Under the EU Renewable Energy Directive (2009/28/EC), estimating biofuel GHG emissions is essential to gauge emissions reductions compared to fossil fuels. Within this framework, the carbon footprint (CF) was calculated for four bioethanol cropping systems: a maize-wheat-sorghum rotation without the harvest of crop residues (MWS), a maize-wheat-sorghum rotation with harvested crop residues (MWS-R), switchgrass (Sw), and continuous sweet sorghum (Ss). The estimation followed a life-cycle analysis strategy. The CF varied between 0.04 and 3.68 kg CO2-eq l - 1 ethanol. Switchgrass had the smallest CF and the highest ethanol yield per hectare (4,263 L [ha yr] - 1). However, for annual systems, Ss had the highest CF (3.68 kg CO2-eq l - 1 ethanol), 2 and 4 times larger than MWS-R and MWS systems. The soil preparation, planting, and post-planting emissions were 80% of the mean emissions in the annual cropping systems. By comparison, 60% of Sw's CF came from post-planting, and 46% from fertilizers. In Sw, soil erosion accounted for 11% of the soil organic carbon lost in the MWS-R and Ss systems. In addition, Sw was the system with the most significant carbon sequestration (-1,957 kg CO2-eq [ha yr - 1]), a value corresponding to 94% of the CF of this bioethanol cropping system.

Bioenergy is the most widely used type of renewable energy. However, an assessment of water consumption and pollution is necessary to determine the water demand of this energy source. The Uruguayan public policy to decarbonize energy sources highlighted the use of bioenergy. In this regard, we analyzed the water footprint (WF) of four bioethanol cropping systems: (1) maize-wheat-sorghum rotation without harvested crop residues (MWS), (2) maize-wheat-sorghum rotation with harvested crop residues (MWS-R), (3) continuous sweet sorghum (Ss), and (4) switchgrass (Sw). In order to assess the WF of bioethanol production, green (WFgreen) and gray (WFgray) components of crop production were calculated by considering the different volumes of water involved in evaporation, rainfall, and fertilizer pollution. Annual cropping systems (i.e., MWS, MWS-R, Ss) had the largest WFs (23.1-30.9 m(3) L-ethanol(-1)). Switchgrass had the lowest values per hectare and per liter of ethanol (12,735 m(3)(ha yr)(-1) and 3.8 m(3) L-ethanol(-1), respectively). The volume required to assimilate phosphorous (P) and nitrogen (N) fertilizers played a significant role in bioethanol cropping systems. In annual systems, WFgray was the main fraction (87%) of total WF (WFT). Averaged across all cropping systems, WFgray related to P was 13 times larger than WFgray related to N.

Besides its bioenergy potential, perennial grasses can also have positive impacts on soil quality. However, responses of soil organic carbon (SOC) and total nitrogen (TN) depend on multiple factors, including grass species selection and N and P addition. We investigated the effect of four N and P fertility treatments (control = 0 kg N + 0 kg P ha(-1) [N0P0]; 100 kg N + 0 kg P ha(-1) [N1P0]; 0 kg N + 100 kg P ha(-1) [N0P1]; 100 kg N + 100 kg P ha(-1) [N1P1] applied annually] across 9 yr in Uruguay on soil nutrient balances, C and N pools, and biomass yields of elephantgrass (EG) (Pennisetum purpureum Schum.), giant reed (GR) (Arundo donax L.), and switchgrass (SW) (Panicum virgatum L.). Across years, EG had the highest biomass yield, followed by GR and SW (18.9, 16.3, and 14.1 Mg ha(-1) yr(-1), respectively). Across species, aboveground biomass increased by 46% with N addition. Yield response to P fertilization was lower (+11%). Elephantgrass had the highest N and P negative balance. Soil organic C and TN concentration were affected by species but not by fertilizer treatments. Giant reed had the highest SOC content gain in the first 0-40 cm (540 kg C ha(-) yr(-1)), and was the only species maintaining TN content from the beginning of the study. Giant reed could be an excellent option as a bioenergy crop due to its high aboveground biomass production, and its positive impacts on SOC and TN pools.

