Soil Tillage

In established Australian vineyards compacted soil either created naturally or by trafficking prevents root growth to desirable depths and restricts root systems from getting water and nutrients. This can reduce the life span and productivity of grapevines considerably over a period of years. To break up these compacted soil layers using small tractors a deep working oscillatory ripper was developed at University of South Australia which had two deep working oscillating tines. One of the most important factors for the performance of this oscillatory ripper is the oscillation angle of the tines which is described as the relationship between tine pivot point and tine tip. To find the optimum oscillation angle a series of field tests were conducted in a sand-loam soil at 6 different oscillation angles. The tines oscillated at a frequency of 4.9 Hz and with amplitudes of between ±60-69mm, with a nominal forward speed of 3 km/h. The trial results are quantified based on draft requirement, power saving, power ratio and loosened area. The greatest draft reduction of 50% was achieved for negative oscillation angles, where power ratio was less than one. Power saving was significantly affected by changing oscillation angle. In general, vibration of the driver seat was higher for negative angles. In terms of performance-22.5º oscillation angle was the optimum for draft reduction and power saving, whereas the least vibration was obtained at an oscillation angle of +16º which was equal to Australian Standard threshold for 8 hours continuous work.

Several management systems can improve soil productivity. By studying aggregate stability it is possible to quantify whether or not the management is ameliorating the natural soil properties and the land capability for agriculture. The effect of three tillage systems on the stability of soil aggregates and soil organic carbon was studied in comparison to reference plots with grass and bare soil. Samples were collected at the Pesagro Experimental Research Station in Paty do Alferes, state of Rio de Janeiro, Brazil, from an experiment that has been carried out from 1995 to 2001, on a Dystrophic Red Latosol (Typic Haplorthox). Aggregate size distribution mean weight diameter, geometric mean diameter of the aggregates, and total organic carbon in each aggregate size fraction were determined. The proportion of aggregates with diameter ≥2 mm appeared to be a suitable indicator of the influence of tillage systems on aggregation. At a depth of 0-5 cm, aggregates ≥2 mm were 50% of soil under no-tillage, which was greater than under animal traction (35%) and conventional tillage (30%). Total organic carbon concentration was greater under no-tillage (19 g kg −1 ) than under conventional tillage (11 g kg −1 ) at a depth of 0-5 cm, but not significantly different (average 13 g kg −1 ) at a depth of 5-10 cm. Soil exposure with tillage and lack of residue inputs caused declines in aggregation and organic carbon, both of which make soil susceptible to erosion. Adoption of no-tillage led to a decline in aggregation compared with grass reference, but did significantly alter soil organic concentration, suggesting it was a valuable conservation practice for vegetable production on sloping soils.

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 À1 ) to clay + silt content (g kg À1 ) 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. #

Reduced tillage with appropriate crop rotation could increase the viability of dry land agriculture in semiarid zones. The effects of tillage and crop rotation on soil physico-chemical properties, soil organic carbon (SOC) and N have been studied widely in long and short-term experiments. However, their effects on nutrient levels and fertility losses have not been extensively studied in Mediterranean soils. We determined SOC, N, P, K, Fe, Mn, Cu and Zn distribution in the soil profile and in plant uptake, on a Calciortidic Haploxeralf in Spain. Three tillage systems [CT, conventional tillage (mouldboard plow); MT, minimum tillage and NT, no tillage] and three crop rotations [BB, continuous barley (Hordeum vulgare v. Tipper), FB, fallow-barley and VB, vetch (Vicia sativa v. Muza)-barley] were compared. SOC and N were higher for CT than for MT and NT in the first year, but higher for NT and MT than CT in the next years. In the 0-15 cm depth, SOC and N in NT also became higher than in MT for the fourth crop season. In the 15-30 depths, NT and MT had also higher SOC than CT since the second year. However, NT had only higher N than MT after three crop seasons. The increase in SOC was 75% for NT and MT while CT had a decrease of 17% in the 0-15 cm layer. The increase in N was 154% for NT, 108% for MT and 30% for CT in the upper 15 cm. NT had higher P, K and Cu than MT and higher P, K, Fe, Mn, Cu and Zn than CT in the upper layers due to the higher SOC level and to the fact that these systems maintain surfaceapplied K and P fertilizer. On the other hand, neither SOC nor N were affected by crop rotation. Tillage and rotation interactions were not significant for SOC, N and, in general, nutrient levels in the different soil depths. In general, the main factor that affected SOC, N and nutrients was tillage, which had reduced influence with depth. Highest yield was for CT-FB and CT-VB, but not different from NT-FB and NT-VB, meanwhile highest nutrient levels were obtained for interactions that included NT. These results suggest that NT, and to a lesser extend MT, preserved SOC and nutrient levels in the upper layers and, with NT-VB and NT-FB interaction, could also obtain high yields and keep soil fertility in the upper depths during the first 4 years. #

