Long-term Tillage Study Research Articles

Manure addition influences the effect of tillage on soil aggregation and aggregate associated carbon in a Vertisol of central India

Aim: To study the combined effect of tillage and manure addition on bulk soil and aggregate associated carbon and nitrogen in Vertisol. Methodology: The study was conducted in a long-term tillage experiment having two tillage treatments (reduced tillage and no-tillage) together with100% NPK fertilizer without (T1) and with addition of farm yard manure (T2) @ 2.0 ton C ha-1 to soybean in a soybean-wheat cropping system in a Vertisol of Central India, with three replicates in a split plot design. The parameters studied were aggregate size distribution, mean weight diameter, water stable aggregates, bulk soil and aggregate associated organic carbon, available nitrogen and rate of carbon mineralization. Results: The results indicated significantly higher SOC in reduced tillage (0.87%) than no-tillage (0.71%) under100% NPK fertilization in the bulk soil for 0-15 cm depth. However, 100% NPK + FYM showed a significant increase in the bulk soil organic carbon in the no-tillage treatment only. Available nitrogen content in the bulk soil and aggregate fractions were significantly lower under no-tillage than the corresponding reduced tillage treatments. Manure addition led to significantly higher available N content and proportion of WSA in both the tillage practices. The carbon mineralization was significantly higher by 1.4 to 1.6 times under reduced tillage than no-tillage. Interpretation: Long-term tillage study in Vertisol of Central India indicated reduced tillage to be a better option than no-tillage in maintaining organic carbon and nitrogen availability in soil.

What do meteorological indices tell us about a long-term tillage study?

The pattern of hydrological events is expected to become more variable as the climate changes at specific geographic locations; rainfed agricultural systems will be potentially more vulnerable. Understanding how to adjust management practices will be critical for successful adaptation, therefore, long-term agriculture experiments, conducted over a range of years provides an opportunity to gain insight into future crop responses. The objective of this study is to analyze the results of a long-term tillage-rotation-nitrogen rate study (1986–2016) in northeast Nebraska using two meteorological drought indices, the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI), to determine if either helps differentiate the tillage, nitrogen and rotation treatments across the indices ranges and in making management decisions. The experimental design is a split-split plot with four replications. Whole plots are no-till (NT), spring/fall plow (PL) and disk (DK); subplots are corn-soybean [Glycine max (L.) Merrill] (C–S) rotation and continuous corn [Zea mays L.] (C-C); and sub-subplots are five (0, 40, 80, 120 and 160 kg ha−1) nitrogen (N) rates (NR). The SPEI accounted for about 20% more variation in corn yields compared to SPI and was used to segregate years into dry, normal, and wet years. Under normal conditions (-0.99 ≤ SPEI≤0.99) and dry conditions (SPEI≤-1.00), optimum NR was 120 kg N ha−1. Under dry conditions for both rotations, NT had 10% and 24% greater yield than DK and PL. However, under wet conditions (SPEI ≥ 1.00), corn yield in PL and DK was 3% greater than NT and yield continued to increase with NR from 0 to 160 kg N ha−1 without reaching a maximum. Rotation (C–S) under normal and wet conditions increased corn yields 28% and 17% compared to C-C, respectively, but for extreme drought conditions (SPEI≤-2.00) and prolonged drought conditions (more than a year) corn yield was 17% greater in C-C compared to C–S. The results of this study indicate that if the future seasonal climatic conditions will be wetter, NR may need to be increased, and reduced tillage will reduce yields. Similar analysis of other long-term research will provide insight into future management practices.

Soil Carbon Response to Projected Climate Change in the US Western Corn Belt.