Perennial grasses are the promising source of bioenergy in South America which could provide several environmental benefits such as reduction in the greenhouse gasses emissions and reduction of nutrients and soil losses. Our objective was to determine the impact of N and P fertilization on biomass yield, N use efficiency (NUE), apparent N recovery (ANR), and nutrient removal (NR) on three perennial grasses: elephantgrass (Pennisetum purpureum Schum.), giant reed (Arundo donax L.), and switchgrass (Panicum virgatum L.). Four fertility treatments were evaluated in a 8-year field study in northwestern Uruguay: 1. control (No fertilizer), 2.100 kg N ha(-1) year(-1), 3.100 kg P2O5 ha(-1) year(-1), and 4.100 kg N + 100 kg P2O5 ha(-1) year(-1). Across years, elephantgrass had the highest biomass yield followed by giant reed and switchgrass (18.9, 16.3, and 14.1 Mg ha 1, respectively). Biomass yield increased 46% when N fertilizer was added, compared to the control. A low response was detected for P fertilization on all grasses, probably for initial P soil content (>= 9 g kg(-1)). Elephantgrass had the highest NUE (70 kg kg(-1) N), however, it had the highest total NR on these eight years (899, 226, and 2800 kg ha 1 for N-P-K, respectively) among the grasses, indicating a potential for increased fertilization input over time. Switchgrass had the lowest average ANR (19%) and NR (334, 45, and 166 kg ha(-1), respectively). Therefore, even though switchgrass presented the lowest biomass yield, it is an excellent option as low-input bioenergies grass for temperate regions.

Sustainable rice production systems are key to food security. Diversified farming systems are essential for ecological intensification and environmental enhancement. Energy use efficiency is one of the main sustainability indicators in agroecosystems. Thus, an assessment of consumption and efficiency of energy in contrasting cropping systems can discriminate their management practices and components sustainability. The goal of this study was to evaluate the energy performance through energy return on investment (EROI) in four rice-based rotation systems that belong to a long-term experiment located in the Temperate Grassland Terrestrial Ecoregion, at the Atlantic side of South America. Rotations analyzed consisted in: a) continuous rice (Rc); b) rice-soybean (R−S); c) rice-pasture for 1.5 years (R−PS); and, d) rice-pasture for 3.5 years (R−PL). The EROI estimations considered all the inputs and outputs of energy from cradle to farm gate. The greatest EROI was observed in R–S (7.2 MJMJ−1) and the lowest energy consumption in R−PL (10,607 MJ(hayr)−1). The R−PL’s EROI (6.7 MJMJ−1) was 6.5% and 8% higher than Rc and R−PS EROI, respectively. Rotations without pastures produced 79% more energy compared with rotations including pastures. However, energy inputs of rice-pasture rotations were 40% lower than either R−S or Rc. The EROI (without animal production) of R−PS, R–S and Rc was 25%, 28% and 43% lower than the EROI of R−PL (10 MJMJ−1), respectively. For the analyzed South American ecoregion, EROI assessments of four business as usual rice production systems allowed to discriminate and hierarchize their sustainability and diversity.

When crop-pasture rotation is converted to a single fallow/soybean or winter crop/soybean annual cropping, wheat grain yield declines progressively as the annual cropping phase lengthens, regardless of the tillage system. This decline can be attributed to i) depletion of the soil nutrient supply capacity and ii) subtle but cumulative degradation of soil physical properties. The objectives of this study were to disentangle and quantify the limitations on wheat yield imposed by these processes, and to identify the cropping sequence that preserves soil quality and enables high wheat yield. Wheat was grown for two years at three nitrogen (N) fertilization rates (0, 80 and 190 kg ha(-1)) in soils after a 20-years experiment with six cropping systems. The cropping systems are crop-pasture rotations with tillage (ROT_CT) or no-till (ROT_NT), continuous cropping with no-till and high frequency of sorghum and maize (CC_NTC4) or soybean and sunflower (CC_NTC3) or winter fallow (CC_NTWF), and continuous annual cropping under conventional tillage (CC_CT). Soil quality was assessed based on chemical (soil organic carbon, total soil N concentration and potentially mineralizable N) and physical properties (field water infiltration rate and soil aggregate stability). In each system, we estimated the yield gap due to N supply (Y-g(N)) limitations and the yield gap due to soil properties other than N supply limitations (Y-g(others)), so that the total yield gap (Y-g(T)) is the sum of Y-g(N) and Y-g(others). Systems that degraded chemical and physical properties had lower yield, grain N concentration and fertilizer N use efficiency (NUEf, kg of grain kg(-1) of N added). Only two systems, ROT_NT and CC_NTC4, achieved Y-max (7.2 Mg ha(-1)). For these two systems Y-g(T) = Y-g(N). For the other systems, the percentage of Y-g(T) explained by Y-g(others) varied between 23 % and 50 %. Rotations that increased the soil N supply (N uptake with no N fertilizer) also increased NUEf. Wheat under ROT_NT reached the maximum yield obtained under CC_CT with 45 % less N fertilizer (104 vs 190 kg ha(-1)) and higher NUEf (50 vs 27 kg kg(-1)). Comparing ROT_NT and CC_NTC4 to other continuous no-till cropping systems (CQNT(WF) and CC_NTC3), the N fertilizer required was increased from 104 and 107 to 152 and 163 kg ha(-1), respectively. In conclusion, rotating annual crops under no-till is not enough to preserve soil productivity. Sustainable intensification under continuous no-till would require either re-balancing crop sequences towards crop-pasture rotations or a shift towards a lower frequency of soybean in favor of higher frequency of maize and sorghum in the summer phase of the rotation.

