Continuous No-tillage Research Articles

Labile and Recalcitrant Carbon in Crop Residue and Soil under No-Till Practices in Central Region of Argentina

We evaluated the effects of the amount and type of C compounds (labile/recalcitrant) of crop residues on the soil organic matter (SOM) components under no-tillage practices in semiarid region of Argentina, with the aim of establishing criteria for sustainable agriculture. Five agricultural situations were evaluated: soybean/wheat rotation (wheat crop and at bare fallow); soybean monoculture; soybean/maize rotation and maize/wheat/potato rotations with biannual ploughing. In each situation crop residues and soil samples were collected. In residue samples, biomass (total and compo- nents), organic carbon, insoluble fibers, and soluble C compounds were evaluated. In soil samples total SOM, non-humic substances (NHS), humic substances (HS), humic (HA), and fulvic acids (FA) were analyzed. The total biomass and its components differed among situations and were lower in the situation with plough, while the fiber contents were higher in situations that includes wheat crop. Total SOM, NHS, HA content were higher in the plowed situation (57.20 g kg -1 , 47.30 g kg -1 , 7.80 g kg -1 respectively). We concluded that the total SOM quantity in continuous no-tillage is not affected by the different crop rotations and sequences, but the HA quantity (stable SOM) seems to be favored by the high recalcitrant compounds amount of the crop residues (particularly wheat). For these reasons, the following criteria for sustainable agri- culture management in semiarid zones can be suggested: a) continuous no-tillage utilization; b) summer crop annual rota- tions; and c) winter wheat crop instead of bare fallow.

Increasing Crop Rotation Diversity Improves Agronomic, Economic, and Environmental Performance of Organic Grain Cropping Systems at the USDA‐ARS Beltsville Farming Systems Project

Increasing Crop Rotation Diversity Improves Agronomic, Economic, and Environmental Performance of Organic Grain Cropping Systems at the USDA‐ARS Beltsville Farming Systems Project

Changes in Soil Organic Carbon and Nitrogen Fractions with Duration of No‐Tillage Management

The influence of no-tillage (NT) management on labile soil N is poorly defined. To quantify changes in soil C and N fractions with duration of NT, we sampled Kempsville sandy loam (fine-loamy, siliceous, subactive, thermic Typic Hapludults) soils in the Coastal Plain of Virginia from farm fields that had similar cropping histories and nutrient management but varied in amount of time in continuous NT from 0 to 11 yr. At the 0- to 2.5-cm soil depth, there was a linear increase with time in NT for total organic C, total organic N, particulate organic matter (POM)-C, POM-N, POM-C/total organic C, POM-N/total organic N, hydrolyzable unidentified-nitrogen (hUN-N) and NH4–N (hNH4–N), and various biochemical classes of pyrolysate compounds determined by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). At the 2.5- to 7.5-cm soil depth, there was a linear increase with time in NT for total organic C and N, hUN-N, hNH4–N, hydrolyzable α amino acid-nitrogen (AA-N) and amino sugar-nitrogen (AS-N) only; these rates of increase were lower than at the 0- to 2.5-cm depth. No measured C and N fractions increased at the 7.5- to 15-cm soil depth but POM-C/total organic C and POM-N/total organic N declined (p ≤ 0.10) at this depth, suggesting that the recalcitrance of C and N fractions increased at 7.5- to 15-cm in 11 yr. These patterns indicate that a new equilibrium level for these C and N fractions had not been reached but that their stratification of C and N pools with soil depth increased during 11 yr in NT. At the 0- to 2.5-cm depth, the labile N fractions, AA-N and AS-N approached or reached new equilibrium levels within 11 yr. Since these fractions are derived from soil microbial and plant biomass, the initial rapid increase in these fractions likely reflects an increase in N immobilization in the short term (3–6 yr) following adoption of NT. After this initial transition period, levels of AA-N and AS-N approach new elevated equilibrium levels, which would be reflected in a higher net N mineralization rate than under the previous tilled system. These results indicate that absolute values for labile soil N fractions such as AA-N and AS-N may not be readily interpretable with respect to soil fertility recommendations without considering whether these values are changing over time or are at an equilibrium level. Different patterns of change in POM-N vs. AA-N and AS-N indicate that these labile N fractions are distinct and may provide different types of information with respect to quantifying changes in soil fertility with time under NT.

