C Management Index Research Articles

Divergent effects of long-term fertilization on the carbon management index across soil profiles in key Chinese croplands

Evidence for the variability of the carbon (C) management index (CMI) across surface and subsurface soil layers due to long-term fertilization in diverse agroecological settings is inadequate. Thus, our study aimed to explore the variations in soil organic C (SOC), CMI, and its response ratio (RR-CMI) along soil profiles (0–60 cm) across four croplands in China. These croplands represented two high-fertility sites in Gongzhuling (GZL) and Chongqing (CQ) and two low-fertility sites in Zhengzhou (ZZ) and Qiyang (QY). We evaluated various treatments: control (CK; no fertilizer), inorganic fertilizer (NPK), NPK combined with standard manure (MNPK), and 1.5 times the standard rate of manure and NPK (1.5MNPK). The results indicated a significant increase in SOC content across all depths, ranking as 1.5MNPK > MNPK > NPK > CK, with ranking for the pattern observed across sites as GZL > CQ ≈ QY > ZZ. This led to the most substantial increases, reaching 107, 86, 105, and 62 % more than CK across the soil profile (0–60 cm) under 1.5MNPK across all sites. Moreover, the same treatment showed a significantly higher CMI at 0–60 cm compared to CK, with increases of 37, 19, 65, and 25 % for ZZ, QY, GZL, and QY, respectively. Notably, for the low-fertility soils (ZZ and QY), a higher CMI was observed in the 0–20-cm soil layer), whereas the opposite was true for the high-fertility soil (GZL). Consequently, low-fertility soils exhibited a higher RR-CMI in the 0–20-cm soil layer, whereas the high fertility site (GZL) showed a higher RR-CMI in the 40–60-cm soil layer, suggesting differential accumulation and loss of SOC regulated by soil depth and inherent site fertility. Partial least squares regression analysis further indicated that soil and climatic factors predominantly influenced CMI under long-term fertilization in typical Chinese soils. In conclusion, the long-term application of manure combined with inorganic fertilizer promotes SOC sequestration and enhances CMI, presenting a viable management strategy for enhancing soil quality in the studied regions.

Gypsum, crop rotation, and cover crop impacts on soil organic carbon and biological dynamics in rainfed transitional no-till corn-soybean systems.

Soil organic carbon (SOC), a core soil quality indicator, is influenced by management practices. The objective of our 2012-2016 study was to elucidate the impact of gypsum, crop rotation, and cover crop on SOC and several of its biological indicators under no-till in Alabama (Shorter), Indiana (Farmland), and Ohio (Hoytville and Piketon) in the USA. A randomized complete block design in factorial arrangement with gypsum (at 0, 1.1, and 2.2 Mg/ha annually), rye (Secale cereal L.) vs no cover crop, and rotation (continuous soybean [Glycine max (L) Merr., SS] vs corn [Zea mays, L.]-soybean, both the CS and SC phases) was conducted. Composite soils were collected (0-15 cm and 15-30 cm) in 2016 to analyze microbial biomass C (SMBC), SOC, total N, active C, cold and hot-water extractable C, C and N pool indices (CPI and NPI), and C management index (CMI). Results varied for main effects of gypsum, crop rotation, and cover crop on SOC pools, total N, and SOC lability within and across the sites. Gypsum at 2.2 Mg/ha increased SMBC within sites and by 41% averaged across sites. Likewise, gypsum increased SMBC:SOC, active C, and hot-water C (as indicators of labile SOC) averaged across sites. CS rotation increased SOC, active C, CPI, and CMI compared to SS, but decreased SMBC and SMBC:SOC within and across sites. CPI had a significant relationship with NPI across all sites (R2 = 0.90). Management sensitive SOC pools that responded to the combined gypsum (2.2 Mg/ha), crop rotation (CS), and cover crop (rye) were SMBC, SMBC:SOC, active C, and CMI via SMBC. These variables can provide an early indication of management-induced changes in SOC storage and its lability. Our results show that when SOC accumulates, its lability has decreased, presumably because the SMBC has processed all readily available C into a less labile form.

