Effects of tillage,nitrogen placement,and wheel compaction on denitrification rates in the corn cycle of a corn‐oats rotation

Denitrification rates under various tillage systems were determined in the corn (Zea mays L.) cycle of a corn‐oats (Avena sativa L.) rotation. Denitrification was measured directly with an in‐situ soil cover method which supplied the soil with acetylene (C₂H₂) and evacuated the nitrous oxide (N₂O) produced. Denitrification rates were measured in both a field or non‐wheel track (NWT) area and in a compacted wheel track (WT) area for the no‐till (NT), chisel plow (CH), moldboard plow (MP) tillage systems after nitrogen (N) was applied by broadcast/incorporation with 112 kg N/ha as ammonium nitrate. Nitrogen was also applied to the NT treatment by injection with modified anhydrous ammonia knives prior to planting. Most of the cumulative N loss occurred over a 22 day period following heavy rainfall in June. Denitrification was greatest on days after rainfall events for the NT systems. Cumulative N loss was estimated at 25, 16, and 11 kg N/ha from May 29‐September 8 for NT, CH, and MP treatments, respectively, for the broadcast/incorporated N application. Mean denitrification rates from WT areas were about 1.6 times greater than the NWT areas.     

Dryland corn response to tillage and nitrogen fertilization. I. Growth‐yield‐N relationships

Abstract

Crop response to fertilizer nitrogen (N) is dependent upon tillage management. This study was conducted to determine how tillage rotation influences non‐irrigated crop growth, N uptake and yield. The effects of tillage rotation, N rate and N timing schedule on early season dry matter production and N uptake, ear leaf N concentration at silking, and yield of corn [Zea mays (L.) Pioneer 3378] were investigated at Painter, VA, on an Altavista loam (fine‐loamy, mixed, thermic Aquic Hapludult). In 1986, maximum yields achieved in the 6‐year continuous no till (NT) [5.82 Mg/ha] and first year no till (AT) [5.64 Mg/ha] were significantly greater than that of the 6‐year continuous conventional till (CT) [3.67 Mg/ha], but no yield differences were obtained in the drier 1987 season. A higher rate of N fertilizer was required to obtain maximum yield in the first year no till (168 kg N/ha) than in the NT (112 kg N/ha) during 1986. Early 1986 N uptake and growth response with and without N at planting increased in the order CT < AT = NT and AT < CT < NT, respectively, indicating greatest immobilization of soil N occurred in the newly established no till soil. Lack of differences in critical ear leaf N values developed for NT and CT in each year imply that plant norms developed for one tillage system may accurately assess N status of corn grown under different tillage practices.     

Comparison of broiler litter and inorganic nitrogen,phosphorus, and potassium for double‐cropped sweet corn and broccoli

Two rates of broiler litter (20 and 40 mt/ha) were compared to recommended rates of inorganic nitrogen (N), phosphorus (P), and potassium (K) in a double cropping system of spring sweet corn (Zea mays L. ‘Silverqueen') and fall broccoli (Brassica oleracea L, ‘Southern Comet')‐ Sweet corn matured one week earlier both years when fertilized with 40 mt/ha of broiler litter compared to commercial fertilizer. The early maturity may be due to improved P nutrition. Similar or higher yields of fall broccoli were produced with broiler litter following sweet corn than with commercial fertilizer.     

Reduced‐till spring wheat response to fertilizer sources and placement methods

Abstract

Field studies were conducted to determine the effect of nitrogen (N) and phosphorus (P) fertilizer sources and placement configurations on spring wheat growth, yield and quality. Different standard and experimental N and P sources at two rates and in different placement methods provided 32 fertilizer treatments at three locations. Banding of N and P together resulted in the greatest yields. Of the fertilizer combinations where N and P were applied separately, only broadcast N with deep banded P gave similar yields to N and P together. Banding fertilizer with the seed at these levels damaged seedling growth and limited yield. Elevated protein levels, when found, were likely due to lower yields and subsequent concentration of N in grain protein. Careful consideration of fertilizer rate, source and placement strategies to optimize production and water utilization are essential in dryland environments.     