In the semi-arid zone of West Africa, the growth of annual crops is severely constrained by soil and climatic conditions. Soil physical properties, specifically low porosity resulting from the particle-size distribution and predominantly low-activity clay, restricts root system development and crop growth. Using intensive mechanical tillage is an effective method in enhancing soil porosity and physical properties.

Experiments were carried out to study which soil physical factors, if any, would restrict germination and emergence of sorghum (Sorghum bicolor (L.) Moench.) and cowpea (Vigna unguiculata (L.) Walp.), under field conditions in Tanzania. The study also aimed to consider the usefulness of mulching as a strategy to overcome such problems, and to contribute to the development of a strategy for modelling seedling emergence in seedbeds in the field.

Soil fertility, one of the important determinants of agricultural productivity, is generally thought to be supplemented through the application of nutrients mainly through inorganic fertilizers. The physical fertility of the soil, which creates suitable environment for the availability and uptake of these nutrients, is generally ignored. The present study aims to characterize the soil physical environment in relation to the long term application of farm yard manure (FYM) and inorganic fertilizers in rice–wheat. The treatments during both rice and wheat crops were (i) farm yard manure @ 20 t ha−1 (FYM); (ii) nitrogen @ 120 kg ha−1 (N120); (iii) nitrogen and phosphorus @ 120 and 30 kg ha−1 (N120P30) and (iv) nitrogen, phosphorus and potassium @ 120, 30 and 30 kg ha−1 (N120P30K30) in addition to (iv) control treatment, i.e. without any fertilizer and/or FYM addition. The treatments were replicated four times in randomized block design in a sandy loam (typic Ustipsament, non-saline, slightly alkaline). Bulk density, structural stability of soil aggregates and water holding capacity of 0–60 cm soil layer were measured.The average mean weight diameter (MWD) was highest in FYM-plots both in rice (0.237 mm) and wheat (0.249 mm) closely followed by that in N120P30K30 plots. The effect of FYM in increasing the MWD decreased with soil depth. The addition of both FYM and N120P30K30 increased the organic carbon by 44 and 37%, respectively in rice. The total porosity of soil increased with the application of both FYM and N120P30K30 from that in control plots. In 0–15 cm soil layer, the total porosity increased by 25% with FYM from that in control plots. This difference decreased to 13% in 15–30 cm soil layer. The average water holding capacity (WHC) was 16 and 11% higher with FYM and N120P30K30 application from that in control plots. The MWD, total porosity and WHC improved with the application of balanced application of fertilizers. The grain yield and uptake of N, P and K by both rice and wheat were higher with the application of FYM and inorganic fertilizers than in control plots. The carbon sequestration rate after 32 years was maximum (0.31 t ha−1 year−1) in FYM-plots, followed by 0.26 t ha−1 year−1 in N120P30K30-plots, 0.19 t ha−1 year−1 in N120P30 and minimum (0.13 t ha−1 year−1) in N120-plots.

