C. Raynal-Lacroix, J. Bohec, F. Dily
A carrot crop (Nandor variety, from clause) was grown in soilless culture, in non-calcareous sand (0–1mm) to monitor the supply of water and minerals to the plants. The inverstigation focused on plant response to three different nitrogen dosages (R1 = controls specimen, N = 5 to 10 meq [70 – 140mg/1]; N-NO3 alone beginnig 26 July /R2 rationed/R3 also rationed): The basic plot has 810 plants. Begining 26 July, nitrogen is supplied only in the nitrate form to minimize acidification of the nutritional medium at the root level.

An analysis of growth parametes of the root reveals that 80% of the maximum length and diameter as measured at time of harvest is achieved 2.5 months after sowing,regardless of the type of nitrate fertilizer. At the same stage, the respective weights of fresh matter and dry matter have reached about 50% of their weights at harves. This percentage approaches 90% one month before harvest. Large nitrate concentrations favor development of the leaves, with little effect on the average weight of the root.

Limiting the nitrogen supply results in a better leaf/root balance with no conseuquence on yield. Moreover, it enables a reduction in the nitrate content ov the carrots. Eliminating nitrogen during the last two months of growing does not alter the production of dry matter in the root, but reduces the weight of fres matter. The anabolic activity of the plant thus appears sufficient to ensure root growth. Reduction turgescence of the tissus would be due to a decline in the osmotic nitrogen content or «storage pool».

Conditions of nitrate fertilization that ensure a higher water and nitrate content of the roots also make the plant vulnerable to parasites, and undermine the stability of stored vegetables. In addition, crops intended for the manufacture of baby food are likely to be rejected for exceeding admissible nitrate levels.

All results point to a rational use of nitrate fertilizer.

The evolution of nitrate content in leaves and roots is being monitored for various nitrogen supplies, in order to acquire the practical elements neede to direct fertilization once the methodological aspects have been taken into account.

Raynal-Lacroix, C., Bohec, J. and Dily, F. (1994). LA NUTRITION AZOTEE DE LA CAROTTE. Acta Hortic. 354, 119-124
DOI: 10.17660/ActaHortic.1994.354.13

Acta Horticulturae