Comparative response of corn and soybean to seed‐placed phosphorus over a range of soil test phosphorus

Abstract

The responses of corn and soybean to seed‐placed fertilizer were compared over NaHCO₃‐extractable soil phosphorus (P) levels ranging from 3 to 35 ppm in a two‐year experiment. Early season corn and soybean shoot‐P concentrations were increased with increasing soil test P and were increased with seed‐placed P regardless of soil test P, although the increases were greater for corn than soybean. Corn grain yield increased with increasing soil test P to a plateau level and increased with seed‐placed P regardless of soil test P. A side‐band (5 cm × 5 cm) application of 39 kg P ha^‐1 at a low soil test P increased yield more (P<0.15) than application of 7 kg P ha^‐1 with the seed. A side‐band application of 9 kg P ha^‐1 at a medium soil P test did not increase yield. Soybean yield was increased with increasing soil test P one year out of two, but did not respond to seed‐placed P in either year. The yield response of corn was attributed to the increased P concentration prior to the 6‐leaf stage.     

Cover crop nitrogen availability to conventional and no‐till corn: Soil mineral nitrogen,corn nitrogen status,and corn yield

Abstract

Understanding seasonal soil nitrogen (N) availability patterns is necessary to assess corn (Zea mays L.) N needs following winter cover cropping. Therefore, a field study was initiated to track N availability for corn in conventional and no‐till systems and to determine the accuracy of several methods for assessing and predicting N availability for corn grown in cover crop systems. The experimental design was a systematic split‐split plot with fallow, hairy vetch (Vicia villosa Roth), rye (Secale cereale L.), wheat (Triticum aestivum L.), rye+hairy vetch, and wheat+hairy vetch established as main plots and managed for conventional till and no‐till corn (split plots) to provide a range of soil N availability. The split‐split plot treatment was sidedressed with fertilizer N to give five N rates ranging from 0–300 kg N ha^‐1 in 75 kg N ha^‐1 increments. Soil and corn were sampled throughout the growing season in the 0 kg N ha^‐1 check plots and corn grain yields were determined in all plots. Plant‐available N was greater following cover crops that contained hairy vetch, but tillage had no consistent affect on N availability. Corn grain yields were higher following hairy vetch with or without supplemental fertilizer N and averaged 11.6 Mg ha^‐1 and 9.9 Mg ha^‐1 following cover crops with and without hairy vetch, respectively. All cover crop by tillage treatment combinations responded to fertilizer N rate both years, but the presence of hairy vetch seldom reduced predicted fertilizer N need. Instead, hairy vetch in monoculture or biculture seemed to add to corn yield potential by an average of about 1.7 Mg ha^‐1 (averaged over fertilizer N rates). Cover crop N contributions to corn varied considerably, likely due to cover crop N content and C:N ratio, residue management, climate, soil type, and the method used to assess and assign an N credit. The pre‐sidedress soil nitrate test (PSNT) accurately predicted fertilizer N responsive and N nonresponsive cover crop‐corn systems, but inorganic soil N concentrations within the PSNT critical inorganic soil N concentration range were not detected in this study.     

Predicting nitrogen fertilizer response in unthinned stands of Douglas‐fir

Abstract

The mineralization potential of forest soils is a useful tool in predicting nitrogen fertilizer response in unthinned stands of Douglas‐fir. As the mineralization potential of the soil increased, diameter growth for 200 lbs/A of added N decreased. Significant growth response could not be detected when mineralizable nitrogen level was above 46 ppm.

Percent stocking is also an important variable in predicting diameter growth response in these stands. For a given nitrogen level, response decreased with increasing stocking.

When stocking and mineralizable nitrogen are used together, they account for a significant portion (86%) of the variation in growth response.     

Variation of early growth and nutrient content of no‐till corn and soybean in relation to soil phosphorus and potassium supplies

Abstract

Knowledge of relationships between variation in early plant growth and soil nutrient supply is needed for effective site‐specific management of no‐till fields. This study assessed relationships between soil test phosphorus (STP) and potassium (STK) with early plant growth and P or K content of young corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] plants in eight no‐till fields. Composite soil (0–15 cm depth) and plant (V5‐V6 growth stages) samples were collected from 400‐m² areas at the center of 0.14‐ha cells of a 16‐cell square grid and from 2‐m² areas spaced 3 m along each of two 150‐m intersecting transects. Correlation, regression, multivariate factor analyses were used to study the relationships between the variables. Variability was higher for samples collected from the transects. Plant dry weight (DW), P uptake (PU), and K uptake (KU) usually were correlated with STP and STK but the correlations varied markedly among fields. Relationships between soil and plant variables could not always be explained by known nutrient sufficiency levels for grain production. Plant P concentration (PC) was not always correlated with STP and sometimes it increased linearly with STP, but other times increased curvilinearly until a maximum was reached. Plant K concentration (KC) usually was correlated with STK, however, and increased linearly with increasing STK even in fields with above‐optimum STK. The results suggest greater susceptibility of early growth to STP than to STK and greater plant capacity to accumulate K compared with P over a wide range of soil nutrient supplies. Variation in STK likely is a major direct cause of variation in KC over a wide range of conditions but variation in STP is not likely a major direct cause of variation in PC when high STP predominates.     

