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Grain corn (Zea mays L.) production occupies more farmland than any other annual crop in Quebec and is expanding demand from the livestock sector and the emerging bioethanol industry. Corn production requires high nutrient inputs and intensive tillage (IT). Many producers have thus switched to conservation tillage systems like ridge-tillage (RT) to overcome soil compaction and erosion problems that are common in IT systems. However, fertilizer guidelines developed for IT soils are used in RT although RT adoption greatly modifies phosphorus (P) dynamics. Lower fertilizer P requirements are expected because arbuscular mycorrhizal (AM) symbiosis known to enhance plant P nutrition are minimally disrupted under RT, compared to IT systems. A two-year study was conducted on a commercial farm in the Monteregie region (Quebec, Canada) to investigate the effects of P fertilizer rates and soil P-saturation status on corn early growth, nutrition and yield. Surface soil plant-available P was monitored in situ with anionic exchange membranes (P AEM) from seeding to the end of July. The effects of indigenous AM fungi on corn parameters and rhizosphere soil P pools were also investigated in untreated (AMNI) or AM-inhibited fungicide-treated (AMI) soils. Quebec's P fertilizer guidelines underestimated the soil P fertility in studied soils. Adding inorganic P (Pi) did not improve the early corn P nutrition, growth or yield, and had little impact soil PAEM. Variations in PAEM were better explained by climatic variables. AMNI corn had similar early development and high yield, regardless of whether P fertilizer was applied, whereas AMI plants needed P fertilizer to produce optimal yield. AMNI corn had reduced dependence on Pi inputs due to more efficient uptake of soil solution P i in surface and rhizosphere soils during the first 22 days after seeding (DAS), In the rhizosphere, available-Pi pool appeared to be used first to replenish the resin-P pool, but over the longer term, AM symbiosis also enhanced NaHCO3-Po mobilization through a mechanism that remains unclear. Deeper understanding of the mechanisms by which AM fungi alter soil P dynamics will contribute to the development of more sustainable P fertilizer programs for RT systems.

Note: / Nature has used shrubbery in the glades of her woods, along the edges of her waterways, softening the angles, changing them into graceful curves. This shows us that if we are to have beautiful surroundings we must copy nature, and use shrubs liberally around our homes, in our public parks and plaqygrounds. [...]

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Cereal aphids started to infest cereals in the first week of June and reached their peak in the second and third week of July. They could affect both the quantity and quality of grain yields, but I recommend chemical control only when the aphid population reaches the economic threshold level, which was calculated as 16 aphids/tiller. Pirimicarb is recommended for chemical control, as it controlled aphids efficiently and had a minimal effect on the available predators and parasites. A sequential sampling plan has been developed to detect if populations reach economic threshold. Temperature accumulation, starting from the first detection of aphids on the crop, allowed prediction of the time of peak population on the crop.

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Increasing levels of nitrate (NO3-) in groundwater have become a major environmental and health concern. In situations where NO3-concentrations in the soil-water system pose an environmental hazard, water table management may be a desirable practice to reduce such pollution. Careful management of N applications is also believed to reduce NO3- levels. / A field experiment was conducted in 1996 and 1997 at St. Emmanuel, Quebec, about 30 km South-West of Macdonald Campus of McGill University, to investigate the effect of water table management (WTM) and N fertilizer combinations on potentially leachable NO3- and denitrification rates in the top soil layer (0--0.15 m). The field was planted with monocrop corn (Zea mays. L) in both years. Treatments consisted of a factorial combination of two water table managements, free drainage (FD) and subirrigation (SI) (about 1.0 m and 0.6 m, respectively, below the soil surface) and two N fertilizer rates, 200 kg ha-1 (N200) and 120 kg ha-1 (N120). / Water table management had a significant effect on reducing NO3 - concentrations in the soil profile. Subirrigation treatment reduced NO3- in the top soil layer by 41% and 15% in 1996 and 1997, respectively. Similarly, NO3 - levels were 50% and 20% lower in N120 compared to N200 treatment. / Climatic conditions (rainfall and temperature) played a large role in regulating denitrification rates. Due to drier and cooler conditions in 1997, denitrification rates were lower compared to 1996, leaving more NO3 - in the soil profile. Following harvest, this high NO 3- concentration may be subject to leaching.