Tillage and residue management effects on arylamidase activity in soils

Recent interest in soil tillage and residue management has focused on low-input sustainable agriculture. This study was conducted to investigate the effect of three tillage systems (no-till, chisel plow, and moldboard plow) and four residue placements (bare, normal, mulch, and double mulch) on a most recently detected enzyme in soils, arylamidase activity. This enzyme catalyzes the hydrolysis of an N-terminal amino acid from peptides, amides, or arylamides. Results showed that arylamidase activity is greatly affected by tillage and crop residue placement. The greatest activity was found with chisel/mulch, moldboard plow/mulch, and no-till/double mulch, and the lowest with moldboard plow/normal and no-till/bare. Arylamidase activity was significantly correlated with organic C (r=0.59**) and soil pH _CaCl2 (r=0.55**)_, and decreased with soil depth. Results of this work suggest that the activity of this enzyme is affected by soil management, and indicate its potential ecological significance because of its role in the N cycle.     

Tillage effects on shear strength and bulk density of soil aggregates

An experiment was conducted to determine the effect of four tillage systems (moldboard plow, chisel plow, Paraplow and no-till) on soil aggregate shear strength and bulk density. Two soils, a Canisteo clay loam (fine-loamy, mixed (calcareous), mesic, Typic Haplaquoll) and a Haig silt loam (fine, montmorillonitic, mesic, Typic Argiaquoll) were used in this study. Soil samples were collected from the 0.075–0.15-m-depth increment in 1983 and the 0.075–0.15- and 0.225–0.30-m-depth increments in 1985. Shear strength of soil aggregates 0.02–0.03 m in diameter was measured by a fall-cone penetrometer and bulk density of the same aggregates was measured by gamma-ray attenuation. Aggregates were tested at soil water matric potentials (ψ_m) of −0.2, −1.1 and −4.0 kPa in 1983 and at ψ_m of −0.2, −1.1, −4.0 and −7.9 kPa in 1985. Tillage for the 1983 growing season was conducted under very wet conditions, whereas tillage for the 1985 growing season was conducted under much drier conditions. Samples collected in 1983 showed little tillage effect on shear strength or bulk density. In 1985, tillage had an effect on shear strength and bulk density for the Haig soil, but not for the Canisteo soil. Much of the tillage effect on soil aggregate shear strength could be explained by tillage-induced changes in the aggregate bulk density. As bulk density decreased, soil aggregate shear strength decreased.Sampling depth had no effect on soil aggregate shear strength or bulk density. Matric potential had an effect on soil aggregate shear strength and bulk density. As matric potential decreased, both shear strength and bulk density increased.     

Effect of tillage and residue management on enzyme activities in soils: III. Phosphatases and arylsulfatase

This study was carried out to investigate the effect of tillage and residue management on activities of phosphatases (acid phosphatase, alkaline phosphatase, phosphodiesterase, and inorganic pyrophosphatase) and arylsulfatase. The land treatments included three tillage systems (no-till, chisel plow, and moldboard plow) in combination with corn residue placements in four replications. The activities of these enzymes in no-till/double mulch were significantly greater than those in the other treatments studied, including no-till/bare, no-till/normal, chisel/normal, chisel/mulch, moldboard/normal, and moldboard/mulch. The effect of mulching on activities of phosphatases was not as significant as on activities of arylsulfatase. The lowest enzyme activities were found in soil samples form no-till/bare and moldboard/normal treatments, with the exception of inorganic pyrophosphatase, which showed the lowest activity in no-till/bare only. Among the same residue placements, no-till and chisel plow showed comparable arylsulfatase activity, whereas the use of moldboard plow resulted in much lower arylsulfatase activity. The activities of phosphatases and arylsulfatase were significantly correlated with organic C in the 40 soil samples studies, with r values ranging from 0.71*** to 0.92***. The activities of alkaline phosphatase, phosphodiesterase, and arylsulfatase were significantly correlated with soil pH, with r values of 0.85***, 0.78***, and 0.77***, respectively, in the 28 surface soil samples studied, but acid phosphatase and inorganic pyrophosphatase activities were not significantly correlated with soil pH. The activities of phosphatases and arylsulfatase decreased markedly with increasing soil depth and this decrease was associated with a decrease in organic C content. The activities of these enzymes were also significantly intercorrelated, with r values ranging from 0.50*** to 0.92***. Received: 4 October 1995     

