Utilização do estéril da extração do gesso, como condicionador das propriedades físicas de um neossolo quartzarênico do semiárido pernambucano

Abstract

The effects of the addition of the sterile material resulting from the gypsite mining as a soil conditioner were studied. The sterile was incorporated into a Neossolo Quartzarênico collected in the county of Petrolina, PE. Initially the sterile was separated into six granulometric intervals through sieving in the following grades: <1mm, <2mm, <4mm, between 1 and 2mm, between 2 and 4mm and between 4 and 6mm. Soil bulk and particle densities, porosity and water retention curves of these fractions and their mixtures in the proportions of 0, 2, 4, 6 and 8 dag.kg-1 with the soil were analyzed to determine which granulometria fraction which, when mixed with the soil, presented the highest increment in the retention and availability of soil water (AW=FC-PWP, where AW is available water, FC is the field capacity defined as water retained at -10 kPa, PWP is the permanent wilting percentage, defined as the water retained at -1500 kpa ) in relation to unamended soil. The > 4 mm fraction was chosen, not only for presenting results equal to or better than the other granulometric fractions, as well as its lower processing cost. This fraction incorporated to the soil in the proportions described previously was submitted to more precise determinations of water availability, where field capacity was obtained bysimulating of a soil profile with a column of PVC cylinders of 100 cm height with the several proportions of sterile incorporated in the top 40 cm, and the permanent wilting point determined by the physiological method. Finally, a greenhouse experiment with a melon crop was setup using PVC columns of 20 cm diameter by 100 cm depth with the same proportions and materials incorporated to the top 40 cm, simulating field conditions and practices. The incorporation of increasing dosages of sterile increased the available soil water from 4,8% to 8,67% with doses from 0 to 8 dag.kg-1, determined by the traditional method, and from 14,76% to 15,08% in the same dosages when available water was defined with the FC and the PWP were determined by the column and physiological methods respectively. In the melon crop experiment , although the initial growth and development of the plants were greater in the highest dosages ( 6 and 8 dag.kg-1 ) , at the end of the experiment there was no significant difference between the treatments relative to the fresh mass of the fruits. However, in the dry mass of the stems (DMS) and of the leaves (DML), there were significant differences only in the dosages of 6 and 8 dag.kg-1 ofsterile. It was also shown that there was a linear increase in the Calcium, Magnesium, Potassium, and pH values with increasing dosages of sterile, easing the management of fertigation with the addition of sterile.