M.R. Carter

Impact of tillage practices on organic carbon and nitrogen storage in cool, humid soils of eastern Canada

Abstract Soil organic matter storage capacity in agroecosystems varies with soil type, climate and agricultural management practices. The effects of different tillage systems on organic C and N storage were determined for a range of soils of eastern Canada mainly under continuous corn and small grain cereal production. Soil profiles from eight sites on which comparative tillage experiments had been performed for up to 11 years were sampled to a 60 cm depth in four increments (0–10, 10–20, 20–40 and 40–60cm). Organic C and N contents and dry bulk density were determined for each sampling depth. Bulk density measurements showed that the total soil mass in the soil profiles was not influenced by the tillage systems. No significant differences were found between tillage treatments in the total organic C and N storage down to 60 cm depth; the soil profiles under no-till (NT) and chisel plowing (CP) generally did not contain more C and N than those under conventional moldboard plowing (MP). However, the depth distribution of soil C and N varied with tillage. In the surface 0–10cm, C and N contents were higher under NT than under MP, whereas at deeper levels (20–40cm) the reverse trend was observed. It is concluded than under eastern Canadian conditions, where crop production and residue inputs are not affected by tillage, reduced tillage systems would not result in the storage of more soil organic matter in the entire soil profile at least in a 5–10 year period. Placement of the residues would be a major factor influencing the C and N distribution at specific depths.

Developing disease-suppressive soils through crop rotation and tillage management practices

Abstract A field laboratory was established in Prince Edward Island, Canada, to determine the effects of 2- and 3-year crop rotations, with conventional and minimum tillage treatments, on the severity of soilborne diseases of potato. The 2-year rotation consisted of spring barley and potato (cv. ‘Russet Burbank’), and the 3-year rotation was barley (undersown with red clover), red clover and potato. Examination of potato stem, stolon, and tuber tissues revealed significantly ( P =0.05) lower levels of canker and black scurf caused by Rhizoctonia solani , in plants grown in 3-year vs. 2-year rotations. The severity of dry rot ( Fusarium spp.) and silver scurf ( Helminthosporium solani ) was significantly ( P =0.05) lower in tubers from plots managed with 3-year rotations and minimum tillage practices. Potato tubers harvested from 3-year rotational soils were significantly ( P =0.05) less diseased than those from 2-year rotational soils following inoculation with Phytophthora erythroseptica , causal agent of pink rot. In greenhouse experiments using field soils from 2- and 3-year rotations, we found that potato plants growing in 3-year rotational soils were significantly ( P =0.05) less diseased than those growing in 2-year rotational soils following inoculation with P. erythroseptica . Analysis of root zone bacteria recovered from the rhizosphere (exoroot) and potato root tissues (endoroot) showed that the greatest antibiosis activity inhibiting the growth of soilborne pathogens in vitro occurred in bacterial isolates recovered from the endoroot tissues of 3-year rotation crops under minimum tillage management. Our evidence supports the view that soil agroecosystems can be modified through rotation and conservation tillage practices to improve disease suppression by enhancing the antibiosis abilities of endophytic and root zone bacteria (endo- and exoroot).

A review of plant disease, pathogen interactions and microbial antagonism under conservation tillage in temperate humid agriculture

Abstract The advent of conservation tillage presents a need for a greater understanding of plant disease and disease interactions in temperate humid agriculture, where excessive crop residues, continuous moist soil conditions and soil compaction are potential constraints. In this review, biotic and abiotic factors, and aspects of microbial antagonism, which can influence plant disease development in the root zone, are characterized in the context of conservation tillage in humid climates. Soil densification and reduction in macroporosity can aggravate abiotic root disease. Changes in soil aeration and permeability status can alter the quantitative and qualitative differences between soil rhizofloral populations, and survival and distribution of pathogen inoculum. Further-more, anaerobic soil conditions can result in root-pathogen interactions leading to plant disease development. A good quality soil physical environment is an important indicator for root health under conservation tillage in humid climates. Conservation tillage tends to concentrate plant debris and consequently microbial biomass in the top 5 to 15 cm of soil, and thus promotes survival of pathogens. However, disease-causing microbes make up only a proportion of the rhizofloral population. Relatively high soil microbial activity can lead to competition effects that may ameliorate pathogen activity and survival, and counteract a high pathogen inoculum pressure. Microbial antagonism in the root zone can lead to the formation of disease-suppressive soils. This phenomenon, which is important for the adoption of conservation tillage in humid climates, can be influenced by soil and crop management practices, especially crop rotation.