Tillage and residue management effects on β-glucosaminidase activity in soils

There is an increasing interest in assessing the effects of tillage systems and residue management on biochemical processes, especially enzyme activities, of soils. This study was carried out to investigate the effects of three tillage systems (no-till, chisel plow and moldboard plow) and four residue placements (bare, normal, mulch and double mulch) on the activity of N-acetyl-β-glucosaminidase (NAGase, EC 3.2.1.30) involved in C and N cycling in soils. The activity values were significantly affected by tillage and residue management practices, being greatest in soils with no-till/double mulch and least with no-till/bare and moldboard/normal. Also, they were the highest under no-till/ double mulch-treated soils. Linear regression analyses showed that the activity of NAGase was significantly correlated with organic C in the surface soils (r=0.89***) and with organic C content at different depths (r=0.97***). The NAGase activity values were significantly correlated with the arylamidase activity values of the soils (r=0.63**), suggesting that tillage and residue management practices have similar impacts on the activities of these enzymes. The activity of this enzyme decreased markedly with increasing depth of the surface soil (0-15 cm) of the no-till/ double mulch-treated plots.     

Spatial and temporal variability of soil physical properties of norfolk loamy sand as affected by tillage

Physical properties of field soil vary both spatially and temporally. Because so little information is available concerning the changes in magnitude of soil physical properties as functions of soil depth, distance normal to a crop row, and time, they have largely been ignored in model development. The purpose of this study was to evaluate quantitatively the spatial and temporal variability imposed by several tillage operations on several soil physical properties. Three tillage treatments, replicated 4 times in a randomized complete block design, were (1) conventionally-disked 3 times before planting, (2) full width strip chisel plowed to a 27-cm depth, and (3) in-row-subsoiled plus bedding. Soil physical properties measured were cone index (CI), weight percentage water (Pw), bulk density (Db), soil water characteristic curve, saturated hydraulic conductivity (Ksat) and soil settling. These properties were measured 3 times: immediately after planting soybeans (Glycine max (L.) Merr.) on 16 May; on 3 June; on 8 July 1977. Soil properties were measured at the 0–14, 14–28, and 28–41-cm soil depths at 3 positions relative to the row i.e., in the row, in the trafficked interrow, and in the non-trafficked interrow. Significant differences due to tillage treatment were found for Db, CI, and the soil water characteristic. The greatest spatial variation occurred in the 0–14-cm depth and decreased with depth. Significant differences for most variables were also found for the tillage by depth and tillage by position interactions. All properties exhibited significant temporal variation.     

Soil carbon and nitrogen accumulation with long-term no-till versus moldboard plowing overestimated with tilled-zone sampling depths

Numerous investigators of tillage system impacts on soil organic carbon (OC) or total nitrogen (N) have limited their soil sampling to depths either at or just below the deepest tillage treatment in their experiments. This has resulted in an over-emphasis on OC and N changes in the near-surface zones and limited knowledge of crop and tillage system impacts below the maximum depth of soil disturbance by tillage implements. The objective of this study was to assess impacts of long-term (28 years) tillage and crop rotation on OC and N content and depth distribution together with bulk density and pH on a dark-colored Chalmers silty clay loam in Indiana. Soil samples were taken to 1 m depth in six depth increments from moldboard plow and no-till treatments in continuous corn and soybean–corn rotation. Rotation systems had little impact on the measured soil properties; OC content under continuous corn was not superior to the soybean–corn rotation in either no-till or moldboard plow systems. The increase in OC (on a mass per unit area basis) with no-till relative to moldboard plow averaged 23 t ha⁻¹ to a constant 30 cm sampling depth, but only 10 t ha⁻¹ to a constant 1.0 m sampling depth. Similarly, the increase in N with no-till was 1.9 t ha⁻¹ to a constant 30 cm sampling depth, but only 1.4 t ha⁻¹ to a constant 1.0 m sampling depth. Tillage treatments also had significant effects on soil bulk density and pH. Distribution of OC and N with soil depth differed dramatically under the different tillage systems. While no-till clearly resulted in more OC and N accumulation in the surface 15 cm than moldboard plow, the relative no-till advantage declined sharply with depth. Indeed, moldboard plowing resulted in substantially more OC and N, relative to no-till, in the 30–50 cm depth interval despite moldboard plowing consistently to less than a 25 cm depth. Our results suggest that conclusions about OC or N gains under long-term no-till are highly dependent on sampling depth and, therefore, tillage comparisons should be based on samples taken well beyond the deepest tillage depth.     