Reduced tillage with residue retention improves soil labile carbon pools and carbon lability and management indices in a seven-year trial with wheat-mung bean-rice rotation

Soil total organic carbon (TOC) is a composite indicator of soil quality with implications for crop production and the regulation of soil ecosystem services. Research reports on the dynamics of TOC as a consequence of soil management practices in subtropical climatic conditions, where microbial carbon (C) loss is high, are very limited. The objective of our study was to evaluate the impact of seven years of continuous tillage and residue management on soil TOC dynamics (quantitative and qualitative) with respect to lability and stratification under an annual wheat-mung bean-rice cropping sequence. Composite soil samples were collected at 0-15 and 15-30 cm depths from a three-replicate split-plot experiment with tillage treatment as the main plots and crop residue levels as the sub-plots. The tillage treatments included conventional tillage (CT) and strip tillage (ST). Residue levels were high residue level (HR), 30% of the plant height, and low residue level (LR), 15%. In addition to TOC, soil samples were analyzed for particulate organic C (POC), permanganate oxidizable C (POXC), basal respiration (BR), specific maintenance respiration rate (qCO2), microbial biomass C (MBC), potentially mineralizable C (PMC), and TOC lability and management indices. The ST treatment significantly increased the TOC and labile C pools at both depths compared with the CT treatment, with the effect being more pronounced in the surface layer. The HR treatment increased TOC and labile C pools compared with the LR treatment. The ST + HR treatment showed significant increases in MBC, metabolic quotient (qR), C pool index (CPI), C lability index (CLI), and C management index (CMI), indicating improved and efficient soil biological activities in such systems compared with the CT treatment. Similarly, the stratification values, a measure of soil quality improvement, for POC and MBC were > 2, indicating improved soil quality in the ST + HR treatment compared with the CT treatment. The ST + HR treatment not only significantly increased the contents of TOC pools, but also their stocks. The CMI was correlated with qCO2, BR, and MBC, suggesting that these are sensitive indicators of early changes in TOC. The qCO2 was significantly higher in the CT + LR treatment and negatively correlated with MBC and CMI, indicating a biologically stressed soil condition in this treatment. Our findings highlight that medium-term reduced tillage with HR management has profound consequences on soil TOC quality and dynamics as mediated by alterations in labile C pools.

Changes in soil organic matter fractions induced by cropland and pasture expansion in Brazil's new agricultural frontier

Recently, the so-called Matopiba region (northeastern Brazil) has experienced an accelerated agricultural expansion, with large areas of native vegetation (NV: Cerrado biome) converted to extensive pasture (PA) and cropland under no-tillage (CL). However, because soils from this region contain a large amount of sand (> 60%) and a high susceptibility to erosion, concerns have been raised about the impacts of land-use change (LUC) on soil organic matter (SOM) dynamics. Therefore, we assessed the magnitude that agricultural expansion affects SOM fractions in the most common LUC scenarios observed in the Matopiba region. Soil samples were collected to a depth of 1-m in three adjacent sites (i.e., NV, PA, and CL) located in a representative agricultural area of the region. Soil organic matter was physically fractioned into particulate organic matter (POM) and mineral-associated organic matter (MAOM); and carbon (C) and nitrogen (N) were determined in SOM fractions, in addition to in bulk soil samples. Additionally, the C management index (CMI) was used as a proxy to infer soil health changes. The conversion from NV to PA decreased C (by ~28 Mg ha−1 at 0–100 cm) and N (by ~0.5 Mg ha−1 at 0–50 cm) stocks at an annual loss rate of ~1.3 and 0.02 Mg ha−1, respectively. Carbon loss occurred in both POM and MAOM fractions, which were lower in ~36% and 34%, respectively, compared with NV (0–100 cm). This C depletion resulted in the smallest CMI value (75%) in the 0–30 cm soil layer in PA. The conversion from NV to CL had no effect on total C and N stocks (0–100 cm), but impacted C dynamics in SOM fractions. A lower value was observed for MAOM-C (~22%) in the 30–70 cm layer compared to NV, but the C accrual in the POM fraction (~24%) in the uppermost soil layers (0–30 cm) offset MAOM-C loss. This increase in the POM stocks enhanced the CMI, which was 37% higher than NV for the 0–30 cm layer. Our results revealed that PA expansion in the Matopiba region, besides declining C and N levels, reduced soil health as indicated by the low CMI values. On the other hand, land conversion from NV to CL did not impact C and N stocks and increased CMI. However, we advocated that agriculture expansion over NV areas is not a sensible option to promote the region's sustainable development. It should be prioritized on degraded PA areas and be based on best management practices as a strategy to recarbonize PA soils and restore soil health. This is paramount to mitigate climate change and increase sustainable food production in the Matopiba region over time.