Changes in soil nitrogen,phosphorus, and potassium under intensive cropping in sub‐humid tropics of India

Abstract

Efficient soil fertility management is essential for sustained production of high crop yields. Field experiments were conducted on an Entisol soil during 1984 to 1987 at Bidhan Chandra Agricultural University, West Bengal, India, to study the changes in soil N, P, and K in sub‐humid tropics under irrigated intensive cropping in rice‐potato‐mung bean (Oryza sativa L.‐ Solanum tuberosum L.‐ Vigna radiatus Roxb.) and rice‐potato‐sesame (O. sativa L.‐ S. tuberosum L.‐ Sesamum indicum L.) cropping sequences. The crops were grown with or without application of farmyard manure and with or without incorporation of crop residues. Different quantities of inorganic fertilizers based on locally recommended practices for fertilization were applied to rice and potato, and their residual effects on succeeding mung bean or sesame crops were assessed. At the end of experimentation, the total N status of soil improved more under the rice‐potato‐mung bean sequence than under the rice‐potato‐sesame sequence. The available phosphorus status of soil showed a positive balance in both sequences except in the treatment receiving 50% of the recommended amounts of N, P, and K. A reduction in the recommended fertilization without a compensating application of manure or crop residues resulted in the depletion of soil‐available K. All treatments reduced nonexchangeable K, and depletion was low wherever manure or crop residues were added into the cropping system. Integration of inorganic fertilizers with organic fertilizers, such as manure or crop residues, maintained soil N, P, and K under intensive agriculture and sustained soil productivity.     

Availability of phosphorus in a Brazilian Oxisol cultivated with eucalyptus after nine years as influenced by phosphorus‐fertilizer source,rate, and placement

Abstract

This work evaluated the effect of different placement and rates of two phosphorus (P) fertilizers on P‐availability by three methods of extraction, nine years after application to a Brazilian Oxisol cultivated with Eucalyptus camaldulensis. The treatments were applied to 24x18 m plots and 96 seedlings of E. camaldulensis were planted (3.0x1.5 m) in each plot. Single superphosphate (SSP) and rock phosphate (RP) were tested in three rates (100, 200, and 400 kg ha^‐1 of P₂O₅). Each fertilizer was either (1) surface‐applied in bands (0.6 m either side of the rows of trees) and incorporated before planting or (2) incorporated into furrows (0.2 m deep in the tree rows) before planting. As additional treatments, the combination of RP (96 kg ha^‐1 of P₂O₅ applied in broadcast, or bands, or in furrows) + SSP (54 kg ha^‐1 of P₂O₅ localized in the planting hole before planting) were tested. Twelve soil subsamples from two layers (0–15 and 25–40 cm) were taken from each plot (from the planting rows or between the planting rows) and were analyzed for pH in water (1:2.5), available P by Mehlich‐1, Bray‐1 and anionic resin, exchangeable Ca, and Al by 1 mol L^‐1 Kcl. For both methods of fertilizers placement, the highest values of available P were observed in the surface soil and in the planting row, and were strongly related to fertilizer rate. Samples taken between the planting rows did not exhibit treatment effects on available P. The higher values of available P obtained with Mehlich‐1 and the lower eucalyptus plant uptake efficiency of fertilizer‐P from banded RP confirms the fact that this extractant can overestimate the availability of P in soils receiving RP. The use of anion exchange resin in this situation to estimate available P is supported. The results obtained with the localized application of RP indicate root system activity (P and Ca uptake and acidification of rhizosphere) as a factor in increasing fertilizer dissolution rates.     

