Tillage and cover effects on soil microbial properties and fluometuron degradation

This research concerns the influence of no tillage (NT) or conventional tillage (CT) and a ryegrass (Lolium multiforum Lam.) cover crop in a cotton (Gossypium hirsutum L.) production system on soil and ryegrass microbial counts, enzyme activities, and fluometuron degradation. Fluorescein diacetate hydrolysis, aryl acylamidase, and colony-forming units (CFUs) of total bacteria and fungi, gram-negative bacteria, and fluorescent pseudomonads were determined in soil and ryegrass samples used in the degradation study. Fluometuron (14C-labelled herbicide) degradation was evaluated in the laboratory using soil and ryegrass. The CT and NT plots with a ryegrass cover crop maintained greater microbial populations in the upper 2 cm compared to their respective no-cover soils, and CT soils with ryegrass maintained greater bacterial and fungal CFUs in the 2–10 cm depth compared to the other soils The highest enzymatic activity was found in the 0–2 cm depth of soils with ryegrass compared to their respective soils without ryegrass. Ryegrass residues under NT maintained several hundred-fold greater CFUs than the respective underlying surface soils. Fluometuron degradation in soil and ryegrass residues proceeded through sequential demethylation and incorporation of residues into nonextractable components. The most rapid degradation was observed in surface (0 to 2 cm) soil from CT and NT–ryegrass plots. However, degradation occurred more rapidly in CT compared to NT soils in the 2 to 10 cm depth. Ryegrass cover crop systems, under NT or incorporated under CT, stimulated microbiological soil properties and promoted herbicide degradation in surface soils.     

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.     

Finger millet (Eleucine corocana L. Gaertn.) as a cover crop on weed control, growth and yield of soybean under different tillage systems

Adoption of conservation tillage systems has become more popular in recent years due to erosion control and economics. Weed control is often identified as the limiting factor in the adoption of such systems. Although herbicides are efficient and convenient, the need to reduce herbicide use has been emphasized. Cover crops have become a viable option in this context, but the contribution of cover crops to weed control has not been clearly defined. A 2-year field experiment compared minimum tillage (MT), no-tillage (NT) and conventional tillage (CT) for soybean [Glycine max (L.) Merr.] following paddy rice (Oryza sativa L.) with finger millet (Eleucine corocana L. Gaertn.) as a cover crop. Weed emergence, cover crop biomass, main crop growth and yield were observed. Finger millet effectively controlled weeds but total weed biomass was greater with NT than other tillage methods and seeding method had no effect at early stage of growth. Neither crop growth nor leaf chlorophyll content was affected by finger millet under given tillage treatments. Weed biomass was almost half under MT than NT. Finger millet was able to effectively manage weed biomass under MT to a level achieved under CT without a cover crop at the early stage of growth. Number of seeds per pod and 100 seed weight were not affected by tillage treatments but number of pods per square meter was significantly higher with row seeding than broadcast seeding of finger millet cover crop in 2002. The absence of finger millet under MT in 2003, significantly reduced soybean grain yield. Finger millet can be managed with a single mechanical suppression as a cover crop under MT with no yield reduction.     

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.     

Effects of tillage practices combined with mucuna fallow on soil erosion and water dynamics on Ishigaki Island,Japan

Abstract

This study was conducted on a sloping field at the Japan International Research Center for Agricultural Sciences, Okinawa Subtropical Station, Ishigaki Island, Okinawa Prefecture, Japan, to evaluate the effects of zero tillage farming combined with mucuna fallow as a cover crop on soil erosion and water dynamics. Two fallow systems (natural and mucuna) in combination with two soil tillage treatments (zero tillage and conventional tillage) were imposed on three sloping fields (2.0°, 3.5° and 5.0°). A sorghum crop (Sorghum bicolor (L) moench) was planted after the soil tillage treatment. Soil loss for zero tillage farming combined with mucuna fallow was equivalent to only 3% of that for the conventional tillage farming with natural fallow. Runoff water was also reduced by between 74% and 77% when compared with the conventional tillage system with natural fallow. These results indicate that zero tillage with mucuna fallow is a very effective measure for the control of soil erosion and water runoff. Moreover, this farming system improved water infiltration during both the fallow and the sorghum cropping periods. For the zero tillage plot, water loss as deep percolation increased 1.6-fold compared with that for the conventional farming under heavy rainfall conditions. It is expected that under less rainfall areas or seasons, the effects of zero tillage farming combined with the mucuna cover crop may be more pronounced on water runoff control and, therefore, may greatly improve soil water conditions.     

