A METHOD OF PRODUCING HORTICULTURAL SEEDLINGS FOR TRANSPLANTATION IN OPEN FIELD

Abstract: A method of producing horticultural seedlings (P) for transplantation in open fields is described and comprises the steps of providing at least one container (1) with honeycomb-like cells (2), with a cell density of no less than 2000 cells/m<2>. During the germination and growth stage, the cultivation temperature is kept above 15 DEG C for at least two weeks after sowing; there is provision for a step for the daily irrigation of the seedlings (P) throughout the period of cultivation in the container (1), a step for fertilization of the seedlings (P) by irrigation with a ratio of at least one fertilization by irrigation operation for every three irrigation operations, and there is also provision for a step for growth-inhibiting treatment to limit the development of the plant growth of the seedlings (P), performed approximately two weeks after sowing.

Description: n A method of producing horticultural seedlings for transplantation in open field" Technical field The present invention relates to a method of producing horticultural seedlings for transplantation in the open field, according to the preamble to main Claim 1. Background art In the field of the production of horticultural seedlings for transplantation, there are known methods which provide for the seedlings to be grown in containers with honeycomb-like cells, in which each cell has a substrate for the sowing of a respective seed. The term "seedling" is intended to define herein a plant having a size and morphological characteristics suitable to enable it to be transplanted in the open field. After sowing, the containers are moved into germination chambers and subsequently into greenhouses in order, at the end of a preselected cultivation period, to obtain seedlings having the desired morphological characteristics, for example, a suitable size an d stem strength as well as good root and plant development, such as to permit effective transplantation in the open an d consequently to achieve good cultivation productivity. I n this field, a need has been encountered to increase the density of the seedlings grown in containers with cel l s, that is, to increase the number of seedlings per unit o f container area. An increase in density can in fact advantageously permit an increase in output for eac h individual container and also permits a reduction in the number of containers handled during the cultivation steps provided for, from sowing to transplantation in the open field, for a given required output, with a consequent reduction in costs. However, an increase in density which, nowadays, with known cultivation methods, reaches values of 1500-2000 seedlings per square metre, has some limitations. A principal limitation is that a greater seedling density leads to the seedlings being closer together with the result that they tend to develop in height to a greater extent in a search for light for their own development. As a result, the seedlings tend to become "spindly", developing relatively watery and weak stems which are quite sensitive to the stress of transplantation, and the seedlings do not therefore thrive well in the field. Disclosure of the invention The problem upon which the present invention is based is that of providing a method of producing horticultural seedlings for transplantation in the open which can overcome the problems complained of with reference to the prior art mentioned and which can achieve a greater density of seedlings in the cultivation containers in comparison with known production methods, at the same time producing seedlings with morphological characteristics which are suitable for effective transplantation in the field. This problem is solved by the invention by means of a method of producing horticultural seedlings for transplantation according to the following claims. Brief description of the drawings The characteristics and advantages of the invention will become clearer from the following detailed description of a preferred embodiment thereof, described by way of non- limiting example with reference to the single appended drawing, which is a partial perspective view of a container with honeycomb-like cells for the production of horticultural seedlings, used in accordance with the method of the invention. Best mode of carrying out the invention With reference to the drawing, a tray-like container, generally indicated 1, preferably made of polystyrene or of rigid plastics material, comprises a plurality of honeycomblike cells 2 defined by partitions 3 extending longitudinally and transversely relative to the walls of the container 1. Each cell 2 is intended to house a sowing substrate, for example, peaty soil, for the cultivation of a respective horticultural seedling P. It is thus possible to identify, in the container 1 with cells, a cell density per unit of area equal to the number of seedlings which can be produced (a significant parameter for these containers consists of the number of seedlings per square metre) . In the field of the production of horticultural seedlings for transplantation, a respective seed is first of all sown in each cell 2 and the container is then moved to a germination chamber and then into a greenhouse so that, at the end of the preselected cultivation period, the seedlings P have achieved a size and morphological characteristics suitable for their transplantation in the open field, ensuring that the seedlings thrive well and that optimal productivity is achieved. The production method of the invention provides for the use, during the preselected period of cultivation in the tray, of cultivation steps directed mainly towards four factors which are responsible for crop development, that is, the management of the heating and the watering of the crop, the nutritional ratios and levels, as well as techniques for limiting growth with the use of growth-inhibiting products. These steps, which are described in detail below, have enabled cultivation to be optimized and, in particular, have enabled crop density to be increased for given morphological characteristics achievable by conventional methods at the end of the preselected cultivation period. During the step of germination and growth of the crop, the method of the invention provides for the temperature to be kept at values above 15°C and preferably between 18 and 20°C until the 14th-15th day after sowing. The temperature is then reduced to a minimum threshold of 6-7°C during the last 8-10 days of the growth period. The above-mentioned heating levels enable a greater initial elongation of the hypocotyl to be achieved, which is advantageous for producing a seedling ready for transplantation having a height of 8-9 cm, which is larger than the dimensions achieved by conventional techniques and suitable for avoiding the mechanical stresses of transplantation