The effect of long-term soil surface mulching on SOC fractions and the carbon management index in a semiarid agroecosystem

Soil organic carbon (SOC) and its fractions are widely considered to be valuable indicators for monitoring soil carbon (C) pools and dynamics induced by mulching practices. Thus, a 10-year experiment with three treatments, including no mulching (CK), gravel mulching (GM) and film mulching (FM), was established on the Loess Plateau. The results showed that SOC under GM treatment (7.88 g kg−1) in surface soil (0–20 cm) decreased significantly compared with that of CK (8.59 g kg−1), and that of FM (8.09 g kg−1) did not change significantly. Compared with CK in surface soil, water soluble C (WSC) under FM treatment decreased by 9.36% on average, and hot-water extractable C (HWC) under GM and FM treatments increased by 12.36% and 24.56% on average, respectively. Labile organic C (LOC) determined by the potassium permanganate (P-P) method did not decrease significantly under FM treatment in surface soil, but recalcitrant organic C (ROC), determined by the P–P method, significantly decreased by 9.88% on average. Compared with CK, less labile C (CLL), determined by the modified Walkley-Black (M–W–B) method under GM and FM treatments, significantly decreased by 11.21% and 17.54% on average, respectively, which suggested that CLL was converted to very labile C (CVL) and labile C (CL). This result indicated that the M-W-B method was superior in explaining C turnover. Combined with the C management index (CMI) results of previous studies, CMI was consistently lower under GM treatment, and it was unstable under FM treatment. The sensitivity index (SI) results indicated that HWC was the most sensitive SOC fraction, and LOC and ROC determined by the M–W–B method were more sensitive than those determined by the P–P method. Moreover, CMI calculated by the M–W–B method (10–35%) was more sensitive than that calculated by the P–P method (9–12%). In conclusion, the decrease in SOC under long-term mulching is mainly from ROC, and the M–W–B method is superior to the P–P method.

Organic amendments affect soil organic carbon sequestration and fractions in fields with long-term contrasting nitrogen applications

Organic amendments are widely used to both manage soil organic C (SOC) and improve soil fertility in agro-ecosystems. However, crop production and the mechanisms of SOC sequestration following organic amendment may be affected by long-term differential N fertilizations, hence driving the dynamics in SOC fractions in cultivated fields. Our 3-yr (2016–2019) field experiment evaluated the responses of SOC sequestration and SOC fractions to organic amendments in soils with long-term contrasting N applications in a winter wheat monoculture system. We compared wheat straw return (St) and farmyard manure application (Fm) in soils with either long-term (2002–2019) N absence (-N) or normal N application (+N). Both St and Fm increased SOC stocks in the 0–20-cm layer, but Fm increased it more than St did. However, St exhibited a greater SOC sequestration rate in +N soils than that in –N soils, whereas Fm exhibited both a lower SOC sequestration rate and efficiency in +N soils than in –N soils. SOC increased across all fractions in all soils after both St and Fm. However, compared with –N soils, +N soils exhibited a lower SOC increase, specifically in the very labile fraction after St, but in the non-labile fraction after Fm. St, Fm, and +N all increased the soil C management index (CMI), but only +N increased wheat yield and its sustainable yield index (SYI). Those relationships indicated that both straw and manure amendments were responsible for both SOC sequestration and increasing the CMI, and N input was fundamentally responsible for an increased SYI and associated plant-C input. Consequently, straw return was expected to be more effective at sequestering SOC when applied to soil having had adequate long-term N application, whereas farmyard manure application was likely more effective when applied in N-deficient soil. Our field study findings provide empirical evidence that soil N availability affects SOC sequestration capacities following organic amendments, and that impacts strategies aimed at further increasing soil fertility improvements via organic amendment, especially considering that different agro-ecosystems are subject to different fertilization regimes.

Responses of Soil Carbon Pools, Enzymatic Activity, and Crop Yields to Nitrogen and Straw Incorporation in a Rice-Wheat Cropping System in North-Western India

Fertilizer-N application and straw incorporation impacts crop productivity due to changes in total organic carbon (TOC), its labile pools and the soil enzymatic activity. A field experiment was established (in 2010) to study the effect of fertilizer-N application (0, 90, 120 and 150 kg N ha-1) and rice straw (RS) incorporation (0, 5.0, 7.5 and 10 Mg ha-1) on crop yield, C input, TOC and its labile pools and soil enzymatic activity under rice (Oryza sativa L.) - wheat (Triticum aestivum L.) cropping system (RWCS) in north-western India. Data showed that fertilizer-N application and RS incorporation significantly (p<0.05) increased the rice and wheat grain yield, compared with control (CK). However, the RS incorporation alone did not impact crop yields. The sustainable yield index (SYI) for wheat was significantly lower with RS incorporation alone as compared with the other treatments. For rice, SYI was significantly higher for RS7.5N120, and was non-significant compared with the RS10.0N120. Annual total C input in soil plough layer (0-15 cm) under RWCS varied between 3.34 and 9.78 Mg C ha-1, which was higher by 4.4 Mg C ha 1 yr-1 (~2.3-times) in RS10.0, compared with CK. The conjoint application of fertilizer-N and RS incorporation (RS10.0N150) significantly increased the TOC, water extractable organic C (WEOC), hot water C (HWC), microbial biomass C (MBC) and basal soil respiration (BSR) due to increased soil enzymatic activity viz. dehydrogenase activity (DHA), fluorescein diacetate (FDA) and alkaline phosphatise (Alk-P). A significant increase in potassium permanganate oxidizable C (KMnO4-C) with RS incorporation under RS10.0N150 increased the C management index (CMI), and hence the soil quality. The inter-correlations between highly weighted soil variables among different principle components (PCs) revealed that KMnO4-C in PC1, FDA activity in PC2, and BSR in PC3 with the highest correlation were the sensitive indicators for assessing soil quality in a RWCS.

