Adoption Of No-till Research Articles

Cover cropping and no-tillage improve soil health in an arid irrigated cropping system in California’s San Joaquin Valley, USA

The concept of soil health has attracted considerable attention during the past two decades, but few studies have focused on the effects on soil health of long-term soil management in arid irrigated environments. We investigated the effects of cover cropping and no-till management on soil physical and chemical properties during a 15-year experiment in California’s San Joaquin Valley (SJV) USA. Our objective was to determine if soil health could be improved by these practices in an annual crop rotation. The impact of long-term no-tillage (NT) and cover cropping (CC) practices, alone and in combination, was measured and compared with standard tillage (ST) with and without cover crops (NO) in irrigated row crops after 15 years of management. Soil aggregation, rates of water infiltration, content of carbon, nitrogen, water extractable organic carbon (WEOC) and organic nitrogen (WEON), residue cover, and biological activity were all increased by NT and CC practices relative to STNO. However, effects varied by depth with NT increasing soil bulk density by 12% in the 0–15cm depth and 10% in the 15–30cm depth. Higher levels of WEOC were found in the CC surface (0–5cm) depth in both spring and fall samplings in 2014. Surface layer (0–15cm) WEON was higher in the CC systems for both samplings. Tillage did not affect WEON in the spring, but WEON was increased in the NT surface soil layer in the fall. Sampling depth, CC, and tillage affected 1-day soil respiration and a soil health index assessment, however the effects were seasonal, with higher levels found in the fall sampling than in the spring. Both respiration and the soil health index were increased by CC with higher levels found in the 0–5cm depth than in the 5–15 and 15–30cm depths. Results indicated that adoption of NT and CC in arid, irrigated cropping systems could benefit soil health by improving chemical, physical, and biological indicators of soil functions while maintaining similar crop yields as the ST system.

Matéria orgânica e agregação do solo após conversão de "campos de murundus" em sistema plantio direto

Resumo O objetivo deste trabalho foi avaliar o efeito da conversão de áreas de campos de murundus para sistemas agrícolas de plantio direto (PD) nos estoques de C orgânico e de N total do solo, em suas frações na matéria orgânica do solo e na estabilidade de agregados. O estudo foi realizado em uma cronossequência com 7, 11 e 16 anos de conversão para o PD, e em duas áreas de referência caracterizadas como topo dos murundus (TM) e entre os murundus (EM). O teor de C nos solos variou de acordo com o tempo de conversão para áreas agrícolas, em todas as profundidades, com exceção da área EM. Os estoques de C sofreram efeitos negativos da conversão da área nativa em agrícola, e os maiores estoques foram observados nas áreas EM e TM. O índice de manejo de C aumentou com o tempo de adoção do PD, em relação ao TM, e os atributos do solo melhoraram com o aumento no tempo de adoção de 7 para 16 anos de PD, mas os estoques de C orgânico nas áreas convertidas não retornam aos níveis observados nas áreas referências.

Can no-till grain production restore soil organic carbon to levels natural grass in a subtropical Oxisol?

The conversion of native vegetation (NV) to agricultural systems, especially with intensive tillage and low carbon (C) input, decreases soil organic carbon (SOC) stocks. However the adoption of conservation agriculture (CA) may partially restore SOC stocks. However, the magnitude of this restoration is dependent on the cropping system, quality and quantity of C input, soil, and climate. In this study, we assessed the redistribution and recovery of SOC stocks in six no-till (NT) fields (>20years) in the small grain production area of southern Brazil. The adoption of NT in the fields investigated started between 1978 and 1990 and represent a range of textural and mineralogical characteristics. Soil samples were collected in paired fields (NV vs. long-term NT) to a depth of 1m. The pioneer NT areas of Rio Grande do Sul State investigated in this study were managed according to the principles of CA (minimum soil disturbance, permanent soil cover and diverse crop rotation). The sites had recovered to 92–100% of the original SOC stocks. The sites which represented medium cropping intensity recovered 79.5 and 85.4%, of NV SOC stocks. The sites representative of high cropping intensity had recovered 84.9–116.5% of NV SOC stocks. The lowest recovery of SOC stock (60.6%) had higher frequency of soybean (Glycine max L. Merril) in the crop rotation. Therefore, NT following the principles of CA was an efficient system to restore SOC stock lost due to land-use change, performing a crucial role in the system productivity and soil quality.