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.     

Short-term organic matter mineralisation following different types of tillage on a Swedish clay soil

Reduced tillage is proposed as a method of C sequestration in agricultural soils. However, tillage effects on organic matter turnover are often contradictory and data are lacking on how tillage practices affect soil respiration in northern Europe. This field study (1) quantified the short-term effects of different tillage methods and timing on soil respiration and N mineralisation and (2) examined changes in aggregate size distribution due to different tillage operations and how these relate to soil respiration. The study was conducted on Swedish clay soil (Eutric Cambisol) and compared no-tillage with three forms of tillage applied in early or late autumn 2010: mouldboard ploughing to 20–22 cm and chisel ploughing to 12 or 5 cm depth. Soil respiration, soil temperature, gravimetric water content, mineral N and aggregate size distribution were measured. The results showed that respiration was significantly higher (P?<?0.001) in no-till than in tilled plots during the 2 weeks following tillage in early September. Later tillage gave a similar trend but treatments did not differ significantly. Soil tillage and temperature explained 56 % of the variation in respiration. In the early tillage treatment, soil respiration decreased with tillage depth. Mineral N status was not affected by tillage treatment or timing. Soil water content did not differ significantly between tillage practices and therefore did not explain differences in respiration. The results indicate that conventional tillage in early autumn may reduce short-term soil respiration compared with chisel ploughing and no-till in clay soils in northern Europe.     

Tillage intensity and fertility level effects on nitrogen and carbon cycling in a vertisol

Abstract

Because of erosion problems, an effort has been undertaken to evaluate the effect of tillage intensity on carbon (C) and nitrogen (N) cycling on a vertisol. Soil samples at 0–10, 10–20, and 20–30 cm depth were collected from a split plot experiment with five different levels of tillage intensity on Houston Black soil (fine, montmorillonitic, thermic Udic Pellusterts). The experiment was a split plot design with 5 replications. The main plots were chisel tillage, reduced tillage, row tillage, strip tillage, and no tillage. The subplots were soil fertility levels with either high or low fertilizer application rate. Total N, total phosphorus (P), organic C, inorganic N, and C:N ratio were measured on soil samples as well as the potential C mineralization, N mineralization, C turnover, and C:N mineralization ratio during a 30 d incubation. Total P and organic C in soil were increased, with 0.9 and 0.8 kg P ha^‐1 and 20.6 and 20.0 kg C ha^‐1, for high and low soil fertility, respectively. Fertilizer application had no effect on either total N at the 0–10 cm depth, or on soil nutrient status below 10 cm. Potential soil N mineralization was decreased at the 0–10 cm depth and increased at the 20–30 cm depth by the high fertilizer treatment. Chisel tillage decreased total N and P in the 0–10 cm depth, with 1.4 and 1.6 kg N ha^‐1 and 0.8 and 0.9 kg P ha^‐1. However, chisel tillage increased total N and P at the 10–20 cm depth, with 1.3 and 1.2 kg N ha^‐1, and 0.72 and 0.66 kg P ha^‐1 for chisel tillage and no tillage, respectively. Tillage intensity increased C mineralization and C turnover, but reduced N mineralization at the 0–10 cm depth. The results indicate that intensively tilled soil had a greater capacity for C mineralization and for reductions in soil organic C levels compared to less intensively tilled systems.     