Importance of sugarcane straw maintenance to prevent soil organic matter depletion in a Nitisol in the central-southern region of Brazil

Sugarcane straw is a potential feedstock to increase bioenergy production. However, leaving straw on the soil surface is important to sustaining soil organic matter (SOM). We conducted a field experiment to evaluate the impacts of two years of straw removal on SOM in a sugarcane area – on an Eutric Nitisol in south-eastern Brazil – with low straw production (7 Mg ha–1). The experiment was a randomised complete block design (four blocks) with four rates of straw removal: (i) no removal, (ii) medium removal, (iii) high removal and (iv) total removal. We evaluated straw decomposition, soil carbon (C) and nitrogen (N) stock (0–30 cm), labile C, and microbial biomass C and N (0–10 cm). Increases in the straw removal rates reduced decomposition, with 30–42% of the initial straw amount remaining on the soil after one year (first year) and 33–38% remaining at the end of the second year. During the first year, no effect was found on soil C (8 kg m–2) and N (0.7 kg m–2) stocks; however, during the second year, total straw removal reduced soil C stock by 10% (0–30 cm) compared with no straw removal. Straw removal rates negatively affected the labile C (6–10% and 20–25%, first and second year respectively) and microbial C (correspondingly 10–15% and 21–27%). Microbial N was not altered in the first year, but decreased 26% due to straw maintenance (no removal) during the second year. Total straw removal decreased the C management index (CMI) by 15% (first year) compared with no straw removal. However, during the second year, all rates of straw removal decreased the CMI: by 15% for medium, 22% for high and 26% for total removal. Our findings indicate that any straw removal in areas with low straw production negatively affects SOM, initially through reduction in labile C pools. Although slight impacts on soil C and N stock were detected, reduction in straw-derived inputs stimulates microbial utilisation of soil C pools, and consequently reduces SOM over time.

Chemical and Spectroscopic Parameters Are Equally Sensitive in Describing Soil Organic Matter Changes After Decades of Different Fertilization

The composition and dynamics of soil organic matter (SOM) are decisive factors in soil quality. In this work, total organic C (Ctot), hot water extractable C (Chwl), and aliphatic and aromatic SOM components detected by Fourier transform infrared (FTIR) spectroscopy were determined to evaluate SOM quantity and quality in soil samples taken between 2004 and 2017 from 13 field experiments established in different soil and climatic conditions of the Czech Republic. In addition, the C pool index (CPI), lability index (LI), C management index (CMI), and SOM decomposition index (DI) were assessed. Treatments were selected as follows: Unfertilized control (Nil), mineral fertilized treatment (NPK), farmyard manured treatment (FYM), and organic and mineral fertilized treatment (FYM+NPK). Both organic and combined fertilization significantly increased soil Ctot, Chwl, CPI, LI, CMI, and labile aliphatic SOM components (FTIRaliph) in most of the experiments compared to unfertilized treatments (p ≤ 0.05). In contrast, the highest content of recalcitrant aromatic SOM components (FTIRarom) and increased DI were determined in majority of unfertilized soils. Our results show that: (1) fertilization regimes increased both labile and total C pools; the highest increase was nearly uniformly observed for NPK+FYM treatment; (2) SOM chemical and FTIR spectral detection had equal sensitivity to the changes; and (3) none of the parameters or indices tested can be used as a stand-alone SOM quality descriptor.