Microsite assessment of forest soil nitrogen,phosphorus, and potassium supply rates in‐field using ion exchange membranes

Abstract

A new method for microsite assessment of soil nutrient supply in forest soil was developed. The method involves the use of ion exchange membranes to assess differences in soil nitrogen (N), phosphorus (P), and potassium (K) supply rates in‐field over small depth increments in the forest floor (i.e., the L, F, and H horizons). Ion exchange membranes were buried and retrieved from the forest floor in an aspen forest stand in Saskatchewan, Canada. Small (6 mm diameter) sections of the membrane were cut out and ion concentration on the sections measured to provide a nutrient supply rate at that location. Soil nutrient supply rates at the site ranged from 4.6–6.0, 7.3–8.5, 11.6–21.5, and 122–196μg 10 cm²#lb2 h^‐1 for NH₄ ⁺‐N, NC₃ ^‐‐N, P, and K, respectively. On average, the highly humified H horizon had the highest N and P supply rates, followed by the F horizon, with the surface litter (L horizon) having the lowest N supply rates. The simplicity and sensitivity of the procedure make this method appropriate for in‐field assessment of differences in soil nutrient supply over small vertical and horizontal distance and was especially appropriate for the forest floor horizons in forest soils.     

Longevities and nitrogen,phosphorus, and potassium release patterns of polymer‐coated controlled‐release fertilizers at 30°C and 40°C

Abstract

The weekly nitrogen (N), phosphorus (P), and potassium (K) release from 17 polymer‐coated controlled‐release fertilizer (CRF) formulations of Nutricote, Apex Gold, Osmocote, and a 9‐month Macrocote were measured at 30.6±0.8°C and 40.0±1.5°C. Five grams of each CRF were placed at a depth of 50 mm in 280x50 mm acid washed then rinsed silica sand columns which were leached with deionized water three times each week until nutrient recovery ceased. The volume of leachate was recorded each week and subsampled for ammonium‐N, nitrate‐N, phosphate‐P, and K analyses. Each CRF treatment was replicated three times at each temperature. Nutrient release profiles were determined. Longevities, measured as weeks to 90% nutrient recovery, were considerably shorter than the nominated release periods for all formulations. Within each CRF product group, the longevity of 9 and 12 month formulations were similar with Apex Gold 12–14 month high nitrate having the longest (38 weeks for N at 30°C) and Osmocote 8–9 month the shortest (23 weeks for N at 30°C). There were consistent trends in the nutrient release periods across all CRFs with P>K>N and with differences of around 10% in duration between nutrients. The P:N release ratio exceeded 0.10 for most CRFs during the early release period indicating an adequate P supply for most plant species. The mean reduction in longevity for Nutricote, Apex Gold, and Osmocote formulations for an increase in incubation temperature from 30°C to 40°C was 19–21 % for N, 13–14% for P, and 14–15% for K. All CRFs released nutrients unevenly with the highest rate occurring during the early part of the release period. This pattern was accentuated at 40°C and by the shorter term release formulations. The nutrient release rates of all CRFs declined steadily after their maxima.     

Effect of no‐tillage vs. conventional tillage on soil organic matter and nitrogen contents

Abstract

Four treatments (no‐tillage plus subsoiling, no‐tillage, conventional tillage plus subsoiling, and conventional tillage) were continuously in place for 6 yr and a second set of no‐tillage plus subsoiling and conventional plus subsoiling treatments were continuously in place for 3 yr to study the long‐term effects of conventional and no‐tillage corn on soil organic matter (OM) and N contents. Soil samples were taken at random between the rows and in the rows to a depth of 60 cm, in 5‐cm increments to a depth of 30 cm, and then in 15‐cm increments from the 30 to 60‐cm depth for OM and N determination. No‐tillage resulted in A3 and 20% more Kjeldahl N than conventional tillage in the 0 to 5‐cm soil depth after 6 and 3 yr, respectively. after 6 yr, the 0 to 5‐cm depth had 36% more OM in no‐tillage treatments than in conventional tillage treatments, and soil from no‐tillage treatments averaged 27% more OM than the conventional tillage plus subsoiling treatment at the 0 to 15‐cm soil depth.     

Topsoil and subsoil potassium as affected by long‐term potassium fertilization of corn‐soybean rotations

