Maize root development and grain production as affected by soil and water management on a sandy soil in a semi-arid region of southern Mozambique

Average yield of maize (Zea mays L.) in Mozambique is low, mainly due to low use of inputs in agriculture, high seasonal rainfall variability and inadequate soil preparation. A study conducted in two summer crop seasons (November–March 2012/2013 and 2013/2014) examined the impact of three tillage methods (hand hoeing, strip tillage and conventional tillage), two fertiliser levels (0 and 40% N) and two water supply regimes (rainfed and irrigated) on maize root development and grain yield on a sandy soil in a semi-arid region of Mozambique. Tillage had a major effect on soil penetration resistance, but little effect on root growth and limited effect on yield. Thus, there appears to be little need for loosening on this soil. There was also no interaction between tillage and the other experimental factors, meaning that tillage system can be chosen irrespective of fertiliser and water supply. Irrigation had the largest impact on root and shoot growth and crop yield, increasing yield in season 2 from 670 to 4780?kg ha^–1.There was a very strong interaction between fertiliser and water supply, with no yield increase for fertiliser in the rainfed treatment, while combined with irrigation it increased yield by 1590?kg ha^–1 in season 1 and 1840?kg ha^–1 in season 2. Thus, for the conditions studied here, it was rational to add fertiliser only in combination with irrigation and not in a rainfed system.     

Earthworm populations and growth rates related to long-term crop residue and tillage management

Conventional tillage creates soil physical conditions that may restrict earthworm movement and accelerate crop residue decomposition, thus reducing the food supply for earthworms. These negative impacts may be alleviated by retaining crop residues in agroecosystems. The objective of this study was to determine the effects of various tillage and crop residue management practices on earthworm populations in the field and earthworm growth under controlled conditions. Population assessments were conducted at two long-term (15+ years) experimental sites in Québec, Canada with three tillage systems: moldboard plow/disk harrow (CT), chisel plow or disk harrow (RT) and no tillage (NT), as well as two levels of crop residue inputs (high and low). Earthworm growth was assessed in intact soil cores from both sites. In the field, earthworm populations and biomass were greater with long-term NT than CT and RT practices, but not affected by crop residue management. Laboratory growth rates of Aporrectodea turgida (Eisen) in intact soil cores were affected by tillage and residue inputs, and were positively correlated with the soil organic C pool, suggesting that tillage and residue management practices that increase the soil organic C pool provide more organic substrates for earthworm growth. The highest earthworm growth rates were in soils from RT plots with high residue input, which differed from the response of earthworm populations to tillage and residue management treatments in the field. Our results suggest that tillage-induced disturbance probably has a greater impact than food availability on earthworm populations in cool, humid agroecosystems.     

Soil tillage for crop production and for protection of soil and environmental quality: a Scandinavian viewpoint

Based on experience from 35 years of tillage research in Sweden, future development of soil tillage is discussed and some research problems are identified. Tillage and seeding methods must be more carefully adapted to conditions at individual sites and occasions. Low-pressure typres, better weed control and improved seed coulters favour the increased use of reduced tillage. In order to diminish the impact of agriculture on the environment, it is necessary to develop methods for establishment of crops in the early spring or immediately after harvest, even in soils with large amounts of crop residues or high moisture content. The roles of tillage methods, and of soil compaction and structure on environmental impact of agriculture must be investigated. World food production must increase, since the world population is rapidly increasing. Therefore, it is necessary to develop improved crop production systems, including crop establishment systems, which favour efficient use of basic crop growth factors, while protecting or increasing soil productivity. Compaction, decreased organic matter content, and erosion are important long-term threats to soil productivity.     

