Effects Of Different Tillage Practices Research Articles

Identification of soil quality indicators for assessing the effect of different tillage practices through a soil quality index in a semi-arid environment

Tillage is known to potentially affect soil quality in various ways. In this study, a soil quality index (SQI) was developed by quantifying several soil attributes either sensitive or insensitive to physical disturbance, using factor analysis as a dimension reduction technique, in order to discriminate different tillage systems. Soil properties including physical (MWD), chemical (pH, organic C, total N, available P and POM contents) and microbial (MBC, MBN, PCM, PNM and three enzymes) parameters were measured to establish a minimum data set (MDS) for the assessment of overall SQI. The soil attributes were determined on samples (0–20cm depth) collected under moldboard (MP) and disk (DP) plows as conventional tillage (CT), and rotary (RP) and chisel (CP) plows as reduced tillage (RT) systems with a similar plant C input rate and cover crop over a period of six years (2005–2011) in a semi-arid calcareous soil (Calcixerepts) from Central Iran. Results indicated a clear difference in soil quality among the tillage systems with a significant increase of SQI under RT over time, particularly under CP practices. Although RT improved most soil microbial attributes, not all attributes contributed to SQI because of their close interrelationship. The final SQI consisted only of geometric mean of microbial activity (GMA, the square root of the product of PCM and PNM) and geometric mean of enzyme activity (GME, the cube root of the product of enzyme activities). Soil GME and GMA were found to be as key indicators contributing 55% and 36% to SQI, respectively. Therefore, the GME and GMA were the most important indicators effectively discriminating tillage systems, and could be used to monitor the enhancement of soil quality under RT in this semiarid environment. The influence of tillage year on SQI was greater than that of tillage practices. In conclusion, RT systems were characterized by a higher value of SQI, suggesting a good recovery of soil capacity and functions after abandoning CT in the studied area. Smallholder farmers should therefore be aware of the potential for high soil quality in future as a result of continuing RT systems, especially with surface tillage using CP practices.

English

Excessive tillage in conventional agriculture systems may cause plough pan, which alters soil physical properties, and thus adversely affects the crop growth and productivity. This study was conducted to monitor the effect of different tillage practices in wheat-based cropping systems on soil physical properties, allometry and grain yield of wheat. Wheat was planted in different cropping systems (viz. fallow-wheat, rice-wheat, cotton-wheat, mungbean-wheat and sorghum-wheat with zero tillage, conventional tillage, deep tillage and on two types of beds (60/30 cm with four rows) and (90/45 cm with six rows). Interaction between different tillage practices and cropping systems had significant effect on soil bulk density and total porosity, wheat allometry and grain yield. Minimum bulk density tied with higher total porosity was recorded in both types of bed sowing followed by deep tillage. This improvement in soil physical properties caused improvement in leaf area index and duration, specific leaf area, crop growth, and net assimilation rates. As a result, the productivity of bed sown wheat was better; however, grain yield of zero tilled wheat was low due to poor crop growth and net assimilation rate. Wheat productivity was substantially low when planted after sorghum; nonetheless, and was quite high when sown after mungbean. In crux, wheat planting on beds after mungbean is the best option considering the long-term environmental sustainability of wheat-based cropping systems. © 2016 Friends Science Publishers

Long term effects of tillage practices and N fertilization in rainfed Mediterranean cropping systems: durum wheat, sunflower and maize grain yield

