Years Of Conventional Tillage Research Articles

Relationship of soil fertility to biochemical properties under agricultural practices aimed at controlling land degradation

AbstractConservation agriculture (CA) is an essential strategy to avoid agricultural land degradation. It affects nutrient availability to plants and soil biological activity. However, an integral view of the effects of CA on soil fertility and biological indicators has been rarely described. Here, we examined the long‐term effects of no‐till and residue mulching on chemical properties, biological functionality indicators (enzyme activity), and nutrient availability indices of soil, and also their potential relationships, in order to provide a comprehensive view of the effects of CA on soil quality improvement. To this end, we assessed the effects after 27 years of conventional tillage (CT) and no‐tillage (NT) on a vertisol. NT increased Fe and Mn bound to organic matter when compared with CT. P and K availability in the soil surface was greater under NT than under CT by effect of more marked fertilizer stratification, and in the case of P by a decreased precipitation rate of Ca phosphates ascribed to an increased soil organic matter (SOM). The availability indices for Fe, Mn, Cu, P, and B were correlated with some enzyme activities. Our results reveal a relationship of soil biological functionality indicators, which were higher under CA, to nutrient availability to plants. This was explained at least in part by changes in soil properties, in particular an increased SOM, affecting both biological properties and nutrient availability. Thus, enzyme activities can be considered effective indicators of change in soil fertility, that is, nutrient availability to plants, a crucial factor for soil quality and functioning.

The molecular dynamics of soil humus as a function of tillage

AbstractSoil degradation processes due to intensified agriculture may be counteracted by an extended knowledge on soil humus dynamics at molecular level. Here, we show that the molecular composition of the soil Humeome changes substantially after 1 and 3 years of conventional tillage under maize cropping. Application of Humeomics sequential chemical fractionation not only separated from soil more than twice the organic carbon extracted by traditional methods, but also enabled to identify 10 times more molecular structures using GC–MS and high‐resolution ESI‐Orbitrap‐MS. The fine molecular description of the soil Humeome revealed a decrease of soil organic matter (SOM) hydrophobic protection with prolonged tillage and a potential loss of small nitrogen‐rich compounds. We showed for the first time an abundance of heterocyclic nitrogen compounds that are persistent in SOM due to a covalent binding to soil iron. The formation of organo‐Fe complexes appeared not only as a major mechanism of molecular stabilization of SOC but also as an adsorption substrate for other nitrogen‐rich soil components. The detailed molecular insight of SOM composition reached by Humeomics may become the key to develop new technologies for the control of soil carbon.

Modelling the Effect of Land Management Changes on Soil Organic Carbon Stocks in a Mediterranean Cultivated Field

AbstractLand management in agricultural lands has important effects on soil organic carbon (SOC) dynamics. These effects are particularly relevant in the Mediterranean region, where soils are fragile and prone to erosion. Increasing interest of modelling to simulate SOC dynamics and the significance of soil erosion on SOC redistribution have been linked to the development of some recent models. In this study, the SPEROS‐C model was implemented in a 1.6‐ha cereal field for a 150‐year period covering 100 years of minimum tillage by animal traction, 35 years of conventional tillage followed by 15 years of reduced tillage by chisel to evaluate the effects of changes in land management on SOC stocks and lateral carbon fluxes in a Mediterranean agroecosystem. The spatial patterns of measured and simulated SOC stocks were in good agreement, and their spatial variability appeared to be closely linked to soil redistribution. Changes in the magnitude of lateral SOC fluxes differed between land management showing that during the conventional tillage period the carbon losses is slightly higher (0.06 g C m−2 yr−1) compared to the period of reduced till using chisel (0.04 g C m−2 yr−1).Although the results showed that the SPEROS‐C model is a potential tool to evaluate erosion induced carbon fluxes and assess the relative contribution of different land management on SOC stocks in Mediterranean agroecosystems, the model was not able to fully represent the observed SOC stocks. Further research (e.g. input parameters) and model development will be needed to achieve more accurate results. Copyright © 2016 John Wiley & Sons, Ltd.