The western US Corn Belt is projected to experience major changes in growing conditions due to climate change over the next 50 to 100 yr. Projected changes include increases in growing season length, number of high temperature stress days and warm nights, and precipitation, with more heavy rainfall events. The impact these changes will have on soil organic carbon (SOC) needs to be estimated and adaptive changes in management developed to sustain soil health and system services. The process-based model CQESTR was used to model changes in SOC stocks (0-30 cm) of continuous corn ( L.) and a corn-soybean [ (L.) Merr.] rotation under disk, chisel, ridge, and no-tillage using projected growing season conditions for the next 50 yr. Input for the model was based on management and harvest records from a long-term tillage study (1986-2015) in eastern Nebraska, and model output was validated using measured changes in SOC from 1999 to 2011 in the study. The validated model was used to estimate changes in SOC over 17 yr under climatic conditions projected for 2065 under two scenarios: (i) crop yields increasing at the observed rate from 1971 to 2016 or (ii) crop yields reduced due to negative effects of increasing temperature. CQESTR estimates of SOC agreed well with measured SOC ( = 0.70, < 0.0001). Validated model simulated changes in SOC under projected climate change differed among the three soil depths (0-7.5, 7.5-15, and 15-30 cm). Summed over the 0- to 30-cm depth, there were significant three-way interactions of year × rotation × yield ( = 0.014) and year × tillage × yield ( < 0.001). As yield increased, SOC increased under no-tillage continuous corn but was unchanged under no-tillage corn-soybean and ridge tillage regardless of cropping system. Under chisel and disk tillage, SOC declined regardless of cropping system. With declining yields SOC decreased regardless of tillage or cropping system. These results highlight the interaction between genetics and management in maintaining yield trends and soil C.

The potential mechanism of long-term conservation tillage effects on maize yield in the black soil of Northeast China

The severe soil deterioration and the accompanying decline in maize yield are the main factors jeopardizing the sustainability of agricultural production in the black soil region of Northeast China. Conservation tillage practices have been proposed as new practices to enhance soil fertility and to produce food from a dwindling land resource in this region, but wide adoption of these practices can occur only when the practices demonstrate a steady increase in agricultural production. To compare the effects of tillage on corn yield, the structural equation modeling (SEM) was used in analyzing the relationships between maize growth/yield and soil properties (physical and chemical characteristics) based on a long-term (12 years) tillage study that included no tillage (NT), ridge tillage (RT) and conventional tillage (CT) practices. Compared with CT, NT and RT had higher maize grain yield, soil carbon/nitrogen ratio and soil moisture, and lower soil temperature and seedling emergence rate. The advantages of NT and RT in maize yield were primarily ascribed to the favorable soil nutrients and soil water content, which could increase plant size at the later growing season and ultimately yield more maize grain. The lower soil temperature and subsequently lower emergence rates in NT and RT at early stages (sowing to emergence) of maize growth did not exert negative effects on maize yield. These adverse effects of low soil temperature and low emergence rates could be offset by postponing sowing date without compromising the maize yield. Our study indicated that both NT and RT practices could offer a potentially significant improvement over the current conventional tillage practice in the black soil region of Northeast China.

Soil microaggregate and macroaggregate decay over time and soil carbon change as influenced by different tillage systems

Soil tillage can affect the formation and stability of soil aggregates. The disruption of soil structure weakens soil aggregates to be susceptible to the external forces of water, wind, and traffic instantaneously, and over time. The choice of tillage system or land management changes the soil physical condition and soil organic matter content, which is an essential factor in building soil aggregates. This study was conducted to investigate the effects of different tillage systems on the rate of decay of different sizes of soil aggregate fractions and other associated properties over time as subjected to a continuous wetting process. This research was conducted on a long-term tillage study, established in 2002 at the Iowa State University Agronomy Research Farm near Ames, Iowa. The soil association in this study is Clarion-Nicollet-Webster (Clarion [fine-loamy, mixed, mesic, Typic Hapluduolls], Nicollet [fine-loamy, mixed, mesic, Aquic Hapluduolls], and Webster [fine-loam, mixed, mesic, Typic Endoaquolls]). The experimental design was a randomized complete block design with four replications. Main plot treatments were five tillage systems: moldboard-plow, chisel-plow, deep-rip, strip-till, and no-till. The cropping system was corn ( Zea mays L.)–soybean ( Glycine max L.) rotation. Wet aggregate stability was measured using the Wet Sieving Apparatus (Eijkelkamp, Agrisearch Equipment. Art no. 08.13). Soil organic carbon (SOC) and soil total nitrogen (N) were analyzed by dry combustion using CHN Analyzer (TruSpec CHN Version 2.5x). Results show no-till with the highest carbon (C) content and the highest macro- and microaggregate stability over time. The findings also show a strong relationship between the increase in SOC content and the stability of macro- and microaggregate under continuous wetting process. Furthermore, the findings suggest that aggregate stability and moisture content are highly correlated with SOC content, and the rate of decay of both aggregate sizes (macro and micro) is highly influenced by the intensity of tillage. The implication of this research is the importance of no-till not only in increasing the stability of micro- and macroaggregates and SOC storage, but also in its effect on increasing the stability of all aggregate fractions in continuous wet conditions for extended periods of time.

