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- Author or Editor: Nicolas Tremblay x
Processing plants requires that cultivars be categorized as either small, medium, or large peas to meet the different markets. A reliable nutrient diagnosis system based on sweet pea leaf analysis should be robust to the type of cultivar. The objective of this study was to determine whether the type of cultivar should be taken into account in producing the nutrient diagnosis. Proportions of peas in categories 1 (small) to 5 (large) were determined for 18 cultivars produced under commercial conditions over 3 years. Cluster analysis was conducted with the constraint of revealing three groups, as homogeneous as possible with regard to their proportions in the different categories. Three cultivars were identified as belonging to the small, nine to the medium, and six to the large group. The archetype of each group was characterized. The function discriminated among the cultivars perfectly along the canonical axes. However, no classification was possible when the nutrient composition variables (N, P, K, Ca, Mg, B, Fe, Mn, Zn) were used for discriminating cultivars' types. Hence, sweet pea cultivars of different types do not differ substantially in leaf composition.
Since they grow nearly exponentially, plants in their juvenile phase can benefit more than mature ones of optimal growing conditions. Transplant production in greenhouses offers the opportunity to optimize growing factors in order to reduce production time and improve transplant quality. Carbon dioxide and light are the two driving forces of photosynthesis. Carbon dioxide concentration can be enriched in the greenhouse atmosphere, leading to heavier transplants with thicker leaves and reduced transpiration rates. Supplementary lighting is often considered as more effective than CO2 enrichment for transplant production. It can be used not only to speed up growth and produce higher quality plants, but also to help in production planning. However, residual effects on transplant field yield of CO2 enrichment or supplementary lighting are absent or, at the best, inconsistent.
As plant color is often modified by nutrient status, the use of spectoradiometric properties of leaf tissues appears to be a promising tool for quick and inexpensive diagnosis of crop fertility problems. This study was conducted to examine spectral variability associated with celery cultivars. Seedlings of Florida 683, Matador, Utah 5270, and Ventura were grown in a growth chamber for 10 weeks (transplant stage; TS). Reflectance and transmittance measurements were taken on the tallest leaf with a LI-COR LI-1800 spectroradiometer. Remaining seedlings were potted and transferred to a greenhouse for another 8 weeks (mid-growth stage; MS). Transmittance was established as the parameter most suitable to distinguish cultivars. Maximum F ratio was obtained at λ = 630 mn at TS, while there were two peeks (λ = 470 and 60 mn) at MS. A discriminant function was based on λ = 470; 630 and 670 mn correctly classified cultivars more than 8 times out of 10 at TS, and more than 7 times out of 10 at MS. Further studies should focus on the induction of nutrient deficiencies and the potential interferences of cultivars with their diagnosis.
Weather is the primary driver of both plant growth and soil conditions. As a consequence of unpredictable weather effects on crop requirements, more inputs are being applied as an insurance policy. Best management practices (BMPs) are therefore about using minimal input for maximal return in a context of unpredictable weather events. This paper proposes a set of complementary actions and tools as BMP for nitrogen (N) fertilization of vegetable crops: 1) planning from an N budget, 2) reference plot establishment, and 3) crop sensing prior to in-season N application based on a saturation index related to N requirement.
Abstract
Celery seedlings (Apium graveolens L. cv. Florida 683) were seeded in multicell styrofoam trays containing a commercial peat mix. They were irrigated with nutrient solutions containing three N fertilizations (150, 250, or 350 mg N/liter) and three NO3:NH4 ratios (1:1, 2:1, or 3:1) in factorial combinations. Growth measurements and saturated medium extracts were obtained on days 38, 45, and 52 after seeding. Increasing N fertilization increased leaf area and shoot dry weight, but decreased root dry weight and root : shoot ratio. The lowest NO3:NH4 ratio had increased the percentage of shoot dry matter by the end of the experiment. Nitrogen was preferentially taken up as NH4-N. The composition of the fertilizer solution had a greater effect on young celery seedlings than on older ones. A minimum of 250 mg N/Iiter at a NO3:NH4 ratio of 2:1 appears to be adequate for celery seedlings grown in multicells.
Abstract
Celery seedlings (Apium graveolens L. cv. Florida 683) were seeded in multicell styrofoam trays containing a commercial peat mix. They were fertilized with nutrient solutions at two nitrogen fertilizations (150 or 350 mg N/liter), two NO3:NH4 ratios (2:1 or 3:1), and two urea-N levels (0% or 50%) in factorial combinations to determine main and interactive effects of urea on seedling growth, nutrient status, and crop yield. Urea used in combination with low N improved the percentage of shoot dry matter and increased leaf area, shoot and root dry weight, and root: shoot ratio of the seedlings. Urea proved beneficial in improving transplant yield potential under high-N fertilization.