Long-term impacts of different tillage intensities on the C and N dynamics of a Haplic Luvisol

The objectives of the study were to quantify the effects of 40 years of conventional tillage (CT) and reduced tillage (RT, maximum tillage depth of 8 cm) on C and N dynamics in the surface (0–5 cm) and subsurface (5–25, 25–40 cm) soils of a silty Luvisol in a long-term trial at Garte Süd, Germany (temperate climate). Stocks of C and N and contents of microbial biomass C and N were significantly higher in the surface soil of the RT treatment than in the CT treatment. However, over the entire profile (0–40 cm), C and N stocks did not differ significantly. Cumulative net N mineralization (determined in a laboratory incubation at 13.7°C and 60% water holding capacity) was significantly higher in the surface soil of RT (58.6 mg kg−1) than that of CT (26.7 mg kg−1), whereas in the subsurface soil depths, cumulative N mineralization was higher in the CT treatment. By contrast, gross N mineralization rates did not generally differ significantly between the treatments. Overall, different tillage intensities affected C and N dynamics only slightly in the entire profile because increases in C and N stocks and N mineralization rates in the surface soil of RT were counterbalanced at greater depths.

Conservation Systems to Enhance Soil Carbon Sequestration in the Southeast U.S. Coastal Plain

Tillage systems that promote minimal surface disturbance combined with high residue cover crops can sequester C, but additional research to quantify carbon sequestration with conservation agricultural systems is needed for modelers, policymakers, and landowners. A factorial arrangement of conservation tillage (no-till, fall paratill, spring paratill, and spring strip-till) and winter cover crops (no cover, rye [Secale cereale L.], and wheat [Triticum aestivum L.]) were established in a corn/cotton (Zea mays L./Gossypium hirsutum L.) rotation from 2004 to 2009 to (i) evaluate cover crop biomass production and associated changes in soil organic carbon (SOC) to 15 cm, (ii) evaluate the potential of conservation systems to sequester SOC after years of conventional tillage, and (iii) compare measured changes in SOC to predicted soil conditioning index (SCI) values. Carbon returned to the soil each year averaged 2500 and 1340 kg C ha–1 for cover crops and corn residue, respectively. The average SOC sequestration rate in the top 15 cm was 926 ± 344 kg C ha–1 yr–1. Soil organic C values measured after 6 yr related well with predicted SCI values (r2 = 0.81; P = 0.0004). However, discrepancies between SCI and SOC values for conservation systems highlighted the need to improve the SCI for the Southeast U.S. Conservation systems following years of conventional monocropping were equivalent in their ability to sequester considerable amounts of C that will improve soil quality in the Coastal Plain of the southeastern USA.

Physical properties and organic matter of Fluvisols under forest, grassland, and 100 years of conventional tillage

Although a large number of papers deal with effects of land-use change on soil properties, less attention is directed to the long-term effects of different land-use types on soil physical properties and organic matter in the lowland ecosystems.The objective of this study is to assess the long-term cumulative effects of change in land-use type on some soil properties in the continental lowland ecosystems of Western Serbia. Three adjacent land-use types (deciduous forest, natural grassland and arable soils that have been converted from forests for more than 100years) were chosen for the study. Disturbed and undisturbed soil samples were collected from nine sites at each of the three different land-use types from the depths of 0–10, 10–20 and 20–30cm in noncarbonated Fluvisol. Conversion of forest to grassland and arable soil has led to significant decrease in total porosity (TP), infiltration rate (IR) and soil organic matter (SOM). The bulk density (BD) was lower in forest compared to the adjacent grassland and arable (ex-forest) soils. In addition, microaggregate stability, determined by the clay dispersion ratio (CDR) and aggregated silt and clay (ASC) indices, was significantly higher in forest than in grassland and arable soil. In conclusion, the results of this study indicate that removal of permanent vegetation in the conversion process from forest and grassland areas to cultivated land may lead to loss of soil productivity and serious soil degradation. Obviously, there is a need for greater attention to developing sustainable land use practices in management of these ecosystems to prevent further degradation of soils in the region.