Effects of Tillage on Soil Microarthropods in Winter Wheat

A long-term tillage study plot was sampled to evaluate the effects of tillage on soil-dwelling microarthropods. Soil (300 cm3) was sampled on four dates during two growing seasons from conventional and no-till plots of winter wheat. Microarthropods were extracted using Tullgren funnels and enumerated into seven taxonomic categories: 1) Total abundance, 2) Oribatida, 3) Mesostigmata, 4) Prostigmata, 5) Astigmata, 6) Collembola, and 7) other invertebrates. Abundance within six of the seven groups was greater in no-till than conventionally tilled soil on seven of the eight sampling dates: 1) Total abundance in conventional till 6.44 ± 1.68 and 21.39 ± 5.35 in no-till, 2) Oribatida in conventional till 1.06 ± 0.36 and 7.33 ± 2.23 in no till, and 3) Other invertebrates in conventional till 4.50 ± 0.82 and 10.67 ± 2.85 in no till. The Mesostigmata and Collembola showed significant differences between conventionally tilled and no-till plots on multiple dates. In contrast, mites in the group Prostigmata were more abundant in conventionally tilled soil (3.89 ± 1.13 versus 2.00 ± 0.88 in no till). Abundance of soil microarthropods in no-till plots generally increased (21.39 ± 5.35 in Season 1 to 42.42 ± 4.59 in Season 2), which might indicate gradual recovery of the habitat. Assessments of soil quality in no-till agricultural systems should include evaluations of beneficial soil fauna such as microarthropods.

Predicting soil organic carbon and total nitrogen using mid- and near-infrared spectra for Brookston clay loam soil in Southwestern Ontario, Canada

Xie, H. T., Yang, X. M., Drury, C. F., Yang, J. Y. and Zhang, X. D. 2011. Predicting soil organic carbon and total nitrogen using mid- and near-infrared spectra for Brookston clay loam soil in Southwestern Ontario, Canada. Can. J. Soil Sci. 91: 53–63. Mid-infrared (MIR) and near-infrared (NIR) spectroscopy of soils have been tested to estimate soil organic carbon (SOC) and total N (TN) concentrations at local, regional and national scales. However, these methods have rarely been used to assess SOC and TN concentrations of the same soil under different management practices. The objective of this study was to determine if models developed from infrared spectra of Brookston clay loam soils under different management practices could be used to estimate SOC, and TN concentrations and the C:N ratio. Soils used for model calibration included 217 samples from a long-term fertilization and crop rotation study and a long-term compost study, whereas 78 soil samples from a long-term tillage study on the same soil type were used for model validation. Soil organic carbon and TN concentrations of all samples were also analyzed using dry combustion techniques. Soil samples were scanned from 4000 to 400 cm−1 (2500–25 000 nm) for MIR spectra and from 8000 to 4000 cm−1 (1250–2500 nm) for NIR spectra. Partial least squares regression (PLSR) analysis was used for the calibration dataset to build prediction models for SOC, TN and C:N ratio. The SOC and TN concentrations determined using dry combustion techniques were compared with the prediction from the models using the calibration datasets. The predictions of SOC and TN concentrations by the PLSR method using infrared spectra were statistically sound, with high coefficient of determination with the calibration dataset (R2cal, SOCMIR=0.99 and SOCNIR=0.97, TNMIR=0.98 and TNNIR=0.97) and the validation dataset (R2val, SOCMIR=0.96 and SOCNIR=0.95, TNMIR=0.96 and TNNIR=0.95) and low root mean square error (RMSEPcal, SOCMIR=0.93 and SOCNIR=1.60, TNMIR=0.08 and TNNIR=0.12; RMSEPval, SOCMIR=1.40 and SOCNIR=1.75, TNMIR=0.11 and TNNIR=0.12). The predictions of SOC and TN concentrations in the 5 to 30 cm depth were better than the predictions for either the surface (0 to 5 cm) soils or for soils from lower depths (&gt;30 cm). The models could be used as an alternative method for determining SOC and TN concentrations of Brookston clay loam soils; however, larger sample populations and improved model algorithms could further improve predictions.

