Quantification of tillage and landscape effects on soil carbon in small Iowa watersheds

Knowledge of the long-term effects of tillage on soil organic carbon is important to our understanding of sustainable agricultural systems and global carbon cycles. In landscapes susceptible to erosion, tillage can exacerbate losses of soil and C by increasing erodibility and stimulating microbial respiration. We measured long-term changes in soil carbon and soil loss in three small watersheds located in southwest Iowa, USA. The following soil series were formed on deep loess hills: Ida and Dow (Typic Udorthents), Napier and Kennebec (Cumulic Hapludolls) and Monona (Typic Hapludolls). All watersheds were cropped to continuous corn (Zea mays L.) and two were moldboard plowed and disk tilled while the third was ridge-tilled. The ridge-tillage system had greater C contents in the surface soil than the disk tillage soils, but ridge-tillage was not different from the conventional tillage in carbon retention over time. The ridge-tillage system, however, was more effective in retaining soil within the watershed. Microbial respiration by soil microorganisms accounted for 97% of the carbon loss in the ridge-tilled watershed compared to carbon loss in eroded sediment (3%). Terrain analysis was used to segment the landscape into landform elements. Less total carbon was present in the soil profiles of backslope elements than in footslope or toeslope elements, reflecting the combined effects of soil erosion and deposition within the watersheds. Profile C content was also positively correlated with the wetness index, a compound topographic attribute, that identifies areas of the landscape where runoff water and sediment accumulate.     

A preliminary watershed scale soil quality assessment in north central Iowa, USA

Soil quality assessment has been recognized as an important step toward understanding the long-term effects of conservation practices within agricultural watersheds. Our objective was to assess soil quality within the South Fork watershed of the Iowa River using various indicators and assessment approaches. Soil samples were collected during 2003 and 2004 from 29 areas of 32 ha (80 acres) each along two transects traversing the watershed. Soil pH, Mehlich III extractable P, K, Ca and Mg, electrical conductivity (EC), total organic carbon (TOC), and total N (TN) were measured. The Soil Management Assessment Framework (SMAF) was used to compute a soil quality index (SQI), while soil loss, the soil tillage intensity rating (STIR), N-leaching potential, and soil conditioning index (SCI) were determined for each sampling area using the 2003 version of the Revised Soil Loss Equation (RUSLE2). Overall, there were no soil fertility limitations within the watershed based on an average pH of 6.96 and extractable P and K levels of 36 and 162 mg kg⁻¹, respectively. Soil loss, STIR, N-leaching, and SCI averaged 1.13 Mg ha⁻¹, 68, 3, and 0.4, respectively. The SMAF analysis indicated soils within the watershed were functioning at 87% of their full potential. The lowest indicator score was associated with TOC (0.60) because the average value was only 28.4 g kg⁻¹. The SCI and SQI indices were positively correlated although since it used measured data, the SMAF appears to provide more information about the effects of management practices within the watershed. Soils in upper landscape positions had lower TOC and C:N ratios indicating an increased risks for both erosion and for nitrate leaching. Management of soils on hilltops may be the most effective way to minimize N and P losses within the watershed.     

Bulk density as a soil quality indicator during conversion to no-tillage

Producers often identify compaction as an important problem, so bulk density is usually included in minimum data sets used to evaluate tillage and crop management effects on soil quality. The hypothesis for this study was that bulk density and associated water content would be useful soil quality indicators for evaluating the transitional effects associated with changing tillage and crop management practices on deep-loess soils. The study was conducted on three deep-loess, field-scale watersheds located in western Iowa, USA. The soils are classified as Haplic Phaeozems, Cumulic-Haplic Phaeozems, and Calcaric Regosols. Watersheds 1 and 2 were converted in 1996 from conventional tillage to no-tillage, while watershed 3 was maintained using ridge-tillage and continuous corn (Zea mays L.), a practice implemented in 1972. Watershed 1 was converted to a corn—soybean (Glycine max (L.) Merr.) rotation while watershed 2 was converted to a 6-year rotation that included corn, soybean, corn plus 3 years of alfalfa (Medicago sativa L.). Bulk density and water content were measured at three landscape positions (summit, side-slope, and toe-slope), in 20 mm increments to a depth of 300 mm, five times between September 1996 and May 2000. Organic C and total N were also measured to a depth of 160 mm during the initial sampling. Neither bulk density nor water content showed any significant differences between the two watersheds being converted to no-tillage or between them and the ridge-till watershed. There also were no significant differences among landscape positions. Bulk densities and water contents showed some differences when adjacent sampling dates were compared, but there was no overall or consistent trend. Our results show that bulk density is not a useful soil quality indicator for these soils within the bulk density range encountered (0.8–1.6 Mg m³). Our results also confirm that producers do not necessarily have to worry about increased compaction when using ridge-tillage or changing from conventional to no-tillage practices on these or similar deep-loess soils.     