Crop yield, P uptake and soil organic phosphorus fractions in response to short-term tillage and fertilization under a rape-rice rotation in central China

We conducted a 3-year field experiment on an Anthrosol paddy soil to investigate changes in crop yield, P uptake and soil organic phosphorus (P) fractions after 3 years of conventional tillage (CT) conversion to no-tillage (NT) under a rape - rice rotation in central China. Treatments were established following a split-plot design of a randomized complete block with tillage practice as the main plot and fertilizer as the sub-plot treatment. The yields of rape and rice ranged from 1378 to 2264 kg ha-1 and from 5895 to 9453 kg ha-1 across 3 years, respectively. Moreover, P uptake for rape and rice (aboveground) varied from 3.9 to 10.4 kg ha-1 and from 9.5 to 32.0 kg ha-1, respectively. Fertilization significantly enhanced crop yields and P uptake, but tillage did not affect the yields and P uptake. Fertilization significantly increased total P concentrations, acid phosphatase activity, Bray-1 P and labile organic P in the 0-5 cm soil layer. Compared to the CT treatments, the NT treatments had significantly higher acid phosphatase activity, total P, Bray-1 P, total organic P and organic P fractions in the 0-5 cm soil layer but lower organic P fractions in the 5-20 cm soil layer. Therefore, our results suggest that short-term NT does not enhance organic P concentrations in the 0-20 cm soil layer, and only improve P availability on the soil surface.

Effects of Topographic Feedback on Erosion and Deposition Prediction

Abstract. Soil erosion and depositional processes result in changes in topographic and soil profile properties over time. In spite of this, few current soil erosion models account for these changes. To begin to address this deficiency, a spatially distributed version of RUSLE2 was developed and used in combination with the tillage erosion model TELEM. These models were applied to a 6.6 ha research watershed near Treynor, Iowa, where runoff and sediment yield were measured from 1975 to 2002. The watershed contained a grassed waterway, and ~1 m wide grass hedges were established in 1991, with 15.4 m intervals between the grass hedges. Beginning in 1996, no-till management replaced conventional tillage management in the watershed. Using a 3 m raster DEM, concentrated flow channels that ended RUSLE2 hillslope profiles were delineated wherever contributing areas exceeded 600 m 2 . Average monthly runoff and sediment delivery to concentrated flow areas were compared with measured monthly runoff and sediment delivery at the watershed outlet. For conventional tillage, monthly runoff patterns reasonably matched observations, but measured watershed sediment yield was lower than RUSLE2-predicted hillslope sediment delivery, suggesting that sediment was deposited in the grassed waterway. Grass hedges reduced sediment yield similarly in the RUSLE2 estimates and the measured watershed sediment yield. Conversion to no-till had a much greater impact in reducing RUSLE2 estimates of hillslope erosion than it did on measured watershed sediment yield, suggesting that ephemeral gully erosion remained an important sediment source in this watershed under no-till conditions. To assess the potential influence of distributed patterns of soil erosion and deposition behind the hedges on future erosion estimates, the terrain elevation was modified by summing estimates of water and tillage erosion and deposition that would be expected from 50 years of conventional tillage. As expected, reduced slope gradients generally reduced future erosion. The lack of consideration of erosion or deposition in concentrated flow channels limited the ability of the modeling scheme to reinforce existing ephemeral gully channels.