Abstract Long term investigations on the combined effects of tillage systems and other agronomic practices such as mineral N fertilization under Mediterranean conditions on durum wheat are very scanty and findings are often contradictory. Moreover, no studies are available on the long term effect of the adoption of conservation tillage on grain yield of maize and sunflower grown in rotation with durum wheat under rainfed Mediterranean conditions. This paper reports the results of a 20-years experiment on a durum wheat-sunflower (7 years) and durum wheat–maize (13 years) two-year rotation, whose main objective was to quantify the long term effects of different tillage practices (CT = conventional tillage; MT = minimum tillage; NT = no tillage) combined with different nitrogen fertilizer rates (N0, N1, N2 corresponding to 0, 45 and 90 kg N ha −1 for sunflower, and 0, 90 and 180 kg N ha −1 for wheat and maize) on grain yield, yield components and yield stability for the three crops. In addition, the influence of meteorological factors on the interannual variability of studied variables was also assessed. For durum wheat, NT did not allow substantial yield benefits leading to comparable yields with respect to CT in ten out of twenty years. For both sunflower and maize, NT under rainfed conditions was not a viable options, because of the unsuitable (i.e., too wet) soil conditions of the clayish soil at sowing. Both spring crops performed well with MT. No significant N × tillage interaction was found for the three crops. As expected, the response of durum wheat and maize grain yield to N was remarkable, while sunflower grain yield was not significantly influenced by N rate. Wheat yield was constrained by high temperatures in January during tillering and drought in April during heading. The interannual yield variability of sunflower was mainly associated to soil water deficit at flowering and air temperature during seed filling. Heavy rains during this latter phase strongly constrained sunflower grain yield. Maize grain yield was negatively affected by high temperatures in June and drought in July, this latter factor was particularly important in the fertilized maize. Considering both yield and yield stability, durum wheat and sunflower performed better under MT and N1 while maize performed better under both CT and MT and with N2 rates. The results of this long term study are suitable for supporting policies on sustainable Mediterranean rainfed cropping systems and also for cropping system modelling.

Spatial analysis of long‐term effects of different tillage practices based on penetration resistance

AbstractMeasuring penetration resistance (PR) is a common technique for evaluating the effects of field management on soils. This study focuses on the effects of long‐term tillage on the spatial distribution of PR, comparing reduced and conventional tillage (CT) practices. The study site, located in Lower Saxony (Germany), has been subdivided into three plots, with one plot having been managed conventionally, whereas reduced tillage (RT) practices have been applied to the other two. In total, PR was measured at 63 randomly selected points. The PR data were stepwise interpolated using kriging with external drift. Core samples have been taken at 20 additional sites. The results show significant differences in PR between the different tillage practices. Within the conventionally managed plot, PR ranges to 2.3 MPa less in the topsoil than under RT. However, measured saturated hydraulic conductivity and amount of biopores at the depth of 30–35 cm are significantly greater under RT, indicating improved soil properties under RT. Comparisons between the headlands (HL) and the inner field point out the effects of intense field traffic in the HL, where maximum PR values of about 6 MPa have been measured. The spatial prediction of PR values show that long‐term effects of different tillage practices result in clearly structured patterns between CT and RT and the HL. Combining extensive PR measurements and point measurements of additional soil properties supports an adequate interpretation of PR data and can lead to fieldwide derivation of soil functions influenced by field management.

Effect of Different Tillage Practices and Two Cropping Patterns on Soil Properties and Crop Productivity

Effect of Different Tillage Practices and Two Cropping Patterns on Soil Properties and Crop Productivity

Effects of different tillage practices on soil water-stable aggregation and organic carbon distribution in dryland farming in Northern China

Knowledge about the changes in soil aggregate stability and soil organic carbon (SOC) under different tillage treatments is necessary to assess the feasibility of adoption of conservation practices for sustaining productivity and protecting the environment in dryland farming in northern China. In this study, four treatments, no-till with straw mulching (NTSM), all straw return tillage (ASRT), shallow rotary treatment (SRT) and conventional tillage (CT) were set and a 5years field experiment was carried out to study the effects of different tillage practices on soil aggregates stability and organic carbon distribution. We found that macro-aggregate (>2mm and 0.25–2mm) proportion, mean weight diameter, total amount, content of SOC in macro-aggregate and proportion of SOC in macro-aggregate were significantly improved by NTSM, ASRT and SRT. In all treatments, soil ability to sequester carbon was improved more prominently in NTSM, and macro-aggregate proportion, mean weight diameter, total amount SOC in macro-aggregate and proportion of SOC in macro-aggregate were improve by 29.4%,30.9%,84.9% and 30.7% respectively by NTSM. In addition, improvement effects on soil aggregates stability and carbon sequestration ability in ASRT were all higher than in SRT, and compared to NTSM, macro-aggregate proportion was slightly higher (1.7%) in ASRT, but SOC content and amount in aggregates were remarkably lower. Our results revealed that reducing soil disturbance, increasing straw returning and especially their combined application (i.e. NTSM in this study) can effectively be used to reduce soil erosion and improve carbon sequestration in dryland farming in northern China.