Short-term buildup of carbon from a low-productivity pastureland to an agrisilviculture system in the Brazilian savannah

Agrisilviculture systems that combine two or more species with agricultural practices may potentially increase soil organic matter (SOM) quality due to its diversified and large carbon (C) inputs. The implementation of integrated agricultural systems in Brazil has reached over 11 Mha of area and is a promising strategy to revert widespread land degradation and increase ecological intensification for cropping systems. This study aimed to evaluate the transition of a low-productivity pasture to an agrisilviculture system (corn + Gliricidia sepium + Panicum maximum cv. Massai) along a four-year field experiment under a clayey Oxisol on SOM fractions, C stocks and C management index (CMI). A native Cerrado vegetation was used as a reference. Soil samples were collected in four cropping seasons: T0 - under low-productivity pasture, T1, T2, T3 – 2nd, 3rd and 4th years after implementing the integrated production system, respectively. Both mineral associated and total soil organic C (TC) increased from T0 to T3. Accordingly, C from the particulate SOM increased by 476%, 305% and 368% at 0.00–0.10, 0.10–0.20 and 0.20–0.40 m layers, respectively, and was found to be the most sensitive indicator for changes in soil management systems. Surprisingly, inert C increased up to 0.20 m layer from T0 to all the other seasons and represented 21 to 42% of TC. C stocks at the 0.00–0.40 m layer increased from 52.6 Mg ha−1 at T0 to 66.5 Mg ha−1 at T3. The CMI significantly increased from T0 to T3 – reaching CMI of native vegetation (considered CMI = 100%). The no-till agrisilviculture system with the use of Panicum maximum cv. Massai and Gliricidia sepium managed to accomplish the goal of building up soil organic C and increasing SOM quality, thus showing its potential to be used as a sustainable agricultural practice in terms of soil quality improvement and short-term C sequestration.

Carbon and nutrient dynamics under long-term nutrient management in tropical rice-wheat-jute system

ABSTRACTImpacts of 43-year nutrient management on carbon (C) and nutrient dynamics were studied in a rice-wheat-jute system in tropical India. Carbon dynamics was investigated on the basis of its distribution of labile (microbial biomass C, permanganate oxidizable C and water soluble C) and slow pools (Walkley Black oxidizable organic C), its indices (C pool index, lability index) and C management index (CMI) at different soil depths. Nutrient dynamics was judged by major nutrients availability, and related soil enzymatic activities. We studied seven treatments including unfertilized control, 100% NPK (N:P2O5:K2O 60:30:60), 50% NPK, 150% NPK, 100% NP, 100% N, 100% NPK + farm yard manure (10 tonnes FYM ha−1). Nutrients availability and soil enzymatic activities were significantly increased under balanced fertilization (100% NPK + FYM) over other treatments. Labile, slow and total C was also found highest in 100% NPK + FYM. Enhanced C indices under 100% NPK + FYM over 100% NPK and other treatments signified the importance of long term balanced fertilization on soil C stabilization. Lability indexes were lower at sub-soil (30-45cm). In terms of favourable nutrient dynamics and CMI, balanced application of NPK plus organics were recommend for long term sustainability of rice-wheat-jute system in tropics.

Increasing Soil Organic Carbon Through Crop Diversification in Cereal–Cereal Rotations of Indo-Gangetic Plain

Continuous practices of cereal–cereal rotations in Indo-Gangetic plain (IGP) region have emerged with several soil related issues including depletion of soil organic carbon (SOC). Crop diversification remains a conceivable option to address this issue. Here, the authors envisaged the long-term alternate-year inclusion of chickpea in upland maize–wheat and lowland rice–wheat systems on SOC, C-dynamics and C management indices under organic, inorganic, and control nutrient management. Inclusion of chickpea in rice–wheat and maize–wheat systems increased total organic C (TOC) by 6.5 and 13.4%, and particulate organic C (POC) by 94.7 and 41.3% in the surface soil (0–0.2 m), respectively. In both the production systems, enrichment of very-labile C (Cfrac1) and labile C (Cfrac2) fractions were apparent with inclusion of chickpea. Very-labile (Cfrac1) (36.6–37.9%) in upland and less-labile (Cfrac3) (29.1–31.7%) in lowland were the dominant C-fractions. Subsequently, upland conditions had higher active C-pool; conversely, lowland ecosystem enriched passive C-pool, which is desirable for long-term persistence of soil C. The higher values of TOC, POC, and C-fractions were registered in organic nutrient treatment over inorganic and control treatment. In lowland, chickpea residue C had a low rate of stabilization as compared to cereal residue. In lowland, crop diversification with chickpea increased lability-index and C-management index; however, the effect was marginal in upland. Thus, inclusion of chickpea in the cereal–cereal rotations of IGP would be a potential long-term strategy to improve SOC and to ensure production sustainability.