Seedbank and Emerged Weed Communities Following Adoption of Glyphosate-Resistant Crops in a Long-Term Tillage and Rotation Study

The compositions of the germinable weed seedbank and aboveground weed communities in a long-term tillage and rotation study were characterized 4, 5, and 6 yr (2002 to 2004) after the adoption of glyphosate-tolerant corn and soybean. Averaged across rotation, mean germinable weed seed density and diversity were greatest in the no-tillage treatment as compared to the minimum- and conventional-tillage treatments. Averaged over tillage, density and diversity were greater in the corn–oat–hay (ryegrass + alfalfa) system as compared to the continuous corn and corn–soybean rotations. Similar trends in density and diversity were observed for the aboveground weed communities. Differences in community composition among treatments were quantified with the use of a multiresponse permutation procedure. Results indicated that the weed seedbank community in a corn–oat–hay rotational system differed from the communities associated with the continuous corn and corn–soybean rotational systems. Weed seedbank communities developing under a no-tillage operation differed from those in minimum- and conventional-tillage scenarios. Compositional differences among the aboveground weed communities were less pronounced in response to tillage and rotation. Indicator species analyses indicated that the number of significant indicator weed species was generally higher for no tillage than minimum or conventional tillage for both the seedbank and the aboveground weed communities. The number of significant indicator species for the seedbank and weed communities was generally greater in the three-crop rotation as compared to the continuous corn and corn–soybean rotations. The trends observed in density, diversity, and community composition after the adoption of glyphosate-tolerant corn and soybeans, and a glyphosate-dominated weed management program, were also observed when soil-applied herbicides were included in the study. We suggest that the switch to a POST-glyphosate protocol did not significantly alter weed communities in the short term in this study.

Using a sequential density and particle-size fractionation to evaluate carbon and nitrogen storage in the profile of tilled and no-till soils in eastern Canada

Tillage influences the retention and storage of organic matter (OM) in soil. We used a sequential density and particle-size fractionation to evaluate the total quantity and distribution of organic carbon (C) and nitrogen (N) in the profile of soils under mouldboard ploughing and no-till. Cores (0-60 cm) from four long-term tillage studies (in Prince Edward Island, Quebec, and two sites in Ontario) on soils of different textures, from sandy loam to clay were collected and divided into six depth increments. Four soil OM fractions were isolated on the basis of size and density from each sample. At two sites the standing stocks of C and N were larger in tilled than in no-till soil profiles at depths slightly greater than plough depth; tillage effects were also evident at a third site, where the mass of C in a layer close to the depth of ploughing was greater in tilled soils. Ploughing also had a substantial and consistent positive effect in all four soils on the quantity of C (and in some cases N) protected within aggregates, particularly at or near the bottom of the plough layer, and sometimes in surface soil layers. We attribute differences observed in whole soil C and N due to tillage mostly to differences in mineral-associated OM, particularly in soils with heavier textures, but the other size and density fractions could, together, account for as much as 25% of the difference. Because the C capacity level was not reached in heavy-textured soils, these soils show greater potential for further accumulation of C in the soil profile than coarse-textured soils, especially near the bottom of the plough layer.Key words: Light fraction, soil organic matter, soil tillage, physically-protected organic matter, no-till, soil texture