Biological soil properties in a long‐term tillage trial in Germany

After 37 years of different soil‐tillage treatments in a long‐term field experiment in Germany, a number of biological soil characteristics was measured. The field trial comprised six major treatments with different implements and various depths. In this paper, results from a comparison of long‐term use of a plow (to 25 cm depth), a chisel plow (to 15 cm depth), and no‐tillage are presented. The biological soil characteristics measured include the soil‐organic‐carbon (SOC) content, microbial biomass, enzyme activities, and the abundance and biomass of earthworms. Long‐term use of a chisel plow and no‐tillage increased the organic‐C content in the uppermost soil layer (0–10 cm) compared with the plow treatment. The microbial biomass and the enzyme activities arginine‐ammonification, β‐glucosidase, and catalase decreased with depth in all treatments. Arginine‐ammonification and catalase were higher in the plow treatment in soil layers 10 to 30 cm. Additionally, the chisel plow caused an increase in number and biomass of earthworms compared to both other tillage treatments. Differences in earthworm numbers and biomass between plowing and no‐tillage were not statistically significant.     

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, NH₄-N, and NO₃-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.     

Seasonal variation of microbial biomass, activity, and community structure in soil under different tillage and phosphorus management practices

No-tillage systems contribute to physical, chemical and biological changes in the soil. The effects of different tillage practices and phosphorus (P) fertilization on soil microbial biomass, activity, and community structure were studied during the maize growing season in a maize–soybean rotation established for 18 years in eastern Canada. Soil samples were collected at two depths (0–10 and 10–20 cm) under mouldboard plow (MP) and no-till (NT) management and fertilized with 0, 17.5, and 35 kg P ha^?1. Results show that the duration of the growing season had a greater effect on soil microbiota properties than soil tillage or P fertilization at both soil depths. Seasonal fluctuations in soil microbial biomass carbon (SMB-C) and nitrogen (SMB-N), in dehydrogenase and alkaline phosphomonoesterase activities, and in total phospholipids fatty acid (PLFA) level, were greater under NT than MP management. The PLFA biomarkers separated treatments primarily by sampling date and secondly by tillage management, but were not significantly affected by P fertilization. The abundance of arbuscular mycorrhizal fungi (AMF; C16:1ω5) and fungi (C18:2ω6,9) was lower under NT than MP at the 10–20-cm soil depth in July. Phosphorus fertilization increased soil microbial biomass phosphorus (SMB-P) and Mehlich-3 extractable P, but had a limited impact on the other soil properties. In conclusion, soil environmental factors and tillage had a greater effect on microorganisms (biomass and activity) and community structure than P fertilization.     

Tillage and nitrogen effects on growth,nitrogen content,and yield of corn

Abstract

The use of conservation tillage methods, including ridge tillage, has increased dramatically in recent years. At the present time, there is great concern that farmers are applying more nitrogen (N) fertilizer than is environmentally or economically sound. In order to determine if N requirement for optimum yield differs with tillage system, tests were initiated to study tillage and N effects on N content, soil moisture content, and yield of corn (Zea mays L.). The study was established in 1987 on two soil types, an Estelline soil (Pachic Haploboroll) and an Egan soil (Udic Haplustoll), located in eastern South Dakota. Five rates of N (0, 65, 130, 195, and 260 kg ha^?1) were applied to plots managed with 3 tillage systems: chisel plow, moldboard plow, and ridge. On the Estelline soil, in both 1988 and 1989, ridge‐tilled plots contained a greater amount of water in the soil profile at emergence and at mid silk than did plots in the other two tillage systems. Soil moisture content at mid silk was significantly correlated with earleaf N, total N uptake, and grain yield in 1988 and earleaf N and grain yield in 1989. However, the correlation coefficients were higher in 1988 than in 1989. On the Egan soil, there were no significant differences in soil moisture content among tillage systems. On the Estelline soil, corn grain yield was affected by a tillage x N‐rate interaction in 1988. Maximum yield within the ridge system was achieved with the 130 kg ha^?1 rate. In 1989 on the Estelline soil, yield was affected by tillage and N rate, but there was no interaction between factors. When averaged over N rates, yields were 7.1, 6.6, and 6.5 Mg ha^?1 in the ridge, moldboard, and chisel systems, respectively. In 1988 plant total N uptake was greater in the ridge system than the moldboard or chisel systems; in 1989 uptake was affected by N rate alone. On the Egan soil, tillage did not affect soil moisture, total N uptake or grain yield in either year. Corn grain yield increased with increasing N rate up to the 195 kg ha^?1 rate. This study indicates that, on some soil types, ridge tillage can improve soil water holding capacity, N utilization and yield of corn.     

