Tesis
Disponibilidade de potássio afetada por cultivos em solos com longo histórico de adubação
Fecha
2008-02-15Registro en:
MOTERLE, Diovane Freire. Potassium availability affected for sucessive cultivations in soils with long therm fertilization. 2008. 110 f. Dissertação (Mestrado em Agronomia) - Universidade Federal de Santa Maria, Santa Maria, 2008.
Autor
Moterle, Diovane Freire
Institución
Resumen
In soils containing minerals with potassium in non-exchangeable forms, crops
uptake a larger amount of this nutrient than that the chemical method can extract,
making more difficult the establishment of availability classes and sufficiency levels
for potassium. The aims of this study were: a) investigate crop response with
potassic fertilization in an Ultisol; b) estimate the capacity of potassium supply in
Ultisol and Oxisol, with a long report of addition of potassic fertilization; and c) verify
mineralogical alterations of the clay fraction in these soils submitted to successive
crop cultivations. The study was based on two experiments: The first one was
installed in 1991 in an Ultisol with addition of 0, 30, 60 and 90 kg ha-1, evaluating crop
yield and potassium levels in soil using Mehlich-1. The second one consisted in a
succession of plant cultivation in two types of soil with long history of potassic
fertilization. The first experiment was located in the experimental field of the Federal
University of Santa Maria, RS, a typical Ultisol, and the second one, classified as
Oxisol, in the experimental field of Embrapa Soja, Londrina-PR. The soil samples
were collected in the experiments with less and higher concentration of potassium
combined with an addition of 0, 30 and 90 mg kg-1 of potassium for every cultivation.
There were 11 cultivations in the Ultisol and 8 in the Oxisol. From every cultivation
soil samples were collected and the amount of potassium extracted by Mehlich-1
after the 5° and 11° cultivation in the Oxisol 4° and 8° cultivation in the Oxisol was
determined. The samples were submitted at extraction with NaTPB, HNO3 and HF.
The mineralogy of the clay fraction of the treatments with less and higher
concentration of potassium was characterized. Crops respond to the potassium
fertilization when the concentration in soil was lower then 50 mg kg-1. This result
shows that the doses to maintain potassium concentration do not need to be larger
than the amount exported by crops and that the fertilization of correction is only
necessary when exhaustion of potassium occurs. The chemical extractor Mehlich-1
was sensitive to evaluate the availability of potassium in short time, while the
chemical extractors NaTPB and HNO3 can estimate satisfactorily the depletion of
potassium with successive cultivations. The Ultisol showed a greater ability to supply
the plant needs than the Oxisol. The crop cultivation in the Ultisol, without the
addition of potassium, has altered the soil mineralogy, as detected by X-ray
diffraction. On the other hand, in the Oxisol, after successive cultivations, none
mineralogy alteration was perceptible by X-ray diffraction.