Characteristics of labile organic carbon fractions in reclaimed mine soils: Evidence from three reclaimed forests in the Pingshuo opencast coal mine, China

The reclamation of discarded spoils has the potential to stimulate carbon (C) sequestration in reclaimed mine soils (RMSs). Nevertheless, to date the temporal dynamics of labile organic C fractions have not been sufficiently elucidated in RMSs. In this study, soil organic carbon (SOC) and labile organic C fractions, including microbial biomass organic C (MBC), easily oxidizable organic C (EOC) and dissolved organic C (DOC), were determined in Robinia pseudoacacia monoculture forests (reclamation periods of 0, 8, 10, 13, 15, 18 and 30years), Pinus tabuliformis forests (reclamation periods of 0, 10, 19, 23 and 25years) and Ulmus pumila forests (reclamation periods of 0, 18, 20 and 22years) situated on RMSs in the Pingshuo opencast coal mine, China. Changes in labile organic C fractions within the soil profiles (0–100cm) were also identified at the 18- or 19-year plots under the three monoculture forests. Our results showed that, SOC and labile organic C fractions, together with soil microbial quotient (SMQ) and C management index (CMI), increased with time since reclamation, indicating that the quality of RMSs improved over time after initial reclamation under the three forest types. R. pseudoacacia significantly increased the accretion of SOC and EOC in the early stage of reclamation while P. tabuliformis accelerated the accumulation of the MBC fraction. Results for U. pumila indicated that this species had a better ability to store C in RMSs 10years or more after reclamation. SOC and labile organic C fractions both had S-shaped distributions within the soil profiles (0–100cm), with the 0–20cm layer recording the highest values (P<0.05). Labile organic C fractions were closely associated and correlated with soil physicochemical properties; our results also showed that nitrogen played an important role in the development of labile organic C fractions. Overall, reclamation accelerated the accretion of both SOC and labile organic C fractions, results of which varied among the reclaimed forests.

Long-term biochar application influences soil microbial community and its potential roles in semiarid farmland

Biochar addition to soil can change soil physicochemical properties, resulting in a shift of the soil microbial community. However, it is uncertain how long-term biochar application affects the soil microbial community and diversity in drylands. To determine the underlying mechanism, a 3.5-year spring maize (Zea mays L.) field experiment with biochar applications was conducted to elucidate the effect of biochar on soil microbial abundance and community composition as well as its potential applications in drylands of the Loess Plateau in Northwest China. Soil samples from a 0–20cm depth for four biochar treatments, including 0 (C0, as the control), 10 (C10), 30 (C30) and 50 (C50) tha−1, were examined using phospholipid fatty acid (PLFA) analysis. It was found that the proportion of arbuscular mycorrhizal fungi (AMF) and the ratio of AMF/saprotrophic fungi (SF) correlated with the biochar levels, for example, the C30 treatment significantly decreased the absolute SF but increased the ratio of AMF/SF. Especially, both the AMF/SF and Fungi/Bacteria ratios were significantly increased in the C50 treatment, suggesting that high amounts of biochar could increase fungal rather than bacterial diversity. In addition, soil organic C (SOC) (P<0.01), KMnO4-oxidizable C (KMnO4-C) (P<0.01), and the C management index (CMI) (P<0.01) were confirmed to play significant roles in shaping the soil microbial community composition. SOC and total N were significantly increased by biochar application, and total P was increased in the C30 treatment. However, compared with the C0 treatment, the C50 treatment significantly decreased KMnO4-C and the CMI, suggesting the proper level of biochar addition to soil should be considered for the improvement of soil organic materials. Accordingly, biochar application at 30tha−1, which was connected with a decreased absolute SF and an increased AMF/SF ratio, could be a choice for improving soil quality and nutrient availability in semiarid farmland.

Long-term effects of NPK fertilizers and organic manures on carbon stabilization and management index under rice-wheat cropping system

The potential of storing carbon (C) in soil and offsetting the atmospheric CO2 depends on the management practices. This study investigated the long-term (15 years) effects of using nitrogen: phosphorous: potassium (NPK) fertilizers with and without organic manures namely farmyard manure (FYM), green manure (GM), and straw incorporation (SI) on soil C stabilization, and C management index (CMI) in intensive rice-wheat system in Typic Ustochrepts soil of a semiarid region in Punjab, India. The long-term effects of different fertilizer treatments as control, NPK, NPK+GM, NPK+SI, and NPK+FYM on soil organic carbon (SOC), labile fractions of SOC (LFSOC), C stabilization, C sequestration, and C management index (CMI) were determined. Prolonged application of NPK fertilizers alone or in combination with organic manures significantly decreased soil bulk density (from 7.3 to 16.6%) and increased total soil porosity of (from 11.7 to 26.2%) as compared to the control in surface soil (0–15cm). Fertilizations had positive and variable effects on different LFSOC, namely water soluble C (WSC), labile carbon (LC), particulate organic C (POC), hot water soluble carbon (HWSC), and total organic carbon (TOC). Long-term intensive cultivation and fertilization significantly increased the SOC in surface soil (0–15cm) up to 5.16gkg−1 as compared with its antecedent value of 2.42gkg−1 in 1999. The sensitivity index indicated that among LFSOC, LC (51–85%), WSC (67–131%), POC (64–159%), and HWSC (38–131%) were more sensitive compared with SOC (29–59%). NPK+SI (5.06MgCha−1) or NPK+FYM (5.31MgCha−1) along with NPK sequestered significantly higher C than the application of NPK (3.57MgCha−1) or NPK+GM (4.10MgCha−1). The fraction of C in stable fractions (Cfrac3+Cfract4) increased from 7 to 29% with application of NPK fertilizers and organic manures compared with that of the control. The CMI indicated that the use of NPK+SI or NPK+FYM was statistically superior to the use of NPK+GM for improving the SOC status. The study concluded that a relatively high sensitivity index of LFSOC may be used as an early indicator for determining the potential of different management practices for improving SOC on short-term basis. The results indicated that the stability of SOC varies with the nature of the added organic manures, suggesting that the selection of organic manure is important for long-term C sequestration.