Aggregate size distribution and associated organic C and N under different tillage systems and Ca-amendment in a degraded Ultisol

The physical protection and stabilization of soil organic carbon in soil aggregates are important processes for the mitigation of greenhouse gas emissions through carbon sequestration. Compared with temperate soils, the relationships between management practices, soil aggregation and soil organic matter (SOM) are not well understood in subtropical and tropical soils. The objectives of this study were to assess the influence of tillage system and Ca-amendment on the size distribution of soil aggregates and aggregate-associated organic C and N, as well as to contribute to the understanding of the role of soil organic matter in the aggregation process in a soil with tropical mineralogical characteristics. Our study was conducted on an annual forage agrosystem with a degraded Palexerult soil in SW Spain with mineralogical and morphological characteristics inherited from a pre-Quaternary humid-subtropical climate. The experiment had a split-plot design with tillage (no-tillage vs. traditional tillage) as the main factor and with or without Ca-amendment as the second factor. Aggregate size distribution was dominated by microaggregates (0.053–0.250mm). Compared with tilled plots, after six years, no-tillage increased the macroaggregates (>0.250mm) to a depth of 10cm by about 40%. The relatively low clay content of the surface soil may explain the strong impact of tillage on macroaggregation and the relatively slow recovery after the adoption of no-tillage. In contrast to the tillage system, the Ca-amendment barely influenced aggregation parameters. No-tillage also favored accumulation of organic C and N in all aggregate fractions but no size preference between macro- and microaggregates was observed while Ca-amendment enhanced accumulation only in large macroaggregates. Our results indicate an aggregation hierarchy in these kaolinitic soils, as well as an important role of SOM in enhancing soil aggregation.

No-tillage effects on N and P exports across a rice-planted watershed.

No tillage (NT) can be used as a management tool to alleviate the negative effects of agricultural practices on the environment by reducing the runoff volume and nutrient exports. The main objective of this research was to quantify the effect of NT on nitrogen (N) and phosphorus (P) exports across a rice-planted watershed using the soil and water assessment tool (SWAT) model. Results show that total N and P runoff exports from rice fields across the watershed ranged from 7.2 to 22.8kg N/ha and 0.56 to 6.80kg P/ha, respectively, over five rice-growing seasons under conventional tillage (CT) practice. The adoption of NT reduced the runoff volume, and the total N and total P exports by 25.9, 8.5, and 7.8%, respectively, compared with the total exports under CT practice in the same study area. Rice yields were reduced by 0.7-1.9% within the first 4years after the adoption of NT, but began to rise in the fifth year. These results suggest that a long-term period of NT practice is necessary to reduce N and P exports without comprising the rice yield on rice-planted watersheds. In addition, the benefits of implementing NT practice alone were limited, and other practices, such as water and nutrient management, should be combined with NT practice.

Soil organic matter fractions as affected by tillage and soil texture under semiarid Mediterranean conditions

The inherent complexity of soil organic matter (SOM) and its stabilization processes make suitable the identification of SOM fractions that reflect the management-induced changes in soil organic carbon (SOC) dynamics. This is of special interest in semiarid regions where the capacity of soil for agricultural production is limited. This study aims to evaluate the effect of different tillage and soil management practices on the distribution of C among SOM fractions and determine the influence of soil texture on the protection of SOC in a semiarid Mediterranean region (Aragon, NE Spain). Under on-farm conditions, pairs of adjacent fields under long-term no tillage (NT) and conventional tillage (CT) were compared in five different cereal production areas. In all cases, a nearby undisturbed soil under native vegetation (NAT) was included. Results indicate that the two isolated mineral-associated OM (Min) fractions, d-Min and μagg-Min (outside and within stable microaggregates, respectively), constituted the main part of total SOC (mean contributions of 54 and 26%, respectively) and were not consistently affected by soil management. Soil clay was a determinant factor for d-Min-C and total SOC (r2=0.60–0.70; P<0.001), indicating that chemical stabilization, through clay–organic complexes, seems to be a main preservation mechanism in the studied soils. Physical protection seems to be another SOC stabilization process in these soils due to strong correlation found between μagg-Min-C and the mass of water-stable microaggregates (r=0.900; P<0.0001). With smaller contributions to total SOC, the two labile fractions, coarse and fine particulate OM (cPOM and fPOM) were sensitive to soil management and their concentrations decreased as soil disturbance increased (NAT>NT>CT). The highest differences between NT and CT corresponded to fPOM at the soil surface where this fraction was 1.2–3 times higher under NT. Higher soil stratification ratios in NT, always >2 for the POM fractions, indicate an improvement in soil quality with long-term NT adoption in this semiarid Mediterranean region.