Organic C and N storage, and organic C fractions, in adjacent cultivated and forested soils of eastern Canada

As a major attribute of soil quality, organic matter is responsive to agricultural land use practices including tillage. A study was initiated in eastern Canada to characterize changes in the masses of organic C and total N, and organic matter fractions in forested and adjacent cultivated or forage sites. Generally, the cultivated and forage sites had denser soil profiles than the forest sites. Based on an equivalent soil mass, to accommodate differences in soil bulk density, the paired forest and cultivated sites showed that cultivation decreased the mass of organic C (35%) and total N (10%) in the soil profile of the Podzolic soils, but increased organic C (25%) and total N (37%) in the Brunisolic (Cambisol) and Gleysolic soils. For the Podzolic soils, use of forages increased soil stored organic C and N by 55% and 35%, respectively. Organic C fractions were mainly of significance in the A horizon. Soil microbial biomass C was greater in the forested, compared to the cultivated soil, but the proportion of soil organic C as microbial biomass C (1.3% to 1.6%) was similar. The proportion, however, was greater (2.1%) for the forage soil, compared to the corresponding cultivated (1.3%) soil, suggesting that organic C was continuing to increase under the former. The relatively large proportion (19%) of organic C found in the light fraction of forest soils in the A horizon was decreased (up to 70%) by cultivation. In contrast, the proportion of macro-organic C present in the soil sand fraction was not greatly influenced by cultivation. Overall, soils in eastern Canada have a relatively large potential to store organic matter. The study illustrates the importance of soil type and cultivation interactions for maintenance of soil organic matter storage, and the positive influence of forages in this regard in agroecosystems.

Characterization of soil physical properties and organic matter under long-term primary tillage in a humid climate

Abstract Chisel ploughing is considered to be a potential conservation tillage method to replace mouldboard ploughing for annual crops in the cool-humid climate of eastern Canada. To assess possible changes in some soil physical and biological properties due to differences in annual primary tillage, a study was conducted for 9 years in Prince Edward Island on a Tignish loam, a well-drained Podzoluvisol, to characterize several mouldboard and chisel ploughing systems (at 25 cm), under conditions of similar crop productivity. The influence of primary tillage on the degree of soil loosening, soil permeability, and both organic matter distribution throughout the soil profile and organic matter content in soil particle size fractions was determined. At the time of tillage, chisel ploughing provided a coarser soil macrostructure than mouldboard ploughing. Mouldboard ploughing increased soil loosening at the lower depth of the tillage zone compared to chisel ploughing. These transient differences between primary tillage treatments had little effect on overall soil profile permeability and hydraulic properties of the tilled/non-tilled interface at the 15–30 cm soil depth. Although soil microbial biomass, on a volume basis, was increased by 30% at the 0–10 cm soil depth under chisel ploughing, no differences were evident between tillage systems over the total tillage depth. Mouldboard ploughing increased total orgainc carbon by 43% at the 20–30 cm soil depth, and the carbon and nitrogen in the organic matter fraction ≤ 53 μm by 18–44% at the 10–30 cm soil depth, compared to chisel ploughing.

Direct drilling and soil loosening for spring cereals on a fine sandy loam in Atlantic Canada

Abstract Changes in soil structure and properties, plant growth and diseases and agronomic aspects were determined, after 3 years, on a Charlottetown fine sandy loam, an Orthic Podzol with a perhumid soil moisture regime, subjected to three tillage systems for spring cereals. The tillage systems consisted of direct drilling, soil loosening with a “paraplow” followed by direct drilling and mouldboard ploughing. Rate of plant growth and other crop measurements were not changed by the tillage systems, except for the depth of seeding. Direct drilling reduced the accumulation of N and K in the plant, and reduced grain N, compared with mouldboard ploughing. Soil loosening prior to direct drilling prevented the decline in N and K accumulation, and increased grain yield and N content, in comparison with mouldboard ploughing. Direct drilling caused changes in soil macro-aggregation and reduced the evaporation rate, and increased microbial biomass C and N, total organic C and N and extractable ions at the soil surface (0–5 cm), compared with mouldboard ploughing. In addition, earthworm numbers were increased under direct drilling. Root lesion and spiral nematodes were not influenced by tillage differences. Soil loosening prior to direct drilling alleviated the significant reductions in soil macroporosity, and prevented the increase in soil bulk density, soil strength and percentage water-filled pore space (%WFPS) associated with direct drilling alone. Although soil permeability was optimum under direct drilling alone, the relative increase in %WFPS and reduction in soil aeration were associated with a concomitant increase in common root rot.

