Monoculture corn (Zea mays L.) production may result in increased soil degradation through intensive cultivation and N fertilizer use. Intercropping may reduce these negative effects. The objectives of the study were to examine at two sites the effects of monocropping and intercropping corn on soft physical and chemical properties. A sandy loam soil of the Chateaugay series and a sandy loam soft of St Dainase series were used in a field experiment for 1993 and 1994 growing seasons. Soil with corn monoculture planted at 60 and 90 cm row width had lower soil, organic matter than that under intercrops. Soil aggregate stability treatment effects varied with soil. Corn intercropped with perennial rye grass (Lolium perenne L.) showed the highest of aggregate stability. Similar trends were noted with wet-sieved aggregate diameters. Monoculture corn tended to produce higher soil bulk density than intercrops. There was some evidence of compaction after late seeding of intercrops. Monoculture corn resulted in more acidity and lower pH than corn with intercrops. Extractable P and K by Mehlich III were lower in monoculture corn than corn-soybean intercrops. Intercropping tended to reduce residual soil NO3 -- levels but this effect varied with depth. Single and broadcast N application resulted in higher N residues with corn planted at 75 cm row width than split and banded application. Intercropping tended to reduce soil degradation and pollution as measured by aggregate stability and NO3 -- residues.

Mycorrhizal fungi are a major component of agricultural systems and play a key role in plant nutrition. Little is known about the effects of tillage practices and manuring on arbuscular mycorrhizal fungi (AMF). The purpose of this study was to evaluate the effect of soil disturbance on winter survival, development and distribution of AMF in soil and on plant nutrient uptake and productivity. This research was conducted in long-term corn plots in two soils and under controlled conditions. / A growth chamber study with field soil demonstrated that most of the fungal hyphae with mycorrhizal plants were mycorrhizal rather than saprophytic. This result was extrapolated to subsequent experiments. Soil disturbance reduced corn nutrient uptake and growth by disrupting the AMF hyphal network. Similarly, fallow periods reduced density of AMF hyphae, leading to reduced mineral nutrients uptake and plant growth. Soil disturbance was also found to severely reduce winter survival of AMF hyphae in agricultural soil. AM hyphae could survive the winter in soil, even when they were not attached to roots. Their survival however, was improved when they remained attached to roots. / Under field conditions, indigenous AMF were more abundant in no-till soil, less abundant under reduced tillage and least abundant under conventional tillage. Under all tillage systems, most of AMF hyphae were located in the top 15 cm of the soil profile suggesting that deep plowing could result in dilution of AMF propagules in the seeding zone. There was a seasonal variation in the abundance of hyphae in soil. Soil hyphae and root colonization declined after the silking stage of corn. Hyphal abundance decreased further over the winter, to reach their lowest level in the spring. / The spatial distribution of fungal hyphae in the field was not homogenous. Hyphal density was maximal directly under the corn rows and decreased linearly up to the mid-row. Marked seasonal variations in hyphal densities were observed on the row but fluctuations at mid-row were not significant suggesting that little AMF hyphae were ever present between the rows. Liquid dairy manure had little effect on the abundance of hyphae and spores.

Persistent soil compaction by heavy-axle-load vehicles is a growing concern for the long-term productivity of clay soils. For optimum soil management, however, we must be able to evaluate adequately soil structural damages. This study compares different methods of assessing soil structure as affected by compaction and subsoiling treatments in a clay soil under corn production. / The tests used were: total porosity as calculated from densimeter readings and from soil cores; structural porosity; water desorption characteristics; and soil profile examination. These tests were performed in three layers of 20 cm and evaluation was based on their practicality and their ability to differentiate between treatments and to correlate with corn yield. / The results confirm that total porosity is a poor indicator of compaction in the subsoil. In soil profile assessments, ped descriptions were preferable to examination of pores. Water content and saturation deficit at $-$4.0 and $-$100 kPa were the best indicators of treatments and plant response.

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