The proposed alternative model to predict adoption of innovations: The case of no-till technology in Iran

Most Iranian farmers use conventional tillage while the high energy consumption, soil compaction, degradation of soil structure and intensive water and wind erosion are the effects of this system. So there is a necessity to use conservational tillage as one of the sustainable agricultural innovations to protect the soil. Compared to other conservational methods no-tillage is considered because of more environmental benefits. The purpose of this study is to examine the predictive models to adoption of no-till innovation. Survey research was conducted in Fars province, Iran. Using multi-stage stratified random sampling, 330 farmers were interviewed including 165 adopters and 165 non-adopters of no-till technology. In this study diffusion of innovation, economic constraint, task-technology fit, learning communication and proposed alternative models were examined using discriminant analysis. The results showed that proposed alternative model is a better predictive of farmers’ adoption behavior than the other models. The most important variables to classify adopters and non-adopters were agricultural experience, available resources, conservational technology experience, awareness of the benefits of no-till technology, value attributed to the no-tillage technology, interpersonal communication, knowledge of no-till technology, income, knowledge of the technology property and perceived task-no-tillage technology fit. To improve no-tillage adoption as an strategy against soil erosion, systematic thinking should be considered as an effective approach.

Nitrogen fertilization reduces yield declines following no-till adoption

Conservation agriculture (CA) has been promoted as a method of sustainable intensification and climate change mitigation and is being widely practiced and implemented globally. However, no-till (NT), a fundamental component of CA, has been shown to reduce yields in many cases. In order to maintain yields following adoption of CA, it has been recently suggested that fertilizer application should be an integral component of CA. To determine the contribution of nitrogen (N) fertilizer in minimizing yield declines following NT implementation, we assessed 2759 paired comparisons of NT and conventional tillage (CT) systems from 325 studies reported in the peer-reviewed literature between 1980 and 2013. Overall, we found that NT yields decreased −10.7% (−14.8% to −6.5%) and −3.7% (−5.3% to −2.2%) relative to CT in tropical/subtropical and temperate regions, respectively. Among management and environmental variables that included: the rate of N fertilization; the duration of the NT/CT comparison; residue, rotation, and irrigation practices; the crop type; and the site aridity, N rate was the most important explanatory variable for NT yield declines in tropical/subtropical regions. In temperate regions, N fertilization rates were relatively less important. NT yield declines were most consistently observed at low rates of N fertilization during the first 2 years of NT adoption in tropical/subtropical regions. Applications of N fertilizer at rates of up to 85±12kgNha−1yr−1 significantly reduced NT yield declines in these scenarios. While this result should not be viewed as a rate recommendation, it does suggest that farmers applying rates of N fertilizer that are low for their specific system will, on average, see higher NT yields if they increase application rates. In addition, when crop rotation was not practiced or residues were removed from the field, NT yield declines were magnified by low rates of N fertilization in tropical/subtropical regions. These results, based on a global data set and across a broad range of crops, highlight the importance of N fertilization in counteracting yield declines in NT systems, particularly in tropical/subtropical regions.

No-tillage effect on rice yield in China: A meta-analysis

Rice production in China has been constrained by changes in socioeconomic and physical environments such as decreased labor availability and degraded soil. No-tillage (NT) may be an alternative system for rice production in China because it has potential benefits including labor saving and soil conservation. Here, we conducted a meta-analysis to evaluate the effect of NT on rice yield in China and to investigate how the effect varies with the environmental and management factors. Results showed that decrease in panicle number per unit land area was observed in NT rice across a wide range of environmental and management conditions in China, but grain yield was not reduced because it was compensated for by more spikelet number per panicle and higher spikelet-filling percentage. Grain yield responses to NT were affected by region (climate), soil, cropping system and proportion of N applied during the vegetative period (PNVP). Typically, grain yield showed a positive response to NT in south-west region (where the climate during rice-growing season is characterized by frequent fog and clouds, high humidity and insufficient sunlight). NT resulted in a decreased grain yield in soils with pH lower than 6.0 and low fertility. Grain yield was decreased in rice–rice cropping systems but increased in rice–upland cropping systems by NT. NT had negative effect on grain yield under PNVP of 70% and 80% but had no significant effect under PNVP of 90%. However, responses of grain yield to NT did not vary with establishment method (transplanting vs. seedling throwing vs. direct seeding), cultivar type (hybrid vs. inbred), duration of NT adoption (<3 years vs. 3–6 years vs. >6 years) and residue management practice (removal vs. retention). We conclude that adoption of NT for rice production in China should be site-specific and depend on agronomic practices including cropping system and N management.