Los cultivos lignocelulósicos se han desarrollado como alternativa en la matriz energética. Tres especies de interés en Uruguay son Arundo donax, Pennisetum purpureum y Panicum virgatum. El objetivo fue comparar la producción de estas tres especies, cuantificar la respuesta al agregado de nitrógeno, fósforo y sus efectos en el carbono del suelo (COS) luego de 6 años. Los cultivos se instalaron en 2007 y se evaluaron desde setiembre de 2011 a agosto de 2013. Los tratamientos de fertilización consistieron en: 1. testigo sin fertilización; 2. 100 kg ha-1 de N; 3. 100 kgha-1 de P2O5; y 4. 100 kg ha-1 de N y de P2O5. La producción fue mayor en el año 2013. Arundo donax produjo significativamente más biomasa área (18,6 Mgha-1 año-1) que P. virgatum (15,6 Mg ha-1año-1) y P. purpureum (14,9 Mg ha-1año-1). La fertilización con N aumentó 50 % la producción en las tres especies, aunque en A. donax el incremento no fue significativo. No hubo respuesta a la fertilización con P. Las diferencias debido a especies o en producción de biomasa debido a la fertilización no generaron diferencias de contenidos de COS luego de 6 años. Panicum virgatum, fue la especie que presentó menor contenido de humedad (16 %), lo que es una característica favorable como materia prima para la producción de energía. Los rendimientos fueron los esperables para nuestra región, con variabilidad anual atribuible a las condiciones climáticas y se pueden aumentar al fertilizar con N.

The diversification of the energy matrix through biomass production is being evaluated in Uruguay. The species Arundo donax, Panicum virgatum and Pennisetum purpureum would be an option. The objective of this paper was to compare their biomass and energy production, with different cutting moments. The crops were planted in the spring of 2007 and evaluated from January 2012 to August 2013. Two harvest treatments were performed: cuts in January and August; and a single cut in August. Arundo donax produced 18.6 Mg ha(-1) year(-1) dry matter, more than P. virgatum and P. purpureum, which produced 15.0 and 14.6 Mg ha(-1) year(-1) dry matter, respectively. In A. donax and P. virgatum, the single cut treatment produced more than two cuts. In P. purpureum, the difference between treatments was significant in 2012, and the August cut produced more than the January cut. Arundo donax and P purpureum presented higher ash contents, and the August values were lower than the January ones. In P. virgatum there were no differences between harvests. The highest energy production was achieved with A. donax (407 GJ ha(-1) year(-1)) by harvesting it once. Panicum virgatum was the crop of the lowest energy production with a single cut (292 GJ ha(-1) year (-1)), but it had the lowest moisture (15 %) and ashes (4.9 %) content. With a single harvest, in August, a material with lower ash and moisture content would be achieved in all three species.