Impact of Biosolids and Tillage on Soil Organic Matter Fractions: Implications of Carbon Saturation for Conservation Management in the Virginia Coastal Plain

In the Virginia Coastal Plain, growers have practiced rotational no-tillage (RT) and continuous no-tillage (NT) for more than 30 yr to reduce runoff and improve soil quality. We sampled 48 grower's fields representing three soil series varying in texture and managed under RT and NT. Half the fields received biosolids (S) application in 2001. We evaluated soil organic carbon (SOC) stocks, C distribution, and potential saturation limits in particulate organic matter (POM) and silt+clay (<53 μm) fractions in three soil series with different silt+clay protective capacities. Across the three soil series, NT increased SOC stocks compared to RT (33.2 ± 1.8 vs. 28.3 ± 0.9 Mg C ha−1) and S compared to no biosolids application (33.1 ± 1.8 vs. 28.4 ± 1.1 Mg C ha−1) for the 0- to 20-cm depth. Tillage and biosolids effects on SOM fractions were only significant for POM and showed no evidence of C saturation with statistical modeling. Silt+clay-associated C showed no tillage or S effects and in one soil were better fit with a C saturation compared to a linear model, indicating saturating dynamics. In two soils, measured silt+clay C content was significantly greater than the calculated 1:1 and 2:1 protective capacity, also suggesting silt+clay saturation. Since these soils are near or exceed their silt+clay protective capacity, additional C storage will primarily occur in aggregate and POM C pools that are sensitive to subsequent changes in management practice. Best management practices that decrease soil disturbance and increase C input are crucial to these agroecosystems where even single tillage events can cumulatively cause significant C loss.

Short-term effects of conservation management practices on soil labile organic carbon fractions under a rape–rice rotation in central China

Conservation management practices, such as no-tillage (NT) or crop residue mulch, alter soil organic carbon (C) lability, thus affecting soil quality. However, inconsistent effects of conservation management practices on soil labile organic C have been commonly reported. We hypothesized, however, that conservation management practices can improve soil labile organic C fractions and then C management index (CMI) and soil quality. Thus, our objective was to quantify labile organic C contents on a clay loam soil (Anthrosols, World Reference Base for Soil Resources) 3 years after implementing four tillage/crop residue management treatments under a rice Liangyoupeijiu (Oryza sativa L.)–rape Huayouzaliuhao (Brassica napus) rotation in Wuxue City of central China. The experiment included four treatments: (1) single conventional tillage (CT) without crop residue (rape with NT–rice with CT); (2) double CT without crop residue (rape with CT–rice with CT); (3) double NT without crop residue (rape with NT–rice with NT); and (4) double NT plus crop residue (rape with NT+rice residue mulch–rice with NT+rape residue mulch). Five soil organic C fractions were determined from 0 to 30cm layer in October 2009 (3 years after a rape–rice double crop rotation). Total organic C, microbial biomass C, dissolved organic C, particulate organic C, easily oxidizable C, and water stable aggregation were measured. A CMI was also calculated. The concentrations of total organic C, microbial organic C, dissolved organic C, and particulate organic C under the double NT plus crop residue treatment were 1.07–1.17, 1.20–1.26, 1.08–1.30 and 1.17–1.76 times higher than those under the other three treatments. The total organic C and labile organic C contents under the double NT with or without crop residue treatment were generally higher at 0–5cm than at greater sampling depths. The proportions of 0.5–2mm water-stable aggregates at the 0–5cm depth under the double NT with or without crop residue treatment were significantly greater (P<0.05) than those under the single or double CT without crop residue treatment, but lower (P<0.05) at the 5–30cm depth. Soil labile organic C fractions were positively correlated with each other. The greater C pool index (CPI) at the 0–5cm depth observed under double NT with or without crop residue treatment compared to single or double CT without crop residue treatment led to greater CMI at the same depth. However, CMI at the 5–30cm depth was lower for the double NT with or without crop residue treatment compared to the single or double CT without crop residue treatment. Thus, our results indicated that soil labile organic C fractions were only sensitive to changes in management practices in the upper soil profile, and that short-term effects of continuous NT or NT with crop residue mulch in a rape–rice rotation system appeared to only improve soil quality in the upper soil profile. Based on these results, we suggested that greater quantities of labile organic C can be concentrated in the 0–30cm soil layer of a soil under rape–rice rotation by more sustainable practices than those currently being used in central China.

