Conservation Tillage Systems Research Articles

Design and evaluation of ground-driven rotary subsoilers

Compacted soil hardpans restrict crop growth by limiting root access to moisture and nutrients in the subsoil. Mechanically disrupting this hardpan profile is necessary in many soils to promote proper root elongation and crop growth. Subsoiling is the primary deep soil tillage practice which needs to be done once every two to three years depending on soil type and conditions. To maintain an adequate amount of residue for conservation systems, subsoiling should be performed without excessively disturbing the soil surface. However, most subsoilers disrupt the soil surface excessively and cover valuable crop residues. The objective of this study was, therefore, to design an alternative subsoiler for conservation tillage systems that minimized soil disturbance and energy requirements while adequately disrupting compacted soil profiles. Ground-driven rotary subsoilers were designed and manufactured by dividing a 1.2m diameter coulter into multiple blades. Minimizing the sliding soil resistance on the side of the coulter was one of the main considerations in forming the shape and number of blades. An experiment was conducted in the soil bins of the USDA-ARS National Soil Dynamics Laboratory in Auburn, AL, USA to determine the effects of ground-driven rotary subsoilers on soil disturbance and energy requirements compared with a large coulter and a typical subsoiler. Treatments were four different types of subsoilers (coulter-no-blade, coulter-5-blade normal direction, coulter-5-blade reverse direction, and shank-type) and two tillage depths (25 and 38cm). Soil disturbance, cone index, bulk density and draft were measured and statistical analyses conducted to determine the differences between subsoilers. The coulter-5-blade normal direction and coulter-5-blade reverse direction subsoilers required considerably less draft power (from 10 to 68%) for both operation depths than coulter-no-blade and shank type subsoilers. Coulter subsoilers minimized soil disturbance and required higher draft energy (from 22.5 to 33.5%) per volume of disturbed soil than the shank-type subsoiler. The soil disruption paths of coulter-5-blade subsoilers have an advantage for row crops due to limited above-ground disturbance if seeds can be placed in the middle of the disrupted zone.

Optimum Water Use in Conservation Tillage for Wheat Cultivation

Conservation tillage system offers numerous benefits over intensive tillage system. This experiment was conducted on conservation tillage using zero tilldrill, power tiller operated seeder (PTOS) and bed planter along with farmer’s practice of tillage by rotary tiller under different irrigation levels at Wheat Research Centre (WRC), Nashipur, Dinajpur. Irrigation water was applied by 5 irrigation levels at different growth stages of the crop. The irrigation levels were I0 (No irrigation), I1 (17-21 DAS), I2 (17-21 DAS + 50-55 DAS). I3 (17-21 DAS+ 50-55 DAS + 75-80 DAS), and I4 (17-21 DAS + 35-40 DAS + 50-55 DAS + 75 – 80 DAS). It was observed that the sowing cost was reasonably reduced than that of the farmer's practice. Seasonal water use was less in PTOS than other tillage methods. Grain yield was significantly affected by tillage methods. The higher grain yield was found from PTOS, bed planting, and zero tillage than that of farmer's practice. There was no significant difference within the interaction effect of tillage methods and irrigations. The effect of irrigation level was found highly significant on grain yield. Water use efficiency increased with decrease of irrigation water use and decreased with increase of irrigation. Average yields in all tillage methods under I1, I2, I3, and I4 irrigation levels were found to increase by 33, 43, 52, and 51 percent, respectively, compared to that of I0. DOI: http://dx.doi.org/10.3329/bjar.v37i1.11172 Bangladesh J. Agril. Res. 37(1): 27-37, March 2012

Cotton Production as Affected by Irrigation Level and Transitioning Tillage Systems