冲沟不同部位土壤机械组成及抗冲性差异

选取3类典型冲沟(活跃、较活跃和稳定)的集水区、沟头和沟床土壤,探明冲沟不同空间部位土壤机械组成特性及其抗冲性差异,结果表明:1活跃、较活跃冲沟土壤质地均为砂质壤土,稳定冲沟各部位土壤质地各不相同;黏粒含量、粉粒含量总体为活跃冲沟较活跃冲沟稳定冲沟;细砂粒含量为较活跃冲沟活跃冲沟稳定冲沟;粗砂粒含量则是活跃冲沟较活跃冲沟稳定冲沟。23类冲沟各部位土壤抗冲性均是沟床最高,而3类冲沟同一部位抗冲性大小比较中,沟头和沟床土壤抗冲性为稳定冲沟较活跃冲沟活跃冲沟,集水区以活跃冲沟土壤抗冲性最小,较活跃与稳定冲沟的土壤抗冲性相当。3线性回归分析表明:砂粒含量是影响3类冲沟各部位土壤抗冲性的主要指标,黏粒含量影响稳定冲沟各部位土壤抗冲性,粉粒含量与较活跃冲沟沟头、稳定冲沟集水区和沟床的土壤抗冲性有关。研究结果从土壤机械组成和土壤抗侵蚀性的关系角度为冲沟研究提供一定的理论参考。     

Soil quality response to tillage and crop residue removal under subarctic conditions

Little is known about the long-term effects of tillage and crop residue management on soil quality and organic matter conservation in subarctic regions. Therefore, we quantified wet aggregate stability, bulk density, pH, total organic C and N, inorganic N, microbial biomass C and N, microbial biomass C:N ratio, microbial quotient, and potential C and N mineralization for a tillage/crop residue management study in central Alaska. Soil from no-till (NT), disked once each spring (DO), and disked twice (DT, spring and fall) treatments was sampled to 20 cm depth in spring and fall of the 16th and 17th years of the study. Crop residues were either retained or removed after harvest each year. Reducing tillage intensity had greater impact on most soil properties than removing crop residues with the most notable effects in the top 10 cm. Bulk density was the only indicator that showed significant differences for the 10–20 cm depth, with values of 0.74 Mg m⁻³ in the surface 10 cm in NT compared to 0.86 in DT and 1.22 Mg m⁻³ in NT compared to 1.31 in DT for the 10–20 cm depth. Wet aggregate stability ranged from 10% in DT to 20% in NT. Use of NT or DO conserved soil organic matter more than DT. Compared to measurements made in the 3rd and 4th years of the study, the DT treatment lost almost 20% of the soil organic matter. Retaining crop residues on the soil conserved about 650 g m⁻² greater C than removing all residues each year. Soil microbial biomass C and mineralizable C were highest in NT, but the microbial C quotient, which averaged only 0.9%, was not affected by tillage or crop residue treatment. Microbial biomass C:N ratio was 11.3 in DT and 14.4 in the NT, indicating an increasing predominance of fungi with decreasing tillage intensity. Barley grain yield, which averaged 1980 kg ha⁻¹ over the entire 17 years of the study, was highest in DO and not significantly different between NT and DT, but weeds were a serious problem in NT. Reduced tillage can improve important soil quality indicators and conserve organic matter, but long-term NT may not be feasible in the subarctic because of weed problems and build up of surface organic matter.     

