V. Garcia, A. Iriarte[12] [13], G. Lesino1, 2, S. Flores Larsen2,3, C. Matias

Grupo Energia Renovable Catamarca, INENCO — CONICET — Facultad de Ciencias Agrarias —

Universidad Nacional de Catamarca.

M. Quiroga 93 — 4700 Catamarca, Argentina. vga rcia @ plab. unca. edu. a r

Abstract

One of the difficulties in walnut and carob trees propagation is the genetic variability and insufficient offer of grafted plants. In walnut trees, it is necessary to graft high quality buds in a walnut stem; whereas in carob trees, one of the techniques used is the stem cutting propagation. Both techniques require different temperature, light and humidity conditions. With the purpose of producing both species simultaneously, an existing chamber was set up to control the hygrothermal conditions inside it. In order to obtain the best rooting conditions, the proposal is to heat beds using a mixed sun-gas system by means of solar collectors and a gas water tank to heat the water circulating in pipes. In this work, the aim is to analyze the hygrothermal behavior of the chamber, the whole system operation, and the agronomic results obtained with the simultaneous walnut grafting and the carob rooting. Results show the advisibility of using solar collectors to heat the beds in production systems with the purpose of saving energy, stressing the high percentage of plants obtained.

Keywords: Growth/Production, chamber, bioclimatic

1. Introduction

Due to the agronomic enterprises great demand for fruit plants, and the possibility to provide plants for the reforestation of degraded areas in the province of Catamarca — Argentina (28.38° South, 66° West, 600m above sea level), the need emerges to produce an important amount of young plants, specially walnut trees (Juglares regia L.) and carob trees (Prosopis Sp.). The technique most nurserymen use is the agamic propagation by means of micro grafts in walnuts, and rooting in carob plants. This latter technique consists of separating one stem from the mother plant and putting it in a mist system for root and stem growth. To obtain good results with these techniques, well controlled hygrothermal and light conditions are required so as to maintain all the qualities of the mother plant.

The walnut grafting technique used in nurseries is not completely defined and the steps to reach success in the operation are not implemented in the right way. Reproduction in our region shows some problems caused mainly by the great room temperature amplitude and the strong North wind by the time of grafting, which results in an important reduction of the stem taking percentage. To this respect, [1] emphasize the significance of controlling temperature and moisture levels in the

cicatrization area in order to promote cell activity; they state that callus exposure to certain temperatures promotes the disorderly and variable cell multiplication in the grafting union and the root and stem growing zone.

The walnut of the Prosopis genus multiplies itself naturally through dormant seeds in the soil. For this reason, the trees populations are heterogeneous, and inter specific hybridization is common. One way to obtain uniformity and superiority of the clones is by the vegetative propagation method, which eliminates the growing phase and shortens the time to reach reproductive maturity. To this end, stems of vigorous, healthy and identifiable plants should be selected.

For the rooting process, beds are used which are heated with electric elements colocated under the cabinet containing the substrate where the stems are placed. Another alternative is the circulation of a hot fluid through pipes or tubes suitably placed. When the fluid is air, the infrastructure required is not expensive, but distant points piping becomes more expensive due to its low density and thermal capacity. This problem can be avoided by using water, but the investment is higher.

[2]

For the walnut propagation, temperature and humidity ranges must be within certain limits. The temperatures ranges required are: from 18°C to 21°C for rooting, and from 21°C to 25°C in the apex and middle part of the plant. In order to avoid dehydration due to leaf water loss, room humidity must be about 80% for walnuts. For carob trees, optimum temperature in the rooting area is between 32°C and 35°C and a photoperiod of 12 to 18 hours [3].

To carry out the simultaneous production of both species, a chamber was bioclimatically conditioned in already existing premises (like a greenhouse), located in the Experimental Station of the National Institute of Agricultural Technology (Instituto Nacional de Tecnologia Agropecuaria, INTA — Catamarca). The chamber was monitored in the initial stage [4], and modifications arising from the results obtained were implemented in the new period. For carob rooting, a bed was prepared by heating the place with water circulating through pipes placed under the substrate in order to maintain the optimum temperature. The water is heated by a mixed sun-gas system with the aid of a solar collector and a liquid gas container.

In this work, the thermal behavior of the modified chamber is assessed analyzing the possibility of using it for simultaneous micro grafting and rooting, and the behavior of the rooting bed with the combined sun-gas system is also assessed. The hygrothermal and agronomic results of the trials are also presented here.