Soil compactibility which basically depends on soil texture, organic matter and soil water content during farm machinery traf®cking are major factors affecting soil conservation. In a ®eld experiment, cattle farmyard manure was applied to a silty clay loam soil (®ne-loamy, mixed, thermic Typic Haplargids, USDA; Calcaric Cambisols, FAO) in Isfahan, Iran. Three rates, 0, 50, 100 Mg ha À1 (on oven dry basis) of farmyard manure, were incorporated into the topsoil. After 5 months, a two-wheel drive tractor (48.5 kW) was passed over the plots once (P1) or twice (P2) at soil moisture contents associated with the plastic limit (PL), 0.8PL, and 0.6PL. A randomized complete block design with four replicates with treatments nested (split-block) into the blocks was used. Bulk density (BD), cone index (CI) and soil sinkage were measured as indices of soil compactibility and traf®cability. Applying 50 and 100 Mg ha À1 of manure signi®cantly counteracted the effects of load and wetness on BD and CI. There was a signi®cant difference between the effects of 50 and 100 Mg ha À1 of manure on BD, but not on CI. Manure application also reduced the subsoil compaction. Double passes of the tractor (P2) signi®cantly increased compaction. There was a limitation for traf®cability for no-manure treatment even at 0.6PL, whereas this limit was reached at 0.8PL for the 50 Mg ha À1 treatment. Results from this study demonstrate that manure application at a rate of 50 Mg ha À1 reduced soil compactibility and increased soil moisture traf®cability range. Thus, increasing soil organic matter could bring about an appropriate solution for sustainable soil management in the region. # (M.A. Hajabbasi) 0167-1987/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 -1 9 8 7 ( 0 0 ) 0 0 1 0 2 -1

The physical properties of coarse-textured soils in semi-arid regions often deteriorate with use. We hypothesize that compaction is related to the cropping systems employed in accordance with the different water balances of the soils. Surface samples of 52 Entic Haplustolls under three different regimes (24 under continuous cultivation, 18 under rotation with grass leys and 10 virgin soils) were analysed for clay, silt, organic matter and water content, bulk density, resistance to penetration, hydraulic conductivity and susceptibility to compaction. Data were statistically analysed using regression equations and soils were distinguished on the basis of organic matter content and susceptibility to compaction. In soils of similar texture we found resistance to penetration and susceptibility to compaction to be inversely related to organic matter content and therefore higher under continuous cultivation. Hydraulic conductivity was lower in cultivated soils, especially those with a ®ne texture. The results show that in sandy to loam soils an increase of about 5 g kg À1 organic matter is required to achieve a 0.06 Mg m À3 decrease in bulk density at the proctor optimum. The results also indicate that the loss of organic matter occurring in the cultivated soils of the study region makes them more susceptible to compaction, which not only has adverse mechanical effects on plants but also gives rise to a considerable reduction in hydraulic conductivity. # .ar (N. Peinemann) 0167-1987/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 -1 9 8 7 ( 9 9 ) 0 0 0 4 9 -5

In the last centuries, the need for tillage was to provide suitable soil conditions for plant growth (crop-focusing tillage). During the last decades, traditional goals of soil tillage have really been improved considering environmental consequences (environment-focusing tillage). In the next decade a new task is stressed, that is mitigating the climate induced losses (climate-focusing tillage). New challenges for the future are prevention of tillage-induced soil quality deterioration, and to reduce climate induced damages by the use of environmentally-sound adaptable tillage. In the adaptable tillage program ten important steps are suggested, namely: Risk assessment in the fields. (2) Prevention of tillage induced defects affecting climate stresses. (3) Maintaining an optimal soil physical and biological state and fertility. (4) Use soil structure conservation methods in any seasons. (5) Mulch the surface at least in summer. (6) Improve soil loading capacity connected with carbon conservation. (7) Utilize stubble residues rationally. (8) Maintain an optimal water management in soils by the soil state improving. (9) Create small water-loss surface at tillage operations. (10) Improve a harmony between soil disturbance and environmental requirements. Birkás M., Jolánkai M., Schmidt R. 2008. Environmentally-sound adaptable tillage -Solutions from Hungary. 1 st Scientific Agronomic Days ,[13][14] Nitra, Slovakia. Proc. of reviewed sci. papers (Eds. Hrubá, M., et al.),