Assessment of soil quality under different tillage practices during wheat cultivation: soil enzymes and microbial biomass

Microbial processes, particularly enzyme activities, play crucial functional roles in soil ecology, hence serving as sensitive indicators of soil quality. We assessed the temporal dynamics of microbial biomass and selected soil enzymes (β-d-glucosidase, cellobiohydrolase, polyphenol oxidase, urease, glycine-aminopeptidase and alkaline phosphatase) during wheat cultivation, under four different tillage practices in the rice–wheat system. The four practices involved conventional tilling of soil before cultivating each crop (CTR-CTW); no tilling before cultivating rice but conventional tillage before wheat (NTR-CTW); conventional tilling before cultivating rice but no tilling before wheat (CTR-NTW) and no tilling before cultivation of each crop (NTR-NTW). Microbial biomass and activities of hydrolytic enzymes increased under NTR-NTW followed by CTR-NTW and NTR-CTW with respect to the conventional practice CTR-CTW, thus reflecting improvement in microbial activities with reduced tillage frequency. Enzyme activities generally depended on soil moisture and temperature, but nature of relationships varied among different practices. Nutrient demand appeared to be the strongest driver of alkaline phosphatase and urease, and soil temperature for glycine-aminopeptidase. Under CTR-CTW, activities of most of the extracellular enzymes were related with β-d-glucosidase or urease, but such relations altered under rest of the practices. The study showed that extracellular soil enzymes respond sensitively to tillage practices as well as environmental variables, particularly soil temperature and moisture and hence can serve as a sensitive indicator of changes in soil processes. Considering improvement in microbial biomass and enzymatic activities as indicators of better soil quality, adoption of no tillage apparently improved soil quality. Still, more number of field studies are required under tillage managements to explore the relationships between different enzyme activities and environmental factors.

Property rights enforcement and no-till adoption in crop-livestock systems

In developing country agriculture property rights over crop residue left on privately farmed land are often poorly enforced, resulting in common grazing. The introduction of no-till agriculture, a technology that presents an alternative use for residue, may sufficiently increase its value so that farmers enforce property rights over this resource. Enforcement of property rights diminishes the amount of common residue available for grazing, and consequently makes the adoption of no-till by other farmers more costly. Using a model of property rights enforcement and technology adoption in a mixed crop-livestock system calibrated with data from Morocco, I demonstrate how one farmer’s no-till adoption can prevent other farmers from adopting and present some welfare implications of technology induced property rights enforcement.

Tillage and residue management effects on temporal changes in soil organic carbon and fractions of a silty loam soil in the North China Plain

AbstractSoil degradation and associated depletion of soil organic carbon (SOC) have been major concerns in intensive farming systems because of the subsequent decline in crop yields. We assessed temporal changes in SOC and its fractions under different tillage systems for wheat (Triticum aestivum L.) – maize (Zea mays L.) cropping in the North China Plain. Four tillage systems were established in 2001: plow tillage (PT), rotary tillage (RT), no‐till (NT), and plow tillage with residues removed (PT0). Concentrations of SOC, particulate organic carbon (POC), non‐POC (NPOC), labile organic carbon (LOC), non‐LOC (NLOC), heavy fraction carbon (HFC) and light fraction carbon (LFC) were determined to assess tillage‐induced changes in the top 50 cm. Concentrations of SOC and C fractions declined with soil depth and were significantly affected by tillage over time. The results showed that SOC and its fractions were enhanced under NT and RT from 0 to 10 cm depth compared with values for PT and PT0. Significant decreases were observed below 10 cm depths (P &lt; 0.05) regardless of the tillage system. The SOC concentration under NT for 0–5 cm depth was 18%, 8%, and 10% higher than that under PT0 after 7, 9, and 12 yr of NT adoption, respectively. Apparent stratification of SOC occurred under NT compared with PT and PT0 for depths &gt;10 cm. All parameters were positively correlated (P &lt; 0.01); linear regressions exhibited similar patterns (P &lt; 0.01). Therefore, to maintain and improve SOC levels, residue inputs should be complemented by the adoption of suitable tillage systems.