Tillage Depth Effects on Soil Physical Properties,Sugarbeet Yield,and Sugarbeet Quality

Tillage depth influences the soil–water–plant ecosystem, thereby affecting crop yield and quality. The effects of tillage depth on soil physical properties and sugarbeet (Beta vulgaris L.) yield and quality were evaluated. A field study composed of two tillage depths [10 cm, referred to as shallow (ST), and 20 cm, referred to as deep (DT)] was conducted on a Lihen sandy loam soil in spring 2007 at the Agricultural Research Service (ARS) irrigated research farm near Williston, North Dakota. Soil bulk density (ρ_b), gravimetric water content (θ_w), and saturated hydraulic conductivity (Ks) were measured three times during the growing season at four depth increments to 40 cm deep. Samples were taken approximately 0.5 m apart within the crop row of irrigated sugarbeet. Soil air-filled pore volume (ε_a) was calculated from soil bulk density and water content data. Soil penetration resistance (PR) was also measured in 2.5-cm increments to a depth of 35 cm. Roots were hand-harvested from each plot, and each sample consisted of the roots within an area consisting of two adjacent rows 1.5 m long. Soil ρ_b was greater in ST than in DT, whereas Ks was greater with DT than with ST. Soil PR was significantly greater in ST than in DT at the 0- to 20-cm depth. Soil θ_w and ε_a were slightly greater in DT than those under ST. Although tillage depth had no significant effect on sugarbeet population, root yield, or sucrose content, a small difference in sucrose yield between two depths of tillage may be attributed to reduced ρ_b, increased water intake, improved aeration, and increased response to nitrogen uptake under DT than under ST. It was concluded that tillage depth enhanced soil physical quality and had little effect on sugarbeet yield or quality.     

Twelve‐year tillage and crop rotation effects on yields and soil chemical properties in northeast Iowa

Abstract

Long‐term tillage and crop management studies may be useful for determining crop production practices that are conducive to securing a sustainable agriculture. Objectives of this field study were to evaluate the combined effects of crop rotation and tillage practices on yield and changes in soil chemical properties after 12 years of research on the Clyde‐Kenyon‐Floyd soil association in northeastern Iowa. Continuous corn (Zea mays L.) and a corn‐soybean [Glycine max L. (Herr.)] rotation were grown using moldboard plowing, chisel plowing, ridge‐tillage, or no‐tillage methods. Tillage and crop rotation effects on soil pH, Bray P1, 1M NH₄OAc exchangeable K, Ca, and Mg, total C, and total N in the top 200 mm were evaluated. Profile NO₃‐N concentrations were also measured in spring and autumn of 1988. Crop yields and N use efficiencies were used to assess sustainability. Bray P1 levels increased, but exchangeable K decreased for all cropping and tillage methods. Nutrient stratification was evident for no‐tillage and ridge‐tillage methods, while the moldboard plowing treatment had the most uniform soil test levels within the 200 mm management zone. Chisel plowing incorporated fertilizer to a depth of 100 mm. Soil pH was lower with continuous corn than with crop rotation because of greater and more frequent N applications. Profile NO₃‐N concentrations were significantly different for sampling depth and among tillage methods in spring 1988. In autumn the concentrations were significantly different for sampling depth and for a rotation by tillage interaction. Estimated N use efficiencies were 40 and 50 kg grain per kg N for continuous corn, and 48 and 69 kg grain per kg N for rotated corn in 1988 and 1989, respectively. The results suggest that P fertilizer rates can be reduced, but K rates should probably be increased to maintain soil‐test levels for this soil association. Crop rotation and reduced tillage methods such as ridge‐tillage or chisel plowing appear to meet the criteria for sustainable agriculture on these soils.     

