Charlottetown Fine Sandy Loam Research Articles

Increasing potato profitability through rotation systems and winter cover, nitrogen fertilizer, and supplemental irrigation in Atlantic Canada

AbstractAverage potato yield in Prince Edward Island, Canada, has been stagnant since 2006. Two field studies were conducted on Charlottetown fine sandy loam soil to address this concern. In the first experiment, two alternative crop rotations, grain corn (Zea mays L.)–sorghum sudan grass (Sorghum × drummondii)–potato (C–SS–P) and soybean (Glycine max (L.) Merr.)–mustard (Brassica juncea (L.) Czern.)–potato (Soy–M–P), were compared to a conventional barley (Hordeum jubatum L.) (under seeded with red clover)–red clover (Trifolium pratense L.)–potato (Solanum tuberosum L.) (B–RedCl–P) rotation. This experiment was conducted for two 3‐year cycles comparing the effects of potato rotation, nitrogen fertilizer, and supplemental irrigation. The second experiment evaluated the inclusion of winter cover crops in a 3‐year potato crop rotation. The profitability of potatoes in each rotation was assessed using a stochastic budget of yields and fertilizer and crop prices. The effects of supplemental irrigation were not significant; however, nitrogen fertilization increased potato yields by 48%. Potato yields and net revenues in C–SS–P increased by 10.5% and 32.6% and in Soy–M–P by 6.7% and 20.5%, respectively, compared to potato in B–RedCl–P rotation. The use of winter rape cover increased potato yields by 18.6% compared to a system without winter covers, although some of these increases could be due to the use of sudan grass instead of red clover in B–RedCl–P rotation. It is recommended that potato producers implement the alternative rotation with additional fertilization and winter cover crops to increase yields and profits.

Long-term conservation tillage in potato rotations in Atlantic Canada: Potato productivity, tuber quality and nutrient content

Conservation tillage in combination with mulches in potato (Solanum tuberosum L.) farming systems can maintain crop productivity and improve soil properties, in comparison with conventional tillage systems. However, information is needed on the long-term influence of such practices on potato crop parameters. A study was initiated in 1994 on a Charlottetown fine sandy loam (Orthic Podzol) in Prince Edward Island to assess the feasibility of using conservation tillage practices in combination with crop residue mulches (after the potato harvest) on potato production in two different potato rotations: a 2-yr barley-potato rotation and a clover-based 3-yr (barley-red clover -potato) rotation. In the conservation tillage system, the primary tillage event was moved from the autumn to spring and the degree and depth of tillage were reduced by replacing the conventional mouldboard plough (20 cm depth) with a shallow (15 cm depth) one-pass chisel plough just prior to potato planting. Potato yield and tuber quality, surface residue levels after potato planting, and tuber mineral content were evaluated from 2000 to 2007. Adoption of conservation tillage over the long-term did not adversely influence total or marketable potato yield, or tuber quality. The clover-based 3-yr rotation, compared with the 2-yr rotation, had little effect on total potato yield (42 vs. 44 Mg ha-1), but produced significantly higher marketable tuber yields (38 vs. 32 Mg ha-1), for four of the eight yrs of the study. The conservation tillage system, for both rotations, provided relatively high surface residue levels (>30%) after potato planting, compared with the bare soil surface in the conventional tillage system. Nutrient and trace element contents in tuber dry matter were similar between conservation and conventional tillage. Tuber uptake of nitrogen and other nutrients were slightly greater under the 3-yr, compared with the 2-yr rotation, and associated with tuber dry-matter yield differences. The results of the 14-yr study confirm the conclusions of previous short-term studies that a reduction in depth and intensity of tillage for potato culture is yield neutral, and a viable alternative to conventional tillage systems for potato production on sandy loams in eastern Canada. Key words: Conservation tillage, potato, crop rotation, fine sandy loam, crop yield, surface residue, eastern Canada

Long-term influence of compost on available water capacity of a fine sandy loam in a potato rotation