Impacts of different management systems on the physical quality of an Amazonian Oxisol

The physical quality of Amazonian soils is relatively unexplored, due to the unique characteristics of these soils. The index of soil physical quality is a widely accepted measure of the structural quality of soils and has been used to specify the structural quality of some tropical soils, as for example of the Cerrado ecoregion of Brazil. The research objective was to evaluate the physical quality index of an Amazonian dystrophic Oxisol under different management systems. Soils under five managements were sampled in Paragominas, State of Pará: 1) a 20-year-old second-growth forest (Forest); 2) Brachiaria sp pasture; 3) four years of no-tillage (NT4.); 4) eight years of no-tillage (NT8); and 5) two years of conventional tillage (CT2). The soil samples were evaluated for bulk density, macro and microporosity and for soil water retention. The physical quality index of the samples was calculated and the resulting value correlated with soil organic matter, bulk density and porosity. The surface layers of all systems were more compacted than those of the forest. The physical quality of the soil was best represented by the relations of the S index to bulk density and soil organic matter.

Model based analysis of lateral and vertical soil carbon fluxes induced by soil redistribution processes in a small agricultural catchment

ABSTRACTSoil redistribution on arable land significantly affects lateral and vertical soil carbon (C) fluxes (caused by C formation and mineralization) and soil organic carbon (SOC) stocks. Whether this serves as a (C) sink or source to the atmosphere is a controversial issue. In this study, the SPEROS‐C model was modified to analyse erosion induced lateral and vertical soil C fluxes and their effects upon SOC stocks in a small agricultural catchment (4·2 ha). The model was applied for the period between 1950 and 2007 covering 30 years of conventional tillage (1950–1979) followed by 28 years of conservation tillage (1980–2007). In general, modelled and measured SOC stocks are in good agreement for three observed soil layers. The overall balance (1950–2007) of erosion induced lateral and vertical C fluxes results in a C loss of −4·4 g C m–2 a–1 at our test site. Land management has a significant impact on the erosion induced C fluxes, leading to a predominance of lateral C export under conventional and of vertical C exchange between soil and atmosphere under conservation agriculture. Overall, the application of the soil conservation practices, with enhanced C inputs by cover crops and decreased erosion, significantly reduced the modelled erosion induced C loss of the test site. Increasing C inputs alone, without a reduction of erosion rates, did not result in a reduction of erosion induced C losses. Moreover, our results show that the potential erosion induced C loss is very sensitive to the representation of erosion rates (long‐term steady state versus event driven). A first estimate suggests that C losses are very sensitive to magnitude and frequency of erosion events. If long‐term averages are dominated by large magnitude events modelled erosion induced C losses in the catchment were significantly reduced. Copyright © 2011 John Wiley & Sons, Ltd.

Cultivation Intensity in Relation to Organic Matter and Related Properties in a Vertisol in Southern Turkey

As most of the organic carbon (C) in the biosphere resides in the soil in the form of soil organic matter (SOM), tillage practices can potentially increase C losses to the atmosphere as carbon dioxide, thus contributing to greenhouse gases that exacerbate climate change. In the past century, conventional tillage, involving plowing and secondary cultivation, has unwittingly decreased C stocks in arable soils in North America, Europe, and Australia. The information on the effects of tillage on soil C and related properties in the Mediterranean region is scant, with evidence of resilience being even rarer. While long-term trials that directly measure tillage effects are rare in the Mediterranean, the alternative is a retrospective based on soil management history. In this study of a Vertisol in southern Turkey, we sampled sections of a field that had been intensively cultivated for about 20 years and 40 years, as well as a section left undisturbed in native vegetation for 14 years following years of conventional tillage. The SOM and total nitrogen (N) values were inversely related to cultivation intensity or duration, while the highest values were from the uncultivated site. Labile biomass C and N values followed the same trends with cultivation, whereas available P increased with cultivation time; in contrast, the percentage of water-stable aggregates decreased with cultivation duration. The study showed that such clay soils show a high degree of resilience and can recover in a relatively short time period if left uncultivated or in fallow. While preservation or set aside of arable crop land is not a viable option for farmers, reducing tillage intensity is feasible. The study suggests that minimum tillage or no-till could promote resilience and mitigate the adverse soil effects of conventional tillage that have already occurred.

