was better under these treatments. However, significant soil water depletion in deeper (>100
cm) soil layers was detected at harvest time under PM compared with CK, implying that higher yields might not be sustained in the long run. In conclusion, crop residue mulching combined with no-tillage is not recommended for spring-sown maize system under these temperate climate conditions. Instead, use of ridges mulched with plastic film combined with crop residues in furrows may be an efficient measure to increase crop yield and maintain or improve soil fertility.
Soil aggregation was studied in a 21-year experiment conducted on an Anthrosol. The soil management regimes consisted of cropland abandonment, bare fallow without vegetation and cropping system. The ...cropping system was combined with the following nutrient management treatments: control (CONTROL, no nutrient input); nitrogen, phosphorus and potassium (NPK); straw plus NPK (SNPK); and manure (M) plus NPK (MNPK). Compared with the CONTROL treatment, the abandonment treatment significantly increased the formation of large soil macroaggregates (>2 mm) and consequently improved the stability of aggregates in the surface soil layer due to enhancement of hyphal length and of soil organic matter content. However, in response to long-term bare fallow treatment aggregate stability was low, as were the levels of aggregating agents. Long term fertilization significantly redistributed macroaggregates; this could be mainly ascribed to soil organic matter contributing to the formation of 0.5-2 mm classes of aggregates and a decrease in the formation of the >2 mm class of aggregates, especially in the MNPK treatment. Overall, hyphae represented a major aggregating agent in both of the systems tested, while soil organic compounds played significantly different roles in stabilizing aggregates in Anthrosol when the cropping system and the soil management regimes were compared.
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.
The effect and relative contributions of C and P inputs on soil microbial biomass P (MBP) accumulation were studied in three long-term soil fertility experiments with various soil and climate ...characteristics at Qiyang, Yangling, and Wulumuqi. The maximum of soil MBP in all three sites was 47.8 mg P kg
-1
. The MBP accumulated per unit in soil (mg P kg
-1
soil) was correlated with a 4.91 mg kg
-1
increase in Olsen P. For each unit increase in P surplus (kg P ha
-1
), manure C (kg C ha
-1
), and stubble C (kg C ha
-1
), MBP accumulation increased by 330, 3.7, and 13 units (μg P kg
-1
soil), respectively. The soil MBP was positively correlated with crop yield and P uptake, making the soil MBP a useful soil P fertility index. The critical levels of the soil MBP pool were 140 kg ha
-1
, 57–62 kg ha
-1
, and 33–35 kg ha
-1
in acidic red soil, loessial soil, and grey desert soil, respectively. This is the first report to establish a quantitative index of soil fertility based on the soil MBP pool. Our findings demonstrate that C input is a good driver of soil MBP accumulation. Integration of the soil MBP as an index of soil P fertility into agricultural P management is useful to help manage mineral P fertilizers as part of sustainable agricultural practices.
As labile organic pools, soluble organic matter and soil microbial biomass are sensitive to changes in soil management and therefore good indicators of soil quality. Effects of a 17-year long-term ...fertilization on soil microbial biomass C (SMBC) and N (SMBN), soluble organic C, and soluble organic N during the maize growing season were evaluated in a loess soil (Eum-Orthic Anthrosol) in northwest China. The fertilization treatments included no fertilizer (CK), inorganic N, P, and K fertilizer (NPK), cattle manure plus NPK fertilizer (MNPK), and straw plus NPK fertilizer (SNPK). Our results showed that C storage in the 0-20 cm soil layer was 28% to 81% higher in the fertilized treatments compared to the unfertilized treatment. In the 0-10 cm soil layer, SMBC and SMBN in the three fertilized treatments were higher than in the unfertilized treatment on all sampling dates, while microbial biomass C and N in the 0−10 cm soil layers were the highest at grain filling. In the same soil layer, soil-soluble organic C generally decreased in the order MNPK > SNPK > NPK > CK, while soluble organic N was the highest in the MNPK followed by the SNPK treatment. There was no significant difference in soluble organic N in the NPK and CK treatments throughout most of the maize growing season. Changes in soluble organic N occurred along the growing season and were more significant than those for soluble organic C. Soluble organic N was the highest at grain filling and the lowest at harvest. Overall, our results indicated that microbial biomass and soluble organic N in the surface soil were generally the highest at grain filling when maize growth was most vigorous. Significant positive relationships were found between soluble organic C and SMBC and between soluble organic N and SMBN.