An improved soil physical structure, associated with organic amendments in crop rotations, can be viewed as an emergent property. A study was conducted to evaluate the effect of applied compost on soil water retention and available water capacity, and other associative soil properties in a long-term 3-yr potato rotation established on a Charlottetown fine sandy loam (Orthic Humo-Ferric Podzol) in Prince Edward Island. Soil samples (0–10 cm) were obtained from two crop phases (barley and potato) during the fourth cycle of the rotation (after four compost applications) in the 12th year of the experiment. Except for particulate N, compost had little effect on soil organic matter. In comparison to the barley phase, a combination of compost and surface tillage in the potato phase was associated with improved soil porosity parameters and increased soil water contents at −33 kPa (“field capacity” ), −100 and −300 kPa matric potential, compared with the no-compost control. These results indicate that compost stabilized the tillage induced soil aggregates and macro-porosity in the potato phase. Regression analysis showed that soil volumetric water content at both −33 and −1500 kPa matric potential was significantly related to soil C concentration, although the soil available water capacity remained unchanged. The results imply that the “non-nutrient” compost effect on potato productivity was related to soil water retention. Key words: Soil water retention, soil physical and biochemical properties, compost amendment, tillage, potato rotation, eastern Canada

Influence of tillage and liquid swine manure on productivity of a soybean-barley rotation and some properties of a fine sandy loam in Prince Edward Island

Interactions between tillage management for manure incorporation and rate of manure application may influence crop productivity and soil properties. This study was conducted to evaluate the effect of liquid swine (Sus scrofa L.) manure (LSM) applied at three N rates (40, 80, 160 kg ha-1), compared with mineral N fertilizer, in a 2-yr barley (Hordeum vulgare L.)-soybean (Glycine max L. Merr.) rotation, incorporated by two tillage methods (chisel plough and disc), on crop yield and quality and some soil properties, especially C parameters. The LSM was applied every second year in the spring, prior to barley seeding. The study was conducted over a 5-yr period on a Charlottetown fine sandy loam (Orthic Humo-Ferric Podzol) in Prince Edward Island. The experimental design was a split-plot with four replicates. Soil samples (0–60 cm) were obtained at the termination of the study to determine residual effects of the LSM on soil properties. The two methods of LSM incorporation had no differential effect on crop response. Generally, increasing the application rate of LSM increased the barley yield, but had no effect on grain N concentration. A residual effect on crop grain yield for the high rate of LSM was evident in the soybean year. Crop response to LSM was similar to that of mineral fertilizer. Application operations for LSM had no adverse effect on soil strength or soil bulk density. Soil properties (microbial biomass C, carbohydrates, water-stable aggregates) were not greatly influenced by LSM application, however, increases in particulate C (POM-C) were evident for the high LSM rate at the 10- to 30-cm soil depth. The study showed that for fine sandy loams in Prince Edward Island low to medium rates of LSM applied every second year could serve as a source of N for barley in barley-soybean rotations. Key words: Barley, soybean, liquid swine manure, fine sandy loam, soil properties, tillage incorporation, eastern Canada

Influence of compost on the physical properties and organic matter fractions of a fine sandy loam throughout the cycle of a potato rotation

Potato (Solanum tuberosum L.) rotations often require organic amendments to maintain or improve soil organic matter levels and soil physical properties. However, beneficial effects of compost can be modified by time of application and rotating tillage depth and intensity. This study was conducted to evaluate the effect of compost applied once at different phases in a 3-yr potato, barley (Hordeum vulgare L.), and red clover (Trifolium pretense L.) rotation on a range of soil physical properties and organic matter fractions for a Charlottetown fine sandy loam (Orthic Humo-Ferric Podzol) in Prince Edward Island. Soil samples (0–8 cm) were obtained during the second cycle of the rotation (after two compost applications) in the fifth year of the experiment. Soil properties were influenced by compost addition, time of compost addition, and crop phase. Compost-induced benefits in soil physical properties (bulk density, macro-porosity, oxygen diffusion rate, shear vane strength, water-filled pore space) were mainly expressed in the red clover phase of the rotation, where soil density was relatively high compared to the barley and potato phases, due to the absence of tillage. The soil physical parameters, however, were mainly within their established optimum ranges for this soil type. Soil water content at −0.033 MPa was increased by compost in the potato phase, compared to the control. Soil organic matter was influenced by both compost and crop C inputs. Compost increased soil particulate organic matter (POM) in the potato and barley phases. Due to differences in crop residue inputs, compost-related differences in organic matter were minimized in the red clover phase of the rotation. Compost addition increased potato tuber yield above the maximum yield obtained with nitrogen application. This “non-nitrogen” compost yield effect may be related to the slight, but significant, improvement in soil water-holding capacity. Overall , compost application in an intensive 3-yr potato rotation provided benefits for potato productivity and in both soil physical and biological properties. Key words: Soil organic carbon, particulate organic matter, soil physical properties, compost amendment, potato yield, eastern Canada