Composition and stability of soil aggregates in Fluvisols under forest, meadows, and 100 years of conventional tillage

AbstractConversion of meadow and forest ecosystems to agricultural land generally leads to changes in soil structure. This comparative study presents the composition and stability of structural aggregates in humus horizons (0–30 cm) of noncarbonate silty‐clay Fluvisols in the Kolubara River Valley, W Serbia. Aggregates collected from under a native forest were compared to aggregates from meadows and arable fields which underwent crop rotation for > 100 y. The results show that size distribution and stability of structural aggregates in the humus horizons of arable soil are significantly impaired due to long‐term anthropogenization. In the humus horizons, the content of the agronomically most valuable aggregates (0.25–10 mm) decreased by a factor of ≈ 2, from 68%–74% to 37%–39%, while the percentage of cloddy aggregates (>10 mm) increased by a factor of ≈ 2, from 23%–31% to 48%–62%, compared to forest aggregates. The long‐term‐arable soil had significantly (p < 0.05) lower aggregate stability, determined by wet sieving, than meadow and forest soils. The lowest aggregate stability was found in aggregates > 3 mm. Their content is ≈ 2.5–3 times lower in arable soil (13%–16%) than in forest soil (32%–42%) at a depth of 0–20 cm. The largest mean weight diameters of dry aggregates (dMWD) with a range between 12.6 and 14.7 mm were found in arable soil, vs. 9.5–9.9 mm in meadow and 6.5–8.3 mm in forest. The arable soil had significantly lower mean weight diameters of wet‐stable aggregates (wMWD) and a lower structure coefficient (Ks) than forest and meadow soils. The dispersion ratio (DR) of arable soil was significantly higher than that of forest and meadow soils. Forest and meadow showed a significantly higher soil organic‐matter content (SOM) by 74% and 39%, respectively, compared with arable soil, while meadow uses decreased the SOM content by 57% compared with forest at a depth of 0–10 cm. In conclusion, the results showed that long‐term conventional tillage of soils from natural forest and meadow in the lowland ecosystems of W Serbia degraded soil aggregate–size distribution and stability and reduced SOM content, probably resulting in lower productivity and reduced crop yields.

Carbon and nitrogen stocks in a Brazilian clayey Oxisol: 13-year effects of integrated crop–livestock management systems

Integrated crop–livestock management systems (ICLS) have been increasingly recommended in Brazilian agroecosystems. However, knowledge of their effect on soil organic carbon (SOC) and total nitrogen (TN) concentrations and stocks is still limited. The study was undertaken to evaluate the effects of ICLS under two tillage and fertilization regimes on SOC and TN concentrations and stocks in the 0–30 cm soil layer, in comparison with continuous crops or pasture. The following soil management systems were studied: continuous pasture; continuous crop; 4 years’ crop followed by 4 years’ pasture and vice-versa. The adjacent native Cerrado area was used as a control. Under the rotation and continuous crop systems there were two levels of soil tillage (conventional and no-tillage) and fertility (maintenance and corrective fertility). The stock calculations were done using the equivalent soil mass approach. The land use systems had a significant effect on the concentrations of SOC and TN in the soil, but no effect was observed for the soil tillage and fertilizer regimes. For these two latter, some significant discrepancies appeared in the distribution of SOC and TN concentrations in the 0–30 cm layer. Carbon storage was 60.87 Mg ha −1 under Cerrado, and ranged from 52.21 Mg ha −1 under the ICLS rotation to 59.89 Mg ha −1 with continuous cropping. The decrease in SOC stocks was approximately 8.5 and 7.5 Mg ha −1, or 14 and 12%, for continuous pasture and ICLS respectively. No-tillage for 10 years after the conversion of conventional tillage to no-tillage under the continuous crop system, and 13 years of conventional tillage in continuous cropping did not result in significant changes in SOC stocks. The SOC and TN stocks in surface layers, using the equivalent soil mass approach rather than the equivalent depth, stress the differences induced by the calculation method. As soil compaction is the principal feature of variability of stocks determinations, the thickness should be avoid in these types of studies.