Soil organic and organomineral fractions as indicators of the effects of land management in conventional and organic sugar cane systems

Brazilian sugar cane production has undergone changes in residue management. To better understand the dynamics of soil C and N in soil organic matter (SOM) fractions resulting from sugar cane management practices, we determined: the effects of different sugar cane management on the C and N content of SOM fractions; the effects of crop management, soil texture, depth and different organic matter additions on changes in 13C/12C and 15N/14N isotope composition; and the amount of SOC derived from different sources. Physical fractionation of SOM was performed for soils cultivated under four sugar cane managements, namely straw burning(SB), green cane (GC) and organic systems consisting of sugar cane grown under GC harvesting with high inputs of organic residues for 4 and 12 years (O-4 and O-12 respectively), as well as from a native vegetation (NV) area (Goianésia, Brazil). Ultrasonic dispersion of soil samples from 0–5, 5–10, 10–20 and 90–100-cm depths resulted in three organomineral fractions (&lt;53, 75–53 and 2000–75µm) and one organic fraction denoted as light fraction (2000–75µm). C and N concentrations, 13C and 15N natural abundance and the proportion of C derived from C4 sugar cane plant residues (C-C4) were determined for each fraction. The C management index (CMI), derived from the total C pool and C lability, is useful in evaluating the capacity of management systems to improve soil quality and was calculated using the NV as the reference. Highest C and N concentrations were found for O-12 and O-4, mainly for the &lt;53-µm organomineral fraction at 0–5cm depth. The 13C and C-C4 values indicated a greater accumulation of C-C4 in SOM fractions in organic compared with burned and unburned systems. GC combined with organic management is a strategy for long-term storage of total C and N in the SOM fraction associated with &lt;53-µm fraction and light fraction. In addition, the highest CMI and its positive relationship with C-C4 in O-12 suggest the role of this system to foster soil quality improvement. The results allow infer regarding the potential of management practices on C accumulation in SOM fractions, which, in turn, can be used as indicators of the effects of land management.

Assessing labile organic carbon in soils undergoing land use change in Brazil: A comparison of approaches

The labile organic C (LC) and C management index (CMI) may be useful indicators of alterations of soil organic matter (SOM) in areas undergoing land use change (LUC) for biofuels production. However, there is no consensus on which methodology is best suited for quantifying LC and CMI. The main goal of this study was to assess alterations on LC contents and CMI values in sites undergoing the LUC native vegetation (NV)-pasture (PA)-sugarcane (SC) in south-central Brazil, and evaluated the sensitivity of different methods commonly used to assess LC and CMI, in order to select a best-suited method to quantify these indicators in tropical regions. The conversion NV-PA decreased the LC and CMI, whilst the conversion of PA-SC tended to increase the CMI. Accordingly, cropping sugarcane in areas previously used as pastures, as currently has been observed in Brazil, enhance SOM quality. The methodology used to quantify the LC and the CMI is critical to infer about LUC effects. Both methods proposed by Blair et al. (1995) and Diekow et al. (2005) were highly sensitive to the conversions evaluated in this research. However, Diekow et al. (2005) is the most suitable method to estimate the LC and CMI in sites undergoing LUC in Brazil, since the approach of Blair et al. (1995) notably overestimates these SOM quality indicators. We reiterate that the SOM changes are well expressed by the total soil organic C in areas undergoing LUC and, integrated approaches, such as the CMI, are quite suitable to evaluate the effects of LUC on SOM.