Variação nos atributos do solo em sistemas de manejo com adição de cama de frango

A cama de frango constitui-se em adubo orgânico com boas características agronômicas, podendo ser bom condicionador das propriedades físicas do solo. Assim, o objetivo deste trabalho foi verificar alterações nas propriedades do solo em sistemas de plantio direto com adição de cama de frango. O estudo foi feito em três camadas (0-10, 10-20 e 20-30 cm) e três repetições, em Latossolo Vermelho-Amarelo distrófico submetido a plantio direto contínuo nos últimos anos, com rotação principalmente de soja, milho, algodão e milheto. Os tratamentos foram: sistema com adubação mineral (S2), com adição de cama de frango crua (S3), com adição de cama de frango compostada (S4) e uma área não manejada de Cerrado nativo (S1). Os sistemas de manejo induziram em ordem crescente - S4, S2, S3 - à degradação dos atributos do solo em relação à vegetação nativa (S1), e isso foi quantificado pelos menores valores de carbono total, diâmetro e estabilidade de agregados, macroporosidade e condutividade hidráulica saturada e pelos maiores valores de densidade e resistência do solo à penetração e microporosidade. A cama de frango crua revelou-se mais vantajosa na disponibilidade de nitrogênio total e menos eficiente em garantir a qualidade física do solo. A cama de frango compostada proporcionou atributos mais semelhantes às condições naturais.

No tillage in rainfed Aragon (NE Spain): Effect on organic carbon in the soil surface horizon

Conservation tillage has been encouraged as a management alternative to preserve soil and water resources in semiarid Aragon (NE Spain). In fact, its adoption by farmers, and especially of no tillage (NT) systems, has increased in recent years. However, little information concerning the soils on which these techniques are applied is available for this region. The objective of this study was to assess the potential of NT to increase organic carbon content at the soil surface (0–20 cm) in rainfed Aragon. To this aim, 22 pairs of adjacent farm fields under NT and conventional tillage (CT) were compared in different cereal production areas. The fields were under continuous NT between 5 and 19 years but half were over 10 years. Soil organic carbon (SOC) in NT ranged from 7.06 to 18.53 g kg −1 (0–20 cm depth) and was higher than 12 g kg −1 in nearly 30% of the fields. These contents represented between 8% less (only one case) and 55% more SOC under NT than under CT with an average gain of 20% in favour of NT. The highest SOC contents were found in the NT fields of longer duration (>10 years) and/or managed with practices that enhance the return of more crop biomass to the soil (complete residue return, cropping intensification and manure application). The identification of the current management practices used by farmers has allowed us to know the diversity of the NT-based cropping systems and the reality of the conservation agriculture in our region. Overall, results from this on-farm study indicate that NT can be recommended as a viable alternative to CT to increase organic carbon at the soil surface in cereal production areas of Aragon.

