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  • Author or Editor: N. Tremblay x
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The necessity of achieving appropriate nitrogen fertilization of vegetable crops relates to both economical and environmental sustainability. Split nitrogen applications have been shown to improve N-use efficiency, in line with the aforementioned objective and should therefore be encouraged. Given the variation in the amount of N naturally provided to, or uptaken by, the crop, strategies are required to tailor supplementary fertilization to actual crop needs, keeping in mind the absolute requirement for optimal yield in quality and quantity. It is suggested that the fertilization rates applied at sowing or later in the season can be figured in two manners. The first relies on modelling; the second on measurements. The modelling (N budget) approach, mostly linked to initiatives on the European continent, would be most applicable to the determination of the first fertilizer dressing. When a plant stand is established, however, canopy-based measurements made either directly or remotely could be developed to make use of the capability of the plants to integrate the properties of the soil environment and to decide upon further top-dressed applications. For this purpose, a fully fertilized “reference plot” has to be introduced in the field in order to overcome the variability induced by season, site and cultivar. With the emergence of “precision farming” and “remote sensing technologies” it is now possible to adjust fertilizer inputs not only at the field level but also within fields based on actual, localized requirements.

Free access

Abstract

Celery transplants (Apium graveolens L. cv. Florida 683) were fertilized with complete nutrient solutions at three N concentrations and three concentrations of P in a factorial combination, both with or without atmospheric CO2 enrichment. They then were planted on a muck soil and harvested at the end of July. Carbon dioxide enrichment increased the transplant leaf area as well as shoot and root dry weight and decreased the leaf area ratio (LAR), but had no significant effect on growth parameters at harvest. Nitrogen affected leaf area, dry weight, leaf area ratio, and dry matter content of transplant shoots together with root: shoot dry weight ratio. Total, marketable, and side shoot weights at harvest were significantly increased by the intermediate N concentration (400 ppm N) provided during transplant raising. Phosphorus had no effect on transplant growth but interacted with N on the weight of marketable shoots harvested.

Open Access

Compositional nutrient diagnosis (CND) provides undistorted (linearized) variates amenable to principal component analysis (PCA) using a row-centered logratio transformation of foliar nutrient data. Our objectives were to carry PCA on raw or transformed nutrient data for carrot (Daucus carota L.) crops and to compare the critical value approach (CVA), diagnosis and recommendation integrated system (DRIS), and CND diagnoses using independent data. PCA conducted on percentage or log-transformed data produced similar multivariate structures difficult to interpret. PCA conducted on DRIS indexes and on row-centered logratios produced PCs (K-Ca+), (N+K-Ca-Mg+), and (P-Mg+) and PCs (K-Mg+), (N-Ca+), and (P-), respectively. Nutrient contrasts were easiest to interpret with CND and reflected either K-Mg antagonism or N dilution and Ca accumulation over time. CVA diagnosis of independent samples was generally not in line with DRIS or CND. DRIS and CND diagnostic indexes were highly correlated (r = 0.98 to 0.99). By summing bivariate DRIS functions, the DRIS index calculation procedure effectively row-centered the nutrient values for carrots. DRIS and CND index diagnosis indicated treatment-dependent Ca shortage. In contrast, CND PC diagnosis indicated overall stationary values for PC (N-Ca+) whatever treatment was applied. CND PC diagnosis is a multivariate (PCA) approach providing simplified computational effort and a theoretical basis for further improvements in foliar diagnosis.

Free access