Frequent machinery traffic on sloping vineyard influences spatial distribution of soil physical properties. Our objective was to assess the effects of crawler tractor traffic across the slope (20%) on spatial distribution of soil strength and water content of silt loam soil under controlled grass cover and conventionally cultivated vineyard. The experiment was situated on hillside vineyard (NW, Italy) arranged with rows crosswise the slope. The grass covered treatment included periodical mowing and chopping of herbs and the cultivated treatment-autumn ploughing (18 cm) and spring and summer rotary-hoeing in the vineyard inter-rows (2.7 m). A crawler tractor (2.82 Mg) was used at the same locations across the slope for all tillage and chemical operations. The measurements of soil bulk density, penetration resistance and volumetric water content were done in autumn (after vintage) within the sloping inter-row. The results were analyzed using classic statistics and geostatistics with and without trend. The highest variability was obtained for penetration resistance (CV 56.6%) and the lowest for bulk density (9.6%). In most cases, the semivariograms of the soil parameters were well described by spherical models. The semivariance parameters of all properties measured were influenced by trend. Three-dimensional (3D) maps well identified areas with the highest soil strength in lower crawler ruts being positioned in the upper side of vine row and successively lower strength in upper ruts situated on other side of the same row and inter-rut area. Higher strength in lower than upper ruts was induced by tractor's tilt and resulting higher ground contact pressure. Soil water content in both treatments was the lowest below the upper rut and increased in inter-rut and lower rut areas. The differences in the soil properties between the places within the inter-row were more pronounced in grass covered than in cultivated soil. #

Soils in semi-arid Mediterranean areas are generally characterized by low organic matter content and are subjected to progressive degradation and deterioration of workability. Because de-oiled two-phase olive mill waste (DW) contains an important level of organic matter content, its recycling as organic amendment or fertilizer may be an alternative for its disposal that also improves soil quality and productivity. A ten-year field study was conducted to evaluate the long-term sustainability of raw deoiled two-phase olive mill waste (DW) disposal as a soil amendment on an olive grove in Elvas, Portugal. The soil was amended with DW at rates of 0, 27, and 54 Mg ha À1 , dry weight equivalent, for eight years, with cumulative and residual effects being assessed in the last year and two years after the last application. The DW amendments significantly increased the olive yield only in the residual year at the 27 Mg ha À1 application rate. Long-term applications of DW to soil led to positive cumulative and residual effects on the soil's chemical (total organic carbon and its humified fractions, total N, available P, and K), properties. Simultaneously, dehydrogenase, urease, b-glucosidase, alkaline phosphatase, and arylsulfatase activities increased even at the higher DW application rates. Electrical conductivity rose significantly with DW application, especially in the residual year, ranging from 0.513 dS m À1 for the unamended soil to 1.89 dS m À1 at the 54 Mg ha À1 application rate. The addition of raw DW to an olive grove may be considered to be a good strategy for recycling this waste, converting it into a resource that could be used for a long time as organic amendment without negatively affecting yield, while improving many soil properties. However, the greatest concern regarding the long-term use of DW is the risk of soil salinity, especially if application rates are greater than 27 Mg ha À1 .

Management systems influence soil quality over time. A randomized block design in 2 (tillage system) Â 3 (crop rotation) factorial arrangement was laid-out to evaluate the impact of tillage and crop rotation (2002-2007) on soil quality. Conventional tillage and No-till were factored into continuous corn, corn-soybean, and corn-soybean-wheat-Cowpea systems. Ten soil cores were collected at 0-7.5, 7.5-15, 15-22.5 and 22.5-30 cm depths and analyzed for biological, chemical and physical parameters. The inductive additive approach was used to calculate biological, chemical, physical and composite soil quality indices. A significant impact of no tillage on different physical chemical and biological parameters was observed. The estimated soil quality index was significantly higher in soil under No-till than conventional tillage. Soil biological quality is a sensitive and consistent indicator of soil quality in response to management practices.

