Efeito do superfosfato triplo no crescimento inicial de porta-enxertos de citros, em diferentes tipos de solos

Abstract

Citrus trees are propagated commercially by bud-scion seedlings obtained from rootstocks in seed-beds, which require some consideration, such as the type of soil that composes the substrate and adequate fertilization. In Minas Gerais, where citrus culture is expanding, the Isoils have low leveis of phosphorus. To correct this problem the addition of phosphorus is being used. The most common rootstocks in Brazil are 'Rangpur' lime, 'Cleópatra» mandarin, Pancilu* tuiboliata L (Raf.) and 'Caipira' orange, these varieties present different requirements in relation to the type of soil and quantities of nutrients. The objective of this work was to verify the effect of five types of soils and of increasing doses of the concentrate superphosphate on the initial growth of four varieties of citrus rootstocks till transplanting. Besides the leveis of macronutr ients and micronutrients in dry matter of the rootstocks, the dry matter, height of the rootstocks, root length and diameter of plants were also measured. The experiment was conducted in the fru it icu 1ture sector of ESAL, Lavras - MG, from June to December of 1982. The experimental design used was sub-subplots with three replicates. The plots were composed of the five types of soils, "Latossolo Roxo", Dark Red Latosol, Reddish Brown laterite soils, yellow Red Latosol and Yellow Red Podzolic; the subplots were composed of the four rootstocks varieties, 'Rangpur» lime, 'Cleópatra* mandarin, P. tli£oliata and 'Caipira» orange and sub-subplots were composed of the doses of concentrate superphosphate 0; 170; 340 and 680 ppm of soluble P. The best growths were obtained in the "Latossolo Roxo" and Dark Red Latosol when 650 ppm of P were applied, with increases of 419% and 365% in dry matter respec tively, in comparison to the treatment where concentrate superphosphate was not applied. With the aplication of 575 ppm of P in Reddish Brown Laterite, 339 ppm of P in Yellow Red Latosol and 145 ppm of P in Yellow Red Podzolic, there was an increase in growth of 283%, 332% and 163% respectively in comparison to the treatment where the concentrate superphosphate was not applied. The Yellow Red Podzolic was the soil that had the highest leveis of P, K, Ca, Mg and pH values when the highest doses of concentrate superphosphate were applied, although it did not promote the best growth of the rootstocks. Of the varieties used, that which showed best growth was 'Caipira' orange, followed by 'Rangpur' lime, P. tU&olia£a and 'Cleópatra' mandarin. The CS applied to the soils promoted increases in the leveis of P, ca, Mg and S and decreasded K, B, Cu, Mn and Zn in dry matter . Six months after sowing, the 'Rangpur' lime and P. tKiiolUta reached the stage of transplanting with ali of the doses of concentrate superphosphate applied independent of the soil. Meanwhile the 'CleSpatra' mandarin and 'Caipira' orange only reached the stage of transplanting when they were fertilized with the highest doses of concentrate superphosphate, that is, approximately 534 ppm of soluble P.