which may even lead to the seedling being buried if it is too small. During these first stages of development there is as yet no competition between the seedlings in the search for light for their own development and, although the hypocotyl reaches heights of 4- 5 cm, it remains sufficiently strong and in an erect position. The maintenance of the temperature at the above- mentioned levels until the 14th-15th day after sowing also enables greater advantage to be taken of growth-inhibiting operations for limiting plant growth since, in these thermal conditions, the active ingredient used can be absorbed more quickly. In the final period of cultivation, the temperature is reduced to the minimum survival threshold to prevent further growth of the seedlings either because of greater competition in the search for light or because of simultaneous progressive cancelling-out of the growth-inhibiting effect. The method of the invention also provides for a step for daily irrigation of the seedlings throughout the preselected cultivation period. In particular, there is provision for irrigation to be performed daily and several times a day to ensure an optimal degree of moistening of the soil and sufficiently uniform wetting of the cells. It should be noted that, with the greater density of cells per unit of area which can be achieved, the cell volume is reduced to values of between 4.5 and 5 cm 3 , thus necessitating abundant and frequent irrigation, particularly upon the appearance of plant cover above the container 1. To prevent problems due to root asphyxia (lack of air available to the roots) , the use of a soil with a low apparent density of less than 80g/litre and a very high water absorption capacity greater than 1100 grams per 100 grams of dry matter is preferred. Similar values of the above-mentioned parameters can be identified in soils produced from very young "tawny" peats, for example Baltic and Canadian peats. The method of the invention further provides for a step for fertilizing the seedlings by irrigation with a ratio of at least one fertilization by irrigation operation to three irrigation operations. The plant growth is preferably washed with water upon completion of each fertilization by irrigation operation and this operation is preferably performed on alternate days. The ratio between the nutritive elements in the fertilizer used is 13-23-15 (N.P.K) - that is, nitrogen, phosphorus, potassium - in the form of N0 3 , H 4 , P 2 0 5 and K 2 0. The addition of micro-elements and meso- elements such as: Mg, Ca, B, Fe, n, Zn and Mo, is also provided for. In the fertilization step, there is also provision for a first additional fertilization by irrigation operation with the supply of calcium nitrate in a proportion of 2 per thousand by weight relative to the solution, performed at the beginning of the fertilization step and 10- 12 days after sowing, the latter to restore the nitrogen lost owing to washing out during irrigation in the initial growth stage. A second and a third additional fertilization by irrigation operation are provided for at weekly intervals, with the supply of calcium nitrate in a proportion of 3 per thousand by weight relative to the solution. In each additional operation, the nitrogen is supplied mainly in nitric form. Finally, the method of the invention provides for a growth-inhibiting treatment step in order to limit plant development during the period of growth and to limit competition between the seedlings due to their greater density. A main growth-inhibiting operation is performed between the 12th and the 14th days after sowing, even though the seedling starts to develop in height in the search for light at about the 20th day when the plant growth covers the container. For very vigorous horticultural seedlings or with varieties in which a pre-germinated seed is used, the main growth-inhibiting operation may be advanced at most by a couple of days so as to prevent the development of a hypocotyl of excessively small dimensions. Naturally, the time at which the growth-inhibiting treatment is carried out is closely connected with optimal management of the heating, watering and nutrition of the seedling during the cultivation period. The main growth-inhibiting treatment provides for the use of a product such as Chlormequat chloride (according to BSI and ISO standards) introduced via the foliage with a dosage of about 100 cc/hl. In addition to this growth- inhibiting treatment, a plant-growth limiting operation with the exclusive use of Bordeaux mixture in increasing doses, preferably starting with 800 gr/hl up to a maximum of 1500 gr/hl is provided for, from the 14th-16th day after sowing (that is, two days after the main treatment) up to the end of the cultivation cycle and performed on alternate days. It has been found that, with the production method of the invention, it is possible to achieve densities equal to and greater than 3000 seedlings per square meter for almost all horticultural species intended for transplantation in the open and with cultivation periods variable between approximately 35 and 40 days (which are typical, for example, for the cultivation of tomatoes and aubergines) . Tests carried out have shown that this method achieves the advantages set out above in the cultivation of horticultural seedlings performed in containers having 693 cells with a volume of each cell of about 5 cubic centimetres . Naturally, the duration of the steps provided for by the method of the invention may be adjusted appropriately for horticultural seedlings of various species and within the same species, in the latter case, for example, in order to ensure optimal conditions in winter and in summer production. Moreover, the operations to limit plant growth may also be partially assisted, for example, by single or repeated cutting of the foliage for species which tolerate this technique . The method of the invention thus solves the problem set, achieving the advantages set out above with reference to known production methods . A first advantage consists of the fact that the seedlings produced by the method of the invention have improved resistance to the shock of transplantation as well as to hydric stresses. A further advantage lies in the fact that greater productivity per unit of cultivated area is achieved with a reduction of about 30% in the handling of the containers from sowing to transplantation in the open and a consequent reduction in the related costs. Another advantage is constituted by the fact that the method of the invention induces in the solanaceae, and particularly in tomato plants, after transplantation in the open, the development of a root system tending to have a taproot which is developed in depth and is thus suitable for making better use of fertilizers supplied, which translates into greater robustness of the plant in the open and a better productive yield.