Soil compaction by tractor tillage in horticultural fields at Molelwane research farm, Mafikeng, North West Province

The study was prompted by concerns that soil compaction in horticultural fields at the University research farm was limiting the performance of fruit trees and vegetable crops after fifteen years of conventional tillage with tractors. Soil penetrometer resistance and bulk density were measured in the profiles of three adjacent fields (vegetable, orchard & vineyard). Over the years, tractor traffic was used in the vegetable field and orchard for seedbed preparation and weeding respectively, while the vineyard was not trafficked. Higher soil compaction was evident in the orchard and vegetable fields compared to vineyard. The location of compacted layers within the profiles was related to the nature of tractor traffic. There was subsoil compaction in the orchard and vegetable fields while shallow compaction was observed in the vineyard. Apart from tractor traffic, low organic matter content and the hardsetting behavior of the soil could have exacerbated the compaction. It was recommended that controlled traffic and deep ripping should be adopted, to not only ameliorate the existing compaction, but also sustain the productivity of the soils.

Tillage effects on maize yield in a Colombian savanna oxisol: Soil organic matter and P fractions

Soil organic matter (SOM) and phosphorus (P) fractions play a key role in sustaining the productivity of acid-savanna oxisols and are greatly influenced by tillage practices. In 1993, a long-term experiment on sustainable crop rotation and ley farming systems was initiated on a Colombian acid-savanna oxisol to test the effects of grain legumes, green manures, intercrops and leys as possible components that could increase the stability of systems involving annual cereal crops. Five agropastoral treatments (maize monoculture—MMO, maize–soybean rotation—MRT, maize–soybean green manure rotation—MGM, native savanna control—NSC and maize-agropastoral rotation—MAP) under two tillage systems (no till-NT and minimum tillage-MT) were investigated. The effects of NT and MT on SOM and P fractions as well as maize grain yield under the five agropastoral treatments were evaluated. Results showed that soil total C, N and P were generally better under no-till as compared to minimum-tilled soils. While P fractions were also generally higher under no-till treatments, SOM fractions did not show any specific trend. Seven years after establishment of the long-term ley farming experiment (5 years of conventional tillage followed by 2 years alternative tillage systems), MT resulted into moderately higher maize grain yields as compared to NT. The MGM rotation treatment had significantly higher values of maize yield under both tillage systems (4.2 Mg) compared to the NSC (2.3 Mg ha −1). Results from this study indicate that the rotational systems (maize–soybean green manure and maize-pastures) improved the soil conditions to implement the no-till or minimum tillage systems on Colombian savanna oxisol.

