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Thesis (MScAgric (Agronomy))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: See full text for the abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

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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.

The use of crop growth simulation models such asthose incorporated into Decision Support Systems for Agrotechnology Transfer (DSSAT) are useful tools for assessing the impacts of various management practices on crop productivity. The maize growth model of DSSAT is CERES-maize. To evaluate its predictive capability under western Quebec conditions, data on corn (Zea mays L.) yield and above-ground biomass were collected from a field-scale water table management experiment conducted during the 1996 and 1997 growing seasons at St. Emmanuel, Soulanges County, Quebec. The model was calibrated using various crop growth and development data observed during the 1996 growing season. Cultivar-specific coefficients were determined during the calibration. All measured data on phenology, grain yield and biomass collected in 1997 were used for model validation. / Validation results showed good agreement between predicted and measured yields. In 1996, the Root Mean Square Error (RMSE) was 0.64 and 0.66 Mg/ha for the free drainage plots with 200 kg/ha N (FD200) and 120 kg/ha N (FD120), respectively. In 1997, the RMSE for FD200 and FD120 were 1.07 and 1.23 Mg/ha respectively. However, the model overpredicted the biomass for 1997, and grain number for both FD200 and FD120 treatments in both years. The mean difference (MD) between simulated and observed biomass at maturity was statistically significant at (P < 0.01) for both treatments. Sensitivity analyses showed that the CERES-Maize model was most sensitive to changes in air temperature. The model was also sensitive to soil water and crop genetic parameters.

A two-year field study was carried out in eastern Ontario to investigate the effects of water table management (WTM) on water quality and crop yields. Corn (Zea mays L.) and soybean (Glycine max Merr.) were planted in alternate strips across the three treatments of 50 cm controlled water table (CWT), 75 cm CWT and free drainage (FD). Drainflow volume and nitrate-N concentration of the drainage water were measured. Soil samples were collected and analysed for total N, P, K, available N, soil moisture and organic matter levels. Chlorophyll-meter readings and plant harvest parameters were also measured. Rainfall, soil and air temperatures were recorded throughout the growing seasons. / The obtained data show that in 1995, the CWT plots significantly increased total drainflow, as compared to FD. In 1996, overall drainflow and nitrate concentrations were significantly reduced. Both the corn and soybean yields were higher with WTM than with FD for both years. (Abstract shortened by UMI.)

An incubation study was conducted to evaluate the effects of added urea, NH$ sb4$Cl, and KCl on fixation of NH$ sb4 sp{+}$ and K$ sp{+}$. A field study was carried out to observe the effects of rates and methods of added urea and KCl on the forms and distribution of N and K in soils, and on yields and nutrient uptake of silage corn. / Generally, the fixation of NH$ sb4 sp{+}$ was increased by added N but reduced by added K and vice versa. One exception was that added K increased NH$ sb4 sp{+}$ fixation when NH$ sb4$Cl was the N source. In comparison with NH$ sb4$Cl, urea resulted in greater K$ sp{+}$ fixation but less NH$ sb4 sp{+}$ fixation. / Band placement of urea and KCl showed apparent accumulation of NH$ sb4$-N and NO$ sb3$-N, and exchangeable K$ sp{+}$ in the fertilizer bands, particularly early in the growing season. On the other hand, band placement resulted in lower levels of available N and K in soil between the bands in comparison with broadcast. / Yields of silage corn and nutrient uptake values were increased by N and K fertilizers, except for one soil in the first year. Band placement of urea was superior in the case of frequent and light rainfall but inferior with dry surface soil conditions followed by a relatively large rainfall 3 or 4 days after application. In the latter condition, banding K resulted in less yields on one soil, and banding the two fertilizers together further reduced N utilization on another soil. / Additions of K suppressed Ca and Mg uptake but did not influence N uptake, whereas K uptake was usually enhanced by added N.