Tillage and crop residue effects on rainfed wheat and maize production in northern China

Dryland farming in the dry semi-humid regions of northern China is dominated by mono-cropping systems with mainly maize (Zea mays L.) or wheat (Triticum aestivum), constrained by low and variable rainfall, and by improper management practices. Addressing these problems, field studies on tillage and residue management for winter wheat and spring maize were conducted at 4 sites in Linfen, Tunliu and Shouyang (Shanxi province) and Luoyang (Henan province). These studies (a.o.) explored the impacts of different tillage and residue application methods on soil physical conditions, water storage, water use, water use efficiency (WUE) and crop yields of wheat and maize. An analysis of the results of these studies is presented. Conservation tillage, comprising no-till as well as reduced tillage practices (subsoiling, deep ploughing) showed benefits which were more prominent in combination with residue application. Benefits compared to conventional tillage were found in the form of improved soil physical conditions, such as higher topsoil bulk densities but lower subsoil bulk densities. This resulted in a better water storage during the summer fallow or rainy season in winter wheat fields, and a better water conservation and soil protection in spring maize fields. Compared to conventional methods, reduced tillage gave yields around 13–16% higher in spring maize and round 9–37% higher in winter wheat. Yields under no-till were very close to those from conventional methods. Surface application of crop residue for maize was found to increase the risk for delayed seedling emergence, because of low temperatures, leading to a recommendation for incorporation of residue in combination with reduced tillage. For winter wheat, subsoiling in combination with straw mulching after harvest in summer every other two or three year, and no-till seeding is a promising practice for sandier soils and low rainfall conditions. For heavier clay loam soils, deep ploughing with straw mulching after wheat harvest in summer every other two or three year, and no-till seeding practice is recommended. For spring maize, deep ploughing with straw and fertilizers incorporation after harvest in fall, and no-till seeding practices are recommended. Subsoiling or no-till with residue mulching after harvest in fall, and no-till seeding practices in spring are also promising practices, the latter only in situations where low spring temperatures are not a problem. Continuous no-till is not recommended.

Nitrogen dynamics in soil management systems: II - mineralization and nitrification rates

Nitrogen is the main limiting factor in crop productivity and thereby soil management systems may change the mineralization and nitrification rates. In an experiment on soil management systems implemented in 1988 at the experimental station Fundação ABC, Ponta Grossa, in the central South region of the State of Paraná, inorganic N dynamics were examined to find a soil management strategy with a view to a sustainable environment. The objective of this study was to calculate the net mineralization and nitrification rates of soil N and the correlation with soil pH under management systems. Randomized complete block design was used, in split plots, in three replications. The following soil management systems (SMSs) were adopted in the plots: 1) conventional tillage (CT); 2) minimum tillage (MT); 3) no-tillage with chisel plow every three years (NT CH); and 4) continuous no-tillage (CNT). To evaluate the dynamics of inorganic N, samples were collected from sub-plots at different times (11 sampling times - T1 to T11). In the CNT and NT CH, the net mineralization rates were higher in the MT and CT systems in the 0-2.5 cm soil layer, while the nitrification rate was higher in the 2.5-5 cm layer. Soon after implementing the white oat management, the mineralization and nitrification rates in all soil layers were higher in the MT and CT systems. In the period of soybean development, in the 0-2.5 and 2.5-5 cm soil layers, the mineralization and nitrification rates were higher in the CNT and NT CH than in the MT and CT systems.

Nitrogen dynamics in soil management systems. I - flux of inorganic nitrogen (NH4+ and NO3-)