Nitrous oxide emissions in a winter wheat – summer maize double cropping system under different tillage and fertilizer management

AbstractAn accurate estimation of nitrous oxide (N2O) emission from 110 million ha of upland in China is essential for the adoption of effective mitigation strategies. In this study, the effects of different tillage practices combined with nitrogen (N) fertilizer applications on N2O emission in soils were considered for a winter wheat (Triticum aestivum L.) – summer maize (Zea mays L.) double cropping system. Treatments included conventional tillage plus urea in split application (CTF1), conventional tillage with urea in a single application (CTF2), no‐tillage with straw retained plus reduced urea in a split application (NTSF1) and no‐tillage with manure plus reduced urea in a split application (NTMF1). The amounts of N input in each treatment were 285 and 225 kg N/ha for wheat and maize, respectively. Both NTSF1 and NTMF1 were found to reduce chemical N fertilizer rates by 33.3% (wheat) and 20% (maize), respectively, compared to CTF1 and CTF2. N2O emissions varied between 3.2 (NTSF1) and 9.9 (CTF2) kg N2O‐N/ha during the wheat season and between 7.6 (NTFS1) and 14.0 (NTMF1) kg N2O‐N/ha during the maize season. The yield‐based emission factors ranged from 21.9 (NTSF1) to 60.9 (CTF2) g N2O‐N/kg N for wheat and 92.5 (NTSF1) to 157.4 (NTMF1) g N2O‐N/kg N for maize. No significant effect of the treatments on crop yield was found. In addition to reducing production costs involved in land preparation, NTSF1 was shown to decrease chemical fertilizer input and mitigate N2O emissions while sustaining crop yield.

Wheat management with different tillage practices under rice-wheat cropping system

Timely sowing of wheat is one of the major problems under rice-wheat cropping system in Indo-Gangetic plains of India. Traditionally farmers used to burn the rice straw to facilitate seed bed preparation for wheat. Decline in soil organic matter and crop productivity in rice-wheat cropping system has become a major concern to the researcher. At the same time farmers are now interested to use a machinery to facilitate the timely sowing of wheat crop and rice straw management. The soil tillage system may affect the incorporation of crop residue and influence the nutrient dynamics. Considering the above, a field experiment was conducted for four consecutive years at the Crop Research Center of G. B. Pant University of Agriculture and Technology, Pantnagar (India) to evaluate the effect of different tillage practices on soil health and crop productivity of wheat (var. PBW-343) under rice-wheat cropping system. Five different tillage practices, namely conventional tillage (CT), Conservational tillage I (CMB), Conservational tillage II (CSD), Zero till sowing (ZT) and strip till sowing (ST) were followed for experimentation. Mean data of four years showed that the CSD produced significantly higher number of ear bearing shoots over ZT, but there was no any significant increase in grain yield. The grain weight per spike and test weight were lower in CSD and ZT than other tillage practices.

Effect of tillage practices on soil properties under rice-wheat cropping system

A field experiment was conducted for consecutive four years at the Crop Research Center of G.B. Pant University of Agriculture and Technology, Pantnagar, India, to evaluate the effect of different tillage practices on soil health and crop productivity of wheat under rice wheat cropping system. Five different tillage practices, namely conventional tillage (CT), Conservational tillage I (CMB), Conservational tillage II (CSD), Zero till sowing (ZT) and strip till sowing (ST) were implemented for testing. Mean data of four years showed that the soil health in terms of bulk density, organic carbon, available nitrogen, phosphorus and potash were superior in ZT than in other tillage practices. ZT practice retained higher numbers of phytopathogenic and non phytogenic fungi and nematodes than other tillage practices.