Soil organic matter stratification ratio as an indicator of soil quality

Soil quality is a concept based on the premise that management can deteriorate, stabilize, or improve soil ecosystem functions. It is hypothesized that the degree of stratification of soil organic C and N pools with soil depth, expressed as a ratio, could indicate soil quality or soil ecosystem functioning, because surface organic matter is essential to erosion control, water infiltration, and conservation of nutrients. Stratification ratios allow a wide diversity of soils to be compared on the same assessment scale because of an internal normalization procedure that accounts for inherent soil differences. Stratification ratios of soil organic C were 1.1, 1.2 and 1.9 under conventional tillage (CT) and 3.4, 2.0 and 2.1 under no tillage (NT) in Georgia, Texas, and Alberta/British Columbia, respectively. The difference in stratification ratio between conventional and NT within an environment was inversely proportional to the standing stock of soil organic C to a depth of 15–20 cm across environments. Greater stratification of soil C and N pools with the adoption of conservation tillage under inherently low soil organic matter conditions (i.e., warmer climatic regime or coarse-textured soil) suggests that standing stock of soil organic matter alone is a poor indication of soil quality. Stratification of biologically active soil C and N pools (i.e., soil microbial biomass and potential activity) were equally or more sensitive to tillage, cropping intensity, and soil textural variables than stratification of total C and N. High stratification ratios of soil C and N pools could be good indicators of dynamic soil quality, independent of soil type and climatic regime, because ratios >2 would be uncommon under degraded conditions.     

Duration of tillage management affects carbon and phosphorus stratification in phosphatic Paleudalfs

Surface accumulation of soil organic carbon (SOC) under conservation tillage has significant effects on stratification of other nutrients, on crop productivity and in ameliorating the greenhouse effect via atmospheric CO₂ sequestration. A measure of SOC stratification relative to deeper soil layers has been proposed as a soil quality index. Our objective was to determine the effects of the duration of tillage practices upon the SOC and extractable P distribution with depth in Maury silt loams (Typic Paleudalfs) at similar levels of corn (Zea mays L.) productivity without P fertilization. Soil samples (0–20.0 cm in 2.5 cm increments) were collected under moldboard tillage (MT), chisel tillage (CT) and no-tillage (NT) and in surrounding tall fescue (Festuca arundinacea L.) sods selected from three tillage experiments (1–2-, 8- and 29-year durations) in Kentucky. SOC stratification was greater under conservation tillage (CT and NT) and sods than under MT. SOC and soil-test-extractable P stratification were positively related. Increasing the duration under NT caused the thickness of C stratification to increase. In NT soils, C stratification ratio (CSR) approached CSR in the nearby long-term sods with time. Conservation tillage rapidly promoted the occurrence of CSR greater than 2 while MT always resulted in values lower than 2. The rapid initial change in CSR suggests characterization of thin soil layers (i.e. 2.5 cm depth increments) is desirable under conservation tillage.     

Factors determining soil nutrient distribution in a small-scaled watershed in the purple soil region of Sichuan Province, China

Determining soil nutrient distribution is critical to identify sites which are at risk of N and P loading. Equally important are determining factors that influence such distribution (e.g. land use, land management, topography, etc.). In this research, soil nutrient distribution and its influencing factors were studied in a small-scaled watershed in the purple soil region of Sichuan Province, China. The watershed is 1.3 km² with a complex land management system including agriculture and forestry. Surface soil samples (0–20 cm) from 48 sites within the watershed were collected in the spring of 1999 and analysed for chemical properties. When spatial distribution patterns of soil organic matter and soil nutrients were considered, several patterns were evident. Soil organic matter and total nitrogen coincided with high soil nutrients in the center of the watershed. Total phosphorus was linked to low soil nutrient contents on hilltops, while total potassium was characterized by low variability and high soil nutrient content throughout the watershed. Water-soluble nutrients in soils were highly variable throughout the watershed. Results of this study indicate that land use, topography and other variables play important roles in controlling the spatial distribution of most soil nutrients. However, the relative roles of these indices were nutrient specific. The relationship was therefore complex. Land use, silt, and sand content contributed to a high level of heterogeneity for soil organic matter and total nitrogen with the former being the dominant factor. Land use, particle size distribution (silt and sand) and topographic factors (slope and elevation) contributed to the variability of total phosphorus. However, particle size distribution and topographic factors were the dominant factors affecting total phosphorus. Elevation influenced the concentration of total potassium and land use controlled the concentration of dissolved phosphorous. No significant relationship was found between the studied characteristics and nitrate nitrogen.     