In agricultural systems the N-NH4+ and N-NO3- contents is significantly affected by soil management. This study investigated the dynamics of inorganic nitrogen (N; NH4+ and NO3-) in an experimental evaluation of soil management systems (SMSs) adopted in 1988 at the experimental station of the ABC Foundation in Ponta Grossa, in the Central South region of the State of Paraná. The objective of this study was to evaluate the changes in N-NH4+ and N-NO3- flux in the surface layer of a Red Latosol arising from SMSs over a 12-month period. The experiment was arranged in a completely randomized block design in split plots, in three replications. The plots consisted of the following SMSs: 1) conventional tillage (CT); 2) minimum tillage (MT); 3) no-tillage with chisel plow every three years (NT CH); and 4) continuous no-tillage (CNT). To evaluate the dynamics of inorganic N, the subplots represented samplings (11 sampling times, T1 - T11). The ammonium N (N-NH4+) and nitric N (N-NO3-) contents were higher in systems with reduced tillage (MT and NT CH) and without tillage (CNT) than in the CT system. In the period from October 2003 to February 2004, the N-NH4+ was higher than the N-NO3- soil content. Conversely, in the period from May 2004 to July 2004, the N-NO3- was higher than the N-NH4+ content. The greatest fluctuation in the N-NH4+ and N-NO3- contents occurred in the 0-2.5 cm layer, and the highest peak in the N-NH4+ and N-NO3- concentrations occurred after the surface application of N. Both N-NH4+ and N-NO3- were strongly correlated with the soil organic C content, which indicated that these properties vary together in the system.

Implications of the variability in soil penetration resistance for statistical analysis

Soil penetration resistance (PR) is a measure of soil compaction closely related to soil structure and plant growth. However, the variability in PR hampers the statistical analyses. This study aimed to evaluate the variability of soil PR on the efficiency of parametric and nonparametric analyses in indentifying significant effects of soil compaction and to classify the coefficient of variation of PR into low, medium, high and very high. On six dates, the PR of a typical dystrophic Red Ultisol under continuous no-tillage for 16 years was measured. Three tillage and/or traffic conditions were established with the application of: (i) no chiseling or additional traffic, (ii) additional compaction, and (iii) chiseling. On each date, the nineteen PR data (measured at every 1.5 cm to a depth of 28.5 cm) were grouped in layers with different thickness. In each layer, the treatment effects were evaluated by variance (ANOVA) and Kruskal-Wallis analyses in a completely randomized design, and the coefficients of variation of all analyses were classified (low, intermediate, high and very high). The ANOVA performed better in discriminating the compaction effects, but the rejection rate of null hypothesis decreased from 100 to 80 % when the coefficient of variation increased from 15 to 26 %. The values of 15 and 26 % were the thresholds separating the low/intermediate and the high/very high coefficient variation classes of PR in this Ultisol.

Tillage and Lime Rate Effects on Soil Acidity and Grain Yields of a Ten-Year Corn–Soybean Rotation

Reduced tillage and no-tillage systems provide shallow incorporation of surface applied materials at best. Due to concern of over-liming the surface of agricultural soils, producers either reduce lime rates (and apply more often) or perform some sort of soil inversion to mix the lime deeper into the soil profile. The objective of the authors in this field study was to evaluate the effects of tillage, lime rate, and time of limestone application on corn and soybean growth, and assess the changes in soil acidity to an already acidic soil. Treatments consisted of a no lime check, two no-tillage systems with either a 4.5 ton ha−1 lime application every two years or an annual application of 450 kg pelleted lime ha−1, a continuous annual chisel tillage system with a 9.0 ton ha−1 lime application every four years, and two inversion systems utilizing a rotary tiller (Howard Rotovator) where 9.0 ton lime ha−1 was mixed into the soil followed by either continuous chisel tillage or continuous no-tillage. Inversions occurred in 1999, 2003, and 2007. Soil samples were collected annually in increments of 5 cm to a 30 cm depth for pH determinations. After 10 years, the continuous chisel system increased soil pH in the top 20 cm and had grain yields comparable to the no-tillage system, but not different than the no lime treatment. The no-tillage system increased the pH in the surface 15 cm of soil. The inversion treatments after soybean mixed the lime more thoroughly in the top 15 cm than inversion after corn and also increased the pH to a deeper depth. The pelleted lime had no effect on soil acidity. Soybean yields were affected by lime treatment with the no lime and pelleted lime having the lowest yields. This is most likely due to manganese (Mn) toxicity with these treatments. There was no perceived benefit of inversion of the soil with no-till or chisel systems.