Crop-pasture rotations (CPR) are unusual around the world but have been the predominant cropping system in Uruguay since the 1960s. Uruguay has a temperate sub-humid climate, 80% of its landscape (16 Mha) is climax grasslands C 3 and C 4 species. Beef, wool, and dairy are the main commodities. Crops occupy a portion of the remaining 20% land area, primarily on Argiudolls and Vertisols, rotated with seeded grass and legume pastures. Continuous cropping (CC) with conventional tillage (CT) has proven unsustainable due to decreased soil productivity. Seeded pasture periods increased soil productivity. CPR adoption created less variable inter-annual economic results, but soil degradation remained a major concern during the crop cycle using CT. Farmers and technicians became interested in no-till (NT) to reduce erosion and production cost. Currently, approximately 52% of crop producing farms and 25% of dairy farms have adopted NT. This paper synthesizes research results (mainly from long-term experiments) contrasting CC versus CPR with CT (1960CT ( -1990 and NT (from 1990). Soil erosion was reduced more than six times with NT in CC, and almost three times in CPR compared with CC using CT; but combining the use of CPR and NT resulted in the same low erosion rate as under natural pasture. The transition from CT to NT is not always easy. The time between herbicide application to pasture and planting of the first crop of the rotation crop cycle with NT is a critical transition factor to optimize N and water availability, and soil tilth. Chiseling or paraplowing can alleviate plow-pans inherited by NT from previous CT; but higher soil strength at the soil surface under NT contributes to better forage utilization under grazing. Soil organic carbon (SOC) content in CC decreased with CT, and was maintained with NT only if grain was harvested. In CC systems with harvested forage, SOC decreased even with NT. CPR with NT maintained or increased the original SOC content. The paper concludes with a discussion on the relative sustainability of CC versus CPR with NT. Both are sustainable from the soil quality and productivity standpoints. But compared with CC, CPR is a more economically and climatically buffered system, due to higher diversity. Also, CPR systems are more environmentally sustainable since fuel and agrochemicals usage is reduced approximately 50%.

Residue retention and reduced tillage are both conservation agricultural management options that may enhance soil organic carbon (SOC) stabilization in tropical soils. Therefore, we evaluated the effects of long-term tillage and residue management on SOC dynamics in a Chromic Luvisol (red clay soil) and Areni-Gleyic Luvisol (sandy soil) in Zimbabwe. At the time of sampling the soils had been under conventional tillage (CT), mulch ripping (MR), clean ripping (CR) and tied ridging (TR) for 9 years. Soil was fully dispersed and separated into 212-2000 mm (coarse sand), 53-212 mm (fine sand), 20-53 mm (coarse silt), 5-20 mm (fine silt) and 0-5 mm (clay) size fractions. The whole soil and size fractions were analyzed for C content. Conventional tillage treatments had the least amount of SOC, with 14.9 mg C g À1 soil and 4.2 mg C g À1 soil for the red clay and sandy soils, respectively. The highest SOC content was 6.8 mg C g À1 soil in the sandy soil under MR, whereas for the red clay soil, TR had the highest SOC content of 20.4 mg C g À1 soil. Organic C in the size fractions increased with decreasing size of the fractions. In both soils, the smallest response to management was observed in the clay size fractions, confirming that this size fraction is the most stable. The coarse sand-size fraction was most responsive to management in the sandy soil where MR had 42% more organic C than CR, suggesting that SOC contents of this fraction are predominantly controlled by amounts of C input. In contrast, the fine sand fraction was the most responsive fraction in the red clay soil with a 66% greater C content in the TR than CT. This result suggests that tillage disturbance is the dominant factor reducing C stabilization in a clayey soil, probably by reducing C stabilization within microaggregates. In conclusion, developing viable conservation agriculture practices to optimize SOC contents and long-term agroecosystem sustainability should prioritize the maintenance of C inputs (e.g. residue retention) to coarse textured soils, but should focus on the reduction of SOC decomposition (e.g. through reduced tillage) in fine textured soils. #