Carbon sequestration in two Brazilian Cerrado soils under no-till

A considerable proportion of the 200 million hectares of the Brazilian Cerrado is suitable for annual crops but little is known about the effects of tillage on the C dynamics of Cerrado soils. We evaluated the role of two representative Cerrado Oxisols (350 and 650 g clay kg −1) as sources or sinks of atmospheric C when managed under three tillage systems (conventional tillage (CT), reduced tillage (RT), and no-till (NT)) in 8- and 5-year long-term experiments. A literature review was also carried out and the mean C sequestration rates in no-till soils of tropical and subtropical regions of Brazil were calculated and compared with values for soils from temperate regions of the world. The original C stocks in 0–20 cm layer of soils under native Cerrado were higher in the clayey (54.0 Mg ha −1) than in the sandy clay loam soil (35.4 Mg ha −1), suggesting a higher physical stability of organic matter associated with variable clay minerals in the clayey Oxisol. The original C stocks of the native Cerrado soils appear not to have decreased after 23 years of conventional tillage in the sandy clay loam Oxisol, except when the soil had been subjected to erosion (15% loss of C), or after 25 years in the clayey Oxisol. Compared to conventionally tilled soil, the C stocks in no-till sandy clay loam Oxisol increased by 2.4 Mg ha −1 (C sequestration rate = 0.30 Mg ha −1 year −1) and in the clayey Oxisol by 3.0 Mg ha −1 (C sequestration rate = 0.60 Mg ha −1 year −1). The mean rate of C sequestration in the no-till Brazilian tropical soils was estimated to be 0.35 Mg ha −1 year −1, similar to the 0.34 Mg ha −1 year −1 reported for soils from temperate regions but lower than the 0.48 Mg ha −1 year −1 estimated for southern Brazilian subtropical soils. Considering the large area (about 70 million hectares) of the Cerrado which is currently used and potentially available for cropland, the adoption of no-till systems could turn the Cerrado soils into a significant sink for atmospheric C and contribute to the mitigation of global climate change.

Impact of tillage practices and burrows of a native Australian anecic earthworm on soil hydrology

Anecic earthworms are rare in Australian soils and potential benefits of introduction of exotic anecic earthworms have been suggested. The contribution of the native anecic earthworms to soil hydrology is unknown. The impact of tillage on the abundance and continuity of burrows formed by the native earthworm, Spenceriella hamiltoni (Fletcher) and consequent effect on hydrology were investigated in a red earth (Ultisol) in the Central Tablelands of New South Wales, Australia. On the permanent pasture site, the burrows occurred at a density of 157 (±65) m −2, had an average diameter of 6.0 mm (S.D.=1.6), and a predicated median length of 1.8 m. Dye infiltration studies showed that only 53% of the burrow openings were conducting and therefore available for infiltration under high rainfall conditions. It was estimated that a single burrow over an area of one square metre had an infiltration rate of 1.9 times that of the soil matrix (6.7 mm h −1 versus 3.6 mm h −1). Prediction using the rainfall characteristics of the region and the existing density of transmitting burrows under permanent pasture suggests that runoff should be a rare event (<once every 100 years). While earthworm burrow density under no-tillage (NT) cropping was similar to that found under permanent pasture, 3 years of conventional tillage (CT) involving discing reduced transmitting burrows by nearly 90% (to only 10 m −2) and this had the effect of a 8.3-fold reduction in maximum infiltration rate of the soil, thereby significantly increasing the likelihood of runoff and erosion.

Effect of No-Tillage and Conventional Tillage Systems on the Chemical Composition of Soil Solid Phase and Soil Solution of Brazilian Savanna Oxisols

No-tillage (NT) cropping systems are becoming increasingly important in the Brazilian savanna. To evaluate their sustainability we compared soil chemical properties in 1- to 3-year-old NT systems following 9 to 11 years of conventional tillage (CT) with systems where CT was continuously in place for 12 years. In the rainy season 1997/98, NT was cropped with soybean and CT with corn while in the rainy season 1998/99 both systems were cropped with soybean. Soil solid phase samples were taken from the 0-0.15, 0.15-0.3, 0.3-0.8, 0.8-1.2, and 1.2-2 m layers on three spatially separated plots under each of NT and CT. Soil solution samples were collected weekly at 0.15, 0.3, 0.8, 1.2, and 2 m soil depth during two rainy seasons (14 October to 28 April 1997/98 and 1998/99). We determined soil moisture contents, pH, the concentrations of exchangeable cations, the electrical conductivity (EC) of the soil solution, and the concentrations of Al, C, Ca, Cl - , K, Mg, Mn, Na, NH 4 + , NO 3 - , P, S, and Zn in solid soil and soil solution samples. Differences in soil solid phase properties and moisture content between NT and CT were small, few were significant. Under NT, the average solution pH was significantly lower (5.5), Al (26 tag 1 -1 ), Mn (17 μg 1 -1 ) and total organic C concentrations (TOC, 6.5 mg 1 -1 ) were higher than under CT (pH: 6.0, Al: 14μg 1 -1 , Mn: 14μg 1 -1 , TOC: 5.5 mg 1 -1 ). Irrespective of the different crops in the first rainy season, under NT, the EC (205 μS cm -1 ), Ca (17 mg 1 -1 ), and Mg (2.9 mg 1 -1 ) concentrations at 0-0.3 m depth were lower than under CT (EC: 224 μS cm -1 , Ca: 25 mg 1 -1 , Mg: 5.6 mg 1 -1 ). At 1.2-2 m depth, the reverse order was observed (EC: 124 μS cm -1 under NT and 84 μS cm -1 under CT, Ca: 11 mg 1 -1 under NT and 7.5 mg 1 -1 under CT, Mg: 3.1 mg 1 -1 under NT and 1.8 mg 1 -1 under CT). Our results indicate that enhanced soil acidification because of higher rates of organic matter mineralization and a more pronounced nutrient leaching because of increased pore continuity may limit the sustainability of NT.

