Showing papers by "Nicolas Tremblay published in 2000"

Nutrient stress of corn plants: early detection and discrimination using a compact multiwavelength fluorescent lidar

Abstract: The objectives of this study were to assess the capability of laser-induced fluorescence (LIF) to discrimi- nate between nitrogen and sulfur deficiencies in corn that result in similar effects on leaf colour, and to de- termine the relationship between changes in LIF emission spectra and plant growth inhibition. Corn plants were grown in the greenhouse and fertilised for 35 days with nutrient solutions of different nitrogen (N) and sulfur (S) concentrations. Every 6 to 8 days during the experiment, fluorescence data were remotely ob- tained using an FLS-PL compact multiwavelength fluorescence lidar developed by our group. Excitation wavelengths varied from the UV to the VIS spectral range over the measurement cycle. The corresponding fluorescence spectra were recorded at each laser pulse with a CCD-based multi-channel detector. On the same day as the fluorescence measurements were made, the leaf reflectance was measured and leaf sam- ples were collected for the N, S and chlorophyll {a+b} (Chl{a+b}) content analyses. N deficiency caused a significant decrease in the accumulation of plant biomass and the Chl{a+b} leaf contents after 6 days of treatments, whereas S deficiency led to significant decreases in Chl{a+b} leaf contents and the accumulation of plant biomass after 6 and 18 days of treatments, respectively. The losses of Chl{a+b} in N- and S-deficient plants were similarly correlated to the changes in the R740/R540 re- flectance ratio and in the F690/F740 fluorescence ratio (the numbers shown are the corresponding wave- lengths at which fluorescence intensities were measured). The R740/R540 and F690/F740 ratios proved useful for the detection of decreases in the leaf Chl{a+b} contents but they could not discriminate between N and S deficiencies. On the other hand, throughout the experiment we observed large differences be- tween the effects of N and S deficiencies on LIF emission spectra. Only the N deficiency induced changes, which could be related to a decreased transmittance of the UV radiation through the leaf epider- mis. The value of this transmittance was estimated using ratios of the far-red fluorescence intensities in- duced by 360 nm- and 440 nm-laser pulses (FRF ex360 /FRF ex440 ). The FRF ex360 /FRF ex440 ratio correlated linearly (R 2 =0.93) with the leaf nitrogen content. These results demonstrate that LIF offers po- tential for early nutrient stress discrimination.

Improving the Prediction of Processing Bean Maturity Based on the Growing-degree Day Approach

Abstract: The heat-unit system, involving the sum of daily mean temperatures above a given base temperature, is used with processing pea ( Pisum sativum L.) to predict relative maturity during the growing season and to schedule planting dates based on average temperature data. The Quebec pea processing industry uses a base temperature of 5 °C to compute growing-degree days (GDD) between sowing and maturity. This study was initiated to verify if the current model, which uses a base temperature of 5 °C, can be improved to predict maturity in Quebec. Four pea cultivars, 'Bolero', 'Rally', 'Flair', and 'Kriter', were grown between 1985 and 1997 on an experimental farm in Quebec. For all cultivars, when using a limited number of years, a base temperature between 0.0 and 0.8 °C reduced the coefficient of variation ( CV) as compared with 5.0 °C, indicating that the base temperature used commercially is probably not the most appropriate for Quebec climatic conditions. The division of the developmental period into different stages (sowing until emergence, emergence until flowering, and flowering until maturity) was also investigated for some years. Use of base temperatures specific for each crop phase did not improve the prediction of maturity when compared with the use of an overall base temperature. All years for a given cultivar were then used to determine the base temperature with the lowest CV for predicting the time from sowing to maturity. A base temperature from 0 to 5 °C was generally adequate for all cultivars, and a common base temperature of 3.0 °C was selected for all cultivars. For the years and cultivars used in this study, the computation of GDD with a base temperature of 3 °C gave an overall prediction of maturity of 2.0, 2.4, 2.2, and 2.5 days based on the average of the absolute values of the differences for the cultivars Bolero, Rally, Flair, and Kriter, respectively.

Évolution des calibres et des rendements de cultivars de haricot destinés à la transformation

Abstract: The evolution of sieve-size, yield and quality are all factors that contribute to the determination of an optimal harvest date for snap beans (Phaseolus vulgaris L.) destined for processing. The evolution of two of these parameters was evaluated in two cultivars of processing beans (Applause and Goldmine) over seven harvesting dates from 1996 to 1997. Three sieve size groups were compared: Small (P, categories 1, 2, 3), Medium (M, category 4) and Large (G, categories 5, 6). At the optimal harvest date, Goldmine had a significantly higher yield in 1997 (17.6 t ha−1) than in 1996 (10.9 t ha−1), whereas no significant difference was found for Applause. Total yields increased at a constant rate (13.2% d−1 for Goldmine and 8.4% d−1 for Applause) (weight for weight), which did not vary year to year. Sieve size evolution was generally linear except for size P in Applause, which exhibited a curvilinear pattern. The rate of change in sieve size varied from year to year, except in the case of size G in Goldmine. Ke...