Applications in food quality and environmental contamination

Compost was made from source‐separated municipal waste with or without disposable diapers included in the compostable waste stream. The composts were applied prior to planting of barley in a barley ‐ red clover ‐ potato rotation on a Charlottetown fine sandy loam soil. A control which did not receive compost was included in the randomized complete block experiments with four replications at each of the seven locations. Nutrient levels in the compost were determined by sampling compost material delivered to each location prior to, and during, the spreading operation. Nutrient levels in barley (Hordeum vulgare L.) and red clover (Trifolium pratense L.) tissue were determined. Some nutrients were found at slightly higher concentrations in the compost made from the waste stream containing disposable diapers than from the waste stream where disposable diapers were excluded. Nutrient levels in barley and red clover from compost‐treated plots were generally higher than from the untreated plots. The two compost sources generally produced barley and clover with similar nutrient levels.

Soil organic matter quality and aggregate stability under eight potato cropping sequences in a fine sandy loam of Prince Edward Island

Soil degradation and soil organic matter (SOM) reduction have long been suspected to occur under intensive potato (Solanum tuberosum L.) production in Prince Edward Island. Thus, this study was conducted to evaluate the effect of eight potato cropping sequences involving barley (Hordeum vulgare L.), ryegrass (Lolium multiflorum L.), red clover (Trifolium pratense L.) and barley under-seeded with red clover on aggregate stability and SOM properties of a Charlottetown fine sandy loam (Orthic Humo-Ferric Podzol). Total C and N, light-fraction (density < 1.7 g cm−3) C (LF-C) and light-fraction N (LF-N), microbial biomass C (MBC), carbohydrate content, alkaline phosphatase activity (APA) and aggregate stability were determined in the 0- to 15-cm soil layer in the 6th and 10th years of the trial. Average C and N contents were 20 to 27% greater in sequences that included 3 or 4 yr of potatoes and a high frequency of red clover than in a 9-yr potato sequence; and were attributed to the less frequent tillage and higher organic matter inputs associated with the forage component. The response for MBC, LF-C, LF-N and APA was greater than those for total C and N suggesting that the former parameters may better reveal SOM changes caused by variations in potato management than the latter. Light-fraction N was particularly sensitive to the inclusion of perennial legumes in the cropping sequence. Wet-aggregate stability was 33% higher after 6 yr in the sequence with 50% frequency of red clover than in the continuous potato system, but no effect was noted after 10 yr. The results of this study indicate that sequences which are limited to 30 to 40% of potatoes and have a high frequency of perennial forage such as red clover, lead to greater SOM content and quality of a Charlottetown fine sandy loam compared to continuous potatoes. Trends in aggregate stability generally followed those of SOM fractions but the effects were relatively smaller and varied with time. Key words: Potato, Solanum tuberosum L., soil aggregation, organic matter, carbon, nitrogen, light fraction, microbial biomass

Glyphosate application and timing of tillage of red clover affects potato response to N, soil N profile, and root and soil nematodes