The effects of land use and soil management on the physical properties of an Oxisol in Southeast Brazil

Soils of the tropics are prone to a decrease in quality after conversion from native forest (FO) to a conventional tillage system (CT). However, the adoption of no-tillage (NT) and complex crop rotations may improve soil structural quality. Thus, the aim of this study was to evaluate the physical properties of an Oxisol under FO, CT, and three summer crop sequences in NT: continuous corn (NTcc), continuous soybean (NTcs), and a soybean/corn rotation (NTscr). Both NT and CT decreased soil organic carbon (SOC) content, SOC stock, water stable aggregates (WSA), geometric mean diameter (GMD), soil total porosity (TP), macroporosity (MA), and the least limiting water range (LLWR). However they increased soil bulk density (BD) and tensile strength (TS) of the aggregates when compared to soil under FO. Soil under NT had higher WSA, GMD, BD, TS and microporosty, but lower TP and MA than soil under CT. Soil under FO did not attain critical values for the LLWR, but the lower limit of the LLWR in soils under CT and NT was resistance to penetration (RP) for all values of BD, while the upper limit of field capacity was air-filled porosity for BD values greater than 1.46 (CT), 1.40 (NTscr), 1.42 (NTcc), and 1.41 (NTcs) kg dm-3. Soil under NTcc and NTcs decreased RP even with the increase in BD because of the formation of biopores. Furthermore, higher critical BD was verified under NTcc (1.62 kg dm-3) and NTcs (1.57 kg dm-3) compared to NTscr and CT (1.53 kg dm-3).

A long-term sustainability assessment of an Argentinian agricultural system based on emergy synthesis

By tracking the different flows of emergy (the total amount of solar energy that was directly or indirectly required in a production process) it is possible to account for all environmental work previously involved in generating a resource, product or service. This donor-side perspective for environmental assessment has the advantage over usual economic and energy analysis in the ability to value renewable and non-renewable environmental resource inputs both from the economy (purchased resources) and from nature (free resources) and compute their values on a common basis. On this basis, this paper presents the use of emergy synthesis on three cropping systems of the Pampa Region (Argentina) with the aim of evaluating the long-term trends (1984–2010) in emergy use and the effect of the adoption of new technologies in the study area. The cropping systems evaluated were wheat/soybean double cropping (W/S); maize (M), and spring soybean (S). Results form the emergy synthesis showed that the cropping systems studied were not only more productive but also more efficient over time. The range of the observed values for the emergy yield ratio (EYR) were 1.77–5.59, proving that the three cropping systems are considerably supported by renewable and locally available resources. The environmental load ratio (ELR) that represents the ratio between non-renewable and renewable resource inputs ranged between 0.3 and 1.43, a significant lower range compared to other extensive cropping systems. However, when inspecting the temporal dynamics of the emergy indicators, M and W/S showed a statistically significant optimum behavior, with the most favorable values just before the use of a more intensive cropping management represented by the use of genetically modified cultivars, the no-tillage adoption and the more frequent use of fertilizers at higher doses. By the time of these adoptions, both the EYR and ELR showed a breakpoint in their temporal dynamic, exhibiting a negative slope during the last years of the time series. Although the observed ranges of the emergy indicators can place these production systems among the most efficient and with the lower environmental impact, the negative trend in the emergy indicators shown in recent years constitutes a risky scenario in terms long-term sustainability.

Weed Community Dynamics and Suppression in Tilled and No-Tillage Transitional Organic Winter Rye–Soybean Systems

Grower adoption of no-tillage (NT) approaches to organic soybean production has been limited, in part because of the perceived risks of ineffective cover crop management and lack of season-long weed suppression. We conducted research in 2008 and 2009 to assess those risks by quantifying the effects of winter rye cover-crop management (tilling, crimping, or mowing), soybean planting date (mid May or early June), and row width (19 or 76 cm) on weed recruitment, emergence patterns, season-long suppression, and late-season weed community composition in transitional organic production systems. The weed plant community consisted largely of summer annual species in each year, with velvetleaf or common lambsquarters as the most abundant species. Seedling recruitment from the soil seedbank varied between years, but velvetleaf recruitment was consistently greater in the tilled rye than in the NT rye treatments. Weed emergence tended to peak early in the season in the tilled rye treatment, but in the NT rye treatments, the peak occurred in mid or late season. More-diverse summer annual and perennial species were associated with the NT rye treatments. Even so, weed suppression (as measured by late-season weed shoot mass) was much greater in crimped or mowed rye NT treatments than it was in the tilled treatment. Weed suppression among NT rye treatments was greater in 19- than in 76-row spacing treatments in each year and was greater for mid May than it was for early June planted soybean in 2009. The NT planting of soybean into standing rye before termination (crimping or mowing) facilitated timely planting of soybean, as well as effective, season-long weed suppression, suggesting that those approaches to rye and weed management are of less risk than those typically perceived by growers. Our results suggest that NT systems in winter rye provide effective weed-management alternatives to the typical tillage-intensive approach for organic soybean production.

