Richard P. Dick

Field management effects on soil enzyme activities

There is growing recognition for the need to develop sensitive indicators of soil quality that reflect the effects of land management on soil and assist land managers in promoting long-term sustainability of terrestrial ecosystems. Eleven soil enzymes assays were investigated relative to soil management and soil quality at two study sites. Soils were sampled from the Vegetable Crop Rotation Plots (VRP) (established in 1989 in humid western Oregon) which compared continuous fescue (Festuca arundinacea) and four winter cover crop treatments in annual rotation with a summer vegetable crop. The second site was the Residue Utilization Plots (RUP) (initiated in 1931 in semi-arid Eastern Oregon) which is under a winter wheat–summer fallow and compared inorganic N, green manure and beef manure treatments. Soil also was sampled at the research center from a nearby grass pasture that is on the same soil type. The enzymes were α- and β-glucosidase, α- and β-galactosidase, amidase, arylsulfatase, deaminase, fluorescein diacetate hydrolysis, invertase, cellulase and urease. At both sites there was a significant treatment effect for each enzyme tested (P<0.05). Enzyme activities (except α- and β-glucosidase and α- and β-galactosidase) were generally higher in continuous grass fields than in cultivated fields. In cultivated systems, activity was higher where cover crops or organic residues were added as compared to treatments without organic amendments. It was found that use of air-dried soil samples provided the same ranking of treatments by a number of enzyme assays and would facilitate adoption of these assays for practical or commercial applications. Deaminase was not a good indicator of soil quality, while β-glucosidase was suggested as an assay that reflects soil management effects and has microbial ecological significance because of its role in the C cycle.

A review: long-term effects of agricultural systems on soil biochemical and microbial parameters

Abstract This paper provides a review of recent developments on assessing the effect of agricultural systems on long-term productivity of soils. Cultivation of soils, besides affecting soil chemistry and structure, reduces biological activity due to the reduction of macroaggregates which provides an important microhabitat for microbial activity. Indirect evidence suggests that soil amendments such as animal and green manures, and plant diversity (crop rotations) may be more important in maintaining soil microbial activity/diversity than conservation tillage in monocultural systems. There is increasing evidence that crop rotation promotes crop productivity by suppressing deleterious microorganisms that flourish under monoculture. Additions of inorganic fertilizers can increase soil biological activity because of an increased plant biomass production which upon incorporation stimulates soil biological activity. Conversely, limited evidence suggests that repeated applications of inorganic fertilizer nutrients can suppress production of certain soil enzymes that are involved in cycling of a given nutrient. The observed transitory decrease in crop productivity during conversion from chemical intensive input to alternative systems (greater reliance on biological resources) may be due to the initial diminished biological potentials of conventionally managed soils to efficiently cycle and mineralize organic nutrient sources. This review reaffirms the continuing need for the maintenance of existing long-term experimental sites and establishment of new studies in major agroecosystems throughout the world.

Influence of long-term residue management on soil enzyme activities in relation to soil chemical properties of a wheat-fallow system

SummarySoil enzyme activities (acid and alkaline phosphatase, arylsulfatase, β-glucosidase, urease and amidase) were determined (0- to 20-cm depth) after 55 years of crop-residue and N-fertilization treatment in a winter wheat (Triticum aestivum L.)-fallow system on semiarid soils of the Pacific Northwest. All residues were incorporated and the treatments were: straw (N0), straw with fall burn (N0FB), straw with spring burn (N0SB), straw plus 45 kg N ha−1 (N45), straw plus 90 kg N ha−1 (N90), straw burned in spring plus 45 kg N ha−1 (N45SB), straw burned in spring plus 90 kg N ha−1 (N90SB), straw plus 2.24 T ha−1 pea-vine residue and straw plus 22.4 T ha−1 of straw-manure. Enzyme activities were significantly (P<0.001) affected by residue management. The highest activities were observed in the manure treated soil, ranging from 36% (acid phosphatase) to 190% increase in activity over the control (N0). The lowest activities occurred in the N0FB (acid phosphatase, arylsulfatase and β-glucosidase) and N90 treated soils (alkaline phosphatase, amidase and urease). Straw-burning had a significant effect only on acid phosphatase activity, which decreased in spring burn treated soil when inorganic N was applied. Urease and amidase activity decreased with long-term addition of inorganic N whereas the pea vine and the manure additions increased urease and amidase activity. There was a highly significant effect from the residue treatments on soil pH. Arylsulfatase, urease, amidase and alkaline phosphatase activities were positively correlated and acid phosphatase activity was negatively correlated with soil pH. Enzyme activities were strongly correlated with soil organic C and total N content. Except for acid phosphatase, there was no significant relationship between enzyme activity and grain yield.