Identifying management practices that conserve and protect water resources are very important to a wide variety of stakeholders within semiarid environments. The objective of this study was to develop water management strategies for transitioning tillage systems in cotton (Gossypium hirsutum L.) production within the Texas Rolling Plains when in a subsurface drip irrigation (SDI) system. Five irrigation regimes (0, 33, 66, 100, and 133% evapotranspiration [ET] replacement) and four tillage systems (conventional till, reduced till, no‐till, and no‐till with a terminated cover crop) were evaluated. The study was conducted for 3 yr and treatments were replicated three times in a randomized complete block design. Lint yields were not affected by the main effects of tillage or the interaction of tillage and ET replacement. In contrast ET replacement was a significant factor for lint yields, irrigation water use efficiency, and net returns. Greatest lint yields and net returns were achieved at 100% ET replacement. Fitted models indicated that optimum lint yields and net returns were achieved at 104.5% ET and 102% ET, respectively. Irrigation at 83% ET was within the 95% confidence interval for lint yield. Net returns were significantly higher for no‐till systems compared with conventional till. Thus, adoption of conservation tillage systems should not negatively affect lint yield or net returns in deficit irrigated SDI cotton systems within the Texas Rolling Plains, particularly during the transition from intensively tilled systems to conservation tilled systems.

Conservation tillage systems for cotton advance in the San Joaquin Valley

Cotton production in the San Joaquin Valley has traditionally relied heavily on tillage for its presumed benefits to plant establishment, yields and insect management. Research in the 1960s and 1970s demonstrated the potential of precision or zone tillage, which foreshadowed the introduction of a variety of minimum tillage implements in the early 1990s. During a 3-year comparison study from 2001 to 2003, cotton yields in strip tillage plots matched or exceeded yields of standard tillage plots in all 3 years. In a 12-year study from 1999 to 2011, tillage costs were lowered an average of $70 per acre in 2011 dollars using no-tillage compared to standard tillage while achieving statistically comparable yields, provided that adequate crop stands were achieved. If bottom-line profitability can be maintained, conservation tillage may become increasingly attractive to cotton producers in the San Joaquin Valley.

Water pressure head and temperature impact on isoxaflutole degradation in crop residues and loamy surface soil under conventional and conservation tillage management

Laboratory incubations were performed in order to evaluate the dissipation of the proherbicide isoxaflutole in seedbed layer soil samples from conventional and conservation tillage systems and in maize and oat residues left at the soil surface under conservation tillage. The effects of temperature and water pressure head on radiolabelled isoxaflutole degradation were studied for each sample for 21d. Mineralisation of isoxaflutole was low for all samples and ranged from 0.0% to 0.9% of applied 14C in soil samples and from 0.0% to 2.4% of applied 14C in residue samples. In soil samples, degradation half-life of isoxaflutole ranged from 9 to 26h, with significantly higher values under conservation tillage. In residue samples, degradation half-life ranged from 3 to 31h, with significantly higher values in maize residues, despite a higher mineralisation and bound residue formation than in oat residues. Whatever the sample, most of the applied 14C remained extractable during the experiment and, after 21d, less than 15% of applied 14C were unextractable. This extractable fraction was composed of diketonitrile, benzoic acid derivative and several unidentified metabolites, with one of them accounting for more than 17% of applied 14C. This study showed that tillage system design, including crop residues management, could help reducing the environmental impacts of isoxaflutole.