Spatial and temporal variability of some soil physical properties following tillage of a Nigerian Paleustult

The objective of this study was to evaluate quantitatively the magnitude of the spatial and temporal variation for 7 soil physical properties on a conventionally-tilled Nigerian Paleustult. A 0.4-ha plot was disc-ploughed, disc-harrowed twice, subjected to tractor-wheel traffic at regular space intervals and then seeded to maize (Zea mays, L.). There were significant differences in the physical properties owing to tillage position (spatial variability) and date of sampling (temporal variability), more so in the 0–10-cm layer than in the 10–20-cm layer. In the surface layer, bulk density (Db) and penetrometer resistance (PR) were significantly higher (P ⩽ 0.01) along the tyre marks (maximum Db = 1.76 Mg m⁻³) than in the uncompacted crop row (maximum Db = 1.35 Mg m⁻³) and interrow positions (maximum Db = 1.46 Mg m⁻³). Saturated hydraulic conductivity (K_sat), total porosity (TP) and macroporosity (M) were significantly lower along the tyre mark than in the crop row and interrow positions. K_sat ranged from 0.6 to 42.8 cm h⁻¹, TP, from 0.34 to 0.50 cm³ cm⁻³ and M from 0.06 to 0.25 cm³ cm⁻³ along the tyre mark and crop row positions, respectively. Significant temporal changes were noticed only in K_sat, soil moisture content (MC) and PR. K_sat increased steadily with time along the tyre mark, but showed an irregular trend in the other two positions. PR did not change with time along the tyre marks but it increased significantly with time along the other two positions. MC changed according to the periodicity of rainfall. Only TP varied, owing to tillage position × date interaction. The 10–20-cm layer was spatially less variable but temporally more viarable than the surface layer. Only K_sat and PR showed significant changes owing to the tillage positions, but Db, K_sat, PR and moisture retained at 10 kPa suction (τv10) showed significant temporal changes. Only τv110 varied owing to position × date interaction in this layer.     

Effect of tillage and residue management on enzyme activities in soils

Recent interest in soil tillage and residue management has focused on low-input sustainable agriculture. In this study we investigated the effect of three tillage systems (no-till, chisel plow, and moldboard plow) and four residue placements (bare, normal, mulch, and double mulch) on the activities of four amidohydrolases (amidase, L-asparaginase, L-glutaminase, and urease) in soils from four replicated field-plots. Correlation coefficients (r) for linear regressions between the activities of each of the enzymes and organic C or pH and between all possible paired amidohydrolases were also calculated. The results showed that the effects of tillage and residue management on pH in the 28 surface soil (0–15 cm) samples were not significant. The organic C content, however, was affected significantly by the different tillage and residue-management practices studied, being the greatest in soils with notill/double mulch treatment, and the least with no-till/bare and moldboard/normal treatments. Within the same tillage system, mulch treatment resulted in greater organic C content compared with normal or bare treatment. The activities of the amidohydrolases studied were generally greater in mulch-treated plots than in non-treated plots, and were significantly correlated with organic C contents of soils, with r values ranging from 0.70^*** to 0.90^***. Linear regression analyses of enzyme activities on pH values (in 0.01 M CaCl₂) of the 28 surface soils showed significant correlations for L-asparaginase, L-glutaminase, and urease, with r values of 0.74^***, 0.77^***, and 0.72^***, respectively, but not for amidase (r=0.24). The activities of the four amidohydrolases studied in the 40 soil samples tested were significantly intercorrelated, with r values ranging from 0.72^*** to 0.92^***. The activities of the four amidohydrolases decreased with increasing soil depth of the plow layer, and were accompanied by a decrease in organic C content.     