Organic matter distribution in aggregate sizes of a mollisol under contrasting management

Total and particulate organic matter content in different aggregate sizes can be used as an indicator of land use effect. We hypothesized that tillage reduction increases total (SOC) and particulate soil organic C (POC) contents and the stability of larger aggregates of high-SOC-content Mollisols. Three management systems (continuous pasture (Pp), and continuous cropping under conventional tillage (CT) and notillage (NT)) were evaluated. Oven dried soil samples (0-5 and 5-20 cm), were wet sieved through 2000, 250 and 50 µm sieves after immersion (IW) and capillary (CW) wetting. Particulate organic matter (>50 µm) was separated in both the whole soil and in each aggregate fraction, SOC and mineral associated organic C contents were determined, and POC was calculated by subtraction. Reduced soil disturbance (Pp and NT) yielded more SOC and POC in the whole soil and macroaggregates with higher stability (Pp>NT>CT). Under Pp, macroaggregates showed the highest SOC and POC. Under NT, macroaggregates showed higher SOC and POC and aggregate stability than CT though lower than Pp. Less tillage-induced disruption (Pp and NT) led to higher SOC and POC contents in more stable macroaggregates but continuous no-tillage appeared not to be enough to reverse the effects of long lasting conventional management practices on these Mollisols.

Long-term rice-based cropping system effects on near-surface soil compaction

Irrigated rice (Oryza sativa L.) production is as-sociated with frequent cycling between anaero-bic and aerobic conditions, which can lead to a greater rate of soil organic matter (SOM) de-composition, thus potentially increasing soil bulk density (BD) over time. A study was con-ducted in the Mississippi River Delta region of eastern Arkansas, USA to evaluate the long-term effects of rice-based crop rotations, tillage [conventional tillage (CT) and no-tillage (NT)], soil fertility regime (optimal and sub-optimal), and soil depth (0-10 and 10-20 cm) after 10 years of consistent management on near-surface soil compaction, as measured by BD. Soil BD was greater under NT than CT in the top 10 cm, but was similar between NT and CT in the 10- to 20-cm depth interval. Soil BD differed among common rice-based cropping systems with corn, soybean, and winter wheat, but few consistent trends were evident. It appears that, even after 10 years of continuous CT or NT rice production on a silt-loam soil, substantially increased near-surface soil BD has not occurred to the point where soil compaction would be a likely culprit responsible for a reduced early season stand establishment or crop yield differences among rice-based copping systems.

Changes of soil physical and chemical properties under continuous no-tillage and no-ridge cultivation of soybean in paddy converted field

Changes of soil physical and chemical properties under continuous no-tillage and no-ridge cultivation of soybean in paddy converted field

Soil Microbial Community Change and Recovery after One‐Time Tillage of Continuous No‐Till

Continuous no‐till (NT) results in soil improvements, primarily in the surface 5 cm of soil. One‐time tillage may improve NT systems by inverting surface soil with less improved deeper soil. Research was conducted to determine the change in abundance of soil microbial groups after a one‐time tillage of NT and their recovery dynamics. Experiments were conducted under rainfed corn (Zea mays L.) or sorghum [Sorghum bicolor (L.) Moench] rotated with soybean [Glycine max (L.) Merr.] in eastern Nebraska with one‐time moldboard plow (MP) and mini‐moldboard plow (mini‐MP) tillage compared with continuous NT. Fatty acid methyl ester (FAME) profiles were used as biomarkers of soil microbial groups. The biomass of microbial groups within the soil profile was affected by tillage treatment, soil depth, and time after one‐time tillage. Soil microbial biomass under NT was greatest at the 0‐ to 5‐cm depth with 50% less in the 5‐ to 20‐cm depth, and least in the 20‐ to 30‐cm depth. Microbial group biomass was decreased by one‐time MP tillage, and generally by mini‐MP tillage, compared with NT. On an equivalent soil mass basis, the quantity of the arbuscular mycorrhizal (AM) biomarker C16:1(c11) in the second year after tillage was 22% less for tilled treatments compared with NT. In contrast, the fungal biomarker C18:2(c9,12) was 6% more in the second year after tillage for tilled compared with NT. Tillage affected biomass and recovery of microbial groups differently, with all except AM returning to the NT microbial biomass levels within 1 to 3 yr.