Short- and long-term tillage effects on Heterodera glycines reproduction in soybean monoculture in west Tennessee

Soybean cyst nematode, Heterodera glycines has been documented as the pathogen most consistently causing yield loss in US soybean production fields almost since its discovery in the US. No-tillage has been adopted in much of the soybean production areas to preserve soil and nutrients. The impact of this production practice change on soybean cyst nematode has been evaluated since the introduction of the practice over thirty years ago and mixed results on the impact have been recorded. This study was initiated to determine if tillage practices and timing of changes impacted soybean cyst nematode reproduction. The study was imposed on a long-term tillage study and treatments were changed to measure short-term as well as long-term effects of tillage on soybean cyst nematode. Significant differences in soybean cyst nematode population density were found between treatments. However, significant differences found could be attributed to short-term changes in tilled and no-tilled treatments. Soybean cyst nematode reproduction was almost twice as high in treatments which changed from no-tillage to disc than tilled treatments changed to no-tillage. No significant differences were found in yield among the treatments. Grain yield was reflective of cultivar grown and environmental conditions.

Weed seed bank affected by tillage intensity for barley in Alaska

The weed seed bank of a long-term tillage study in subarctic Alaska was studied at the end of 10 years of continuous spring barley ( Hordeum vulgare L.). Tillage treatments were: no-till, disked once (spring), disked twice (spring and fall), and chisel plow (fall). Soil cores were obtained from each tillage treatment and seeds were manually separated from soil after washing through sieves. Tillage treatment had a significant effect on seed density of shepherds purse ( Capsella bursa-pastoris (L.) Medic.), cinquefoil ( Potentilla norvegica L.), foxtail barley ( Hordeum jubatum L.), and on total seed density. Seed density was higher for these species and total seed density was greater under no-till than under other tillage treatments. Seed density was higher near the soil surface under no-till and chisel plow treatments than under disked treatments, which helps explain the greater difficulty of controlling weeds under reduced tillage.

Effects of Soil Moisture, Physical, and Chemical Characteristics on Abiotic Nitric Oxide Production

The objective of this study was to examine the effect of soil water content, and other physical and chemical factors, on the abiotic component of nitric oxide (NO) production in laboratory studies using soils from agricultural fields in Minnesota, California, and Connecticut. In all soils, gross NO production decreased with increasing gravimetric water content (ϑ) in nitrite (NO 2 − )-amended sterilized soils. The rate coefficient describing nitrous acid (HNO2)-mediated NO production (kp) also decreased with increasing ϑ in both gamma-irradiated and autoclaved soils. Significant correlations were found between ln kp and several soil properties including: content of silt, clay, total carbon, total N, and extractable iron, and an estimate of the cation exchange capacity of the clay fraction. Multiple regression models incorporating these variables explained 85–93% of the variance in ln kp. The relationships obtained suggest that the mechanism of abiotic NO production is primarily mediated at the soil solution–surface interface. These findings provide consistent evidence of a previously unrecognized mechanism by which soil water content can affect NO production by mediating a chemical process. Application of a dynamic process model indicated that the simulated variation in NO emissions as a consequence of this effect is comparable to the variation observed in previous studies of NO emissions. Comparison of soils from two different long-term tillage studies also indicated that reduced pH in no-till systems may lead to greater NO emissions for a given level of NO 2 − accumulation. Overall, these results suggest that current views of controls over N oxide gas emissions may need to be revised to include abiotic reactions, in addition to microbial and physical processes, as yet another category of factors that is highly sensitive to soil water content.