Aspartase Activity of Soils Under Different Management Systems

Abstract

Recent interest in soil tillage, cropping systems, and residue management has focused on low‐input sustainable agriculture. This study was carried out to evaluate the effects of various management systems on aspartase activity in soils. This enzyme [L‐aspartate ammonia‐lyase, EC 4.3.1.1] catalyzes the hydrolysis of L‐aspartate to fumarate and NH₃. It may play a significant role in the mineralization of organic N in soils. The management systems consisted of three cropping systems [continuous corn (Zea mays L.) (CCCC); corn‐soybean [Glycine max (L.) Merr.]‐corn‐soybean (CSCS); and corn‐oat (Avena sativa L.)‐meadow‐meadow (COMM) {meadow was a mixture of alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.)] at three long‐term field experiments initiated in 1954, 1957, and 1978 in Iowa and sampled in June 1987. The plots received 0 or 180 (or 200) kg ha^?1 before corn and an annual application of 20 kg P and 56 kg K ha^?1. The tillage systems (no‐tillage, chisel plow, and moldboard plow) were initiated in 1981 in Wisconsin and sampled in May 1991. The crop residue treatments were: bare, normal, mulch, and double (2×) mulch. The residue in the study was corn stalks. Results showed that, in general, crop rotation in combination with N fertilizer treatments affected aspartase activity in the following order: COMM>CSCS>CCCC. Because of nitrification of the NH₄ ⁺ or NH₄ ⁺‐forming fertilizers, which resulted in decreasing the pH values, N fertilizer application, in general, decreased the aspartase activity in soils in the order: CCCC>CSCS>COMM. The effect of tillage and residue management practices on aspartase activity in soils showed a very wide variation. The trend was as follows: no‐till/2× mulch>chisel plow/mulch>moldboard plow/mulch>no‐till normal>chisel plow/normal>no‐till bare>moldboard plow/normal. Aspartase activity decreased with increasing depth in the plow layer (0–15 cm) of the no‐till/2× mulch. The decreased activity was accompanied by decreasing organic C and pH with depth. Statistical analyses using pooled data (28 samples) showed that aspartase activity was significantly, linearly correlated with organic C (r=0.78^***) and exponentially with soil pH (r=0.53**). The variation in the patterns and magnitudes of activity distribution among the profiles of the four replicated plots was probably due to the spatial variability in soils.     

Quantifying seedbed condition using soil physical properties

Soil physical condition following tillage influences crop yield, but the desired condition cannot be adequately evaluated with current techniques. This study was conducted to determine a soil condition index (SCI) that could be used to select the type of implement needed to achieve an optimal seedbed with minimum energy input. Effects of bulk density, moisture content, and penetration resistance resulting from three tillage systems (no-till, chisel plow and moldboard plow), on the growth of corn (Zea mays L.) were studied. The experiment was conducted in Boone County, Ames, IA, on soils that are mostly Aquic Hapludolls, Typic Haplaquolls and Typic Hapludolls with slopes ranging from 0 to 5%. The results are from the 2000 season, which had normal weather conditions and yield levels for the Iowa state. The average corn grain yield at this site was 9.36 Mg/ha. At the V2 corn growth stage, the average dry biomass was 1.34 g per plant. The soil physical properties were normalized with respect to reference values and combined via multiple regression analysis against corn biomass at V2 stage into the SCI. Mean SCI values for the no-till, chisel and moldboard plow treatments were 0.86, 0.76, and 0.73, respectively, all with a standard error of 0.0127. The lower the SCI, the more optimum the soil physical conditions. An analysis of variance showed significant differences among mean SCI for each treatment (p-value=0.001). The use of the SCI could improve the tillage decision-making process in environments similar the one studied.     

Impact of Fly Ash Amendment and Incorporation Method on Hydraulic Properties of a Sandy Soil

Coal fly ash has physical and chemical characteristics that makeit useful as a soil amendment, one of the more important beingthe potential to permanently improve the soil water relations ofsandy, drought-prone soils. We axemined changes in theinfiltration rate and water holding capacity of a sandy soilafter application of high rates (up to 950 Mg ha^-1) of aClass F fly ash. Fly ash was applied to large field plots byeither conventional tillage (CT; moldboard plow-disk) orintensive tillage (IT; chisel plow-rotovate-disk), and tomicroplots using a rototiller. Infiltration rate (i) wasmeasured in both studies with a disk permeameter on threeoccasions over a 12-month period. Ash effects on gravimetric water content (θ_g) at the 0–40 cm soil depth were measuredduring a 168 hr period following a 2.5 cm rainfall event andwater release curves (33 to 500 kPa) were constructed in thelaboratory using soils from the large plots. In both studiesi was decreased by ～80% one year after additionof fly ash and θ_gin ash-amended soil was higher than unamended soil throughoutthe 168 hr monitoring period. Soil water distribution variedwith tillage; the IT treatment had the highest θ_g increasesin the 0–20 cm depth while the CT treatment had θ_gincreases throughout the 0–40 cm depth. Soil water content anddistribution in ash-amended microplots were similar to ITtreatments. Fly ash amendment not only increased water holdingcapacity but also increased plant available water by 7–13% inthe 100–300 kPa range. These results suggest fly ash amendmentmay have the potential to improve crop production in excessivelydrained soils by decreasing i and increasing the amountof plant available water in the root zone.