Crop Rotations and Nitrogen Fertilization to Manage Soil Organic Carbon Dynamics

Sustainability is influenced in many production systems by the variation of soil organic C (SOC) content and dynamics, and crop rotations. We hypothesized that arable layer SOC under conventional tillage can be managed through the amount of residue C (RC) returned to the soil as affected by tillage and fertilization. Soil organic C dynamics of a complex of Typic Argiudoll and Petrocalcic Paleudoll soils under conventional tillage between 1984 and 1995 at Balcarce, Argentina was studied for 16 crop sequences. Crops included were spring wheat (Triticum aestivum L.), soybean [Glycine max (L.) Merr.], sunflower (Helianthus annuus L.), and corn (Zea mays L.). Eleven years of conventional tillage decreased SOC 4.1 to 8.8 g kg−1 without supplemental N and 2.8 to 7.2 g kg−1 when N fertilizer was applied. Soil organic C loss increased when soybean (1.2 Mg RC ha−1 yr−1) was present in the sequence and decreased when corn (3.0 Mg RC ha−1 yr−1) was present. The amount of RC returned by the sequences correlated with SOC in 1995 and with SOC at equilibrium , but the sequences with two summer crops (soybean, sunflower, or corn) every 3 yr showed lower SOC in 1995 (28.9–33.8 g kg−1) and at equilibrium (24.0–34.4 g kg−1) than sequences with none or one summer crop (29.7–35.0 g kg−1 either in 1995 or at equilibrium) for the same range of RC (1.4–2.6 Mg RC ha−1 yr−1). The difference between sequences in the relationship between RC and SOC were attributed to tillage timing. Under conventional tillage, arable layer SOC can be managed through the selection of the crops in the rotation and N fertilization, but the timing and intensity of tillage have to be taken into account.

Nonpoint source (NPS) model simulation of tillage effects on water quality

Three agricultural non‐point source (NPS) models, GLEAMS, EPIC, and WEPP, were used to simulate the effects of two tillage systems on runoff and losses of sediment, N, and P from a field‐sized watershed in the Tennessee valley region of Alabama. The field was cultivated with three years of conventional tillage (CvT) followed by three years of conservation tillage (CsT) of cotton. GLEAMS and EPIC underpredicted NO3‐N losses in runoff for both tillage systems. EPIC simulated tillage effects on soluble‐P losses better than GLEAMS. However, EPIC poorly predicted annual organic‐N and P losses in sediment, mainly due to overpredicted sediment losses. The GLEAMS prediction of annual organic‐N and P losses in sediment was more acceptable than that of EPIC. WEPP predicted sediment losses close to observed data for both tillage systems. However, EPIC simulation of sediment loss was not as accurate, because its limited definition of watershed profile prevented the model accounting for sediment deposition on the watershed depressional area.