Calhas com substrato de casca de arroz “in natura” e recirculação da solução nutritiva drenada: um sistema alternativo para o cultivo de minimelancia

Abstract

The cultivation system and the substrate are directly related to the absorption of the nutrient solution by the plants and, therefore, to the growth of the crop, the productivity and the quality of the fruits. This work introduces the system of gutters filled with fresh rice husks with recirculation of the drained nutrient solution for the mini watermelon, as an alternative to the pot system, usually used in a protected environment. For a new system to be viable and to allow good fruit productivity and quality, several aspects must be studied, including the physical and chemical characteristics of the substrate, the possibility of reusing it in successive crops and the proper management of plants. In this last aspect, the way of conduction of the plants, combined with the other factors, can determine the behavior of the crop. The objective of this work was to study the effect of cultivation system and time of use on changes in physical characteristics of fresh rice husk substrate, plant growth, yield and quality of fruits of mini watermelon cultivated with different numbers of stems per plant. Two experiments using systems with nutrient solution recirculation were carried out in a plastic greenhouse, located in the Didactic and Experimental Field of the Department of Phytotechnics, at the Eliseu Maciel School of Agronomy, at the Federal University of Pelotas. In the first one, the plants were grown in pots and gutters. In the second, substrates of first and second use in gutter were compared. In both experiments, plant conduction was studied in one (with a density of 2.9 plants/ m2) and two stems (with a density of 1.45 plants/ m2). The variables evaluated in both experiments were: leaf number, leaf area per plant, leaf area index, the fresh mass of fruits and total, harvest index, leaf dry mass, stems, fruits and total, number of fruits, average fruit mass, yield per plant and fruit yield per unit area, total soluble solids content (SST) fruits, titratable acidity (ATT), and fruit SST / ATT ratio. The physical and chemical characteristics of the substrates before and after each cultivation were also evaluated. The results obtained in experiment 1 indicate that the gutter system had the greatest positive impact on the physical characteristics of the substrate, whose water retention capacity (CRA) went from the initial value of 7.9% to 15.6% at the end, while which in the vessels increased to 11.2%. The gutter system did not affect the production and distribution of plant biomass in relation to the cultivation in pots, both systems did not affect the yield, with an average of 8 Kg m-2, and the fruit quality. Plants with two stems presented higher dry mass production and higher fruit yield (4.2 Kg plant-1), with higher total soluble solids content (TSS 11.4ºBrix), although without effect on average fruit weight, but did not exceed the growth per unit area of plants of a stem, which also presented a higher number (7.3 fruits m-2) and fruit yield (9.7 kg m-2) per m2. In experiment 2, the substrate of second use presented higher CRA (12.4%) than the new substrate (9.9%) and negatively affected the plant biomass production, with a reduction of 184% in relation to 2nd use substrate, as well as the partition of dry mass destined to fruits had a reduction of 30%. The substrate of second use provided better yield and quality results for most of the studied variables, yielding 5.9 fruits and 5.3 kg m-2, with 10.5ºBrix TSS. In experiment 1, the fruit dry mass partition was 74.9%, while in experiment 2, the fruit dry mass ratio was, on average, 63.3%. Plants with two stems had better results on average fruit weight and, consequently, on yield per plant than plants on one stalk, with no effect on the number of fruits plant-1, yield per m2 and quality. From the results obtained in both experiments, it is possible to conclude that mini watermelon plants have equal production and partition of biomass in both potted and gutter cultivation. Both cultivation systems positively affect the physical characteristics of fresh rice husks, but in the gutter system, this effect is superior. Time of use benefits the production and distribution of photoassimilates to the fruits and improves the physical characteristics of fresh rice husk. The substrate electrical conductivity (EC) remained low even after two cultivations. The growth and yield of a two-stemmed plant are lower than that of two single-stemmed plants, but the biomass partition for the fruits is not affected by the number of the stem of the plants.