Use of Length Heterogeneity PCR and Fatty Acid Methyl Ester Profiles To Characterize Microbial Communities in Soil

ABSTRACT In length heterogeneity PCR (LH-PCR) a fluorescently labeled primer is used to determine the relative amounts of amplified sequences originating from different microorganisms. Labeled fragments are separated by gel electrophoresis and detected by laser-induced fluorescence with an automated gene sequencer. We used LH-PCR to evaluate the composition of the soil microbial community. Four soils, which differed in terms of soil type and/or crop management practice, were studied. Previous data for microbial biomass, nitrogen and carbon contents, and nitrogen mineralization rates suggested that the microbial characteristics of these soils were different. One site received two different treatments: no-till and conventional till perennial ryegrass. The other sites were no-till continuous grass plots at separate locations with different soil types. Community composition was characterized by assessing the natural length heterogeneity in eubacterial sequences amplified from the 5′ domain of the 16S rRNA gene and by determining fatty acid methyl ester (FAME) profiles. We found that LH-PCR results were reproducible. Both methods distinguished the three sites. The most abundant bacterial community members, based on cloned LH-PCR products, were members of the β subclass of the classProteobacteria, theCytophaga-Flexibacter-Bacteriodes group, and the high-G+C-content gram-positive bacterial group. Strong correlations were found between LH-PCR results and FAME results. We found that the LH-PCR method is an efficient, reliable, and highly reproducible method that should be a useful tool in future assessments of microbial community composition.

Microbial biomass in soils under different tillage and crop rotation systems

A long-term study on the effect of different crop rotations [soybean/wheat, S/W; maize/wheat, M/W or cotton/wheat, C/W] and tillage regimes [no-tillage (NT) or conventional tillage (CT)] on microbial biomass and other soil properties is reported. The experiment was established in 1976 in southern Brazil as a split-plot experimental design in three replications. Soil samples were taken in 1997 and 1998 at 0- to 5-, 5- to 10- and 10- to 20-cm depths and evaluated for microbial biomass C, N, P and S by direct extraction methods. The NT system showed increases of 103%, 54%, 36%, and 44% for microbial biomass C, N, P, and Cmic:Corg percentage, respectively at the 0- to 5-cm depth. NT systems also increased the C to N:S:P ratios. These results provide evidence that tillage or crop rotation affect microbial immobilization of soil nutrients. The larger amount of C immobilized in microbial biomass suggests that soil organic matter under NT systems provides higher levels of more labile C than CT systems.

Organic amendments and phosphorus dynamics : I. Phosphorus chemistry and sorption

The influence of the amount and kinds of organic and inorganic amendments on phosphorus (P) sorption characteristics was determined on two soils from Oregon, Jory (Xeric Haplohumult) and Tolo (Typic Vitrandept), and three soils from Rwanda, Mata (Sombrihumult), Kibeho (Paleudult), and Kinigi (Typic

Organic Amendments And Phosphorus Dynamics: Ii. Distribution Of Soil Phosphorus Fractions

Previously, we found that organic amendments decreased P sorption that was related to changes in some soil chemical properties (e.g., pH and exchangeable Al). However, addition of organic residue to soils may also affect P sorption by adding PO4 (Pi) or releasing organic P (Po) during mineralization

Soil enzyme activities after 1500 years of terrace agriculture in the Colca Valley, Peru