Soil nitrogen conservation with continuous no-till management

Tillage management is an important regulator of organic matter decomposition and N mineralization in agroecosystems. Tillage has resulted in the loss of considerable organic N from surface soils. There is potential to rebuild and conserve substantial amounts of soil N where no-till management is implemented in crop production systems. The objectives of our research were to measure N conservation rate with continuous no-till management of grain cropping systems and evaluate its impact on mineralizable and inorganic soil N. Samples were collected from 63 sites in production fields using a rotation of corn (Zea mays L.)—wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.)—double-crop soybean (Glysine max L.) across three soil series [Bojac (Coarse-loamy, mixed, semiactive, thermic Typic Hapludults), Altavista (Fine-loamy, mixed semiactive, thermic Aquic Hapludults), and Kempsville (Fine-loamy, siliceous, subactive, thermic Typic Hapludults)] with a history of continuous no-till that ranged from 0 to 14 yrs. Thirty-two of the sites had a history of biosolids application. Soil cores were collected at each site from 0–2.5, 2.5–7.5 and 7.5–15 cm and analyzed for total N, Illinois soil N test-N (ISNT-N), and [NH4 + NO3]-N. A history of biosolids application increased the concentration of total soil N by 154 ± 66.8 mg N kg−1 (310 ± 140 kg N ha−1) but did not increase ISNT-N in the surface 0 – 15 cm. Continuous no-till increased the concentration of total soil N by 9.98 mg N kg−1 year−1 (22.2 ± 21.2 kg N ha−1 year−1) and ISNT-N by 1.68 mg N kg−1 year−1 in the surface 0–15 cm. The implementation of continuous no-till management in this cropping system has resulted in conservation of soil N.

Impacts of long-term and recently imposed tillage practices on the vertical distribution of soil organic carbon

Although many studies suggest that no-tillage (NT) increases soil organic carbon (SOC) within the soil profile relative to mouldboard ploughing, other studies indicate that no net change occurs. The latter studies suggest that NT only stratifies the SOC, where a near-surface increase in SOC is offset by a concomitant decrease in the subsurface. We examined the SOC distribution and stocks in a cool, humid Brookston clay (Typic Argiaquoll) soil under four soil management systems with a corn–soybean rotation. The objectives of this study were to compare the profile distribution and total amount of SOC under long-term (21 years) NT and mouldboard plough (MP) tillage with the changes that occur over 8 years when 13-years continuous NT is converted to MP, and when 13-years continuous MP is converted to NT. In the top 5 cm of soil, the long-term NT management accumulated greater SOC compared with the long-term MP treatment. However, this near-surface increase was offset by lower SOC concentrations in the 10–20 cm depth, resulting in similar total amounts of SOC stored in 0–20 cm for both long-term NT and MP. The SOC stratification that existed after 13 years of NT management was eliminated with one mouldboard ploughing operation, however the total SOC content in the plough layer of the new-MP treatment remained relatively constant over the subsequent 8 years. Soil organic carbon stratification was evident in the new no-tillage treatment 3 years after the cessation of tillage. The continuous build-up of SOC in the surface of new-NT soils was associated with no change in the total amount of SOC in the plough layer relative to long-term NT. This implies that the diminution of SOC in the 10–20 cm depth was at the same rate as the accumulation of SOC in the 0–5 cm depth. Although there was no net effect of tillage on total carbon stocks in this fine-textured soil, SOC stratification required several years to build-up after adoption of NT, but only a single year to destroy under MP.