Claims: CLAIMS 1. A method of producing horticultural seedlings for transplantation in the open, comprising the steps of: - providing at least one container (1) with honeycomb-like cells (2) , with a cell density of no less than 2000 cells/m 2 , each cell containing a sowing substrate for a respective seedling (P) , sowing the seeds in the respective cells (2) of the container, - moving the container (1) into a germination chamber and subsequently into a greenhouse to bring about growth of the seedlings (P) until morphological characteristics suitable to permit transplantation of the seedlings (P) in the open are achieved in each seedling (P) , - the cultivation temperature being kept above 15°C during the germination and growth step for at least two weeks after sowing, providing for a step for daily irrigation of the seedlings (P) throughout the period of cultivation in the container, - providing for a step for fertilization of the seedlings (P) by irrigation with a ratio of at least one fertilization by irrigation operation for every three irrigation operations, and - providing for a step for growth-inhibiting treatment to limit the development of the plant growth in the seedlings (P) , performed approximately two weeks after sowing. 2. A method according to Claim 1, in which the cultivation temperature is kept between 18°C and 20°C for a period between sowing and the 14th-15th day of cultivation. 3. A method according to Claim 1 or Claim 2 , in which the temperature is reduced to values of 6-7°C during the last 8- 4. A method according to one or more of the preceding claims, in which a ratio of 13-23-15 (N.P.K) between nutritive elements is provided for in the fertilization step. 5. A method according to one or more of the preceding claims, in which washing of the plant growth with water is provided for after each fertilization operation. 6. A method according to one or more of the preceding claims, in which the addition of Mg, Ca, B, Fe, Mn, Zn, Mo is provided for in the fertilization step. 7. A method according to one or more of Claims 4 to 5 , in which the fertilization step comprises at least a first additional fertilization operation with the supply of calcium nitrate in a proportion of 2 per thousand by weight. 8. A method according to Claim 7, in which the first additional fertilization operation is performed at the beginning of the fertilization step and 10-12 days after sowing . 9. A method according to Claim 7 or Claim 8 , in which a second and a third fertilization operation with the supply of calcium nitrate at 3 per thousand by weight are provided for at weekly intervals. 10. A method according to one or more of the preceding claims, in which the growth-inhibiting treatment is provided for between the 12th and 14th day of the cultivation period. 11. A method according to Claim 10, in which the growth- inhibiting treatment is performed via the foliage with the use of a product such as Chlormequat chloride with a dosage of the order of 100 cc/hl . 12. A method according to Claim 11, in which the growth- inhibiting treatment further provides for the use of Bordeau mixture with increasing doses greater than 500 gr/hl. 13. A method according to Claim 12, in which the dosage of the Bordeaux mixture is between 800 gr/hl and 1500 gr/hl. 1 . A method according to Claim 13 , in which the growth- inhibiting treatment with the use of Bordeaux mixture is performed on alternate days, starting from the 14th-16th day after sowing until the end of the period of cultivation in the container. 15. A method according to one or more of the preceding claims, in which the seedlings (P) belong to the solanaceae family. 16. A method according to Claim 15, in which the seedlings (P) are tomato seedlings. 17. A method according to one or more of Claims 1 to 15, in which the seedlings (P) belong the the liliaceae family. 18. A method according to one or more of the preceding claims, in which the container (1) comprises a cell density of at least 3000 cells/m 2 with a volume of each cell (2) of no less than 4.5 cm 3 and preferably between 4.5 and 5 cm 3 .

Inventors: BERTO ODDONE, BOSCOLO ANDREA, BERTO, ODDONE, BOSCOLO, ANDREA
Applicants: MASTERPLANT S P A, MASTERPLANT S.P.A.
Application year: 1999
Main classification: A01G31
IPC codes: A01G9