Affects of different tillage managements on soil physical quality in a clayey soil.

This study, conducted in 2011, researches the effects of different tillage practices on the physical soil quality of clayey soil. This soil quality index (SQI) assessment was made by studying the changes in physical soil functions such as suitability for root development, facilitation for water entry, movement and storage, and resistance against surface degradation based on tillage management. When compared with the control parcel, statistically significant decreases were seen in the SQI with different tillage practices (p < 0.05). Among the tillage practices, the highest SQI was seen with the plow + rotary tiller + direct seeding machine, while the lowest SQI was seen with the direct drilling practice. On the other hand, the statistically insignificant effects of tillage practices on the soil quality of the study area were considered to be a result of either the study period or the joint effect of soil texture and climatic features. Thus, long-term tillage practices were recommended in order to get healthier information about soil quality by considering soil and climatic conditions. In addition, for heavy clayey soils, reduced tillage practices, which included plowing, were thought to develop physical soil qualities of root development and water movement.

Using Cesium-137 to investigate soil quality under conservation tillage on steep lands

Few studies have demonstrated the long-term effects of different tillage practices on changes of soil quality; however, understanding such effects is vital for the selection and establishment of appropriate soil conservation measures on steep hillslopes. This study was conducted at two adjacent sites in the Sichuan Basin, China, with one cultivated by traditional tillage (TT; i.e., hoeing starts at the bottom position and soil is moved downslope because of gravity and drag) and the other cultivated by conservation tillage (CT; i.e., hoeing is performed from hilltop to bottom, but soil is moved uphill because of drag). We used the Cesium-137 (¹³⁷Cs) tracer technique to identify the pattern of soil constituent distribution and soil quality differences between the two tillage practices. The ¹³⁷Cs residual rate for the CT practice ranged from −29.44% to 34.16% with an average of −8.56%, and the TT practice ranged from −57.12% to 4.63% with an average of −29.49%. A greater increase (ranging from 18.43% to 50.69%) in soil constituents (i.e., soil organic matter, total nitrogen [N], phosphorus [P], and potassium [K], available N, and extractable P and K) was found in the CT soils than in the TT soils. The CT treatment site exhibited markedly higher concentrations of soil constituents in each soil depth profile (0 to 40 cm [0 to 15.7 in] and each 5 cm [2 in] in length increment). The soil degradation index (SDI) for the CT practice significantly increased compared to the TT practice in the 0 to 15 cm (0 to 5.9 in) and 15 to 40 cm (5.9 to 15.7 in) depth of the profiles (<i>p</i> &lt; 0.05). The greatest difference in SDI induced by these two tillage practices occurred at the summit and toeslope positions, with an increase in SDI of 28.07% and 15.76% in the 0 to 15 cm (0 to 5.9 in) depth and of 49.16% and 31% in the 15 to 40 cm (5.9 to 15.7 in) depth, respectively. The ¹³⁷Cs residual rate showed a corresponding relationship with the SDI changing trend, which implied that the ¹³⁷Cs residual rate may be considered an indicator for appraising soil quality for eroding hillslopes. It is suggested that the long-term practice of CT largely diminishes soil degradation because of upslope soil translocation; therefore, it would also significantly improve soil quality in steeply sloping fields.