Agricultural soils can constitute either a net source or sink of the three principal greenhouse gases, carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and methane (CH 4 ). We compiled the most up-to-date information available on the contribution of agricultural soils to atmospheric levels of these gases and evaluated the mitigation potential of various management practices in eastern Canada and northeastern USA. Conversion of native ecosystems to arable cropping resulted in a loss of $22% of the original soil organic carbon (C)-a release of about 123 Tg C to the atmosphere; drainage and cultivation of organic soils resulted in an additional release of about 15 Tg C. Management practices that enhance C storage in soil include fertilization and legume-and forage-based rotations. Adopting no-till did not always increase soil C. This apparent absence of no-till effects on C storage was attributed to the type and depth of tillage, soil climatic conditions, the quantity and quality of residue C inputs, and soil fauna. Emission of N 2 O from soil increased linearly with the amount of mineral nitrogen (N) fertilizer applied (0.0119 kg N 2 O-N kg N À1 ). Application of solid manure resulted in substantially lower N 2 O emission (0.99 kg N 2 O-N ha À1 year À1 ) than application of liquid manure (2.83 kg N 2 O-N ha À1 year À1 ) or mineral fertilizer (2.82 kg N 2 O-N ha À1 year À1 ). Systems containing legumes produced lower annual N 2 O emission than fertilized annual crops, suggesting that alfalfa (Medicago sativa L.) and other legume forage crops be considered different from other crops when deriving national inventories of greenhouse gases from agricultural systems. Plowing manure or crop stubble into the soil in the autumn led to higher levels of N 2 O production (2.41 kg N 2 O-N ha À1 year À1 ) than if residues were left on the soil surface (1.19 kg N 2 O-N ha À1 year À1 ). Elevated N 2 O emission during freeze/thaw periods in winter and spring, suggests that annual N 2 O emission based only on growing-season measurements would be underestimated. Although measurements of CH 4 fluxes are scant, it appears that agricultural soils in eastern Canada are a weak sink of CH 4 , and that this sink may be diminished through manuring. Although the influence of agricultural management on soil C storage and emission of greenhouse gases is significant, management practices often appear to involve offsets or tradeoffs, e.g., a particular practice may increase soil C storage but also increase emission of N 2 O. In addition, because of high variability, adequate spatial and temporal sampling are needed for www.elsevier.com/locate/still Soil & Tillage Research 83 (2005) 53-72

The unsaturated soil hydraulic functions involving the soil-water retention curve (SWRC) and the hydraulic conductivity provide useful integrated indices of soil quality. Existing and newly devised methods were used to formulate pedotransfer functions (PTFs) that predict the SWRC from readily available soil data. The PTFs were calibrated using a large soils database from Hungary. The database contains measured soil-water retention data, the dry bulk density, sand, silt and clay percentages, and the organic matter content of 305 soil layers from some 80 soil profiles. A three-parameter van Genuchten type function was fitted to the measured retention data to obtain SWRC parameters for each soil sample in the database. Using a quasi-random procedure, the database was divided into ''evaluation'' (EVAL) and ''test'' (TEST) parts containing 225 and 80 soil samples, respectively. Linear PTFs for the SWRC parameters were calculated for the EVAL database. The PTFs used for this purpose particle-size percentages, dry bulk density, organic matter content, and the sand/silt ratio, as well as simple transforms (such as logarithms and products) of these independent variables. Of the various independent variables, the eight most significant were used to calculate the different PTFs. A nonlinear (NL) predictive method was obtained by substituting the linear PTFs directly into the SWRC equation, and subsequently adjusting the PTF parameters to all retention data of the EVAL database. The estimation error (SSQ) and efficiency (EE) were used to compare the effectiveness of the linear and nonlinearly adjusted PTFs. We found that EE of the EVAL and the TEST databases increased by 4 and 7%, respectively, using the second nonlinear optimization approach.

Sustainable agricultural management is essential not only to maintain productivity of current farmlands, but also to conserve natural environments. Records of agricultural activities are required to assist rapid assessment of agricultural lands, and thus, designation of management plans and policies. By the 1980s, when unfavorable environmental impacts of conventional tillage practices were widely recognized, agronomists introduced conservation tillage to benefit soils and agricultural environments, and soon began programs to monitor adoption of conservation tillage practices. The role of remote sensing in acquiring this information has been increasing because remote sensing technologies can provide the broad scope and the ability to collect sequential imagery to estimate trends and patterns of adaption of alternative tillage practices. This review encompasses comparisons of remote sensing techniques with more conventional methods for surveying and estimating tillage status, applications of remote sensing technologies, data processing and analysis, validation and field data collection, impacts of terrain, spectral and spatial resolution, timing and temporal detail, and prospects of future instruments.