The effects of glyphosate application and time of tillage of red clover on soil NO3-N profiles, the response of the subsequent potato crop to varying rates of N fertilizer application, and root and soil nematodes, were evaluated. The study was conducted over three cropping seasons on a Charlottetown fine sandy loam on Prince Edward Island. Red clover was moldboard ploughed in mid-September (early fall), or moldboard or chisel ploughed in mid-October (late fall), or moldboard ploughed in the spring. Glyphosate was applied in early fall and the dead clover was moldboard or chisel ploughed in mid-October or left undisturbed until spring. A barley control, where barley was harvested and straw incorporated with a tandem disc harrow in early September, was included. Potato were planted with 6 rates of N (0 to 250 kg ha–1 in 50-kg increments) band applied at planting. The barley control treatment produced lower potato yield without fertilizer N in all 3 yr of the study compared to red clover treatments, but potato yields were similar at high rates of applied N. Potato tuber yields after spring moldboard ploughing of red clover were higher at low N rates and lower at high N rates than yields after late fall treatment in one year of the study. Concentrations of nitrate-N in the soil in mid-November were highest following the early fall moldboard ploughing and lowest in the undisturbed clover plots. Fall soil nitrate-N levels were intermediate following the glyphosate application and late fall tillages. Early spring soil nitrate-N levels in the surface 30 cm were generally highest with the spring and late fall tillage and lowest with the early fall tillage. Levels of nitrate-N in potato petioles increased with increased rates of N application and generally increased as tillage of the red clover was delayed from early fall to late fall to spring. In general, cultivation and the application of glyphosate did not affect soil and root nematode populations. In two instances, the moldboard plough tillage treatments were associated with higher levels of the clover-cyst nematode, Heterodera trifolii. One of the tillage treatments was combined with glyphosate, but this was the only case where the herbicide had an impact on nematodes. To maximize the benefits to the subsequent potato crop and to minimize leaching of nitrate, incorporation of legume residue should be delayed until the rate of mineralization and nitrification of the legume N is minimized. It is suggested that incorporation of red clover be delayed until after mid-October for clover–potato systems on PEI. Key words: Glyphosate, nematodes, nitrate leaching, petiole nitrate-N, potato, soil nitrate-N, tillage time

Influence of time of tillage on soil physical attributes in potato rotations in Prince Edward Island

In Atlantic Canada, lack of soil cover over the cool season due to conventional primary tillage in the fall, in potato rotations, leaves the soil vulnerable to redistribution processes. The suitability of shifting primary mouldboard plough tillage operations from the fall to the spring in the potato ( Solanum tuberosum L.) phase of a 3-year rotation (spring barley ( Hordeum vulgare L.)–red clover ( Trifolium pratense L.)–potato, or replacing fall mouldboard with fall chisel ploughing, was assessed over a 3-year period on Charlottetown fine sandy loam, an Orthic Podzol. A suite of soil physical attributes was used to assess the influence of primary tillage on the degree of soil loosening, permeability, and macro-structure. Potato yield and quality were also determined. Although, mouldboard ploughing provided an additional 2–10 cm of loose (i.e. penetration resistance <1.5 MPa) soil at the lower depth of the tillage zone, compared to chisel ploughing, there were no differences in soil permeability as measured by bromide movement. Soil macro-structure, or clod size, in the potato ridge just prior to harvest reflected the degree of secondary tillage rather than the influence of primary tillage. Clod size distribution in the potato ridge was not a problem for harvesting operations as clods did not exceed 20 mm in diameter. Soil permeability at the base of the potato ridge, as assessed by oxygen diffusion rate (>55 μg m −2 s −1), air permeability, and macropore continuity (quotient of air permeability and macropore volume, >100 μm 2), and soil shear strength (<22 kPa) were not limiting for root growth. However soil pore space, as reflected by bulk density (>1.25 Mg m −3) and macropore volume (<12%) would pose a soil aeration limitation in this soil-type at the base of the ridge under wet soil conditions. Potato total yield and marketable yield were not influenced by differences in primary tillage over the 3-year period. Use of spring primary tillage and replacement of the mouldboard with a chisel plough, within the potato phase of a 3-year rotation, caused little change in soil physical quality compared to the conventional tillage system and appears to be a suitable conservation tillage technique for sandy loam soils in the climate of Atlantic Canada.

Influence of non-inversion loosening on permanent pasture productivity

Non-inversion tillage can have significant benefits over inversion tillage in loosening soils under permanent pasture. A suite of attributes was used to characterize the degree of compaction at the 0- to 20-cm depth of a Charlottetown fine sandy loam under a 10-yr pasture in Prince Edward Island. Non-inversion tillage, using a paraplow, a slant-legged cultivator loosened the soil at the 10- to 20-cm depth. Penetrometer resistance profiles showed that the loosened soil condition persisted for 3 to 4 yr. Non-inversion soil loosening caused a negative yield response, which was possibly related to root injury. Key words: Podzol, penetration resistance, Kentucky bluegrass, white clover

Soil Structural Form and Stability, and Organic Matter under Cool‐Season Perennial Grasses