Abstract
Broccoli (Brassica oleracea L. var. Italica), celery (Apium graveolens L.), lettuce (Lactuca sativa L.), and pepper (Capsicum annuum L.) seedlings were grown in multicells and fertilized with complete nutrient solutions at two N rates (150 or 350 mg·liter−1) and three K rates (50, 200, or 350 mg·liter−1) in factorial combination. Shoot growth of all species was enhanced at higher N rates but root growth decreased. Broccoli leaf area and shoot dry weight increased curvilinearly with K rate with a maximum at 200 mg·liter−1. For celery K rates increased leaf area linearly. The effect of K rates on growth characteristics was generally a function of the N status and differed among species, celery being the least affected. Under the high N rate, maximum percentage of shoot dry matter, root dry weight, and root:shoot dry weight ratio, as well as minimum specific leaf area of broccoli were obtained with the intermediate K rate. Increasing K rates under high N status enhanced both lettuce leaf area and dry matter accumulation. For pepper, this caused leaf expansion and resulted in more succulent plants.
The experiment was conducted to determine the effects of CO, enrichment (900 μl·liter-1, 8 hours/day) in combination with supplementary lighting of 100 μmol·s-1·m-2(16-h photoperiod) on tomato (Lycopersicon esculentum Mill.) and sweet pepper (Capsicum annuum L.) seedling growth in the greenhouse and subsequent yield in the field. Enrichment with CO2 and supplementary lighting for ≈ 3 weeks before transplanting increased accumulation of dry matter in shoots by ≈ 50% compared with the control, while root dry weight increased 49% for tomato and 6270 for pepper. Early yields increased by =1570 and 11% for tomato and pepper, respectively.
Diagnosing nitrogen (N) sufficiency in crops is used to help insure more effective management of N fertilizer application, and several indicators have been proposed to this end. The N nutrition index (NNI) offers a reliable measurement, but it is relatively difficult to determine. This index is based on the relationship between plant tissue N concentration and the biomass of the plant's aerial parts. However, a good estimate of the NNI should be obtained by nondestructive methods that can be carried out quickly. Although dependent on sites, chlorophyll meter (CM) measurements have been correlated with the NNI in corn (Zea mays). Since chlorophyll can be estimated through remote sensing, the possibility of quickly obtaining measurements for large surface areas points to practical applications for precision agriculture. When combined with the mapping of soil properties such as apparent electrical conductivity (EC), elevation and slope, such chlorophyll measurements make it possible to derive N fertilization recommendations by taking into account natural variations in the soil. Recently, an instrument called the Dualex (FORCE-A, Orsay, France) is marketed, which uses measurement methods based on the fluorescent properties of plant tissues. It is similar to the CM in terms of its operating principle but it measures polyphenolics (Phen), compounds that accumulate in the epidermis of leaves under N stress. Epidermal transmittance to ultraviolet light is assessed by the fluorescence excitation ratio F(ultraviolet)/F(REF), where F(ultraviolet) is the fluorescence excitation detected following ultraviolet excitation, and F(REF) is the fluorescence detected on excitation at a reference wavelength, not absorbed by the epidermis. Although the Dualex generally did not identify more differences among treatments than the CM in our studies on wheat (Triticum aestivum), corn, and broccoli (Brassica oleracea ssp. italica), combining the two measurements in a chlorophyll/Phen ratio improved the relationships with crop N nutrition status appreciably. This ratio can also be estimated by remote sensing techniques. The NNI on its own does not constitute an economically optimal recommendation for N fertilizer [economically optimal N rate (EONR)]. The EONR is the N rate at which profit is greatest. Work is currently being done to use overfertilized reference plots for this purpose and to permit an improved correlation between the indicator (NNI or chlorophyll) and EONR.
This experiment was initiated to determine the effects of supplementary lighting of 100 μmol·s-1·m-2 (PAR) in combination with four N rates (100, 200, 300, and 400 mg N/liter) on growth of celery (Apium graveolens L.), lettuce (Luctuca sativa L.), broccoli (Brassica oleracea italica L.), and tomato (Lycopersicon esculentum Mill.) transplants in multicellular trays. Supplementary lighting, as compared with natural light alone, increased shoot dry weight of celery, lettuce, broccoli, and tomato transplants by 22%, 40%, 19%, and 24%, and root dry weight by 97%, 42%, 38%, and 21%, respectively. It also increased the percentage of shoot dry matter of broccoli and tomato, leaf area of lettuce and broccoli, and root: shoot dry weight ratio (RSDWR) of celery and broccoli. Compared with 100 mg N/liter, a N rate of 400 mg·liter-1 increased the shoot dry weight of celery, lettuce, broccoli, and tomato transplants by 37%, 38%, 61%, and 38%, respectively. High N fertilization accelerated shoot growth at the expense of root growth, except for tomato where a 16% increase of root dry weight was observed. High N also reduced percentage of shoot dry matter. Supplementary lighting appears to be a promising technique when used in combination with high N rates to improve the production of high quality transplants, particularly those sown early.