Soil erosion under simulated rainfall in relation to phenological stages of soybeans and tillage methods in Lages, SC, Brazil

Soil tillage may increase vulnerability to water erosion, whereas no tillage and other conservation cultivation techniques are viewed as strategies to control soil erosion. The objective of this research was to quantify runoff and soil losses by water erosion under different soil tillage systems at the Santa Catarina Highlands, southern Brazil. A field study was carried out using a rotating-boom rainfall simulator with 64 mm h⁻¹ rainfall intensity on a Typic Hapludox, between April 2003 and May 2004. Five rainfall tests were applied along successive cropstages. Surface cover was none (fallow) or soybean (Glycine max, L.). Five treatments were investigated, replicated twice. These treatments were conventional tillage on bare soil (BS) as a control treatment and the following treatments under soybean: conventional tillage (CT), no tillage over burnt crop residues on never before cultivated land (NT-B), no tillage over desiccated crop residues, also on never before cultivated land (NT-D) and traditional no tillage over desiccated crop residues on a soil tilled 4 years before this experiment (NT-PT). Water losses by surface runoff seemed to be more influenced by vegetative crop stadium than by tillage system and consequently a wide range of variation in surface runoff was found, following successive cropstages. The most efficient tillage system in reducing surface runoff and soil losses was no tillage, particularly the NT-PT treatment. Sediment losses were more influenced by tillage system than water losses. In the NT-B, NT-D and NT-PT treatments the rate of sediment losses along the crop vegetative cycle showed a tendency to increase from the first to the second cropstages and later to decrease from the third cropstage onwards. In the conventionally tilled treatment (CT) soil losses were greater than in any of the no tillage treatments (NT-D, NT-B and NT-PT) during the initial growth periods, but at the end of the vegetative period differences in sediment rates between tilled and non-tilled treatments tended to be smaller. In the BS control treatment, soil losses progressively increased following the vegetative growth season of soybean.     

The effect of various residue mulch-tillage combinations on soil physical conditions and performance of irrigated cotton

Cotton is a major irrigated summer field crop in Israel, and is commonly grown in the same field for 3–5 years in succession. There is only a narrow time window between harvest and early rains for pest control by means of clearing the land surface of residues, and to perform preparatory tillage. The time available may be insufficient to achieve this with the conventional deep plowing tillage system, and some operations may have to be carried out on moist soil between rainfall events. In response to indications of decreasing yield due to compaction, various limited-tillage systems in permanent traffic lanes have been developed, culminating in a machine that performs all residue-disposal and tillage operations in a single pass through the field. A comparison of several limited-traffic and conventional practices was carried out for 2 years on a loessial silt loam (Calcic Haploxeralf). It was found that both soil condition and yield were worst in the two treatments commonly used by farmers: deep plowing and deep incorporation of residues with the combination machine. Tillage effects were dominant, masking any effect of residue amount and disposal method. Large differences were found between the zones of the permanent wheel track treatments, as were cyclic changes in soil condition reflecting the seasonal sequence of tillage operations. Some cumulative compaction occurred, due mainly to a gradual widening of the wheel tracks rather than to repeated passes in the original rut. The findings of this work show that the optimal choice is to replace the previously preferred field practices by shallow slot-mulching with simultaneous subsoiling by the combination machine, which meets the sanitation requirements, maintains satisfactory yields and saves energy and labor.     

Is conservation tillage suitable for organic farming? A review

Conservation tillage covers a range of tillage practices, mostly non‐inversion, which aim to conserve soil moisture and reduce soil erosion by leaving more than one‐third of the soil surface covered by crop residues. Organic farmers are encouraged to adopt conservation tillage to preserve soil quality and fertility and to prevent soil degradation – mainly erosion and compaction. The potential advantages of conservation tillage in organic farming are reduced erosion, greater macroporosity in the soil surface due to larger number of earthworms, more microbial activity and carbon storage, less run‐off and leaching of nutrients, reduced fuel use and faster tillage. The disadvantages of conservation tillage in organic farming are greater pressure from grass weeds, less suitable than ploughing for poorly drained, unstable soils or high rainfall areas, restricted N availability and restricted crop choice. The success of conservation tillage in organic farming hinges on the choice of crop rotation to ensure weed and disease control and nitrogen availability. Rotation of tillage depth according to crop type, in conjunction with compaction control measures is also required. A high standard of management is required, tailored to local soil and site conditions. Innovative approaches for the application of conservation tillage, such as perennial mulches, mechanical control of cover crops, rotational tillage and controlled traffic, require further practical assessment.     