VARIATION IN SOIL ORGANIC CARBON AND NITROGEN STOCKS ALONG A TOPOSEQUENCE IN A TRADITIONAL MEDITERRANEAN OLIVE GROVE

The impact of the topographical position on soil properties was evaluated in an olive grove with traditional tillage. Three topographical positions: summit, backslope and toeslope were chosen for evaluation. The soil samples were taken from four soil sections of 0·25 m (0–1 m). The soil organic carbon (SOC) and N content increased along the downslope direction (5·5, 6·5 and 7·1 g C kg⁻¹ and 0·3, 0·8 and 0·9 g N kg⁻¹ in the surface layer in the summit, backslope and toeslope respectively) as well as SOC and N stocks, considering the two first soil sections. In addition, there was movement of the most erodible textural fraction (silt). However, the total SOC stock (refer to 1 m of depth) did not vary with respect to the topographical position, but the total N stock (refer to 1 m of depth) varied significantly. These increases were due to erosion processes that occur along the toposequence, leading to organic matter transfers from the summit to the toeslope. All the stratification ratios calculated were lower than 2, indicating the low quality of the soils. Therefore, alternative management techniques that avoid soil erosion must be considered in olive grove in order to increase the soil quality and fertility. Copyright © 2014 John Wiley & Sons, Ltd.     

Tillage effects on microbial biomass and nutrient distribution in soils under rain-fed corn production in central-western Mexico

Quantifying how tillage systems affect soil microbial biomass and nutrient cycling by manipulating crop residue placement is important for understanding how production systems can be managed to sustain long-term soil productivity. Our objective was to characterize soil microbial biomass, potential N mineralization and nutrient distribution in soils (Vertisols, Andisols, and Alfisols) under rain-fed corn (Zea mays L.) production from four mid-term (6 years) tillage experiments located in central-western, Mexico. Treatments were three tillage systems: conventional tillage (CT), minimum tillage (MT) and no tillage (NT). Soil was collected at four locations (Casas Blancas, Morelia, Apatzingán and Tepatitlán) before corn planting, at depths of 0–50, 50–100 and 100–150 mm. Conservation tillage treatments (MT and NT) significantly increased crop residue accumulation on the soil surface. Soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were highest in the surface layer of NT and decreased with depth. Soil organic C, microbial biomass C and N, total N and extractable P of plowed soil were generally more evenly distributed throughout the 0–150 mm depth. Potential N mineralization was closely associated with organic C and microbial biomass. Higher levels of soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were directly related to surface accumulation of crop residues promoted by conservation tillage management. Quality and productivity of soils could be maintained or improved with the use of conservation tillage.     

黑土坡耕地横坡垄作对减少径流及土壤有机碳流失的作用

东北黑土坡耕地受土壤侵蚀和习惯顺坡耕作措施的影响,水土流失严重,土壤有机碳含量呈逐年下降趋势.针对东北黑土坡耕地不同垄作措施水土流失及土壤有机碳变化特征不明确的问题,采用田间定位试验的方法,探究了顺坡垄作和横坡垄作对坡耕地水土流失及土壤有机碳变化的影响.结果表明:(1)横坡垄作相对于顺坡垄作能显著减少径流总量97.1％...     

Long-term cultivation impacts on selected soil properties in the northern Great Plains