In the realm of forest resource inventory and monitoring, stand-level biomass carbon models are especially crucial. In China, their importance is underscored as they form the bedrock for estimating ...national and international forest carbon storage. This study, based on the data from 52,700 permanent plots in the 9th National Forest Inventory (NFI) of China, was directed towards developing these models. After computing biomass and carbon storage per hectare using specific tree models for 34 species groups, we devised robust volume-derived biomass and carbon storage models for 20 forest types. The application of these models and historical data reveals notably a decline in China's forest carbon storage to 4.90Pg by the late 1970s due to aggressive forest exploitation. However, subsequent conservation and afforestation campaigns have affected a recovery, culminating in a storage of 8.69Pg by the 9th NFI. Over the past 40 years, China's forest carbon storage has surged by 3.79Pg, split between natural forests (2.25Pg) and planted forests (1.54Pg). In benchmarking against three pre-existing models, we discerned discernible biases, underscoring the need for larger modeling sample sizes. Overall, our models stand as a monumental stride in accurately gauging forest carbon storage fluctuations in China, both regionally and nationally.
The carbon-to-phosphorus (C:P) ratios of microorganisms were quantified in the rhizosphere and bulk soil collected from six typical fertilization regimes across three long-term experiments in humid ...(wheat–maize rotation), semiarid (wheat–maize rotation), and arid (maize–wheat–cotton rotation) climate zones. A
32
P labeling incubation experiment allowed to test the relationship between microbial biomass P (MBP) turnover time and the C:P stoichiometric imbalance (Soil
C:P
/Microb
C:P
) between soil (dissolved organic carbon:Olsen-P) and microorganisms (MBC:MBP). The MBC and MBN in the rhizosphere were 1.2 and 1.3 times higher than those in bulk soils, respectively, while the MBP was similar. The MBC:MBP ratio in the rhizosphere was 1.1 times higher than that in bulk soil, while the MBC:MBN ratio was similar. This finding suggested that C and P accumulation in the rhizosphere microorganisms was decoupled from that in the bulk soil. Compared to that in bulk soil, the MBP turnover in the rhizosphere was 1.1 times faster and microbially mediated P release was increased by 13% because of the decrease in the Soil
C:P
/Microb
C:P
. Shoot P content was correlated with the rhizosphere Soil
C:P
/Microb
C:P
and P flux mediated by microorganisms. The Soil
C:P
/Microb
C:P
thresholds allowed to predict the start of an intensive competition between plants and microorganisms for P. Concluding, the stronger the Soil
C:P
/Microb
C:P
in the rhizosphere decrease, the faster is the MBP turnover of homeostatic microorganisms, and furthermore, the microbially mediated P release leads to the decoupling of microbial biomass C and P at the root–soil interface. Soil
C:P
/Microb
C:P
may be a predictor of the competition between plants and microorganisms.
► The 15N-labeled micro-plots were established in three long-term fertilized soils. ► We compared the N use efficiency (NUE) of wheat and maize rotation in the soils. ► Addition of manure and ...inorganic fertilizer synchronized N supply and demand. ► It significantly increased crop yields, NUE, and reduced N losses.
High soil organic matter content may improve synchronization between N supply and crop demand. To test this hypothesis, we compared the fate of 15N-labeled fertilizer in soil with different management history. The soils had received no fertilizer (No-F soil), inorganic N, P, and K fertilizer (NPK soil), or manure plus N, P, and K fertilizer (MNPK soil) as part of a 19-year long-term fertilization trial. The N use efficiency (NUE) of wheat (Triticum aestivum L.) was 62% in the MNPK soil, higher than that in the NPK soil (50% NUE), and in the No-F soil (13% NUE). At wheat harvest, 38% of the fertilizer 15N remained in the 0–100cm depth of the MNPK soil, significantly less that the amount of fertilizer 15N that remained in the NPK soil (45%) or in the No-F soil (88%). More than 50% of the fertilizer 15N in the No-F soil had leached below the 20cm depth by wheat harvest, significantly more than in the NPK or MNPK soils. The amount of immobilized 15N at wheat stem elongation was significantly (P<0.05) greater in the MNPK soil than in the NPK soil. The mineralization of immobilized 15N between stem elongation and flowering was also significantly higher in the MNPK soil than in the NPK soil (P<0.05). The succeeding maize (Zea mays L.) crop took up 9% of the fertilizer 15N in the No-F soil, 6% of the fertilizer 15N in the NPK soil, and 2% of the fertilizer 15N in the MNPK soil. Combined soil profile and crop removal analyses at wheat harvest accounted for nearly 100% of the fertilizer 15N for all three soils. However, only 45% of the fertilizer 15N added to the No-F soil could be accounted for at maize harvest, significantly less than the recovery rate in the NPK (83%) and MNPK (85%) soils (P<0.01). These results indicate that the fertilizer 15N was mainly lost from these soils during the maize growing season. We conclude that the combined application of manure and inorganic fertilizers improves synchrony between N supply and crop demand, thus reducing N losses from agriculture.
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