INFLUÊNCIA DE SISTEMAS AGRÍCOLAS NA RESPOSTA DO FEIJOEIRO (Phaseolus vulgaris L.) IRRIGADO À ADUBAÇÃO NITROGENADA EM COBERTURA

In recent years emphasis has been placed upon the systemic approach of agricultural practices to increase food production. Common bean ( Phaseolus vulgaris L.) has demonstrated to be a suitable crop species as a component of several production systems as it has been shown on the irrigated areas of the Brazilian Central Region. However, general crop management techniques have to be adjusted as a function of the different crop systems available and nitrogen fertilization is one of those. To confirm this hypothesis, common bean response to nitrogen application was evaluated using cultivar Apore under four different irrigated production systems using different crop rotations and soil management practices: A - bean-corn crop rotation, using moldboard plowing in the spring-summer (November/December) and harrowing in the autumn-winter (May-June) season; B – ricebean crop rotation and moldboard plowing only; C - rice/calopogonium-bean crop rotation and harrowing only; D – cornbean crop rotation using continuous no-tillage. Urea, used as the nitrogen source, was applied in topdressing using 0, 25, 50, 75, 100 and 125 kg.ha -1 of N. Field trials were conducted during the fallwinter season, in 1996 and 1997, in a distrofic Dark Red Latosol, at the experimental farm of Embrapa Rice & Beans. Treatment effects were detected on the number of pods per plant, 100 grain weight and grain yield. Higher yields were obtained for systems C and D in which there was less soil disturbance. In system C, the effect of different nitrogen doses fit in a quadratic model and 109 kg.ha -1 , estimated by the regression equation, provided the highest grain yields. In system D the effect was linear indicating that the bean crop demanded more nitrogen under no-tillage. In systems A and B the effect of different nitrogen doses varied according to the year of cultivation. KEY-WORDS: Crop rotation; soil preparation; yield production; productivity; dry beans.

One‐Time Tillage of No‐Till Systems: Soil Physical Properties, Phosphorus Runoff, and Crop Yield

Continuous no‐till (NT) has numerous benefits, including improved soil aggregate stability in the surface soil and increased rate of water infiltration, but accumulation of soil P at the soil surface with NT can increase P concentration in runoff. We hypothesized that occasional one‐time tillage of NT land, conducted once in 10 or more years, can reduce P runoff and improve crop yields without reducing soil aggregation or increasing runoff. Research was conducted in long‐term NT fields under rainfed corn [Zea mays (L.)] or sorghum [Sorghum bicolor (L.) Moench.] rotated with soybeans [Glycine max (L.) Merr.] at two locations in eastern Nebraska. Tillage treatments were applied in the spring or fall and included continuous NT, tandem disk (disk), chisel with 10‐cm‐wide twisted shanks, moldboard plow (MP), and mini‐moldboard plow (miniMP). Subplots had either 0 or 87.4 kg P ha−1 applied as composted feedlot manure before tillage. Yield and yield components were measured for 2 and 3 yr after the spring and fall one‐time tillage, respectively. In Year 2 or 3 after tillage, soil sorptivity, field‐saturated infiltration rate, runoff volume, runoff P loss, and soil aggregate stability were determined. Yield was not affected by the tillage × compost interaction, but was increased by compost application at one location and sorghum yield was affected by tillage treatments at the second location. Grain yield was never significantly more or less with one‐time tillage as compared with NT. Soil aggregate stability was not affected by tillage treatments. Sorptivity and infiltration were increased with MP tillage compared with NT at one location but reduced at the other. One‐time MP tillage reduced dissolved P loss at both locations and total phosphorus (TP) loss at one location. The benefit of one‐time MP tillage in terms of reduced dissolved reactive P loss in runoff was positive with no negative effect on soil aggregate stability but no gain in yield.