Residual effect of soil tillage on water erosion from a Typic Paleudalf under long-term no-tillage and cropping systems

Soil erosion is one of the chief causes of agricultural land degradation. Practices of conservation agriculture, such as no-tillage and cover crops, are the key strategies of soil erosion control. In a long-term experiment on a Typic Paleudalf, we evaluated the temporal changes of soil loss and water runoff rates promoted by the transition from conventional to no-tillage systems in the treatments: bare soil (BS); grassland (GL); winter fallow (WF); intercrop maize and velvet bean (M+VB); intercrop maize and jack bean (M+JB); forage radish as winter cover crop (FR); and winter cover crop consortium ryegrass - common vetch (RG+CV). Intensive soil tillage induced higher soil losses and water runoff rates; these effects persisted for up to three years after the adoption of no-tillage. The planting of cover crops resulted in a faster decrease of soil and water loss rates in the first years after conversion from conventional to no-tillage than to winter fallow. The association of no-tillage with cover crops promoted progressive soil stabilization; after three years, soil losses were similar and water runoff was lower than from grassland soil. In the treatments of cropping systems with cover crops, soil losses were reduced by 99.7 and 66.7 %, compared to bare soil and winter fallow, while the water losses were reduced by 96.8 and 71.8 % in relation to the same treatments, respectively.

Carbon stock and humification index of organic matter affected by sugarcane straw and soil management

The maintenance of sugarcane (Saccharum spp.) straw on a soil surface increases the soil carbon (C) stocks, but at lower rates than expected. This fact is probably associated with the soil management adopted during sugarcane replanting. This study aimed to assess the impact on soil C stocks and the humification index of soil organic matter (SOM) of adopting no-tillage (NT) and conventional tillage (CT) for sugarcane replanting. A greater C content and stock was observed in the NT area, but only in the 0-5 cm soil layer (p < 0.05). Greater soil C stock (0-60 cm) was found in soil under NT, when compared to CT and the baseline. While C stock of 116 Mg ha-1 was found in the baseline area, in areas under CT and NT systems the values ranged from 120 to 127 Mg ha-1. Carbon retention rates of 0.67 and 1.63 Mg C ha-1 year-1 were obtained in areas under CT and NT, respectively. Laser-Induced Fluorescence Spectroscopy showed that CT makes the soil surface (0-20 cm) more homogeneous than the NT system due to the effect of soil disturbance, and that the SOM humification index (H LIF) is larger in CT compared to NT conditions. In contrast, NT had a gradient of increasing H LIF, showing that the entry of labile organic material such as straw is also responsible for the accumulation of C in this system. The maintenance of straw on the soil surface and the adoption of NT during sugarcane planting are strategies that can increase soil C sequestration in the Brazilian sugarcane sector.

Assessing soil carbon storage rates under no-tillage: Comparing the synchronic and diachronic approaches