Abstract

Long‐term potassium (K) fertilization practices are likely to affect the K content of soils. This study assessed the effect of long‐term K fertilization strategies for corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotations on extractable K in the soil profile of a major Iowa soil type at two locations. The soil type was a Webster fine‐loamy, mixed, mesic, Typic Haplaquoll at both sites. Soil samples were collected from the 0–15, 15–30, 30–60, and 60–90 cm depths after 17 years (Site 1) or 19 years (Site 2) of K fertilization with combinations of two initial rates and four annual rates. The initial rates were 0 and 1,344 or 1,120 kg K ha^‐1 at Site 1 and 2, respectively, and the annual rates ranged from 0 to 100 kg K ha^‐1. Samples were analyzed for ammonium acetate‐extractable K (STK) and nitric acid (HNO₃)‐extractable nonexchangeable K (HNO₃‐K). Concentrations of STK and HNO₃‐K in the top 0–15 cm soil layer at the two sites were higher for the high initial K rates and were linearly related with the annual K rate. Results for the subsoil layers varied between sites and extractants. At Site 1, annual rates of 30 kg K ha^‐1 or higher resulted in a relative accumulation of HNO₃‐K in the 15–30 cm layer. At Site 2, these rates resulted in relative accumulations of STK in the 30–60 cm layer and of HNO₃‐K in the 60–90 cm layer, but with relative depletions of STK in the 15–30 and 60–90 cm layers. Thus, use of one extractant may not always be sufficient to evaluate cropping and fertilization effects on subsoil K. Long‐term K fertilization of corn and soybean rotations affected extractable K of both the topsoil and subsoil. The effects on subsoil K, however, were smaller compared with effects on the topsoil and varied markedly between sites, subsoil layers, and extractants.     

Sampling depth effects on sodium bicarbonate (NaHCO3)‐extractable phosphorus and potassium and fertilizer recommendations

Abstract

Soil test nutrient concentrations vary with depth, especially in perennial cropping systems where fertilizer is broadcast on the soil surface without incorporation. The objective of this study was to determine the effect of fertilizer rate and sampling depth on soil test phosphorus (P) and potassium (K), and P and K fertilizer recommendations for alfalfa (Medicago sativa L.). Five rates of P and K (0, 56, 112, 224, and 336 kg ha^‐1 P₂O₅ and K₂O) were broadcast on established alfalfa stands at three sites with different soil properties and tillage and fertilization histories. In separate plots at one site the same rates of P and K were also incorporated to a depth of 15 cm prior to seeding alfalfa. Soil samples were collected at depths of 0 to 10, 0 to 15, and 0 to 30 cm during the growing season. Fertilizer rates and soil sample depth affected soil test P and K at all sites. Relative to the 30‐cm sample depth, soil test values were higher in fertilized treatments with 10 and 15 cm sample depths due to the concentration of immobile P and K near the soil surface. Sample depths of 10 and 15 cm frequently resulted in lower P and K fertilizer recommendations than those of the 30‐cm depth. Sample depth is an important consideration in routine soil sampling for the purpose of making fertilizer recommendations. If research data used for developing soil test‐based fertilizer recommendation are obtained using a standard sampling depth, routine sampling must also be to the same depth.     

Influence of organic compounds on nitrogen‐fertilizer solubilization

Abstract

In the attempt to find new products which release nutrients in gradual forms, the behavior of two commercial fertilizers was studied, Nitrophoska® (N) and urea (U), covered with two organic materials, humic acid (HA) and alginic acid (AA). The release of nitrogen from the fertilizers was determined by electroultrafiltration (EUF). These applied materials on the fertilizer surface resulted in a slowing of the release of nitrogen, although strictly speaking, these compounds do not function as coated fertilizers. Their effectiveness depends on the fertilizer, for with Nitrophoska®, the addition of alginic acid was more effective, while for urea, the addition of humic acid slowed the release of nitrogen.     

Relationship between soil‐test P and K and yield response of runner peanuts to fertilizer

Abstract

Direct fertilization of peanuts (Arachis hypogaeaL.) with P and K has generally shown few yield responses, resulting in only limited information concerning critical soil‐test levels of P and K. The purpose of the experiments in this report was to determine the critical soil‐test levels of P and K for runner peanuts using the double‐acid extraction procedure. Fertilizer experiments were conducted on farmers’ fields from 1973 to 1986. Site selection was based on soil test data that indicated “medium”; or “low”; levels of available P or K but “high”; in Ca and Mg. Phosphorus and potassium were applied together at all sites at rates of 20 and 74 kg/ha, respectively, as concentrated superphosphate and potassium chloride.

There were yield increases to fertilizer in 6 of the 39 experiments. Soil‐test P for these six ranged between 4 and 53 kg/ha; soil‐test K ranged between 10 and 31 kg/ha. Delineating the yield effect into their P and K components with the aid of multiple regressions of yield on soil test values showed that yield increases were due to the K component of the fertilizer. The critical soil‐test K value was calculated to be 37 kg/ha. Sound mature kernels (SMK) were generally unaffected by fertilizer.     