Benefits of GPS agricultural guidance for sustainable agriculture

The Global Positioning System (GPS) together with sophisticated machinery guidance systems represents great benefit concerning precise production inputs, minimizing machine errors in the fields and, therefore, lower costs inputs for the agriculture. One of the problems in modern agriculture is soil compaction caused by heavy machinery in the fields. Right the excessive traffic is connected with soil compaction phenomena and its unfavourable effects. Machinery traffic monitoring and detailed analysis of machinery passes across the field can be used as determination of the field areas which are intensively loaded with agricultural traffic. This paper focuses on data obtained from agriculture machinery guidance systems to asses and minimise frequency of agricultural machinery passes across a field and to ensure maximum field job efficiency. Firstly, traffic intensity on a selection of fields was evaluated. Vehicle passes all of field operations and using range of machinery across selected fields were monitored during one year which resulted in a one year traffic intensity map of the fields. Further different tillage systems, machinery working widths and field jobs were evaluated by an evaluation of the number of vehicle passes across the field. The system with ploughing resulted in 86.1 % of total area covered with wheel passes, while the conservation tillage system showed 63.8 % of the area affected by machinery tyres. Secondly, the pass-to-pass accuracy with or without the satellite navigation was evaluated. The measured data were obtained from RTK guidance autopilots which are a prerequisite for precise in-field jobs. The results show significant benefits of satellite navigation. Without using the satellite navigation during a field operation, a tendency to passes overlapping was found out. Overall, the experiments revealed enormous intensity of the agriculture machinery passes, randomly trafficking agricultural fields. The application of GPS machinery guidance was a potential to decrease the number of machinery passes in the fields and can reduce the costs of field jobs.

Interaction of Tillage System and Irrigation Amount on Peanut Performance in the Southeastern U.S

Abstract A five-year study to investigate the potential interaction of conservation tillage with reduced irrigation amounts was conducted near Dawson, GA on peanut (Arachis hypogaea L.). Conventional tillage was compared to two conservation tillage programs (wide-strip and narrow-strip tillage) under four irrigation levels (100, 66, 33, and 0% of a recommended amount). Peanut yield did not exhibit a tillage by irrigation interaction as expected, although the main effects of irrigation and tillage were each significant by year due to weather variations. Peanut yield in narrow-strip tillage or wide-strip tillage were individually superior to conventional tillage in three seasons out of five, however only in one year did both conservation tillage systems outperform the conventional system. No detrimental effects on yields could be attributed to conservation tillage. Peanut quality and digging loss were dependent on the tillage by year effect as well as the main effect of irrigation. Irrigation increased total sound mature kernels (TSMK) 2% versus non-irrigated (0% irrigation level); tillage was not significant each year of the study but increased TSMK 2% in three of five years. Digging losses were greater in plots with increased yield potential such as those receiving irrigation. Net economic returns revealed a moderate trend towards sustained profitability under reduced irrigation levels through narrow-strip tillage and to a lesser extent, wide-strip tillage. Under conventional tillage systems, returns decreased with decreasing amounts of irrigation applied.

Subsoiling improves conservation tillage in cereal production of severely degraded Alfisols under Mediterranean climate

Central Chile has a Mediterranean climate with a mean annual precipitation of 695mm, 80% concentrated in winter. In this context, water erosion and inappropriate agricultural management along hillslopes are the major causes of soil degradation. From 2007 to 2010, different agricultural systems were compared: conservation tillage with stubble retained: no tillage (Nt), Nt+subsoiling (Nt+Sb), Nt+barrier hedges (Nt+Bh) and Nt+contour plowing (Nt+Cp). All the systems were compared to conventional tillage (Ct) without crop stubble on the surface. The runoff plots were 50m×20m on a hillside with 12.5% slope in an oat–wheat crop rotation. Runoff, sediment and nutrient losses measured for every rainfall event, occurred during winter months when rainfall energy was also the highest of the whole year. Conservation tillage systems mitigate water erosion compared to the Ct system. In heavy rains, conservation tillage systems reduced soil loss by more than 72% compared to Ct. In addition, the runoff coefficient during the rainy period was 70% lower in conservation tillage systems when the crop was at the initial tillering stage and 90% lower at final tillering. These results show the importance of conservation tillage and crop stubble to decrease erosion, especially in years when extreme precipitation presented a high potential for soil erosion. Moreover, cereal production showed higher biomass and grain yield in Nt+Sb. It was concluded that no tillage with stubble retained on the surface was the best option to mitigate soil erosion. However, the effects of subsoiling decrease over time, making new subsoiling necessary with the implied costs. Due to the strong fluctuations in the prices of the agricultural products, it is impossible to estimate the balance of costs/benefits of this system. On other hand, the duration of the experiment may have been too short to measure the real impacts of no-tillage practices.