Long-term cultivation impacts soil properties. During the early 1920s a study comparing non-cultivated and cultivated soils was done in eastern SD (Beadle, McCook, Minnehaha, and Union Counties), USA. The objectives of the current study were to: (1) determine the long-term (>80 years) impact of cultivation on selected soil properties; and (2) establish baseline soil data that can be used for future comparisons. Sample sites were located in well-drained summit and upper backslope positions. These topographic positions are strongly influenced by erosion processes from tillage, wind, and water. Previous studies at other locations in the region suggest that one might expect a loss of 10–20 cm of soil in >80 years of cultivation at these topographic positions. In the early 1920s the soils were tested for carbon (C) (total, organic, inorganic), total nitrogen (N), total sulfur (S), total calcium (Ca), total phosphorus (P), total potassium (K), and total magnesium (Mg). The 1920s study sites were resampled at 0–15, 15–50, and 50–100 cm depths and analyzed for C (total, organic, inorganic), N (total, nitrate-N), extractable P, extractable K, delta N (¹⁵N/¹⁴N or δ¹⁵N) for total N, delta C (¹³C/¹²C or δ¹³C) for total C, and pH. Long-term cultivation (>80 years) in the northern Great Plains of the United States has caused many significant reductions in surface soil (0–15 cm) extractable P, extractable K, surface pH, total C, organic C, total N, and δ¹⁵N for total N. In addition, the organic C to total N ratio for the 15–50 cm depth of cultivated soils was significantly lower when compared to non-cultivated soils. Cultivation caused significant increases in nitrate-N, delta C, inorganic C, and in the total C to total N and inorganic C to total N ratios (15–100 cm depths). Soil properties varied significantly with increasing soil depth. Soil pH, δ¹³C for total C, inorganic C, total C to total N ratio, and inorganic C to total N ratio increased significantly as soil depth increased. Nitrate-N, extractable P, extractable K, δ¹⁵N for total N, organic C, and total N decreased significantly as soil depth increased. Soil carbon changes at the sample sites are a combined result of differences in the reference surface elevation, carbon mineralization, and redistribution of carbon due to erosion. Changes in soil nutrient levels reflect crop removal, leaching, erosion, and pedogenic processes.     

Barley yield response to soil organic matter and texture in the Pampas of Argentina

Soil organic matter (SOM) is known to play a major role in soil fertility due to its influence on physical, chemical and biological properties of soil; and it is closely related to particle size distribution. The ratio of SOM (g kg⁻¹) to clay + silt content (g kg⁻¹) was evaluated as an indicator of soil quality for barley (Hordeum vulgare) grain yield, reflecting N availability and soil physical conditions to which crop development is sensitive. Thirty-eight sites in the semiarid Pampa region of Argentina with a wide range of SOM and texture were evaluated for malting barley yield during three growing seasons. In control plots, 51% of grain yield could be explained by this indicator. The threshold value between high and low N-fertilization response was 4.4. Better yield prediction to almost 68% was achieved by combining the SOM to clay + silt indicator with initial nitrate content of the soil at seeding. This combined indicator was also able to explain a high proportion of water use efficiency, particularly in the early growth stages. The ratio of SOM to clay + silt content provided a better tool for estimating grain yield than nutrient availability or SOM alone.     

Short-term green manure and tillage management effects on maize yield and soil quality in an Andisol

Andisols are very important land resources supporting high human population density. Maize (Zea mays L.) production on Andisols located in the Purhepecha Region of central Mexico is representative of the highlands conditions of Mexico and Latin America. Farmers struggle with low crop yield and low soil nutrient availability. A 2-year field study was conducted to evaluate the effects of green manures either tilled into the soil (CT) or cut and left on the surface as a mulch (ZT), on maize yield and soil quality. Green manure treatments were: vetch (Vicia sativa L.), oat (Avena sativa L.) and none. No extra N was added to maize. Green manure and tillage had a significant effect on maize grain yield, N uptake and P uptake with CT vetch performing better than ZT oat. Soil organic C and total N were significantly higher under ZT than under CT management. Soils with vetch had higher P concentration. Soil under ZT oat had the highest infiltration rate and penetration resistance compared with other treatments. There appears to be a trade off between soil productivity and intrinsic soil physical properties among soil treatments.     

Tillage and cropping effects on soil quality indicators in the northern Great Plains