Abstract Long-term productivity and conservation of soils is critical for sustaining agricultural ecosystems. Long-term sites can provide important information about the effects of soil management practices on soil properties but there are relatively few such sites available worldwide. The Colca Valley of Peru provided a unique opportunity to study the effects of 1500 years of cultivation on Mollisols. The specific objective of the work reported was to determine the effects of cultivation at this site on soil enzyme activity as an index of soil biology and biochemistry. The study compared three key soil enzyme activities (phosphatase, β-glucosidase, and amidase) in presently cultivated and abandoned agricultural terraces, and matched uncultivated soils. Results showed that levels of organic matter, nitrogen and phosphorus were greater in agricultural than uncultivated soils. Unlike temperate regions where monoculture, intensive tillage and/or inorganic fertilizer practices have depressed soil enzyme activities, cultivated Colca soils have maintained similar or higher activities than the uncultivated/native soils. Maintenance of enzyme activities over hundreds of years in agricultural soils is partly attributed to traditional management practices including rotations with legumes, additions of animal manures, and minimum tillage.

Thermal stability and activities of soil enzymes as influenced by crop rotations

Soil samples were collected to a depth of 10 cm in 1991 and 1993 from a vegetable crop rotation experiment initiated in 1989. The two cropping treatments, with either 0 or 280 kg N ha−1, represented the traditional vegetable rotation (TVR) and an alternative legume vegetable rotation (LVR) when a vegetable crop alternated with a red clover (Trifolium pratense L.) seed-crop that was incorporated as green manure in the following spring. The enzyme activities of L-asparaginase, amidase and β-glucosidase were determined on whole soil and five soil aggregate size fractions: 1.00–2.00, 0.50–1.00, 0.25–0.50, 0.10–0.25 and <0.1 mm. Thermal stability of the enzymes was determined by conditioning soil samples at 85°C for 2 h or by exposing soil samples to five successive freeze-thaw cycles prior to enzyme assays. Enzyme activities for LVR were significantly greater (P < 0.05) than TVR for β-glucosidase and amidase at both N-rates in 1991. This difference in activity for these enzymes was sustained only at the high N-rate in 1993. The activity of L-asparaginase was significantly higher (P < 0.01) in the LVR in 1993. Sixty to seventy percent of the soil enzyme activity (on a mass basis) was associated with macroaggregates with specific distribution of activity across aggregate fractions varying with enzyme. Average β-glucosidase activity decreased by 50% from 1991 to 1993. In contrast, amidase activity increased 1.43-fold over the same period. β-glucosidase activity was sensitive to temporal trends, showing proportional decreases in activities in each system that were consistent with decreases in organic C. Furthermore, β-glucosidase activity showed significantly higher (P < 0.05) resistance to heat-induced thermal stress in the LVR in both sampling years. Amidase and L-asparaginase activities showed no such treatment effects. The results showed that soil enzyme activity is a sensitive biological indicator of the effects of soil management practices.

Soil enzyme activities under long-term tillage and crop rotation systems in subtropical agro-ecosystems

Agricultural practices that reduce soil degradation and improve agricultural sustainability are needed particularly for tropical/subtropical soils. No-tillage planting causes minimal soil disturbance and combined with crop rotation may hold potential to meet these goals. Soil enzyme activities can provide information on how soil management is affecting the potential to perform the processes in soils such as decomposition and nutrient cycling. Soil enzyme activities were investigated in a split-plot experiment (3 replications) where tillage (no till and conventional) was the main plot and crop rotation (soybean/wheat, S/W; maize/wheat, M/ W or cotton/wheat, C/W) was the subplot. The experiment was established in 1976 in southern Brazil. Soil samples were taken at 0-5, 5-10 and 10-20 cm depths in 1997 and 1998. The 0-5 cm layer under NT system showed increases up 68% for amylase, 90% for cellulase, 219% for arylsulfatase, 46% for acid phosphatase, and 61% for alkaline phosphatase. There were significant correlations of soil enzyme activities with total organic C, and C and N microbial biomass. These results showed that NT increased microbial activity and that soil enzyme activity is a sensitive indicator of alteration soil quality by management.