Tillage methods and soil and water conservation in Australia

Tillage in Australia has evolved from ‘imported’ European practices to tillage systems more in tune with ‘older’ fragile soils and more severe climatic conditions. Cereal yields are commonly limited by water supply and the native fertility of many soils is poor. Crop/pasture rotations involving pasture legumes have been the mainstay of cereal production in the winter rainfall areas while production in much of the summer rainfall area has relied more on exploiting native fertility. Soil erosion and structural decline are still considered major issues facing long-term production. The general trend in tillage methods is for less tillage and greater retention of crop residues for soil and water conservation.

Tillage experiments have shown that management strategies involving retention of crop residues (stubble), reduced tillage and crop rotation can reduce erosion and improve yield. Results from experimentation are highly variable, both in magnitude and direction of responses to tillage treatments. Much of this variation is due to variation in seasonal conditions. Simulation models are being used to examine management options and to design experiments based on a knowledge of climate variability and physical and biological processes.     

北方农牧交错带免耕对农田耕层土壤温度的影响

针对北方农牧交错带部分地区免耕措施生态效益好但作物产量有所下降的现状,为了找出影响作物生长的因素,对比分析了免耕和翻耕两种耕作方式下耕层土壤温度的变化。结果表明：免耕地升温和降温都比较缓慢且幅度小,翻耕地土壤温度在日间总体高于免耕地。在垂直方向上,土壤温度随土层深度降低,但一天中不同时刻的表现差异显著。土壤温度变化与当时气温呈正相关关系, 相关系数大于0.5。与免耕地相比,翻耕地气温与土壤温度的直线回归关系更显著。受土壤温度等物理性状的影响,免耕地作物生物量及产量明显不如翻耕地。因此,北方农牧交错带要通过农艺措施改善土壤物理结构,提高免耕农田作物产量。     

不同耕法及秸秆还田对土壤水分运移变化的影响

[目的]探讨不同耕法与秸秆还田方式下,旱地草甸土土壤水分随深度运移的变化,为今后生产中因地制宜制定科学合理的耕作与培肥技术提供理论依据。[方法]采用田间定位试验,研究3种耕法免耕、浅翻、深翻与3种秸秆还田方式覆盖还田、浅翻还田、深翻还田条件下,作物生长不同时期、不同深度土层土壤含水量、田间持水量和容重的变化。[结果]土壤水分的年际间变化与降水量和降水变率有一定的关系。秸秆不还田条件下,连续2 a免耕,年际间土壤含水量随深度变化的特征曲线基本一致,0—20 cm耕层田间持水量降低13.62%,而浅翻与深翻分别增加11.32%和27.98%;耕翻深度对20—30 cm土层水分的影响较大,随作物生长和地表覆盖度增加,40 cm以下土层含水量的变化减弱。秸秆还田条件下,0—20 cm耕层浅翻还田与深翻还田田间持水量分别增加16.24%,5.08%,而土壤容重降低0.12,0.09 g/cm~3。[结论]同一耕法有秸秆还田处理土壤水分含量高于无秸秆还田,降水量越少,差异越明显。与免耕和免耕覆盖比较,翻耕与翻耕还田均增加了作物生长期间土壤含水量,提高了作物抗旱能力,产量有增加趋势。     

Soil compaction in cropping systems: A review of the nature, causes and possible solutions

Soil compaction is one of the major problems facing modern agriculture. Overuse of machinery, intensive cropping, short crop rotations, intensive grazing and inappropriate soil management leads to compaction. Soil compaction occurs in a wide range of soils and climates. It is exacerbated by low soil organic matter content and use of tillage or grazing at high soil moisture content. Soil compaction increases soil strength and decreases soil physical fertility through decreasing storage and supply of water and nutrients, which leads to additional fertiliser requirement and increasing production cost. A detrimental sequence then occurs of reduced plant growth leading to lower inputs of fresh organic matter to the soil, reduced nutrient recycling and mineralisation, reduced activities of micro-organisms, and increased wear and tear on cultivation machinery. This paper reviews the work related to soil compaction, concentrating on research that has been published in the last 15 years. We discuss the nature and causes of soil compaction and the possible solutions suggested in the literature. Several approaches have been suggested to address the soil compaction problem, which should be applied according to the soil, environment and farming system.