Bioassay-Directed Isolation and Identification of Phytotoxic Terpenoids from Horseweed (Conyza Canadensis)

Horseweed [Conyza canadensis (L.) Cronquist, syn. Erigeron canadensis L.], Asteraceae, is a common weed with known allelopathic effects but few studies on the isolation and identification of the phytotoxic compounds have been reported [1]. C. canadensis infests orchards, vineyards, field crops such as corn, soybean and cotton, particularly in herbicide-resistant crops where conservation tillage or no-till systems are used. The objective of this study was to identify the phytotoxic compounds present by systematically performing bioassay-directed isolation and subsequent identification of the bioactive constituents according to Dayan et al. [2]. No significant phytotoxic activity against Lactuca sativa or Agrostis stolonifera was detected in methanol, or water extracts when tested at 1.0mg·mL-1; however, the dichloromethane extract was active. Further fractionation using liquid-liquid partitioning with hexane, chloroform, ethyl acetate and water was performed with the DCM extract. The most active extract (chloroform) was subjected to preparative HPLC and the fractions were tested again. The active compounds were isolated and identified by GC-MS and 1H- and 13C-NMR. The isolated compounds (Figure 1) were identified as (2Z,8Z)-matricaria acid methyl ester, (4Z,8Z)-matricarialactone and (4Z)-lachnophyllumlactone. Compound 3 shows similar activity as compound 2.

Loss and Recovery of Soil Organic Carbon and Nitrogen in a Semiarid Agroecosystem

Soils typically show 20 to 40% decline in soil organic carbon (SOC) due to cultivation, most of it in the fi rst 10 yr, but studies on SOC depletion may actually underestimate losses of the original SOC. Starting 40 to 50 yr ago, expanding use of non-inversion tillage, fertilizers, and herbicides lead to reduced disturbance and increased residue production that undoubtedly began recovery of SOC depleted during previous decades when farmers used only intensive tillage to control weeds and stimulate release of nutrients from crop residues. We measured SOC and total N stocks, density fractions, and labile C and N at 10 study sites in two rain-fed production areas in southeastern Wyoming. Systems evaluated include historic inversion- tillage-based winter wheat (Triticum aestivum L.)-fallow with no inputs, conventional winter wheat-fallow, minimum- and no-till continuous rotations and permanent grass cover. Results were then compared to SOC under nearby native grasslands. Soils beneath historic wheat-fallow were the most depleted in SOC, with 13.8 and 17.6 Mg C ha -1 in the upper 30 cm at the two study areas, or 37% of the SOC under the two native sites. Soil OC contents were statistically similar across conventional, minimum- till, and no-till systems, ranging from 64 to 78% of native SOC levels, and signifi cantly higher under permanent grass, with both sites having 90% of native SOC levels. Free light fraction organic carbon (LFOC) contents were lowest beneath the historic system, but increased in systems with fewer disturbances. When normalized by SOC and total N, the labile C and N pools generally increased with increasing disturbance, especially microbial biomass carbon (MBC) and dissolved organic carbon (DOC). Soil OC contents under the historic, inversion tillage system were much lower relative to native grasslands than found in other studies, which, together with other fi ndings, suggest that SOC levels have begun to recover under the modern conventional system. Free LFOC and labile pool C and N contents indicate that conservation tillage systems in place for a relatively short time are facilitating further recovery of SOC.