Characterization of tillage effects on the spatial variation of soil properties using ground-penetrating radar and electromagnetic induction

Tillage practices influence physical, chemical, and biological soil properties, which also affect soil quality and consequently plant growth. In this study, the main objective was to evaluate the effects of different tillage practices on soil physical properties such as soil water content (SWC) by using geophysical methods, namely, ground-penetrating radar (GPR) and electromagnetic induction (EMI). Additional measurements such as soil sampling, capacitance probe, and soil penetrometer data were acquired as ground truths. The study was performed for three contrasting tillage practices, i.e., conventional tillage (CT), deep loosening tillage (DL), and reduced tillage (RT), applied on different plots of an agricultural field. The data showed that tillage influences soil resistance in shallow soil layers (deeper tillage decreases soil resistance), which could be partly seen in on-ground GPR data. In addition, reference SWC measurements (capacitance probes and soil sampling) were in fairly good agreement with the water content estimates from off-ground GPR. We also observed a tillage effect on shallow surface SWC, while deeper SWC seems to be unaffected by tillage. Mean surface SWC was significantly lower for CT compared to DL and RT, which was partly explained by lower pore connectivity between the topsoil and the deeper layers after conventional tillage. Moreover, the variance of the SWC within the conventional tillage plots was larger than within the other plots. This larger SWC variability could be explained by a greater soil heterogeneity induced by the plowing process. Overall, this study confirms the potential of GPR and EMI for the determination of soil physical properties at the field scale and for the assessment of agricultural management practices.

Seasonal variation of microbial biomass, activity, and community structure in soil under different tillage and phosphorus management practices

No-tillage systems contribute to physical, chemical and biological changes in the soil. The effects of different tillage practices and phosphorus (P) fertilization on soil microbial biomass, activity, and community structure were studied during the maize growing season in a maize–soybean rotation established for 18 years in eastern Canada. Soil samples were collected at two depths (0–10 and 10–20 cm) under mouldboard plow (MP) and no-till (NT) management and fertilized with 0, 17.5, and 35 kg P ha−1. Results show that the duration of the growing season had a greater effect on soil microbiota properties than soil tillage or P fertilization at both soil depths. Seasonal fluctuations in soil microbial biomass carbon (SMB-C) and nitrogen (SMB-N), in dehydrogenase and alkaline phosphomonoesterase activities, and in total phospholipids fatty acid (PLFA) level, were greater under NT than MP management. The PLFA biomarkers separated treatments primarily by sampling date and secondly by tillage management, but were not significantly affected by P fertilization. The abundance of arbuscular mycorrhizal fungi (AMF; C16:1ω5) and fungi (C18:2ω6,9) was lower under NT than MP at the 10–20-cm soil depth in July. Phosphorus fertilization increased soil microbial biomass phosphorus (SMB-P) and Mehlich-3 extractable P, but had a limited impact on the other soil properties. In conclusion, soil environmental factors and tillage had a greater effect on microorganisms (biomass and activity) and community structure than P fertilization.

The effects of different tillage methods on the post-wheat second crop sesame: seed yield, energy budget, and economic return

Field experiments were carried out to assess the effects of different tillage practices on second crop sesame (Sesamum indicum L.) after wheat (Triticum aestivum L.) during the growing seasons of 2008 and 2009 in Aksu, Antalya, Turkey. The experimental design included no-till sowing into wet soil (NTW), no-till sowing into dry soil (NTD), reduced tillage (RT), and conventional tillage (CT) with 3 registered sesame cultivars, Muganli-57, Gölmarmara, and Özberk. In the no-till methods, the field was passed over only once for planting, which was directly performed into soil with stubble. In the RT method, the soil was not inverted and the field was tilled only once with a powered rotary tiller. The CT method consisted of 1-time moldboard plowing and 2-time disc harrowing, and leveling. According to the seed yield means of 2 years, the RT method provided the highest yield with a value of 855.2 kg ha^{-1}, while the lowest yield was recorded for NTW with a value of 413.0 kg ha^{-1}. Statistically, the RT and CT methods produced higher yields than the no-till methods. In addition to seed yield, days to 50% flowering, stem length to the first capsule, plant height, number of capsules per plant, and number of seeds per capsule were positively affected by the RT and CT methods. As expected, the no-till methods resulted in significantly less fuel consumption, with 7.5 L ha^{-1}, than RT (26.4 L ha^{-1}) and CT (71.5 L ha^{-1}). Although the no-till methods provided higher energy savings and lower land preparation costs, they fell behind RT and CT in regard to seed yield. When fuel consumption, inputs, and seed yield were considered together, the RT method was the most economical. Therefore, the RT method was advised to farmers for second crop sesame after wheat with the highest income potential.