Pear seedling response to phosphorus in a phosphorus‐fixing soil

Abstract

The effect of P on growth of ‘Bartlett’ pear (Pyrus communis L.) seedlings was evaluated on the P‐fixing, Parkdale soil (Vitrandepts) from Oregon, USA. The P treatment levels were 0.03, 0.04, 0.06, 0.09, 0.15, 0.25, and 0.40 mg P/L of soil solution, based on a P‐sorption isotherm. At age 145 days, the dry weight response to P was significant. Seedlings required 0.25 mg P/L for maximum growth. This corresponds to 723 mg P/kg soil based upon the P‐sorption isotherm. Standard P soil tests did not accurately predict seedling response to P. About one‐half of the soil P was in the chemisorbed fraction.     

Response of no‐tillage and conventional‐tillage cotton to starter fertilization on loess soils

Starter fertilizers have been utilized to improve cotton (Gossypium hirsutum L.) yields, but yield increases have differed with soil type, application method, application rates, and tillage. Starter fertilizer tests were conducted from 1991 through 1993 on a Gigger silt loam (Typic Fragiudalf) in Louisiana and on a Loring silt loam soil (Typic Fragiudalf) in Tennessee to evaluate methods and application rates of 11–37–0 liquid fertilizer for cotton. Treatments were evaluated under conventional‐tillage (CT) and no‐tillage (NT) production systems. Application methods included in‐furrow application at planting (IF), spraying a 4‐inch wide surface band behind the planter (SB), and banding fertilizer two inches to the side and two inches below the seed at planting (2×2). The IF treatments were applied at 1.5, 3.0, and 4.5 gal/A. The SB and 2×2 treatments were applied at 7.5 gal/A. Starter fertilizer treatments were supplemented with broadcast granular fertilizers to achieve a total fertilization rate of 80–40–60 (N‐P₂O₅‐K₂O lb/acre). Starter fertilizer treatments were compared to broadcasting 80–40–60 and 80–0–60. Soil test levels for phosphorus (P) were high on both soil types. In‐furrow applications of 3.0 and 4.5 gal/acre usually reduced plant population for both tillage systems on both soil types. The 1.5 gal/acre IF treatment was less detrimental to stand establishment than the higher IF rates. The effect of starters on plant height varied from year to year. Starter fertilizers usually did not affect early‐season plant height relative to broadcast treatments. In several experiments starter fertilization increased plant height compared to one, but not both, of the broadcast fertilization treatments. High IF rates (3.0 and 4.5 gal/acre) reduced plant height in one experiment. The 2×2 starter fertilizer treatment increased leaf area per plant relative to the broadcast fertilization treatments in two of six experiments on the Gigger soil. Responses for NT and CT studies were similar. In one CT experiment on the Loring soil, the 1.5 gal/acre IF treatment increased leaf area relative to the broadcast treatments. Lint yield responses to starter fertilization were inconsistent. Starter fertilization increased lint yield in one of six experiments on the Gigger soil and in two of six experiments on the Loring soil. Increased yields from starters varied with year and application method, however, the 2×2 and SB treatments tended to provide better responses than IF treatments. Starter fertilizer responses for NT and CT tests were generally similar.     

Interactive effects of wheel‐traffic and tillage system on soil carbon and nitrogen

Abstract

Wheel‐traffic induced soil compaction has been shown to limit crop productivity, and its interaction with tillage method could affect soil nutrient transformations. A study was conducted during 1993–1994 to determine interactive effects of tillage method (conventional tillage and no‐tillage) and wheel‐traffic (traffic and no traffic) on soil carbon (C) and nitrogen (N) at a long‐term (initiated 1987) research site at Shorter, Alabama. The cropping system at this study site is a corn (Zea mays L.) ‐ soybean [Glycine max (L.) Merr] rotation with crimson clover (Trifolium incarnatum L.) as a winter cover crop. Soil organic C, total N, and microbial biomass carbon (MBC) were not significantly affected by six years of traffic and tillage treatments. However, conventional tillage compared to no‐tillage almost doubled the amount of CO₂‐C respired over the entire observation period and during April 1994 field operations. Soil respiration was stimulated immediately after application of wheel‐ traffic, but nontrafficked soils produced greater amounts of CO₂‐C compared to trafficked soils during other periods of observation. Nitrogen mineralization was significantly lower from no‐tillage‐trafficked soils compared to conventional tillage‐trafficked and no‐tillage‐nontrafficked soils for the 1993 growing season. A laboratory incubation indicated the presence of relatively easily mineralizable N substrates from conventional tillage‐trafficked soil compared to conventional tillage‐nontrafficked and no‐till‐trafficked soils. For the coarse textured soil used in this study it appears that conventional tillage in combination with wheel‐traffic may promote the highest levels of soil microbial activity.