耕作方式对华北冬小麦.夏玉米周年产量和水分利用的影响

在冬小麦季设置秸秆不还田翻耕(CT)、秸秆还田翻耕(CTS)、秸秆还田旋耕(RTS)和免耕秸秆覆盖(NTS)4种处理,研究耕作方式对华北小麦-玉米两熟区作物周年产量和水分利用的影响。结果表明:耕作方式对当季冬小麦产量和水分利用影响显著,对夏玉米产量和水分利用影响不大,但秸秆还田提高了夏玉米产量。RTS、CTS、CT 3个处理小麦季产量差异不显著,而NTS由于有效穗数不足,产量显著低于其他处理;与CT相比,NTS周年产量平均减产5.13%,RTS增产2.69%,CTS增产2.33%。耕作方式对当季小麦土壤水分含量影响大,而对后茬夏玉米土壤水分含量的影响较小。NTS提高了小麦季土壤水分含量,增加了土壤储水量,与CT相比,0~60 cm土壤储水量2010年和2011年分别增加39.07 mm和26.65 mm。从耗水构成来看,土壤水在冬小麦耗水中所占比例最大,其次为灌水和降水;而夏玉米耗水以降水为主,且降水中有一部分转化为土壤水储存起来。NTS提高了冬小麦季土壤储水量,降低了土壤水分的消耗,冬小麦季耗水最少。与CT相比,NTS小麦季平均节水22.40 mm,周年耗水量也以NTS最少;但NTS冬小麦产量降低导致其小麦季和周年水分利用效率均最低。从作物周年产量和水分利用的角度来看,如何提高免耕秸秆覆盖小麦季产量,进而提高周年产量,发挥其节水优势,是该耕作模式在华北地区冬小麦?夏玉米两熟区推广应用亟需解决的关键问题。     

A conservation tillage research update from the Coastal plain soil and water conservation research center of South Carolina: A review of previous research

In the U.S. Southeastern Coastal Plains conservation tillage (CT) became useful as a management system with the development of in-row subsoiling systems capable of planting into heavy residues. Research priorities associated with the development of CT included: reducing cover crop water loss, improving stand establishment, assessing nutrient and water management requirements, determining optimal subsoiling strategies, understanding long-term conservation tillage effects on soil properties, evaluating the interaction of crop residue removal with tillage systems, and documenting tillage impact on pests and beneficial organisms. Since the late 1970s the Coastal Plains Soil and Water Conservation Research Center in Florence, SC has made a concerted effort to study these interactions and alleviate them as obstructions to the use of CT management. These studies showed that for Coastal Plain soils such as Norfolk sandy loam (fine-loamy, siliceous thermic, Typic Paleudults) winter cover crops such as rye (Secale cereale L.) desiccated the soil profile by evapotranspiration in the spring. This delayed emergence and early season growth of corn (Zea mays L.) but not full-season soybean (Glycine max (L.) Merr.). Conservation tillage helped manage soil strength by gradually increasing soil organic matter content, restricting traffic patterns and maintaining higher soil water contents. Laboratory studies demonstrated a negative correlation (R²=0.85) between proctor soil strength and organic matter content. Conservation tillage affected nematode, Bradyrhizobium japonicum and Heliothis species populations. Alternate cropping systems using rapeseed (Brassica napus L.) as a winter crop or sunflower (Helianthus annuus L.) either before soybean or after corn provided crop cover against potential soil loss from late autumn through early spring, when bare soil is exposed to intense rainfall. Water quality questions associated with CT have been raised but remain unanswered. Although CT can reduce runoff and erosion, the crop residues can support higher insect populations and pathogen inoculum levels, and thus prompt greater pesticide use. Quantifying relationships between soil strength, macropore formation and persistence, and water infiltration with surface and subsurface water quality is the focus of new long-term evaluations. The findings of these studies, published to date, are summarized in this paper.     

Tillage and application effects on herbicide leaching and runoff

Herbicides are key products in sustaining agricultural production and, to minimize agro-environmental concerns regarding their use, continued assessment of their behavior under different management practices is required. Leaching and runoff losses of four herbicides applied preplant-incorporated (PPI) were evaluated in two tillage systems over a 3-year period (1989–1991). Scant leaching during the droughty 1991 growing season limited treatment evaluations to 2 years. Herbicides were applied at recommended rates (1.7 and 2.2 kg active ingredient (a.i.) ha⁻¹) to conventional tillage (CT) and mulch tillage (MT) corn (Zea mays L.) fields on Hagerstown silty clay loam (fine, mixed, mesic Typic Hapludalf). Tillage treatments were defined as moldboard plow-disk-harrow (CT) and single-disking (MT). During this study, CT followed 5 years of corn production in a comparable CT system on this site and, similarly, MT followed a 5-year no-tillage (NT) system. Herbicides were applied preemergence (PRE) to CT and NT in the 5-year study and preplant-incorporated (PPI) in this study. Herbicide mobility in subsurface drainage was evaluated from herbicide mass transported to pan lysimeters installed 1.2 m deep. Surface drainage losses of these chemicals were determined from residues in runoff collected with automated sampling and recording equipment.