AbstractTemperate grasses conserve soil by providing vegetative cover and by favoring soil aggregation. A field study was conducted on a Charlottetown fine sandy loam (a coarse‐loamy, mixed, frigid Typic Haplorthod) to determine the effect of cultivars of orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.), in comparison to timothy (Phleum pratense L.), on soil structure and organic matter fractions after 4 yr of growth. Timothy is one of the main grasses grown in the cool humid climate of eastern Canada. Bulk density (1.27–1.32 Mg m−3), pore‐size distribution, and shear strength (12.5–15.6 kPa), as a measure of soil structural form, were within the optimum range for this soil type under each grass species. Dry‐aggregate mean weight diameter (MWD) was similar (3.66–4.30 mm) among grass species. Wet‐aggregate MWD was greater under tall fescue cultivars and ‘Farol’ timothy (2.81–3.22 mm) compared with the orchardgrass and ‘Champ’ timothy (2.08–2.36 mm). These differences were also reflected by the difference or ratio of MWD between dry and wet sieving. Aggregate‐size distribution indicated that wet‐aggregate MWD differences were associated with greater levels of macroaggregates (&gt;2 mm). Differences in water‐stable aggregate stability were not related to differences in plant parameters, organic matter, or organic matter fractions (i.e., microbial biomass C, carbohydrates, and particulate organic matter). These data suggest that organic matter parameters, commonly used to characterize soil stability in cropping systems, are less useful for soils under perennial grass with stable microaggregate structures.

Influence of reduced tillage systems on organic matter, microbial biomass, macro-aggregate distribution and structural stability of the surface soil in a humid climate

Studies were conducted to determine changes in organic matter and microbial biomass carbon in comparison with structural stability at the surface soil (0–5 cm) of a Charlottetown fine sandy loam, an Orthic Podzol, at three tillage and grassland sites situated in Prince Edward Island. The tillage experiments, established for 3–5 years, included comparisons of mouldboard ploughing, direct drilling, shallow tillage, and chisel ploughing. Two indices of soil structural stability were used: mean weight diameter (MWD) and aggregation index (AI). The latter index assigns a weight factor to aggregate size ranges based on their value for plant germination and root growth. Direct drilling and reduced tillage increased the level of soil organic carbon by 10–17%, relative to mouldboard ploughing. Organic carbon was more enriched in 1–2 mm and 4.75–9.00 mm macroaggregates, especially the former, compared with whole soil. The MWD of aggregates after wet sieving was 33% and 55%, relative to the grassland sites, for mouldboard ploughing and direct drilling, respectively. On these soils of similar mineralogy and particle size, a close linear relationship ( r=0.942) was observed between organic carbon ( r=0.947) and nitrogen ( r=0.923). The AI was significantly correlated to both organic carbon and microbial biomass carbon using power regression. In contrast to MWD, the AI under direct drilling and reduced tillage, associated with an organic carbon level of 2.5%, approximated the AI under grass. Overall, the study showed that minimum tillage systems in humid climates can improve structural stability at the soil surface of fine sandy loams over a relatively short time frame.

Evaluation of shallow tillage for spring cereals on a fine sandy loam. 2. Soil physical, chemical and biological properties

Changes in the soil condition were determined over a 4-year period, to assess the use of shallow tillage for the low-input production of spring cereals in Prince Edward Island. The soil was a Charlottetown fine sandy loam (Orthic Podzol) which has a low resistance to compaction. Shallow tillage (rotary harrow, disc harrow) was conducted to the 10 cm soil depth and compared with mouldboard ploughing (20 cm) and direct-drilling. Shallow tillage caused excessive compaction in the middle portion of the Ap horizon (8–16 cm) as characterized by reduced macroporosity (<12%, v/v) and increased relative compaction (>85%). Penetrometer resistance measurements indicated that both shallow tillage and direct-drilling reduced the depth of loose soil (<1.5 MPa) to 10–15 cm, compared with 20–25 cm under ploughing. Shallow tillage improved the size distribution of macro-aggregates and increased the stability of 1–9 mm aggregates at the soil surface (0–3 cm). Differences in placement and incorporation of crop residues and amendments caused a redistribution of organic matter, microbial biomass, and extractable P and Ca within the Ap horizon. An acidic, lower Ap horizon developed over time in the shallow-tillage system. The tillage requirement for acidic, fine sandy loams would necessitate a periodic increase in tillage depth for long-term shallow-tillage systems to remove middle Ap horizon compaction and to provide deeper soil mixing of lime amendments to neutralize soil acidity.