En Uruguay se plantea diversificar la matriz energética a través de la producción de biomasa. Las especies Arundo donax L., Panicum virgatum L.y Pennisetum purpureum L. Schumach serían una opción. Los objetivos de este trabajo fueron comparar su producción de biomasa y energía, con diferentes manejos de corte. Los cultivos se implantaron en la primavera del 2007 y se evaluaron desde enero de 2012 hasta agosto de 2013. Se realizaron dos tratamientos de cosecha: corte en enero y agosto; y un solo corte en agosto. Arundo donax produjo 18,6 Mg ha-1 año-1, más que P. virgatum y P. purpureum, que produjeron respectivamente 15,0 y 14,6 Mg ha-1 año-1 de materia seca. En A.donax y P. virgatum un solo corte produjo más que dos cortes. En P. purpureum la diferencia entre tratamientos fue significativa en 2012 y el corte de agosto produjo más que el de enero. Arundo donax y P. purpureum presentaron mayores contenidos de cenizas y los valores de agosto fueron menores a enero, en P. virgatum no hubo diferencias entre cosechas. La mayor producción de energía se logró con A. donax (407 GJ ha-1 año-1) al cosecharlo una sola vez. Panicum virgatum fue el cultivo de menor producción de energía con un solo corte (292 GJ ha-1 año-1), pero tuvo el menor contenido de humedad (15 %) y cenizas (4,9 %). Con una sola cosecha, en agosto, se lograría un material con menor contenido de cenizas y humedad, en las tres especies.

Although perennial grasses are being evaluated as a renewable source of biomass for energy production in many countries, no information exits regarding the use of these grasses in Uruguay. In 2008, an 8-year field study was implemented in western Uruguay to determine harvest frequencies for optimal biomass yield and nutrient removal for selected grass species. Elephantgrass (Pennisetum purpureum Schum.), giant reed (Arundo donax L.), and switchgrass (Panicum virgatum L.) were compared using two harvest frequencies: a single harvest after freeze (August) or two harvests (January and August) per year. We evaluated biomass yield, moisture content, nutrient concentration, and nutrient removal of these grasses. This study demonstrated the ability of these grasses to produce high biomass yields. Across years, the double harvest system significantly reduced cumulative biomass yield (~15%) compared to the single harvest of elephantgrass and giant reed; however, switchgrass had 18% more biomass yield (12.70 Mg ha−1 year−1) than the other grasses at the summer harvest but no cumulative difference was detected. The single winter harvest of elephantgrass had the highest cumulative biomass yield (140.8 Mg ha−1) and total nutrient removal (563 k N ha−1, 199 kg P ha−1, 2704 kg K ha−1) across a 6-year period among the grasses. Switchgrass may be the grass best suited for dual use systems under Uruguayan conditions because a farmer may utilize initial growth as forage while biomass regrowth is a good direct combustion o biofuel feedstock due to lower moisture content and nutrient removal compared to the other species evaluated.

The use of crop rotation systems involving winter-annual grazing can help peanut (Arachis hypogaea L.) producers increase profitability, although winter-annual grazing could result in excessive soil compaction, which can severely limit yields. We conducted a 3-yr field study on a Dothan loamy sand in southeastern Alabama to develop a conservation tillage system for integrating peanut with winter-annual grazing of stocker cattle under dryland conditions. Winter-annual forages and tillage systems were evaluated in a strip-plot design, where winter forages were oat (Avena sativa L.) and annual ryegrass (Lolium mutiflorum L.). Tillage systems included moldboard and chisel plowing, and combinations of noninversion deep tillage (none, in-row subsoil, or paratill) with/without disking. We evaluated soil water content, peanut leaf stomatal conductance, plant density, peanut yield, peanut net return, and total system annual net return. Peanut following oat increased soil water extraction (15%), stands (12%), and yields (21%) compared with peanut following ryegrass. Strict no-till resulted in the lowest yields (2.29 Mg ha(-1), 42% less than the mean) and noninversion deep tillage (especially in-row subsoil) was required to maximize water use and yields with conservation tillage. Net return from annual grazing ($185 ha(-1), USD) represented 40% of the total return for the best treatment (no-tillage with in-row subsoil following oat = $462 ha(-1)). Integrating winter-annual grazing in this region using noninversion deep tillage following oat in a conservation tillage system can benefit peanut growers, allowing extra income without sacrificing peanut yields.