Effect of four different tillage practices on maize performance under rainfed conditions

An experiment was conducted on Ferric Acrisol under rainfed conditions during the 2010 minor crop growing season in Kumasi, Ghana to determine the effect of different tillage practices on Akposoe maize (Zea mays .L) variety performance. The experiment was arranged in a randomised complete block design with four treatments namely disc ploughing only, disc ploughing followed by disc harrowing, disc harrowing only and No Tillage. Each treatment was replicated three times. At ten weeks after planting, the disc harrowing only plots produced the tallest plant, biggest stem girth, highest number of leaves per plant, and highest leaf area index. On the other hand the No Tillage plots presented the shortest plant, smallest stem girth, lowest number of leaves per plant, and smallest leaf area index. At harvest, the longest root, highest dry matter yield and highest fresh cob weight were obtained from the disc harrowing only plots while the shortest root, lowest dry matter yield, lowest fresh cob weight, lowest dry cob weight, and smallest 1000-seed weight were located in the No Tillage plots. The disc ploughing followed by disc harrowing treatment produced the highest dry cob weight and highest 1000-seed weight. There was no significant difference in Akposoe maize plant growth, dry matter yield and yield components between the disc harrowing only and the disc ploughing followed by disc harrowing treatments. Thus, considering the soil and weather conditions of the experiment, the optimum tillage practice for producing Akposoe maize variety is disc harrowing only.

Effect of four different tillage practices on soil physical properties under cowpea

Cowpea (Vigna unguiculata [L.] Walp) is grown by resource poor farmers in Ghana using different tillage practices. Most of these farmers perform tillage operations without being aware of the effect of these operations on soil physical properties and crop responses. A field study was conducted during the 2009 and 2010 major crop growing seasons under rainfed conditions on sandy loam soil (Ferric Acrisol) to compare the effect of different tillage practices on some selected soil physical properties under Asontem cowpea variety. The experiment was arranged in a randomized complete block design with three replications. The treatments consisted of disc ploughing only, disc ploughing followed by disc harrowing, disc harrowing only and no tillage. Compared with the other treatments, the disc ploughing followed by disc harrowing treatment gave the most favourable soil conditions (i.e. lowest soil penetration resistance, lowest dry bulk density, highest soil moisture content, and highest total porosity). The no tillage plots produced the most unfavourable soil conditions (i.e. highest soil penetration resistance, highest dry bulk density, lowest soil moisture content, and lowest total porosity). Therefore, under the soil and weather conditions of the experiment, the best tillage practice identified for Asontem cowpea production is disc ploughing followed by disc harrowing.

Effect of Tillage Practices and Neem Leaves(Azadirachta indica A. Juss) on the Incidence and Severity of Termites on Cassava(Manihot esculenta Crantz) in Owerri

Termites have been identified as one of the major pests of cassava in Nigeria especially on infested soils. Effect of different tillage practices and rates of neem leaves on the incidence and severity of termites on cassava field was investigated in this study. Field experiment was conducted in 2007 at the teaching and research Farm of the Federal University of Technology, Owerri. The experiment was laid out in a 3x3 factorial in a randomized complete block design(RCBD) with three replications. The TMS 4(2)1425 was the cassava cultivar used. Treatments comprised three tillage methodsnamely: zero, flats and mounds, and neem leaves at 0 (control), 20 and 30 tons/ha. Results show that mounds and control plots significantly recorded highest termites incidence and severity on Cassava stems, while neem application at 30 tons/ha suppressed termites incidence and severity most. On the other hand mounds and neem leaves at 30 tons/ha produced highest fresh tuber and stem cutting yields .