Tillage causes changes to soil structure, and if the soil is too wet when tillage is performed, the change to the soil structure will be detrimental. A methodology that could be used for estimating the maximum gravimetric soil water content for optimum tillage would be helpful to prevent soil structural damage. The objective of this study was to compare five methods for estimating the soil water content for tillage. These methods utilized existing data of water retention, Atterberg limits, and Proctor compaction tests. The database included 80 soils, 51 from Germany and 29 from north central USA. Additionally, on three sites in Germany, soil water content in the field was measured intensively and related to the estimates of soil water content for workability. Maximum soil water content for optimum tillage of cohesive soils was at a consistency index of 1.15 and 90% of the water content at the lower plastic limit. For both cohesive and non-cohesive soils, the maximum soil water content for optimum workability was equal to either the water content at maximum Proctor density or 70% of the water content at a tension of −5 kPa. At the water content of the inflection point of the water retention curve, in many cases the soil would be too wet for tillage. The results provide methods for estimation of the maximum water content for optimum tillage from databases with existing soil physical properties.

Although the development of animal drawn tillage tools in the world has been on the agenda for thousands of years, there is still room for their improvement. The present study attempts to give an overview of previous works toward development of animal drawn tillage tools and to identify the areas having most potential for future improvement. The socio-economy, natural resource situation, historic perspective of animal traction in eastern and southern Africa and more specifically the ard plough history in Ethiopia are presented. The design, construction, performance and attempts done since 1939 for the improvement of the ard plough in Ethiopia are also presented. Moreover, trials towards the development of appropriate farm implements for Vertisols management, i.e. the broad bed maker (BBM) were also surveyed. From the review, it can be concluded that previous developments in animal traction tillage implements relied on cultural, trial and human experience. With the recent development in farm technologies and mathematical modelling techniques supported by computer-based simulations, new methodologies in research are available to improve animal traction tillage implements. When adopted, these methodologies could significantly assist in optimising the implement designs and operational conditions aiming at minimum draught requirement and best soil manipulation performance. #

Tillage is the base operation in agriculture and its energy represents a considerable portion of the energy utilized in crop production. To measure the implement force requirements, are used dynamometers that are pull or three-point hitch types. In this research, an 82 kW research tractor equipped with an instrumentation system was used to determine the draft force inputs for four common tillage Implements applied to a clay loam soil in west Azarbaijan, Iran. Implements included moldboard plow plus chisel plow as primary and disk harrow plus field cultivator as secondary implements. Operating depth for the primary and secondary implements was about 250 and 100 mm, respectively. Draft measurements were compared to those predicted by ASABE Standard D497.5 (ASABE Standards, 2006) and were found to vary. It was declared that draft force of moldboard plow and field cultivator was about 2.14 and 1.8 times as much as the chisel plow and disk harrow, respectively. The large difference in implement draft indicates that substantial energy savings can be readily obtained by selecting energy-efficient tillage implements. INTRODUCTION hitch dynamometers [4]. Many research studies have

Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro-and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information.

Free and fair elections are pre-requisite in democratization. The electoral process is quandary with rule of law, supremacy of Constitution with basic rights of peoples and socio-economic justice and accountability of leaders who are exercising state power. Democratization process ensures the opportunity of equality in social economic and political domain. The political leaderships enunciate the commitment but question is to make operational. The authoritarian pattern also provides elected bodies for legislation but not awarded power to institutions and the people holding key positions in them. It is question to create and sustain institutions which are reflecting the spirit of democracy and participatory government in India and Pakistan. The most accepted and preferred system in the modern world"s democratic system. It is able to integrate the needs of the maximum people"s partaking and rational in the legislative process. The public of India and Pakistan has wished to establish democratic system.

Electrical resistivity of the soil can be considered as a proxy for the spatial and temporal variability of many other soil physical properties (i.e. structure, water content, or fluid composition). Because the method is non-destructive and very sensitive, it offers a very attractive tool for describing the subsurface properties without digging. It has been already applied in various contexts like : groundwater exploration, landfill and solute transfer delineation, agronomical management by identifying areas of excessive compaction or soil horizon thickness and bedrock depth, and at least assessing the soil hydrological properties. The surveys, depending on the areas heterogeneities can be performed in one-, two-or three-dimensions and also at different scales resolution from the centimetric scale to the regional scale. In this review, based on many electrical resistivity surveys, we expose the theory and the basic principles of the method, we overview the variation of electrical resistivity as a function of soil properties, we listed the main electrical device to performed one-, two-or three-dimensional surveys, and explain the basic principles of the data interpretation. At least, we discuss the main advantages and limits of the method.