No-tillage (NT) practices with crop residue mulching are seen as an effective way to accumulate soil carbon (C). The rate of soil C accumulation can be determined by measuring soil C stocks over time (diachronic approach) or along a chronosequence that substitutes spatial history differences for time differences (synchronic approach). The objective of this communication is to compare the diachronic and synchronic approaches for determining the rates of soil C storage under NT in the Cerrado region of Brazil. In 2003 and 2007, soil C stocks (0–20cm) were determined in three NT fields with 5, 9 and 17 years of NT adoption in 2007 (NT-5, NT-9 and NT-17, respectively), one conventionally tilled field (CT, 30 years of tillage in 2007) and one native Cerrado plot (CE) in Rio Verde (Goiás state, Brazil). Soil C accumulation rates were calculated following both the synchronic and diachronic approach. Results from the synchronic approach showed that 30 years of cropping under CT depleted the soil C stock to 34.4MgCha−1, which is a decrease of about 27% of the original levels observed under the native vegetation (CE, 47.1 and 47.3MgCha−1, respectively, in 2003 and 2007). Instead, NT adoption had been accumulating soil C through the evaluated years. Soil C stocks measured under NT areas in 2003 and 2007 were 29.9 and 31.3MgCha−1 (NT-5), 33.4 and 34.4MgCha−1 (NT-9) and 45.8 and 46.4MgCha−1 (NT-17), respectively. Much more moderate rates of soil C accumulation were observed diachronically (0.12–0.28MgCha−1year−1) than with the synchronic approach (1.33 and 1.27MgCha−1year−1 in 2003 and 2007, respectively). Soil C stocks under CE between 2003 and 2007 (in the diachronic approach) did not change, indicating that diachronic measurements were accurate. Thus, it appears to be very difficult to eliminate all non-wanted sources of soil C variation (i.e. soil texture, land-use history) analysing the soil C accumulation in a chronosequence (synchronic approach). In spite of a time span of years between sampling dates, our results suggest the need for using the diachronic approach when assessing soil C changes under altering land-use or management patterns. Increasing the number of diachronic assessments may also help the parameterization of process-oriented models for exploring the effects of no-tillage systems on soil C storage rates more accurately.

Contrasting approaches for estimating soil carbon changes in Amazon and Cerrado biomes

The Brazilian Amazon and Cerrado are among the principal agricultural frontiers of the world, and have attracted global attention because of their potential to be a source or sink of atmospheric CO2. However, accurately quantifying alterations in soil organic carbon (SOC) due to land-use changes remains to be a major challenge. Using a meta-analysis, our objective was to evaluate tillage effects on SOC stocks in Brazil's Amazon and Cerrado biomes. Two approaches: (1) the classical SOC annual change rate which provides only an arithmetic average of SOC changes, and (2) the rate of annual change adjusted from management factors derived according to the Intergovernmental Panel on Climate Change (IPCC) SOC methodology, which allows a temporal dataset adjustment, were used. Regardless of approach, conservation technologies such as no-tillage (NT) and integrated crop-livestock (ICL) systems were identified as viable options for SOC sequestration, increasing it between 9 and 16%. One exception was adoption of NT in the Amazon forest, where SOC decreased by 9% over 20 years. Comparing results of the two approaches showed substantial differences between them. For conversions from NT to ICL or from native vegetation to full tillage (FT), the IPCC-based approach produced SOC stock estimates that were 65 and 47% lower, respectively, than with the classical approach. The IPCC approach also identified modeling covariate effects and was influenced less by outliers, thus reducing the risk of under or overestimating soil management effects on SOC.

Emissions of CH4 and N2O under Different Tillage Systems from Double-Cropped Paddy Fields in Southern China

Understanding greenhouse gases (GHG) emissions is becoming increasingly important with the climate change. Most previous studies have focused on the assessment of soil organic carbon (SOC) sequestration potential and GHG emissions from agriculture. However, specific experiments assessing tillage impacts on GHG emission from double-cropped paddy fields in Southern China are relatively scarce. Therefore, the objective of this study was to assess the effects of tillage systems on methane (CH4) and nitrous oxide (N2O) emission in a double rice (Oryza sativa L.) cropping system. The experiment was established in 2005 in Hunan Province, China. Three tillage treatments were laid out in a randomized complete block design: conventional tillage (CT), rotary tillage (RT) and no-till (NT). Fluxes of CH4 from different tillage treatments followed a similar trend during the two years, with a single peak emission for the early rice season and a double peak emission for the late rice season. Compared with other treatments, NT significantly reduced CH4 emission among the rice growing seasons (P<0.05). However, much higher variations in N2O emission were observed across the rice growing seasons due to the vulnerability of N2O to external influences. The amount of CH4 emission in paddy fields was much higher relative to N2O emission. Conversion of CT to NT significantly reduced the cumulative CH4 emission for both rice seasons compared with other treatments (P<0.05). The mean value of global warming potentials (GWPs) of CH4 and N2O emissions over 100 years was in the order of NT<RT<CT, which indicated NT was significantly lower than both CT and RT (P<0.05). This suggests that adoption of NT would be beneficial for GHG mitigation and could be a good option for carbon-smart agriculture in double rice cropped regions.