Leachate volumes were greater from MT than CT in 1989 and 1990 and exceeded all seasonal losses during the previous 5 years under NT management. Comparisons of total seasonal leachate discharged to pan lysimeters within and among studies and herbicide mass leached showed that timing of leachate-inducing precipitation relative to herbicide application was the key factor in regulating herbicide translocation. Herbicide mass transported through the root zone averaged from less than 0.1% to 0.9% of applied rates in CT and from 1.4% to 5.1% in MT.

Leachate-availability of herbicide residues and extent of herbicide longevity in this soil under MT conditions were similar to previous findings under NT management. Despite these behavioral similarities for herbicides among tillages, herbicide mass discharged per unit of percolate was most often lower for MT compared with NT, particularly in early growing seasons of comparable precipitation. Thus, the PPI treatment in MT appeared to reduce leaching of these chemicals compared with PRE application in NT.

Runoff losses of PPI herbicides ranged from 0.35% to 0.77% of applied rates in CT and from 0.13% to 0.28% in MT. Losses of PRE-applied herbicides from NT averaged less than 0.1% of applied rates; maximum yearly losses ranged from 0.06% to 0.18%. Thus, the character of the disked, minimally tilled surface provided a level of impedance to runoff that was greater than achieved with the tilled surface on this 3 to 5% slope, but less than previously obtained with an untilled, mulch-covered surface.     

Effects of conservation agriculture on runoff,soil loss and crop yield under rainfed conditions in Tigray,Northern Ethiopia

The aim of conservation agriculture (CA) is to improve soil quality and crop yield whilst reducing runoff and topsoil erosion. An experiment was carried out in a rainfed field using a permanent raised bed planting system for 3 yr (2005–2007) in Adigudem, northern Ethiopia in order to evaluate the effect of CA on runoff, soil loss and crop yield. CA practices were introduced in fields with Vertisols in a randomized complete block design on permanent 5 × 19 m plots. Three treatments were evaluated: (1) conventional tillage (CT) with a minimum of three tillage operations and removal of crop residues, (2) terwah (TER) that was similar to CT except that contour furrows were included at 1.5 m intervals, and (3) derdero+ (DER+), which consists of permanent raised beds with a furrow and bed system, retention of 30% of standing crop residues and zero tillage on the top of the bed. All ploughing as well as the maintenance of the furrows of the permanent raised beds was done using a local ard plough called maresha. Results from monitoring over 3 yr showed that soil loss and runoff were significantly higher (P < 0.05) in CT followed by TER and DER+. Average soil losses of 5.2, 20.1 and 24.2 t/ha were recorded from DER+, TER and CT, respectively. Runoff was 46.3, 76.3 and 98.1 mm from DER+, TER and CT, respectively. Grain yield was significantly lower (P < 0.05) in DER+ under teff in 2006, probably due to the high sensitivity of teff to weeds. The yield of wheat in 2007 was significantly higher in DER+ followed by TER. The terwah system is recommended as a first measure for wider adoption to reduce runoff and soil loss and to increase crop yield. The long‐term goal is to achieve a derdero+ system, i.e. a permanent raised bed planting system along with the application of crop residues.     

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.     

中国云南滇池流域农田径流磷污染负荷影响因素研究

Effects of factors such as slope, surface soil texture, fertilization and crop cover with different rainfall intensities on phosphorus (P) losses in farmland runoff of the Dianchi Lake Watershed in Yunnan Province of China were studied through a rainfall simulation test using a red soil, one of the most widely distributed soils of the study area. Results showed that the runoff concentrations of total phosphorus (TP) and P losses differed with the slope, being highest when the slope was 18°. At two different rainfall intensities, the runoff TP and P losses had a similar decreasing trend as the surface soil texture became coarser, therefore applying the grit would decrease P in runoff from soils of farmland on slopes with heavier textures. With wheat as a crop cover the runoff TP concentrations and P losses were significantly lower than those of the bare soil. This showed that plant cover would greatly decrease P in runoff from the farmland of the study area. The TP concentration in runoff from the soil two days after fertilization doubled when compared with that from the non-fertilized soil, indicating that fertilization could mean a dramatic rise in P runoff if irrigation or heavy rainfall occurred immediately after application and that no fertilization before a rain and no irrigation immediately after fertilization would reduce runoff P loss from the farmland of the study area.     