The extreme climate of the northern Great Plains of North America requires cropping systems to possess a resilient soil resource in order to be sustainable. This paper summarizes the interactive effects of tillage, crop sequence, and cropping intensity on soil quality indicators for two long-term cropping system experiments in the northern Great Plains. The experiments, located in central North Dakota, were established in 1984 and 1993 on a Wilton silt loam (FAO: Calcic Siltic Chernozem; USDA¹: fine-silty, mixed, superactive frigid Pachic Haplustoll). Soil physical, chemical, and biological properties considered as indicators of soil quality were evaluated in spring 2001 in both experiments at depths of 0–7.5, 7.5–15, and 15–30 cm. Management effects on soil properties were largely limited to the surface 7.5 cm in both experiments. For the experiment established in 1984, differences in soil condition between a continuous crop, no-till system and a crop–fallow, conventional tillage system were substantial. Within the surface 7.5 cm, the continuous crop, no-till system possessed significantly more soil organic C (by 7.28 Mg ha⁻¹), particulate organic matter C (POM-C) (by 4.98 Mg ha⁻¹), potentially mineralizable N (PMN) (by 32.4 kg ha⁻¹), and microbial biomass C (by 586 kg ha⁻¹), as well as greater aggregate stability (by 33.4%) and faster infiltration rates (by 55.6 cm h⁻¹) relative to the crop–fallow, conventional tillage system. Thus, soil from the continuous crop, no-till system was improved with respect to its ability to provide a source for plant nutrients, withstand erosion, and facilitate water transfer. Soil properties were affected less by management practices in the experiment established in 1993, although organic matter related properties tended to be greater under continuous cropping or minimum tillage than crop sequences with fallow or no-till. In particular, PMN and microbial biomass C were greatest in continuous spring wheat (with residue removed) (22.5 kg ha⁻¹ for PMN; 792 kg ha⁻¹ for microbial biomass C) as compared with sequences with fallow (SW–S–F and SW–F) (Average=15.9 kg ha⁻¹ for PMN; 577 kg ha⁻¹ for microbial biomass C). Results from both experiments confirm that farmers in the northern Great Plains of North America can improve soil quality and agricultural sustainability by adopting production systems that employ intensive cropping practices with reduced tillage management.     

Soil Nutrients Status after Fifty Years of Tillage and Nitrogen Fertilization

Long-term studies are valuable in assessing the impact of crop management practices on soil sustainability and function. This study used two calculation scenarios, fixed depth and Equivalent Soil Mass (ESM) to assess (i) soil nutrient status and (ii) soil organic carbon (SOC) after 50 years of nitrogen (N) fertilizer application rates (0, 22, 45, and 67 kg N ha^?1) and tillage [clean tillage (CT), reduced tillage (RT), and no-tillage (NT)] in a dryland winter wheat-sorghum-fallow cropping system. The soil organic matter (SOM) content increased by 33% with NT and RT compared with CT. The SOC at 0–30 cm was 39% greater than 30–60 cm depth with both fixed depth and ESM calculations. Soil nutrient specifically soil calcium (Ca), magnesium (Mg), and phosphorus (P) associated with N rates were no different than the control. Crop nutrient removal may eventually reduce soil nutrient contents with only N application. Nutrient addition specifically P should be considered in the future.     

Modeling spatial variation in productivity due to tillage and water erosion

The advent of precision farming practices has heightened interest in managing field variability to optimize profitability. The large variation in yields across many producer fields demonstrated by yield–monitor–equipped combines has generated concern about management-induced causes of spatial variation in soil productivity. Soil translocation from erosion processes may result in variation in soil properties across field landscape positions that produce long-term changes in soil productivity. The objective of this study was to examine the relationships between soil redistribution caused by tillage and water erosion and the resulting spatial variability of soil productivity in a soil catena in eastern South Dakota. An empirical model developed to estimate tillage erosion was used to evaluate changes expected in the soil profile over a 50-year period on a typical toposequence found in eastern South Dakota and western Minnesota. Changes in the soil profile due to water erosion over a 50-year period were evaluated using the WEPP hillslope model. The tillage erosion model and the WEPP hillslope model were run concurrently for a 50-year period to evaluate the combined effect of the two processes. The resulting changes in soil properties of the root zone were evaluated for changes in productivity using a productivity index model. Tillage erosion resulted in soil loss in the shoulder position, while soil loss from water erosion occurred primarily in the mid to lower backslope position. The decline in soil productivity was greater when both processes were combined compared to either process acting alone. Water erosion contributed to nearly all the decline in soil productivity in the backslope position when both tillage and water erosion processes were combined. The net effect of soil translocation from the combined effects of tillage and water erosion is an increase in spatial variability of crop yields and a likely decline in overall soil productivity.     

Variation of soil microbial biomass C and hydrolytic enzyme activities in a rangeland ecosystem: are slope aspect and position effective?