Evaluation of shallow tillage for spring cereals on a fine sandy loam. 1. Growth and yield components, N accumulation and tillage economics

Shallow tillage was assessed over a 4-year period for low-input production of spring cereals in Prince Edward Island. The soil was a Charlottetown fine sandy loam, an Orthic Podzol, which is marginally suitable for direct drilling. The tillage systems consisted of mouldboard ploughing, shallow tillage (rotary harrow, disc harrow) to the 10 cm soil depth, and direct-drilling. Plant populations were similar between tillage systems. Shallow tillage and direct-drilling produced similar grain yields as mouldboard ploughing when environmental conditions were optimum, but wet or very dry growing seasons favoured mouldboard ploughing and direct-drilling, respectively. Rotary harrowing prevented reduced plant growth rates prior to tillering and subsequently reduced accumulation of N in the plant and grain, associated with direct-drilling. Generally, the ability of plants to utilize N for growth was considered to be the main factor influencing N yield differences between tillage systems. In comparison to mouldboard ploughing, shallow tillage reduced machinery costs and energy requirements by 25–48% for seedbed production. In addition, shallow tillage had the advantage of timeliness and increased the potential area which could be prepared for seeding during the limited early spring period. Overall, shallow tillage removed some of the constraints associated with direct-drilling and provides an alternative, in rotational farming systems on fine sandy loams, to mouldboard ploughing.

Association of soil macroporosity and relative saturation with root rot severity of spring cereals

An empirical model was developed using multiple regression to describe the relationship between measured values of relative saturation, macropore volume, and soil moisture content in a Charlottetown fine sandy loam, an Orthic Humo-Ferric Podzol (Cryorthod). The model was used to characterize the incidence of root rot severity in spring cereals, under a mouldboard ploughed and direct drilled tillage system. As soil macropore volume decreased from 14.5 to 8.5% (v/v) root rot severity increased from 50 to 72%. This was associated with an increase in relative saturation from 60 to 74%. The results illustrate the interaction between soil structure and root disease under humid soil moisture regimes.

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

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.

Temporal variability of soil macroporosity in a fine sandy loam under mouldboard ploughing and direct drilling

The temporal variability of soil porosity, especially macropores (> 50 μm), and associated porosity factors such as pore continuity, percent water-filled pore space (% WFPS), and earthworm numbers and biomass were determined over 3 years under direct-drilling and mouldboard ploughing. The study was conducted on a Charlottetown fine sandy loam, an Orthic Podzol with a humid to perhumid soil-moisture regime. Differences in soil porosity between tillage systems were mainly confined to the surface 0–8-cm soil depth. Fissures (> 300 μm), or large pores, were reduced under direct drilling compared with mouldboard ploughing, but subject to regeneration over the winter period. The absence of soil loosening caused the volume of macropores to fall below 10% during the growing season. Tillage had a residual effect on soil porosity, maintaining the volume of macropores between 11 and 18%. Differences between tillage and ice-induced porosity influenced the degree of macropore regeneration. In general, water-storage pores were similar between tillage systems. A close relationship ( r 2 = 0.832) was observed between dry bulk density and macroporosity under both tillage systems. The relationship between macroporosity and pore continuity ( K sat), which differed between tillage systems, indicated that a macroporosity of between 8 to 10% (v/v) would maintain adequate soil permeability. In contrast, the % WFPS, which was closely related ( R 2 = 0.952) to macroporosity and soil water content, indicated that the volume of macropores should exceed 14% to provide an optimum level of air-filled pore space. Under humid soil-moisture regimes, the use of macroporosity as an index of critical soil structure or limiting density needs to be based both on adequate soil permeability and on water-filled pore space. Although direct drilling maintained adequate functional porosity, the need for an optimum aerobic environment may necessitate loosening of the surface soil on an annual basis.