The effect of various long-term tillage systems on soil properties and spring barley yield

This study, performed on a soil that is classified as Albic Luvisols that developed on loamy sands overlying loamy material (1.4% organic matter and pH 6.5), concerns the impact of tillage systems on soil properties and the yield of spring barley. The experiment design included 3 tillage systems: conventional tillage, reduced tillage, and no-tillage. Continuous cultivation for 7 consecutive years by reduced tillage and no-tillage led to changes in the physical properties of the surface soil layer (0-5 cm). At the stem elongation growth stage of spring barley, conservation tillage systems resulted in a higher water content and bulk density in relation to conventional tillage. Conservation soil tillage resulted in decreased penetration resistance in the 0-10 cm layer, as compared with conventional tillage. Reduced tillage and no-tillage favored the surface accumulation of organic C and total N in the soil, as well as that of available K and Mg. Our results suggest that conservation tillage systems lead to progressive improvement in soil nutrient status, but have little or no effect on crop yield. Only the no-tillage system had a negative effect on yield of spring barley, by 6.8% in comparison with conventional tillage.

Utilizing cover crop mulches to reduce tillage in organic systems in the southeastern USA

AbstractOrganic systems in the southeastern USA offer unique challenges and solutions to crop production due to regional soil and climate characterized by highly weathered soil types, high precipitation and the capacity to grow cover crops in the winter. Recently, the interest of producers and researchers in high-residue cover crops and conservation tillage systems has increased. Various designs of the roller–crimper to manage cover crops have been invented and demonstrated to growers in the southeastern region of the USA over the past 17 years. The impacts of high-residue cover crop mulches on the agronomic systems in the region are diverse. Legume cover crops assist with meeting N demand from cash crops though they decompose rapidly and are seldom sufficient for N demanding crops such as corn. Cereal cover crop mulches can have the opposite effect by immobilizing N and have a longer impact on soil moisture and weed dynamics. While undesirable for many crops, N immobilization is one possible mechanism for weed suppression in legume cash crops planted into cereal residues. Other cover crop weed suppression mechanisms include physical impedance, light availability, allelopathy and microclimate effects. Regardless of the cause, successful weed control by mulches is highly dependent on having substantial biomass. The southeastern region is capable of producing cover crop biomass in excess of 9000 kg ha−1, which is sufficient for weed control in many cash crops, although supplementary weed control is sometimes necessary. Long-term data are needed to predict when farmers should add supplementary weed control. More work is also needed on how much additional N is required for the cash crops and how best to deliver that N in a high-residue environment using organic sources.

Weed Management and Cotton Yield under Two Row Spacings in Conventional and Conservation Tillage Systems Utilizing Conventional, Glufosinate-, and Glyphosate-based Weed Management Systems

A field experiment was conducted during three cropping seasons to compare weed control and cotton yield provided by conventional (CV), glufosinate-resistant (LL), and glyphosate-resistant (RR) weed management systems under standard (102 cm) and narrow (38 cm) row spacing grown in conventional and conservation tillage systems. The conventional tillage and/or CV cotton received a PRE application of pendimethalin. The CV, LL, and RR cotton varieties received two POST applications of pyrithiobac, glufosinate, and glyphosate, respectively, at two- and four-leaf cotton growth stages. A final (LAYBY) application of trifloxysulfuron was applied to 38-cm row cotton while a LAYBY POST-directed spray of prometryn plus MSMA was used in 102-cm row cotton. The LL and RR weed management systems controlled at least 97% of large crabgrass, Palmer amaranth, sicklepod, and smallflower morningglory, while the CV system controlled 89, 73, and 87 to 98% of large crabgrass, smallflower morningglory, and Palmer amaranth, respectively. Sicklepod control increased from 85% in 102-cm rows to 95% in 38-cm rows in the CV herbicide system. Yellow nutsedge and pitted morningglory control exceeded 98% and was not affected by tillage, row spacing, or weed management system. Cotton yield was not affected by row spacing any year, by tillage in 2005, or by weed management system in 2004 and 2005. In 2006, yield in the RR weed management system was 27 and 24% higher than LL and CV weed management systems, respectively. In 2004, yield of conventional tillage cotton was 18% higher than conservation tillage cotton, but in 2006 the yield in conservation tillage was 12% higher than conventional tillage.