Crop and soil nitrogen status of tilled and no-tillage systems in semiarid regions of Saskatchewan

We examined 1990-1996 crop and soil N data for no-tillage (NT), minimum tillage (MT) and conventional tillage (CT) systems from four long-term tillage studies in semiarid regions of Saskatchewan for evidence that the N status was affected by tillage system. On a silt loam and clay soil in the Brown soil zone, spring what (Triticum aestivum L.) grain yield and protein concentration were lower for NT compared with tilled (CT or MT) systems for a fallow-wheat (F-WM) rotation. Grain protein concentration for continuous wheat (Cont W) was also lower for NT than for MT. For a sandy loam soil in the Brown soil zone, durum (Triticum durum L.) grain protein concentration was similar for MT and NT for both Cont W and F-W, but NT had higher grain yield than MT (P &lt; 0.05 for F-W only). For a loam soil in the Dark Brown soil zone, wheat grain yield for NT was increased by about 7% for fallow-oilseed-wheat (F-O-W) and wheat-oilseed-wheat (W-O-W) rotations. The higher grain yields for NT reduced grain protein concentration by dilution effect as indicated by similar grain N yield. However, at this site, about 23 kg ha-1 more fertilizer N was required for NT than for CT. Elimination of tillage increased total organic N in the upper 7.5 cm of soil and N in surface residues. Our results suggest that a contributing factor to decreased availability of soil N in medium- and fine-textured soils under NT was a slower rate of net N mineralization from organic matter. Soil nitrates to 2.4 m depth did not indicate that nitrate leaching was affected by tillage system. Current fertilizer N recommendations developed for tilled systems may be inadequate for optimum production of wheat with acceptable grain protein under NT is semiarid regions of Saskatchewan. Key words: Tillage intensity, N availability, soil N fractions, N mineralization, crop residue decomposition, grain protein

Runoff and soil loss from midwestern and southeastern US silt loam soils as affected by tillage practice and soil organic matter content

No-till practices generally reduce runoff (RO) and soil loss (SL) by contributing to accumulations of soil organic matter (SOM) in the near-surface zone. This research was conducted to determine the effects of SOM contents on RO and SL from two highly erodible soils using crops that produce a wide range of residue, in the context of long-term tillage studies in widely separated climatic regions. Rainfall simulator plots, measuring 6.1 m×0.9 m , were imposed on a 9-year-old corn ( Zea mays L.) and cotton ( Gossypium hirsutum L.) conservation tillage study at Senatobia, Mississippi, and on a similar 34-year-old corn study at Coshocton, Ohio. All RO was collected from two replications of conventional (CT) and no-till (NT) treatments following application of simulated rainfall at an intensity of 50 mm h −1 for 1 h. Soil samples collected in depth increments of 0–1, 1–3, 3–7.6 and 7.6–15.2 cm were characterized for SOM content, aggregate stability (AS), water dispersible clay (WDC) and particle size distribution. Bulk density (BD) samples were collected in increments of 0–3.8, 3.8–7.6, 7.6–15.2 and 15.2–30.5 cm. Overall, RO from the CT and NT treatments averaged 27.8 and 16.5 mm, respectively. SL loss from the CT treatments averaged 3.9 Mg ha −1 and 0 for the NT. BDs in the surface 3.8 cm averaged 1.34 Mg m −3 for CT and 1.26 Mg m −3 for NT. Correlation coefficients ( r) for SOM content versus AS, WDC and BD were 0.92, −0.90 and −0.64, respectively. Regression models indicated that BD, as a single-variable, explained 87% of the variability in RO from the NT treatments. BD alone was less effective in accounting for the variability in RO from CT treatments, but contributed to a three-variable model with AS and WDC to produce an R 2 of 0.97. These results indicate that as SOM contents gradually increase in NT treatments, RO decreases due to the development of greater porosity in the near-surface zone attributable to enhanced AS at the soil surface. Thus, surface sealing tendencies are diminished which promotes an increase in infiltration rates.