The following practical techniques have emerged on how to avoid, delay or prevent soil compaction: (a) reducing pressure on soil either by decreasing axle load and/or increasing the contact area of wheels with the soil; (b) working soil and allowing grazing at optimal soil moisture; (c) reducing the number of passes by farm machinery and the intensity and frequency of grazing; (d) confining traffic to certain areas of the field (controlled traffic); (e) increasing soil organic matter through retention of crop and pasture residues; (f) removing soil compaction by deep ripping in the presence of an aggregating agent; (g) crop rotations that include plants with deep, strong taproots; (h) maintenance of an appropriate base saturation ratio and complete nutrition to meet crop requirements to help the soil/crop system to resist harmful external stresses.     

Residue Decomposition and Fate of Nitrogen‐15 in a Wheat Crop under Different Previous Crops and Tillage Systems

Abstract

Nitrogen (N) management may be improved by a thorough understanding of the nutrient dynamics during previous‐crop residue decomposition and its impact on fertilizer N fate in the soil–plant system. An experiment was conducted in the Argentine Pampas to evaluate the effect of maize and soybean as previouscrops and plow‐till and no‐till methods on N dynamics and ¹⁵N‐labeled fertilizer uptake during a wheat growing season. Maize and soybean residues released N under both tillage treatments, but N release was faster from soybean residues and when residues were buried by tillage. Net immobilization of N on decomposing residues was not detected. A regression model that accounted for 92% of remaining N variability included time, previous crop, and tillage treatment as independent variables. The rapid residue decomposition with N release was attributed to the high temperatures of the agroecosystem. The recovery of ¹⁵N‐labeled fertilizer in the wheat crop, soil organic matter, and decomposing residues was not statistically different between previous crop treatments or tillage systems. Crop uptake of fertilizer N averaged 52% across treatments. Forty percent of fertilizer N was removed in grains. Immobilization of labeled N on soil organic matter was substantial, averaging 34% of the ¹⁵N‐labeled fertilizer retained, but was very small on decomposing residues, averaging 0.2–3.0%. Fertilizer N not accounted for at harvest in the soil–plant system was 12% and was ascribed to losses. Previous crop or tillage system had no impact on wheat yield, but when soybean was the previous crop, N content of grain and straw+roots increased. Discussion is presented on the potential availability of N retained in wheat straw, roots, and soil organic matter for future crops.     

Managing traffic-induced soil compaction by using conservation tillage

The term ‘Konservierende Bodenbearbeitung’ has a somewhat different meaning than conservation tillage as used worldwide. In Germany the term is used not only in relation to the retention of surface residues to reduce erosion but in association with compaction control by carefully timed loosening operations.Field experiments were conducted from 1985 to 1990 on a loamy sand (Dystric-Luvisol) in north-central Germany. The effect of crop rotation-specific soil loosening on some soil physical properties and crop yields was studied in the presence and absence of wheel-induced soil compaction when growing sugar beet, winter wheat, winter barley and a cover crop. Five tillage treatments were studied in a 3-year crop rotation: sugar beet; winter wheat; winter barley; cover crop. These included conventional mouldboard ploughing, conservation tillage with no loosening and conservation tillage where loosening was carried out with a wide blade chisel plough, (1) before winter barley, (2) before the cover crop (mustard or California bluebell) and (3) before winter barley and the cover crop.Wheel-induced compaction decreased the pore space and in most cases eliminated differences due to tillage practice. Pore space on the wheel-tracked plots of the conventional treatment was considerably lower than on the non-wheel-tracked plots. Similar results were obtained for the conservation tillage plots but only where loosening had been carried out within the last 18 months.In summary of the 6 years experiment, there was in general no evidence that conventional tillage was superior to conservation tillage with respect to the yields of sugar beet, winter wheat, or, within certain limits, winter barley on loamy sand.Accordingly, conservation tillage with crop rotation-specific non-inverting soil loosening, promises to be a potential strategy not only with regard to reducing soil erosion, but a programme for reducing costs and alleviating traffic-induced soil compaction.     