Performance of Wheat Varieties (Triticum aestivum L.) under Conservation Tillage Practices in Organic Agriculture

Field experiments were conducted to determine the effects of tillage systems and varieties on growth, yield and quality of wheat crop (Triticum aestivum L.). The experiments conducted at two sites were laid out in a split-plot design with four replicates, three main plots [conventional tillage (CT), no-tillage (NT) and minimum tillage (MT)] and four sub-plots (‘Siette’, ‘Panifor’, ‘Myrto’, ‘Estero’). The soil porosity and total nitrogen were higher in soils subjected to conservation tillage systems (NT and MT) than under conventional tillage. There were no differences in root growth neither between the tillage systems nor among the varieties. Yield was influenced by the tillage system and variety. The highest grain yield (421-459 kg ha-1) was found under the CT system with ‘Siette’, ‘Myrto’ and ‘Estero’ varieties. In contrast, the highest grain yield was observed under conservation tillage (NT and MT) with ‘Panifor’ variety. There were no significant differences between the tillage systems concerning the protein content and Zeleny value. In contrast, the highest Hagberg falling number was found with MT. Zeleny value was positively and significantly correlated with protein content. High flour quality, as demonstrated by high protein content and Zeleny value, and low Hagberg falling number, was produced in the ‘Estero’ variety.

Effects of tillage and fallow period management on soil physical behaviour and maize development

Abstract Effects of two tillage treatments and two fallow period managements under continuous maize cropping on soil temperature, soil water dynamics and maize development were evaluated over a 4-year period (2005–2008). Tillage treatments were conventional tillage with mouldboard ploughing and conservation tillage with disk harrowing. The fallow period managements were bare soil or soil sown with a cover crop after maize harvest. For each year, topsoil temperature (0–20 cm-depth) was lower under conservation tillage systems at sowing, from 0.8 to 2.8 °C. This difference persisted several weeks after sowing, and disappeared afterwards. Under conservation tillage, higher soil water content was generally measured at sowing and during the growing season strong fluctuations were observed at 40 cm-depth. Under conventional tillage, soil water content varied mainly in the tilled layer (20 cm-depth). Tillage and fallow period management affected water flow rate at 40 cm-depth. During the maize growing season, the lowest drainage volumes were measured in 2006 and 2008 under conservation tillage in cover cropped plots. No effect of fallow period management on maize development and yield was observed but significantly higher yields were measured under conservation tillage in 2005 and 2007. From this 4-year experiment under continuous maize cropping, using cover crop and reducing tillage intensity enhanced water use efficiency while maintaining or increasing maize yields.

Yield and water use efficiency of barley in a semiarid Mediterranean agroecosystem: Long-term effects of tillage and N fertilization