Mediterranean Dryland Farming: Effect of Tillage Practices on Selected Soil Properties

It is widely accepted that conservation tillage management affords benefits to soil properties and reduces production costs; therefore these practices could be attractive to farmers from semiarid regions. The objective of this study was to assess the long‐term effects of different tillage practices under semiarid conditions on macroaggregate stability (water stable aggregates, WSA), soil organic carbon (SOC), and particulate organic carbon (C‐POM) content of an Alfisol from Spain. The experimental design involved a split plot and four randomized blocks in which tillage was the main factor and crop rotation (fallow–wheat–pea–barley) the secondary factor. Three tillage systems were compared: no tillage (NT), minimum tillage (MT), and conventional tillage (CT). Soil samples were collected on November 2006 and October 2007. In November 2006 no significant differences in WSA were found among the tillage treatments. In October 2007, however, the mean WSA in the upper soil layer for the NT was significantly higher, 24%, that in the CT. No significant differences were seen for the subsurface layer. Under NT, the SOC and C‐POM values for the surface soil layer were significantly higher than those for the other treatments on both sampling dates. At the subsurface depth, no significant differences were seen in either of these variables. The SOC and C‐POM values were more homogeneous throughout the soil profile in the plowed soil than in the NT for which the corresponding values were more stratified. The results show that NT will help improve soil structure and soil fertility, which is particularly relevant to semiarid conditions like the area studied.

Effect of tillage practices on structural properties and content of organic carbon in tilth soil

To further explore tillage practices for improving soil structure, the effect of different tillage practices on the structure and organic carbon of tilth soils were investigated using routine method (Wet-sieving, Potassium dichromate volumetry and Core-cutting sampling). The 7-year research was conducted at an experimental station in the semiarid Loess Plateau zone in central Gansu Province. The conservative management practices of no-tillage (NT), conventional tillage with straw incorporation (TS) and no-tillage with straw mulch (NTS) increase soil organic C and water-stable soil aggregates contents, with the highest effect under NTS tillage. Soil bulk density decreases while soil porosity increases, greatly improving soil structure under NTS in the 0~10 cm soil layer. Content of soil water-stable aggregate (1~0.5 mm) is the highest in all 3 soil layers, 0~5 cm, 5~10 cm and 10~30 cm. Soil wa- ter-stable aggregate (0.25 mm) has a significant positive correlation with soil organic C content and porosity, but is significantly negatively correlated with soil bulk density.

Evaluation of CO 2 fluxes from an agricultural field using a process-based numerical model

During 2004, soil CO 2 fluxes, and meteorological and soil variables were measured at multiple locations in a 30-ha agricultural field in the Sacramento Valley, California, to evaluate the effects of different tillage practices on CO 2 emissions at the field scale. Field scale CO 2 fluxes were then evaluated using the one-dimensional process-based SOILCO2 module of the HYDRUS-1D software package. This model simulates dynamic interactions between soil water contents, temperature, and soil respiration by numerically solving partial–differential water flow (Richards) and heat and CO 2 transport (convection–dispersion) equations using the finite element method. The model assumes that the overall CO 2 production in the soil profile is the sum of soil and plant respiration, whose optimal values are affected by time, depth, water content, temperature, and CO 2 concentration in the soil profile. The effect of each variable is introduced using various reduction functions that multiply the optimal soil CO 2 production. Our results show that the numerical model could predict CO 2 fluxes across the soil surface reasonably well using soil hydraulic parameters determined from textural characteristics and the HYDRUS-1D software default values for heat transport, CO 2 transport and production parameters without any additional calibration. An uncertainty analysis was performed to quantify the effects of input parameters and soil heterogeneity on predicted soil water contents and CO 2 fluxes. Both simulated volumetric water contents and surface CO 2 fluxes show a significant dependency on soil hydraulic properties.