The influence of a compacted plow sole on saturation excess runoff

Subsoil compaction due to conventional tillage techniques and its relation to subsurface flow and runoff was investigated on a sloped field. The presence of a plow sole was confirmed by significantly higher penetration resistances between 20 and 40 cm depth, a significantly higher soil bulk density and a 14% decrease in drainage pore space compared to the top layer. Ring infiltrometer measurements also confirmed a significant reduction of the saturated hydraulic conductivity at 30 cm depth, indicating a limited permeability. With the use of an extensive grid of tensiometers, matric heads were monitored and the occurrence of a temporary water table on top of the plow sole was confirmed in a number of cases. Equipotential lines in the top saturated layer indicated the occurrence of subsurface flow parallel to the slope surface in a downward direction. For the whole measuring period, when a perched water table was observed, 91% of the rainfall events caused runoff and this number increased with increasing rainfall intensity. For low and medium rainfall intensities (<10 mm h⁻¹), 66% and 63% of the runoff events were related to saturation of the top soil. Therefore, it was concluded that over a period of 20 months saturation excess runoff as a result of subsoil compaction was an important contributor to surface runoff and soil loss.     

Traffic and residue management systems: effects on fate of fertilizer N in corn

Soil compaction has been recognized as a problem limiting crop production, especially in the Southern Coastal Plain of the USA. Development of tillage and residue management systems is needed to alleviate soil compaction problems in these soils. Fertilizer nitrogen (N) management is also an important factor in these management systems. In 1988, a study was initiated with a wide-frame (6.3 m) vehicle to determine the interactive effects of traffic, deep tillage, and surface residue management on the fate of fertilizer N applied to corn (Zea mays L.) grown on a Norfork loamy sand (fine-loamy, siliceous, Thermic, Typic Kandiudults). Corn was planted into a winter cover crop of ‘Tibbee’ crimson clover (Trifolium incarnatum L.). Treatments included: traffic (conventional equipment or no traffic); deep tillage (no deep tillage, annual in-row subsoiling, or one-time only complete disruption); residue management (no surface tillage or disk and field cultivation). The one-time only complete disruption was accomplished by subsoiling at a depth of 43 cm on 25 cm centers in spring 1988. In 1990–1991, fertilizer applications were made as ¹⁵N-depleted NH₄NO₃ to microplots inside each treatment plot. The 1990 and 1991 data are reported here. In 1990 an extreme drought resulted in an average grain yield of 1.8 Mg grain ha⁻¹, whereas abundant rainfall in 1991 resulted in 9.4 Mg grain ha⁻¹. Deep tillage increased corn dry matter production in both years. In 1991, grain yields indicated that corn was susceptible to recompaction of soil owing to traffic when residues were incorporated with surface tillage. In the dry year, plant N uptake was increased 27% with deep tillage and decreased 10% with traffic. In the wet year, a surface tillage × deep tillage × traffic interaction was observed for total N uptake, fertilizer N uptake, and total fertilizer N recovery in the plant-soil system. When combined with traffic, plant N uptake was reduced with the highest intensity tillage treatment (135 kg N ha⁻¹) because of rootrestricting soil compaction, and with the lowest intensity tillage treatment (129 kg N ha⁻¹) because of increased N losses. In these soils, leaving residues on the soil surface can reduce the detrimental effect of traffic on corn production, but if no surface tillage is performed, deep tillage is needed.     

Effect of straw management, tillage timing and timing of fertilizer nitrogen application on the crop utilization of fertilizer and soil nitrogen in an irrigated cereal rotation