Review of management and conduct of long-term tillage studies with special reference to a 25-yr experiment on barley in Scotland

We review the management procedures and conduct of long-term tillage experiments in relation to the achievements of a 25-yr experiment established at South Road, near Edinburgh, Scotland, to study soil and barley ( Hordeum vulgare L.) responses to mouldboard ploughing, chisel ploughing and zero tillage (direct drilling). We consider experimental objectives, design, tillage and fertiliser treatments, agronomic problems, sources of finance, soil sampling, vehicle traffic, weather and economics. The application of experimental results to farming practice and the suitability of the soils for non-ploughing tillage are also discussed. Trends in soil condition, crop yields, weeds and weather over the 25-yr period are considered, together with the impact of research findings on farming practice in Scotland. Recommendations are made for the planning and conduct of long-term tillage experiments.

The role of soil organic matter in maintaining soil quality in continuous cropping systems

Maintenance and improvement of soil quality in continuous cropping systems is critical to sustaining agricultural productivity and environmental quality for future generations. This review focuses on lessons learned from long-term continuous cropping experiments. Soil organic carbon (SOC) is the most often reported attribute from long-term studies and is chosen as the most important indicator of soil quality and agronomic sustainability because of its impact on other physical, chemical and biological indicators of soil quality. Long-term studies have consistently shown the benefit of manures, adequate fertilization, and crop rotation on maintaining agronomic productivity by increasing C inputs into the soil. However, even with crop rotation and manure additions, continuous cropping results in a decline in SOC, although the rate and magnitude of the decline is affected by cropping and tillage system, climate and soil. In the oldest of these studies, the influence of tillage on SOC and dependent soil quality indicators can only be inferred from rotation treatments which included ley rotations (with their reduced frequency of tillage). The impact of tillage per se on SOC and soil quality has only been tested in the ‘long-term’ for about 30 yrs, since the advent of conservation tillage techniques, and only in developed countries in temperate regions. Long-term conservation tillage studies have shown that, within climatic limits: Conservation tillage can sustain or actually increase SOC when coupled with intensive cropping systems; and the need for sound rotation practices in order to maintain agronomic productivity and economic sustainability is more critical in conservation tillage systems than conventional tillage systems. Long-term tillage studies are in their infancy. Preserving and improving these valuable resources is critical to our development of soil management practices for sustaining soil quality in continuous cropping systems.

Effect of Paraplowing on Crop Yields with No-Till Planting

No-till acreage has expanded rapidly in the past 5 yr in the U.S. Corn Belt. Yield potential often improves with no-till planting on well drained and low organic matter (OM) soils, but no-till yields are sometimes at a disadvantage on dark, poorly drained soils. Restricted plant rooting due to increased soil density is sometimes reported with no-till planting. Deep tillage with a Paraplow 1 (Tye Co., PO Box 218, Lockney, TX 79241), leaving most surface residue undisturbed, was evaluated on three soils in Indiana for continuous corn (Zea mays L.). Annual paraplowing and biennial paraplowing were used with no-till and moldboard plow systems. On dark, poorly drained silty clay loam, annual paraplowing improved stand, growth, and yield, compared with traditional no-till planting. On a silt loam soil with 2% OM, response to paraplowing for no-till was variable and on a 1% OM soil, paraplowing did not improve no-till yield. Carryover effect from biennial paraplowing for no-till planting was not consistent, even on silty clay loam. Paraplowing did not improve plowed yields on any of the three soils. Paratilling was also used on four rows of each 12-row plot in the 15th year of a long-term tillage study on silty clay loam soiL Plow, chisel, ridge, and no-till systems were used in continuous corn, corn after soybean [Glycine max (L.) Merr.], soybean after corn, and continuous soybean. In no-till continuous corn, there was a positive response to paratilling, but yield for no-till plus paratilling was significantly lower than plowed yield. With conditions similar to conditions in these studies, deep soil loosening is likely to improve no-till continuous corn yield on dark poorly drained soil, but is not likely to improve yield on well drained or low OM soils where traditional no-till is well adapted.