Conservation tillage systems, fungal complexes and disease development in soybean and barley rhizospheres in Prince Edward Island

Abstract A potential for reduced soil macroporosity (below 12% soil volume) under direct drilling, with a concomitant increase in soil relative saturation, is associated with an increase in crown and root rots in Prince Edward Island field crops. Four long-term tillage systems (moldboard plowing, paraplowing-direct drilling, rotary cultivation and direct drilling) were compared in relation to the pathogenic fungal complexes formed in a two crop rotation in spring barley ( Hordeum vulgare L.) and soybean ( Glycine max L. Merrill) over a 3 year period in a cool humid region of eastern Canada. The principal phytopathogenic fungal complex of Rhizoctonia solani Kuhn, Fusarium avenaceum (Fr.) Sacc. and F. oxysporum Schl. remained constant over the treatments. Tillage practice did not affect the number of colony forming units of R. solani in the rhizosphere. The recovery of R. solani from root tissues tended to be lower following conservation tillage and was attributed to antagonism associated with elevated numbers of saprophytic trash microflora concentrated at the soil surface. Disease levels in potato ( Solanum tuberosum L.) plantlet bioassays were not influenced significantly by soil source or tillage regime. However, plantlet growth tended to be depressed following transplantation into soil from soybean plots in 1993. Under optimum soil physical conditions conservation tillage did not appear to influence disease levels in barley and soybean rotations.

Development of direct-drilling systems for sandy loam soils in the cool humid climate of Atlantic Canada.

This study provides an overview of the adaptation of direct-drilling systems on sandy loam soils under the cool boreal, humid to perhumid soil climate of Prince Edward Island in Atlantic Canada, where the growing season is relatively short (May–October). Direct drilling can overcome the constraints of limited field workdays for seeding of spring cereals, owing to wet soil conditions in early May, or the integration of planting date with optimum soil temperatures for silage corn (Zea mays L.). However, the advantage of timeliness may be offset under sequential direct drilling for these crops, owing to a combination of reduced macroporosity at the soil surface and increased percentage of water-filled pore space, especially in soils with levels of organic carbon below 2% (w/w). In contrast, the presence of standing-crop residue, in pasture-renovation studies, allowed sequential or regular direct drilling of various forage species to occur with no adverse effect on soil structure. Use of direct drilling for spring cereals and silage corn on a rotational basis allowed intermittent soil loosening to prevent increasing surface soil compaction. Overall, direct drilling on perhumid, sandy loam soils proved successful when soil surface compaction was alleviated or circumvented.

Agriculture Management Effects on Soil Carbon Sequestration in Eastern Canada

A large amount of C is stored in soil organic matter. (SOM). Over most of the earth’s land surface, the quantity of C as SOM (1400–1500 Gt C) exceeds by a factor of two or three the amount stored in living vegetation (560 Gt C) (Schlesinger, 1990). The contribution of CO2 released to the atmosphere from farmland has been estimated to represent 20–25% of the total amount released due to human activity (Duxbury et al, 1993). However, the estimation of the quantities of CO2 released from farmlands is subject to many uncertainties. Most studies on the losses of SOM from agricultural soils often consider only the surface layer in terms of % C, rather than total C in the whole soil profile which requires measurement of bulk density (Duxbury and Mosier, 1993). It is therefore difficult to separate increased mineralization rates from a possible dilution and redistribution of SOM in the profile, which could be due to tillage, erosion or other disturbances of the ecosystem. There is therefore a need for more information on the quantitative distribution of C throughout the whole soil profile.

Conservation Tillage in Potato Rotations in Eastern Canada

Potato (Solanum tuberosum L.) farming systems are often associated with soil degradation due to their excessive use of tillage and production of low levels of crop residue in the potato year. Results from a 12-year study, initiated on a fine sandy loam (Orthic Podzol) in Prince Edward Island (eastern Canada), were evaluated to assess the use of conservation tillage (CT), compared to conventional tillage, in 2-year (barley-potato) and 3-year (barley – red clover – potato) rotations. The CT strategy was to shift the primary tillage event for the potato phase from the autumn to spring, and to reduce the degree and depth of tillage. Mulches were used on all plots after potato harvest to provide soil cover over the cool season. Potato yield, soil cover, soil organic matter and structure, and soil-borne diseases were used as indicators to assess the feasibility of the cropping systems. Marketable potato yield was similar between the two tillage systems. The CT system provided relatively high surface residue levels after potato planting, compared to the bare soil surface in the conventional tillage system. Soil organic carbon and soil structural stability were significantly increased at the 0–10 cm soil depth in the CT, compared to the conventional system. Soil-borne diseases of potato were significantly reduced in 3-year rotations compared to 2-year rotations, but were mainly unaffected by tillage practice. Overall, use of CT in 3-year potato systems has the potential to maintain crop productivity and protect the soil resource.