Conservation tillage systems (no-tillage, NT; and minimum tillage, MT) are being adopted in rainfed agroecosystems of the Mediterranean basin where water availability is the main limiting factor for crop productivity. We hypothesized that long-term adoption of conservation tillage systems would increase water use efficiency (WUE) and its response to N fertilizer additions due to improved soil water content. A field experiment was established in 1996 on a loamy Xerofluvent Typic in the Ebro river valley (NE Spain). The experiment compared three nitrogen (N) fertilization levels (zero, 0 kg N ha −1, medium, 60 kg N ha −1, and high, 120 kg N ha −1), under three tillage systems (CT, conventional tillage; MT and NT), annually cropped to barley ( Hordeum vulgare, L.) as is usual in the region. Ten years after the experiment establishment, during four consecutive growing seasons, 2005–2006 to 2008–2009, we evaluated the response of soil water content, soil nitrate, above-ground dry matter, grain yield and yield components to long-term (>10 years) tillage and N fertilization treatments. The long-term sustainability of NT and MT was confirmed. Mean yield and WUE under long-term conservation tillage systems were 66% and 57% higher than under CT, respectively. This improvement was mainly attributed to improved soil water usage under conservation tillage, mainly due to reduced water use during the pre-anthesis period. However, in a wet year yield did not significantly differ among tillage systems. The improvement of WUE with N fertilization was confirmed under NT, which medium and high N fertilizer level increased 98% mean grain yield and 77% mean WUE compared to CT. The increased response of crop and yield to N fertilization under NT was due to improved soil water content. Soil N accumulation together with the lower water accumulation explained the lack of response to N fertilization under CT, even on a wet growing season (i.e., 2008–2009). Long-term NT adoption was a sustainable practice for barley monoculture in the region, allowing for reduced costs and yield increase with N fertilizer additions. N fertilizer rates on rainfed Mediterranean croplands should be adjusted depending on the reduction of tillage intensity and rainfall of the year. In our system and as an example for this agroecosystems, N fertilizer rates should be kept at or below 60 kg N ha −1, and should be further reduced on intensively cultivated soils.

Effects of tillage intensity and anionic polyacrylamide on sediment and nitrogen losses in irrigated wheat field

Degradation of agricultural soils and nutrient losses affected by intensive agriculture and tillage is of environmental and agricultural concerns. These concerns lead to emergence and development of conservative technologies such as conservation tillage systems [reduced tillage (RT) and no-till (NT)] and anionic polyacrylamide (PAM). A study was done in order to investigate the interactive effects of three tillage systems and three PAM concentration on sediment loss, runoff nitrate concentration, nitrogen losses from the soil-plant system and nitrogen recovery. The experimental design was a randomized complete block with split-plot arranged in three replications. The anionic polyacrylamide (PAM) were in three levels of zero (P0), 10 (P10) and 20 (P20) mg L-1 as the main plot and different tillage intensities as the subplot including moldboard plowing plus two disk harrow passes (CT1), one stubble cultivator pass (RT) and moldboard plowing plus one power harrow pass (CT2). The RT treatment relative to CT2 led to soil loss reduction by 23.56% during the first irrigation. The P10 and P20 treatments relative to P0, caused sediment concentration reduction by 98.1 and 98.09% and soil loss reduction by 98.7% and 98.8%, respectively. The RT × P20 treatment had a greater impact in reduction runoff nitrate losses than CT1 × P20 and CT2 × P20 treatments. Losses of N in the fertilized plots and recovery of applied N (RAN) was influenced by both tillage system and PAM application. Key words: Tillage, polyacrylamide, polyacrylamide, soil losses, nitrate.

Enhancing Crop Productivity via Weed Suppression in Organic No-Till Cropping Systems in Santa Catarina, Brazil

In Santa Catarina, southern Brazil, family farmers modified the conventional no-till system by flattening cover crop mixtures on the soil surface as a strategy to reduce soil erosion and lower fluctuations in soil moisture and temperature, improve soil quality, and enhance weed suppression and crop performance. During 2007 and 2008, we conducted three experiments aimed at understanding the processes and mechanisms at play in successful organic conservation tillage systems (OCT), especially the underpinnings of ecological weed suppression, a key advantage of OCT systems over conventional no-till systems. Our results, as well as farmers observations, suggest that cover crops can enhance weed suppression and hence crop productivity through physical interference and allelopathy and also a host of effects on soil quality, fertility, and soil moisture that we did not measure. Results from the three trials indicate that the best cover crop mixture should include a significant proportion of rye, vetch, and fodder radish as these mixtures produce large biomass, and are readily killed by rolling forming a thick mulch sufficient to provide effective weed control in the subsequent vegetable crop.