In irrigated grain-growing soils on Canada's prairies, straw management can affect nitrogen (N) fertility and long-term soil organic matter reserves. We conducted a 2-year field experiment in southern Alberta, on a Dark Brown Chernozemic Lethbridge loam (Typic Boroll), to determine the effects of straw removal, tillage, and fertilizer timing on crop uptake of soil and fertilizer N. During the study (1991 and 1992), the crop was oat (Avena sativa L.) and wheat (Triticum aestivum L.), respectively, in an experiment that had been in a wheat-wheat-oat-wheat rotation since 1986. Five straw-tillage treatments were: straw-fall plow, straw-pring plow, no straw-fall plow, no straw-spring plow and no straw-direct seeding. Fertilizer N was applied in fall or spring. Ammonium nitrate (5 at.% ¹⁵N) was added at 100 kg N ha⁻¹ in fall 1990 or spring 1991. For oat (1991), plant N derived from soil was higher under fall plow than under spring plow, higher with tillage than direct seeding, and unaffected by straw removal. The plant N derived from fertilizer was not affected by straw removal in fall plow treatments, but under spring plow, it was higher with straw removal. The plant N derived from fertilizer showed a significant straw-tillage × fertilizer timing interaction; with fall incorporated straw, plant N derived from fertilizer was 44.0 kg N ha⁻¹ for spring-applied, and 30.6 kg N ha⁻¹ for fall-applied N, but in other straw-tillage treatments there was no effect of fertilizer timing. Cumulative fertilizer N recovery (plant + soil) over the 2 years averaged 64.2%, and was unaffected by straw-tillage treatment. Fertilizer N recovery, however, was less with fall-applied N (61.3%) than spring applied N (66.8%). At mid-season, fall plow treatments had higher soil inorganic N and inorganic N derived from fertilizer than spring plow treatments, apparently because of less immobilization. The fall plow treatments also retained higher inorganic N after harvest. Straw removal and fertilizer timing did not influence soil inorganic N and soil inorganic N derived from fertilizer. N removal in straw (16 kg N ha⁻¹ yr⁻¹) could deplete soil N in the long-term. Long-term effects of tillage timing on soil N will depend on the relative amount of N lost by leaching with fall plowing and that lost by denitrification under spring plowing. With direct seeding, crop yield and uptake of soil N was less, and N losses by denitrification could be greater. Application of N in spring, rather than fall, should enhance crop N uptake, reducing N losses and enhancing long-term soil organic N.     

Hydraulic conductivity, residue cover and soil surface roughness under different tillage systems in semiarid conditions

The objective of this study was to investigate the effect of tillage and cropping system on near-saturated hydraulic conductivity, residue cover and surface roughness to improve soil management for moisture conservation under semiarid Mediterranean conditions. Three tillage systems were compared (subsoil tillage, minimum tillage and no-tillage) under three field situations (continuous crop, fallow and crop after fallow) on two soils (Fluventic Xerochrept and Lithic Xeric Torriorthent). Soil under no-tillage had lower hydraulic conductivity (5.0 cm day⁻¹) than under subsoil tillage (15.5 cm day⁻¹) or minimum tillage (14.3 cm day⁻¹) during 1 of 2 years in continuous crop due to a reduction of soil porosity. Residue cover at sowing was greater under no-tillage (60%) than under subsoil or minimum tillage (<10%) in continuous crop. Under fallow, residue cover was low (10%) at sowing of the following crop for all tillage systems in both soils. Surface roughness increased with tillage, with a high value of 16% and decreasing following rainfall. Under no-tillage, surface roughness was relatively low (3–4%). Greater surface residue cover under no-tillage helped conserve water, despite indications of lower hydraulic conductivity. To overcome the condition of low infiltration and high evaporation when no-till fallow is expected in a cropping sequence, either greater residue production should be planed prior to fallow (e.g. no residue harvest) or surface tillage may be needed during fallow.     

Tillage and residue management effects on arylamidase activity in soils

Recent interest in soil tillage and residue management has focused on low-input sustainable agriculture. This study was conducted to investigate the effect of three tillage systems (no-till, chisel plow, and moldboard plow) and four residue placements (bare, normal, mulch, and double mulch) on a most recently detected enzyme in soils, arylamidase activity. This enzyme catalyzes the hydrolysis of an N-terminal amino acid from peptides, amides, or arylamides. Results showed that arylamidase activity is greatly affected by tillage and crop residue placement. The greatest activity was found with chisel/mulch, moldboard plow/mulch, and no-till/double mulch, and the lowest with moldboard plow/normal and no-till/bare. Arylamidase activity was significantly correlated with organic C (r=0.59**) and soil pH _CaCl2 (r=0.55**)_, and decreased with soil depth. Results of this work suggest that the activity of this enzyme is affected by soil management, and indicate its potential ecological significance because of its role in the N cycle.     