不同自然植被管理措施对红壤丘陵果园水土流失的影响

丘陵是“山—丘—谷”的过渡地带，生态系统脆弱，一旦植被遭破坏，极易水土流失。在红壤丘陵园地应用除草剂调控水土流失试验结果表明：与传统的清耕法相比，克无踪、草甘膦、草草克、克克草和生草法可使地表径流量分别减少47.7%，20.8%，31.4%，41.3%和45.5%；可使土壤侵蚀量分别减少52.4%，39.0%，48.1%，50.7%和55.2%；可使土壤养分分别减少50.2%，37.0%，41.8%，45.8%和60.3%。除草剂对杂草再生率影响，与生草法比较，克无踪可达67.2%，草甘膦达30.3%，草草克36.8%，克克草51.2%和清耕法55.1%；克无踪调控杂草效果分别是草甘膦的2.2倍，清耕法的1.2倍。克无踪调控杂草效果显著，有望成为红壤丘陵园地培肥与水保相得益彰的有效措施。     

Effect of tillage and crop management on runoff,soil erosion and organic carbon loss

Proper management of soil organic matter is an important issue in the context of sustainable agriculture. The intensification of production and the loss of organic carbon associated with agriculture reduce the efficiency of production and the quality of the environment, especially in relation to areas exposed to erosion. The aim of this study was to determine the impact of specific tillage systems and plant cover on the organic carbon losses, as well as on runoff and soil losses, over a 6-year study period following the introduction of no-till. The first factor in the experiment was the tillage system: conventional tillage (CT) and no-till (NT). The second factor was plant cover: horse bean, spring wheat and winter oilseed rape. The results showed that runoff was 4.3 ± 0.6% higher under NT than under CT, while soil loss was 66.8 ± 2.7% lower under NT than under CT. Compared to CT, NT limited the total organic carbon losses by an average of 46.0 ± 2.9% and organic carbon bound with sediment losses by 53.2 ± 0.7%, whereas for dissolved organic carbon, there were no significant differences for the tillage systems. The anti-erosion effectiveness of NT was lower in the first year, but it increased in subsequent years after the introduction of this tillage system. Plant cover also had a significant impact on organic carbon losses and soil protection. The crops were ranked according to runoff, soil losses and organic carbon losses in the following order from lower to higher losses: winter oilseed rape > spring wheat > horse bean.     

Experiment of "No-Tillage" Farming System on the Volcanic Soils of Tropical Islands of Micronesia

The soils of southern Guam are formed from very deep; well-drained Saprolite derived from volcanic based tuff and tuff breccias. These soils suffer severe erosion as the result of rapid overland flow, wind and intensive rain events typical of southern Guam. An integrated approach to control the accelerated soil erosion was designed to include conservation tillage, crop rotation with leguminous plant, and residue management for soil surface cover.The objectives of this study are; 1) to evaluate the use of crop rotation and tillage management for increasing organic-matter content to improve the overall quality of these severely eroded soils, 2) to evaluate the effect of conservation practices on harvested yield and crop productivity of these eroded soils and, 3) to assess the effects of conservation techniques including no-tillage systems on water runoff and infiltration. This paper discusses the effect of conservation strategies and techniques on these severely eroded soils of southern Guam.     

凌源市推广“金字塔”模式开发治理成效显著

凌源市推广“金字塔”模式开发治理成效显著刘海潮，张凤山，祁放（辽宁省凌源市水利局，１２２５００）凌源市水土保持小流域综合治理，经过多年的不断完善、总结、提高，形成了一林戴帽，二林围顶，果牧拦腰，两回穿靴，一龙坐底的产金字塔＂综合治理模式ＪＩ９８８年经...     