Response of labile organic C and N pools to plastic film removal from semiarid farmland soil

AbstractTo examine the effects of plastic film removal on grain yield and soil organic matter (SOM), a spring maize (Zea may L.) field experiment was conducted for 5 yr at Changwu Agricultural and Ecological Experimental Station of Northwest China. Compared with traditional plastic film mulching during entire growing stages (FM), plastic film removal at the silking stage (RM) resulted in a 6.3% higher average maize yield. Under the RM treatment, soil organic carbon and total nitrogen significantly increased after the 5‐yr cultivation in the 0‐ to 20‐cm layer. Significant increases in extractable organic C (EOC), KMnO4‐oxidizable C (KMnO4‐C) and C management index (CMI) in the 0‐ to 20‐cm layer, and light fraction organic C and EOC in the 20‐ to 40‐cm layer were observed in response to plastic film removal after the 1‐yr treatment; the responses were more significant after 5 yr. Under the RM treatment, significant increases in microbial biomass C, light fraction organic N, extractable organic N, KMnO4‐C and CMI were also observed after five years in the 20‐ to 40‐cm layer. Moreover, KMnO4‐C and EOC were much more sensitive than other labile SOM fractions to the application of RM, even after only 1 yr of cultivation. Therefore, compared with mulching for the whole growing season, plastic film removal at the maize silking stage is an effective option for increasing yields and enhancing SOM concentration and soil sustainability in the regions with semiarid monsoon climates that have sufficient rainfall during maize reproductive stages.

Soil organic matter and nutrient accumulation in areas under intensive management and swine manure application

Land use change and soil management are frequently associated to land degradation and soil organic matter (SOM) losses in tropical regions. In Brazil, in order to avoid this process, different management strategies have been applied, such as no-tillage and agricultural disposal of swine manure (SM). This study was carried out to evaluate the quantity and quality of SOM, as well as the occurrence of nutrient accumulation in soils of areas under contrasting management systems that have received consecutive applications of SM over the last decades in Brazil. Five land uses were sampled: native vegetation (NV), pasture with SM application (PA + SM), no-tillage with SM application (NT + SM), no-tillage (NT), and conventional tillage with SM application (CT + SM). Soil organic carbon (SOC), N, labile C, C management index (CMI), P, Ca2+, Mg2+, K+, Al3+, Fe, Zn, Mn, Cu, and H + Al were quantified. Except for PA + SM, the agricultural land uses caused decreases in SOC contents comparing to NV. PA + SM showed the highest C stocks, 138.9 ± 3.4 Mg ha−1 down to 0.4 m. The application of SM can be associated to the greater C stocks in PA + SM, NT + SM, and CT + SM and to the higher N contents in all land uses under this practice. Land uses which receive higher rates of swine manure application (PA + SM and CT + SM) have shown CMI greater than 100. However, this practice is associated to the accumulation of P, Cu, Na, and Zn in these soils. The SM application is associated to improvement on C stocks and SOM quality in area under pasture, no-tillage, and conventional tillage in Parana State, Brazil. However, this practice is the main driver of nutrient accumulation in these areas.

Organic Matter Fractions and Quality of the Surface Layer of a Constructed and Vegetated Soil After Coal Mining. II - Physical Compartments and Carbon Management Index

Soils constructed after mining often have low carbon (C) stocks and low quality of organic matter (OM). Cover crops are decisive for the recovery process of these stocks, improving the quality of constructed soils. Therefore, the goal of this study was to evaluate the effect of cover crops on total organic C (TOC) stocks, C distribution in physical fractions of OM and the C management index (CMI) of a soil constructed after coal mining. The experiment was initiated in 2003 with six treatments: Hemarthria altissima (T1), Paspalum notatum (T2), Cynodon dactylon (T3), Urochloa brizantha (T4), bare constructed soil (T5), and natural soil (T6). Soil samples were collected in 2009 from the 0.00-0.03 m layer, and the TOC and C stocks in the physical particle size fractions (carbon in the coarse fraction - CCF, and mineral-associated carbon - MAC) and density fractions (free light fraction - FLF; occluded light fraction - OLF, and heavy fraction - HF) of OM were determined. The CMI components: carbon pool index (CPI), lability (L) and lability index (LI) were estimated by both fractionation methods. No differences were observed between TOC, CCF and MAC stocks. The lowest C stocks in FLF and OLF fractions were presented by T2, 0.86 and 0.61 Mg ha-1, respectively. The values of TOC stock, C stock in physical fractions and CMI were intermediate, greater than T5 and lower than T6 in all treatments, indicating the partial recovery of soil quality. As a result of the better adaptation of the species Hemarthria and Brizantha, resulting in greater accumulation of labile organic material, the CPI, L, LI and CMI values were higher in these treatments, suggesting a greater potential of these species for recovery of constructed soils.