Long‐Term Tillage and Poultry Litter Impacts on Soybean and Corn Grain Yield

Reduced tillage, poultry litter applications, crop rotations, and winter cover cropping are management practices that could be used with conservation tillage systems to increase yields compared to conventional monoculture systems. This study evaluated cropping sequences of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and corn–soybean rotations with wheat (Triticum aestivum L.) covers in conventional, strip, and no‐tillage (no‐till) systems, following poultry litter additions to wheat cover. The study was conducted from 1991 to 2001 on a Hartsells fine sandy loam (fine‐loamy, siliceous, subactive, thermic Typic Hapludults). Poultry litter (112 kg N ha−1) was applied to wheat each year in fall. Wheat not receiving poultry litter received equivalent inorganic N. Corn was fertilized with inorganic fertilizer in spring with 56 kg N ha−1 at planting followed by 168 kg N ha−1 3 wk after emergence; soybean received no fertilizer. Corn yields were influenced by tillage in 1991, 1992, 1993, 1994, 1996, 1997, 1998, and 2001 with conventional tillage producing greater yields, except in 1993 (strip tillage) and 2001 (no‐till). Poultry litter increased corn yield in 1991, 1997, and 1998. Crop rotations increased corn yield for all years, except 2001. Soybean yields were not impacted by differences in tillage. Crop rotations significantly impacted soybean yield in 1992, 1995, and 1998, with higher yields observed in 1992, and 1995, and lower yields in 1998. Poultry litter significantly increased soybean yield 8 of the 9 yr evaluated. This study suggests that poultry litter use for these crop rotations in conservation tillage systems could increase sustainable yield production.

Influence of no-tillage and organic mulching on tomato ( Solanum Lycopersicum L.) production and nitrogen use in the mediterranean environment of central Italy

In conservation tillage systems based on legume mulches it is important to optimize N management strategies. The present study evaluated the effect of some winter legume cover crops converted into mulches on the following no-tillage tomato ( Solanum Lycopersicum L.) yield, tomato nitrogen uptake, tomato use efficiency (NUE), soil nitrate and the apparent N remaining in the soil (ARNS) in a Mediterranean environment. Field experiments were carried out from 2002 to 2004 in a tomato crop transplanted into: four different types of mulches coming from winter cover crops [hairy vetch ( Vicia villosa Roth.), subclover ( Trifolium subterranem L.), snail medic ( Medicago scutellata L. Miller), and Italian ryegrass ( Lolium multiflorum Lam.)]; a conventional tilled soil (CT); and a no-tilled bare soil (NT). All treatments were fertilized with three different levels of nitrogen (N) fertilizer (0, 75, and 150 kg N ha −1). Cover crop above-ground biomass at cover crop suppression ranged from 4.0 to 6.7 t ha −1 of DM and accumulated from 54 to 189 kg N ha −1, hairy vetch showed the highest values followed by subclover, snail medic and ryegrass. The marketable tomato yield was higher in no-tilled legume mulched soil compared to no-tilled ryegrass mulched soil, CT, and NT (on average 84.8 vs 68.7 t ha −1 of FM, respectively) and it tended to rise with the increase of the N fertilization level. A similar trend was observed on tomato N uptake. Hairy vetch mulch released the highest amount of N during tomato cultivation followed by subclover, snail medic, and ryegrass (on average 141, 96, 90 and 33 kg N ha −1). The tomato NUE tended to decrease with the increase of the N fertilization rates, it ranged from 39 to 60% in no-tilled legume mulched soil and from −59 to 30% in no-tilled ryegrass mulched soil when compared to the CT. The soil NO 3-N content and the ARNS was always higher in the soil mulched with legumes compared to the soil mulched with ryegrass and in NT and CT. This study shows that direct transplanting into mulches coming from winter legume cover crops could be useful for improving the yield and the N-uptake in a no-tillage tomato crop. Furthermore, considering the high N content in the upper soil layer and the remaining N content in the organic mulch residues after tomato harvesting, there is a large amount of N potentially available which could be immediately used by an autumn–winter cash crop.