Soil degradation associated with tillage is a major problem in Uruguayan agriculture. Either rotation of crops with pastures (ROT) or no-till (NT) cropping have been proposed as alternatives to minimize the impact of agriculture on soil quality. The combined impact on soil properties of ROT and NT has not been evaluated. In this study, we report results of the first 12 years of a long-term experiment established on a clay loam soil in western Uruguay. The objective was to determine the influence of conventional tillage (CT) and NT on systems under continuous cropping (CC, two crops per year) or ROT (3.5-year annual crops/2.5-year pastures). Soil samples taken at the beginning of the experiment in 1994 and in 2004 were analyzed for organic carbon (SOC), total organic carbon (TSOC) and total nitrogen content (STN), and for water-stable aggregation (WAS). Soil loss and erodibility indicators were studied using microrain simulator. With 12 years, the cumulative carbon (C) inputs of aboveground biomass were similar between tillage, but C input in CC was 50% higher than ROT. This difference was explained because 84% of the pastures dry matter was consumed by animals. Nevertheless we estimated a higher below ground biomass in ROT compared to CC systems (24.9Mgha−1 vs. 10.9Mgha−1). NT presented 7% higher SOC than CT (0–18cm) with no differences between rotation systems. While all treatments declined in STN during 12 years, ROT had 11% and 58% higher STN and WAS than CC systems, with a large impact of the pasture under CT. Runoff and erosion were minimized under NT in both rotations systems. Thus, including pastures in the rotation, or switching from CT to NT improved soil quality properties. The expected benefit of combining NT and ROT will likely require more years for the cumulative effect to be detectable in both C input and soil properties.

Integrating livestock with cotton (Gossypium hirsutum L.) offers profitable alternatives for producers in the southeastern USA, but could result in soil water depletion and soil compaction. We conducted a 3‐yr field study on a Dothan loamy sand (fine‐loamy, kaolinitic, thermic Plinthic Kandiudult) in southern Alabama to develop a conservation tillage system for integrating cotton with winter‐annual grazing of stocker cattle under rainfed conditions. Winter annual forages and tillage systems were evaluated in a strip‐plot design where winter forages were oat ( Avena sativa L.) and annual ryegrass ( Lolium mutiflorum L.). Tillage systems included moldboard and chisel plowing and combinations of noninversion deep tillage (none, in‐row subsoil, or paratill) with or without disking. We evaluated forage dry matter, N concentration, average daily gain, net returns from grazing, soil water content, and cotton leaf stomatal conductance, plant populations, and yield. Net returns from winter‐annual grazing were between US$185 to US$200 ha −1 yr −1 Soil water content was reduced by 15% with conventional tillage or deep tillage, suggesting that cotton rooting was increased by these systems. Oat increased cotton stands by 25% and seed‐cotton yields by 7% compared with ryegrass. Strict no‐till resulted in the lowest yields—30% less than the overall mean (3.69 Mg ha −1 ). Noninversion deep tillage in no‐till (especially paratill) following oat was the best tillage system combination (3.97 Mg ha −1 ) but deep tillage did not increase cotton yields with conventional tillage. Integrating winter‐annual grazing can be achieved using noninversion deep tillage following oat in a conservation tillage system, providing producers extra income while protecting the soil resource.

Soil degradation due to unnecessary tillage is the main restrain to sustainable agriculture in Uruguayan soils. The impact of crop-pasture rotation by tillage systems interaction has not been evaluated or is scare in the long-term. The experiment located in western Uruguay was established in 1993 on a clay loam (Typic Argiudol) to determine the influence of tillage systems and inclusion of perennial pasture on soil properties. Pasture (with or without perennial pasture) and tillage systems (conventional and no-till) were evaluated through 1993 to 2005. Soil samples at three depths (0-2.4, 2.4-4.8, and 4.8-7.2 in) were taken twice (1994 and 2005) and analyzed for soil organic carbon content (SOC), Total SOC (TSOC) and water stable aggregate (WAS). Interaction among inclusion of perennial pasture and tillage systems occurred on SOC and TSOC after 12- y. Conventional tillage without pasture resulted in the lowest SOC and TSOC (9% and 10% less than the overall mean, respectively). Within no-till systems, perennial pasture did not have effect on SOC content. No-till systems had more SOC and TSOC stratification than conventional ones. Within conventional tillage, continuous agriculture had 58% lower WAS than crop pasture rotation. On the other hand, within no-till systems did not have effect on WAS. No­ till systems significantly improved soil fertility indicators with or without pasture, but for conventional tillage, the inclusion of pasture was necessary.