Long-term tillage effects on soil quality

Public interest in soil quality is increasing, but assessment is difficult because soil quality evaluations are often purpose- and site-specific. Our objective was to use a systems engineering methodology to evaluate soil quality with data collected following a long-term tillage study on continuous corn ( Zea mays L.). Aggregate characteristics, penetration resistance, bulk density, volumetric water content, earthworm populations, respiration, microbial biomass, ergosterol concentrations, and several soil-test parameters (pH, P, K, Ca, Mg, Total-N, Total-C, NH 4-N, and NO 3-N) were measured on Orthic Luvisol soil samples collected from Rozetta and Palsgrove silt loam (fine-silty, mixed, mesic Typic Hapludalfs) soils. Plots managed using no-till practices for 12 years before samples were collected for this study had surface soil aggregates that were more stable in water and had higher total carbon, microbial activity, ergosterol concentrations, and earthworm populations than either the chisel or plow treatments. Selected parameters were combined in the proposed soil quality index and gave ratings of 0.48, 0.49, or 0.68 for plow, chisel, or no-till treatments, respectively. This indicated that long-term no-till management had improved soil quality. The prediction was supported by using a sprinkler infiltration study to measure the amount of soil loss from plots that had been managed using no-till or mold-board plow tillage. We conclude that no-till practices on these soils can improve soil quality and that the systems engineering methodology may be useful for developing a more comprehensive soil quality index that includes factors such as pesticide and leaching potentials.

Comparison of alternative farming systems. II. Earthworm population density and species diversity

Effects of soil fauna on soil quality are largely unknown. Our objective was to learn whether long-term soil management has significantly affected earthworm species and populations at two Iowa locations. Soil cores were collected in fall 1989, spring 1990, and fall 1990 from a long-term tillage study in Polk County, Iowa, involving monoculture of corn (Zea mays L.) with either no-tillage, fall disking, fall chisel plowing, or fall moldboard plowing. Species found wereLumbricus terrestris(L),Octolasion tyrtaeum(Savigny),Aporrectodea trapezoides(Duges),A. turgida(Eisen), andA. tuberculata(Eisen), withO. tyrtaeumdominant across all treatments. As the amount of tillage increased, the number of earthworms generally decreased. InBoone County, Iowa, we compared the populations of mature and immature earthworms and cocoons on two adjacent fields, one managed conventionally, the other managed with an alternative farming system for more than 20 years. The predominant species was A. tuberculata. Regardless of management practice, the most worms were found in Canisteo soil on the toeslope landscape position.

Nitrate‐N in the soil profile and tile drainage water as influenced by tillage

Conservation tillage systems facilitate the infiltration of greater amounts of precipitation into the soil profile by reducing surface runoff. Concern has developed among some scientists because higher infiltration and percolation rates are often linked to potentially higher leaching losses of agricultural chemicals. Soil samples were taken in 1 foot increments to a depth of 5 feet to ascertain the accumulation and distribution of nitrate-nitrogen (NO3-N) in the soil profile as influenced by tillage. Two long-term tillage studies on fine-textured, clay loam soils were sampled in July and November 1977 following 2 years of limited rainfall. Nitrate-N accumulation in the 0 to 3 foot profile in late July was reduced by 75% (no tillage) to 38% (chisel plow) compared with the conventional moldboard tillage system in this 8-year-old study. Accumulation in the 0 to 5 foot profile after harvest was 751, 546, 345, and 198 lb NO3-N/A for the moldboard plow, chisel-plow, disk-, and no-tillage systems, respectively. Another 3 year study showed accumulations of 625, 619, 468, and 391 pounds NO3-N/A after harvest with the moldboard plow, ridge-plant, chisel-plow, and no-tillage systems, respectively. These data indicate that tillage can have substantial effects on the accumulation of NO3 in soils and that additional research is needed to determine the mechanisms responsible for these differences.