One of the most important terrestrial pools for carbon (C) storage and exchange with atmospheric CO 2 is soil organic carbon (SOC). Following the advent of large-scale cultivation, this long-term balance was disrupted and increased amounts of SOC were exposed to oxidation and loss as atmospheric CO 2 . The result was a dramatic decrease in SOC. If amounts of C entering the soil exceed that lost to the atmosphere by oxidation, SOC increases. Such an increase can result from practices that include improved: (1) tillage management and cropping systems, (2) management to increase amount of land cover, and (3) ef®cient use of production inputs, e.g. nutrients and water. Among the most important contributors is conservation tillage (i.e., no-till, ridge-till, and mulch-tillage) whereby higher levels of residue cover are maintained than for conventional-tillage. Gains in amount of land area under conservation tillage between 1989 and 1998 are encouraging because of their contributions to soil and water conservation and for their potential to sequester SOC. Other important contributors are crop residue and biomass management and fallow reduction. Collectively, tillage management and cropping systems in the US are estimated to have the potential to sequester 30±105 million metric tons of carbon (MMTC) yr À1 . Two important examples of management strategies whereby land cover is increased include crop rotations with winter cover crops and the conservation reserve program (CRP). Such practices enhance SOC sequestration by increasing the amount and time during which the land is covered by growing plants. Crop rotations, winter cover crops, and the CRP combined have the potential to sequester 14±29 MMTC yr À1 . Biomass production is increased by ef®cient use of production inputs. Optimum fertility levels and water availability in soils can directly affect quantity of crop residues produced for return to the soil and for SOC sequestration. Nutrient inputs and supplemental irrigation are estimated to have the potential to sequester 11±30 MMTC yr À1 . In the future, it is important to acquire an improved understanding of SOC sequestration processes, the ability to make quantitative estimates of rates of SOC sequestration, and technology to enhance these rates in an energy-and input-ef®cient manner. Adoption of improved tillage practices and cropping systems, increased land cover, and ef®cient use of nutrient and water inputs are examples where such information is necessary. Published by Elsevier Science B.V.

Ast, A. van, 2006. The influence of time and severity of Striga infection on the Sorghum bicolor -Striga hermonthica association. PhD thesis, Wageningen University, Wageningen, The Netherlands, with summaries in English, French and Dutch, 154 pp. This thesis presents the results of a study on the interaction between the parasitic weed Striga hermonthica (Del.) Benth. and sorghum (Sorghum bicolor [L.] Moench). The main objective of the study was to investigate the effects of time and level of Striga infection on the interaction between host plant and parasite. Consequences for sorghum performance and the growth and development of the parasite were examined. A comparison between two sorghum cultivars differing in level of Striga tolerance, revealed that the absence of a negative effect of Striga infection on photosynthetic rate and a delayed time of first Striga infection both contributed to the lower extent of yield reduction of the tolerant cultivar. Likewise, in an experiment with a wide range of Striga seed infestation levels, it was observed that higher soil infestations levels did not only result in a higher Striga infection level, but also in an advanced time of first Striga infection. The importance of time of infection was further investigated in a pot experiment in which the time of infection was artificially delayed. Striga parasitism and reproduction, and the detrimental effects of Striga on crop performance could be strongly reduced by delaying the time of first infection. Prospects of reducing Striga parasitism by means of cultural control methods that are based on the principle of a delayed onset of Striga attachment were assessed. In a pot experiment, the combination of shallow soil tillage, deep planting and the use of transplants resulted in a four-week delay in first emergence of the parasite, a strongly reduced infection level of the sorghum host and highly improved sorghum yields. Evaluation of these methods under field conditions resulted in a 85% reduction in Striga-infection level, but as no delay in time of parasite infection was established, no beneficial effect on crop yield was obtained. Potential causes of the absence of a delay in Striga infection time under field conditions were discussed and alternative options for establishing a delayed infection in the field were proposed.