Integrating livestock with cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.) production systems by grazing winter-annuals can offer additional income for producers provided it does not result in yield-limiting soil compaction. We conducted a 3-year field study on a Dothan loamy sand (fine-loamy, kaolinitic, thermic plinthic kandiudults) in southern Alabama, USA to determine the influence of tillage system prior to cotton–peanut planting on soil properties following winter-annual grazing. Two winter-annual forages [oat (Avena sativa L.) and annual ryegrass (Lolium mutiflorum L.)] and four tillage practices [chisel+disk, non-inversion deep tillage (paratill) with and without disking and no-till] were evaluated in a strip-plot design of four replications. We evaluated cone index, bulk density, infiltration, soil organic carbon (SOC), and total nitrogen (N). Paratilling prior to cotton or peanut planting, especially without surface soil tillage, reduced compaction initially to 40cm and residually to 30cm through the grazing period in winter. There were no significant differences in cone index, bulk density, or infiltration between forage species. No-tillage resulted in the greatest bulk density (1.65 Mg m−3) and lowest infiltration (36% of water applied), while paratilling increased infiltration in no-tillage to 83%. After 3 years, paratilling increased SOC 38% and N 56% near the soil surface (0–5cm), as compared to concentrations at the beginning of the experiment, suggesting an improvement in soil quality. For coastal plain soils, integrating winter-annual grazing in a cotton–peanut rotation using a conservation tillage system of non-inversion deep tillage (paratill) with no surface tillage can improve soil quality by reducing cone index, increasing infiltration, and increasing SOC in the soil surface.

Measuring and mapping apparent soil electrical conductivity (ECa) is a potentially useful tool for delineating soil variability. The "Old Rotation," the world's oldest continuous cotton (Gossypium hirsutum L.) experiment (ca. 1896), provides a valuable resource for evaluating soil spatial variability. The objectives of this study were to determine the relationship between soil chemical and physical properties and ECa in the Old Rotation, to determine spatial differences in these properties, and to relate differences in these properties to long-term management effects. Soils at the site classified as fine, kaolinitic, thermic Typic Kanhapludults. Soil ECa was measured at 0-30- and 0-90-cm depths (ECa-30 and ECa-90) using a Veris((R)) 3100 direct contact sensor with georeferencing. Soils were grid sampled (288 points) at close intervals (1.5 x 3.0m) for chemical properties and grid sampled (65 cells, 7.5 x 6.9 m) for soil texture. Soil organic carbon (SOC) and total nitrogen (N), extractable phosphorus (P), potassium (K), calcium (Ca), pH, buffer pH, and estimated cation exchange capacity (CECest) were measured at two depths (0-5- and 5-15-cm). Soil ECa was highly spatially correlated. The ECa-30 was more highly correlated with clay content (r = 0.58, P <= 0.01) and P(r = 0.43, P <= 0.01) than other soil properties. Total nitrogen and SOC had little or no relationship with ECa-30. Cropping systems affected chemical properties in the Old Rotation, indicating crop rotation and cover crops are beneficial for soil productivity. The relatively poor relationship between soil chemical parameters and ECa suggest that mapping plant nutrients and SOC using ECa is problematic because of strong dependence on clay content.

Soil degradation due to unnecessary tillage is the main restrain to sustainable agriculture in Uruguayan soils. The impact of crop-pasture rotation by tillage systems interaction has not been evaluated or is scare in the long-term. The experiment located in western Uruguay was established in 1993 on a clay loam (Typic Argiudol) to determine the influence of tillage systems and inclusion of perennial pasture on soil properties and crop productivity. Pasture (with or without perennial pasture) and tillage systems (conventional and no-till) were evaluated through 1993 to 2002. Soil samples at three depths (0-6, 6-12, and 1218 cm) were taken twice (1994 and 2002) and analyzed for soil bulk density (BD), soil organic carbon (SOC), total nitrogen (TN) and water aggregate stability (WAS). No-till systems presented higher soil fertility parameters (0-18 cm) than conventional tillage (13%, 11%, and 14% more TN, SOC, and TSOC, respectively) in 9 years alone. The effect of pasture had a moderate tendency to improve these soil parameters. Additionally, there were interactions between SOC and TN with depth. No-till systems had more SOC and TN stratification than conventional ones. The soil under no-till had 25% higher WAS than under conventional tillage after 9 years. No-till systems significantly increased crop productivity under continuous cropping, while under crop pasture rotation the effect was minimal. As determined from soil fertility indicators, adoption of crop-pasture rotation using no-till systems can maintain or promote sustainability for these Uruguayan soils.