Tillage implement disturbance effects on soil properties related to soil and water conservation: a literature review

The effects of tillage implement distrubance on the physical properties of soil have been widely studied. However, because soil properties resulting from the use of a given implement vary due to implement factors (depth and speed of tillage) and soil factors (water content, texture, residue cover, etc.), soil properties for a given operation are difficult to visualize, let alone predict. This report summarizes the ranges of selected soil property responses observed in previous tillage studies and identifies factors that must be considered in developing useful models to predict the effects of tillage on soil properties that are related to soil and water conservation. Considered are soil mechanical properties (surface micro-relief, aggregate size distribution and bulk density) and hydraulic properties and processes (water retention, saturated conductivity, infiltration and evaporation). For future literature reports on tillage to be useful for developing comprehensive relationships between tillage and soil properties, the reports should include information on: soil classification, texture, water content (or time of precipitation), bulk density, mechanical impedance and organic matter concentration; tillage method, depth and speed of operation; previous crop, including availability of crop residues; and previous soil management history (compacted soil, irrigated or dryland, etc.).     

Soil Hydraulic Properties: Influence of Tillage and Cover Crops

Understanding the effects of cover crops and tillage on soil physical properties is important for determining soil productivity. This study was conducted at Lincoln University's Freeman Center, USA to evaluate the effects of tillage and cover crop management on soil hydraulic properties. The field site included three replicate blocks in a randomized complete block design with each plot measuring 21.3 m in length and 12.2 m in width. Treatment factors were tillage at two levels(moldboard plow tillage vs. no tillage) and cover crop at two levels(cereal rye(Secale cereal) cover crop vs. no cover crop). Soil samples were collected in late spring/early summer from each treatment at 10-cm depth increments from the soil surface to a depth of 40 cm using cores(76.2-mm diameter and 76.2-mm length). Soil bulk density was 13% lower with tillage compared with no-tillage. Volumetric water content was significantly higher at 0.0 and -0.4 k Pa pressures with tillage compared with no tillage. Tillage increased the proportion of coarse mesopores by 32% compared with no tillage, resulting in 87% higher saturated hydraulic conductivity(K_(sat)). Cover crop increased the proportion of macropores by 24% compared with no cover crop; this can potentially increase water infiltration and reduce runoff. As a result of higher macroporosity, Ksat was higher under cover crop compared with no cover crop. This study demonstrated that tillage can benefit soil hydraulic properties in the short term, but these effects may not persist over time. Cover crops may slightly improve soil hydraulic properties, but longer term studies are needed to evaluate the long-term effects.     

Twenty years of conservation tillage research in subarctic Alaska: II. Impact on soil hydraulic properties

Soil management practices are needed in the subarctic that stabilize the soil against the forces of wind and water as well as conserve soil water for crop production. There is a paucity of information, however, regarding the long-term effects of conservation tillage on soil hydraulic properties in subarctic Alaska. The objective of this study was therefore to characterize infiltration, water retention, and saturated hydraulic conductivity of a soil 20 years after establishing tillage and straw management treatments in interior Alaska. The strip plot experimental design, established on a silt loam and maintained in continuous barley (Hordeum vulgare L.), included tillage as the main treatment and straw management as the secondary treatment. Tillage treatments included no tillage, autumn chisel plow, spring disk, and intensive tillage (autumn and spring disk) while straw treatments included retaining or removing stubble and loose straw from the soil surface after harvest. Soil properties were measured after sowing in spring 2004; saturated hydraulic conductivity was measured by the falling-head method, infiltration was measured using a double-ring infiltrometer, and water retention was assessed by measuring the temporal variation in in-situ soil water content. No tillage resulted in greater saturated hydraulic conductivity and generally retained more water against gravitational and matric forces than other tillage treatments. Infiltration was greater in autumn chisel plow than other tillage treatments and was presumably suppressed in no tillage by an organic layer overlying mineral soil. Infiltration was also enhanced by retaining straw on rather than removing straw from the soil surface after harvest. No tillage is not yet a sustainable management practice in this region due to lack of weed control strategies. In addition, the formation of an organic layer in no tillage has important ramifications for the soil hydrological and thermal environment. Therefore, minimum tillage (i.e., autumn chisel plow or spring disk) appears to be a viable management option for maximizing infiltration in interior Alaska.