Factors Influencing Runoff P Losses from Farmlandsof the Dianchi Lake Watershed in Yunnan, China

Effects of factors such as slope, surface soil texture, fertilization and crop cover with different rainfall intensitieson phosphorus (P) losses in farmland runoff of the Dianchi Lake Watershed in Yunnan Province of China were studiedthrough a rainfall simulation test using a red soil, one of the most widely distributed soils of the study area. Resultsshowed that the runoff concentrations of total phosphorus (TP) and P losses differed with the slope, being highest whenthe slope was 18~. At two different rainfall intensities, the runoff TP and P losses had a similar decreasing trend asthe surface soil texture became coarser, therefore applying the grit would decrease P in runoff from soils of farmland onslopes with heavier textures. With wheat as a crop cover the runoff TP concentrations and P losses were significantlylower than those of the bare soil. This showed that plant cover would greatly decrease P in runoff from the farmland ofthe study area. The TP concentration in runoff from the soil two days after fertilization doubled when compared withthat from the non-fertilized soil, indicating that fertilization could mean a dramatic rise in P runoff if irrigation or heavyrainfall occurred immediately after application and that no fertilization before a rain and no irrigation immediately afterfertilization would reduce runoff P loss from the farmland of the study area.     

Arkansas Discovery Farms: documenting water quality benefits of on-farm conservation management and empowering farmers

Arkansas Discovery Farms (ADFs) are private farms that collaborate with on-farm research, verification, and demonstration of farming's impact on the environment. We have nine ADFs representing livestock (broiler poultry and pasture grazed beef and sheep) and row crop agriculture (corn, cotton, rice, soybean, and wheat), where we collect water use and water quality data as a function of conservation management, using autosamplers equipped with edge-of-field H-flumes or weir flow structures, which measure and collect surface runoff. On the poultry farms, we are monitoring nutrient and sediment runoff originating immediately near poultry houses due to concerns with spillage of litter during bird removal and house clean out, as well as dust from tunnel ventilation. On a nearby farm we are assessing the impact of rotational grazing on water quality, soil organic matter, and soil health metrics. On the row crop farms we are assessing the impacts of conservation tillage and cover crops on soybean–corn rotations and cotton on nutrient and sediment runoff and the benefits of water harvesting and reuse of water conservation and quality. The information in this paper while preliminary, demonstrates how a state-wide on-farm demonstration program operates. Elevated nutrient and sediment runoff from around poultry production areas are decreased three-fold by directing runoff into ponds or through grassed waterways. While conservation tillage and cover crops do decrease nutrient and sediment runoff, no significant difference between conventional and conservation operations is yet to be realized. Importantly, ADF empowers farmers to proactively address environmental concerns. This paper discusses the development, guidance, principals, and goals of ADF and contrasts this with other farm monitoring projects, where the sources of nutrient impairment are the subject of ongoing litigation. Monitoring in divisive and transparent situations presents unique challenges with data ownership and release of findings, which can hinder productive outcomes of such monitoring.     

Analysis of the effects of soil management on runoff generation in olive orchards using a physically based model.

Abstract. A numerical model that incorporates the spatial variability of infiltration, surface storage and resistance to overland flow was developed, calibrated and validated for olive orchards. The model reproduced accurately amounts of runoff used in validation, and predicted runoff in olive orchards managed in different ways, in line with published results. The model was used to analyse the runoff generation in a virtual, 180 m length, 5% steep, olive grove, using 54 different scenarios which combined three different soil types, two tree canopy sizes and nine soil management techniques (four tillage scenarios: freshly or degraded tillage with and without a compacted plough layer; no-till, and four cover crops in strips differing in width and plant density). The results of the numerical experiment showed that no-till had the highest runoff coefficient, while a dense cover crop had the lowest. Recently tilled soils also exhibited some of the lowest runoff coefficients. The effects of increasing soil cover due to a greater tree canopy on runoff were significant and caused by the greater area of high infiltration beneath the canopy. Effects of tree canopy size were less important than the impact of soil management practices on runoff.     

Activity,Adsorption, and Lixiviation of Acetochlor in Soil under No Tillage and Conventional Tillage: Influence of Straw Coverage

Abstract

The activity of residual herbicides employed for weed control varies with adsorption, lixiviation, degradation, and biological transformation of these compounds in the soil. The purpose of this study was to evaluate the activity of the herbicide acetochlor (2‐chloro‐N‐ethoxymethyl‐6′‐ethylacet‐o‐toluidine) in Typic Paleodult under no tillage and conventional tillage. Field and laboratory experiments were carried out at the Universidade Federal do Rio Grande do Sul. Weed control with and without straw coverage, and adsorption and lixiviation of acetochlor, in soil with both tillage systems were evaluated. Adsorption and lixiviation processes were determined by high‐performance liquid chromatography (HPLC) with UV detector. The coefficients K _d and K _oc were higher in no‐tillage soil, indicating a more effective acetochlor adsorption. The maximum concentration of acetochlor was found in a depth of 15–20 cm, indicating a higher lixiviation in this soil. The acetochlor was more effective in weed control using conventional tillage when compared to no tillage. The straw coverage reduced the control efficiency of the herbicide.