Recent research in Alabama found that contract grazing of stocker cattle in winter-ea rly spring (100 to 140 days) offers re­ turns from $70 to $225 per acre (Bransby et al., 1999). Such a system is ideal for small farmers with limited capital and offe rs potential for added income for producer's doublecropping cotton behind winter grazing of annual pastures. Soil management strategies that improve soil quality include conservation tillage, cropping intensification, and inclusion of sod-based rotations. Crop rotation is critical to cropping intensification and has long been recognized as being agronomically and economically beneficial (Bayer et al ., Reeves, 1994). Short-term forage rotations with cotton not only offer reduced eco­ nomic risks for producers but also could increase soil organic carbon, improving soil quality and productivity and enhancing profitability for producers. However, winter-annual grazing results in excessive soil compaction, which can severely limit yields of double-cropped cash crops (Miller et al., 19 97). Although, in-row subsoiling at planting is frequently used to allevi­ ate soil compaction for cotton grown on sandy coastal plain soils (Raper et al., 1994), tillage requirements for cotton follow­ ing winter-annual grazing have not been researched or developed. The objective of the study was: compare two winter pasture forages under grazing and their residual effect on cotton, deter­ mine depth and degree of compaction from grazing, and determine an optimal tillage system for establishment, growth, yield and quality of cotton grown following winter annual grazing. The experiment was conduced in 2001 and 2002 at the Alabama Agricultural Experiment Station's Wiregrass Research and Ex­ tension Center in southeastern Alabama. The soil was a loamy sandy (Plinthic Paleudults). Winter forage and tillage were evalu­ ated in a strip plot design with four replications. Winter forage (main plots) were oat (Avena sativa L.) and ryegrass (Lolium multiflorum L.) planted with a no-till drill. G razing was continuous as contract grazing from January to April at a stocking rate of two head/acre. Tillage systems for cotton (subplots) included: moldboard with disk leveling, chisel and disk; and non- inversion deep tillage (none, in-row subsoiling or paratilling) with and without disking. We evaluated soil cover after grazing, plant population, cotton lint yield for 2001 and 2002, cotton quality parameters for 2001, and soil compaction in 2002. Gross returns from grazing averaged between $141 to $160/acre/year; annual production costs averaged around $75. Rye­ grass and no-tillage systems (averaged over deep tillage treatments) provided the greatest residue cover (average of 2001 and 2002 = 77%). Conventional tillage systems (moldboard, chisel and disking) resulted in the lowest residue cover. Grazing in­ creased soil compaction in the first 4 inches (9% more soil strength averaged all treatments after 60 da ys grazing) but con­ ventional tillage or non-inversion deep tillage conservation tillage systems alleviated this problem at planting. Cotton popula­ tions were 17% greater following oat than ryegrass. Strict no-tillage had the lowest plant stand, but strip-tillage, i.e., subsoiling alleviated this problem. Cotton lint yields were affected by forage species and tillage system interactions, how­ ever, strict no-tillage (934 lb cotton lint/acre averaged over years) resulted in the lowest lint yields (18% less than the mean) for both species and subsoiling was necessary to maximize yields. Cotton required more intensive tillage or more aggressive non-inversion deep disturbance (paratilling) to maximize lint yield following grazing of ryegrass compared to grazing of oat (1006 and 1120 lb acre -1 in ryegrass and 1131 and 1097 acre -1 in oat for no intensive tillage and intensive tillage respectively). With respect to fiber quality, tillage system affected only micronaire, and strict no-tillage resulted in the lowest value (38.3 vs. 40.5 averaged over treatments). There were minor effects of forage species on strength and color grade.