COMPARISON OF TILLAGE AND DIRECT DRILLING FOR ITALIAN RYEGRASS ON THE PROPERTIES OF A FINE SANDY LOAM SOIL

The soil physical, biological, and chemical condition was assessed under cultivated and direct-drilled systems for the annual establishment of Italian ryegrass (Lolium multiflorum Lam.) on Prince Edward Island. After 3 yr, the degree of tillage-induced soil compaction and change in soil biological and chemical properties were determined over the 0- to 24-cm soil depth, and compared with the soil structure under a permanent timothy (Phleum pratense L.) pasture. The study was conducted at two sites on a Charlottetown fine sandy loam, an Orthic Humo-Ferric Podzol (Haplorthod). Although the tillage comparisons produced significant changes in soil porosity, pore-size distribution, pore continuity, aggregation and soil strength, the range in physical properties was within the range considered optimum for soil structure. Soil strength was shown to exhibit marked temporal variation over the growing season. Changes in the distribution of soil microbial biomass C and N, percent organic C, pH and plant nutrients were evident between the establishment methods. Generally, soil chemical and biological conditions under direct-drilling were similar to those under permanent pasture. Comparison of the actual with the estimated maximum bulk density down the soil profile indicated that the propensity for soil consolidation or compaction was the same under the direct-drilling and cultivated systems and similar to that measured under permanent pasture. The annual establishment of Italian ryegrass, for 3 yr, by direct-drilling did not adversely affect soil structure or increase soil compaction. Key words: Direct-drilling, Italian ryegrass, soil structure, soil biological properties, tillage

EFFICACY OF THREE DINITROANILINE HERBICIDES IN PROCESSING PEAS AND THEIR RESIDUES IN SOILS

The efficacy and relative persistence of dinitramine (N′,N′-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2-4-diamine), ethalfluralin [N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4(trifluoromethyl) benzenamine], and trifluralin (α,α,α -trifluoro-2,6-dinitro-N,N-diproply-p-toluidine) were studied in a series of field trials conducted on a Charlottetown fine sandy loam (P.E.I.) and on a Somerset loamy sand (N.S.). Phytotoxicity, as reflected by weed control and injury to the peas (Pisum sativum L.), was greater on the sandy soil and herbicide rates recommended for the region may reduce yields on light soil types. The margin of crop tolerance was also reduced in one year characterized by an extremely wet growing season. Under field conditions, there was little practical difference in weed control obtained with the three herbicides. Dinitramine and ethalfluralin were more persistent in the Somerset sand than in the Charlottetown sandy loam. The order of decreasing persistence was trifluralin&gt;ethalfluralin&gt;dinitramine, except in the Somerset sand where the persistence of ethalfluralin and trifluralin was similar. Significant detectable levels of all three herbicides remained 320 days after application.Key words: Processing peas, dinitramine, ethalfluralin, trifluralin, residue

EFFECT OF METHODS OF APPLICATION AND RESIDUAL EFFECT OF MOLYBDENUM ON THE MOLYBDENUM CONCENTRATION AND YIELD OF FORAGES ON PODZOL SOILS

Alfalfa (Medicago sativa L. ’Saranac’), red clover (Trifolium pratense L. ’Lakeland’), and timothy (Phleum pratense L. ’Climax’) were grown at two locations on Charlottetown fine sandy loam soils in Prince Edward Island. The pH values of the soils were 5.6 and 5.7, respectively. The three levels of lime were 0, 2.24 and 4.48 metric tonnes/ha and the Mo treatments included no Mo, Mo added as foliar spray and Mo added to the soils. In the first sampling, applications of 0.44 kg Mo/ha as foliar spray to soil limed to pH 5.9 and 6.3 in the three crops resulted in tissue Mo concentrations of greater than 10 ppm which when fed to livestock could produce Mo toxicity. With soil applications of 0.88 kg Mo/ha, tissue Mo concentrations of greater than 10 ppm occurred only in alfalfa and red clover limed to soil pH 5.6, 5.9 and 6.3. The tissue Mo levels in the second sampling decreased sharply when compared to those in the first sampling. The differences in Mo concentrations in second, third and fourth samplings were very small. There was a significant interaction (Mo × lime) because the increases of Mo concentration in red clover due to liming were much greater at higher rates of Mo than at lower rates of Mo. In the case of a suspected Mo deficiency, addition of about 0.2 kg Mo/ha as foliar spray or of 0.4 kg Mo/ha applied to the soil should alleviate a Mo deficiency problem. Residual effects at these levels of Mo should last for 2–3 yr from the crop sufficiency point of view. Molybdenum applied as foliar spray increased timothy yields by 15–17% at one location.