This study was conducted to investigate the effects of slope aspect and position on microbial biomass C (MBC) and some hydrolytic enzyme activities involved in soil N, P, and S cycles in a rangeland ecosystem of west central Iran. Soil samples were collected from three slope positions (summit, backslope, and footslope) of contiguous north- and south-facing slopes. Results indicated higher silt and clay content, soil organic C (SOC), total N (TN), and C/N ratio on the north-facing slope. Furthermore, MBC, alkaline phosphomonoesterase (ALP), acid phosphomonoesterase (ACP), arylsulfatase (ARS), urease (URS), L-asparaginase (LAS), and L-glutaminase (LGL) activities were greater by 46.1, 65.9, 58.6, 59.6, 52.6, 62.8, and 65.7%, respectively, on the north-facing slope compared to the south-facing one. Higher ratios of enzyme activities to MBC were observed on the north-facing slope. In contrast, per cent of inorganic N and microbial quotient were greater on the south-facing slope. The activity of ALP, ACP, ARS along with SOC, TN, and MBC values decreased from summit to footslope. Overall, our findings indicate that north-facing slope and summit position support greater microbial biomass and hydrolytic diversity.     

Twenty years of tillage research in subarctic Alaska: I. Impact on soil strength, aggregation, roughness, and residue cover

Soil properties and surface characteristics affecting wind erosion can be manipulated through tillage and crop residue management. Little information exists, however, that describes the impact of long term tillage and residue management on soil properties in the subarctic region of the United States. This study examines the impact of 20 years of tillage and residue management on a broad range of physical properties that govern wind erosion processes on a silt loam in interior Alaska. A strip plot experimental design was established in 1983 and included intensive tillage (autumn and spring disk), spring disk, autumn chisel plow, and no tillage with straw either retained on or removed from the soil surface. Soil and residue properties measured after sowing barley (Hordeum vulgare L.) in May 2004 included penetration resistance, soil water content, shear stress, bulk density, random roughness, aggregate size distribution, and residue cover and biomass. No tillage was characterized by larger aggregates, greater soil strength (penetration resistance and shear stress), wetter soil, and greater residue cover compared to all other tillage treatments. Despite crop failures the previous 2 years, crop residue management influenced residue biomass and cover, but not soil properties. Autumn chisel and spring disk appeared to be viable minimum tillage options to intensive tillage in controlling erosion. Autumn chisel and spring disk promoted greater roughness, aggregation, and residue cover as compared with intensive tillage. Although no tillage appeared to be the most effective management strategy for mitigating wind erosion, no tillage was not a sustainable practice due to lack of weed control. No tillage also resulted in the formation of an organic layer on the soil surface over the past 20 years, which has important ramifications for long term crop production in the subarctic where the mean annual temperature is <0 °C.     

Total, particulate organic matter and structural stability of a Calcixeroll soil under different wheat rotations and tillage systems in a semiarid area of Morocco

Wheat production in Morocco is constrained by both scarce climate and degraded soil quality. There is an urgent need to revert production decline while restoring country’s soils. Among conservation tillage systems known for their improvement in yield, no-till technology was found to influence soil quality as well. Soil quality indices are also affected by wheat rotations at medium and long-terms. This paper discusses changes in selected properties of a Calcixeroll soil, including total and particulate soil organic matter (SOM), pH, total N and aggregation, subjected, for 11 consecutive years, to various conservation and conventional agricultural systems. Tillage systems included no-tillage (NT) and conventional tillage (CT). Crop rotations were continuous wheat, fallow–wheat, fallow–wheat–corn, fallow–wheat–forage and fallow–wheat–lentils. Higher aggregation, carbon sequestration, pH decline and particulate organic matter (POM) buildup are major changes associated with shift from conventional- to NT system. Better stability of aggregates was demonstrated by a significantly greater mean weight diameter under NT (3.8 mm) than CT system (3.2 mm) at the soil surface. There was 13.6% SOC increase in (0–200 mm) over the 11-year period under NT, while CT did not affect much this soil quality indicator. Another valuable funding is the stratification of SOC and total nitrogen in NT surface horizon (0–25 mm) without their depletion at deeper horizon compared to tillage treatments. Fallow–wheat system resulted in reduction of SOC compared to WW, but 3-year wheat rotation tended to improve overall soil quality. Benefits from crop rotation in terms of organic carbon varied between 2.6 and 11.7%, with fallow–wheat–forage exhibiting the maximum. Combined use of NT and 3-year fallow rotation helped to improve soil quality in this experiment.