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Les répercussions agronomiques de l'épandage d'effluents (ou margines) de moulins à huile d'olive sont étudiées au moyen de cultures de ray-grass en pots sous serre et de tests d'incubation sur l'azote minéral. L'épandage de 40 mm (40 I/m 2) de margines sur une plantation de ray-grass diminue le rendement moyen de 45 p. 100 par rapport à celui de la culture de référence. La production de matière sèche des ray-grass semés immédiatement après l'épandage (doses de 40 et 80 mm) est égale au tiers de la production de référence. La salinité extrêmement élevée des margines, leur acidité, la présence possible de polyphénols ou d'autres substances toxiques biodégradables et l'absence de fourniture d'azote minéral, peuvent expliquer ces répercussions négatives. Les semis réalisés 45 j après l'épandage montrent que, lorsque les margines ont eu un effet sur la croissance des végétaux, il a toujours été favorable : si dans 5 traitements (doses de 40 à 80 mm), l'apport des margines n'a pas significativement augmenté les rendements, dans 5 autres cas (doses de 20 à 80 mm), il les a améliorés. Les analyses de sols permettent d'attribuer une partie de cet effet fertilisant à l'enrichissement en potassium échangeable. Les tests d'incubation révèlent que les margines peuvent provoquer une légère disparition d'azote nitrique, limitée dans ces essais à 0,2 p. 1 000 du poids de margines. L'ensemble de ces tests montre que, dans ces conditions expérimentales et aux doses indiquées, on ne peut pas imputer aux margines une inhibition des microflores ammonifiantes et nitrifiantes du sol. La disparition d'azote nitrique serait provoquée soit par dénitrification, soit par réorganisation. Mots clés additionnels : Margines, azote, azote nitrique, potassium, phytotoxicité. SUMMARY Agronomic effects of land disposal of waste from olive oil crushers. The agronomic effects of land disposal of waste from olive oil crushers were studied. Experimental crops of rye-grass were grown in pots in the greenhouse, and nitrogen mineralization trials were carried out. The input of the equivalent of 40 mm (40 I/ M 2) of waste on an established rye-grass crop, resulted in a 45 0 7o decrease in yield. When the rye-grass was sown immediately after the input of waste (amounts equivalent to 40 and 80 mm) the dry matter yield equaled one third of the reference yield. These negative effects could be explained by the very high salinity of these effluents, their acidity, the possible presence of polyphenols or other toxic biodegradable substances and a lack of nitrate nitrogen. Rye-grass sown 45 days after the input of waste showed positive effects (significant for 5 out of 10 crops). Soil analyses revealed an increase in the amount of exchangeable potassium. Nitrogen mineralization trials revealed a slight decrease of soil nitrate nitrogen, limited to 0,2 mg N/g waste. Neither ammonification, nor nitrification inhibition could be ascribed to the waste from the olive oil crusher, within the conditions and amounts studied. So, the disappearance of nitrate nitrogen coul...
Tomato plants (Lycopersicum esculentum cv. Prisca) were grown on perlite or rock-wool substrates in a greenhouse or in nutrient culture in a growth chamber. At the beginning of flowering and at the fruiting period, the plants were detopped at the base of the stem (1 plant every hour over the 24 hours), then exuded xylem sap was collected hourly for 24 to 48 hours. Exudation rates could be taken into account for about 2 to 10 hours after cutting the stem depending on the development stage of the plants. Cyclic variations of the rate of exudation were observed which followed a daily rhythm with a maximum at midday in the greenhouse as well as under the constant conditions of the growth chamber. The rhythmicity of these variations was also observed in continuous darkness, thus indicating its endogenous nature. The meaning of such a daily rhythm is discussed. INTRODUCTIONWater flow in plants depends on external factors such as light, temperature, relative humidity or nutrition and on internal factors such as age or ontogeny of plants or organs. Diurnal variations of water flow occur whatever the development stage since transpiration rate varies with the daily rhythm of stomatal opening (2,9,7). Translocation of minerals in the plant is linked to water movement in xylem sap and the efficiency of mineral, nutrition of the whole plant depends on how translocation is adjusted to the needs of each part of the plant.Among other methods, exudation after detopping has been used to study the mineral composition of xylem sap. Exudation occurs naturally in plants with high
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